ASTM D6348-98
(Test Method)Standard Test Method for Determination of Gaseous Compounds by Extractive Direct Interface Fourier Transform Infrared (FTIR) Spectroscopy
Standard Test Method for Determination of Gaseous Compounds by Extractive Direct Interface Fourier Transform Infrared (FTIR) Spectroscopy
SCOPE
1.1 This field test method employs an extractive sampling system to direct stationary source effluent to an FTIR spectrometer for the identification and quantification of gaseous compounds. This test method is potentially applicable for the determination of compunds that (1) have sufficient vapor pressure to be transported to the FTIR spectrometer and (2) absorb a sufficient amount of infrared radiation to be detected.
1.2 This field test method provides near real time analysis of extracted gas samples from stationary sources. Gas streams with high moisture content may require conditioning to minimize the excessive spectral absorption features imposed by water vapor.
1.3 This field test method requires the preparation of a source specific field test plan. The test plan must include the following: (1) the identification of the specific target analytes (2) the known analytical interferents specific to the test facility source effluent (3) the test data quality necessary to meet the specific test requirements and (4) the results obtained from the laboratory testing (see Annex A1 for test plan requirements).
1.4 The FTIR instrument range should be sufficient to measure from high ppm(v) to ppb(v) and may be extended to higher or lower concentrations using any or all of the following procedures:
1.4.1 The gas absorption cell path length may be either increased or decreased,
1.4.2 The sample conditioning system may be modified to reduce the water vapor, CO2, and other interfering compounds to levels that allow for quantification of the target compound(s), and
1.4.3 The analytical method may be modified such that interfering absorbance bands are minimized or stronger/weaker absorbance bands are employed for the target analytes.
1.5 The practical minimum detectable concentration is instrument, compound, and interference specific (see Annex A2 for procedures to estimate the achievable minimum detectable concentrations (MDCs)). Detection limits in the parts per billion range are possible; however, the actual sensitivity of the FTIR measurement system for the individual target analytes depends upon the following:
1.5.1 The specific infrared absorptivity (signal) and wavelength analysis region for each target analyte,
1.5.2 The amount of instrument noise (see Annex A6), and
1.5.3 The concentration of interfering compounds in the sample gas (in particular, percent moisture and CO2), and the amount of spectral overlap imparted by these compounds in the wavelength region(s) used for the quantification of the target analytes.
1.6 Practices E 168 and E 1252 are suggested for additional reading.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Additional safety precautions are described in Section 9.
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Standards Content (Sample)
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Designation: D 6348 – 98
Standard Test Method for
Determination of Gaseous Compounds by Extractive Direct
Interface Fourier Transform Infrared (FTIR) Spectroscopy
This standard is issued under the fixed designation D 6348; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This extractive FTIR based field test method is used to quantify gas phase concentrations of multiple
target analytes from stationary source effluent. Because an FTIR analyzer is potentially capable of
analyzing hundreds of compounds, this test method is not analyte or source specific. The analytes,
detection levels, and data quality objectives are expected to change for any particular testing situation.
It is the responsibility of the tester to define the target analytes, the associated detection limits for those
analytes in the particular source effluent, and the required data quality objectives for each specific test
program. Provisions are included in this test method that require the tester to determine critical
sampling system and instrument operational parameters, and for the conduct of QA/QC procedures.
Testers following this test method will generate data that will allow an independent observer to verify
the valid collection, identification, and quantification of the subject target analytes.
1. Scope 1.4.1 The gas absorption cell path length may be either
increased or decreased,
1.1 This field test method employs an extractive sampling
1.4.2 The sample conditioning system may be modified to
system to direct stationary source effluent to an FTIR spec-
reduce the water vapor, CO , and other interfering compounds
trometer for the identification and quantification of gaseous 2
to levels that allow for quantification of the target com-
compounds. This test method is potentially applicable for the
pound(s), and
determination of compounds that (1) have sufficient vapor
1.4.3 The analytical method may be modified such that
pressure to be transported to the FTIR spectrometer and (2)
interfering absorbance bands are minimized or stronger/weaker
absorb a sufficient amount of infrared radiation to be detected.
absorbance bands are employed for the target analytes.
1.2 This field test method provides near real time analysis of
1.5 The practical minimum detectable concentration is in-
extracted gas samples from stationary sources. Gas streams
strument, compound, and interference specific (see Annex A2
with high moisture content may require conditioning to mini-
for procedures to estimate the achievable minimum detectable
mize the excessive spectral absorption features imposed by
concentrations (MDCs)). Detection limits in the parts per
water vapor.
billion range are possible; however, the actual sensitivity of the
1.3 This field test method requires the preparation of a
FTIR measurement system for the individual target analytes
source specific field test plan. The test plan must include the
depends upon the following:
following: (1) the identification of the specific target analytes
1.5.1 The specific infrared absorptivity (signal) and wave-
(2) the known analytical interferents specific to the test facility
length analysis region for each target analyte,
source effluent (3) the test data quality necessary to meet the
1.5.2 The amount of instrument noise (see Annex A6), and
specific test requirements and (4) the results obtained from the
1.5.3 The concentration of interfering compounds in the
laboratory testing (see Annex A1 for test plan requirements).
sample gas (in particular, percent moisture and CO ), and the
1.4 The FTIR instrument range should be sufficient to
amount of spectral overlap imparted by these compounds in the
measure from high ppm(v) to ppb(v) and may be extended to
wavelength region(s) used for the quantification of the target
higher or lower concentrations using any or all of the following
analytes.
procedures:
1.6 Practices E 168 and E 1252 are suggested for additional
reading.
This test method is under the jurisdiction of Committee D22 on Sampling and
1.7 This standard does not purport to address all of the
Analysis of Atmospheres and is the direct responsibility of Subcommittee D22.03
safety concerns associated with its use. It is the responsibility
on Ambient Atmospheres and Source Emissions.
of the user of this standard to establish appropriate safety and
Current edition approved Dec. 10, 1998. Published February 1999.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D6348–98
health practices and to determine the applicability of regula- side lobes of the measured peaks. This procedure alters the
tory limitations prior to use. Additional safety precautions are instrument’s response function. There are various types of
described in Section 9. transformation; the most common forms are boxcar, triangular,
Happ-Genzel, and Beer-Norton functions.
2. Referenced Documents
3.2.7 background spectrum, n—the spectrum taken in the
2.1 ASTM Standards: absence of absorbing species or sample gas, typically con-
D 1356 Terminology Relating to Sampling and Analysis of
ducted using dry nitrogen or zero air in the gas cell.
Atmospheres
3.2.8 bandwidth, adj—the width of a spectral feature as
D 3195 Practice for Rotameter Calibration
recorded by a spectroscopic instrument. This width is listed as
E 168 Practice for General Techniques of Infrared Quanti-
the full width at the half maximum of the feature or as the half
tative Analysis
width at the half maximum of the spectral feature. This is also
E 1252 Practice for General Techniques for Obtaining In-
referred to as the line width (1).
frared Spectra for Qualitative Analysis
3.2.9 beam splitter, n—a device located in the interferom-
2.2 EPA Methods (40 CFR Part 60 Appendix A)
eter that splits the incoming infrared radiation into two separate
Method 1 - Sample and Velocity Traverses for Stationary
beams that travel two separate paths before recombination.
Sources
3.2.10 Beer’s law, n—the principal by which FTIR spectra
Method 2 Series - Determination of Stack Gas Velocity and
are quantified. Beer’s law states that the intensity of a mono-
Volumetric Flow Rate (Type S Pitot Tube)
chromatic plane wave incident on an absorbing medium of
Method 3 Series - Gas Analysis for Carbon Dioxide, Oxy-
constant thickness diminishes exponentially with the number
gen, Excess Air, and Dry Molecular Weight
of absorbers in the beam. Strictly speaking, Beer’s law holds
Method 4 Series - Determination of Moisture Content in only if the following conditions are met: (1) perfectly mono-
Stack Gases
chromatic radiation (2) no scattering (3) a beam that is strictly
collimated (4) negligible pressure-broadening effects (2, 3).
3. Terminology
For an excellent discussion of the derivation of Beer’s law, see
3.1 See Terminology D 1356 for definition of terms related
(4).
to sampling and analysis of atmospheres.
3.2.11 calibration transfer standard, n—a certified calibra-
3.2 Definitions of Terms Specific to This Standard—This
tion standard that is used to verify the instrument stability on a
section contains the terms and definitions used in this test
daily basis when conducting sampling.
method and those that are relevant to extractive FTIR based
3.2.12 classical least squares, n—a common method of
sampling and analysis of stationary source effluent. When
analyzing multicomponent infrared spectra by scaled absor-
possible, definitions of terms have been drawn from authori-
bance subtraction.
tative texts or manuscripts in the fields of air pollution
3.2.13 condenser system,(dryer), n—a moisture removal
monitoring, spectroscopy, optics, and analytical chemistry.
system that condenses water vapor from the source effluent to
3.2.1 absorbance, n—the negative logarithm of the trans-
provide a dry sample to the FTIR gas cell.
mission, A = -log (I/I ), where I is the transmitted intensity of
3.2.14 cooler, n—a device into which a quantum detector is
the light and I is the incident intensity.
0 placed for maintaining it at a low temperature in an IR system.
3.2.2 absorptivity, adj—the amount of infrared radiation
At a low temperature, the detector provides the high sensitivity
that is absorbed by each molecule.
that is required for the IR system. The two primary types of
3.2.3 analyte spiking, n—the process of quantitatively co-
coolers are a liquid nitrogen Dewar and a closed-cycle Stirling
adding calibration standards with source effluent to determine
cycle refrigerator.
the effectiveness of the FTIR measurement system to quantify
3.2.15 electromagnetic spectrum, n—the total set of all
the target analytes.
possible frequencies of electromagnetic radiation. Different
3.2.4 analytical interference, n—the physical effects of
sources may emit over different frequency regions. All elec-
superimposing two or more light waves. Analytical interfer-
tromagnetic waves travel at the same speed in free space (5).
ences occur when two or more compounds have overlapping
3.2.16 extractive FTIR, n—a means of employing FTIR to
absorbance bands in their infrared spectra.
quantify concentrations of gaseous components in stationary
3.2.5 analytical method, n—the method used to quantify the
source effluent. It consists of directing gas samples to the FTIR
concentration of the target analytes and interferences in each
cell without collection on sample media.
FTIR Spectrum. The analytical method should account for the
3.2.17 fingerprint region, n—the region of the absorption
analytical interferences by conducting the analysis in a portion
spectrum of a molecule that essentially allows its unequivocal
of the infrared spectrum that is the most unique for that
identification. For example, the organic fingerprint region
–1
particular compound.
covers the wave number range from 650 to 1300 cm (6).
3.2.6 apodization, v—a mathematical transformation car-
3.2.18 Fourier transform, v—a mathematical transform that
ried out on data received from an interferometer to reduce the
allows an aperiodic function to be expressed as an integral sum
over a continuous range of frequencies (7). The interferogram
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D6348–98
represents the detector response (intensity) versus time, the detection limit is given as three times the standard deviation of
Fourier transform function produces intensity as a function of the noise in the system. In this case, the minimum concentra-
frequency. tion can be detected with a probability of 99.7 % (9, 12).
3.2.19 frequency position, n—the accepted exact spectral
3.2.31 noise equivalent absorbance (NEA), n—the peak-to-
line position for a specific analyte. A wave number or fractional peak noise in the spectrum resulting from the acquisition of
wavenumber is used to determine whether spectral shifts have
two successive background spectra.
occurred with time.
3.2.32 path length, n—the distance that the sample gas
3.2.20 FTIR, n—an abbreviation for Fourier transform
interacts with the infrared radiation.
infrared. A spectroscopic instrument using the infrared portion
3.2.33 reference spectra, n—spectra of the absorbance ver-
of the electromagnetic spectrum. The working component of
sus wave number for a pure sample of a set of gases. These
this system is an interferometer. To obtain the absorption
spectra are obtained under controlled conditions of pressure
spectrum as a function of frequency, a Fourier transform of the
and temperature, pathlength, and known concentration. The
output of the interferometer must be performed. For an
spectra are used to obtain the unknown concentrations of gases
in-depth description of the FTIR, see (8).
in ambient air samples.
3.2.21 infrared spectrum, n—that portion of the electromag-
3.2.34 resolution, n—the minimum separation that two
–1
netic spectrum that spans the region from about 10 cm to
spectral features can have and still, in some manner, be
–1
about 12 500 cm . It is divided (6) into (1) the near-infrared
distinguished from one another. A commonly used requirement
–1
region (from 12 500 to 4000 cm ), (2) the mid-infrared region
for two spectral features to be considered just resolved is the
–1
(from 4000 to 650 cm ), and (3) the far-infrared region (from
Raleigh criterion. This states that two features are just resolved
–1
650 to 10 cm ).
when the maximum intensity of one falls at the first minimum
3.2.22 instrument function, n—the function superimposed
of the other (11, 13). This definition of resolution and the
on the actual absorption line shape by the instrument. This is
Raleigh criterion are also valid for the FTIR, although there is
sometimes referred to as the slit function; a term taken from
another definition in common use for this technique. This
instruments that use slits to obtain resolution.
definition states that the minimum separation in wave numbers
3.2.23 intensity, n—the radiant power per unit solid angle.
of two spectral features that can be resolved is the reciprocal of
When the term spectral intensity is used, the units are watts per
the maximum optical path difference (in centimetres) of the
steradian per nanometer. In most spectroscopic literature, the
two-interferometer mirrors employed. (8, 14)
term intensity is used to describe the power in a collimated
3.2.35 sample interface, n—the entire sampling system
beam of light in terms of power per unit area per unit
consisting of the sample probe, sample transport line, and all
wavelength. However, in the general literature, this definition
other components necessary to direct effluent to the FTIR gas
is more often used for the term irradiance,or normal irradi-
cell.
ance (9, 10).
3.2.36 sampling system interference, n—an interference that
3.2.24 interferogram, n—the effects of interference that are
prohibits or prevents delivery of the target analytes to the FTIR
detected and recorded by an interferometer, the output of a
gas cel
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