1、Designation: D7011 10Standard Test Method forDetermination of Trace Thiophene in Refined Benzene byGas Chromatography and Sulfur Selective Detection1This standard is issued under the fixed designation D7011; 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 test method covers the determination of thiophenein refined benzene using ga
3、s chromatography and sulfurselective detection. The test method is applicable to thedetermination of thiophene at levels of 0.02 to 2.18 mgthiophene per kg in benzene (mg/kg) on the AED, 0.03 to 1.87mg/kg on the PFPD, and 0.03 to 2.11 mg/kg on the SCD. Therange of the test method may be extended by
4、modifying thesample injection volume, split ratios, calibration range, orsample dilution with thiophene-free solvent.1.2 In determining the conformance of the test results usingthis method to applicable specifications, results shall berounded off in accordance with the rounding-off method ofPractice
5、 E29.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 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 establis
6、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1685 Test Method for Traces of Thiophene in Benzene bySpec
7、trophotometry3D2359 Specification for Refined Benzene-535D3437 Practice for Sampling and Handling Liquid CyclicProductsD4734 Specification for Refined Benzene-545D4735 Test Method for Determination of Trace Thiophenein Refined Benzene by Gas ChromatographyD5871 Specification for Benzene for Cyclohex
8、ane Feed-stockD6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and Related Ma-terialsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE69
9、1 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1510 Practice for Installing Fused Silica Open TubularCapillary Columns in Gas Chromatographs2.2 Other Document:OSHA Regulations, 29 CFR paragraphs 1910.1000 and1910.120043. Summary of Test Method3.1 The th
10、iophene concentration in refined benzene is de-termined at the sub-mg/kg to low mg/kg level using conven-tional gas chromatography with a sulfur selective detector. Areproducible volume of sample is injected. Quantitative resultsare obtained by the use of the external standard calibrationtechnique.3
11、.2 The method allows the use of a sulfur chemilumines-cence detector, atomic emission detector, pulsed flame photo-metric detector, or any other sulfur selective detector providedthat its performance meets requirements as set forth in 5.4.Assulfur compounds elute from the gas chromatographic column,
12、they are detected and quantified. While the benzene moleculedoes not contain any sulfur atoms, the possibility of matrixquenching and interference is a concern, especially forthiophene determination at levels less than about 0.5 mg/kg.The column and conditions specified in Table 1 yield accept-able
13、results with minimal matrix quenching and interference.Employing the column and conditions listed in Table 1 is not a1This test method is under the jurisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.04 on Instrumental
14、Analysis.Current edition approved June 1, 2010. Published June 2010. Originallyapproved in 2004. Last previous edition approved in 2004 as D7011 - 04. DOI:10.1520/D7011-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For An
15、nual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.4Available from U.S. Government Printing Office Superintendent of Documents,732 N. Capitol St.
16、, NW, Mail Stop: SDE, Washington, DC 20401, http:/www.access.gpo.gov.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.requirement to meet the needs of all users. For example, thereis less concern of quenching and interference encounte
17、red withthiophene concentration levels greater than 0.5 mg/kg. Users offlame photometric detectors should refer to Test MethodD4735.4. Significance and Use4.1 Accurate gas chromatographic determination of tracelevels of thiophene in benzene involves special analyticalproblems because of the difficul
18、ties of trace level analysis.These problems arise from the low concentration levels thatneed to be measured, the type of column and detector neededfor analysis, and the potential interference from the benzenematrix.4.2 This test method was found applicable for determiningthiophene in refined benzene
19、 conforming to the specificationsdescribed in Specifications D2359, D4734, and D5871 andmay be applicable toward other grades of benzene if the userhas taken the necessary precautions as described in the text.4.3 This test method was developed as an alternative tech-nique to Test Methods D1685 and D
20、4735.5. Apparatus5.1 Gas ChromatographThe gas chromatograph shall becapable of producing retention times for thiophene repeatableto within 0.05 min. The gas chromatograph shall be equippedwith an appropriate sulfur selective detector, column forseparation, and sample inlet system for repeatable inje
21、ction ofsample volume.5.2 ColumnSpecifications and conditions described inTable 1 have been judged satisfactory for this analysis. The useof any column that permits separation and determination ofthiophene in benzene at levels consistent with the scope of thismethod is allowed. Specific chromatograp
22、hic results and con-ditions are illustrated in Fig. 1. The user is referred to PracticeE1510 for information on installation of fused silica capillarycolumns.5.3 Sample Inlet SystemThe sample inlet system shall beable to quantitatively transfer the sample to the analyticalcolumn. It shall be capable
23、 of introducing constant andrepeatable volumes of sample and calibration standards. Use ofa liquid autosampler or liquid sampling valve is permitted forthe analysis of thiophene in benzene.5.4 DetectorA sulfur selective detector is used and shallmeet or exceed the following specifications: (1) linea
24、rity orcompensated linearity of at least 102, (2) minimum detectablelevel of less than 0.02 mg/kg thiophene in benzene, (3)selectivity of sulfur to carbon greater than 105, and (4) absenceof quenching that affect results under the conditions used forthe analysis.5.5 Data Handling SystemUse of an ele
25、ctronic integratingdevice or computer is necessary. The device shall have thefollowing capabilities: (1) graphic presentation of the chro-matogram, (2) digital display of chromatographic peak areas,(3) identification of peaks by retention time, and (4) calculationand use of response factors.5.6 Gase
26、s:5.6.1 Carrier GasesHelium or nitrogen of high purity(99.995+ %). Additional purification is recommended by theuse of molecular sieves or other suitable agents to removewater, oxygen, hydrocarbons, and sulfur contaminants. Gasesshall be regulated to ensure a constant carrier gas flow rate.5.6.2 Det
27、ector GasesHydrogen and air are required asdetector gases (99.995+ % purity). Additionally, oxygen(99.8+ %) may be substituted for air. These gases shall be freeof interfering contaminants, especially sulfur compounds.5.6.3 Carrier and Detector Gas Control Constant flowcontrol of carrier and detecto
28、r gases is critical to optimum andconsistent analytical performance. Control is best provided bythe use of pressure regulators and fixed flow restrictions ormass flow controllers capable of maintaining gas flow constantto 61 % at the required flow rates. The gas flow rate ismeasured by any appropria
29、te means. The supply pressure of thegas delivered to the gas chromatograph shall be at least 70 kPa(10 psig) greater than the regulated gas at the instrument tocompensate for the system back pressure of the flow control-lers. In general, a supply pressure of 550 kPa (80 psig) issatisfactory.5.7 Micr
30、osyringes10, 50, 100, and 250 L capacity(61 % accuracy).5.8 Volumetric Pipettes0.5, 1.0, and 2.0 mL capacity(Class A).5.9 Volumetric Flasks10, 50, 100, and 500 mL capacity(class A).5.10 Separatory Funnel1 L capacity.6. Reagents and Materials6.1 Purity of ReagentsReagent grade chemicals shall beused
31、in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee onAnalytical Reagents of theAmerican Chemical Society,5where such specifications are available. Other grades may beused, provided it is first ascertained that the reagent i
32、s ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean reagent water conformingto Type IV of Specification D1193.6.3 Benzene, Thiophene-free:6.3.1 In a fume hood, w
33、ash 700 mL of benzene in a 1000mL separatory funnel to which has been added 5 mL of isatinsolution, with successive 100 mL portions of concentrated5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlis
34、ted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.TABLE 1 Typical Chromatographic ConditionsColumn 30 m length, 0.32 mm
35、internal diameter, 1 m thick film,cross-linked polyethylene glycol (wax-type)Oven Temperature 40C for 2 min; ramp to 100C at 10C/min, hold at100C for 1 minFlow Rate 2 mL/minSplit Ratio 1:4 to 1:10Injection Temperature 125CInjection Volume 1-2 LD7011 102NOTE 1The shorter retention time obtained with
36、the SCD is primarily due to the column outlet being at sub-ambient pressure.FIG. 1 Chromatograms Illustrating the Analysis of a Sample Containing 0.2 mg/kg Thiophene in Benzene Using AED, PFPD and SCD(Upper, Middle, and Lower Chromatograms, Respectively)D7011 103sulfuric acid until the acid layer is
37、 light yellow to colorless.Wash the benzene with 100 mL of water, then twice with 100mL of cadmium chloride solution (CdCl2). Finally wash withanother 100 mL portion of water and filter the benzene throughmedium filter paper into a storage bottle, stopper the bottletightly and save for future use.6.
38、3.2 Alternatively, thiophene-free benzene can be pur-chased commercially and used within this method, if itsthiophene level meets the criteria within 10.4.6.4 Cadmium Chloride Solution (20 g/L)Dissolve 20 g ofanhydrous cadmium chloride (CdCl2) into 200 mL of waterand dilute to 1 L.6.5 ChloroformReag
39、ent grade or better.6.6 Isatin SolutionAdd 0.5 g of isatin to 200 mL ofchloroform. Heat under a fume hood to a temperature justbelow the boiling point of chloroform (61C) and maintain for5 min with stirring. Filter the hot solution through hardenedrapid-filter paper into a 250 mL volumetric flask an
40、d dilute tovolume with chloroform.6.7 Stock SolutionsCommercially prepared stock solutionof thiophene in benzene are available for use as calibrationstandards or for preparation of calibration standards.6.8 Sulfuric AcidConcentrated H2SO4.6.9 ThiopheneAvailable from commercial sources forpreparation
41、 of calibration standards, minimum 99 % purity.7. Hazards7.1 Benzene is listed as a known carcinogen and is consid-ered a hazardous material. Consult current OSHA regulationsand suppliers Material Safety Data Sheets for all materialsused in this method.7.2 Helium and nitrogen are compressed gases un
42、der highpressure and can cause asphyxiation.7.3 Hydrogen is an extremely flammable gas under highpressure.7.4 Compressed air and oxygen are gases under high pres-sure and they support combustion.7.5 Sulfur compounds are generally flammable, toxic, andproduce noxious odors, and therefore shall be han
43、dled withappropriate precautions for safety.7.6 Isatin is a toxic, cancer causing agent.7.7 Chloroform is flammable, toxic and is a carcinogen.7.8 Cadmium chloride is a highly toxic cancer causingagent.8. Sample Handling8.1 Collect the samples in accordance with Practice D3437.8.2 To preserve sample
44、 integrity and prevent the loss ofvolatile compounds that may be in some samples, collectsamples with a minimal head space and do not uncoversamples any longer than necessary. Some headspace is neces-sary to prevent containers from rupturing if the possibility forthermal expansion exists. Sample con
45、tainers shall be free ofcontaminants that could interfere with the analysis.Analyze thespecimen as soon as possible after transferring it from thesample container to prevent loss of components or contamina-tion.8.3 Since this procedure is intended for trace level contami-nation, care shall be taken
46、to ensure containers used for thesample, the specimen, and the working standard do not alter thesample results.9. Preparation of Apparatus9.1 The chromatographic separation of trace level sulfurcompounds can be complicated by absorption onto active sitesthroughout the chromatographic system. This is
47、 less of aproblem with thiophene, which is very stable relative to mostsulfur compounds. The most likely cause of error in thismethod is presence of thiophene in matrix blanks (see 10.4).9.2 Follow the manufacturers instructions for mounting thecolumn into the gas chromatograph and adjusting the ins
48、tru-ment to typical conditions as described in Table 1. Generalguidelines for the installation of capillary columns can befound in Practice E1510.9.3 The gas chromatograph and detector should be placedinto service in accordance with the manufacturers instructions.10. Calibration10.1 A manual or elec
49、tronic calibration curve shall beprepared for the method of analysis. In some instances, forexample when compliance with a certain specification isdetermined, it is sufficient to use a single point calibrationaccording to user needs.10.2 Prepare a stock solution of thiophene in benzene at the100 mg/kg level by adding 0.1000 g of thiophene to 1000 g ofthiophene-free benzene. Record actual measurements to 4significant figures.10.3 Prepare calibration blends covering the range of deter-mination of thiophene in benzene. For example, use a microsy-ringe
