ISO 20264:2019

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 2019
© ISO 2019
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Published in Switzerland
ii © ISO 2019 – All rights reserved

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
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
iv © ISO 2019 – All rights reserved

Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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different types of ISO documents should be noted. This document was drafted in accordance with the
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.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.
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).
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

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 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
and I is the incident intensity
3.1.2
resolution
minimum separation that two spectral features can have and still, in some manner, be distinguished
from one another
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]
2 © ISO 2019 – All rights reserved

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
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
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.
4 © ISO 2019 – All rights reserved

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).
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 
logl=− og ==Alα c (1)
 
 
IT
 
 
6 © ISO 2019 – All rights reserved

where
I is the intensity of incident radiation;
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
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.
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
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.
8 © ISO 2019 – All rights reserved

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 (cell volume shall be small enough to obtain
a short response time);
— the cell may be either a multi pass cell or a single pass cell;
— the consists of inert materials such as a gold coated mirror and a focus mirror;
— the optical path length can be adjusted by changing an angle of the mirror or it can be
permanently fixed;
— the proper concentration range for measurement depends on both the absorptivity of compound
and the path length.
NOTE For ethylene in nitrogen, the proper concentration against path length is 100 to 400 ppm-m (for
example, a standard of 10 ppm to 40 ppm ethylene in nitrogen is recommended for a 10-meter absorption cell).
b) optical window:
−1 −1
— the window can be selected from the following materials; KBr (40 000 cm ~ 340 cm ), ZnSe
−1 −1 −1 −1
(10 000 cm ~ 550 cm ) and BaF (50 000 cm ~ 770 cm );
NOTE 1 KBr cannot be used for waste gas with high water content.
NOTE 2 If IR spectra in a low wavenumber region are measured, ZnSe is recommended.
c) detector:
— semiconductor (e.g. MCT) or pyroelectric (e.g. DTGS) detectors can be used.
NOTE For semiconductor detectors, cooling with liquid nitrogen improves sensitivity. See Reference [2].
d) interferometer:
— device that devides a beam of radiant energy into two or more paths, generates an optical path
difference between the beams, and recombines them in order to produce repetitive interference
maxima and minima as the optical retardation is varied.
7 Measurement procedure
7.1 General
Comprehensive measurement planning shall be performed before the measurement, taking into
consideration the specific measurement task.
7.2 Choice of the measuring system
To choose an appropriate analyser, sampling line, and conditioning unit, the following characteristics of
waste gases should be known before the field test.
The target VOCs are based on the known composition of the paints, VOCs used in processing, etc. and
their expected concentration range. Examples for IR spectra absorption features of VOCs using the
printing and painting processes are described in Annex B. The effect of the waste gas composition
should be considered in the design of the sampling system. To do so, the following condition of the
waste gas should be estimated:
a) the temperature of the waste gas;
b) the water vapour content of the waste gas (dew point temperature);
c) the expected dust load and composition of the waste gas;
d) the pressure of the waste gas;
e) the expected concentration of potentially interfering substances.
To avoid long response time and memory effects, the sampling line shall be as short as possible; if
necessary, a bypass pump should be used.
Before conducting field measurements, the user shall verify that the necessary QA/QC procedure has
been performed.
7.3 Sampling
7.3.1 Sampling location
The sampling location chosen for the measurement devices and sampling shall be of sufficient size and
construction to enable a representative emission measurement suitable for the measurement task to be
obtained. In addition, the sampling location shall be chosen with regard to the safety of the personnel,
accessibility and availability of electrical power.
7.3.2 Sampling point(s)
It is necessary to ensure that the gas concentrations measured are representative of the average
conditions inside the waste gas duct. Therefore, the sampling point(s) shall be selected to allow for a
representative sampling.
7.3.3 Extractive sampling
The sampling probe is inserted into the waste gas duct, and the sampling system from the probe to
the inlet of the gas cell is purged with the sample gas by using the sampling pump through the bypass
(see Figure 3). A sampling rate of 1–10 l/min is generally acceptable. Higher sampling rates decrease
the effect of adsorption of target analytes in the sampling system, but higher flows increase the rate of
calibration verification gas use. Therefore 1–10 l/min has been successfully used in the past.
A continuous sample gas flow rate through the FTIR at known temperature and pressure is kept while
the analyser continuously scans the sample gas. Periodically a concentration update is processed by the
software depending on the number of scans. This update is between 5 seconds and 5 minutes.
7.3.4 Sampling with a gas bag
If a sampling bag approach is unavoidable, the sampling bag shall be purged with nitrogen gas or dry
air to remove contaminants. The inlet of sampling bag is then connected to the sampling system after
a number of purges to determine if the bag is acceptable for use. The sampling probe is inserted into
the duct and the sampling system purged with sample gas through the probe by using the pump (see
Figure 4). Afterwards, the sample gas is introduced into the bag by opening the inlet of the bag.
10 © ISO 2019 – All rights reserved

7.4 Pre-test and sample quantification procedures
The sampling procedures are described in 7.3.3 or 7.3.4.
1) Before conducting any sample measurements, prepare the instrument according to the
manufacturer’s instructions. Acquire an optical background by introducing the zero gas directly
into the FTIR measurement path. The purpose of the background (I ) is to remove any infrared
adsorption interferences from the instrument optical components.
2) Analyse the zero gas and acquire 10 sequential samples. The purpose of these zero gas analyses
is to calculate an instrument level of detection (LOD) for each of the components in their analyses
range. Calculate the equivalent concentration for each of these 10 samples for the target analytes of
interest, and calculate their standard deviations. Apply a factor of 3 to each target analyte standard
deviation result to produce an equivalent estimated LOD.
3) Analyse the calibration verification gas through the entire sampling system, including the filter. It
should be in the approximate range as the expected concentrations of the source gas. If the source
gas concentration is unknown, the calibration verification gas should approximate a regulatory
limit, an occupational exposure limit, etc.
4) Ensure that all results for the calibration verification gas meet the quality assurance criteria of this
method or take corrective action before proceeding to step 5).
5) Collect source samples for a period of 1 hour or another agreed time period reflective of
representative source conditions.
6) Quantify the source samples and determine the effective residual for each target analyte. It is
considered that negligible interference is present if the maximum absolute peak to peak absorbance
in the residual is not greater than 5 % of the maximum absolute peak to peak absorbance in the
sample spectrum. If this test is failed, it may be considered that there is negligible interference
present if it can be demonstrated that the maximum absolute peak to peak absorbance in the
residual is not greater than twice the maximum absolute peak to peak absorbance of a measurement
of zero gas across the same wavenumbers. If this test is also failed then an interfering compound
might be present in the analysis region. In such cases the analytical program used would need to be
refined if the test program QA needs cannot be met.
7) Present the results as ppm (v) or mg/m actual and also corrected to normal conditions for
temperature, 273,15 K, and pressure 101,325 kPa.
8 Performance chracteristics and criteria
8.1 General
The performance characteristics and criteria for the measurement system of VOCs by using an FTIR
are described in this clause. The methods for determination of the FTIR performance parameters
such as noise equivalent absorption, line position, etc. shall be done according to Annex A prior to
performance tests.
8.2 Performance criteria
Table 1 gives the performance characteristics and performance criteria of the measurmement system
of VOCs by using an FTIR. The tests of the performance characteristics with using the zero gas, and
calibration verification gas during field operation shall be conducted and the results of tests shall meet
the performance criteria in Table 1.
Table 1 — Performance characteristics and criteria of the measurement system of VOCs by FTIR
Performance characteristics Performance criteria Reference
Zero check <±2,0 % of range 8.2.1
Repeatability of calibration <±2,0 % of range 8.2.2
verification gas
Response time <200 s 8.2.3
Losses and leakages in the <±2,0 % of range 8.2.4
sampling line
8.2.1 Zero check
Base line shall be determined by directing zero gas through the entire sampling system including the
primary particulate matter filter. One blank spectra is recorded with the same settings as subsequent
samples from the process. The sample is quantified with the same model as the subsequent samples
from the process. The reading shall be within the limit of detection determined in 7.4 2). If the data
quantification methodology in 10.3 is changed after analysis, it is necessary to quantify the zero check
samples from 7.4 2) and 8.2.1 again as the detection limit can change.
8.2.2 Repeatability of calibration verification gas
After performing 8.2.1 and 8.2.3, apply calibration verification gas upstream of any particle filters in the
probe. The measured signals of the FTIR shall be determined after application of calibration verification
gas by waiting for the time equivalent to one independent reading and then recording 10 consecutive
individual readings. The repeatability standard deviation shall be calculated by using the measured
signals obtained to determine the repeatability of calibration verification gas.
8.2.3 Response time
After performing the zero check as described in 8.2.1, apply calibration verification gas upstream of
any particle filters in the probe. The step change shall be made by swiching the valve from zero gas to
calibration verification gas. Wait for the reading to stabilize at 90 % of final stabilized reading and then
apply zero gas in the same manner. Wait for the reading to stabilize within 10 % of the final stabilized
reading.
The response time is the time interval between application of calibration verification gas to the probe
and the instant when the reading reaches and remains within 90 % of the final stabilized reading.
This time includes lag time and rise time (or fall time). Lag time is the interval between application of
gas and the first instance where the concentration changes by 10 %. Rise time is the time it takes for
the concentration to increase from 10 % of the final stabilized reading to 90 % of the final stabilized
reading, and the fall time is the time it takes for the concentration to decrease from 90 % of the final
stabilized reading to 10 % of the final stabilized reading. Determine both rise time and fall time for the
instrument.
When reporting the average concentration value of the samples from the process, the shortest allowed
averaging period is ten times the rise time or ten times the fall time if fall time exceeds rise time. See
Figure 5 for illustration of lag time and rise time.
12 © ISO 2019 – All rights reserved

Key
1 lag time
2 rise time
3 response time
Y instrument reading (percentage of target value)
Figure 5 — Illustration of lag time and rise time
8.2.4 Losses and leakage in the sampling line
Losses and leakage are tested in conjunction with response time. When applying calibration verification
gas upstream of any particle filters as described in 8.2.2, the stabilized reading shall be within 2,0 % of
calibration verification gas concentration. When applying zero gas after the calibration verification gas,
the stabilized reading shall not deviate from zero by more than 2,0 % of the calibration verification gas
concentration.
9 Quality assurance and quality control procedure
At least the following checks are needed for QA and QC for each analyte;
1) acquire 10 sample spectra of the zero gas and determine the limit of detection as 3 × STDEV of the
zero level readings;
2) measure a calibration verification gas injected upstream of the particle filter in the probe. If
multiple analytes are being measured simultaneously or if the analytes are so reactive that a
compressed gas cylinder is not commercially available, a surrogate gas with absorption peaks in
the same analytical window as the analyte can be used instead;
3) perform sample measurements;
4) repeat calibration verification gas through the probe to ensure 95 % or better sample recovery;
5) repeat zero gas measurement through system to ensure that LOD has not changed during the
sample measurement.
10 Data quantification
10.1 General
IR spectra obtained from Clause 7 (measurement procedure) are analysed by using an analytical
algorithm that is usually provided within the FTIR manufacturer’s software. It should be determined that
the manufacturer’s software is appropriate to complete the required analysis and data quality checks.
10.2 Data quantification techniques
The gas concentrations in FTIR sample spectra can be quantified via univariate or multivariate analysis
(MVA) techniques. It is assumed that the complexity of any sample to be analysed will need to make use
of MVA techniques, although univariate analysis can be used if the sample analysis is simple enough i.e.
one gas species over a low range.
The most common technique to apply MVA to FTIR data is the Classical Least Squares (CLS) or approach.
For a CLS method, all of the species absorbing in the same wavelength region used for the analysis of
the analyte need to be known. The concentration of all gases in the calibration set shall also be known.
Alternative analytical algorithms, such as partial least squares (PLS), inverse least squares (ILS) and
others can also be applied. These alternative methods can offer benefits over CLS, such as PLS whereby
the concentration of interfering gases in the calibration set does not need to be known.
10.3 Data quantification methodology
10.3.1 Calibration set
For each gas species to be measured, a set of reference spectra at a number of concentrations spanning
the range of the required measurement should be collected. The analytical range is the maximum
concentration spectrum in the calibration set. The reference spectra should be collected with, or
have the same collection parameters as the sample spectra i.e. resolution, temperature, path length,
pressure and interferogram processing settings. External library (e.g. NIST) or synthetic (e.g. derived
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