ISO 19087:2018
(Main)Workplace air — Analysis of respirable crystalline silica by Fourier-Transform Infrared spectroscopy
Workplace air — Analysis of respirable crystalline silica by Fourier-Transform Infrared spectroscopy
This document is a standard for the analysis by Fourier-Transform Infrared (FTIR) of respirable crystalline silica (RCS) in samples of air collected on collection substrates (i.e. filters or foams). Three analytical approaches are described for whom the dust from the sample collection substrate is a) analysed directly on sampled filter, b) recovered, treated and deposited onto another filter for analysis, or c) recovered, treated and pressed into a potassium bromide (KBr) pellet for analysis. This document provides information on the instrumental parameters, the sensitivity of different sampling apparatus, the use of different filters and sample treatment to remove interference. In this document the expression RCS includes the most common polymorphs quartz and cristobalite. This document excludes the less common polymorphs of crystalline silica, such as tridymite. Under certain circumstances (i.e. low filter dust loads, low silica content), the analytical approach described in this method cannot fulfil the expanded uncertainty requirements of ISO 20581. Guidance for calculation of uncertainty for measurements of RCS is given in ISO 24095.
Air des lieux de travail — Mesure de la fraction alvéolaire de la silice cristalline par spectrométrie infrarouge
Zrak na delovnem mestu - Analiza respirabilnega kristaliničnega kremena z infrardečo spektroskopijo s Fourierjevo transformacijo (FTIR)
Ta dokument je standard za analizo z infrardečo spektroskopijo s Fourierjevo transformacijo (FTIR) respirabilnega kristalnega kremena (RCS) v vzorcih zraka, zbranih na zbirnih podlagah (filtrih ali penah). Opisani so trije analitični pristopi, pri katerih se prah z vzorčne zbirne podlage
a) analizira neposredno s filtra z vzorcem,
b) zbere, obdela in odloži na drugem filtru za analizo,
c) zbere, obdela in vtisne v pelet iz kalijevega bromida (KBr) za analizo.
Ta dokument podaja informacije o instrumentalnih parametrih, občutljivosti različnih naprav za vzorčenje, uporabi različnih filtrov in vzorčni obdelavi za odstranjevanje motenj. V tem dokumentu izraz RCS vključuje najpogostejši polimorfni kremen in kristobalit. Ta dokument ne zajema manj pogostih oblik kristalnega kremena, kot je tridimit.
Pod določenimi pogoji (majhne količine prahu filtra, majhna vsebnost kremena) analitični pristop, opisan v tej metodi, ne more izpolnjevati razširjenih zahtev negotovosti standarda ISO 20581. Vodilo za izračun negotovosti meritev RCS je podano v standardu ISO 24095.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2019
Zrak na delovnem mestu - Analiza respirabilnega kristaliničnega kremena z
infrardečo spektroskopijo s Fourierjevo transformacijo (FTIR)
Workplace air - Analysis of respirable crystalline silica by Fourier-Transform Infrared
spectroscopy
Air des lieux de travail - Mesure de la fraction alvéolaire de la silice cristalline par
spectrométrie infrarouge
Ta slovenski standard je istoveten z: ISO 19087:2018
ICS:
13.040.30 Kakovost zraka na delovnem Workplace atmospheres
mestu
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
INTERNATIONAL ISO
STANDARD 19087
First edition
2018-07
Workplace air — Analysis of
respirable crystalline silica by Fourier-
Transform Infrared spectroscopy
Air des lieux de travail — Mesure de la fraction alvéolaire de la silice
cristalline par spectrométrie infrarouge
Reference number
©
ISO 2018
© ISO 2018
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Published in Switzerland
ii © ISO 2018 – All rights reserved
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative reference . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus, equipment and reagents . 3
6 Sampling . 7
6.1 Sample collection . 7
6.2 Transport . 8
7 Preparation . 9
7.1 Preparation of calibration samples . 9
7.1.1 Preparation of direct-on-filter calibration samples . . 9
7.1.2 Preparation of redeposition calibration samples .10
7.1.3 Preparation of KBr pellet calibration samples .10
7.2 Preparation of the collection substrate for indirect analysis .11
7.2.1 PVC, MCE and polycarbonate filters .11
7.2.2 Cellulose nitrate filters .12
7.2.3 Polyurethane foams . .12
7.3 Redeposition onto analysis filter .13
7.3.1 Crucibles from the furnace .13
7.3.2 Bottles or beakers from a plasma asher .13
7.4 Preparation of KBr pellets .14
8 Analytical procedure .14
8.1 Gravimetric analysis for respirable dust .14
8.2 Fourier-Transform Infrared analysis .15
8.2.1 Background correction .15
8.2.2 Measurement .15
8.3 Calibration .15
9 Evaluation of Fourier-Transform Infrared spectra .17
9.1 General aspects .17
9.2 RCS quantification using peak height .17
9.3 RCS quantification using peak integral .18
[12][14]
9.3.1 Determination of the absorption in the range of the analytical bands .18
[20]
9.3.2 Subtraction of a reference spectrum .18
9.3.3 Other evaluation methods .20
9.4 Interferences .20
10 Calculation of results .20
10.1 Concentration of RCS .20
11 Performance characteristics .21
11.1 Limit of detection .21
11.2 Limits of quantification .21
11.3 Uncertainty .21
11.4 Differences between samplers .21
12 Test report .22
Annex A (normative) Sample treatment strategies for the removal of interferences .23
Annex B (informative) Differences between samplers (cyclones and other types) .24
Annex C (informative) .26
Annex D (normative) Examples of dust collection substrates and analysis filters .28
Bibliography .29
iv © ISO 2018 – All rights reserved
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www .iso .org/patents).
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URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 2,
Workplace air.
Introduction
Respirable crystalline silica (RCS) is a hazard to the health of workers in many industries through
exposure by inhalation. Industrial hygienists and other public health professionals need to determine
the effectiveness of measures taken to control workers’ exposure. The collection of samples of air
during a work activity and then measuring the amount of respirable crystalline silica are often done to
assess an individual’s exposure, their respiratory protection, or the effectiveness of controls. Fourier-
Transform Infrared (FTIR) analysis of crystalline silica in a sample of respirable dust collected on a
collection substrate is employed in many countries to measure and estimate exposure to RCS. FTIR is
able to measure quartz and cristobalite.
This document specifies the analysis procedures for the measurement of RCS through three methods:
a) Direct-on-filter method: a method of analysing RCS directly on the air sample filter. A specific
requirement of this method is that the sampler used for the workplace measurements is the same
as that used for the preparation of calibration samples.
b) Indirect method by redeposition: a method whereby the dust is recovered from the collection
substrate and deposited onto a filter for analysis.
c) Indirect method by potassium bromide (KBr) pellet: a method whereby the dust is recovered from
the collection substrate and pressed into a potassium bromide (KBr) pellet for analysis.
Many different types of sampling apparatus are used to collect respirable dust, according to the
occupational hygiene convention. This document is designed to accommodate the variety of samplers
and collection substrates available to analysts. This document is used in conjunction with ISO 24095
which promotes best practice for these analyses.
vi © ISO 2018 – All rights reserved
INTERNATIONAL STANDARD ISO 19087:2018(E)
Workplace air — Analysis of respirable crystalline silica by
Fourier-Transform Infrared spectroscopy
1 Scope
This document is a standard for the analysis by Fourier-Transform Infrared (FTIR) of respirable
crystalline silica (RCS) in samples of air collected on collection substrates (i.e. filters or foams). Three
analytical approaches are described for whom the dust from the sample collection substrate is
a) analysed directly on sampled filter,
b) recovered, treated and deposited onto another filter for analysis, or
c) recovered, treated and pressed into a potassium bromide (KBr) pellet for analysis.
This document provides information on the instrumental parameters, the sensitivity of different
sampling apparatus, the use of different filters and sample treatment to remove interference. In this
document the expression RCS includes the most common polymorphs quartz and cristobalite.
This document excludes the less common polymorphs of crystalline silica, such as tridymite.
Under certain circumstances (i.e. low filter dust loads, low silica content), the analytical approach
described in this method cannot fulfil the expanded uncertainty requirements of ISO 20581. Guidance
for calculation of uncertainty for measurements of RCS is given in ISO 24095.
2 Normative reference
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7708, Air quality — Particle size fraction definitions for health-related sampling
ISO 13137, Workplace atmospheres — Pumps for personal sampling of chemical and biological agents —
Requirements and test methods
EN 13205, Workplace exposure — Assessment ofsampler performance for measurement of airborne
particle concentrations
ISO 15767, Workplace atmospheres — Controlling and characterizing uncertainty in weighing collected
aerosols
ISO 18158, Workplace air — Terminology
ISO 24095, Workplace air — Guidance for the measurement of respirable crystalline silica
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18158 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1 General definitions
3.1.1
respirable crystalline silica
RCS
inhaled particles of crystalline silica that penetrate into the unciliated airways according to the
respirable convention described in ISO 7708
3.2 Sampling definitions
3.2.1
analysis filter
suitable filter used to carry out the RCS analysis
Note 1 to entry: For direct-on-filter FTIR analysis the collection substrate is the analysis filter.
Note 2 to entry: For the indirect analysis the dust is removed from the collection substrate and redeposited onto
an analysis filter.
3.2.2
collection substrate
medium on which airborne chemical and/or biological agents are collected for subsequent analysis
Note 1 to entry: For the purpose of this document, filters, polyurethane foams and sampling cassettes are
examples of collection substrates for airborne particles.
4 Principle
This document provides three Fourier-Transform Infrared (FTIR) analytical approaches for the analysis
of RCS in respirable dust collected on a sample collection substrate.
a) Direct-on-filter method:
The respirable dust on the collection substrate (usually a 25 mm diameter filter) is measured
without transferring the dust to an analysis filter. The mass of RCS is determined from the FTIR
response, calibrated against filters loaded with known amounts of RCS reference material.
b) Indirect method (redeposition):
The dust from the sample collection substrate (i.e. a 37 mm diameter filter or a polyurethane
foam) is recovered, treated and deposited on another analysis filter (usually 25 mm diameter or
smaller) for analysis by the instrument. The instrument is calibrated by preparing test samples
from aliquots of a suspension of a reference material. The mass of RCS is determined from the FTIR
response, calibrated against analysis filters loaded with known amounts of RCS reference material.
c) Indirect method (KBr pellet):
The dust from the sample collection substrate (i.e. a 37 mm diameter filter or a polyurethane foam)
is recovered, treated and pressed into a KBr pellet for analysis by the instrument. The instrument
is calibrated by preparing KBr pellets with known amounts of a reference material. The mass of
RCS is determined from the FTIR response, calibrated against pellets loaded with known amounts
of RCS reference material.
Since the volume of air sampled is known, the concentration of RCS in the air is readily calculated.
Because the different aerosol samplers for respirable dust deposit the sample over the surface of the
filter in different ways, the FTIR instruments used for the direct-on-filter analysis approach shall be
calibrated for the aerosol sampler used to collect the samples.
The suitability of FTIR to determine the RCS concentration in a workplace sample depends on the
composition of the dust and potential interferences. If the FTIR method to subtract a reference
spectrum from the sample spectrum (refer to 9.3.2) does not lead to a satisfactory baseline profile, then
2 © ISO 2018 – All rights reserved
the FTIR method is not suitable for the matrix and quantitative FTIR analysis cannot be carried out. As
an alternative XRD analytical method should be used. Qualitative X-ray diffraction (XRD) analysis can
be carried out prior to FTIR analysis to obtain information about the sample.
5 Apparatus, equipment and reagents
5.1 Sampling equipment
5.1.1 Samplers.
5.1.1.1 The particle size-selection performance of the samplers used shall match the criteria for
respirable dust as specified in ISO 7708 according to the test protocol in EN 13205-2.
5.1.1.2 Samplers using a filter or foam pad are suitable for this method.
NOTE Annex B provides information on the performance of different personal respirable samplers that are
currently in use.
NOTE Foam pads and silver membrane filters are not suitable for direct-on-filter method.
5.1.1.3 Cassettes holding filters shall be made of conductive material.
5.1.1.4 Each sampler should be labelled with a unique number, in order to identify samplers that start
to underperform after long-term use.
5.1.1.5 Samplers (sampling train) shall comply with the requirements for calibration in ISO 13137.
NOTE In some countries there can be exceptions due to national regulations.
5.1.2 Collection substrates and analysis filters.
5.1.2.1 Filters as collection substrates shall be of a diameter suitable for use in the selected sampler
and have a capture efficiency for respirable particles as specified in ISO 24095.
5.1.2.2 It is important for the analyst to know the composition of the collection substrate used to
collect the sample since it has a direct bearing on the analytical approach used. The collection substrates
generally used for the sampling of RCS, and their characteristics, are listed in Annex D.
NOTE Additional information about choice of filter material for quartz measurement in coal mine dust can
be found in Reference [24].
5.1.2.3 Filter materials listed in Annex D generally do not contain compounds that interfere with the
measurement of quartz and cristobalite. Impurities can be introduced during the filter manufacturing
process and background absorbance can increase depending on filter material. Therefore, batches of
filters should be regularly tested to detect potential interferences and background levels.
5.1.2.4 Variable background has an effect on the readability of absorbance spectra, increasing the
limit of detection for RCS. PVC and polypropylene used as analysis filters exhibit the least variability and
lowest background levels and thus are useful in situations where low limits of detection are required.
5.1.2.5 Weighing, if required, should be performed following ISO 15767 (see 8.1). Filters shall not be
[18]
weighed in cassettes as large weight variations have been reported . Reference shall be made to the
instructions of the collection substrate manufacturer.
5.1.2.7 An important property for an analysis filter is that it is transparent to infrared and provides a
relatively low background variation near the absorbance for crystalline silica.
5.1.3 Sampling pumps.
Sampling pumps shall comply with the requirements of ISO 13137.
5.1.4 Flow meters.
Flow meters shall comply with the requirements of ISO 13137.
5.1.5 Other equipment required.
Other equipment required for sampling includes the following:
a) belts or harnesses to which the sampling pumps can conveniently be fixed;
b) flexible tubing, to connect the sampler to the sampling pump;
c) a means to transport the samples from the workplace to the laboratory, which minimises the
possibility of accidental transfers of collected dust to or from the collection substrate (filter or
foam). Transportation will usually require caps or covers for the samplers, filter cassettes or other
substrates, as detailed in the manufacturer’s instructions for use of the instruments;
d) a thermometer (readable to 1 °C) and a barometer (readable to 0,1 kPa), to measure atmospheric
temperature and pressure for flow rate correction, when the temperature and pressure at the time
of use differ from the conditions under which the flow meter was calibrated (ISO 24095).
5.2 Equipment for calibration
5.2.1 Dust cloud generator (needed for direct-on-filter analysis).
A device to generate atmospheres of reference material and contain them is needed when following
the direct-on-filter analytical approach. An example of such a device is given in Figure 1. This device is
constructed from borosilicate glass with a lid made from acrylic glass. An aerosol of dust is generated
into the upper cylindrical chamber by applying a short burst of pressurized air to a dust contained in a
bowl at the bottom. Sampling equipment shall be prepared following 6.1.1 to 6.1.6 and 6.1.9. Samplers
are fitted at the top of the device. To avoid agglomerations and charge interactions between the dust
and the filter inside the aerosol sampler it is recommended that the device be earthed (grounded).
NOTE An Aerosol generation device can also be useful for preparing samples for indirect FTIR methods.
4 © ISO 2018 – All rights reserved
Dimensions in centimetre
Key
1 acrylic glass lid
2 holes for cyclone samplers
3 B29/32 cone and socket joint
4 bowl for sample
5 orifice diameter 1 mm
6 compressed air at approximately 50 psi
Figure 1 — Example of an aerosol generation apparatus
5.2.2 Laboratory equipment to prepare suspensions.
For the preparation of calibration samples, suspensions with a defined content of quartz dust can be
used. Volumetric flasks of 100 mL and 250 mL, a bath thermostat with a built-in cooling coil, working
temperature range shall include 20 °C, microlitre pipettes of variable volumes, with a range of between
50 µL and 1 000 µL, an Erlenmeyer flask and a magnetic stirrer.
5.3 Equipment for the determination of dust concentration
5.3.1 Balance.
Weighing should be performed according to ISO 15767. For the preparation of low masses of calibration
samples, a microbalance capable of weighing ±1 µg (or better) is required. An electrostatic eliminator
is needed when weighing collection substrates. For the weighing of foams from the CIP 10-R sampler
for example a balance with an analytical sensitivity of 10 µg with an operational range of 0 g to 20 g is
required.
5.4 Equipment for sample preparation
5.4.1 Redeposition laboratory equipment.
Platinum or glazed ceramic crucibles, beakers, tongs, calibrated pipettes, ultrasonic bath, magnetic
stirrer, apparatus to filter a sample onto a 25-mm diameter filter, a pump to generate vacuum, and a
fume cupboard to contain dusts, vapours and gases.
5.4.2 KBr pellet laboratory equipment.
Platinum or glazed ceramic crucibles, tongs, a pump to generate vacuum, a boron carbide mortar and
pestle, a 50-mm agate or metal microspatula, a laboratory press for preparing KBr pellets, a KBr pellet
evacuable die (typically 13 mm), a pump to generate vacuum, a desiccator with silica gel desiccant, a
hair brush with anti-static effects (e.g. badger or camel hair) and glassine paper.
5.4.3 Equipment to recover dust from the collection substrate.
A furnace capable of operating at a minimum of 600 °C or a low temperature plasma asher to remove
the filter membrane. Tetrahydrofuran (THF) can be used for the dissolution of PVC filters instead of a
plasma asher or furnace.
NOTE To remove interfering substances temperatures of up to 1 000 °C may be required. To prevent
reactions occurring between silica and calcium carbonate at high temperatures, the latter may be removed by
washing with hydrochloric acid (5.6.2.3).
5.5 Equipment for analysis
5.5.1 Spectrometer.
−1 −1 −1
A FTIR spectrometer with a wavelength range from at least 4 000 cm to 400 cm and 4 cm
resolution or better. A suitable sample holder (e.g. a rotatable polarizer mount) is required so that the
sample can be rotated in its own plane. This will enable the effect of non-uniform sample deposition
to be reduced by taking absorbance measurements at several orientations. If the infrared beam in the
instrument has a circular cross-section, rotation is not required.
5.6 Reagents
5.6.1 Direct-on-filter reagents.
Reagents are not normally required for the direct-on-filter analysis method.
5.6.2 Redeposition reagents.
5.6.2.1 Suspension.
Deionised water.
2-Propanol.
Ethanol.
5.6.2.2 Filter dissolution.
Tetrahydrofuran (THF).
1,3-Butanediol, if using cellulose nitrate air sample filters.
6 © ISO 2018 – All rights reserved
5.6.2.3 Removal of interferences.
Hydrochloric acid, 0,1 N to 1 N.
5.6.3 KBr pellet reagents.
Potassium bromide (KBr), infrared quality (stored in a desiccator)
1,3-Butanediol
Hydrochloric acid, 0,1 N to 1 N
Sodium hydroxide (2 N)
5.6.4 Reference materials.
It is important to use a reference material in which the purity and crystalline content is well
characterized. The material used for calibration shall conform to the recommendations in ISO 24095.
NOTE The United States National Institute of Science and Technology (NIST) have developed Standard
Reference Materials (SRM) for respirable quartz (1878 series) and for respirable cristobalite (1879 series).
NOTE A comparison of the crystallinity of calibration materials for the analysis of respirable quartz and
their estimated values can be found in Reference [13].
6 Sampling
6.1 Sample collection
A general guidance for sampling of respirable aerosol fraction is given in CEN/TR 15230 and
ASTM D7948. A guidance specific for the measurement of RCS is given in ISO 24095.
6.1.1 Clean the samplers before use to prevent contamination from previous work. Dismantle the
parts that come into contact with the dust (referring to the manufacturer’s instructions when necessary),
soak the samplers in detergent, ultrasound to remove the fine dust and rinse in water. Allow time for the
apparatus to dry before reassembly.
6.1.2 If gravimetric analysis is required, pre-weigh each uniquely identified collection substrate
(including a minimum of three blanks) at least to the nearest 0,01 mg, according to ISO 15767 using flat
tipped tweezers to avoid contamination and damage.
6.1.3 Load each sampler with a pre-weighed collection substrate, if gravimetric analysis is required,
and connect each loaded sampler to a sampling pump.
NOTE For some sampler types a different procedure could be required; refer to the manufacturer's
instructions.
6.1.4 Ensure each loaded sampler is tested for leaks.
NOTE 1 A leak will change the sampler’s performance which will also affect the mass of respirable dust
sampled.
[8]
NOTE 2 The leak test is used as a benchmark test for proper assembly . Examples for leak tests are: the
[8]
particle count leak test, performed with an optical counter or a condensation particle counter , and the pressure
[9]
drop leak test, performed with a micro manometer .
NOTE 3 The leak test is not applicable to the CIP 10-R.
6.1.5 Connect the sampling train and adjust the flow rate to within ±5 % of the required value. The
maximum deviation in flow rate (before and after sampling) should not exceed ±5 % of the required value.
6.1.6 For personal sampling in the workplace, attach the sampler to the worker within his or her
breathing zone, attach the pump to a belt or harness and connect it to the sampler by a length of flexible
tubing, without impeding the comfort of the worker or his or her activity.
NOTE It is helpful to retain one or more unused collection substrate as a field blank from each site. The field
blank is used for quality assurance purposes. If the field blank differs significantly from the average laboratory
blank, investigate the problem.
6.1.7 To begin sampling, switch on the pump and record the time.
6.1.8 A minimum sampling time shall be calculated taking into account the limit of quantification on
the FTIR method for RCS (see 11.2) and the flow rate of the sampling system, so that compliance with the
limit value or other measurement tasks can be reliably assessed.
For compliance testing, the full working shift should be sampled, when possible. Longer sampling times
improve the measurement precision of all samplers unless overloading occurs.
Care should be taken not to overload the collection substrate.
NOTE Potential sample losses within the sampler, i.e. sample entering the sampler but not carried through
[10]
to the collection substrate, has been observed to occur in field sampling, with large variability . Such losses
are not visible to the naked eye, and cannot be quantified by a direct-on-filter method.
6.1.9 At the end of the sampling period, switch off the pump, record the time and calculate the duration
of the sampling period. Verify the volumetric flow rate of the sampling train according to 6.1.5.
6.1.10 Record the relevant details of the sample collection. The details needed by the laboratory
analyst are:
a) the type of sampler used to collect the sample;
b) the type of collection substrate;
c) the unique identifier of each sample;
d) the volume of the air sampled;
e) the weight of the respirable dust on the collection substrate in order to determine the recovery
after redeposition and to quantify the aliquot for KBr pellet method;
f) information about the industrial process that may aid evaluation of the results.
6.1.11 The results of a qualitative analysis of a sample of dust representative of the workplace or the
activity provides additional information to the analyst to evaluate potential interference. In the absence
of information about the materials involved in the industrial process, a heavily loaded filter sample or a
settled dust sample can provide sufficient qualitative information. The results from the qualitative scan
provides useful information and should be reported to the occupational hygienist (e.g. when sampling a
new process or a process where the materials involved in the work activity may change).
6.2 Transport
Care should be taken to transport aerosol samplers in their upright position to avoid the possible
deposition of dust onto the air sample filter from the grit pot. Cassettes in some samplers can be used
to securely transport the filters. Losses of sample can occur if pressure is applied to the surface of the
dust collected on a filter, especially during the transfer of the filter from a sampler cassette or sample
container. For example, sample losses can occur if the sample surface comes into contact with tweezers,
8 © ISO 2018 – All rights reserved
O-ring seals or the edge of the sampler. Filters can become charged during sampling and may attract
themselves to these items. Losses of dust from the filter surface or found in the cassette shall be noted
on the analyst’s report.
NOTE A filter load up to 4 mg of the respirable fraction (typically on a 25 mm filter) can be transported by
postal service without significant loss, provided that a suitable filter holder and a container designed to prevent
[11]
damage are used .
7 Preparation
7.1 Preparation of calibration samples
Weighing generally is used to quantify the amount of silica in a calibration sample. The accuracy of
weighing does not allow the confirmation of mass collected by a filter below the limit of quantification.
This may be higher than the lowest concentration of the calibration curve (typical figures: 20 μg to
50 μg). However, it is possible that well-characterized mixtures of silica with other dusts could be
employed for this purpose (especially for indirect methods).
NOTE NIST reference quartz and cristobalite on filters can be used as calibration standards in indirect
analysis, and this includes masses below 50 µg.
7.1.1 Preparation of direct-on-filter calibration samples
7.1.1.1 Take at least 12 filters for calibration test samples and three filters to be used as laboratory
blanks from the same lot and ensure unique identification in a suitable manner.
7.1.1.2 In accordance with ISO 15767, condition the filters and weigh them to the nearest 0,001 mg.
Ensure that three consecutive weighing of the same filter are within 15 µg (1σ). For polycarbonate filters
ensure three consecutive weighing are within 3 µg (1σ).
[1]
NOTE A major contribution to the uncertainty of the calibration is the precision of weighing the filters.
7.1.1.3 The apparatus used to generate any dust aerosol (Figure 1) shall be placed inside a fume
cupboard to prevent any potential exposure.
7.1.1.4 Put a pre-weighed filter into the sampler to be used for the sample collection.
7.1.1.5 Connect the sampler to the pump. The pump is usually outside the containment apparatus
connected by a tube to the sampler.
7.1.1.6 Generate aerosols of reference material within the containment apparatus and sample the dust
to obtain loaded filters.
NOTE 1 Filters with a low mass of reference material (<50 µg) are difficult to prepare with good precision and
accuracy.
WARNING — Do not over pressurize the glass chamber.
7.1.1.7 Re-weigh the calibration test filters and the laboratory blanks according to ISO 15767 and
determine the mass of reference material on the filter.
7.1.1.8 This method is suitable for the determination of quartz or cristobalite over the range 10 μg to
1 mg on a 25 mm filter. Over this range, there is a linear relationship between the infrared response and
the quartz/cristobalite content of the sample.
7.1.2 Preparation of redeposition calibration samples
7.1.2.1 Prepare at least two suspensions of the analyte by weighing known amounts of the reference
material to the nearest 0,001 mg.
7.1.2.2 Calculate the mass of reference material in µg/mL of suspension as an aid to plan the aliquots
for the calibration filters.
7.1.2.3 Suspend the reference material in the reagent with an ultrasonic probe or bath for a minimum
of 3 min. Immediately move the suspension to a magnetic stirrer (without heat), add a stirring bar and
allow the suspension to become homogenous before withdrawing aliquots.
7.1.2.4 In accordance with ISO 15767, condition 25-mm diameter filters and weigh them to the
nearest 0,001 mg. Ensure that three consecutive weighings of the same filter are within 15 µg (1σ). For
polycarbonate filters, ensure three consecutive weighings are within 3 µg (1 σ).
[1]
NOTE A major contribution to the uncertainty of the calibration is the precision of weighing the filters.
7.1.2.5 Mount the filter on the filtration apparatus. Place 2 ml to 3 ml of reagent on the filter. Turn off
the stirrer and shake the suspension by hand. Immediately withdraw an aliquot from about the centre of
the suspension and transfer it from the pipette to the filter funnel. Eject the volume from the pipette into
the filter funnel. Wash the sides of the funnel several times with small amounts of reagent.
The diameter of the filter funnel and suction area below the filter will have an influence on the area of
deposition of the sample and hence the sensitivity of the calibration. Filtering apparatus can vary in
both respects and it’s important to use apparatus with similar dimensions.
When using PVC filters, select the rough side of the filter for the redeposition for improved adhesion of
the reference material.
7.1.2.6 Apply vacuum and rapidly filter the suspension. Do not wash down the sides of the funnel after
the deposit is in place since this will rearrange the material on the analysis filter. Leave the vacuum on
until the filter is dry. Remove the filter and allow it to dry completely. When thoroughly dry, reweigh the
filter to determine the mass of deposit.
7.1.2.7 Reweigh the calibration test filters and the laboratory blanks according to ISO 15767 and
determine the mass of reference material on the filter.
7.1.3 Preparation of KBr pellet calibration samples
7.1.3.1 Prepare at least two calibration KBr pellets for a minimum of six equidistant concentrations.
7.1.3.2 Ensure that the KBr is dried overnight at 110 °C and kept in a desiccator to prevent the uptake
of moisture. A low relative humidity environment will facilitate sample handling when using KBr.
7.1.3.3 Weigh different amounts of reference material accurately to the nearest 0,001 mg and transfer
to a crucible. Add the same type of blank collection substrate that was used during sampling in the
workplace to the crucible.
7.1.3.4 Alternatively, suspensions with a defined concentration of reference material can be used to
prepare calibration standards. A defined quantity of the reference material is suspended in water or
ethanol in a 100 mL or 250 mL volumetric flask. Transfer the suspension into an Erlenmeyer flask and stir
(magnetic stirrer) at a controlled temperature of 20 °C (bath thermostat). The quantities of suspension
necessary for the preparation of the respective calibration standard are taken using a microlitre pipette.
10 © ISO 2018 – All rights reserved
After drying the loaded filter, the necessary KBr quantity for preparation, as described above, is added to
the loaded filter.
NOTE 1 The preparation of the calibration test samples can alternatively be performed according to 7.1.1
or 7.1.2 before proceeding with 7.1.3. To obtain the residual reference material, ash the filters using one of the
sample treatment procedures described in 7.2.
NOTE 2 For improved accuracy a suspension of reference material and KBr can be prepared for calibration
test samples below 100 µg. For example, a ratio of 1 990 mg of KBr to 10 mg of reference material can be used.
KBr can be added additionally if the quantity for a pellet is insufficient.
7.1.3.5 To obtain the residual reference material ash the collection substrates using one of the relevant
sample treatment procedures described in 7.2.
7.1.3.6 Weigh 250 mg to 450 mg (accurate to 0,1 mg) KBr and transfer to the crucible with the
calibration sample ash or reference material. The mass of the pellets should not deviate by more than
10 % from each other.
7.1.3.7 Mix the sample ash or reference material thoroughly with the KBr using a pestle. Transfer to a
mortar to complete mixing if necessary.
7.1.3.8 Quantitatively transfer the mixture to a 13-mm evacuable pellet die and ensure a homogenous
distribution in the compression chamber.
7.1.3.9 After inserting the compression tooling into the hydraulic press, the tooling is degassed with
the vacuum pump for approximately 1 min and the KBr disk is compressed with a pressure of 80 kN/cm
for approximately 1 min.
7.1.3.10 Weigh the finished pellet accurately to the nearest 0,1 mg. Calculate the ratio between the
weight of the finished pellet and the weight of KBr that was initially added (usually about 0,98).
7.2 Preparation of the collection sub
...
INTERNATIONAL ISO
STANDARD 19087
First edition
2018-07
Workplace air — Analysis of
respirable crystalline silica by Fourier-
Transform Infrared spectroscopy
Air des lieux de travail — Mesure de la fraction alvéolaire de la silice
cristalline par spectrométrie infrarouge
Reference number
©
ISO 2018
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Published in Switzerland
ii © ISO 2018 – All rights reserved
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative reference . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus, equipment and reagents . 3
6 Sampling . 7
6.1 Sample collection . 7
6.2 Transport . 8
7 Preparation . 9
7.1 Preparation of calibration samples . 9
7.1.1 Preparation of direct-on-filter calibration samples . . 9
7.1.2 Preparation of redeposition calibration samples .10
7.1.3 Preparation of KBr pellet calibration samples .10
7.2 Preparation of the collection substrate for indirect analysis .11
7.2.1 PVC, MCE and polycarbonate filters .11
7.2.2 Cellulose nitrate filters .12
7.2.3 Polyurethane foams . .12
7.3 Redeposition onto analysis filter .13
7.3.1 Crucibles from the furnace .13
7.3.2 Bottles or beakers from a plasma asher .13
7.4 Preparation of KBr pellets .14
8 Analytical procedure .14
8.1 Gravimetric analysis for respirable dust .14
8.2 Fourier-Transform Infrared analysis .15
8.2.1 Background correction .15
8.2.2 Measurement .15
8.3 Calibration .15
9 Evaluation of Fourier-Transform Infrared spectra .17
9.1 General aspects .17
9.2 RCS quantification using peak height .17
9.3 RCS quantification using peak integral .18
[12][14]
9.3.1 Determination of the absorption in the range of the analytical bands .18
[20]
9.3.2 Subtraction of a reference spectrum .18
9.3.3 Other evaluation methods .20
9.4 Interferences .20
10 Calculation of results .20
10.1 Concentration of RCS .20
11 Performance characteristics .21
11.1 Limit of detection .21
11.2 Limits of quantification .21
11.3 Uncertainty .21
11.4 Differences between samplers .21
12 Test report .22
Annex A (normative) Sample treatment strategies for the removal of interferences .23
Annex B (informative) Differences between samplers (cyclones and other types) .24
Annex C (informative) .26
Annex D (normative) Examples of dust collection substrates and analysis filters .28
Bibliography .29
iv © ISO 2018 – All rights reserved
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 2,
Workplace air.
Introduction
Respirable crystalline silica (RCS) is a hazard to the health of workers in many industries through
exposure by inhalation. Industrial hygienists and other public health professionals need to determine
the effectiveness of measures taken to control workers’ exposure. The collection of samples of air
during a work activity and then measuring the amount of respirable crystalline silica are often done to
assess an individual’s exposure, their respiratory protection, or the effectiveness of controls. Fourier-
Transform Infrared (FTIR) analysis of crystalline silica in a sample of respirable dust collected on a
collection substrate is employed in many countries to measure and estimate exposure to RCS. FTIR is
able to measure quartz and cristobalite.
This document specifies the analysis procedures for the measurement of RCS through three methods:
a) Direct-on-filter method: a method of analysing RCS directly on the air sample filter. A specific
requirement of this method is that the sampler used for the workplace measurements is the same
as that used for the preparation of calibration samples.
b) Indirect method by redeposition: a method whereby the dust is recovered from the collection
substrate and deposited onto a filter for analysis.
c) Indirect method by potassium bromide (KBr) pellet: a method whereby the dust is recovered from
the collection substrate and pressed into a potassium bromide (KBr) pellet for analysis.
Many different types of sampling apparatus are used to collect respirable dust, according to the
occupational hygiene convention. This document is designed to accommodate the variety of samplers
and collection substrates available to analysts. This document is used in conjunction with ISO 24095
which promotes best practice for these analyses.
vi © ISO 2018 – All rights reserved
INTERNATIONAL STANDARD ISO 19087:2018(E)
Workplace air — Analysis of respirable crystalline silica by
Fourier-Transform Infrared spectroscopy
1 Scope
This document is a standard for the analysis by Fourier-Transform Infrared (FTIR) of respirable
crystalline silica (RCS) in samples of air collected on collection substrates (i.e. filters or foams). Three
analytical approaches are described for whom the dust from the sample collection substrate is
a) analysed directly on sampled filter,
b) recovered, treated and deposited onto another filter for analysis, or
c) recovered, treated and pressed into a potassium bromide (KBr) pellet for analysis.
This document provides information on the instrumental parameters, the sensitivity of different
sampling apparatus, the use of different filters and sample treatment to remove interference. In this
document the expression RCS includes the most common polymorphs quartz and cristobalite.
This document excludes the less common polymorphs of crystalline silica, such as tridymite.
Under certain circumstances (i.e. low filter dust loads, low silica content), the analytical approach
described in this method cannot fulfil the expanded uncertainty requirements of ISO 20581. Guidance
for calculation of uncertainty for measurements of RCS is given in ISO 24095.
2 Normative reference
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7708, Air quality — Particle size fraction definitions for health-related sampling
ISO 13137, Workplace atmospheres — Pumps for personal sampling of chemical and biological agents —
Requirements and test methods
EN 13205, Workplace exposure — Assessment ofsampler performance for measurement of airborne
particle concentrations
ISO 15767, Workplace atmospheres — Controlling and characterizing uncertainty in weighing collected
aerosols
ISO 18158, Workplace air — Terminology
ISO 24095, Workplace air — Guidance for the measurement of respirable crystalline silica
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18158 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1 General definitions
3.1.1
respirable crystalline silica
RCS
inhaled particles of crystalline silica that penetrate into the unciliated airways according to the
respirable convention described in ISO 7708
3.2 Sampling definitions
3.2.1
analysis filter
suitable filter used to carry out the RCS analysis
Note 1 to entry: For direct-on-filter FTIR analysis the collection substrate is the analysis filter.
Note 2 to entry: For the indirect analysis the dust is removed from the collection substrate and redeposited onto
an analysis filter.
3.2.2
collection substrate
medium on which airborne chemical and/or biological agents are collected for subsequent analysis
Note 1 to entry: For the purpose of this document, filters, polyurethane foams and sampling cassettes are
examples of collection substrates for airborne particles.
4 Principle
This document provides three Fourier-Transform Infrared (FTIR) analytical approaches for the analysis
of RCS in respirable dust collected on a sample collection substrate.
a) Direct-on-filter method:
The respirable dust on the collection substrate (usually a 25 mm diameter filter) is measured
without transferring the dust to an analysis filter. The mass of RCS is determined from the FTIR
response, calibrated against filters loaded with known amounts of RCS reference material.
b) Indirect method (redeposition):
The dust from the sample collection substrate (i.e. a 37 mm diameter filter or a polyurethane
foam) is recovered, treated and deposited on another analysis filter (usually 25 mm diameter or
smaller) for analysis by the instrument. The instrument is calibrated by preparing test samples
from aliquots of a suspension of a reference material. The mass of RCS is determined from the FTIR
response, calibrated against analysis filters loaded with known amounts of RCS reference material.
c) Indirect method (KBr pellet):
The dust from the sample collection substrate (i.e. a 37 mm diameter filter or a polyurethane foam)
is recovered, treated and pressed into a KBr pellet for analysis by the instrument. The instrument
is calibrated by preparing KBr pellets with known amounts of a reference material. The mass of
RCS is determined from the FTIR response, calibrated against pellets loaded with known amounts
of RCS reference material.
Since the volume of air sampled is known, the concentration of RCS in the air is readily calculated.
Because the different aerosol samplers for respirable dust deposit the sample over the surface of the
filter in different ways, the FTIR instruments used for the direct-on-filter analysis approach shall be
calibrated for the aerosol sampler used to collect the samples.
The suitability of FTIR to determine the RCS concentration in a workplace sample depends on the
composition of the dust and potential interferences. If the FTIR method to subtract a reference
spectrum from the sample spectrum (refer to 9.3.2) does not lead to a satisfactory baseline profile, then
2 © ISO 2018 – All rights reserved
the FTIR method is not suitable for the matrix and quantitative FTIR analysis cannot be carried out. As
an alternative XRD analytical method should be used. Qualitative X-ray diffraction (XRD) analysis can
be carried out prior to FTIR analysis to obtain information about the sample.
5 Apparatus, equipment and reagents
5.1 Sampling equipment
5.1.1 Samplers.
5.1.1.1 The particle size-selection performance of the samplers used shall match the criteria for
respirable dust as specified in ISO 7708 according to the test protocol in EN 13205-2.
5.1.1.2 Samplers using a filter or foam pad are suitable for this method.
NOTE Annex B provides information on the performance of different personal respirable samplers that are
currently in use.
NOTE Foam pads and silver membrane filters are not suitable for direct-on-filter method.
5.1.1.3 Cassettes holding filters shall be made of conductive material.
5.1.1.4 Each sampler should be labelled with a unique number, in order to identify samplers that start
to underperform after long-term use.
5.1.1.5 Samplers (sampling train) shall comply with the requirements for calibration in ISO 13137.
NOTE In some countries there can be exceptions due to national regulations.
5.1.2 Collection substrates and analysis filters.
5.1.2.1 Filters as collection substrates shall be of a diameter suitable for use in the selected sampler
and have a capture efficiency for respirable particles as specified in ISO 24095.
5.1.2.2 It is important for the analyst to know the composition of the collection substrate used to
collect the sample since it has a direct bearing on the analytical approach used. The collection substrates
generally used for the sampling of RCS, and their characteristics, are listed in Annex D.
NOTE Additional information about choice of filter material for quartz measurement in coal mine dust can
be found in Reference [24].
5.1.2.3 Filter materials listed in Annex D generally do not contain compounds that interfere with the
measurement of quartz and cristobalite. Impurities can be introduced during the filter manufacturing
process and background absorbance can increase depending on filter material. Therefore, batches of
filters should be regularly tested to detect potential interferences and background levels.
5.1.2.4 Variable background has an effect on the readability of absorbance spectra, increasing the
limit of detection for RCS. PVC and polypropylene used as analysis filters exhibit the least variability and
lowest background levels and thus are useful in situations where low limits of detection are required.
5.1.2.5 Weighing, if required, should be performed following ISO 15767 (see 8.1). Filters shall not be
[18]
weighed in cassettes as large weight variations have been reported . Reference shall be made to the
instructions of the collection substrate manufacturer.
5.1.2.7 An important property for an analysis filter is that it is transparent to infrared and provides a
relatively low background variation near the absorbance for crystalline silica.
5.1.3 Sampling pumps.
Sampling pumps shall comply with the requirements of ISO 13137.
5.1.4 Flow meters.
Flow meters shall comply with the requirements of ISO 13137.
5.1.5 Other equipment required.
Other equipment required for sampling includes the following:
a) belts or harnesses to which the sampling pumps can conveniently be fixed;
b) flexible tubing, to connect the sampler to the sampling pump;
c) a means to transport the samples from the workplace to the laboratory, which minimises the
possibility of accidental transfers of collected dust to or from the collection substrate (filter or
foam). Transportation will usually require caps or covers for the samplers, filter cassettes or other
substrates, as detailed in the manufacturer’s instructions for use of the instruments;
d) a thermometer (readable to 1 °C) and a barometer (readable to 0,1 kPa), to measure atmospheric
temperature and pressure for flow rate correction, when the temperature and pressure at the time
of use differ from the conditions under which the flow meter was calibrated (ISO 24095).
5.2 Equipment for calibration
5.2.1 Dust cloud generator (needed for direct-on-filter analysis).
A device to generate atmospheres of reference material and contain them is needed when following
the direct-on-filter analytical approach. An example of such a device is given in Figure 1. This device is
constructed from borosilicate glass with a lid made from acrylic glass. An aerosol of dust is generated
into the upper cylindrical chamber by applying a short burst of pressurized air to a dust contained in a
bowl at the bottom. Sampling equipment shall be prepared following 6.1.1 to 6.1.6 and 6.1.9. Samplers
are fitted at the top of the device. To avoid agglomerations and charge interactions between the dust
and the filter inside the aerosol sampler it is recommended that the device be earthed (grounded).
NOTE An Aerosol generation device can also be useful for preparing samples for indirect FTIR methods.
4 © ISO 2018 – All rights reserved
Dimensions in centimetre
Key
1 acrylic glass lid
2 holes for cyclone samplers
3 B29/32 cone and socket joint
4 bowl for sample
5 orifice diameter 1 mm
6 compressed air at approximately 50 psi
Figure 1 — Example of an aerosol generation apparatus
5.2.2 Laboratory equipment to prepare suspensions.
For the preparation of calibration samples, suspensions with a defined content of quartz dust can be
used. Volumetric flasks of 100 mL and 250 mL, a bath thermostat with a built-in cooling coil, working
temperature range shall include 20 °C, microlitre pipettes of variable volumes, with a range of between
50 µL and 1 000 µL, an Erlenmeyer flask and a magnetic stirrer.
5.3 Equipment for the determination of dust concentration
5.3.1 Balance.
Weighing should be performed according to ISO 15767. For the preparation of low masses of calibration
samples, a microbalance capable of weighing ±1 µg (or better) is required. An electrostatic eliminator
is needed when weighing collection substrates. For the weighing of foams from the CIP 10-R sampler
for example a balance with an analytical sensitivity of 10 µg with an operational range of 0 g to 20 g is
required.
5.4 Equipment for sample preparation
5.4.1 Redeposition laboratory equipment.
Platinum or glazed ceramic crucibles, beakers, tongs, calibrated pipettes, ultrasonic bath, magnetic
stirrer, apparatus to filter a sample onto a 25-mm diameter filter, a pump to generate vacuum, and a
fume cupboard to contain dusts, vapours and gases.
5.4.2 KBr pellet laboratory equipment.
Platinum or glazed ceramic crucibles, tongs, a pump to generate vacuum, a boron carbide mortar and
pestle, a 50-mm agate or metal microspatula, a laboratory press for preparing KBr pellets, a KBr pellet
evacuable die (typically 13 mm), a pump to generate vacuum, a desiccator with silica gel desiccant, a
hair brush with anti-static effects (e.g. badger or camel hair) and glassine paper.
5.4.3 Equipment to recover dust from the collection substrate.
A furnace capable of operating at a minimum of 600 °C or a low temperature plasma asher to remove
the filter membrane. Tetrahydrofuran (THF) can be used for the dissolution of PVC filters instead of a
plasma asher or furnace.
NOTE To remove interfering substances temperatures of up to 1 000 °C may be required. To prevent
reactions occurring between silica and calcium carbonate at high temperatures, the latter may be removed by
washing with hydrochloric acid (5.6.2.3).
5.5 Equipment for analysis
5.5.1 Spectrometer.
−1 −1 −1
A FTIR spectrometer with a wavelength range from at least 4 000 cm to 400 cm and 4 cm
resolution or better. A suitable sample holder (e.g. a rotatable polarizer mount) is required so that the
sample can be rotated in its own plane. This will enable the effect of non-uniform sample deposition
to be reduced by taking absorbance measurements at several orientations. If the infrared beam in the
instrument has a circular cross-section, rotation is not required.
5.6 Reagents
5.6.1 Direct-on-filter reagents.
Reagents are not normally required for the direct-on-filter analysis method.
5.6.2 Redeposition reagents.
5.6.2.1 Suspension.
Deionised water.
2-Propanol.
Ethanol.
5.6.2.2 Filter dissolution.
Tetrahydrofuran (THF).
1,3-Butanediol, if using cellulose nitrate air sample filters.
6 © ISO 2018 – All rights reserved
5.6.2.3 Removal of interferences.
Hydrochloric acid, 0,1 N to 1 N.
5.6.3 KBr pellet reagents.
Potassium bromide (KBr), infrared quality (stored in a desiccator)
1,3-Butanediol
Hydrochloric acid, 0,1 N to 1 N
Sodium hydroxide (2 N)
5.6.4 Reference materials.
It is important to use a reference material in which the purity and crystalline content is well
characterized. The material used for calibration shall conform to the recommendations in ISO 24095.
NOTE The United States National Institute of Science and Technology (NIST) have developed Standard
Reference Materials (SRM) for respirable quartz (1878 series) and for respirable cristobalite (1879 series).
NOTE A comparison of the crystallinity of calibration materials for the analysis of respirable quartz and
their estimated values can be found in Reference [13].
6 Sampling
6.1 Sample collection
A general guidance for sampling of respirable aerosol fraction is given in CEN/TR 15230 and
ASTM D7948. A guidance specific for the measurement of RCS is given in ISO 24095.
6.1.1 Clean the samplers before use to prevent contamination from previous work. Dismantle the
parts that come into contact with the dust (referring to the manufacturer’s instructions when necessary),
soak the samplers in detergent, ultrasound to remove the fine dust and rinse in water. Allow time for the
apparatus to dry before reassembly.
6.1.2 If gravimetric analysis is required, pre-weigh each uniquely identified collection substrate
(including a minimum of three blanks) at least to the nearest 0,01 mg, according to ISO 15767 using flat
tipped tweezers to avoid contamination and damage.
6.1.3 Load each sampler with a pre-weighed collection substrate, if gravimetric analysis is required,
and connect each loaded sampler to a sampling pump.
NOTE For some sampler types a different procedure could be required; refer to the manufacturer's
instructions.
6.1.4 Ensure each loaded sampler is tested for leaks.
NOTE 1 A leak will change the sampler’s performance which will also affect the mass of respirable dust
sampled.
[8]
NOTE 2 The leak test is used as a benchmark test for proper assembly . Examples for leak tests are: the
[8]
particle count leak test, performed with an optical counter or a condensation particle counter , and the pressure
[9]
drop leak test, performed with a micro manometer .
NOTE 3 The leak test is not applicable to the CIP 10-R.
6.1.5 Connect the sampling train and adjust the flow rate to within ±5 % of the required value. The
maximum deviation in flow rate (before and after sampling) should not exceed ±5 % of the required value.
6.1.6 For personal sampling in the workplace, attach the sampler to the worker within his or her
breathing zone, attach the pump to a belt or harness and connect it to the sampler by a length of flexible
tubing, without impeding the comfort of the worker or his or her activity.
NOTE It is helpful to retain one or more unused collection substrate as a field blank from each site. The field
blank is used for quality assurance purposes. If the field blank differs significantly from the average laboratory
blank, investigate the problem.
6.1.7 To begin sampling, switch on the pump and record the time.
6.1.8 A minimum sampling time shall be calculated taking into account the limit of quantification on
the FTIR method for RCS (see 11.2) and the flow rate of the sampling system, so that compliance with the
limit value or other measurement tasks can be reliably assessed.
For compliance testing, the full working shift should be sampled, when possible. Longer sampling times
improve the measurement precision of all samplers unless overloading occurs.
Care should be taken not to overload the collection substrate.
NOTE Potential sample losses within the sampler, i.e. sample entering the sampler but not carried through
[10]
to the collection substrate, has been observed to occur in field sampling, with large variability . Such losses
are not visible to the naked eye, and cannot be quantified by a direct-on-filter method.
6.1.9 At the end of the sampling period, switch off the pump, record the time and calculate the duration
of the sampling period. Verify the volumetric flow rate of the sampling train according to 6.1.5.
6.1.10 Record the relevant details of the sample collection. The details needed by the laboratory
analyst are:
a) the type of sampler used to collect the sample;
b) the type of collection substrate;
c) the unique identifier of each sample;
d) the volume of the air sampled;
e) the weight of the respirable dust on the collection substrate in order to determine the recovery
after redeposition and to quantify the aliquot for KBr pellet method;
f) information about the industrial process that may aid evaluation of the results.
6.1.11 The results of a qualitative analysis of a sample of dust representative of the workplace or the
activity provides additional information to the analyst to evaluate potential interference. In the absence
of information about the materials involved in the industrial process, a heavily loaded filter sample or a
settled dust sample can provide sufficient qualitative information. The results from the qualitative scan
provides useful information and should be reported to the occupational hygienist (e.g. when sampling a
new process or a process where the materials involved in the work activity may change).
6.2 Transport
Care should be taken to transport aerosol samplers in their upright position to avoid the possible
deposition of dust onto the air sample filter from the grit pot. Cassettes in some samplers can be used
to securely transport the filters. Losses of sample can occur if pressure is applied to the surface of the
dust collected on a filter, especially during the transfer of the filter from a sampler cassette or sample
container. For example, sample losses can occur if the sample surface comes into contact with tweezers,
8 © ISO 2018 – All rights reserved
O-ring seals or the edge of the sampler. Filters can become charged during sampling and may attract
themselves to these items. Losses of dust from the filter surface or found in the cassette shall be noted
on the analyst’s report.
NOTE A filter load up to 4 mg of the respirable fraction (typically on a 25 mm filter) can be transported by
postal service without significant loss, provided that a suitable filter holder and a container designed to prevent
[11]
damage are used .
7 Preparation
7.1 Preparation of calibration samples
Weighing generally is used to quantify the amount of silica in a calibration sample. The accuracy of
weighing does not allow the confirmation of mass collected by a filter below the limit of quantification.
This may be higher than the lowest concentration of the calibration curve (typical figures: 20 μg to
50 μg). However, it is possible that well-characterized mixtures of silica with other dusts could be
employed for this purpose (especially for indirect methods).
NOTE NIST reference quartz and cristobalite on filters can be used as calibration standards in indirect
analysis, and this includes masses below 50 µg.
7.1.1 Preparation of direct-on-filter calibration samples
7.1.1.1 Take at least 12 filters for calibration test samples and three filters to be used as laboratory
blanks from the same lot and ensure unique identification in a suitable manner.
7.1.1.2 In accordance with ISO 15767, condition the filters and weigh them to the nearest 0,001 mg.
Ensure that three consecutive weighing of the same filter are within 15 µg (1σ). For polycarbonate filters
ensure three consecutive weighing are within 3 µg (1σ).
[1]
NOTE A major contribution to the uncertainty of the calibration is the precision of weighing the filters.
7.1.1.3 The apparatus used to generate any dust aerosol (Figure 1) shall be placed inside a fume
cupboard to prevent any potential exposure.
7.1.1.4 Put a pre-weighed filter into the sampler to be used for the sample collection.
7.1.1.5 Connect the sampler to the pump. The pump is usually outside the containment apparatus
connected by a tube to the sampler.
7.1.1.6 Generate aerosols of reference material within the containment apparatus and sample the dust
to obtain loaded filters.
NOTE 1 Filters with a low mass of reference material (<50 µg) are difficult to prepare with good precision and
accuracy.
WARNING — Do not over pressurize the glass chamber.
7.1.1.7 Re-weigh the calibration test filters and the laboratory blanks according to ISO 15767 and
determine the mass of reference material on the filter.
7.1.1.8 This method is suitable for the determination of quartz or cristobalite over the range 10 μg to
1 mg on a 25 mm filter. Over this range, there is a linear relationship between the infrared response and
the quartz/cristobalite content of the sample.
7.1.2 Preparation of redeposition calibration samples
7.1.2.1 Prepare at least two suspensions of the analyte by weighing known amounts of the reference
material to the nearest 0,001 mg.
7.1.2.2 Calculate the mass of reference material in µg/mL of suspension as an aid to plan the aliquots
for the calibration filters.
7.1.2.3 Suspend the reference material in the reagent with an ultrasonic probe or bath for a minimum
of 3 min. Immediately move the suspension to a magnetic stirrer (without heat), add a stirring bar and
allow the suspension to become homogenous before withdrawing aliquots.
7.1.2.4 In accordance with ISO 15767, condition 25-mm diameter filters and weigh them to the
nearest 0,001 mg. Ensure that three consecutive weighings of the same filter are within 15 µg (1σ). For
polycarbonate filters, ensure three consecutive weighings are within 3 µg (1 σ).
[1]
NOTE A major contribution to the uncertainty of the calibration is the precision of weighing the filters.
7.1.2.5 Mount the filter on the filtration apparatus. Place 2 ml to 3 ml of reagent on the filter. Turn off
the stirrer and shake the suspension by hand. Immediately withdraw an aliquot from about the centre of
the suspension and transfer it from the pipette to the filter funnel. Eject the volume from the pipette into
the filter funnel. Wash the sides of the funnel several times with small amounts of reagent.
The diameter of the filter funnel and suction area below the filter will have an influence on the area of
deposition of the sample and hence the sensitivity of the calibration. Filtering apparatus can vary in
both respects and it’s important to use apparatus with similar dimensions.
When using PVC filters, select the rough side of the filter for the redeposition for improved adhesion of
the reference material.
7.1.2.6 Apply vacuum and rapidly filter the suspension. Do not wash down the sides of the funnel after
the deposit is in place since this will rearrange the material on the analysis filter. Leave the vacuum on
until the filter is dry. Remove the filter and allow it to dry completely. When thoroughly dry, reweigh the
filter to determine the mass of deposit.
7.1.2.7 Reweigh the calibration test filters and the laboratory blanks according to ISO 15767 and
determine the mass of reference material on the filter.
7.1.3 Preparation of KBr pellet calibration samples
7.1.3.1 Prepare at least two calibration KBr pellets for a minimum of six equidistant concentrations.
7.1.3.2 Ensure that the KBr is dried overnight at 110 °C and kept in a desiccator to prevent the uptake
of moisture. A low relative humidity environment will facilitate sample handling when using KBr.
7.1.3.3 Weigh different amounts of reference material accurately to the nearest 0,001 mg and transfer
to a crucible. Add the same type of blank collection substrate that was used during sampling in the
workplace to the crucible.
7.1.3.4 Alternatively, suspensions with a defined concentration of reference material can be used to
prepare calibration standards. A defined quantity of the reference material is suspended in water or
ethanol in a 100 mL or 250 mL volumetric flask. Transfer the suspension into an Erlenmeyer flask and stir
(magnetic stirrer) at a controlled temperature of 20 °C (bath thermostat). The quantities of suspension
necessary for the preparation of the respective calibration standard are taken using a microlitre pipette.
10 © ISO 2018 – All rights reserved
After drying the loaded filter, the necessary KBr quantity for preparation, as described above, is added to
the loaded filter.
NOTE 1 The preparation of the calibration test samples can alternatively be performed according to 7.1.1
or 7.1.2 before proceeding with 7.1.3. To obtain the residual reference material, ash the filters using one of the
sample treatment procedures described in 7.2.
NOTE 2 For improved accuracy a suspension of reference material and KBr can be prepared for calibration
test samples below 100 µg. For example, a ratio of 1 990 mg of KBr to 10 mg of reference material can be used.
KBr can be added additionally if the quantity for a pellet is insufficient.
7.1.3.5 To obtain the residual reference material ash the collection substrates using one of the relevant
sample treatment procedures described in 7.2.
7.1.3.6 Weigh 250 mg to 450 mg (accurate to 0,1 mg) KBr and transfer to the crucible with the
calibration sample ash or reference material. The mass of the pellets should not deviate by more than
10 % from each other.
7.1.3.7 Mix the sample ash or reference material thoroughly with the KBr using a pestle. Transfer to a
mortar to complete mixing if necessary.
7.1.3.8 Quantitatively transfer the mixture to a 13-mm evacuable pellet die and ensure a homogenous
distribution in the compression chamber.
7.1.3.9 After inserting the compression tooling into the hydraulic press, the tooling is degassed with
the vacuum pump for approximately 1 min and the KBr disk is compressed with a pressure of 80 kN/cm
for approximately 1 min.
7.1.3.10 Weigh the finished pellet accurately to the nearest 0,1 mg. Calculate the ratio between the
weight of the finished pellet and the weight of KBr that was initially added (usually about 0,98).
7.2 Preparation of the collection substrate for indirect analysis
Analysts using a direct on-air sampling filter analysis approach do not need to prepare the collection
substrate and should proceed to Clause 8.
Ensure that all operations involving flammable solvents are performed in a fume cupboard or under
air extraction. Some samples contain minerals that may interfere on the analysis for RCS. Refer to some
sample treatment strategies outlined in Annex A to remove such interferences. Use the appropriate
treatment based on the type of collection substrate.
7.2.1 PVC, MCE and polycarbonate filters
Use either the furnace treatment (7.2.1.1) or plasma asher (7.2.1.2) to ash sampled filter. As an
alternative, treatment with tetrahydrofuran (THF) to dissolve the sampled filter can also be chosen
(7.2.1.3).
7.2.1.1 Furnace treatment
a) Place each filter into a clean crucible and add 1 ml to 3 ml of 1,3-butanediol to the filter.
NOTE The butanediol is used to improve the control of the heating and combustion process.
b) Slowly heat the crucible in the furnace to a temperature of 450 °C to 600 °C and maintain this
temperature for four to six hours.
b) If graphite is present refer to Annex A for sa
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