1、Designation: D7318 11D7318 13Standard Test Method forExistent Inorganic Sulfate in Ethanol by PotentiometricTitration1This standard is issued under the fixed designation D7318; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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. Scope*1.1 This test method covers a potentiometric titration procedure for determining the existent inorganic sulfate con
3、tent ofhydrous, anhydrous ethanol, and anhydrous denatured ethanol, which is added as a blending agent with spark ignition fuels. It isintended for the analysis of denatured ethanol samples containing between 1.020 mg/kg existent inorganic sulfate.1.2 The values stated in SI units are to be regarded
4、 as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine
5、 the applicability of regulatorylimitations prior to use. Material Safety Data Sheets are available for reagents and materials. Review them for hazards prior tousage.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4052 Test Method for Density, Relative Density, and A
6、PI Gravity of Liquids by Digital Density MeterD4057 Practice for Manual Sampling of Petroleum and Petroleum ProductsD4177 Practice for Automatic Sampling of Petroleum and Petroleum ProductsD6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytica
7、l Measure-ment System Performance3. Terminology3.1 Definitions:3.1.1 existent inorganic sulfate, ninorganic sulfate species present as sulfuric acid, ionic salts of this acid, or mixtures ofthese.actually present in the sample at the time of analysis with no oxidation treatment.3.1.1.1 DiscussionSpe
8、cifically in this test method, inorganic sulfate is present as sulfate in ethanol.3.1.2 inorganic sulfate, nsulfate (SO4-2) species present as sulfuric acid, ionic salts of this acid, or mixtures of these.4. Summary of Test Method4.1 An ethanol sample containing inorganic sulfate is titrated in etha
9、nolic medium with a standard lead nitrate solution. Leadsulfate precipitate is formed during the titration. Perchloric acid is added to remove possible interference from carbonate. Theendpoint is signaled by an increase in lead ion activity, as measured by a leadselective electrode.1 This test metho
10、d is under the jurisdiction of ASTM Committee D02 on Petroleum Products and Lubricants and is the direct responsibility of Subcommittee D02.03 onElemental Analysis.Current edition approved July 1, 2011June 15, 2013. Published August 2011August 2013. Originally approved in 2007. Last previous edition
11、 approved in 20072011 asD731807.D7318 11. DOI: 10.1520/D7318-07.10.1520/D7318-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page
12、on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that use
13、rs consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consho
14、hocken, PA 19428-2959. United States15. Significance and Use5.1 Ethanol is used as a blending agent added to gasoline. Sulfates are indicated in filter plugging deposits and fuel injectordeposits. When fuel ethanol is burned, sulfates may contribute to sulfuric acid emissions. Ethanol acceptability
15、for use dependson the sulfate content. Sulfate content, as measured by this test method, can be used as one measure of determination of theacceptability of ethanol for automotive spark-ignition engine fuel use.6. Apparatus6.1 Potentiometric Titration AssemblyA titration assembly consisting of an aut
16、omatic titrator fitted with a lead ion-selectiveelectrode, a double-junction reference electrode, buret, and stirring is used. Stirring may be accomplished by means of magneticor propeller type stirrer mechanisms. The buret size should ideally be 10 or 20 mL.6.2 Reference ElectrodeAdouble junction r
17、eference electrode with the inner electrode composed of silver/silver chloride witha potassium chloride solution as internal electrolyte. The external solution is composed of 1 M lithium chloride in ethanol. Thisconfiguration is used to prevent silver ion, a lead electrode poison, from leaching into
18、 the analyte solution during titration. Preferredelectrolytes for use in double junction electrodes may vary with the manufacturer; use the manufacturers recommendedelectrolytes for the application. Other types of reference electrodes may be considered with some caveats (for example, singlejunction,
19、 combination, or glassy carbon), but the data presented in this test method were generated using exclusively a doublejunction electrode, which is the best choice for this determination.6.3 Lead ElectrodeA lead sulfidebased crystalline sensor type lead ion selective electrode (ISE) is used.6.4 Drying
20、 OvenA drying oven for drying sodium sulfate at 110C is required.6.5 Pipets or Volumetric Transferring DevicesClass A glass pipets or their equivalent.6.6 Polishing MaterialLead sulfide based crystalline sensor electrodes require polishing to remove oxidation products. Thesematerials are supplied wi
21、th the electrode from the manufacturer.6.7 pH Test StripsTest strips in the range of pH 1 to pH 7.6.8 Titration VesselsStandard glass beakers or titration vessels supplied with titration equipment.7. Reagents and Materials7.1 Lead NitrateReagent grade, 99% minimum purity. (WarningPoison, harmful by
22、inhalation and if ingested. Avoidcontact with the skin.) Dispose of this material in accordance with accepted local requirements.7.2 Sodium SulfateAnhydrous, reagent grade, 99% minimum purity. (WarningDo not ingest.Avoid unnecessary exposure.)7.3 Perchloric Acid 70%A.C.S. reagent grade, minimum puri
23、ty with sulfate concentration 0.001% (m/M). Dispose of thismaterial in accordance with accepted local requirements. It must contain no measurable sulfate. (WarningCorrosive; keep awayfrom skin and eyes. Perchloric acid is a strong oxidizer.)7.4 EthanolDenatured with methanol, formula 3A or histologi
24、cal grade ethanol, anhydrous, denatured with ethyl acetate,methyl isobutyl ketone and hydrocarbon naphtha. It must be free of any measurable sulfate. (WarningFlammable, toxic, maybe harmful or fatal if ingested or inhaled. Avoid skin contact.)7.5 EthanolAbsolute, 200 proof, 99.5%, A.C.S. reagent gra
25、de.7.6 Lithium Chloride99+%, A.C.S. reagent grade.7.7 WaterType III reagent water conforming to Specification D1193.7.8 Anhydrous Calcium Sulfate Desiccant.8. Preparation of Standard Solutions8.1 Lead Nitrate Titrant, 0.0025 MDissolve 0.833 g lead nitrate in 300 mLwater. Pour into a 1-Lbottle and fi
26、ll with denaturedethanol and mix well. Standardize in accordance with 10.1.8.1.1 Alternatively, this solution may be purchased from a commercial vendor, and its exact molarity shall be determined inaccordance with 10.1.8.2 Aqueous Sulfate Standard, 0.01 MDry 5 g anhydrous sodium sulfate at 110C for
27、1 h. Remove it from the oven, and allowit to cool in a desiccator over anhydrous calcium sulfate. Accurately weigh about 0.70 g on an analytical balance to the nearesttenth of a milligram, and place it in a 500-mL volumetric flask. Add Type III water to dissolve the sodium sulfate, then dilute tovol
28、ume. Calculate the exact concentration in accordance with Eq 1.G142.02!0.500!5Molarity (1)Molarity = molarity of sulfate standard solution, mol/L,D7318 132G = weight in grams of Na2SO4, dissolved in 500 mL, and142.02 = gram molecular weight of Na2SO4.8.3 Aqueous Sulfate Stock Solution for Standards
29、in Ethanol, 2000 mg/LAccurately weigh 2.95 g anhydrous sodium sulfateto the nearest tenth of a milligram and transfer it to a 1-L volumetric flask. (Dried anhydrous sodium sulfate should be stored ina desiccator.) Add Type III water to dissolve the sodium sulfate, and make to volume. Calculate the c
30、oncentration of sulfate in thesolution in accordance with Eq 2.Aqueous Stock Sulfate mg/L!5gNa2SO4!0.6764!1000 mg/g!1L (2)g Na2SO4 = weight in grams of Na2SO4 dissolved in 1 L, and0.6764 = fraction of sulfate in Na2SO4.8.4 Sulfate Standards in EthanolEthanol (denatured containing no measurable sulfa
31、te) is weighed into a container (equippedwith a closure to prevent evaporation) in accordance with Table 1 to achieve the desired standard. Aqueous sulfate stock solutionfrom 8.3 is added to the solution in accordance with Table 1, and the final weight of the solution recorded. Standards should bere
32、made weekly or if recovery of less than 90% is noted. The concentration of the standard is calculated by dividing the numberof milligrams sulfate from the sulfate stock solution and dividing by the final solution weight in accordance with Eq 3.EtOH Sulfate Standard mg/kg!5V 3CW (3)V = volume of aque
33、ous sulfate stock (8.3), mL,C = concentration of aqueous sulfate stock (8.3), mg/L, andW = final weight of ethanol and aqueous sulfate stock aliquot, g.8.5 Aqueous Sulfate Blank Solution, 0.01 MThis is the same solution as in 8.2.This solution contains sulfate and will be addedto all samples to allo
34、w a measurable sulfate blank to be measured.8.6 Dilute Perchloric Acid, 0.1 MDissolve 8.8 mL perchloric acid (7.3) in 250-mL water in a 1-L volumetric flask. Mix welland dilute to the mark with Type III water.8.7 Lithium Chloride in Ethanol, 1 MAdd lithium chloride (8.49 g) to absolute ethanol (200
35、mL) while stirring until it isdissolved.9. Titration Equipment Preparation9.1 TitratorPrepare the titrator by filling the titrator reservoir with lead titrant (8.1). Follow the manufacturers procedure forfilling the buret. Perform titrations in monotonic titration mode, using either 25-L or 50-L tit
36、rant addition increments. Use a 10mV/min drift condition or 20-s wait time between additions (whichever is achieved first).9.2 Electrode PreparationProper care of the leadselective electrode is essential for obtaining highquality titration curves.Preparation of the lead electrode should be performed
37、 as specified by the manufacturer. A lead electrode utilizing a solid crystalsensor requires polishing when performance deteriorates. The voltage range for a 10 ppm sulfate in ethanol titration should spanat least 50 mV and produce an acceptably shaped titration curve (see Fig. 1). If this level of
38、electrode performance is not met, thisindicates a need for lead electrode polishing. The lead electrode normally comes supplied with a polishing grit and a clothrectangle. The polishing grit medium is placed on the cloth, wet with ethanol or water, moved over the surface of the cloth for aminute, ri
39、nsed with water to remove the polishing medium, and wiped dry with a tissue. The electrode is then soaked in lead titrant(8.1) for 2 min to re-equilibrate the electrode surface. The double junction reference electrode is filled with 1 M lithium chloridein absolute ethanol (8.7) in the outer chamber.
40、10. Standardization10.1 Measure the exact concentration of the lead nitrate titrant by titration of the sulfate standard (8.2).10.1.1 Transfer 1.00 mL of the 0.01 M aqueous sulfate standard solution (8.2) into a 150-mL beaker. Record this volume as V.10.1.2 Add approximately 100 mL of denatured etha
41、nol (7.4) and 1 mL of 0.1 M perchloric acid (8.6).TABLE 1 Preparation of Sulfate Standards in EthanolEthanolic Sulfate Standard,mg sulfate/kg ethanolEthanol,gAqueous Sulfate StockSolution, mL50 975 2520 990 1010 995 55 997.5 2.51 999.5 0.5D7318 13310.1.3 Prepare the autotitrator for operation, immer
42、se the electrodes in the titration solution, initiate stirring, and titrate to thepotentiometric endpoint with lead titrant. Titration should require approximately 4.0-mL of lead solution to reach the endpoint.Record this volume as T.10.2 Titrate a blank denatured ethanol sample in the same manner w
43、ithout addition of sulfate standard. Record this volume asTb.10.3 Calculate the concentration of the lead nitrate titrant as shown in Eq 4. The standardization should be repeated untilprecision comparable to that shown in Section 15 and Table 2 has been achieved.MPb5 V 3ST 2Tb(4)where:MPb = molarity
44、 of lead in the titrant, mol/L,V = volume of sulfate standard solution added, mL (10.1.1),S = molarity of the sulfate solution from 8.2, mol/L,T = volume of lead titrant used to titrate the sulfate solution, mL, andTb = volume of lead titrant used for the blank, mL (10.2).FIG. 1 Potentiometric Titra
45、tion Curves for Sulfate Standards in EthanolTABLE 2 Test Method PrecisionAnalyte mg/kg Repeatability (r) Reproducibility (R)Existent Inorganic Sulfate 1.0 0.18 0.604.0 0.25 0.8520.0 0.38 1.30D7318 13411. Procedure11.1 Sample AnalysisObtain an ethanol sample in accordance with Practice D4057 or Pract
46、ice D4177. The sample should bewell mixed to ensure homogeneity. A representative portion shall be taken for analysis. Samples should be collected in containerswith closures that seal well to prevent evaporation of ethanol. Samples containers should not contain any residual sulfate. Ifcontainers hav
47、e been cleaned and rinsed with water, they must be rinsed with Type III water and dried prior to use.11.2 Blank Measurement:11.2.1 Determine the blank value by analysis of a denatured ethanol sample used for making standards (100 g) using theprocedure described in 11.3. An aliquot of aqueous sulfate
48、 blank solution (8.5) is added to all samples as part of the blank. Thisis necessary to provide a stable blank value.11.2.2 The average of three blank measurements is recorded as Vb for use in the calculation of sulfate content of samples.11.3 Sample Measurement:11.3.1 Accurately weigh an ethanol sa
49、mple or blank (approximately 100 g) into a 150-mL beaker, and record the weight as G.11.3.2 Carefully pipet 0.200 mL of aqueous sulfate blank solution (8.5) into the beaker containing the ethanol sample.11.3.3 Add 1 mL of 0.1 M perchloric acid (8.6). The sample should be slightly acidic to pH paper before titrating, pH shouldbe in the range of 3 to 5. The pH can be checked by dipping a glass stirring rod into the sample and testing a droplet on the rodwith a moistened pH test strip. If 1 mL of 0.1 M perchloric acid is insuffic
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