1、Designation: D4608 89 (Reapproved 2017)Standard Test Method forCitrate in Detergents1This standard is issued under the fixed designation D4608; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、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 a potentiometric titration pro-cedure for the determination of citrate in liquid and powderdetergents.1.2 The values stat
3、ed in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 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
4、 health practices and determine the applica-bility of regulatory limitations prior to use. Material SafetyData Sheets are available for reagents and materials. Reviewthem for hazards prior to usage. Specific safety precautions aregiven in Section 8.2. Referenced Documents2.1 ASTM Standards:2E70 Test
5、 Method for pH of Aqueous Solutions With theGlass ElectrodeE180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals (Withdrawn 2009)33. Summary of Test Method3.1 The sample is titrated in an aqueous solution buffered atpH 8.5, with st
6、andard copper sulfate solution. The endpoint isdetected potentiometrically using a copper ion selective elec-trode. The citrate content is calculated from the amount ofstandard copper sulfate solution consumed.4. Significance and Use4.1 This test method is suitable in research, development,and manuf
7、acturing control to monitor the level of citrate, asequestering agent, in powder and liquid detergents.4.2 Accurate determination of sequestering agent is impor-tant in evaluating cost and performance of detergent products.5. Interferences5.1 Other complexing agents such as nitrilotriacetic acid(NTA
8、), ethylenedinitrilotetraacetic acid (EDTA), phosphates,etc. will titrate as citrate in this method. For accurate citratedeterminations, such complexing agents must be absent.6. Apparatus6.1 pH Meter, with millivolt capability.46.2 Copper Ion Selective Electrode.56.3 Calomel Reference Electrode.66.4
9、 Glass Electrode Triple Purpose.76.5 Buret, semi-micro, 25 mL capacity with 0.1 mL gradu-ations.6.6 Magnetic Stirrer, and TFE-fluorocarbon-coated mag-netic stirring bars.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended tha
10、tall reagents shall conform to specifications of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications are available.8Other grades may beused, provided it is first ascertained that the reagent is of1This test method is under the jurisdiction of ASTM Committee
11、 D12 on Soapsand Other Detergents and is the direct responsibility of Subcommittee D12.12 onAnalysis and Specifications of Soaps, Synthetics, Detergents and their Components.Current edition approved Jan. 1, 2017. Published February 2017. Originallyapproved in 1986. Last previous edition approved in
12、2009 as D4608 89(2009).DOI: 10.1520/D4608-89R17.2For 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.3The last app
13、roved version of this historical standard is referenced onwww.astm.org.4An automatic titrator may be used.5Orion Model 94-29A or equivalent has been found suitable for this purpose.Available from Orion Inc.6Orion Model 90-22 or equivalent has been found suitable for this purpose.Available from Orion
14、 Inc.7Corning Model No. 476022 or equivalent has been found suitable for thispurpose. Available from Corning Inc.8Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Socie
15、ty, 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Unit
16、ed StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers
17、 to Trade (TBT) Committee.1sufficiently 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 ofequal purity.7.3 Hydrochloric Acid Solution (1 + 1)Slowly m
18、ix 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 solution of sodium hydroxide.7.6 Hydrochloric Acid Solution (0.1 N)Prep
19、are 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. Transfer quantitatively into a 1-L volumetricflask. Dilute to volume wi
20、th 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. Protect thesolution at all times from direct sunlight. Standardi
21、ze 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 and3gofiodate-freepotassium iodide in 50 mL of water. Allow to stand in th
22、e 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/A 30.04902 (1)where:W = weight of K2Cr2O7,A =mLofNa2S2O3solution required for titration ofthe K2C
23、r2O7solution, 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.Standardize against 0.1 N Na2S2O3(prepared in 7.8) by usinga pipet, tran
24、sferring a 25.0-mL aliquot of CuSO4solution intoa 250-mL Erlenmeyer flask. Add 0.1 N NaOH solution drop-wise until slightly turbid. Add 10 mL of acetic acid,2gofiodate-free potassium iodide and mix well. Titrate immediatelywith 0.1 N Na2S2O3standard solution using starch solution asindicator. Calcul
25、ate 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 Acid(C6H8O7).8. Safety Precautions8.1 All reagents and chemicals
26、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 Disposal Manual, Manufacturing ChemistsAssociation, Washington, DC.9.
27、 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. While stirringwith a magnetic stirrer, adjust the pH between 8 and
28、 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 selectiveelectrode.9Set the pH meter4on millivolt and begin to addcopper sulfate
29、 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 derivativemethod or by plotting millilitres of copper sulfate added versusmilliv
30、olts. Calculate percent citrate as citric acid as follows:Citric Acid, % 5 A 3 M 30.192 3100/W (3)where:A = mL of CuSO4solution required for titration ofsample solution,M = molarity of CuSO4solution,0.192 = milliequivalent weight of citric acid, andW = g of sample taken.10. Precision and Bias10.1 Th
31、e following criteria should be used to judge theacceptability of the results:10,1110.1.1 Repeatability (Single Analyst)The standard devia-tion of results (each the average of duplicates), obtained by thesame analyst on different days, has been estimated to be 0.06weight % absolute at 12 df. Two such
32、 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 byanalysts in different laboratories, has been estimated to be 0.1weigh
33、t % absolute at 5 df. Two such averages should be9The life of the copper ion selective electrode is finite. Its response needs to beoccasionally checked by titrating an accurately weighed sample of citric acid.10Supporting data are available from ASTM Headquarters, 100 Barr HarborDrive, West Conshoh
34、ocken, PA 19428. Request RR:D12-1008.11This statistical analysis was performed in accordance with Practice E180 fordeveloping precision estimates.D4608 89 (2017)2considered suspect (95 % confidence level) if they differ bymore than 0.4 % weight absolute.10.1.3 Checking Limits for DuplicatesReport th
35、e percentof citric acid of the sample to the nearest 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
36、 % citric acid and a liquiddetergent found to contain 7.7 % citric acid.10.2 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, duplicate determi-nations on each of 2 days, was 3.5 indicating a hig
37、h 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 respecting the validity of any patent rights asserted in connection with any
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41、rive, 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). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 89 (2017)3
