1、Designation: D 4608 89 (Reapproved 2003)Standard Test Method forCitrate in Detergents1This standard is issued under the fixed designation D 4608; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number i
2、n 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 potentiometric titration pro-cedure for the determination of citrate in liquid and powderdetergents.1.2 This standar
3、d 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. Material SafetyData Sheets are
4、 available for reagents and materials. Reviewthem for hazards prior to usage. Specific safety precautions aregiven in Section 8.2. Referenced Documents2.1 ASTM Standards:E 70 Test Method for pH of Aqueous Solutions with theGlass Electrode2E 180 Practice for Determining the Precision of ASTMMethods f
5、or Analysis and Testing of Industrial Chemicals23. Summary of Test Method3.1 The sample is titrated in an aqueous solution buffered atpH 8.5, with standard copper sulfate solution. The endpoint isdetected potentiometrically using a copper ion selective elec-trode. The citrate content is calculated f
6、rom the amount ofstandard copper sulfate solution consumed.4. Significance and Use4.1 This test method is suitable in research, development,and manufacturing control to monitor the level of citrate, asequestering agent, in powder and liquid detergents.4.2 Accurate determination of sequestering agent
7、 is impor-tant in evaluating cost and performance of detergent products.5. Interferences5.1 Other complexing agents such as nitrilotriacetic acid(NTA), ethylenedinitrilotetraacetic acid (EDTA), phosphates,etc. will titrate as citrate in this method. For accurate citratedeterminations, such complexin
8、g agents must be absent.6. Apparatus6.1 pH Meter, with millivolt capability.36.2 Copper Ion Selective Electrode.46.3 Calomel Reference Electrode.56.4 Glass Electrode Triple Purpose.66.5 Buret, semi-micro, 25 mL capacity with 0.1 mL gradu-ations.6.6 Magnetic Stirrer, and TFE-fluorocarbon-coated mag-n
9、etic stirring bars.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to specifications of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications are ava
10、ilable.7Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean distilled water or water
11、ofequal purity.1This test method is under the jurisdiction of ASTM Committee D12 on Soapsand Other Detergents and is the direct responsibility of Subcommittee D12.12 onAnalysis of Soaps and Synthetic Detergents.Current edition approved May 26, 1989. Published July 1989. Originallypublished as D 4608
12、 86. Last previous edition D 4608 88.2Annual Book of ASTM Standards, Vol 15.05.3An automatic titrator may be used.4Orion Model 94-29A or equivalent has been found suitable for this purpose.Available from Orion Inc.5Orion Model 90-22 or equivalent has been found suitable for this purpose.Available fr
13、om Orion Inc.6Corning Model No. 476022 or equivalent has been found suitable for thispurpose. Available from Corning Inc.7Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemic
14、al 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 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2
15、959, United States.7.3 Hydrochloric Acid Solution (1 + 1)Slowly mix 1 vol-ume of concentrated hydrochloric acid (sp gr 1.19) with 1volume of water.7.4 Sodium Hydroxide Solution (20 %)Prepare a 20 %aqueous solution of sodium hydroxide.7.5 Sodium Hydroxide Solution (0.1 N)Prepare a 0.1 Naqueous soluti
16、on of sodium hydroxide.7.6 Hydrochloric Acid Solution (0.1 N)Prepare a 0.1 Naqueous solution of hydrochloric acid.7.7 Borate Buffer Solution (pH 8.5)Dissolve 12.8 g ofsodium borate (Na2B4O710H2O) and 16.6 g of boric acid(H3BO3) in about 900 mL of water. Adjust pH to 8.5 with 20 %NaOH solution. Trans
17、fer quantitatively into a 1-L volumetricflask. Dilute to volume with water. Mix well.7.8 Sodium Thiosulfate Solution, Standard (0.1 N)Dissolve 25 g of sodium thiosulfate (Na2S2O35H2O) crystals infreshly boiled and cooled water and dilute to 1 L. Add 0.01 gof sodium carbonate and 0.5 mL of chloroform
18、. Protect thesolution at all times from direct sunlight. Standardize againstpotassium dichromate (K2Cr2O7) by accurately weighing 0.221g of finely powdered dry potassium dichromate and transfer-ring solution to a 1-L iodine flask. Add 50 mL of water. Add 10mL of concentrated hydrochloric acid and3go
19、fiodate-freepotassium iodide in 50 mL of water. Allow to stand in the darkfor 5 min. Dilute to 400 mL with water and titrate immediatelywith the sodium thiosulfate using starch solution as indicator.Calculate the normality of the Na2S2O3solution as follows:Normality 5 W/A3 0.04902 (1)where:W = weigh
20、t of K2Cr2O7,A =mLofNa2S2O3solution required for titration ofthe K2Cr2O7solution, and0.04902 = milliequivalent weight of K2Cr2O7.7.9 Copper Sulfate Solution, Standard (0.05 M)Dissolve12.48 g of copper sulfate (CuSO45H2O) in 800 mL of water ina 1-L volumetric flask. Dilute to volume and mix well.Stan
21、dardize against 0.1 N Na2S2O3(prepared in 7.8) by using apipet, transferring a 25.0-mL aliquot of CuSO4solution into a250-mL Erlenmeyer flask. Add 0.1 N NaOH solution dropwiseuntil slightly turbid. Add 10 mL of acetic acid,2gofiodate-free potassium iodide and mix well. Titrate immediatelywith 0.1 N
22、Na2S2O3standard solution using starch solution asindicator. Calculate the molarity of the CuSO4solution asfollows:Molarity 5 A 3 N/25.0 (2)where:A =mLofNa2S2O3solution required for titration of theCuSO4solution,N = normality of Na2S2O3solution, and25.0 = aliquot of CuSO4solution titrated.7.10 Citric
23、 Acid(C6H8O7).8. Safety Precautions8.1 All reagents and chemicals should be handled with care.Before using any chemical, read and follow all safety precau-tions and instructions on the manufacturer label. Clean up anyspill immediately. For information on cleaning up spills refer tothe Laboratory Dis
24、posal Manual, Manufacturing ChemistsAssociation, Washington, DC.9. Procedure9.1 Accurately weigh (to the nearest 0.1 mg) enough sampleto contain about 150 mg citrate as sodium citrate or 100 mg ascitric acid. Quantitatively transfer to a 400-mL beaker withwater and bring the volume to about 200 mL.
25、While stirringwith a magnetic stirrer, adjust the pH between 8 and 9 withdropwise additions of HCl (1 + 1) or NaOH (20 %). Add 25mL borate buffer (pH 8.5). If necessary, carefully adjust the pHto 8.5 with NaOH (0.1 N) or HCl (0.1 N). Remove the glasselectrode and insert the copper ion selectiveelect
26、rode.8Set the pH meter3on millivolt and begin to addcopper sulfate solution in 1.0-mL increments. Near the endpoint add in 0.2-mL increments. Record the millivolt readingsafter each increment. Add at least five 0.2-mL increments pastthe end point. Calculate the end point by the second derivativemeth
27、od or by plotting millilitres of copper sulfate added versusmillivolts. Calculate percent citrate as citric acid as follows:Citric Acid, % 5 A 3 M 3 0.192 3 100/W (3)where:A = mL of CuSO4solution required for titration ofsample solution,M = molarity of CuSO4solution,0.192 = milliequivalent weight of
28、 citric acid, andW = g of sample taken.10. Precision and Bias10.1 The following criteria should be used to judge theacceptability of the results:9,1010.1.1 Repeatability (Single Analyst)The standard devia-tion of results (each the average of duplicates), obtained by thesame analyst on different days
29、, has been estimated to be 0.06weight % absolute at 12 df. Two such averages should beconsidered suspect (95 % confidence level) if they differ bymore than 0.2 weight % absolute.10.1.2 Reproducibility (Multilaboratory)The standard de-viation of results (each the average of duplicates), obtained byan
30、alysts in different laboratories, has been estimated to be 0.1weight % absolute at 5 df. Two such averages should beconsidered suspect (95 % confidence level) if they differ bymore than 0.4 % weight absolute.10.1.3 Checking Limits for DuplicatesReport the percentof citric acid of the sample to the n
31、earest 0.1. Duplicate runsthat agree within 0.1 % absolute are acceptable for averaging(95 % confidence level).10.1.4 The above precision data were derived from resultsof the cooperative tests by six laboratories on a powderdetergent found to contain 3.5 % citric acid and a liquiddetergent found to
32、contain 7.7 % citric acid.8The life of the copper ion selective electrode is finite. Its response needs to beoccasionally checked by titrating an accurately weighed sample of citric acid.9Supporting data are available from ASTM Headquarters, 100 Barr HarborDrive, West Conshohocken, PA 19428. Request
33、 RR: D12-1008.10This statistical analysis was performed in accordance with Practice E 180 fordeveloping precision estimates.D 4608 89 (2003)210.2 BiasThe exact level of citric acid in the powderdetergent (10.1.4) was 3.4 %. The average percent citric acidfound by the six participating laboratories,
34、duplicate determi-nations on each of 2 days, was 3.5 indicating a high bias of2.9 % relative. The exact level of citric acid in the liquiddetergent (10.1.4) was not known.11. Keywords11.1 citrate content; copper ion selective electrode; seques-tering agentASTM International takes no position respect
35、ing the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This stan
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