1、Designation: E 840 95 (Reapproved 2005)Standard Practice forUsing Flame Photometric Detectors in GasChromatography1This standard is issued under the fixed designation E 840; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is intended as a guide for the use of a flamephotometric detector (FPD) as the detection component o
3、f agas chromatographic system.1.2 This practice is directly applicable to an FPD thatemploys a hydrogen-air flame burner, an optical filter forselective spectral viewing of light emitted by the flame, and aphotomultiplier tube for measuring the intensity of lightemitted.1.3 This practice describes t
4、he most frequent use of the FPDwhich is as an element-specific detector for compounds con-taining sulfur (S) or phosphorus (P) atoms. However, nomen-clature described in this practice are also applicable to uses ofthe FPD other than sulfur or phosphorus specific detection.1.4 This practice is intend
5、ed to describe the operation andperformance of the FPD itself independently of the chromato-graphic column. However, the performance of the detector isdescribed in terms which the analyst can use to predict overallsystem performance when the detector is coupled to thecolumn and other chromatographic
6、 system components.1.5 For general gas chromatographic procedures, PracticeE 260 should be followed except where specific changes arerecommended herein for use of an FPD.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 Th
7、is standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific safetyi
8、nformation, see Section 4, Hazards.2. Referenced Documents2.1 ASTM Standards:2E 260 Practice for Packed Column Gas ChromatographyE 355 Practice for Gas Chromatography Terms and Rela-tionships2.2 CGA Standards:CGA P-1 Safe Handling of Compressed Gases in Contain-ers3CGA G-5.4 Standard for Hydrogen Pi
9、ping Systems atConsumer Locations3CGA P-9 The Inert Gases: Argon, Nitrogen and Helium3CGA V-7 Standard Method of Determining Cylinder ValveOutlet Connections for Industrial Gas Mixtures3CGA P-12 Safe Handling of Cryogenic Liquids3HB-3 Handbook of Compressed Gases33. Terminology3.1 DefinitionsFor def
10、initions relating to gas chromatog-raphy, refer to Practice E 355.3.2 Descriptions of TermsDescriptions of terms used inthis practice are included in Sections 7-17.3.3 SymbolsA list of symbols and associated units ofmeasurement is included in Annex A1.4. Hazards4.1 Gas Handling SafetyThe safe handli
11、ng of com-pressed gases and cryogenic liquids for use in chromatographyis the responsibility of every laboratory. The Compressed GasAssociation, (CGA), a member group of specialty and bulk gassuppliers, publishes the following guidelines to assist thelaboratory chemist to establish a safe work envir
12、onment.Applicable CG publications include CGA P-1, CGA G-5.4,CGA P-9, CGA V-7, CGA P-12, and HB-3.1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-tography.Current edition approved Sept. 1, 2005.
13、 Published September 2005. Originallyapproved in 1981. Last previous edition approved in 2000 as E 840 95 (2000).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the
14、 standards Document Summary page onthe ASTM website.3Available from Compressed Gas Association, Inc., 1725 Jefferson DavisHighway, Arlington, VA 22202-4100.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Principles of Flame Photom
15、etric Detectors5.1 The FPD detects compounds by burning those com-pounds in a flame and sensing the increase of light emissionfrom the flame during that combustion process. Therefore, theFPD is a flame optical emission detector comprised of ahydrogen-air flame, an optical window for viewing emission
16、sgenerated in the flame, an optical filter for spectrally selectingthe wavelengths of light detected, a photomultiplier tube formeasuring the intensity of light emitted, and an electrometerfor measuring the current output of the photomultiplier.5.2 The intensity and wavelength of light emitted from
17、theFPD flame depends on the geometric configuration of the flameburner and on the absolute and relative flow rates of gasessupplied to the detector. By judicious selection of burnergeometry and gas flow rates, the FPD flame is usually designedto selectively enhance optical emissions from certain typ
18、es ofmolecules while suppressing emissions from other molecules.5.3 Typical FPD flames are normally not hot enough topromote abundant optical emissions from atomic species in theflame. Instead, the optical emissions from an FPD flameusually are due to molecular band emissions or continuumemissions r
19、esulting from recombination of atomic or molecularspecies in the flame. For sulfur detection, light emanating fromthe S2molecule is generally detected. For phosphorus detec-tion, light emanating from the HPO molecule is generallydetected. Interfering light emissions from general hydrocarboncompounds
20、 are mainly comprised of CH and C2molecularband emissions, and CO + O CO2+hg continuum radia-tion.5.4 Hydrogen air or hydrogen oxygen diffusion flamesare normally employed for the FPD. In such diffusion flames,the hydrogen and oxygen do not mix instantaneously, so thatthese flames are characterized
21、by significant spatial variationsin both temperature and chemical species. The importantchemical species in a hydrogen air flame are the H, O, andOH flame radicals. These highly reactive species play a majorrole in decomposing incoming samples and in the subsequentproduction of the desired optical e
22、missions. Optical emissionsfrom the HPO and S2molecular systems are highly favored inthose regions of an FPD flame which are locally rich inH-atoms, while CH and C2light emissions from hydrocarbonsoriginate mainly from those flame regions which are locallyrich in O-atoms. The highest sensitivity and
23、 specificity forsulfur and phosphorus detection are achieved only when theFPD flame is operated with hydrogen in excess of thatstoichiometric amount required for complete combustion of theoxygen supplied to the flame. This assures a large flamevolume that is locally abundant in H-atoms, and a minima
24、lflame volume that is locally abundant in O-atoms. The sensi-tivity and specificity of the FPD are strongly dependent on theabsolute and relative flow rates of hydrogen and air. Theoptimum hydrogen and air flow rates depend on the detailedconfiguration of the flame burner. For some FPD designs, thef
25、lows which are optimum for phosphorus detection are not thesame as the flows which are optimum for sulfur detection.Also, the flows which are optimum for one sample compoundmay not necessarily be optimum for another sample com-pound.5.5 Although the detailed chemistry occurring in the FPDflame has n
26、ot been firmly established, it is known that theintense emissions from the HPO and S2molecules are theresult of chemiluminescent reactions in the flame rather thanthermal excitation of these molecules (1).4The intensity oflight radiated from the HPO molecule generally varies as alinear function of P
27、-atom flow into the flame. In the case of theS2emission, the light intensity is generally a nonlinear functionof S-atom flow into the flame, and most often is found to varyas the approximate square of the S-atom flow. Since the FPDresponse depends on the P-atom or S-atom mass flow per unittime into
28、the detector, the FPD is a mass flow rate type ofdetector. The upper limit to the intensity of light emitted fromboth the HPO and S2molecules is generally determined by theonset of self-absorption effects in the emitting flame. At highconcentrations of S and P atoms in the flame, the concentra-tions
29、 of ground state S2and HPO molecules becomes sufficientto reabsorb light emitted from the radiating states of HPO andS2.5.6 In the presence of a hydrocarbon background in the FPDflame, the light emissions from the phosphorus and sulfurcompounds can be severely quenched (2). Such quenching canoccur i
30、n the gas chromatographic analysis of samples socomplex that the GC column does not completely separate thephosphorus or sulfur compounds from overlapping hydrocar-bon compounds. Quenching can also occur as the result of anunderlying tail of a hydrocarbon solvent peak precedingphosphorus or sulfur c
31、ompounds in a chromatographic sepa-ration. The fact that the phosphorus or sulfur response isreduced by quenching is not always apparent from a chromato-gram since the FPD generally gives little response to thehydrocarbon. The existence of quenching can often be revealedby a systematic investigation
32、 of the variation of the FPDresponse as a function of variations in sample volume while theanalyte is held at a constant amount.5.7 The chromatographic detection of trace level phospho-rus or sulfur compounds can be complicated by the fact thatsuch compounds often tend to be highly reactive and adso
33、rp-tive. Therefore, care must be taken to ensure that the entirechromatographic system is properly free of active sites foradsorption of phosphorus or sulfur compounds. The use ofsilanized glass tubing as GC injector liners and GC columnmaterials is a good general practice. At near ambient tempera-t
34、ures, GC packed columns made of FEP TFE-fluorocarbon,specially coated silica gel, or treated graphitized carbon areoften used for the analysis of sulfur gases.6. Detector Construction6.1 Burner Design:6.1.1 Single Flame Burner (2, 3)The most popular FPDburner uses a single flame to decompose sample
35、compoundsand generate the optical emissions. In this burner, carrier gasand sample compounds in the effluent of a GC column aremixed with air and conveyed to an orifice in the center of aflame tip. Excess hydrogen is introduced from the outer4The boldface numerals in parentheses refer to the list of
36、 references at the endof this practice.E 840 95 (2005)2perimeter of this flame tip so as to produce a relatively large,diffuse hydrogen-rich flame. With this burner and flow con-figuration, light emissions from hydrocarbon compounds occurprimarily in the locally oxygen-rich core of the flame in clos
37、eproximity to the flame tip orifice, while HPO and S2emissionsoccur primarily in the upper hydrogen-rich portions of theflame. Improved specificity is therefore obtained by the use ofan optical shield at the base of the flame to prevent hydrocar-bon emissions from being in the direct field of view.
38、The lightemissions generated in this flame are generally viewed fromthe side of the flame. Some of the known limitations of thisburner are as follows:6.1.1.1 Solvent peaks in the GC effluent can momentarilystarve the flame of oxygen and cause a flameout. This effectcan be avoided by interchanging th
39、e hydrogen and air inlets tothe burner (5) with a concomitant change in the flame gas flowrates to achieve maximum signal-to-noise response. Whereasinterchanging the H2and air inlets will eliminate flameoutproblems, this procedure will often yield a correspondingdecrease in the signal-to-noise ratio
40、 and hence compromise theFPD detectability.6.1.1.2 Response to sulfur compounds often deviates from apure square law dependence on sulfur-atom flow into the flame.Furthermore, the power law of sulfur response often dependson the molecular structure of the sample compound (4).6.1.1.3 The phosphorus o
41、r sulfur sensitivity often dependson the molecular structure of the sample compound.6.1.1.4 Hydrocarbon quenching greatly reduces the re-sponse to phosphorus and sulfur compounds (2).6.1.2 Dual Flame Burner (2, 5)A second FPD burnerdesign uses two hydrogen-rich flames in series. The first flameis us
42、ed to decompose samples from the GC and convert theminto combustion products consisting of relatively simple mol-ecules. The second flame reburns the products of the first flamein order to generate the light emissions that are detected. Aprincipal advantage of the dual flame burner is that it greatl
43、yreduces the hydrocarbon quenching effect on the phosphorusand sulfur emissions (6). Other advantages of the dual flameburner compared to a single flame burner are that sulfurresponses more uniformly obey a pure square law response,and more uniform responses to phosphorus and sulfur com-pounds are o
44、btained irrespective of the molecular structure ofthe sample compound.Adisadvantage of the dual flame burneris that it generally provides lower sensitivity to sulfur com-pounds than a single flame burner in those analyses wherehydrocarbon quenching is not a problem.6.2 Optical FilterFig. 1 illustrat
45、es the spectral distribu-tions of emissions from the S2, HPO, OH, CH, and C2molecular systems (1). The principle objectives of the opticalfilters used in the FPD are to maximize the transmission ratiosof HPO and S2light compared to the flame background andinterfering hydrocarbon emissions. For phosp
46、horus detection, anarrow-bandpass optical filter with peak transmission at 525 to530 nm is generally used. For sulfur detection, a filter withpeak transmission at 394 nm is most often used although theoptical region between 350 to 380 nm can also be employed.Typically, the filters used have an optic
47、al bandpass of approxi-mately 10 nm.6.3 Photomultiplier Tube:6.3.1 The photomultiplier tube used in the FPD generallyhas a spectral response extending throughout the visiblespectrum with maximum response at approximately 400 nm.Some specific tubes that are used are an end-viewing EMI9524B, and side-
48、viewing RCA 4552 or 1P21 tubes or theirequivalents. For FPD applications, the photomultiplier tubeshould have a relatively low dark current characteristic (forexample, 0.1 to 1.0 nA) so that the FPD background signal andnoise levels are determined by the FPD flame rather than by thephotomultiplier l
49、imitations. The photomultiplier dark currentand its associated noise (see Section 15) depend strongly on thephotomultipliers operating voltage and its ambient tempera-ture.6.3.2 Operating voltages are typically in the range of 400 to900 V, depending on the tube type. Generally, it is unlikely thattwo photomultiplier tubes of the same type have exactly thesame current amplification at a given voltage.Also, the currentamplification of a given photomultiplier tube often decreases asthe tube ages. Therefore, it is generally necessary to periodi-cally adjust the tube opera
