SIST ISO 20264:2021

Stationary source emissions - Determination of the mass concentration of individual volatile organic compounds (VOCs) in waste gases from non-combustion processes

This document specifies the use of FTIR spectrometry for determining the concentrations of individual volatile organic compounds (VOCs) in waste gases from non-combustion processes. The method can be employed to continuously analyse sample gas which is extracted from ducts and other sources. A bag sampling method can also be applied, if the compounds do not adsorb on the bag material, and is appropriate in cases where it is difficult or impossible to obtain a direct extractive sample.
The principle, sampling procedure, IR spectral measurement and analysis, calibration, handling interference, QA/QC procedures and some essential performance criteria for measurement of individual VOCs are described in this document.
NOTE 1 The practical minimum detectable concentration of this method depends on the FTIR instrument (i.e. gas cell path length, resolution, instrumental noise and analytical algorithm) used, compounds, and interference specific (e.g. water and CO2).

Émissions de sources fixes - Détermination de la concentration en masse de composés organiques volatils (COV) individuels dans les gaz résiduaires issus de processus sans combustion

Emisije nepremičnih virov - Določevanje masne koncentracije posameznih hlapnih organskih spojin (VOC) v odpadnih plinih nezgorevalnih procesov

General Information

• Status: Published
• Public Enquiry End Date: 01-Mar-2021
• Publication Date: 15-Apr-2021
• ICS: 13.040.40 - Stationary source emissions
• Technical Committee: KAZ - Air quality
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Apr-2021
• Due Date: 06-Jun-2021
• Completion Date: 16-Apr-2021
• Ref Project: ISO 20264:2019 - Stationary source emissions — Determination of the mass concentration of individual volatile organic compounds (VOCs) in waste gases from non-combustion processes

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ISO 20264:2021
01-maj-2021
Emisije nepremičnih virov - Določevanje masne koncentracije posameznih hlapnih
organskih spojin (VOC) v odpadnih plinih nezgorevalnih procesov
Stationary source emissions - Determination of the mass concentration of individual
volatile organic compounds (VOCs) in waste gases from non-combustion processes
Émissions de sources fixes - Détermination de la concentration en masse de composés
organiques volatils (COV) individuels dans les gaz résiduaires issus de processus sans
combustion
Ta slovenski standard je istoveten z: ISO 20264:2019
ICS:
13.040.40 Emisije nepremičnih virov Stationary source emissions
SIST ISO 20264:2021 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ISO 20264:2021

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SIST ISO 20264:2021
INTERNATIONAL ISO
STANDARD 20264
First edition
2019-09
Stationary source emissions —
Determination of the mass
concentration of individual volatile
organic compounds (VOCs) in waste
gases from non-combustion processes
Émissions de sources fixes — Détermination de la concentration en
masse de composés organiques volatils (COV) individuels dans les gaz
résiduaires issus de processus sans combustion
Reference number
ISO 20264:2019(E)
©
ISO 2019

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SIST ISO 20264:2021
ISO 20264:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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SIST ISO 20264:2021
ISO 20264:2019(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms related to FTIR . 1
3.2 Terms related to performance characteristics . 2
4 Symbols and abbreviated terms . 3
5 Measurement principle . 4
5.1 General . 4
5.2 FTIR Spectrometer components . 4
5.3 Interferogram . 5
5.4 Fast Fourier transform . 6
5.5 Beer’s law. 6
6 Equipment . 7
6.1 Sampling system . 7
6.2 Analytical apparatus (FTIR) . 8
7 Measurement procedure . 9
7.1 General . 9
7.2 Choice of the measuring system . 9
7.3 Sampling .10
7.3.1 Sampling location .10
7.3.2 Sampling point(s) .10
7.3.3 Extractive sampling .10
7.3.4 Sampling with a gas bag .10
7.4 Pre-test and sample quantification procedures .11
8 Performance chracteristics and criteria .11
8.1 General .11
8.2 Performance criteria .11
8.2.1 Zero check .12
8.2.2 Repeatability of calibration verification gas .12
8.2.3 Response time .12
8.2.4 Losses and leakage in the sampling line . .13
9 Quality assurance and quality control procedure .13
10 Data quantification .14
10.1 General .14
10.2 Data quantification techniques .14
10.3 Data quantification methodology .14
10.3.1 Calibration set .14
10.3.2 Analysis band selection .14
10.3.3 Lack of fit (linearity) of the analytical software .15
10.3.4 Validation of analytical model .15
10.3.5 Sample analysis .15
10.3.6 Sample result validation .16
10.3.7 Residual check .16
11 Validation and uncertainty .16
Annex A (normative) Determination of the FTIR performance parameters .17
Annex B (informative) Example for IR spectral absorption features of VOCs .18
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Annex C (informative) Examples for analytical band choice .20
Annex D (informative) The typical spectral regions for the different bond types of VOCs .23
Annex E (informative) The validation of measurement of individual VOC in waste gas .25
Bibliography .32
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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 of 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 www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 1,
Stationary source emissions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
© ISO 2019 – All rights reserved v

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Introduction
There are various volatile organic compounds (VOCs) emitted from stationary sources where organic
solvents are used for painting, printing, cleaning, degreasing and chemicals production. In order to
understand how to reduce the environmental risk due to VOCs, it is necessary to measure not only
the concentration of total VOCs but also the concentration of individual VOCs in waste gases. This is
because individual VOCs have different potentials to form O and suspended particulate matter (SPM).
3
Also, there are VOCs of high toxicity (e.g. benzene, toluene, propyl acetate, propanol, formaldehyde,
some chlorinated organic compounds) of concern.
Fourier Transform Infrared (FTIR) spectrometry is proposed to provide these measurements as it
provides a measurement in the infrared (IR) region over a wide spectral band. Analysis of the recorded
spectra enables the concentration of a wide number of compounds to be quantified simultaneously.
Overlap of IR absorption features with each VOC can affect the quantification of each compound.
However, by using appropriate chemometric procedures for the overlapping IR spectra of VOCs, the
concentrations are quantified for the individual compounds of interest.
This document specifies the measurement method for determining concentrations of individual VOCs
in waste gases from non-combustion processes by using FTIR spectroscopy.
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SIST ISO 20264:2021
INTERNATIONAL STANDARD ISO 20264:2019(E)
Stationary source emissions — Determination of the mass
concentration of individual volatile organic compounds
(VOCs) in waste gases from non-combustion processes
1 Scope
This document specifies the use of FTIR spectrometry for determining the concentrations of individual
volatile organic compounds (VOCs) in waste gases from non-combustion processes. The method can
be employed to continuously analyse sample gas which is extracted from ducts and other sources. A
bag sampling method can also be applied, if the compounds do not adsorb on the bag material, and is
appropriate in cases where it is difficult or impossible to obtain a direct extractive sample.
The principle, sampling procedure, IR spectral measurement and analysis, calibration, handling
interference, QA/QC procedures and some essential performance criteria for measurement of individual
VOCs are described in this document.
NOTE 1 The practical minimum detectable concentration of this method depends on the FTIR instrument (i.e.
gas cell path length, resolution, instrumental noise and analytical algorithm) used, compounds, and interference
specific (e.g. water and CO ).
2
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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 Terms related to FTIR
3.1.1
absorbance
negative logarithm of the transmission, A = −log(I/I ), where I is the transmitted intensity of the light
0
and I is the incident intensity
0
3.1.2
resolution
minimum separation that two spectral features can have and still, in some manner, be distinguished
from one another
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3.2 Terms related to performance characteristics
3.2.1
reference spectrum
plot of absorbance versus wavenumber for a known gas or known mixture of gases, which are obtained
under controlled conditions of pressure and temperature, path length, and known concentration
Note 1 to entry: The reference spectra are used to prepare the chemometric model used to obtain the unknown
concentrations of analytes in sample spectra.
Note 2 to entry: See 10.3.1.
3.2.2
validation spectrum
plot of absorbance versus wavenumber for calibration verification gas (3.2.6)
Note 1 to entry: See 10.3.4.
3.2.3
background spectrum
plot of absorbance versus wavenumber for zero gas (3.2.5)
3.2.4
response time
time interval between the instant when a stimulus is subjected to a specified abrupt change and the
instant when the response reaches and remains within specified limits around its final stable value,
determined as the sum of the lag time and the rise time in the rising mode, and the sum of the lag time
and the fall time in the falling mode
[SOURCE: ISO 9169:2006, 2.2.4]
3.2.5
zero gas
high purity nitrogen (99,999 %) or synthetic air (99,999 %) is used to measure a background spectrum
(3.2.3) and to determine the limit of detection, as well as to purge sample lines and sampling system
components, to dilute sample and calibration verification gas (3.2.6), and to conduct blank measurements
3.2.6
calibration verification gas
gas or gas mixture where the concentration(s) and uncertainty(ies) are known, used to check the high
level concentration point of the measuring system
Note 1 to entry: The gas or gases used is included in the analytical algorithm used to quantify the concentration
of target analyte, and have absorption lines distinguishable from baseline noise at wavenumbers that are within
the upper and lower wavenumber limits where the target analyte displays absorption lines distinguishable from
baseline noise. An absorption feature is considered distinguishable from baseline noise if it is greater than three
times the standard deviation of the baseline noise.
Note 2 to entry: This concentration is often chosen around 70 % to 80 % of full scale.
3.2.7
lack of fit
systematic deviation within the range of application between the measurement results obtained
by applying the calibration function to the observed response of the measuring system, measuring
reference materials and the corresponding accepted value of such reference materials
Note 1 to entry: Lack of fit can be a function of the measurement result.
[SOURCE: ISO 9169:2006, 2.2.9]
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3.2.8
analytical interference
situation that arises when two or more compounds have overlapping absorbance bands in their
infrared spectra
3.2.9
limit of detection
LOD
minimum concentration of a compound that can be detected by an instrument with a given statistical
probability
Note 1 to entry: Usually the detection limit is given as three times the standard deviation of noise in the system.
3.2.10
analytical algorithm
method used to quantify the concentration of the target analytes and interferences in each FTIR
spectrum
Note 1 to entry: The analytical algorithm should be used to account for the analytical interferences (3.2.8) by
conducting the analysis in a portion of the infrared spectrum that is the most unique for that particular
compound.
3.2.11
chemometrics
chemical discipline that uses mathematical and statistical methods, (a) to design or select optimal
measurement procedures and experiments, and (b) to provide maximum chemical information by
analysing chemical data
3.2.12
independent reading
reading that is not influenced by a previous individual reading as the two individual readings are
separated by at least four response times
4 Symbols and abbreviated terms
I intensity of incident radiation
0
I intensity of transmitted radiation
A absorbance
T transmittance
α absorptivity
l optical path length
c sample concentration
C the known concentration from the reference spectra
CLS
C the predicted concentrations from the validation spectra
VAL
FTIR Fourier transform infrared
CLS classical least squares
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PLS partial least squares
ILS inverse least squares
SEV standard error of validation
5 Measurement principle
5.1 General
A sample gas is extracted from ducts and other sources via a sampling system and continually
introduced into a gas cell of an FTIR system. The IR spectra of the sample gas is measured using an
FTIR spectrometer. When a sampling bag is used, the gas sampled in the bag is transferred to the gas
cell. IR spectra obtained are analysed by using analytical algorithm. Some VOCs might adsorb onto the
sampling bag surface, reducing meaured VOC concentration. Losses by absorption shall be tested and
documented before sampling.
5.2 FTIR Spectrometer components
Figure 1 illustrates the basic FTIR spectrometer configuration required for gas phase analyses. The IR
radiation emitted by the IR source contains energy at all wavelengths between 2,5 and 14 μm, which
−1
is 700 to 4 000 cm for most IR systems conducting these analyses. The IR radiation passes through
an interferometer, where the motion of an optical element — usually a mirror — optically modulates
the IR beam. The modulated IR beam then enters an absorption cell through a window and interacts
with the gases of interest. In “multi-pass” (for example “White”) absorption cells, mirrors within the
cell direct the IR beam through the sample gas multiple times; in such cells, the absorption pathlength
can be from 4 to 50 (or more) times the cell’s physical length. (A larger absorption path length generally
leads to greater sensitivity.) The IR beam then exits the sample cell via a second window and is re-
focused onto an IR detector.
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Key
1 IR source 7 absorption cell exhaust
2 aperture or filter 1 (optional) 8 absorption cell inlet
3 interferometer 9 mirror
4 focusing optics 10 absorption cell
5 aperture or filter 2 (optional) 11 infrared window
6 IR detector
Figure 1 — FTIR spectrometer components and beam path
5.3 Interferogram
A beam of the broadband IR radiation is divided into two or more paths with different optical path
lengths and is recombined to give a detector signal with repetitive interference maxima and minima
with the aid of an interferometer. Figure 2 shows the Michelson interferometer as an example.
The interferogram is obtained by plotting the detector signal against the difference in optical path
length. Given a difference in optical path lengths corresponding to an even multiple of the wavelength,
the interference is constructive, and given an odd multiple, the interference is destructive. An additional
laser with its own detector is contained in an FTIR system. The radiation emitted by the laser and the
broad band IR source passes through the interferometer simultaneously, although the interferograms
are recorded by separate detectors. From the positions of the peaks of the interferogram of the laser
irradiation, it is possible to determine the difference in the optical path length, as the laser's input
frequency is known and is constant (e.g. 632,8 nm for a HeNe laser).
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Key
1 IR source
2 beam splitter
3 fixed mirror
4 movable mirror
5 absorption cell
6 detector
Figure 2 — Principle of the Michelson interferometer
5.4 Fast Fourier transform
Every data point in the interferogram contains intensity information about every infrared wavelength
transmitted from the source to the detector. It is possible to recover the intensity information as a
function of wavelength through application of a fast Fourier transform, from which the FTIR technique's
name is derived. This digital transformation of the interferogram can be thought of as the mathematical
inverse of the optical modulation applied to the infrared beam as it passes through the interferometer.
5.5 Beer’s law
The direct proportionality of the absorbance of a compound in a homogeneous sample to its
concentration. See Formula (1) which also describes the more general case of gas mixtures.
 I 
 1 
0
logl=− og ==Alα c (1)
 
 
IT
 
 
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where
I is the intensity of incident radiation;
0
I is the intensity of transmitted radiation;
A is the absorbance;
T is the transmittance;
α is the absorpitivity;
l is the optical path length;
c is the sample concentration.
6 Equipment
6.1 Sampling system
The sampling is the process of extracting a small portion which is representative of the composition of
the main gas stream from a large quantity of waste gas. A partial flow of the waste gas is directed into
the gas cell of the FTIR spectrometer via a sampling probe, a particle filter and sampling line.
An example of the sampling system using a gas cell of the FTIR system is shown in Figure 3. The
system consists of an extractive probe and heated filter to remove fine particles, a bypass valve for N
2
purging gas cell with thermometer and pressure gauge, an FTIR spectrometer, a mass flow meter for
controlling the flow rate of sample gas into the gas cell, a shut-off valve and a sampling pump. When the
sampling line is long, the bypass pump is set to remove a residual gas in the sampling line. The sampling
pump should be installed downstream of a gas cell to prevent adsorptive losses of analytes or other
contamination by the pump. If the pump is made with inert materials and is heated, it can be installed
upstream of a gas cell. The sampling line and the gas cell of the FTIR spectrometer need to be heated
if there is any risk of condensation. The temperature of the upstream sampling components should be
the same as or slightly lower than that of the gas cell. The gas cell temperature and pressure shall be
measured and compensated and should be at the same or a similar temperature and pressure to that of
the reference spectra. Gas flow rate and temperature shall be recorded.
The sampling system including sample lines and particle filter device shall:
a) be made of a material that is chemically and physically inert to the constituents of the waste gas
under analysis;
b) be designed to ensure a short residence time (with long lines or high flow resistance, the use of an
external pump with bypass is recommended);
c) have an inlet for applying a test gas close to the sampling probe, upstream of the particle filter.
When a sampling bag is used, the gas sampled in the bag is to be transferred to the gas cell of the FTIR
spectrometer. The system using the sampling bag is shown in Figure 4. This system constitutes a
sampling probe, a filter, a sampling valve, a sampling bag, a sampling vacuum box, a valve, a sampling
pump and a flow meter to introduce the waste gas into a sample bag. The sampling bag shall be made of
a material which prevents the adsorption of VOCs. This is not a recommended procedure unless it is not
possible to get the sample extractively.
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Key
1 sampling probe 7 gas cell with thermometer and pressure gauge
2 valve for introducing test gases 8 FTIR spectrometer
3 particle filte
...

INTERNATIONAL ISO
STANDARD 20264
First edition
2019-09
Stationary source emissions —
Determination of the mass
concentration of individual volatile
organic compounds (VOCs) in waste
gases from non-combustion processes
Émissions de sources fixes — Détermination de la concentration en
masse de composés organiques volatils (COV) individuels dans les gaz
résiduaires issus de processus sans combustion
Reference number
ISO 20264:2019(E)
©
ISO 2019

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ISO 20264:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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ISO 20264:2019(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms related to FTIR . 1
3.2 Terms related to performance characteristics . 2
4 Symbols and abbreviated terms . 3
5 Measurement principle . 4
5.1 General . 4
5.2 FTIR Spectrometer components . 4
5.3 Interferogram . 5
5.4 Fast Fourier transform . 6
5.5 Beer’s law. 6
6 Equipment . 7
6.1 Sampling system . 7
6.2 Analytical apparatus (FTIR) . 8
7 Measurement procedure . 9
7.1 General . 9
7.2 Choice of the measuring system . 9
7.3 Sampling .10
7.3.1 Sampling location .10
7.3.2 Sampling point(s) .10
7.3.3 Extractive sampling .10
7.3.4 Sampling with a gas bag .10
7.4 Pre-test and sample quantification procedures .11
8 Performance chracteristics and criteria .11
8.1 General .11
8.2 Performance criteria .11
8.2.1 Zero check .12
8.2.2 Repeatability of calibration verification gas .12
8.2.3 Response time .12
8.2.4 Losses and leakage in the sampling line . .13
9 Quality assurance and quality control procedure .13
10 Data quantification .14
10.1 General .14
10.2 Data quantification techniques .14
10.3 Data quantification methodology .14
10.3.1 Calibration set .14
10.3.2 Analysis band selection .14
10.3.3 Lack of fit (linearity) of the analytical software .15
10.3.4 Validation of analytical model .15
10.3.5 Sample analysis .15
10.3.6 Sample result validation .16
10.3.7 Residual check .16
11 Validation and uncertainty .16
Annex A (normative) Determination of the FTIR performance parameters .17
Annex B (informative) Example for IR spectral absorption features of VOCs .18
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Annex C (informative) Examples for analytical band choice .20
Annex D (informative) The typical spectral regions for the different bond types of VOCs .23
Annex E (informative) The validation of measurement of individual VOC in waste gas .25
Bibliography .32
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ISO 20264:2019(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.
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 of 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 www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 1,
Stationary source emissions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
© ISO 2019 – All rights reserved v

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ISO 20264:2019(E)

Introduction
There are various volatile organic compounds (VOCs) emitted from stationary sources where organic
solvents are used for painting, printing, cleaning, degreasing and chemicals production. In order to
understand how to reduce the environmental risk due to VOCs, it is necessary to measure not only
the concentration of total VOCs but also the concentration of individual VOCs in waste gases. This is
because individual VOCs have different potentials to form O and suspended particulate matter (SPM).
3
Also, there are VOCs of high toxicity (e.g. benzene, toluene, propyl acetate, propanol, formaldehyde,
some chlorinated organic compounds) of concern.
Fourier Transform Infrared (FTIR) spectrometry is proposed to provide these measurements as it
provides a measurement in the infrared (IR) region over a wide spectral band. Analysis of the recorded
spectra enables the concentration of a wide number of compounds to be quantified simultaneously.
Overlap of IR absorption features with each VOC can affect the quantification of each compound.
However, by using appropriate chemometric procedures for the overlapping IR spectra of VOCs, the
concentrations are quantified for the individual compounds of interest.
This document specifies the measurement method for determining concentrations of individual VOCs
in waste gases from non-combustion processes by using FTIR spectroscopy.
vi © ISO 2019 – All rights reserved

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INTERNATIONAL STANDARD ISO 20264:2019(E)
Stationary source emissions — Determination of the mass
concentration of individual volatile organic compounds
(VOCs) in waste gases from non-combustion processes
1 Scope
This document specifies the use of FTIR spectrometry for determining the concentrations of individual
volatile organic compounds (VOCs) in waste gases from non-combustion processes. The method can
be employed to continuously analyse sample gas which is extracted from ducts and other sources. A
bag sampling method can also be applied, if the compounds do not adsorb on the bag material, and is
appropriate in cases where it is difficult or impossible to obtain a direct extractive sample.
The principle, sampling procedure, IR spectral measurement and analysis, calibration, handling
interference, QA/QC procedures and some essential performance criteria for measurement of individual
VOCs are described in this document.
NOTE 1 The practical minimum detectable concentration of this method depends on the FTIR instrument (i.e.
gas cell path length, resolution, instrumental noise and analytical algorithm) used, compounds, and interference
specific (e.g. water and CO ).
2
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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 Terms related to FTIR
3.1.1
absorbance
negative logarithm of the transmission, A = −log(I/I ), where I is the transmitted intensity of the light
0
and I is the incident intensity
0
3.1.2
resolution
minimum separation that two spectral features can have and still, in some manner, be distinguished
from one another
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3.2 Terms related to performance characteristics
3.2.1
reference spectrum
plot of absorbance versus wavenumber for a known gas or known mixture of gases, which are obtained
under controlled conditions of pressure and temperature, path length, and known concentration
Note 1 to entry: The reference spectra are used to prepare the chemometric model used to obtain the unknown
concentrations of analytes in sample spectra.
Note 2 to entry: See 10.3.1.
3.2.2
validation spectrum
plot of absorbance versus wavenumber for calibration verification gas (3.2.6)
Note 1 to entry: See 10.3.4.
3.2.3
background spectrum
plot of absorbance versus wavenumber for zero gas (3.2.5)
3.2.4
response time
time interval between the instant when a stimulus is subjected to a specified abrupt change and the
instant when the response reaches and remains within specified limits around its final stable value,
determined as the sum of the lag time and the rise time in the rising mode, and the sum of the lag time
and the fall time in the falling mode
[SOURCE: ISO 9169:2006, 2.2.4]
3.2.5
zero gas
high purity nitrogen (99,999 %) or synthetic air (99,999 %) is used to measure a background spectrum
(3.2.3) and to determine the limit of detection, as well as to purge sample lines and sampling system
components, to dilute sample and calibration verification gas (3.2.6), and to conduct blank measurements
3.2.6
calibration verification gas
gas or gas mixture where the concentration(s) and uncertainty(ies) are known, used to check the high
level concentration point of the measuring system
Note 1 to entry: The gas or gases used is included in the analytical algorithm used to quantify the concentration
of target analyte, and have absorption lines distinguishable from baseline noise at wavenumbers that are within
the upper and lower wavenumber limits where the target analyte displays absorption lines distinguishable from
baseline noise. An absorption feature is considered distinguishable from baseline noise if it is greater than three
times the standard deviation of the baseline noise.
Note 2 to entry: This concentration is often chosen around 70 % to 80 % of full scale.
3.2.7
lack of fit
systematic deviation within the range of application between the measurement results obtained
by applying the calibration function to the observed response of the measuring system, measuring
reference materials and the corresponding accepted value of such reference materials
Note 1 to entry: Lack of fit can be a function of the measurement result.
[SOURCE: ISO 9169:2006, 2.2.9]
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3.2.8
analytical interference
situation that arises when two or more compounds have overlapping absorbance bands in their
infrared spectra
3.2.9
limit of detection
LOD
minimum concentration of a compound that can be detected by an instrument with a given statistical
probability
Note 1 to entry: Usually the detection limit is given as three times the standard deviation of noise in the system.
3.2.10
analytical algorithm
method used to quantify the concentration of the target analytes and interferences in each FTIR
spectrum
Note 1 to entry: The analytical algorithm should be used to account for the analytical interferences (3.2.8) by
conducting the analysis in a portion of the infrared spectrum that is the most unique for that particular
compound.
3.2.11
chemometrics
chemical discipline that uses mathematical and statistical methods, (a) to design or select optimal
measurement procedures and experiments, and (b) to provide maximum chemical information by
analysing chemical data
3.2.12
independent reading
reading that is not influenced by a previous individual reading as the two individual readings are
separated by at least four response times
4 Symbols and abbreviated terms
I intensity of incident radiation
0
I intensity of transmitted radiation
A absorbance
T transmittance
α absorptivity
l optical path length
c sample concentration
C the known concentration from the reference spectra
CLS
C the predicted concentrations from the validation spectra
VAL
FTIR Fourier transform infrared
CLS classical least squares
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PLS partial least squares
ILS inverse least squares
SEV standard error of validation
5 Measurement principle
5.1 General
A sample gas is extracted from ducts and other sources via a sampling system and continually
introduced into a gas cell of an FTIR system. The IR spectra of the sample gas is measured using an
FTIR spectrometer. When a sampling bag is used, the gas sampled in the bag is transferred to the gas
cell. IR spectra obtained are analysed by using analytical algorithm. Some VOCs might adsorb onto the
sampling bag surface, reducing meaured VOC concentration. Losses by absorption shall be tested and
documented before sampling.
5.2 FTIR Spectrometer components
Figure 1 illustrates the basic FTIR spectrometer configuration required for gas phase analyses. The IR
radiation emitted by the IR source contains energy at all wavelengths between 2,5 and 14 μm, which
−1
is 700 to 4 000 cm for most IR systems conducting these analyses. The IR radiation passes through
an interferometer, where the motion of an optical element — usually a mirror — optically modulates
the IR beam. The modulated IR beam then enters an absorption cell through a window and interacts
with the gases of interest. In “multi-pass” (for example “White”) absorption cells, mirrors within the
cell direct the IR beam through the sample gas multiple times; in such cells, the absorption pathlength
can be from 4 to 50 (or more) times the cell’s physical length. (A larger absorption path length generally
leads to greater sensitivity.) The IR beam then exits the sample cell via a second window and is re-
focused onto an IR detector.
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Key
1 IR source 7 absorption cell exhaust
2 aperture or filter 1 (optional) 8 absorption cell inlet
3 interferometer 9 mirror
4 focusing optics 10 absorption cell
5 aperture or filter 2 (optional) 11 infrared window
6 IR detector
Figure 1 — FTIR spectrometer components and beam path
5.3 Interferogram
A beam of the broadband IR radiation is divided into two or more paths with different optical path
lengths and is recombined to give a detector signal with repetitive interference maxima and minima
with the aid of an interferometer. Figure 2 shows the Michelson interferometer as an example.
The interferogram is obtained by plotting the detector signal against the difference in optical path
length. Given a difference in optical path lengths corresponding to an even multiple of the wavelength,
the interference is constructive, and given an odd multiple, the interference is destructive. An additional
laser with its own detector is contained in an FTIR system. The radiation emitted by the laser and the
broad band IR source passes through the interferometer simultaneously, although the interferograms
are recorded by separate detectors. From the positions of the peaks of the interferogram of the laser
irradiation, it is possible to determine the difference in the optical path length, as the laser's input
frequency is known and is constant (e.g. 632,8 nm for a HeNe laser).
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Key
1 IR source
2 beam splitter
3 fixed mirror
4 movable mirror
5 absorption cell
6 detector
Figure 2 — Principle of the Michelson interferometer
5.4 Fast Fourier transform
Every data point in the interferogram contains intensity information about every infrared wavelength
transmitted from the source to the detector. It is possible to recover the intensity information as a
function of wavelength through application of a fast Fourier transform, from which the FTIR technique's
name is derived. This digital transformation of the interferogram can be thought of as the mathematical
inverse of the optical modulation applied to the infrared beam as it passes through the interferometer.
5.5 Beer’s law
The direct proportionality of the absorbance of a compound in a homogeneous sample to its
concentration. See Formula (1) which also describes the more general case of gas mixtures.
 I 
 1 
0
logl=− og ==Alα c (1)
 
 
IT
 
 
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where
I is the intensity of incident radiation;
0
I is the intensity of transmitted radiation;
A is the absorbance;
T is the transmittance;
α is the absorpitivity;
l is the optical path length;
c is the sample concentration.
6 Equipment
6.1 Sampling system
The sampling is the process of extracting a small portion which is representative of the composition of
the main gas stream from a large quantity of waste gas. A partial flow of the waste gas is directed into
the gas cell of the FTIR spectrometer via a sampling probe, a particle filter and sampling line.
An example of the sampling system using a gas cell of the FTIR system is shown in Figure 3. The
system consists of an extractive probe and heated filter to remove fine particles, a bypass valve for N
2
purging gas cell with thermometer and pressure gauge, an FTIR spectrometer, a mass flow meter for
controlling the flow rate of sample gas into the gas cell, a shut-off valve and a sampling pump. When the
sampling line is long, the bypass pump is set to remove a residual gas in the sampling line. The sampling
pump should be installed downstream of a gas cell to prevent adsorptive losses of analytes or other
contamination by the pump. If the pump is made with inert materials and is heated, it can be installed
upstream of a gas cell. The sampling line and the gas cell of the FTIR spectrometer need to be heated
if there is any risk of condensation. The temperature of the upstream sampling components should be
the same as or slightly lower than that of the gas cell. The gas cell temperature and pressure shall be
measured and compensated and should be at the same or a similar temperature and pressure to that of
the reference spectra. Gas flow rate and temperature shall be recorded.
The sampling system including sample lines and particle filter device shall:
a) be made of a material that is chemically and physically inert to the constituents of the waste gas
under analysis;
b) be designed to ensure a short residence time (with long lines or high flow resistance, the use of an
external pump with bypass is recommended);
c) have an inlet for applying a test gas close to the sampling probe, upstream of the particle filter.
When a sampling bag is used, the gas sampled in the bag is to be transferred to the gas cell of the FTIR
spectrometer. The system using the sampling bag is shown in Figure 4. This system constitutes a
sampling probe, a filter, a sampling valve, a sampling bag, a sampling vacuum box, a valve, a sampling
pump and a flow meter to introduce the waste gas into a sample bag. The sampling bag shall be made of
a material which prevents the adsorption of VOCs. This is not a recommended procedure unless it is not
possible to get the sample extractively.
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Key
1 sampling probe 7 gas cell with thermometer and pressure gauge
2 valve for introducing test gases 8 FTIR spectrometer
3 particle filter 9 mass flow meter
4 bypass pump (if necessary) 10 shut-off valve
5 bypass valve for N purging 11 sampling pump
2
6 sampling valve
Figure 3 — An example of a sampling system using a gas cell of an FTIR spectrometer
Key
1 sampling probe 5 sampling vacuum box
2 particle filter (if necessary) 6 valve
3 sampling valve 7 sampling pump
4 sampling bag 8 flow meter
Figure 4 — An example of a sampling system using a sampling bag
6.2 Analytical apparatus (FTIR)
The FTIR spectrometer consists of an IR source, an aperture or filter, an interferometer, an IR detector,
a gas cell, a mirror and an optical window.
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The devices of an FTIR spectrometer recommended for the measurement of VOCs are as follows:
a) gas cell:
— the cell should be made of materials which prevent the adsorption of VOCs;
— materials of the cell shall be Ni, Al, glass or stainless steel (stainless steel is not suitable for
measurement at a high temperature);
— the temperature of the cell should be set at an appropriate temperature to prevent the
condensation of VOCs;
— the volume of the cell is related to a response time (
...

SLOVENSKI STANDARD
oSIST ISO 20264:2021
01-februar-2021
Emisije nepremičnih virov - Določevanje masne koncentracije posameznih hlapnih
organskih spojin (VOC) v odpadnih plinih nezgorevalnih procesov
Stationary source emissions - Determination of the mass concentration of individual
volatile organic compounds (VOCs) in waste gases from non-combustion processes
Émissions de sources fixes - Détermination de la concentration en masse de composés
organiques volatils (COV) individuels dans les gaz résiduaires issus de processus sans
combustion
Ta slovenski standard je istoveten z: ISO 20264:2019
ICS:
13.040.40 Emisije nepremičnih virov Stationary source emissions
oSIST ISO 20264:2021 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST ISO 20264:2021

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oSIST ISO 20264:2021
INTERNATIONAL ISO
STANDARD 20264
First edition
2019-09
Stationary source emissions —
Determination of the mass
concentration of individual volatile
organic compounds (VOCs) in waste
gases from non-combustion processes
Émissions de sources fixes — Détermination de la concentration en
masse de composés organiques volatils (COV) individuels dans les gaz
résiduaires issus de processus sans combustion
Reference number
ISO 20264:2019(E)
©
ISO 2019

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oSIST ISO 20264:2021
ISO 20264:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms related to FTIR . 1
3.2 Terms related to performance characteristics . 2
4 Symbols and abbreviated terms . 3
5 Measurement principle . 4
5.1 General . 4
5.2 FTIR Spectrometer components . 4
5.3 Interferogram . 5
5.4 Fast Fourier transform . 6
5.5 Beer’s law. 6
6 Equipment . 7
6.1 Sampling system . 7
6.2 Analytical apparatus (FTIR) . 8
7 Measurement procedure . 9
7.1 General . 9
7.2 Choice of the measuring system . 9
7.3 Sampling .10
7.3.1 Sampling location .10
7.3.2 Sampling point(s) .10
7.3.3 Extractive sampling .10
7.3.4 Sampling with a gas bag .10
7.4 Pre-test and sample quantification procedures .11
8 Performance chracteristics and criteria .11
8.1 General .11
8.2 Performance criteria .11
8.2.1 Zero check .12
8.2.2 Repeatability of calibration verification gas .12
8.2.3 Response time .12
8.2.4 Losses and leakage in the sampling line . .13
9 Quality assurance and quality control procedure .13
10 Data quantification .14
10.1 General .14
10.2 Data quantification techniques .14
10.3 Data quantification methodology .14
10.3.1 Calibration set .14
10.3.2 Analysis band selection .14
10.3.3 Lack of fit (linearity) of the analytical software .15
10.3.4 Validation of analytical model .15
10.3.5 Sample analysis .15
10.3.6 Sample result validation .16
10.3.7 Residual check .16
11 Validation and uncertainty .16
Annex A (normative) Determination of the FTIR performance parameters .17
Annex B (informative) Example for IR spectral absorption features of VOCs .18
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Annex C (informative) Examples for analytical band choice .20
Annex D (informative) The typical spectral regions for the different bond types of VOCs .23
Annex E (informative) The validation of measurement of individual VOC in waste gas .25
Bibliography .32
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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 of 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 www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 1,
Stationary source emissions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
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Introduction
There are various volatile organic compounds (VOCs) emitted from stationary sources where organic
solvents are used for painting, printing, cleaning, degreasing and chemicals production. In order to
understand how to reduce the environmental risk due to VOCs, it is necessary to measure not only
the concentration of total VOCs but also the concentration of individual VOCs in waste gases. This is
because individual VOCs have different potentials to form O and suspended particulate matter (SPM).
3
Also, there are VOCs of high toxicity (e.g. benzene, toluene, propyl acetate, propanol, formaldehyde,
some chlorinated organic compounds) of concern.
Fourier Transform Infrared (FTIR) spectrometry is proposed to provide these measurements as it
provides a measurement in the infrared (IR) region over a wide spectral band. Analysis of the recorded
spectra enables the concentration of a wide number of compounds to be quantified simultaneously.
Overlap of IR absorption features with each VOC can affect the quantification of each compound.
However, by using appropriate chemometric procedures for the overlapping IR spectra of VOCs, the
concentrations are quantified for the individual compounds of interest.
This document specifies the measurement method for determining concentrations of individual VOCs
in waste gases from non-combustion processes by using FTIR spectroscopy.
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oSIST ISO 20264:2021
INTERNATIONAL STANDARD ISO 20264:2019(E)
Stationary source emissions — Determination of the mass
concentration of individual volatile organic compounds
(VOCs) in waste gases from non-combustion processes
1 Scope
This document specifies the use of FTIR spectrometry for determining the concentrations of individual
volatile organic compounds (VOCs) in waste gases from non-combustion processes. The method can
be employed to continuously analyse sample gas which is extracted from ducts and other sources. A
bag sampling method can also be applied, if the compounds do not adsorb on the bag material, and is
appropriate in cases where it is difficult or impossible to obtain a direct extractive sample.
The principle, sampling procedure, IR spectral measurement and analysis, calibration, handling
interference, QA/QC procedures and some essential performance criteria for measurement of individual
VOCs are described in this document.
NOTE 1 The practical minimum detectable concentration of this method depends on the FTIR instrument (i.e.
gas cell path length, resolution, instrumental noise and analytical algorithm) used, compounds, and interference
specific (e.g. water and CO ).
2
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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 Terms related to FTIR
3.1.1
absorbance
negative logarithm of the transmission, A = −log(I/I ), where I is the transmitted intensity of the light
0
and I is the incident intensity
0
3.1.2
resolution
minimum separation that two spectral features can have and still, in some manner, be distinguished
from one another
© ISO 2019 – All rights reserved 1

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3.2 Terms related to performance characteristics
3.2.1
reference spectrum
plot of absorbance versus wavenumber for a known gas or known mixture of gases, which are obtained
under controlled conditions of pressure and temperature, path length, and known concentration
Note 1 to entry: The reference spectra are used to prepare the chemometric model used to obtain the unknown
concentrations of analytes in sample spectra.
Note 2 to entry: See 10.3.1.
3.2.2
validation spectrum
plot of absorbance versus wavenumber for calibration verification gas (3.2.6)
Note 1 to entry: See 10.3.4.
3.2.3
background spectrum
plot of absorbance versus wavenumber for zero gas (3.2.5)
3.2.4
response time
time interval between the instant when a stimulus is subjected to a specified abrupt change and the
instant when the response reaches and remains within specified limits around its final stable value,
determined as the sum of the lag time and the rise time in the rising mode, and the sum of the lag time
and the fall time in the falling mode
[SOURCE: ISO 9169:2006, 2.2.4]
3.2.5
zero gas
high purity nitrogen (99,999 %) or synthetic air (99,999 %) is used to measure a background spectrum
(3.2.3) and to determine the limit of detection, as well as to purge sample lines and sampling system
components, to dilute sample and calibration verification gas (3.2.6), and to conduct blank measurements
3.2.6
calibration verification gas
gas or gas mixture where the concentration(s) and uncertainty(ies) are known, used to check the high
level concentration point of the measuring system
Note 1 to entry: The gas or gases used is included in the analytical algorithm used to quantify the concentration
of target analyte, and have absorption lines distinguishable from baseline noise at wavenumbers that are within
the upper and lower wavenumber limits where the target analyte displays absorption lines distinguishable from
baseline noise. An absorption feature is considered distinguishable from baseline noise if it is greater than three
times the standard deviation of the baseline noise.
Note 2 to entry: This concentration is often chosen around 70 % to 80 % of full scale.
3.2.7
lack of fit
systematic deviation within the range of application between the measurement results obtained
by applying the calibration function to the observed response of the measuring system, measuring
reference materials and the corresponding accepted value of such reference materials
Note 1 to entry: Lack of fit can be a function of the measurement result.
[SOURCE: ISO 9169:2006, 2.2.9]
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3.2.8
analytical interference
situation that arises when two or more compounds have overlapping absorbance bands in their
infrared spectra
3.2.9
limit of detection
LOD
minimum concentration of a compound that can be detected by an instrument with a given statistical
probability
Note 1 to entry: Usually the detection limit is given as three times the standard deviation of noise in the system.
3.2.10
analytical algorithm
method used to quantify the concentration of the target analytes and interferences in each FTIR
spectrum
Note 1 to entry: The analytical algorithm should be used to account for the analytical interferences (3.2.8) by
conducting the analysis in a portion of the infrared spectrum that is the most unique for that particular
compound.
3.2.11
chemometrics
chemical discipline that uses mathematical and statistical methods, (a) to design or select optimal
measurement procedures and experiments, and (b) to provide maximum chemical information by
analysing chemical data
3.2.12
independent reading
reading that is not influenced by a previous individual reading as the two individual readings are
separated by at least four response times
4 Symbols and abbreviated terms
I intensity of incident radiation
0
I intensity of transmitted radiation
A absorbance
T transmittance
α absorptivity
l optical path length
c sample concentration
C the known concentration from the reference spectra
CLS
C the predicted concentrations from the validation spectra
VAL
FTIR Fourier transform infrared
CLS classical least squares
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PLS partial least squares
ILS inverse least squares
SEV standard error of validation
5 Measurement principle
5.1 General
A sample gas is extracted from ducts and other sources via a sampling system and continually
introduced into a gas cell of an FTIR system. The IR spectra of the sample gas is measured using an
FTIR spectrometer. When a sampling bag is used, the gas sampled in the bag is transferred to the gas
cell. IR spectra obtained are analysed by using analytical algorithm. Some VOCs might adsorb onto the
sampling bag surface, reducing meaured VOC concentration. Losses by absorption shall be tested and
documented before sampling.
5.2 FTIR Spectrometer components
Figure 1 illustrates the basic FTIR spectrometer configuration required for gas phase analyses. The IR
radiation emitted by the IR source contains energy at all wavelengths between 2,5 and 14 μm, which
−1
is 700 to 4 000 cm for most IR systems conducting these analyses. The IR radiation passes through
an interferometer, where the motion of an optical element — usually a mirror — optically modulates
the IR beam. The modulated IR beam then enters an absorption cell through a window and interacts
with the gases of interest. In “multi-pass” (for example “White”) absorption cells, mirrors within the
cell direct the IR beam through the sample gas multiple times; in such cells, the absorption pathlength
can be from 4 to 50 (or more) times the cell’s physical length. (A larger absorption path length generally
leads to greater sensitivity.) The IR beam then exits the sample cell via a second window and is re-
focused onto an IR detector.
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Key
1 IR source 7 absorption cell exhaust
2 aperture or filter 1 (optional) 8 absorption cell inlet
3 interferometer 9 mirror
4 focusing optics 10 absorption cell
5 aperture or filter 2 (optional) 11 infrared window
6 IR detector
Figure 1 — FTIR spectrometer components and beam path
5.3 Interferogram
A beam of the broadband IR radiation is divided into two or more paths with different optical path
lengths and is recombined to give a detector signal with repetitive interference maxima and minima
with the aid of an interferometer. Figure 2 shows the Michelson interferometer as an example.
The interferogram is obtained by plotting the detector signal against the difference in optical path
length. Given a difference in optical path lengths corresponding to an even multiple of the wavelength,
the interference is constructive, and given an odd multiple, the interference is destructive. An additional
laser with its own detector is contained in an FTIR system. The radiation emitted by the laser and the
broad band IR source passes through the interferometer simultaneously, although the interferograms
are recorded by separate detectors. From the positions of the peaks of the interferogram of the laser
irradiation, it is possible to determine the difference in the optical path length, as the laser's input
frequency is known and is constant (e.g. 632,8 nm for a HeNe laser).
© ISO 2019 – All rights reserved 5

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Key
1 IR source
2 beam splitter
3 fixed mirror
4 movable mirror
5 absorption cell
6 detector
Figure 2 — Principle of the Michelson interferometer
5.4 Fast Fourier transform
Every data point in the interferogram contains intensity information about every infrared wavelength
transmitted from the source to the detector. It is possible to recover the intensity information as a
function of wavelength through application of a fast Fourier transform, from which the FTIR technique's
name is derived. This digital transformation of the interferogram can be thought of as the mathematical
inverse of the optical modulation applied to the infrared beam as it passes through the interferometer.
5.5 Beer’s law
The direct proportionality of the absorbance of a compound in a homogeneous sample to its
concentration. See Formula (1) which also describes the more general case of gas mixtures.
 I 
 1 
0
logl=− og ==Alα c (1)
 
 
IT
 
 
6 © ISO 2019 – All rights reserved

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oSIST ISO 20264:2021
ISO 20264:2019(E)

where
I is the intensity of incident radiation;
0
I is the intensity of transmitted radiation;
A is the absorbance;
T is the transmittance;
α is the absorpitivity;
l is the optical path length;
c is the sample concentration.
6 Equipment
6.1 Sampling system
The sampling is the process of extracting a small portion which is representative of the composition of
the main gas stream from a large quantity of waste gas. A partial flow of the waste gas is directed into
the gas cell of the FTIR spectrometer via a sampling probe, a particle filter and sampling line.
An example of the sampling system using a gas cell of the FTIR system is shown in Figure 3. The
system consists of an extractive probe and heated filter to remove fine particles, a bypass valve for N
2
purging gas cell with thermometer and pressure gauge, an FTIR spectrometer, a mass flow meter for
controlling the flow rate of sample gas into the gas cell, a shut-off valve and a sampling pump. When the
sampling line is long, the bypass pump is set to remove a residual gas in the sampling line. The sampling
pump should be installed downstream of a gas cell to prevent adsorptive losses of analytes or other
contamination by the pump. If the pump is made with inert materials and is heated, it can be installed
upstream of a gas cell. The sampling line and the gas cell of the FTIR spectrometer need to be heated
if there is any risk of condensation. The temperature of the upstream sampling components should be
the same as or slightly lower than that of the gas cell. The gas cell temperature and pressure shall be
measured and compensated and should be at the same or a similar temperature and pressure to that of
the reference spectra. Gas flow rate and temperature shall be recorded.
The sampling system including sample lines and particle filter device shall:
a) be made of a material that is chemically and physically inert to the constituents of the waste gas
under analysis;
b) be designed to ensure a short residence time (with long lines or high flow resistance, the use of an
external pump with bypass is recommended);
c) have an inlet for applying a test gas close to the sampling probe, upstream of the particle filter.
When a sampling bag is used, the gas sampled in the bag is to be transferred to the gas cell of the FTIR
spectrometer. The system using the sampling bag is shown in Figure 4. This system constitutes a
sampling probe, a filter, a sampling valve, a sampling bag, a sampling vacuum box, a valve, a sampling
pump and a flow meter to introduce the waste gas into a sample bag. The sampling bag shall be made of
a material which prevents the adsorption of VOCs. This is not a recommended procedure unless it is not
possible to get the sample extractively.
© ISO 2019 – All rights reserved 7

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oSIST ISO 20264:2021
ISO 20264:2019(E)

Key
1 sampling probe 7 gas cell with thermometer and pressure gauge
2 valve for introducing test gases 8 FTIR spectrom
...