1、Designation: D 4046 91 (Reapproved 2005)An American National StandardStandard Test Method forAlkyl Nitrate in Diesel Fuels by Spectrophotometry1This standard is issued under the fixed designation D 4046; the number immediately following the designation indicates the year oforiginal adoption or, in t
2、he 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 a procedure for the determina-tion of 0.03 to 0.30 volume %
3、of alkyl nitrate in diesel fuels.1.2 This test method can be used for the determination ofany alkyl nitrate in diesel fuel provided that standards used forcalibration contain the same alkyl nitrate ester as the testspecimens to be analyzed.1.3 The values stated in SI units are to be regarded as thes
4、tandard.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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For sp
5、ecific hazardstatements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent Water3. Summary of Test Method3.1 The determination is based on the simultaneous hy-drolysis of the ester in 65 % sulfuric acid solution and nitrationof m-xylenol by the nitric acid lib
6、erated. The nitroxylenol isextracted from the reaction mixture and reacted with sodiumhydroxide to form the yellow salt. The color is measuredspectrophotometrically at 452 nm, and the concentration ofalkyl nitrate is determined by reference to the slope of thecalibration curve.4. Significance and Us
7、e4.1 This test method can be used to determine the amount ofalkyl nitrate that has been added to diesel fuel to improveCetane Number. The test method is applicable as a basis forjudging compliance with specifications covering any alkylnitrate.5. Interferences5.1 Other nitrate esters, inorganic nitra
8、te ions, and nitrogenoxides will interfere.6. Apparatus6.1 Absorption Cells, matched, having a 1.000 6 0.002-cmpath length.6.2 Separatory Funnel, Squibb-type glass stoppered withTFE-fluorocarbon stopcock, 125-mL capacity.6.3 Shaking Machine, automatic, capable of multiplesamples and 250 oscillations
9、/min.6.4 Spectrophotometer, capable of measuring absorption inthe region of 452 6 5 nm.6.5 Volumetric Flask, 10- and 100-mL capacity.6.6 Measuring Pipet, 1-mL, 3-mL, 4-mL, and 10-mL.6.7 Buret, 10-mL capacity.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless o
10、therwise indicated, it is intended thatall reagents conform to the specifications of the committee onAnalytical Reagents of the American Chemical Society, wheresuch specifications are available.3Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity
11、to permit its use without lessening the accuracy ofthe determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Type II of Specification D 1193.7.3 Acetic Acid, reagent grade.7.4 Alkyl Nitrate.7.5 Alkyl Nitrate, Standard S
12、olutionPipet 3.0 mL of thealkyl nitrate to be determined into a 100-mL volumetric flaskand dilute to volume with diesel fuel.7.6 Diesel Fuel, additive-free (WarningFlammable.).7.7 Isooctane (2,2,4-trimethylpentane). (WarningFlammable.).1This test method is under the jurisdiction of ASTM Committee D0
13、2 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 1981. Last previous edition approved in 2000 as D 4046 91 (2000)e1.2For referenced ASTM standards, visit
14、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.3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington,
15、 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 States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.1Copyright ASTM
16、International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.8 Isopropyl Alcohol, reagent grade. (WarningFlammable.).7.9 m-Xylenol SolutionsDilute 4 mL of m-xylenol (2,4-dimethylphenol) to 100 mL in acetic acid.7.10 Sodium Hydroxide SolutionDissolve 50 g of so
17、diumhydroxide (NaOH) pellets in 1000 mL of distilled water.7.11 Sulfuric AcidAdd slowly with stirring, 500 mL ofnitrate-free sulfuric acid (H2SO4) (rel dens 1.84) to 269 mL ofcold distilled water.8. Calibration and Standardization8.1 Carefully measure 1.0, 3.0, 5.0, 8.0, and 10 mL of alkylnitrate st
18、andard solution ( see 7.5) from a buret into each of fiveseparate 100-mL volumetric flasks and dilute to the mark withdiesel fuel.8.2 Measure 1.0-mL portions of each standard into each offive 10-mL volumetric flasks. To another 10-mL flask add 1.0mL of blank diesel fuel. Dilute all flasks to volume
19、withisopropyl alcohol.8.3 Pipet 1.0 mL of each standard solution (see 8.2) intoeach of five separate 125-mL separatory funnels. To anotherfunnel add 1.0 mL of the blank solution. This covers concen-trations from 0.03 to 0.30 volume % alkyl nitrate.8.4 Add 1.0 mL of m-xylenol solution (see 7.9) to ea
20、chseparatory funnel and swirl to mix thoroughly.8.5 Add 40 mL of H2SO4(see 7.11). The m-xylenol must beadded before the sulfuric acid. Otherwise low or negativeresults will be obtained.8.6 Secure the stopper with springs or rubber bands andshake the separatory funnel and its content for 30 min on th
21、eautomatic shaking machine set at fast speed.NOTE 1The amount of contact the sample has with the H2SO4determines the extent of hydrolysis. Therefore, the speed and time ofshaking should be the same for both the samples and the calibrationstandards.8.7 To each separatory funnel add 25 mL of isooctane
22、.8.8 Shake the separatory funnel for 1 min by hand. Allowthe layers to separate and discard the acid (bottom) layer. Add25 mL of distilled water and again shake for 1 min to wash outresidual acid. Discard the water (bottom) layer.8.9 Pipet 10.0 mL of NaOH solution into the separatoryfunnel, shake fo
23、r 1 min and allow the phases to separate for atleast 10 min or when phases separate cleanly (see Note 2).Drain a few drops of the lower phase to rinse the stem anddiscard. Fill a 1-cm absorption cell and read the absorbance at452 6 5 nm with respect to water.NOTE 2If no color forms, check the pH. Wh
24、en the solution is notalkaline, add an additional 10.0 mL of NaOH solution and correctcalculations for the increased solution volume.8.10 Subtract the absorbance of the blank from that of eachstandard to obtain corrected absorbance values. Calculate theslope of the curve as follows:Slope, C 5 A/B (1
25、)where:A = sum of the volume percent alkyl nitrate standards andB = sum of corrected absorbances.9. Procedure9.1 Pipet 1.0 mL of test specimen into a 10-mL volumetricflask and dilute to volume with isopropyl alcohol.9.2 Pipet 1.0 mLof the sample test specimen prepared in 9.1into a 125-mL separatory
26、funnel. To another funnel add 1.0 mLof blank isopropyl alcohol.NOTE 3A more accurate blank would be obtained if the same basestock as the samples diluted with isopropyl alcohol, were used.9.3 Follow steps outlined in 8.4-8.9.NOTE 4If an absorbance is too high, dilute an aliquot of the solutionfive-f
27、old with blank solution and correct calculations accordingly.9.4 Subtract the absorbance of the blank from the absor-bance of the samples and calculate the result using the slope ofthe calibration curve.Alkyl nitrate, volume % 5 CD(2)where:C = slope of the calibration curve andD = absorbance of the
28、sample.10. Precision and Bias410.1 The precision of this test method as obtained bystatistical examination of interlaboratory test results is asfollows:10.1.1 RepeatabilityThe difference between successivetest results, obtained by the same operator with the sameapparatus under constant operating con
29、ditions on identical testmaterial, would in the long run, in the normal and correctoperation of this test method, exceed the following values onlyin one case in twenty:0.017 vol %10.1.2 ReproducibilityThe difference between two singleand independent results, obtained by different operators work-ing
30、in different laboratories on identical test material, would inthe long run, in the normal and correct operation of this testmethod, exceed the following values only in one case intwenty:0.036 vol %10.2 BiasThe bias of this test method cannot be deter-mined since an appropriate standard reference mat
31、erial con-taining a known level of alkyl nitrate in diesel fuel is notavailable.11. Keywords11.1 alkyl nitrate; diesel fuel; nitroxylanol;spectrophotometry4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: :D02-1139.D 4046 91 (200
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33、are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional stan
34、dardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Comm
35、ittee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 4046 91 (2005)3
