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Gamal A. Hamid
Gas Analysis Using FTIR
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To everyone who has helped us with support, books,
hard/soft ware And over the internet Special thanks for
THERMO
Thanks
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• Introduction
• Instrumentation
• Sampling Tools
• Analysis
• Quantitation
• Applications
Contents
Introduction
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There is no protection
without detection
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• The IR radiation passes through a sample and
chemical vapors present in gas sample will absorb
the infrared energy at different wavelengths.
• All compounds in the vapor will give unique
fingerprints of absorbance features which will be
compared to a library of spectra.
• Measurement of gases requires reproducible sample
handling techniques, optimized optical bench
settings, and carefully defined quantitative methods
of analysis.
Gas Analysis
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Air pollutants divided into two categories:
• Criteria pollutants with established national regulatory limits: NOx, SOx, CO,
lead, ozone, and particulate matter
• Hazardous Air Pollutants (HAPs),
HAPs, can be divided in the following categories :
Non-volatiles (metals and heavy organics, etc.) - BP>300°C
Semi-volatile Organic Compounds (SVOCs) - BP 120-300°C
Volatile Organic Compounds (VOCs) - BP<120°C
Air pollutants
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• FTIR Spectroscopy is a technique based on the
determination of the interaction between an IR
radiation and a sample that can be solid, liquid or
gaseous.
• It measures the frequencies at which the sample
absorbs, and also the intensities of these
absorptions.
• The frequencies are helpful for the identification of
the sample’s chemical make-up due to the fact that
chemical functional groups are responsible for the
absorption of radiation at different frequencies.
FTIR
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• Infrared spectroscopy is most often used
for qualitative identification.
• An unknown samples can be determined
by comparing the infrared spectrum
acquired on this sample to the spectra of
known compounds.
• IR spectral lines may be interpreted to
provide clues to the structure of an
unknown samples.
Qualitative Analysis
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• The concentration of component can be
determined based on the intensity of the
absorption.
• The spectrum is a two-dimensional plot in
which the axes are represented by intensity
and frequency of sample absorption.
• The absorption spectra of pure gases and of
mixtures of gases are described by a linear
absorbance theory referred to as Beer's
Law.
Quantitative Analysis
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• Quantitative analysis methods are based on Beers Law, which states that spectral
absorbance is proportional to a compound’s concentration.
A=ebc
A is absorbance (no units, since A = log10 P0 / P )
e is the molar absorptivity with units of L mol-1 cm-1
b is the path length of the sample
c is the concentration of the compound in solution, expressed in mol /L.
Thus, if the concentration of a gas doubles, its infrared absorbance will double.
Ideally, the spectral bands chosen for each compound should be in the .1 – .7 AU
Beers Law
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• SCCM Standard Cubic Centimeters per minute.
• SLM or SLPM Standard Liter Per Minute.
• UPC Ultra-pure Carrier “ Nitrogen or Zero air “.
• MDLs Method Detection Limits.
• Torr Is a unit of pressure based on an absolute scale, now defined as
exactly 1/760 of a standard atmosphere.
• mmHg A millimeter of mercury is a manometric unit of pressure, defined
as the extra pressure generated by a column of mercury one millimetre high.
• CTSs Calibration transfer standards
• HAPs Hazardous air pollutants
Definitions
Instrumentation
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I. FTIR
II. ABX
III. Gas Cell
IV. Temperature Control
V. Flow Control
VI. Pressure Control
VII. Vacuum Pump
VIII. Gas Diluter
Gas Analysis System
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Gas Analysis System
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• Combining a high precision FT-IR
spectrometer with a long pathlength gas cell
provides a powerful tool for analyzing trace
levels of contaminants in air and other gas
mixtures .
• The combination of the three beamsplitters,
the three software-selectable detectors
(visible, mid-IR and far-IR) and two sources
(visible and infrared) provides a fully
integrated spectrometer that can
automatically cover the spectrum from
25,000–100
I. FTIR
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• The ABX automatic beamsplitter
exchanger which provides the rapid
and precise switching of the optical
components required for different
spectral ranges.
KBr (7000–400 cm-1),
Solid substrate (700–100 cm-1)
Quartz (25,000–5000 cm-1).
II. ABX Automated Beamsplitter Exchanger
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• The cell can be heated up to 185°C, which requires the
purchase of a separate heating accessory and
temperature controller.
• A choice of three window materials, KBr, BaF2, and
coated ZnSe, is available, as well as configurations for
all major spectrometers.
• A nickel-coated aluminum body and aluminum mirrors
with gold coating are suitable for harsh analyses.
• 10 m pathlength, 2 liter volume, maximum pressure
200 psi for sub-ppm detection capabilities
III. 10 Meter Gas Cell
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• This 200 meter gas cell has a larger volume
associated with a longer base path, the
highest performance and longest
pathlength gas cell.
• The mirrors are larger to collect a larger
solid angle to maximize energy throughput
for this very long pathlength gas cell.
• It has a micrometer barrel adjustment
that allows for easy, reproducible
pathlength adjustment.
200 Meter Gas Cell
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• All samples should be run at a controlled
temperature.
• Allowing for consistent and accurate
temperature readings.
• Measurement temperatures according to the set
point of the test prevent water or heavier
hydrocarbons from condensing and giving
inaccurate results.
• A flexible silicone rubber heater put around the
gas cell.
IV. Temperature Control
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Heater• Silicone rubber gives the heater
dimensional stability without sacrificing
flexibility.
• Shaped to fit the application.
• The heaters are constructed with a wire-
wound element or an etched foil element.
• Stable up to 185 °C.
Temperature Control
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Controller• Is designed to regulate a user-defined
output device at a set point temperature.
• Install controller in a safe operating area.
• Plug the heater into the output connector.
• Connect the thermocouple sensor.
• Plug supplied AC cord into the IEC power
connector.
Temperature Control
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Valve• Is a solenoid valve that, when supplied with a
controlling current, is able to modulate the flow such
that pressure or flow is maintained accurately and
with precision of gas.
• The 148 valve is a metal-sealed design for high purity
applications and for the delivery of hazardous gases
where minute leakage to atmosphere cannot be
tolerated.
• It controls flows in the range of 10 to 30,000 sccm.
V. Flow Control
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Controller • The control module designed to provide optimized
control of the total pressure or flow of a gas (or
gases) in a dynamic closed-loop system.
• The controller compares the measured pressure or
flow to the desired set point and adjusts the gas flow
control valve as necessary to achieve set point.
• The controller can provide a ±15 VDC output and
accepts inputs from a variety of pressure transducers
and mass flow meters.
Flow Control
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• This measurement technique converts
pressure to a linear DC output voltage using
three components:
A sensor,
Signal conditioner,
And power supply/readout unit.
• Many applications can be run at atmospheric
pressures.
• However, variations in pressure will change
the gas density and give less accurate results.
VI. Pressure Control
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• The sensor contains a tensioned metal diaphragm .
• The diaphragm deflects with changing absolute
pressure - force per unit area - independent of the
composition of the measured gas.
• This deflection causes a capacitance change between
the diaphragm and the adjacent electrode assembly.
• The pressure transducer converts pressure to an
electrical signal.
• Keep the unit free from vibration.
Sensor
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• The capacitance change that occurs in
the sensor generates an AC voltage
which is sent to the electronics unit
where it is amplified, demodulated,
and converted into a high level DC
output voltage.
• The output is linear with pressure and
provides a 10 Volt DC output at sensor
F.S. pressure.
Signal Conditioner
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• A Pressure/Flow Controller will control any one of a
variety of flow valves to accurately maintain a set
pressure or flow.
• Comparing the signal from sensor to the required
signal (in most cases, a precision pot whose voltage
is changed by rotating the dial).
• Overpressure Limit 35 psia
• A pressure control gauge set to slightly below
atmospheric pressure (600 – 650 mmHg) increases
the sampling reproducibility for more precise
experiments.
Controller
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• FTIR Cell Pump. Required for the batch
sampling technique, capable of
evacuating the FTIR cell volume within
2 minutes.
• The pumping speed shall allow the
operator to obtain 8 sample spectra in
1 hour at least.
VII.Vacuum Pump
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• In a simple pressure loop The flow rate is
not measured because it is unnecessary.
• The set point of pressure controlling the
loop.
• If the pressure is higher than the set
point, the controller reduces the current
to the valve, which reduces the flow into
the vacuum system, subsequently
reducing the pressure.
Controlling of the loop
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• A gas dilution system can provide known values of
calibration gases through controlled dilution of high-
level calibration gases with an appropriate dilution gas.
• The gas dilution system shall produce calibration gases
whose measured values are within ±2 percent of the
predicted values.
• The gas dilution system shall be recalibrated once per
calendar year.
• Three injections are made at each dilution level, differ
not more than ±2 percent from the average
VIII.Gas Diluter “ Calibrator”
Sampling Tools
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• Are containers used to collect whole air samples.
• Bags constructed from various materials which can
differ in terms of stability characteristics and
cleanliness.
• Bags are equipped with a valve that allows for filling.
• Sample collection requires a pressurized sampling port,
a low flow rate pump or a lung sampler.
• Pumping range rates bet.(50-200 mL/min)
• Bag materials should be selected based on the specific
application.
Samples Bags
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• Is a container for collecting a whole air sample.
• A canister may be spherical or cylindrical and is
constructed of specially treated stainless steel.
• The canister is prepared for sampling by evacuating the
contents
• Opening the stainless steel bellows valve allows the air
sample to enter the canister.
• The volume from less than 1 liter to 6 L.
• Six L canisters are used to collect ambient air samples
and samples requiring time greater than 2 hours.
• One liter canisters used for taking high concentration
Canisters
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• A high-pressure cylinder is a thick-walled
stainless steel container with an
untreated interior and a valve at each
end.
• These cylinders were originally designed
for the petroleum industry to collect
samples from pressurized lines.
• High pressure cylinders are not
recommended for low (sub ppm) sample
concentrations.
High-Pressure Cylinders
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• The sample gas pump is suitable for
delivering gases only. It is not suitable for
liquids.
• The sample gas pump should be operate
d without pressure.
• The corrosive nature of the gas and the
potential of condensate formation are
the real challenges for pump.
Gas Sampling “ Hand "Pump
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• Single Stage Regulators accomplish the pressure reduction in a single step.
• Delivery pressure cannot be as tightly controlled as with a dual stage
regulator.
Single Stage Regulators
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• Reduce the source pressure down to the desired delivery pressure in two steps.
• Each stage consists of a spring, diaphragm, and control valve.
• The first stage reduces the inlet pressure to about 3 times the max. working pressure.
• The final pressure reduction occurs in the second stage.
• Give a constant pressure, even with a decrease in inlet pressure.
Dual Stage Regulators
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Rate regulator - Portable Cylinder Regulator
• Preset flow rate regulators for use with cylinders.
For use in the calibration of gas detection
instrumentation.
• Standard preset flow rate
• 0.5, 1.0, 1.5, 2.5, 0.3 SLPM
• Different psig delivery pressure.
Preset flow Regulator “Controller”
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Stainless Steel Tubing
• Type 316, appropriate diameter and length for
heated connections.
• Higher grade stainless may be desirable in some
applications.
Polytetrafluoroethane Tubing
• Diameter and length suitable to connect
cylinder regulators to gas cell and modules.
Tubing
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• Never mix imperial and metric components.
• External and internal (male and female) threads
must be of the same type.
• Never mix components from different brands.
• Never mix components from different materials.
• Always check the physical markings on all
components. Do not rely on color coding alone.
• Use the correct tool for the fitting.
• Check leakage after fitting.
Fitting Notes
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Tube Fittings Types
Gas Standards
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• All pure gases are classified by grade, so you
can be certain of purity levels.
• The first digit of the classification indicates
the number of nines purity (for example, 5.0
= 99.999% purity).
• The second digit is the number following the
last nine (for example 4.7 helium has a
guaranteed minimum purity of 99.997% and
a corresponding maximum impurity level of
0.003% or 30ppm).
Gas Purity
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• Calibration transfer standard (CTS) gas A gas standard of a compound used to
achieve and/or demonstrate suitable quantitative agreement between sample
spectra and the reference spectra.
• Commercially-Prepared Chemical Standards Chemical standards for
compounds may be obtained from independent sources, such as a specialty gas
manufacturer, chemical company, or commercial laboratory.
• Self-Prepared Chemical Standards Chemical standards may be prepared by
diluting certified commercially prepared chemical gases or pure analytes with
ultra-pure carrier (UPC) grade nitrogen according to the barometric and
volumetric techniques
Calibrations Gas Cylinders
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For each pollutant to be measured, use the following
three calibration gases
• High-Range Gas The concentration should be
between 80 and 100 percent of the analyzer range.
• Mid-range Gas The concentration should be
between 40 and 60 percent of the analyzer range.
• Zero Gas Purified air or, if appropriate, nitrogen .
• The Range is selected so that the sample gas
concentration is between 10 and 95 percent of the
range for each pollutant of interest.
Standards Preparation
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• Evacuate the gas cell to≤5 mmHg absolute pressure, and fill the
FTIR cell to atmospheric pressure with the CTS gas. Alternatively,
purge the cell with 10 cell volumes of CTS gas.
• If purge is used, verify that the CTS concentration in the cell is
stable by collecting two spectra 2 minutes apart as the CTS gas
continues to flow.
• If the absorbance in the second spectrum is no greater than in the
first, within the uncertainty of the gas standard, then this can be
used as the CTS spectrum.
• Record the spectrum.
Pre-Test Calibrations
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• This procedure assumes that the method has been
validated for at least some of the target analytes at the
source.
• For emissions testing perform a QA spike.
• Use a certified standard, if possible, of an analyte, which
has been validated at the source.
• One analyte standard can serve as a QA surrogate for
other analytes which are less reactive or less soluble than
the standard.
QA Spike
Analysis
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1. Pretest preparations
2. The loop connection
3. Preparing the FTIR
4. Run the analysis
5. Quantifying the spectrums
Analysis Sequence
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• Analytes. Select the required detection limit.
• Potential Interferants. List the potential interferants.
This usually includes water vapor and CO2, but may also
include some analytes and other compounds.
• Optical Configuration. Choose an optical configuration that can measure all of the
analytes within the absorbance range of .01 to 1.0
• Analytical Program. Prepare computer program based on the chosen analytical
technique.
• System Leak check Leak check the FTIR cell under vacuum and under pressure
(greater than ambient).
1. Pretest preparations
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2. The Loop Connections
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• Activate the FTIR system according to the manufacturer’s
instructions. Allow sufficient time for the infrared source, the
infrared detector, and (if required) the temperature control
systems to stabilize.
• Verify that the sample temperature and pressure are within
the range of setting points.
• Bypassing the sampling system, flow N2 or zero air directly
into the infrared absorption cell until a stable infrared
response and moisture levels are reached.
3. Preparing The FTIR
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Turn on the spectrometer
• Turn on the spectrometer, the system status and
system scan LEDs next to the power switch flash in
various sequences as the system performs its
diagnostic routines.
• When the routines are finished, the system status LED
stops flashing and remains lit.
• The system scan LED will intermittently blink,
indicating that the interferometer is scanning and
working properly.
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4. Run The Analysis
• Turn on the computer.
• Launch OMNIC on the desktop.
• Make sure the bench Status is √ on the top right corner of the window.
• Make sure purging time using nitrogen or zero air done is enough.
• Click on Col Bkg to take a background. When the confirmation window pops
up, click YES.
• When the confirmation window pops up to ask to add Window 1, click NO.
• Purge your gas sample( calibration or samples) give time for stability.
• Click on Col sample, Collect Sample Window pops up, type in “sample
name”
• and enter, confirmation window pops up, click YES.
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• When the confirmation window pops up to add Window 1, click YES.
• To have peaks labeled, Click Find Pks. Adjust the threshold by clicking on
the window with the left mouse button.
• When peaks are selected, Click on “Replace”.
• If for some reason some of the peaks are not labeled, extra peaks can be
manually labeled by clicking on the “T” on the bottom left corner.
• Use the “Text” too to select and or write a label or description.
• If satisfied with the information on the computer displaced spectrum, then
can be (saved) or printed by clicking on Print icon and then print again in
the print window.
Run ……
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Reference Spectra.
• Is absorption spectra of gases
with known chemical
compositions, recorded at a
known absorption pathlength,
which are used in the
quantitative analysis of gas
samples.
• Obtain reference spectra for
each analyte, interferant,
surrogate, CTS, and tracer.
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End Of Qualitative Analysis
Quantitation
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• TQ Analyst is a standard Windows application .
• The software offers a complete selection of
qualitative and quantitative analytical
techniques.
• It contains all of the algorithms that are
typically used for calculating component
concentrations and classifying spectra based
on a set of standards.
TQA Software
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Creating a Quantitative Analysis
• Double click in TQA icon.
• The File menu to create a new method
window.
• The Save Method As command in the File
menu to create a method file.
• The Description tab and enter a title for
your method.
• Choose an option for the quantitative
analysis options on the Description tab.
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1. Quantitative Analysis
• Select the Simple Beer’s Law analysis type
when each of the components you want to
measure produces a unique peak in the
spectrum of the sample mixture.
• Select the Classic least Squares CLS analysis
type when each component you want to
measure produces a peak or combination of
peaks in the spectrum of the sample mixture,
but the component peaks overlap
significantly.
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2. Pathlength
• The Pathlength tab and select an option for
the Pathlength parameter.
• The Advanced button displays a window
that allows you to access the
temperature/pressure and
dilution/extraction features of TQ Analyst.
• Select Constant pathlength type if you are
using a sampling accessory that has a fixed
pathlength, such as a liquid transmission
cell.
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3. Components
• The Components tab and specify the
components you want to measure and
the analysis limits for each component.
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4. Standards
• Describe the standards that will be used to calibrate, validate.
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View Standards
• View Standards, helps to select the region where the responding of
standards can be detected.
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5. Spectra
• Format for spectral data and to apply processing operations to the data,
such as subtraction, smoothing, and baseline correction.
• The corrections may be applied to the spectra of the method standards as
well as to any sample spectra you use the method to analyze.
• If you want to specify more than one processing step, we recommend
setting them up in this order:
Spectral Subtraction,
Data Format,
Smoothing,
Multipoint Baseline Correction.
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6. Regions
• The Regions tab to see the spectral peaks or regions
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No. Compound Conc. Range (ppm)
Spectral Range (cm-1)
1 CO (high) 1000 – 5% 2000 – 2050
2 CO (low) 1 – 1000 2150 – 2225
3 CO2 2 – 20% 725 – 765
4 NO 5 – 5000 1850 – 1950
5 NO2 5 – 500 1580 – 1650
6 CH4 1 – 5000 2800 – 3000
7 SO2 10 - 100 1010 -1230
8 HCl 50 - 750 2768 - 2849
9 SF6 2.5 - 45 909 - 967
IR Analysis Regions For Gases
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7. Calibrate
• Click the Calibrate button on the toolbar to calibrate your method.
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8. Quantify
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9. Report
• Click the Report tab and specify
the information you want to
include in your sample reports,
including any spectrum or
result warnings.
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10. Save the method
• The Save Method
command in the File
menu to save your
completed method.
Applications
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FTIR Spectrometry Gas Analyzer instruments are capable of ppb sensitivity for
multiple gas species in a variety of gas analysis applications, such as
• Stack gas emissions,
• Vehicle and engine certification testing,
• Continuous emissions monitoring (CEM),
• Formaldehyde emissions,
• Selective catalytic reduction (SCR) and other catalyst performance testing,
• Bulk gas purity analysis and vehicle as well as diesel, marine, locomotive,
• Non-road and other engine exhaust monitoring.
General Applications
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• Monitoring Siloxane Levels Using Gas Analysis.
• Monitoring the Purity of Liquid Carbon Dioxide.
• Analyze NOx Gases in Automobile Exhaust.
• Analyze the Aviator’s Breathing Oxygen .
• Analyzing Vapor Phase Samples .
• Physical Chemistry and Molecular Studies.
• QA/QC and Air Purity.
• Environmental and Air Monitoring.
Applications
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Applications
No. Item Calibration Range1 CO (high) 1000 – 5%
2 CO (low) 1 – 1000 ppm
3 CO2 2 – 20%
4 NO 5 – 5000 ppm
5 NO2 5 – 500 ppm
6 MTBE, ETBE 10 – 200 ppm
7 Formaldehyde 5 – 200 ppm
8 Ammonia 5 – 500 ppm
9 Ethanol 5 – 1000 ppm
10 THC 5 – 1000 ppm
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Applications
No. Item Calibration Range11 Acetylene 0.5 – 10 ppm
12 Carbon dioxide 1 – 20 ppm
13 Carbon monoxide 0.1 – 10 ppm
14 CFC 11 0.5 – 10 ppm
15 CFC 113 0.5 – 10 ppm
16 CFC 12 0.5 – 10 ppm
17 CFC 13 0.5 – 10 ppm
18 CFC 141 b 0.5 – 10 ppm
19 CFC 22 0.5 – 10 ppm
20 CFC 225 0.5 – 10 ppm
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Applications
No. Item Calibration Range21 Ethane 0.5 – 10 ppm
22 Ethylene 1 – 20 ppm
23 Methane 0.1 – 50 ppm
24 Nitrous oxide 0.5 – 10 ppm
25 Propane 0.5 – 10 ppm
26 Propylene 0.5 – 10 ppm
27 Sulfur hexafluoride 0.5 – 10 ppm
28 1,1,1-Trichloroethane 0.5 – 10 ppm
29 Trichloroethylene 0.5 – 10 ppm
30 Water 5 – 100 ppm
