1、Designation: D2908 91 (Reapproved 2017)Standard Practice forMeasuring Volatile Organic Matter in Water by Aqueous-Injection Gas Chromatography1This standard is issued under the fixed designation D2908; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、 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 general guidance applicable tocertain test methods for the qualita
3、tive and quantitative deter-mination of specific organic compounds, or classes ofcompounds, in water by direct aqueous injection gas chroma-tography (1, 2, 3, 4).21.2 Volatile organic compounds at aqueous concentrationsgreater than about 1 mg/L can generally be determined bydirect aqueous injection
4、gas chromatography.1.3 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-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limit
5、ations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization
6、TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D1129 Terminology Relating to WaterD1192 Guide for Equipment for Sampling Water and Steamin Closed Conduits (Withdrawn 2003)4D1193 Specification for Reagent WaterD3370 Practices for Sampling Water from Closed Condu
7、itsE260 Practice for Packed Column Gas ChromatographyE355 Practice for Gas Chromatography Terms and Relation-ships3. Terminology3.1 DefinitionsThe following terms in this standard aredefined in accordance with Terminology D1129. For defini-tions of other chromatographic terms used in this standard,r
8、efer to Practice E355.3.1.1 “ghosting” or memory peaks, nan interference,showing as a peak, which appears at the same elution time asthe organic component of previous analysis.3.1.2 internal standard, na material present in or added tosamples in known amount to serve as a reference measurement.3.1.3
9、 noise, nan extraneous electronic signal which affectsbaseline stability.3.1.4 relative retention ratio, nthe retention time of theunknown component divided by the retention time of theinternal standard.3.1.5 retention time, nthe time that elapses from theintroduction of the sample until the peak ma
10、ximum is reached.4. Summary of Practice4.1 This practice defines the applicability of various col-umns and conditions for the separation of naturally occurringor synthetic organics or both, in an aqueous medium forsubsequent detection with a flame ionization detector. Aftervaporization, the aqueous
11、sample is carried through the columnby an inert carrier gas. The sample components are partitionedbetween the carrier gas and a stationary liquid phase on an inertsolid support. The column effluent is burned in an air-hydrogenflame. The ions released from combustion of the organiccomponents induce a
12、n increase in standing current which ismeasured. Although this method is written for hydrogen flamedetection, the basic technology is applicable to other detectorsif water does not interfere.4.2 The elution times are characteristic of the variousorganic components present in the sample, while the pe
13、ak areasare proportional to the quantities of the components. A discus-sion of gas chromatography is presented in Practice E260.1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.06 on Methods for Analysis forOrganic Substances
14、 in Water.Current edition approved Dec. 15, 2017. Published December 2017. Originallyapproved in 1970. Last previous edition approved in 2011 as D2908 91 (2011).DOI: 10.1520/D2908-91R17.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced AS
15、TM 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 standards Document Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm
16、.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box 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
17、International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15. Significance and Use5.1 This practice is useful in identifying the major organicconstituents in wastewater for support of effective in-plant orpollution control
18、programs. Currently, the most practical meansfor tentatively identifying and measuring a range of volatileorganic compounds is gas-liquid chromatography. Positiveidentification requires supplemental testing (for example, mul-tiple columns, speciality detectors, spectroscopy, or a combi-nation of the
19、se techniques).6. Interferences6.1 Particulate MatterParticulate or suspended mattershould be removed by centrifugation or membrane filtration ifcomponents of interest are not altered. This pretreatment willprevent both plugging of syringes and formation of condensa-tion nuclei. Acidification will o
20、ften facilitate the dissolving ofparticulate matter, but the operator must determine that pHadjustment does not alter the components to be determined.6.2 Identical Retention TimesWith any given column andoperating conditions, one or more components may elute atidentical retention times. Thus a chrom
21、atographic peak is onlypresumptive evidence of a single component. Confirmationrequires analyses with other columns with varying physical andchemical properties, or spectrometric confirmation of theisolated peak, or both.6.3 AcidificationDetection of certain groups of compo-nents will be enhanced if
22、 the sample is made neutral or slightlyacidic. This may minimize the formation of nonvolatile salts incases such as the analysis of volatile organic acids and basesand certain chlorophenols.6.4 GhostingGhosting is evidenced by an interferencepeak that occurs at the same time as that for a component
23、froma previous analysis but usually with less intensity. Ghostingoccurs because of organic holdup in the injection port. Re-peated Type I water washing with 5-L injections betweensample runs will usually eliminate ghosting problems. Thebaseline is checked at maximum sensitivity to assure that theint
24、erference has been eliminated. In addition to waterinjections, increasing the injection port temperature for aperiod of time will often facilitate the elimination of ghostingproblems.6.4.1 Delayed ElutionHighly polar or high boiling com-ponents may unpredictably elute several chromatograms laterand
25、therefore act as an interference. This is particularly truewith complex industrial waste samples. A combination ofrepeated water injections and elevated column temperature willeliminate this problem. Back flush valves should be used if thisproblem is encountered often.7. Apparatus7.1 Gas System:7.1.
26、1 Gas RegulatorsHigh-quality pressure regulatorsshould be used to ensure a steady flow of gas to the instrument.If temperature programming is used, differential flow control-lers should be installed in the carrier gas line to prevent adecrease in flow as the pressure drop across the columnincreases
27、due to the increasing temperature. An unsteady flowwill create an unstable baseline.7.1.2 Gas Transport TubingNew tubing should be washedwith a detergent solution, rinsed with Type I cold water, andsolvent rinsed to remove residual organic preservatives orlubricants. Ethanol is an effective solvent.
28、 The tubing is thendried by flushing with nitrogen. Drying can be accelerated byinstalling the tubing in a gas chromatograph (GC) oven andflowing nitrogen or other inert gas through it, while heating theoven to 50C.7.1.3 Gas LeaksThe gas system should be pressurechecked daily for leaks.To check for
29、leaks, shut off the detectorand pressurize the gas system to approximately 103 kPa (15psi) above the normal operating pressure. Then shut off thetank valve and observe the level of the pressure gauge. If thepreset pressure holds for 10 min, the system can be consideredleak-free. If the pressure drop
30、s, a leak is indicated and shouldbe located and eliminated before proceeding further. A soapsolution may be used for determining the source of leaks, butcare must be exercised to avoid getting the solution inside thetubing or instrument since it will cause a long lasting, serioussource of interferen
31、ce. Leaks may also occur between theinstrument gas inlet valve and flame tip. This may be checkedby removing the flame tip, replacing it with a closed fitting andrechecking for pressure stability as previously noted.7.1.4 Gas FlowThe gas flow can be determined with abubble flow meter. A micro-rotame
32、ter in the gas inlet line isalso helpful. It should be recalibrated after each readjustmentof the gas operating pressure.7.2 Injection PortThe injection port usually is insulatedfrom the chromatographic oven and equipped with a separateheater that will maintain a constant temperature. The tempera-tu
33、re of the injection port should be adjusted to approximately50C above the highest boiling sample component. This willhelp minimize the elution time, as well as reduce peak tailing.Should thermal decomposition of components be a problem,the injection port temperature should be reduced appropriately.C
34、leanliness of the injection port in some cases can be main-tained at a tolerable level by periodically raising the tempera-ture 25C above the normal operating level. Use of disposableglass inserts or periodic cleaning with chromic acid can bepracticed with some designs. When using samples larger tha
35、n5 L, blowback into the carrier gas supply should be preventedthrough use of a preheated capillary or other special design.When using 3.175-mm (0.125-in.) columns, samples largerthan 5 L may extinguish the flame depending on columnlength, carrier gas flow, and injection temperature.7.2.1 SeptumOrgan
36、ics eluting from the septum in theinjection port have been found to be a source of an unsteadybaseline when operating at high sensitivity. Septa should bepreconditioned. Insertion of a new septum in the injection portat the end of the day for heating overnight will usuallyeliminate these residuals.
37、A separate oven operating at atemperature similar to that of the injection port can also be usedto process the septa. The septa should be changed at least oncea day to minimize gas leaks and sample blowback. Septa withTFE-fluorocarbon backings minimize organic bleeding and canbe used safely for long
38、er periods.D2908 91 (2017)27.2.2 On-Column InjectionWhile injection into the heatedchamber for flash vaporization is the most common injectionset-up, some analyses (for example, organic acids) are betterperformed with on-column injection to reduce ghosting andpeak tailing and to prevent decompositio
39、n of thermally degrad-able compounds. This capability should be built into theinjection system. When using on-column injection a shortercolumn life may occur due to solid build up in the injection endof the column.7.3 Column OvenThe column ovens usually are insulatedseparately from the injection por
40、t and the detector. The ovenshould be equipped with a proportional heater and a squirrel-cage blower to assure maximum temperature reproducibilityand uniformity throughout the oven. Reproducibility of oventemperature should be within 0.5C.7.3.1 Temperature ProgrammingTemperature program-ming is desi
41、rable when the analysis involves the resolution oforganics with widely varying boiling points. The column ovenshould be equipped with temperature programming be-tween 15 and 350C (or range of the method) with selectabil-ity of several programming rates between 1 and 20/minprovided. The actual column
42、 temperature will lag somewhatbehind the oven temperature at the faster programming rates.Baseline drift will often occur because of increased highertemperatures experienced during temperature programming.This depends on the stability of the substrate and operatingtemperature range. Temperatures tha
43、t approach the maximumlimit of the liquid phase limit the operating range. Utilizationof dual matching columns and a differential electrometer canminimize the effect of drift; however, the drift is reproducibleand does not interfere with the analysis in most cases.7.4 DetectorThe combination of high
44、 sensitivity and awide linear range makes the flame ionization detector (FID) theusual choice in trace aqueous analysis. The flame ionizationdetector is relatively insensitive to water vapor and to moderatetemperature changes if other operating parameters remainunchanged. If temperature programming
45、is used, the detectorshould be isolated from the oven and heated separately toensure uniform detector temperature. The detector temperatureshould be set near the upper limit of the programmed tempera-ture to prevent condensation. The detector should also beshielded from air currents which could affe
46、ct the burningcharacteristics of the flame. Sporadic spiking in the baselineindicates detector contamination; cleaning, preferably withdiluted hydrochloric acid (HCl, 5 + 95), and an ultrasonic washwith water is necessary. Chromic acid also can be used ifextreme care is taken to keep exposure times
47、short and iffollowed by thorough rinsing. Baseline noise may also becaused by dirty or corroded electrical contacts at switches dueto high impedance feedback.7.5 RecorderA strip-chart recorder is recommended toobtain a permanent chromatogram. Chart speeds should beadjustable between 15 and 90 in./h.
48、7.6 Power SupplyA 105- to 125-V, a-c source of 60-Hzfrequency supplying 20-A service is required as a main powersupply for most gas chromatographic systems. If voltagefluctuations affect baseline stability, a voltage regulating trans-former may be required in addition to the one incorporatedwithin t
49、he chromatographic instrument.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all instances for gas purification, sample stabilization,and other applications. Unless otherwise indicated, it is in-tended that all reagents shall conform to the specifications ofthe Committee onAnalytical Reagents of theAmerican Chemi-cal Society, where such specifications are available.5Othergrades may be used, provided it is first ascertained that thereagent is of sufficiently high purity to permit its use withoutlessening the ac
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1