1、Designation: D 7011 04Standard Test Method forDetermination of Trace Thiophene in Refined Benzene byGas Chromatography and Sulfur Selective Detection1This standard is issued under the fixed designation D 7011; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of thiophenein refined benzene using
3、 gas chromatography and sulfurselective detection. The test method is applicable to thedetermination of thiophene at levels of 0.02 to 2 mg/kgthiophene in benzene.1.2 In determining the conformance of the test results usingthis method to applicable specifications, results shall berounded off in acco
4、rdance with the rounding-off method ofPractice E 29.1.3 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 theresponsi
5、bility 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 hazardstatements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterD 1685 Test
6、 Method for Traces of Thiophene in Benzene bySpectrophotometryD 2359 Specification for Refined Benzene535D 3437 Practice for Sampling and Handling Liquid CyclicProductsD 4734 Specification for Refined Benzene545D 4735 Test Method for Determination of Trace Thiophenein Refined Benzene by Gas Chromato
7、graphyD 5871 Specification for Benzene for Cyclohexane Feed-stockD 6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and Related Ma-terialsE 29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE 1510 Practice for Ins
8、talling Fused Silica Open TubularCapillary Columns in Gas Chromatographs2.2 Other Document:OSHA Regulations, 29 CFR, paragraphs 1910.1000 and1910.120033. Summary of Test Methods3.1 The thiophene concentration in refined benzene is de-termined at the sub-mg/kg to low mg/kg level using conven-tional g
9、as chromatography with a sulfur selective detector. Areproducible volume of sample is injected. Quantitative resultsare obtained by the use of the external standard calibrationtechnique.3.2 The method allows the use of a sulfur chemilumines-cence detector, atomic emission detector, pulsed flame phot
10、o-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,they are detected and quantified. While the benzene moleculedoes not contain any sulfur atoms, the possibility o
11、f 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 results with minimal matrix quenching and interference.Employing the column and conditions listed in Table 1 is
12、not arequirement to meet the needs of all users. For example, thereis less concern of quenching and interference encountered withthiophene concentration levels greater than 0.5 mg/kg. Users offlame photometric detectors should refer to Test MethodD 4735.4. Significance and Use4.1 Accurate gas chroma
13、tographic determination of tracelevels of thiophene in benzene involves special analytical1This 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 Analysis.Current edition ap
14、proved July 1, 2004. Published July 2004.2For 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 standards Document Summary page onthe ASTM website.3Available from U.S.
15、 Government Printing Office Superintendent of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.problems because of the difficulties of trace level analysis.These p
16、roblems 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 conforming to the specificationsdes
17、cribed in Specifications D 2359, D 4734, and D 5871 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 D 1685 and D 4735.5. Apparatus5.1 Gas Chroma
18、tographThe 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 injection ofsample volume.5.2 Colum
19、nSpecifications 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 chromatographic results and con-ditions are
20、 illustrated in Fig. 1. The user is referred to PracticeE 1510 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 of introducing constant andre
21、peatable 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) linearity orcompensated linearity o
22、f 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 electronic integratingdevice or c
23、omputer 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 Gases:5.6.1 Carrier GasesHelium or
24、 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 Detector GasesHydrogen and air ar
25、e 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 detector gases is critical to optimum
26、 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 appropriate means. The supply pressure
27、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 Microsyringes10, 50, 100, and 250
28、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 in all tests. Unless otherwise
29、 indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,4where such specifications are available. Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity
30、 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 D 1193.6.3 Benzene, Thiophene-free:6.3.1 In a fume hood, wash 700 mL of benzene in a
31、1000mL separatory funnel to which has been added 5 mL of isatinsolution, with successive 100 mL portions of concentratedsulfuric acid until the acid layer is light yellow to colorless.Wash the benzene with 100 mL of water, then twice with 100mL of cadmium chloride solution (CdCl2). Finally wash with
32、another 100 mL portion of water and filter the benzene throughmedium filter paper into a storage bottle, stopper the bottletightly and save for future use.6.3.2 Alternatively, thiophene-free benzene can be pur-chased commercially and used within this method, if itsthiophene level meets the criteria
33、within 10.4.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United State
34、s Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.TABLE 1 Typical Chromatographic ConditionsColumn 30 m length, 0.32 mm internal diameter, 1 m thick film,cross-linked polyethylene glycol (wax-type)Oven Temperature 40C for 2 min; ramp to 100C at 10C/min, h
35、old at100C for 1 minFlow Rate 2 mL/minSplit Ratio 1:4 to 1:10Injection Temperature 125CInjection Volume 1-2 LD7011042NOTEThe shorter retention time obtained with the SCD is primarily due to the column outlet being at sub-ambient pressure.FIG. 1 Chromatograms Illustrating the Analysis of a Sample Con
36、taining 0.2 mg/kg Thiophene in Benzene Using AED, PFPD and SCD(Upper, Middle, and Lower Chromatograms, Respectively)D70110436.4 Cadmium Chloride Solution (20 g/L)Dissolve 20 g ofanhydrous cadmium chloride (CdCl2) into 200 mL of waterand dilute to 1 L.6.5 ChloroformReagent grade or better.6.6 Isatin
37、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 and dilute tovolume with chlorofo
38、rm.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 of calibration standards, mini
39、mum 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 under highpressure and can cause
40、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 handled withappropriate precaution
41、s 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 D 3437.8.2 To preserve sample integrity and prevent the los
42、s 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 containers shall be free ofcontam
43、inants 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 to ensure containers used for
44、 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 less of aproblem with thioph
45、ene, 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 instru-ment to typical condition
46、s as described in Table 1. Generalguidelines for the installation of capillary columns can befound in Practice E 1510.9.3 The gas chromatograph and detector should be placedinto service in accordance with the manufacturers instructions.10. Calibration10.1 A manual or electronic calibration curve sha
47、ll 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
48、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 or volumetric pipette to dispense appropriate amounts ofthe stock solutio
49、n into a volumetric flask containing thiophene-free benzene to prepare calibration blends containing nomi-nally 0.02, 0.2, 0.5, 1, and 2 mg/kg thiophene in benzene.10.4 Inject 1-2 L of each solution and benzene blank intothe chromatograph. Integrate the area under the thiophenepeak. Each standard solution and the blank should be analyzedin duplicate. The data collected will be used for generation ofthe calibration curve (see 10.1). The benzene blank shouldcontain less than 0.02 mg/kg thiophene. Higher levels warrantthiophene removal by 6.3.10.5 Quali
