ASTM E1140-95(2017) Standard Practice for Testing NitrogenPhosphorus Thermionic Ionization Detectors for Use In Gas Chromatography.pdf

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1、Designation: E1140 95 (Reapproved 2017)Standard Practice forTesting Nitrogen/Phosphorus Thermionic IonizationDetectors for Use In Gas Chromatography1This standard is issued under the fixed designation E1140; the number immediately following the designation indicates the year oforiginal adoption or,

2、in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers testing the performance of anitrogen/phosphorus thermionic i

3、onization detector (NPD)used as the detection component of a gas chromatographicsystem.1.2 This practice applies to an NPD that employs a heatedalkali metal compound and emits an electrical charge from thatsolid surface.1.3 This practice addresses the operation and performanceof the NPD independentl

4、y of the chromatographic column.However, the performance is specified in terms that the analystcan use to predict overall system performance when thedetector is coupled to the column and other chromatographiccomponents.1.4 For general chromatographic procedures, Practice E260should be followed excep

5、t where specific changes are recom-mended in this practice for the use of a nitrogen/phosphorus(N/P) thermionic detector.1.5 This 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-p

6、riate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.For specific safety information, see Section 5, Hazards.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-izatio

7、n established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E260 Practice for Packed Column Gas ChromatographyE355 P

8、ractice for Gas Chromatography Terms and Relation-ships2.2 CGA Standards:3CGA P-1 Safe Handling of Compressed Gases in ContainersCGA G-5.4 Standard for Hydrogen Piping Systems at Con-sumer LocationsCGA P-9 The Inert Gases: Argon, Nitrogen and HeliumCGA V-7 Standard Method of Determining Cylinder Val

9、veOutlet Connections for Industrial Gas MixturesCGA P-12 Safe Handling of Cryogenic LiquidsHB-3 Handbook of Compressed Gases3. Terminology3.1 Definitions:3.1.1 For definitions of gas chromatography and its variousterms, see Practice E355.3.2 Definitions of Terms Specific to This Standard:3.2.1 drift

10、the average slope of the noise envelope ex-pressed in amps/h as measured over12 h.3.2.2 linear rangerange of mass flow rates of nitrogen orphosphorus in the carrier gas, over which the sensitivity of thedetector is constant to within 5 % as determined from thelinearity plot.3.2.3 minimum detectabili

11、tythe mass flow rate of nitrogenor phosphorus in the carrier gas that gives a detector signalequal to twice the noise level.1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.19 on Separ

12、ation Science.Current edition approved Oct. 1, 2017. Published October 2017. Originallyapproved in 1986. Last previous edition approved in 2010 as E1140 95 (2010)1.DOI: 10.1520/E1140-95R17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servic

13、eastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Compressed Gas Association (CGA), 14501 George CarterWay, Suite 103, Chantilly, VA 20151, http:/.Copyright ASTM International, 100 Barr Harbor Drive, PO Box

14、 C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by th

15、e World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.4 noise (short term)the amplitude, expressed inamperes, of the baseline envelope that includes all randomvariations of the detector signal of a frequency greater than onecycle per minute.3.2.5 selectivitythe ratio of the res

16、ponse per gram ofnitrogen or phosphorus in the test substance to the response pergram of carbon in octadecane.4. Significance and Use4.1 Although it is possible to observe and measure each ofthe several characteristics of a detector under different andunique conditions, it is the intent of this prac

17、tice that acomplete set of detector specifications be obtained at the sameoperating conditions, including geometry, flow rates, andtemperatures. To specify a detectors capability completely, itsperformance should be measured at several sets of conditionswithin the useful range of the detector. The t

18、erms and testsdescribed in this practice are sufficiently general so that theymay be used under any chosen conditions.4.2 Linearity and speed of response of the recorder shouldbe such that it does not distort or otherwise interfere with theperformance of the detector. Effective recorder response sho

19、uldbe sufficiently fast so that its effect on the sensitivity ofmeasurement is negligible. If additional amplifiers are usedbetween the detector and the final readout device, theircharacteristics should first be established.5. Hazards5.1 Gas Handling SafetyThe safe handling of compressedgases and cr

20、yogenic liquids for use in chromatography is theresponsibility of every laboratory. The Compressed Gas Asso-ciation (CGA), a member group of specialty and bulk gassuppliers, publishes the following guidelines to assist thelaboratory chemist to establish a safe work environment.Applicable CGA publica

21、tions include: CGA P-1, CGA G-5.4,CGA P-9, CGA V-7, CGA P-12, and HB-3.6. Application6.1 The N/P thermionic detector is an element-specificionization detector that is essentially a major modification ofthe flame ionization detector (FID). As in the normal FID, itmeasures increase in ionization curre

22、nt passing between twoelectrodes, one of which is polarized relative to the other.Usually these are the inorganic salt source and the collector,with one often being at ground potential.6.2 The mechanism of the detector will only be discussedbriefly in this practice partly because full understanding

23、of thedetector is not presently available and partly because thesubstantial differences in bead chemistry, detector geometry,and bead heating mechanism prevent a singular view beinggiven.6.3 The addition of a heated alkali metal compound in thedetector area causes enhancement of the response for car

24、bon-nitrogen and carbon-phosphorus bonds. In addition, the selec-tivity of response can be further enhanced when the bead iselectrically heated. Lower hydrogen and air flow rates thatdiminish the normal flame ionization response for hydrocarboncompounds can be used. This selective enhancement allows

25、 theNPD to be used for the detection of very small quantities ofnitrogen- and phosphorus-containing compounds without in-terference from the signal of other molecular species.6.4 The selective response to C-N and C-Pbonds means thatthe detector is not suitable for permanent gas or elementalnitrogen

26、or phosphorus analysis in the true definition of theterm. It should be noted, however, that some volatile inorganicphosphorous compounds do give a strong response with thisdetector, comparable to that of organophosphorus compounds.7. Detector Construction7.1 There is a wide variation in the method o

27、f constructionof this detector. It is not considered pertinent to review allaspects of the different detector designs available, but toconsider one generalized design as an example and recognizethat many significant variants may exist. Examples of signifi-cant differences may exist in bead chemistry

28、 and method ofheating, space jet and collector configuration, potential appliedacross the cell, its polarity, and the flow rates and compositionof the three gases used.7.2 An essential part of the N/P thermionic detector is thepresence, in the active area of the detector, of an inorganicmaterial con

29、taining an alkali metal, often rubidium. Theinorganic material may be a salt or silicate. It is usually, but notnecessarily, present in bead form and may be combined withother components for mechanical support, such as a ceramiccore.7.3 The inorganic salt mixture is usually connected to, orsupported

30、 by, a wire of platinum or other noncorrosive mate-rial. In some designs the bead is heated by passing a currentthrough this wire; in others, the bead is heated by hydrogencombustion, for example, the burning flame itself.7.4 The carrier gas (usually helium or nitrogen) flowsthrough a jet as in norm

31、al FID practice and mixes, prior toleaving the jet, with a small volume of hydrogen. Combustiongas (usually air) is fed around the jet in some manner and thenmoves over or around the bead before exiting from thedetector. It is worth noting that if this mixture is lean enough,due to low hydrogen flow

32、, there will be insufficient fuel tomaintain a true flame.8. Equipment Preparation8.1 The detector shall be evaluated as part of a gas chro-matograph using injections of liquid samples that have a rangeof component concentrations.8.1.1 The detector shall be operated with carrier gas typeand hydrogen

33、 and oxidizer gas flow rates as recommended bythe manufacturer of the equipment. No attempt will be made inthis practice to guide the selection of optimum conditions,except to state that because selectivity and sensitivity of theNPD are very dependent on the hydrogen flow rate, severalflow rates (in

34、 the range of 1 to 8 mL/min for the electricallyheated bead detector) should be tested for optimum detectorperformance.8.1.2 The complete set of performance specifications mustbe determined at the same operating conditions, since theE1140 95 (2017)2absolute sensitivity and noise vary independently o

35、ver a widerange depending on the operating conditions. Once selected,the operating conditions should not be changed during thedetermination of the detector characteristics.8.1.3 Detector stability over the course of the evaluation isessential for meaningful results. This may be monitored bychecking

36、the bead temperature, the heating current, gas flows,and other parameters during the evaluation as dictated by theinstrument manufacturer. (Some electrically-heated beads tendto lose sensitivity continuously with operating time and requireincreasing the bead heating current to recover lost sensitivi

37、ty.)8.2 ColumnAny column that fully separates the samplecomponents without causing overload or sample adsorptionmay be used. One suitable column isa4ftby2mmglasscolumn packed with 100/120 mesh deactivated chromosorb Wcoated with 2 wt. % dimethyl silicone oil.8.3 GasesWith N/P thermionic detectors it

38、 is of criticalimportance that all gases are pure and that the gas lines are notcontaminated with oils, solder flux, etc. The use of wellconditioned molecular sieve traps in all lines helps to achievethis purity. If the chromatograph is fitted with in-line chemicalfilters after the gas regulators an

39、d flow controllers, they alsoshould be well conditioned to ensure that no contaminantsreach the column from elastomeric diaphragms contained inthese parts.NOTE 1To condition a molecular sieve 5A column well, heat the trapwith a slow flow of carrier gas at 350 C for a minimum of 2 h.8.4 Gas Connectio

40、nsAll gas tubing and connectionsshould be made of cleaned copper or stainless steel, includingall ferrules and joints within the system. Vespel and graphiteferrules may be used for GC column connections provided thatthey are sufficiently conditioned after installation. These stepswill minimize conta

41、mination problems.9. Sample Preparation9.1 A solution containing three compounds dissolved inisooctane should be used, with great emphasis placed on thepurity of all chemicals and particularly the solvent. Blank runsshould be made on the solvent to ensure that no interferingpeaks elute at the same t

42、ime as the compounds of interest,which would invalidate the results. The three test compoundsare azobenzene for nitrogen response (15.38 % nitrogen),malathion for phosphorus response (9.38 % phosphorus), andoctadecane for specificity (84.95 % carbon). Azobenzene andmalathion should be mixed in an ap

43、propriate ratio to allowcomparable peak heights under the isothermal conditions used.Typical ratios are between 0.5 and 2.0, depending on detectorconstruction and operating conditions. Concentration limitsbetween 1 g/L and 1 mg/L are recommended initial values.The octadecane need be checked only at

44、one concentrationlevel for specificity, and the recommended concentration forthis should be 1 g/L.9.2 Because of the toxicity of malathion, it is recommendedthat a dilute solution be used as the starting material, and thatthis solution be purchased from one of the special supplyhouses that routinely

45、 make chemical standards. Precautions forhandling toxic materials must be followed throughout thedilution sequence as standard good laboratory practice.9.3 Sample InjectionThe recommended procedure for ac-curate injection of liquid samples is the “solvent flush,” orBurke injection technique, in whic

46、h a carefully washed 10-Lsyringe is loaded with 1 to 2 L solvent, 1 L air, 3 L sample,and 1 L air. While time consuming, this procedure allowsrepeatability of 62 % or better, and minimizes needle volumeeffects.10. Data Handling10.1 All manufacturers supply an integral electrometer toallow the small

47、electrical current changes to be coupled torecorders/integrators/computers. The preferred system will in-corporate one of the newer integrators or computers thatconverts an electrical signal into clearly defined peak areacounts in units such as microvolt-seconds. These data can thenbe readily used t

48、o calculate the linear range.10.1.1 Another method uses peak height measurements.This method yields data that are very dependent on columnperformance and therefore not recommended.10.1.2 Regardless of which method is used to calculatelinear range, peak height is the only acceptable method fordetermi

49、ning minimum detectability.10.2 CalibrationIt is essential to calibrate the measuringsystem to ensure that the nominal specifications are acceptableand particularly to verify the range over which the output of thedevice, whether peak area or peak height, is linear with respectto input signal. Failure to perform this calibration may intro-duce substantial errors into the results. Methods for calibrationwill vary for different manufacturers devices but may includeaccurate constant voltage supplies or pulse-generating equip-ment. The inst