ASTM E840-95(2021)e1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
´1
Designation: E840 − 95 (Reapproved 2021)
Standard Practice for
Using Flame Photometric Detectors in Gas
Chromatography
This standard is issued under the fixed designation E840; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Section references in 8.7.2 and 10.2.1.1 were corrected and editorial changes made throughout in May 2021.
1. Scope 1.8 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 Thispracticeisintendedasaguidefortheuseofaflame
ization established in the Decision on Principles for the
photometric detector (FPD) as the detection component of a
Development of International Standards, Guides and Recom-
gas chromatographic system.
mendations issued by the World Trade Organization Technical
1.2 This practice is directly applicable to an FPD that
Barriers to Trade (TBT) Committee.
employs a hydrogen-air flame burner, an optical filter for
selective spectral viewing of light emitted by the flame, and a 2. Referenced Documents
photomultiplier tube for measuring the intensity of light
2.1 ASTM Standards:
emitted.
E260Practice for Packed Column Gas Chromatography
1.3 ThispracticedescribesthemostfrequentuseoftheFPD
E355PracticeforGasChromatographyTermsandRelation-
which is as an element-specific detector for compounds con- ships
taining sulfur (S) or phosphorus (P) atoms. However, nomen-
2.2 CGA Standards:
clature described in this practice are also applicable to uses of
CGAG-5.4Standard for Hydrogen Piping Systems at Con-
the FPD other than sulfur or phosphorus specific detection.
sumer Locations
CGAP-1SafeHandlingofCompressedGasesinContainers
1.4 This practice is intended to describe the operation and
CGAP-9The Inert Gases: Argon, Nitrogen and Helium
performance of the FPD itself independently of the chromato-
CGAP-12Safe Handling of Cryogenic Liquids
graphic column. However, the performance of the detector is
CGAV-7Standard Method of Determining Cylinder Valve
described in terms which the analyst can use to predict overall
Outlet Connections for Industrial Gas Mixtures
system performance when the detector is coupled to the
HB-3Handbook of Compressed Gases
column and other chromatographic system components.
1.5 For general gas chromatographic procedures, Practice
3. Terminology
E260 should be followed except where specific changes are
3.1 Definitions—For definitions relating to gas
recommended herein for use of an FPD.
chromatography, refer to Practice E355.
1.6 The values stated in SI units are to be regarded as
3.2 Descriptions of Terms—Descriptions of terms used in
standard. No other units of measurement are included in this
this practice are included in Sections7–17.
standard.
3.3 Symbols—A list of symbols and associated units of
1.7 This standard does not purport to address all of the
measurement is included in Annex A1.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 4. Hazards
priate safety, health, and environmental practices and deter-
4.1 Gas Handling Safety—The safe handling of compressed
mine the applicability of regulatory limitations prior to use.
gases and cryogenic liquids for use in chromatography is the
For specific safety information, see Section 4, Hazards.
responsibility of every laboratory. The Compressed Gas
1 2
This practice is under the jurisdiction ofASTM Committee E13 on Molecular For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Spectroscopy and Separation Science and is the direct responsibility of Subcom- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
mittee E13.19 on Separation Science. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2021. Published May 2021. Originally the ASTM website.
approved in 1981. Last previous edition approved in 2013 as E840–95(2013). Available from Compressed Gas Association (CGA), 8484 Westpark Drive,
DOI: 10.1520/E0840-95R21E01. Suite 220 McLean, VA 22102, http://www.cganet.com.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E840 − 95 (2021)
Association,(CGA),amembergroupofspecialtyandbulkgas optimum hydrogen and air flow rates depend on the detailed
suppliers, publishes the following guidelines to assist the configuration of the flame burner. For some FPD designs, the
laboratory chemist to establish a safe work environment. flows which are optimum for phosphorus detection are not the
Applicable CG publications include CGAP-1, CGAG-5.4, same as the flows which are optimum for sulfur detection.
CGAP-9, CGAV-7, CGAP-12, and HB-3. Also, the flows which are optimum for one sample compound
may not necessarily be optimum for another sample com-
5. Principles of Flame Photometric Detectors
pound.
5.1 The FPD detects compounds by burning those com-
5.5 Although the detailed chemistry occurring in the FPD
pounds in a flame and sensing the increase of light emission
flame has not been firmly established, it is known that the
from the flame during that combustion process. Therefore, the
intense emissions from the HPO and S molecules are the
FPD is a flame optical emission detector comprised of a
result of chemiluminescent reactions in the flame rather than
hydrogen-air flame, an optical window for viewing emissions
thermal excitation of these molecules (1). The intensity of
generated in the flame, an optical filter for spectrally selecting
light radiated from the HPO molecule generally varies as a
the wavelengths of light detected, a photomultiplier tube for
linearfunctionofP-atomflowintotheflame.Inthecaseofthe
measuring the intensity of light emitted, and an electrometer
S emission,thelightintensityisgenerallyanonlinearfunction
for measuring the current output of the photomultiplier.
of S-atom flow into the flame, and most often is found to vary
as the approximate square of the S-atom flow. Since the FPD
5.2 The intensity and wavelength of light emitted from the
response depends on the P-atom or S-atom mass flow per unit
FPDflamedependsonthegeometricconfigurationoftheflame
time into the detector, the FPD is a mass flow rate type of
burner and on the absolute and relative flow rates of gases
detector. The upper limit to the intensity of light emitted from
supplied to the detector. By judicious selection of burner
both the HPO and S molecules is generally determined by the
geometryandgasflowrates,theFPDflameisusuallydesigned
onset of self-absorption effects in the emitting flame. At high
to selectively enhance optical emissions from certain types of
concentrations of S and P atoms in the flame, the concentra-
molecules while suppressing emissions from other molecules.
tionsofgroundstateS andHPOmoleculesbecomessufficient
5.3 Typical FPD flames are normally not hot enough to
to reabsorb light emitted from the radiating states of HPO and
promoteabundantopticalemissionsfromatomicspeciesinthe
S .
flame. Instead, the optical emissions from an FPD flame
5.6 InthepresenceofahydrocarbonbackgroundintheFPD
usually are due to molecular band emissions or continuum
flame, the light emissions from the phosphorus and sulfur
emissionsresultingfromrecombinationofatomicormolecular
compounds can be severely quenched (2). Such quenching can
speciesintheflame.Forsulfurdetection,lightemanatingfrom
occur in the gas chromatographic analysis of samples so
the S molecule is generally detected. For phosphorus
complex that the GC column does not completely separate the
detection, light emanating from the HPO molecule is generally
phosphorus or sulfur compounds from overlapping hydrocar-
detected. Interfering light emissions from general hydrocarbon
bon compounds. Quenching can also occur as the result of an
compounds are mainly comprised of CH and C molecular
underlying tail of a hydrocarbon solvent peak preceding
bandemissions,andCO+O→CO +hγcontinuumradiation.
phosphorus or sulfur compounds in a chromatographic sepa-
5.4 Hydrogen – air or hydrogen – oxygen diffusion flames
ration. The fact that the phosphorus or sulfur response is
are normally employed for the FPD. In such diffusion flames,
reducedbyquenchingisnotalwaysapparentfromachromato-
the hydrogen and oxygen do not mix instantaneously, so that
gram since the FPD generally gives little response to the
these flames are characterized by significant spatial variations
hydrocarbon.Theexistenceofquenchingcanoftenberevealed
in both temperature and chemical species. The important
by a systematic investigation of the variation of the FPD
chemical species in a hydrogen – air flame are the H, O, and
responseasafunctionofvariationsinsamplevolumewhilethe
OH flame radicals. These highly reactive species play a major
analyte is held at a constant amount.
role in decomposing incoming samples and in the subsequent
5.7 The chromatographic detection of trace level phospho-
production of the desired optical emissions. Optical emissions
rus or sulfur compounds can be complicated by the fact that
from the HPO and S molecular systems are highly favored in
such compounds often tend to be highly reactive and adsorp-
those regions of an FPD flame which are locally rich in
tive. Therefore, care must be taken to ensure that the entire
H-atoms, while CH and C light emissions from hydrocarbons
chromatographic system is properly free of active sites for
originate mainly from those flame regions which are locally
adsorption of phosphorus or sulfur compounds. The use of
rich in O-atoms. The highest sensitivity and specificity for
silanized glass tubing as GC injector liners and GC column
sulfur and phosphorus detection are achieved only when the
materials is a good general practice. At near ambient
FPD flame is operated with hydrogen in excess of that
temperatures, GC packed columns made of FEP TFE-
stoichiometricamountrequiredforcompletecombustionofthe
fluorocarbon, specially coated silica gel, or treated graphitized
oxygen supplied to the flame. This assures a large flame
carbon are often used for the analysis of sulfur gases.
volume that is locally abundant in H-atoms, and a minimal
flame volume that is locally abundant in O-atoms. The sensi-
tivity and specificity of the FPD are strongly dependent on the 4
The boldface numbers in parentheses refer to a list of references at the end of
absolute and relative flow rates of hydrogen and air. The this standard.
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E840 − 95 (2021)
6. Detector Construction
6.1 Burner Design:
6.1.1 Single Flame Burner (2, 3)—The most popular FPD
burner uses a single flame to decompose sample compounds
and generate the optical emissions. In this burner, carrier gas
and sample compounds in the effluent of a GC column are
mixed with air and conveyed to an orifice in the center of a
flame tip. Excess hydrogen is introduced from the outer
perimeter of this flame tip so as to produce a relatively large,
diffuse hydrogen-rich flame. With this burner and flow
configuration, light emissions from hydrocarbon compounds
occur primarily in the locally oxygen-rich core of the flame in
close proximity to the flame tip orifice, while HPO and S
emissions occur primarily in the upper hydrogen-rich portions
of the flame. Improved specificity is therefore obtained by the
FIG. 1 Spectral Distribution of Molecular Emissions from an FPD
use of an optical shield at the base of the flame to prevent
Flame
hydrocarbon emissions from being in the direct field of view.
The light emissions generated in this flame are generally
viewed from the side of the flame. Some of the known
limitations of this burner are as follows:
of HPO and S light compared to the flame background and
6.1.1.1 Solvent peaks in the GC effluent can momentarily
interferinghydrocarbonemissions.Forphosphorusdetection,a
starve the flame of oxygen and cause a flameout. This effect
narrow-bandpass optical filter with peak transmission at
can be avoided by interchanging the hydrogen and air inlets to
525nm to 530 nm is generally used. For sulfur detection, a
the burner (4) with a concomitant change in the flame gas flow
filter with peak transmission at 394 nm is most often used
rates to achieve maximum signal-to-noise response. Whereas
althoughtheopticalregionbetween350nmto380nmcanalso
interchanging the H and air inlets will eliminate flameout
be employed. Typically, the filters used have an optical
problems, this procedure will often yield a corresponding
bandpass of approximately 10 nm.
decreaseinthesignal-to-noiseratioandhencecompromisethe
6.3 Photomultiplier Tube:
FPD detectability.
6.3.1 The photomultiplier tube used in the FPD generally
6.1.1.2 Responsetosulfurcompoundsoftendeviatesfroma
has a spectral response extending throughout the visible
puresquarelawdependenceonsulfur-atomflowintotheflame.
spectrum with maximum response at approximately 400 nm.
Furthermore, the power law of sulfur response often depends
Some specific tubes that are used are an end-viewing EMI
on the molecular structure of the sample compound (5).
9524B, and side-viewing RCA 4552 or 1P21 tubes or their
6.1.1.3 The phosphorus or sulfur sensitivity often depends
equivalents. For FPD applications, the photomultiplier tube
on the molecular structure of the sample compound.
should have a relatively low dark current characteristic (for
6.1.1.4 Hydrocarbon quenching greatly reduces the re-
example, 0.1nAto 1.0 nA) so that the FPD background signal
sponse to phosphorus and sulfur compounds (2).
and noise levels are determined by the FPD flame rather than
6.1.2 Dual Flame Burner (2, 4)—A second FPD burner
by the photomultiplier limitations. The photomultiplier dark
design uses two hydrogen-rich flames in series.The first flame
current and its associated noise (see Section 15) depend
is used to decompose samples from the GC and convert them
strongly on the photomultiplier’s operating voltage and its
into combustion products consisting of relatively simple mol-
ambient temperature.
ecules.Thesecondflamereburnstheproductsofthefirstflame
6.3.2 Operating voltages are typically in the range of 400V
in order to generate the light emissions that are detected. A
to 900 V, depending on the tube type. Generally, it is unlikely
principal advantage of the dual flame burner is that it greatly
that two photomultiplier tubes of the same type have exactly
reduces the hydrocarbon quenching effect on the phosphorus
the same current amplification at a given voltage. Also, the
and sulfur emissions (6). Other advantages of the dual flame
current amplification of a given photomultiplier tube often
burner compared to a single flame burner are that sulfur
decreases as the tube ages. Therefore, it is generally necessary
responses more uniformly obey a pure square law response,
to periodically adjust the tube operating voltage in order to
and more uniform responses to phosphorus and sulfur com-
maintain the same FPD sensitivity.
pounds are obtained irrespective of the molecular structure of
6.3.3 Since the FPD burner housing generally operates at
thesamplecompound.Adisadvantageofthedualflameburner
elevatedtemperatures,acriticaldesignconstraintintheFPDis
is that it generally provides lower sensitivity to sulfur com-
the coupling of the maximum amount of light from the flame
pounds than a single flame burner in those analyses where
to the photomultiplier with minimum thermal coupling. In
hydrocarbon quenching is not a problem.
someFPDdesigns,opticallensesorfiberopticlightguidesare
6.2 Optical Filter—Fig. 1 illustrates the spectral distribu- used to allow the photomultiplier to be operated in as cool an
tions of emissions from the S , HPO, OH, CH, and C environment as possible. Thermoelectric or cryogenic cooling
2 2
molecular systems (1). The principle objectives of the optical are sometimes used to further reduce the photomultiplier dark
filters used in the FPD are to maximize the transmission ratios current.
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E840 − 95 (2021)
6.3.4 Although a photomultiplier tube is a device with a device,whetherpeakareaorpeakheight,islinearwithrespect
definite lifetime, this lifetime is normally in excess of 2 years to input signal. Failure to perform this calibration may intro-
to 3 years unless the tube is used at conditions of high current duce substantial errors into the results. Methods for calibration
levels for extended time periods. FPD users are especially will vary for different manufacturer’s devices but may include
cautioned to avoid exposure of the photomultiplier tube to accurate constant voltage supplies or pulse generating equip-
room light when the tube operating voltage is on. ment.Theinstructionmanualshouldbestudiedandthoroughly
understood before attempting to use electronic integration for
6.4 Electronics:
peak area or peak height measurements.
6.4.1 Electrometer—The current output from the photomul-
tiplier tube is generally measured using an electrometer.
TERMS AND RELATIONSHIPS
Typical currents detected range from noise levels of the order
−12 –10 −5
of 10 Ato10 A to maximum signal levels of 10 Ato
8. Sensitivity (Response)
−4
10 A.
8.1 Description of Term:
6.4.2 Linearizer for Sulfur Responses (7)—The nonlinear
8.1.1 In the phosphorus mode of operation, the FPD gener-
sulfur response is sometimes linearized by using an electronic
ally exhibits a response that is a linear function of mass flow
circuit at the output of the electrometer. Usually this circuit is
one which provides an output signal proportional to the square rate of P-atoms into the flame. Therefore, the phosphorus
sensitivity (response) of the FPD is the signal output per unit
root of the electrometer output. When such a square root
linearizer is used, the analyst should be aware of the following mass flow rate of P-atoms in a test substance in the carrier gas.
A simplified relationship for the phosphorus sensitivity is:
considerations:
6.4.2.1 Thesulfuroutputsignalwillbeexactlylinearonlyif
S 5 A /m (1)
P i P
the sulfur emission from the flame obeys a pure square law
where:
dependence on S-atom flow into the flame.
S = phosphorus sensitivity (response), A·s/gP;
6.4.2.2 The square root of the signal plus baseline offset
P
A = integrated peak area, A·s; and
does not equal the sum of the square root of the signal plus the
I
m = mass of P-atoms in the test substance, gP.
square root of the baseline offset. Therefore, the flame back- P
ground must be suppressed so that the baseline offset at the
8.1.2 In the sulfur mode of operation, the FPD generally
electrometer output is exactly zero in order to obtain output
exhibits a response that is a nonlinear power law function of
signals which vary linearly as a function of S-atom flow into
mass flow rate of S-atoms into the flame. Therefore, sulfur
the flame.
sensitivity requires first a determination of the power law of
6.4.2.3 Square root circuits tend to be very noisy when the
responseinaccordancewiththespecificationsgiveninSection
voltage input to the circuit approaches zero. Therefore, the
11. In general, if the FPD sulfur response varies as the nth
outputnoisemaynotbeanaccuraterepresentationoftheflame
power of S-atom mass flow rate, then the sulfur sensitivity is
noise.
determined as follows:
6.4.2.4 Flame background levels which are drifting in a
n21
S 5 ~A /m !·~1/m˙ ! (2)
S i S S
negativedirectionwillgivenerroneoussampleresponsesatthe
square root output since the square root of negative input
where:
n
voltages is not defined. (Warning—The FPD operates at high
S = sulfur sensitivity (response), A/(gS/s) ;
S
hydrogen flow rate.To avoid an accumulation of hydrogen gas
A = integrated peak area, A·s;
i
and possible fire or explosion hazard, turn off hydrogen flow
m = mass of S-atoms in the test substance, gS; and
S
when removing column or when the FPD is not being used.) m˙ = mass flow rate of S-atoms in the test substance, gS/s.
S
Frequently, the sulfur response of an FPD obeys a pure
7. Data Handling
square law, so that n=2 and the sensitivity, expressed in
7.1 All manufacturers supply an integral electrometer to
A/(gS/s) , is as follows:
allow the small electrical current changes to be coupled to
S 5 ~A /m !~1/m˙ ! (3)
S i S S
recorder/integrators/computers. The preferred system will in-
corporate one of the newer integrators or computers that
8.2 Test Conditions:
converts an electrical signal into clearly defined peak area
8.2.1 Since the FPD response can depend on sample com-
counts in units such as microvolt-seconds.These data can then
poundstructureaswellassamplematrix,thetestsubstancefor
be readily used to calculate the linear range.
the determination of FPD sensitivity may be selected in
7.1.1 Another method uses peak height measurements.This
accordance with the expected application of the detector. The
method yields data that are very dependent on column perfor-
testsubstanceshouldalwaysbewelldefinedchemically.When
mance and therefore not recommended.
specifyingthesensitivityoftheFPD,thetestsubstanceapplied
7.1.2 Regardlessofwhichmethodisusedtocalculatelinear
must be stated.
range, peak height is the only acceptable method for determin-
8.2.1.1 The recommended test substance is tributylphos-
ing minimum detectability.
phate for the phosphorus mode, and sulfur hexafluoride for the
sulfur mode.
7.2 Calibration—It is essential to calibrate the measuring
system to ensure that the nominal specifications are acceptable 8.2.2 The measurement must be made at a signal level
andparticularlytoverifytherangeoverwhichtheoutputofthe between 20-times and 200-times greater than the noise level.
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E840 − 95 (2021)
8.2.3 For the phosphorus sensitivity, the measurement must C 5 C exp 2F t/V (4)
~ !
fS oS f f
bemadewithinthelinearrangeofresponseofthedetector.For
where:
the sulfur sensitivity, the measurement must be made within
C = concentration of S-atoms in the carrier gas at time t
fS
the range of a uniform power law response of the detector
after introduction into the flask, gS/cm ;
versus S-atom flow.
C = initial concentration of S-atoms introduced into the
oS
8.2.4 The magnitude of the flame background current for
flask, gS/cm ;
the detector at the same conditions should be stated.
F = carrier gas flow rate, corrected to flask temperature
f
8.2.5 Since the output signal of a photomultiplier tube
(see Annex A2), cm /min;
depends on its operating voltage, the FPD sensitivity is also a
t = time, min; and
function of the photomultiplier voltage. Therefore, the type of 3
V = volume of flask, cm .
f
photomultiplier tube used and its operating voltage should be
8.4.4 Calculate the sulfur sensitivity of the detector at any
stated.
concentration as follows:
8.2.6 The conditions under which the detector sensitivity is
n
S 5 E 60/C F (5)
measured must be stated. This should include but not neces-
~ !
S fS f
sarily be limited to the following:
where:
8.2.6.1 Mode of operation (S or P),
n
S = sulfur sensitivity, A/(gS/s) ;
S
8.2.6.2 Detector burner geometry (single or dual flame),
E = detector signal, A;
8.2.6.3 Wavelength and bandpass of optical filter,
C = concentration of S-atoms in the carrier gas at time t
fS
8.2.6.4 Hydrogen flow rate,
after introduction into the flask, gS/cm ; and
8.2.6.5 Air or oxygen flow rate,
F = carrier gas flow rate, corrected to flask temperature
f
8.2.6.6 Carrier gas,
(see Annex A2), cm /min.
8.2.6.7 Carrier gas flow rate (corrected to detector
NOTE 1—This method is subject to errors due to inaccuracies in
temperature),
measuring the flow rate and flask volume. An error of 1% in the
8.2.6.8 Detector temperature,
measurement of either variable will propagate to 2% over two decades in
concentration and to 6% over six decades.Therefore, this method should
8.2.6.9 Electrometer time constant, and
not be used for concentration ranges of more than two decades over a
8.2.6.10 Method of measurement.
single run.
8.2.7 Linearity and speed of response of the recording
NOTE 2—A temperature difference of 1°C between flask and flow
system used should be such that it yields a true reading of the
measuring apparatus will, if uncompensated, introduce an error of 0.33%
detector performance. The recorders should have a 0mV to into the flow rate.
NOTE 3—Extreme care should be taken to avoid unswept volumes
1mV range and a 1s response time corresponding to 90% of
betweentheflaskandthedetector,asthesewillintroduceadditionalerrors
full scale deflection.
into the calculations.
3 3
8.3 Methods of Measurement: NOTE 4—Flask volumes between 100cm and 500 cm have been
found to be the most convenient. Larger volumes should be avoided due
8.3.1 Sulfur sensitivity may be measured by any of five
to difficulties in obtaining efficient mixing and the likelihood of tempera-
methods, while only two methods are applicable to the mea-
ture gradients.
surement of phosphorus sensitivity. Methods are as follows:
8.5 Method Utilizing Permeation Devices:
8.3.1.1 Experimental decay with exponential dilution flask
8.5.1 Permeation devices consist of a volatile liquid en-
(8) (see 8.4) for sulfur gas samples.
closed in a container with a permeable wall. These devices
8.3.1.2 Permeation device (9) under steady-state conditions
provide low concentrations of vapor by diffusion of the vapor
(see 8.5) for sulfur gas samples.
through the permeable surface. The rate of permeation for a
8.3.1.3 Dynamic method with Young’s (10) apparatus for
givendeviceisdependentonlyonthetemperature.Theweight
sulfur gas samples (see 8.6).
loss over a period of time is carefully and accurately deter-
8.3.1.4 Diffusion dilution technique (11, 12) (see 8.7) for
mined and these devices have been proposed as primary
sulfur or phosphorus liquid samples.
standards.
8.3.1.5 Actual chromatograms (see 8.8) for sulfur or phos-
8.5.2 Accurately known permeation rates can be prepared
phorus liquid samples.
by passing a gas over the previously calibrated permeation
8.4 Exponential Dilution Method:
device at constant temperature. Knowing the permeation rate
8.4.1 Purge a mixing vessel of known volume fitted with a
of S-atoms in the test substance, the sulfur sensitivity can be
magneticallydrivenstirrerwiththecarriergasataknownrate.
obtained from the following equation:
The effluent from the flask is delivered directly to the detector.
n
S 5 E~60/R ! (6)
S S
Introduce a measured quantity of the test substance into the
flask to give an initial concentration, C , of the test substance where:
o
n
in the carrier gas, and simultaneously start a timer.
S = sulfur sensitivity, A(s/gS) ;
S
8.4.2 Calculate the initial sulfur concentration using the
E = detector signal, A;
equation C =Y C /100, where Y is the mass percent of
R = permeationrateofS-atomsinatestsubstancefromthe
oS S o S
S
sulfur atoms in the test substance. permeation device, gS/min; and
8.4.3 Calculate the concentration of S-atoms in the carrier n = power law of sulfur response (see Section 11).
gas at the outlet of the flask at any time as follows:
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E840 − 95 (2021)
8.6 Dynamic Method: 8.8.3 Calculate the sulfur sensitivity of the detector in
8.6.1 In this method, inject a known weight of S-atoms in a accordance with 8.6.2.
test substance into the flowing carrier gas stream. A length of
8.9 Typical Values of Sensitivity:
empty tubing between the sample injection port and the
NOTE 5—These values will depend on photomultiplier voltage.
detector permits the band to spread and be detected as a
2 2
Gaussian band. Then integrate the detector signal by any
8.9.1 For sulfur, 2A⁄(gS⁄s) to 20 A/(gS/s) .
suitablemethod.Thismethodhastheadvantagethatnospecial
8.9.2 For phosphorus, 20A·s⁄gP to 200 A·s/gP.
equipment or devices are required other than conventional
chromatographic hardware.
9. Minimum Detectability
8.6.2 Calculate the sulfur sensitivity as follows:
9.1 Description of Term:
n
S 5 A /m ~t /m ! (7)
~ !
S i S S S 9.1.1 Minimum detectability for phosphorus is the mass
flow rate of phosphorus atoms in the carrier gas that gives a
where:
detector signal equal to twice the peak-to-peak noise level and
n
S = sulfur sensitivity, A(s/gS) ;
S
is calculated from the measured sensitivity and noise level
A = integrated peak area, A·s;
i
values as follows:
m = mass of sulfur atoms injected, gS;
S
n
D 5 2N /S (9)
t = peakwidthat( ⁄2) ofthemaximumpeakheight,s;and
P P P
S
n = power law of sulfur response (see Section 10).
where:
8.7 Diffusion Dilution Method:
D = minimum detectability for phosphorus, gP/s;
P
8.7.1 This method is analogous to the permeation device
N = noise level in phosphorus mode, A; and
P
methodandmaybeusedforsulfurandphosphorus-bearingtest
S = phosphorus sensitivity of the FPD, A·s/gP.
P
substances that a
...