1、Designation: D7576 10Standard Test Method forDetermination of Benzene and Total Aromatics in DenaturedFuel Ethanol by Gas Chromatography1This standard is issued under the fixed designation D7576; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、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 benzeneand total aromatics in finished denatured
3、 fuel ethanol by gaschromatography.1.2 Total aromatics are determined by adding the concen-trations of benzene, toluene, ethylbenzene, o-xylene, m-xylene,p-xylene, and C9and heavier aromatics.1.3 The aromatic hydrocarbons are separated without inter-ferences from other hydrocarbons in denatured fuel
4、 ethanol.Nonaromatic hydrocarbons having boiling point greater thanthat of n-dodecane can cause interferences with the determi-nation of the C9and heavier aromatics. For the C8aromatics,p-xylene and m-xylene co-elute while ethylbenzene ando-xylene are separated. The C9and heavier aromatics aredeterm
5、ined as a single group.1.4 This test method covers the following concentrationranges: benzene, 0.01 to 0.06 vol% and total aromatics, 0.25 to2.10 vol%.1.5 Results are reported to the nearest 0.01 % by mass orliquid volume.1.6 The values stated in SI units are to be regarded asstandard. The values gi
6、ven in parentheses are provided forinformation only; they may not be exact equivalents.1.7 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 and health practices
7、and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1298 Test Method for Density, Relative Density (SpecificGravity), or API Gravity of Crude Petroleum and LiquidPetroleum Products by Hydrometer MethodD4052 Test Method for Density, Rela
8、tive Density, and APIGravity of Liquids by Digital Density MeterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4307 Practice for Preparation of Liquid Blends for Use asAnalytical StandardsD5580 Test Method for Determination of Benzene, Tolu-ene, Ethylbenzene, p/m-Xylene, o-Xyl
9、ene, C9and HeavierAromatics, and Total Aromatics in Finished Gasoline byGas ChromatographyE355 Practice for Gas Chromatography Terms and Rela-tionships3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 1,2,3-tris-2-cyanoethoxypropane (TCEP)polar gaschromatographic liquid phase.3.
10、1.2 aromatic, nany organic compound containing abenzene ring.3.1.3 low-volume connector, nspecial union for connect-ing two lengths of narrow bore tubing 1.6-mm (0.06-in.)outside diameter and smaller; sometimes this is referred to aszero dead volume union.3.1.4 narrow bore tubingtubing used to trans
11、fer compo-nents prior to or after separation; usually 0.5-mm (0.02-in.)inside diameter and smaller.3.1.5 split ratioin capillary gas chromatography, the ratioof the total flow of carrier gas to the sample inlet versus theflow of the carrier gas to the capillary column, expressed by:split ratio 5 S 1
12、 C!/C (1)where:S = flow rate at the splitter vent, andC = flow rate at the column outlet.3.1.6 wall-coated open tubular (WCOT)type of capillarycolumn prepared by coating the inside wall of the capillarywith a thin film of stationary phase.4. Summary of Test Method4.1 A two-column chromatographic sys
13、tem equipped with acolumn switching valve and a flame ionization detector is used.A reproducible volume of sample containing an appropriate1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.04.0L o
14、n Gas Chromatography Methods.Current edition approved March 1, 2010. Published April 2010. DOI: 10.1520/D757610.2For 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
15、standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.internal standard, such as 2-hexanone, is injected onto aprecolumn containing a polar liquid phase (TCEP). The C9andlighter nonaromati
16、cs are vented to the atmosphere as they elutefrom the precolumn. A thermal conductivity detector may beused to monitor this separation. The TCEP precolumn isbackflushed immediately before the elution of benzene, and theremaining portion of the sample is directed onto a secondcolumn containing a nonp
17、olar liquid phase (WCOT). Benzene,toluene, and the internal standard elute in the order of theirboiling points and are detected by a flame ionization detector.Immediately after the elution of the internal standard, the flowthrough the nonpolar WCOT column is reversed to backflushthe remainder of the
18、 sample (C8and heavier aromatics plus C10and heavier nonaromatics) from the column to the flameionization detector.4.2 The analysis is repeated a second time allowing the C12and lighter nonaromatics, benzene and toluene to elute fromthe polar TCEP precolumn to vent. A thermal conductivitydetector ma
19、y be used to monitor this separation. The TCEPprecolumn is backflushed immediately prior to the elution ofethylbenzene and the remaining aromatic portion is directedinto the WCOT column. The internal standard and C8aromaticcomponents elute in the order of their boiling points and aredetected by a fl
20、ame ionization detector. Immediately aftero-xylene has eluted, the flow through the nonpolar WCOTcolumn is reversed to backflush the C9and heavier aromatics tothe flame ionization detector.4.3 From the first analysis, the peak areas of benzene,toluene, and the internal standard (2-hexanone) are meas
21、uredand recorded. Peak areas for ethylbenzene, p/m-xylene,o-xylene, the C9and heavier aromatics, and internal standardare measured and recorded from the second analysis. Thebackflush peak eluting from the WCOT column in the secondanalysis contains only C9and heavier aromatics.4.4 The flame ionizatio
22、n detector response, proportional tothe concentration of each component, is used to calculate theamount of aromatics that are present with reference to theinternal standard.5. Significance and Use5.1 Regulations in some jurisdictions, such as California,limit the concentration of benzene and total a
23、romatic content ofdenatured fuel ethanol in order to reduce the ozone reactivityand toxicity of automotive evaporative and exhaust emissions.Results from this test method may be used to assess productquality and to meet new fuel regulations.6. Apparatus6.1 Chromatographic SystemSee Practice E355 for
24、 spe-cific designations and definitions. Refer to Fig. 1 for a diagramof the system.6.1.1 Gas Chromatograph (GC)Capable of operating atthe conditions given in Table 1, and having a column switchingand backflushing system equivalent to Fig. 1. Carrier gaspressure and flow control devices shall be cap
25、able of precisecontrol when column head pressures and flow rates are low.6.1.2 Sample Introduction SystemCapable of introducinga representative sample into the gas chromatographic inlet.Microliter syringes and automatic syringe injectors have beenused successfully.6.1.3 Inlet System (Splitting Type)
26、Split injection is neces-sary to maintain the actual chromatographed sample sizewithin the limits required for optimum column efficiency anddetector linearity.6.1.3.1 Some gas chromatographs are equipped with on-column injectors and autosamplers which can inject submi-crolitre sample sizes. Such sys
27、tems can be used provided thatcolumn efficiency and detector linearity are comparable tosystems with split injection.6.1.4 DetectorA flame ionization detector (Detector A) isemployed for quantitation of components eluting from theWCOT column. The flame ionization detector used for Detec-torAshall ha
28、ve sufficient sensitivity and stability to detect 0.01volume % of an aromatic compound.6.1.4.1 It is strongly recommended that a thermal conduc-tivity detector be placed on the vent of the TCEP precolumn(Detector B). This facilitates the determination of valveBACKFLUSH and RESET times (10.5) and is
29、useful formonitoring the separation of the polar TCEP precolumn.6.1.5 Switching and Backflushing ValveTo be locatedwithin a temperature-controlled heated zone and capable ofperforming the functions in accordance with Section 10, andillustrated in Fig. 1. The valve shall be of low internal volumeFIG.
30、 1 Valve Diagram, Aromatics in Denatured Fuel EthanolD7576 102design and not contribute significantly to deterioration ofchromatographic resolution.6.1.5.1 A 10-port valve with 1.6-mm (0.06 in.) outsidediameter fittings is recommended for this test method. Alter-nately, and if using columns of 0.32-
31、mm inside diameter orsmaller, a valve with 0.8-mm (0.03-in.) outside diameterfittings should be used.6.1.5.2 Some gas chromatographs are equipped with anauxiliary oven which can be used to contain the valve. In sucha configuration, the valve can be kept at a higher temperaturethan the polar and nonp
32、olar columns to prevent samplecondensation and peak broadening. The columns are thenlocated in the main oven and the temperature can be adjustedfor optimum aromatic resolution.6.2 Data Acquisition System:6.2.1 Integrator or ComputerCapable of providing real-time graphic and digital presentation of t
33、he chromatographicdata is recommended for use. Peak areas and retention timescan be measured by computer or electronic integration.6.2.1.1 It is recommended that this device be capable ofperforming multilevel internal-standard-type calibrations andbe able to calculate the correlation coefficient (r2
34、) and linearleast square fit equation for each calibration data set inaccordance with 11.4.6.3 Two Chromatographic Columns:6.3.1 Polar PrecolumnTo perform a pre-separation of thearomatics from nonaromatic hydrocarbons in the same boilingpoint range. Any column with equivalent or better chromato-grap
35、hic efficiency and selectivity in accordance with 6.3.1.1can be used.6.3.1.1 TCEP Micro-Packed Column560-mm (22-in.) by1.6-mm (116-in.) outside diameter by 0.76-mm (0.030-in.)inside diameter stainless steel tube packed with 0.14 to 0.15 gof 20 % (mass/mass) TCEP on 80/100 mesh ChromosorbP(AW). This
36、column was used in the cooperative study toprovide the precision and bias data referred to in Section 16.6.3.2 Nonpolar (Analytical) ColumnAny column withequivalent or better chromatographic efficiency and selectivityin accordance with 6.3.2.1 can be used.6.3.2.1 WCOT Methyl Silicone Column30 m long
37、 by0.53-mm inside diameter fused silica WCOT column with a5.0-m film thickness of cross-linked methyl siloxane.6.4 Compatibility with D5580An instrument configuredto run Test Method D5580 can be used for this test method withno modification of hardware or columns.7. Reagents and Materials7.1 Carrier
38、 GasAppropriate to the type of detector used.Helium has been used successfully. The minimum purity of thecarrier gas used must be 99.95 mol %. Additional purificationmay be necessary to remove trace amounts of oxygen.(WarningHelium is usually supplied as a compressed gasunder high pressure.)7.2 Meth
39、ylene ChlorideUsed for column preparation. Re-agent grade, free of nonvolatile residue. (WarningHarmfulwhen ingested or inhaled at high concentrations.)7.3 2,2,4-Trimethylpentane (Isooctane)Used as a solventin the preparation of the calibration mixture. Reagent grade.(WarningIsooctane is flammable a
40、nd can be harmful or fatalwhen ingested or inhaled.)7.4 Standards for Calibration and IdentificationRequiredfor all components to be analyzed and the internal standard.Standards are used for establishing identification by retentiontime as well as calibration for quantitative measurements.These mater
41、ials shall be of known purity and free of the othercomponents to be analyzed. (WarningThese materials areflammable and may be harmful or fatal when ingested orinhaled.)8. Preparation of Columns8.1 TCEP Column Packing:8.1.1 Use any satisfactory method that will produce acolumn capable of retaining ar
42、omatics from nonaromaticcomponents of the same boiling point range in a denatured fuelethanol sample. The following procedure has been used suc-cessfully.TABLE 1 Typical Chromatographic Operating Parameters 130TemperaturesInjection port (split injector) 200CFID (Detector A) 250CTCD (Detector B) 200C
43、Nonpolar WCOT capillaryInitial 60C (6 min)Program rate 2C/minFinal 115C (hold until all components elute)Polar TCEP precolumn (temperature to remain constant before timeto BACKFLUSH, T1 or T2. Do not exceed maximum operatingtemperature.)60C or same as nonpolar WCOT capillary if TCEP/WCOT columnscont
44、ained in identical heated zone.Valve 115C or same as nonpolar WCOT capillary if valve and WCOTcolumn contained in identical heated zone.Flows and ConditionsCarrier gas heliumFlow to TCEP precolumn (split injector) 10 mL/minFlow to WCOT capillary (auxiliary flow) 10 mL/minFlow from split vent 100 mL/
45、minDetector gases as necessarySplit ratio 11:1Sample size 1 LD7576 1038.1.2 Completely dissolve 10 g of TCEP in 100 mL ofmethylene chloride. Next add 40 g of 80/100 mesh Chro-mosorb P(AW) to the TCEP solution. Quickly transfer thismixture to a drying dish, in a fume hood, without scraping anyof the
46、residual packing from the sides of the container.Constantly, but gently, stir the packing until all of the solventhas evaporated. This column packing can be used immediatelyto prepare the TCEP column.8.2 Micro-packed TCEP Column:8.2.1 Wash a straight 560-mm (22-in.) length of 1.6-mm(116-in.) outside
47、 diameter, 0.76-mm (0.030-in.) inside diameterstainless steel tubing with methanol and dry with compressednitrogen.8.2.2 Insert 6 to 12 strands of silvered wire, a small meshscreen or stainless steel frit inside one end of the tube. Slowlyadd 0.14 to 0.15 g of packing material to the column and gent
48、lyvibrate to settle the packing inside the column. Insert silveredwire, mesh screen, or frit to the other end of the tube to preventthe packing material from falling. When strands of wire areused to retain the packing material inside the column, leave 6.0mm (0.25 in.) of space at the top of the colu
49、mn.8.3 WCOT Methyl Silicone ColumnIt is suggested thatthis column be purchased directly from a suitable capillarycolumn manufacturer (see 6.3.2.1).9. Sampling9.1 Ensure that the sample is representative of the sourcefrom which it is taken. Follow the recommendations ofPractice D4057, or its equivalent, when obtaining samplesfrom bulk storage or pipelines.9.2 Take appropriate steps to minimize the loss of lighthydrocarbons from the denatured fuel ethanol sample to beanalyzed. Upon receipt in the laboratory, chill the sample in itsoriginal cont
