ISO 17736:2010
(Main)Workplace air quality — Determination of isocyanate in air using a double-filter sampling device and analysis by high pressure liquid chromatography
Workplace air quality — Determination of isocyanate in air using a double-filter sampling device and analysis by high pressure liquid chromatography
ISO 17736:2010 gives general guidelines for the sampling and analysis of airborne isocyanates in workplace air. ISO 17736:2010 is appropriate for organic compounds containing free isocyanate functional groups and is specific for the quantification of monomers, polymers and prepolymers, vapours and aerosols. Differential air sampling is performed with a segregating device which can show the physical state of the isocyanates analysed as found in the field. This capacity, however, may show limitations for given situations, e.g. when aerosols collected on the first filter contain free monomer that migrates to the second filter and is then quantified as vapour phase isocyanate. The determination of aromatic monomers includes toluene diisocyanate (TDI) and 4,4'-diisocyanato-diphenylmethane (MDI). Aliphatic monomers include isophorone diisocyanate (IPDI), 4,4'-methylene bis-(cyclohexyl isocyanate) (HMDI) and 1,6-hexamethylene diisocyanate (HDI). Isocyanate oligomers and prepolymers can also be determined using this method. The double-filter method is designed to determine short-term (15 min) exposure concentrations of organic isocyanates in a workplace environment by personal monitoring or by fixed location monitoring. However, if the exposure is expected to be in vapour form only, then sampling time can be extended to 8 h. Since the filter is derivatized in the field immediately after sampling, loss of isocyanate aerosol because of its reaction with other chemicals is negligible except for very fast-reacting isocyanate systems such as foam spraying of MDI in polyurethane applications. The method is suitable for the measurement of airborne organic isocyanates in the NCO equivalent concentration range of 0,01 µg/sample to 2,1 µg/sample, corresponding to approximately 0,67 µg/m3 to 140 µg/m3 for a 15 l sample volume. This range brackets about eight times the current established threshold limit value (TLV) of 5 ppb for monomers set by many national authorities.
Qualité de l'air des lieux de travail — Dosage des isocyanates dans l'air au moyen d'un dispositif d'échantillonnage à filtre double et par analyse par chromatographie liquide à haute performance
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 17736
First edition
2010-12-15
Workplace air quality — Determination of
isocyanate in air using a double-filter
sampling device and analysis by high
pressure liquid chromatography
Qualité de l'air des lieux de travail — Dosage des isocyanates dans l'air
au moyen d'un dispositif d'échantillonnage à filtre double et par analyse
par chromatographie liquide à haute performance
Reference number
ISO 17736:2010(E)
©
ISO 2010
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ISO 17736:2010(E)
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ISO 17736:2010(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Principle.1
4 Reagents and materials .2
5 Apparatus.3
6 Air sampling.4
6.1 Calibration of sampling system .4
6.2 Preparation of sampling equipment.4
6.3 Preparation of MAMA-impregnated filter .4
6.4 Collection of samples .4
6.5 Blanks.5
7 Procedure.5
7.1 Safety precautions .5
7.2 Calibration standard.5
8 Sample processing.6
8.1 Vapour analysis .6
8.2 Aerosol analysis .6
9 HPLC conditions.7
9.1 General .7
9.2 HPLC conditions — vapour isocyanates .7
9.3 HPLC conditions — aerosol isocyanates .7
10 Analysis.8
10.1 Calibration curve .8
10.2 Quality control .8
10.3 Sample quantification .8
11 Interference .9
12 Determination of performance characteristics .10
12.1 Introduction.10
12.2 Relevant uncertainty contributions and criteria .10
12.3 Assessment of performance characteristics, following the detailed approach in
[5]
ISO/IEC Guide 98-3 .11
Annex A (informative) Performance characteristics .18
Annex B (informative) Sample chromatograms.20
Bibliography.27
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ISO 17736:2010(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 17736 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 2, Workplace
atmospheres.
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ISO 17736:2010(E)
Introduction
Isocyanates are commercially available chemicals used in the polyurethane industry. They are known to
cause health problems, such as asthma, contact dermatitis and hypersensitivity pneumonitis, in workers even
at very low levels in occupational environments.
Since isocyanates are highly reactive compounds and exposure limits are very low, the sampling and the
analysis of these substances are critical.
This method is based on the standard method developed by the Institut de Recherche en Santé et en Sécurité
du Travail [Occupational Health and Safety Research Institute] (IRSST) of Quebec. It has been in use for
more than 18 years as the standard government method in that province of Canada. Since 1996, it has been
introduced into the marketplace in the USA, Brazil, and the UK. After a year’s study (Reference [10]), the
method was adopted in 1998-11 by the US Air Force as an acceptable alternative to NIOSH Method 5521 for
monomeric isocyanates (now withdrawn).
The method is now routinely used in the Canadian provinces of Alberta, British Columbia, and Ontario, and in
the US state of Washington, which has validated the method for TDI. Thirteen laboratories have been
schooled in this analytical method, three in Canada, eight in the USA and Mexico, one in Brazil, and one in the
UK. This method has been in use in several countries for many years and 13 laboratories participate in round
robin testing on a regular basis in order to maintain their proficiency.
The double-filter method has been validated for different applications of isocyanates such as spray-painting
(Reference [11]) and foam manufacturing. It has also been compared with other established methods and
demonstrated equivalent results (Reference [10]).
[7] [8] [9]
Double-filter methods are also available in ASTM D6561 and ASTM D6562 for HDI, and ASTM D5932
for TDI.
ISO draws attention to the fact that it is claimed that compliance with this document may involve the use of a
patent concerning the double-filter sampling device for isocyanates.
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INTERNATIONAL STANDARD ISO 17736:2010(E)
Workplace air quality — Determination of isocyanate in air
using a double-filter sampling device and analysis by high
pressure liquid chromatography
1 Scope
This International Standard gives general guidelines for the sampling and analysis of airborne isocyanates in
workplace air. This International Standard is appropriate for organic compounds containing free isocyanate
functional groups and is specific for the quantification of monomers, polymers and prepolymers, vapours and
aerosols. Differential air sampling is performed with a segregating device which can show the physical state of
the isocyanates analysed as found in the field. This capacity, however, may show limitations for given
situations, e.g. when aerosols collected on the first filter contain free monomer that migrates to the second
filter and is then quantified as vapour phase isocyanate. The determination of aromatic monomers includes
toluene diisocyanate (TDI) and 4,4'-diisocyanato-diphenylmethane (MDI). Aliphatic monomers include
isophorone diisocyanate (IPDI), 4,4'-methylene bis-(cyclohexyl isocyanate) (HMDI) and 1,6-hexamethylene
diisocyanate (HDI). Isocyanate oligomers and prepolymers can also be determined using this method.
The double-filter method is designed to determine short-term (15 min) exposure concentrations of organic
isocyanates in a workplace environment by personal monitoring or by fixed location monitoring. However, if
the exposure is expected to be in vapour form only, then sampling time can be extended to 8 h. Since the filter
is derivatized in the field immediately after sampling, loss of isocyanate aerosol because of its reaction with
other chemicals is negligible except for very fast-reacting isocyanate systems such as foam spraying of MDI in
polyurethane applications. The method is suitable for the measurement of airborne organic isocyanates in the
NCO equivalent concentration range of 0,01 µg/sample to 2,1 µg/sample, corresponding to approximately
3 3
0,67 µg/m to 140 µg/m for a 15 l sample volume. This range brackets about eight times the current
established threshold limit value (TLV) of 5 ppb for monomers set by many national authorities.
2 Normative references
The following referenced documents are indispensable for the application 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 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method
EN 1232, Workplace atmospheres — Pumps for personal sampling of chemical agents — Requirements and
test methods
3 Principle
A measured volume of air is drawn through a double-filter sampling device in which the first filter made of
polytetrafluoroethylene (PTFE) collects the aerosols and then the isocyanate vapour is absorbed on a glass
fibre (GF) filter impregnated with 9-(methylaminomethyl)anthracene (MAMA). The isocyanate present as an
aerosol is collected on the PTFE filter and derivatized immediately after sampling, in a 5 ml solution of
1-(2-methoxyphenyl)piperazine (MP), 0,1 mg/ml in toluene.
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ISO 17736:2010(E)
Both isocyanate monomer and oligomer urea derivatives solutions are separated using reversed phase high
performance liquid chromatography (HPLC). Vapour monomers are analysed by HPLC using an
ultraviolet (UV) and fluorescence (FL) detector. Fluorescence detection is used when concentrations are less
than 25 % of the TLV. Monomeric and oligomeric aerosols are analysed by HPLC with a UV detector for
quantification and a diode array detector (DAD) for identification. Quantification of the monomeric aerosols is
made by comparison with the relevant isocyanate monomer standard. The total isocyanate-in-air
concentration is calculated from the sum of all the isocyanate-derived peaks calculated as NCO function. In
some cases, a bulk sample is used for calibration and results are reported as mass of base per volume.
The quantitative detection limits for isocyanate, defined as 10s, where s is the standard deviation obtained
from 10 measurements carried out on a standard solution whose concentration is close to the expected
detection limit, has been estimated to be approximately 0,026 µg/sample, 0,029 µg/sample, and
0,036 µg/sample for vapour phase HDI, TDI, and MDI, respectively. The quantitative detection limit for aerosol
phase HDI, TDI, and MDI is 0,031 µg/sample.
NOTE The calculation of oligomeric isocyanates by this method is expressed as the total NCO function equivalent,
utilizing the response factor of the corresponding monomer for the oligomer calculation.
4 Reagents and materials
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and distilled or
demineralized water or water of equivalent purity.
4.1 Water, HPLC grade or equivalent.
4.2 1-(2-Methoxyphenyl)piperazine (MP) [CAS No. 35386-24-4], >98 % mass fraction.
4.3 9-(Methylaminomethyl)anthracene (MAMA) [CAS No. 73356-19-1], >99 % mass fraction.
4.4 Acetic acid, glacial [CAS No. 64-19-7], HPLC grade.
4.5 Acetic anhydride [CAS No. 108-24-7], certified ACS.
4.6 Triethylamine [CAS No. 121-44-8], >98 % mass fraction assay by GC.
4.7 Phosphoric acid [CAS No. 7664-38-2], certified ACS.
4.8 Reagent solvents, commonly toluene [CAS No. 108-88-3], dimethylformamide [CAS No. 68-12-2], and
acetonitrile [CAS No. 75-05-8], should be HPLC grade. They shall be free from compounds co-eluting with the
substance(s) of interest. To avoid any interference from the solvent, perform quality controls on each different
lot of solvent.
4.9 Buffer solution and HPLC mobile phase.
4.9.1 Triethylamine buffer — vapour analysis. In a 1 l volumetric flask, dilute 30 ml triethylamine (4.6) in
water, and make up to the mark with water. Adjust the pH of this solution to 3 using phosphoric acid (4.7).
Filter the solution under vacuum with a 0,22 µm filter.
4.9.2 Sodium acetate buffer — aerosol analysis. Weigh approximately 12,5 g of sodium acetate in 1 l
HPLC grade water (4.1). Adjust the pH of this solution to 6 with glacial acetic acid (4.4). Filter the resulting
solution under vacuum with a 0,22 µm filter.
4.9.3 Mobile phase — vapour analysis. A solvent mixture of acetonitrile (4.8) and triethylamine
buffer (4.9.1). The appropriate proportion of each solvent depends on the isocyanate analysed, see Table 1.
4.9.4 Mobile phase — aerosol analysis. A solvent mixture of acetonitrile (4.8) and sodium acetate
buffer (4.9.2). The appropriate proportion of each solvent depends on the isocyanate analysed, see Table 2.
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ISO 17736:2010(E)
4.10 Reagent solutions.
4.10.1 Desorption solution — vapour analysis. A solvent mixture of 67 % volume fraction of
dimethylformamide (4.8) and 33 % volume fraction mobile phase.
4.10.2 Derivatization solution — aerosol analysis. Weigh 10 mg MP (4.2) and transfer it to a 100 ml
volumetric flask. Dissolve and make up to the mark with toluene (4.8). The final concentration of this MP
solution is equivalent to 0,1 mg/ml.
5 Apparatus
5.1 Sampling system. A three-piece, closed face, 37 mm cassette is used. The sampling train consists of
a 37 mm PTFE filter of porosity 5 µm followed by a binder free 37 mm glass fibre (GF) filter impregnated with
MAMA (4.3) and supported by a cellulose back-up pad (see Figure 1).
Figure 1 — Three-piece cassette 37 mm
1)
This sampling train is commercially available as ISO-CHEK® .
5.2 Sampling pump. The pump shall fulfil the requirements of EN 1232 or equivalent.
The pump should also be in accordance with local safety regulations.
5.3 Tubing, of plastic, rubber or other suitable material, about 900 mm long, of appropriate diameter to
ensure a leakproof fit to both pump (5.2) and double-filter sampling cassette (5.1). Clips shall be provided to
hold the cassette and connecting tubing to the worker's lapel within 300 mm of their breathing zone.
5.4 Flow meter, portable, capable of measuring the appropriate flow rate to within ±5 %, and calibrated
against a primary standard.
1) ISO-CHEK is the trade name of a product supplied by SKC. This information is given for the convenience of users of
this document and does not constitute an endorsement by ISO of the product named. Equivalent products may be used if
they can be shown to lead to the same results.
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ISO 17736:2010(E)
5.5 Glass jar, consisting of a 30 ml glass container equipped with a PTFE lined screw cap, capable of
receiving 37 mm filters.
5.6 Liquid chromatographic system. An HPLC linked to UV and FL detectors is required. The FL detector
should be used for the quantification of monomeric vapours when they are present at less than
0,180 µg/sample of isocyanate. A diode array detector (DAD) is also suitable for confirmation of identification.
5.7 Autosampler, commercially available, with a sampling loop within the range 10 µl to 100 µl.
5.8 HPLC column, of stainless steel, C-18 type, capable of separating the urea derivatives of interest.
6 Air sampling
6.1 Calibration of sampling system
Calibrate the sampling system (5.1) with a representative sampling device assembly in line, using an
appropriate external calibrated meter. One end of the calibrated flow meter (5.4) should be at atmospheric
pressure to ensure proper operation.
6.2 Preparation of sampling equipment
A glass jar (5.5) containing 5 ml MP derivatization solution (4.10.2) should be prepared in the laboratory
before sampling. Prepare one jar for each sample to be used.
6.3 Preparation of MAMA-impregnated filter
Approximately 100 GF filters are put in a beaker containing 25 mg MAMA (4.3) dissolved in 250 ml toluene
(4.8) for a period of 30 min. Remove the filters from the beaker with tweezers and transfer them to dry on a
sheet of aluminium foil placed in a compartment away from light for 12 h. The volume of solution absorbed by
one filter is evaluated to be 500 µl, equivalent to a mass of approximately 50 µg of MAMA on each filter. This
quantity corresponds to approximately 0,11 µmol and is 36 times the amount that would be required during
sampling before the reagent is exhausted (reacts) at a concentration of 5 ppb sampled at 1 l/min for 15 min.
6.4 Collection of samples
The recommended sampling volume for the double-filter sampling system (5.1) is 15 l (1 l/min for a period of
15 min). This sampling volume is used for short-term exposure and for mixtures of airborne particles and
vapour. The sampling time can be extended to 8 h if all the expected exposure is in a vapour form.
In accordance with EN 1232, adjust the pump (5.2) flow rate to approximately 1 l/min. To compensate for any
pressure drop due to the cassette, make sure the flow rate is adjusted with a sampling device in place. Turn
off the pump and use a new sampler. Record the sample identity and all relevant sampling data.
NOTE Keep a sampling device as a calibrator for further pump calibration.
Fix the sampler to the worker's lapel and position the sample as close to the breathing zone as possible.
Place the sampling pump in a convenient pocket (ensure the pump exhaust is not restricted) or fix to a belt
around the waist. Turn on the pump and write down the time of the beginning sampling period. At the end of
the sampling period, check and make a note of the sample flow rate before removing the cassette. The flow
rate of the pump should be within the ±5 % variation of the nominal value; if greater, discard the sample.
Calculate the mean flow rate, in litres per minute, by averaging the flow rate measurements throughout the
sampling period and calculate the volume of air sampled, in litres, by multiplying the mean flow rate by the
sampling time, in minutes.
As soon as the sampling period is over, using tweezers, immediately remove the PTFE filter from the
sampling device and place the filter in a glass jar (5.5) containing 5 ml MP derivatization solution (4.10.2).
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ISO 17736:2010(E)
Take care to avoid contact with the GF filter when removing the PTFE filter from the sampling device. Identify
the jar with the corresponding sampler's identification number. Losses of isocyanate aerosol because of their
reaction with other chemicals are negligible except for very fast-reacting isocyanate systems such as foam
spraying of MDI polyurethane applications (Reference [12]).
6.5 Blanks
Field blanks should be prepared by using cassettes identical to those used for sampling and subjecting them
to the same handling procedures as the samples except for the actual period of sampling. Label these as field
blanks. Provide a blank for every 10 samples or when changing sampler batch.
7 Procedure
7.1 Safety precautions
Wear safety glasses and appropriate disposable gloves during analysis to protect the eyes and hands from
harmful solvents and reagents, and to reduce the possibility of contamination.
WARNING — This International Standard does not purport to address all the safety concerns, if any,
associated with its use. It is the responsibility of the user of this standard to establish appropriate
health and safety practices and to ensure compliance with any national regulatory conditions.
7.2 Calibration standard
7.2.1 Preparation of monomer derivatives
Slowly add the appropriate diisocyanate to a MAMA solution in a ratio 1 mmol diisocyanate +2 mmol MAMA or
1 mmol monoisocyanate +1 mmol MAMA; a slight excess of MAMA may be used. The choice of solvent may
vary from one isocyanate to another; usually dichloromethane is suitable, but some reactions have shown
better performance using diethyl ether. Most reactions are exothermic and so an ice bath may be used to cool
down the resulting mixture.
2)
Collection of the white crystalline urea precipitate is performed using a paper filter [e.g. Whatman No. 42 ].
The resulting precipitate is washed with toluene (4.8) to remove the excess of MAMA. The urea derivatives
are slightly soluble in toluene. If needed, purification of the precipitate may be performed by dissolving in
warm methanol and then, using an ice bath to cool down the solution to re-precipitate the solid, filter and dry
the purified urea derivative. The purity of the derivative is determined by the melting point and HPLC analysis.
7.2.2 Preparation of standard solutions from the isocyanate monomer-urea derivatives (MAMA)
Weigh out precisely about 25 mg of the urea derivative in a 100 ml volumetric flask and make up to the mark
with dimethylformamide (4.8). Take aliquots of this solution and dilute volumetrically with the desorption
solution to create a series of working standard solutions over an NCO concentration range of 0,01 µg/ml to
2,1 µg/ml. Prepare further standard solutions, if the concentration range of the samples exceeds that of the
standards.
The isocyanate concentration in the standard, ρ , in micrograms per millilitre, is given by Equation (1):
NCO,std
ρ M N
ud,std NCO
ρ = (1)
NCO,std
M
ud
2) Whatman No. 42 is the trade name of a product supplied by Whatman. This information is given for the convenience
of users of this document and does not constitute an endorsement by ISO of the product named. Equivalent products may
be used if they can be shown to lead to the same results.
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ISO 17736:2010(E)
where
ρ is the concentration, in micrograms per millilitre, of urea derivative in the standard;
ud,std
M is the relative molecular mass of NCO;
NCO
N is the number of isocyanate groups (functions) per molecule;
M is the relative molecular mass of the urea derivative.
ud
7.2.3 Stability of isocyanate-ureas in solutions
Stock solutions of isocyanate monomer-urea derivatives have been found to be stable over a period of 1 year
if kept in a refrigerator. Isocyanate monomer-urea working solutions have been found to be stable for up to
90 days.
7.2.4 Preparation of standard solution for the aerosol isocyanates analysis
For each isocyanate to be analysed, produce a stock solution from the monomeric isocyanate by dissolving in
a known volume of toluene (4.8) in order to obtain a concentration of approximately 10 mg/l. Working
standards are made by further diluting with toluene to generate a working range from 0,1 µg/ml to 1,0 µg/ml.
When kept in a refrigerator, the stock solutions have been found to be stable for several months. However,
working standard solution should be made weekly.
8 Sample processing
8.1 Vapour analysis
The samples, quality controls, and blanks should receive the same treatment.
Remove the GF filter from the cassette and place it in a 30 ml glass jar (5.5). Add 2 ml desorption solution
(see 4.10.1) to the jar. Close the jar and shake for 30 min on a reciprocating shaker. Filter the solution into an
autosampler (5.7) vial, using a 0,22 µm syringe filter. Analyse using the HPLC vapour conditions specified in
9.2.
8.2 Aerosol analysis
The samples, quality controls and blanks should receive the same treatment.
Transfer the solution from the sampling jar (see 6.2) to an evaporator vial. Rinse the sampling jar and the filter
three times with 1 ml toluene (4.8).
For the standard solution, place 5 ml MP derivatization solution (4.10.2) in an evaporator vial. Add 1 ml
working standard solution (7.2.4) to the vial and mix gently to produce the monomer-urea.
The samples, blanks and standard are then processed as follows.
Place all the vials in a 50 °C pre-heated vacuum evaporator and evaporate to dryness. Allow the vials to cool
to ambient temperature. Dissolve the residue in 1 ml acetic anhydride (4.5) 0,5 % volume fraction in
acetonitrile (4.8). Filter the solution into an autosampler (5.7) vial, using a 0,22 µm syringe filter. Analyse using
the HPLC conditions for NCO oligomers specified in 9.3.
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ISO 17736:2010(E)
9 HPLC conditions
...
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