EPA325_3

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METHOD #: 325.3 TITLE: ANALYTE: INSTRUMENTATION: STORET No. Approved for NPDES (Editorial Rev. 1978, 1982) Chloride (Titrimetric, Mercuric Nitrate) CAS # Cl- Chloride 16887006 Titration 00940 1.0 Scope and Application 1.1 1.2 This method is applicable to drinking, surface, and saline waters, domestic and industrial wastes. The method is suitable for all concentration ranges of chloride content; however, in order to avoid large titration volume, a sample aliquot containing not more than 10 to
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  METHOD #: 325.3 Approved for NPDES (Editorial Rev. 1978, 1982) TITLE: Chloride (Titrimetric, Mercuric Nitrate) ANALYTE: CAS # Cl- Chloride 16887006 INSTRUMENTATION: Titration STORET No. 009401.0Scope and Application1.1This method is applicable to drinking, surface, and saline waters, domestic andindustrial wastes.1.2The method is suitable for all concentration ranges of chloride content;however, in order to avoid large titration volume, a sample aliquot containingnot more than 10 to 20 mg Cl per 50 mL is used.1.3Automated titration may be used.2.0Summary of Method2.1An acidified sample is titrated with mercuric nitrate in the presence of mixeddiphenylcarbazone-bromophenol blue indicator. The end point of the titrationis the formation of the blue-violet mercury diphenylcarbazone complex.3.0Comments3.1Anions and cations at concentrations normally found in surface waters do notinterfere.3.2Sulfite interference can be eliminated by oxidizing the 50 mL of samplesolution with 0.5 to 1 mL of HO. 22 4.0Apparatus4.1Standard laboratory titrimetric equipment including a 1 mL or 5 mLmicroburet with 0.01 mL graduations.5.0Reagents5.1Standard sodium chloride, 0.025 N:Dissolve l.4613 g ± 0.0002 g sodiumchloride (dried al 600°C for 1 hour) in chloride-free water in a 1 litervolumetric flask and dilute to the mark 1 mL = 886.5 F     g Cl.5.2Nitric acid, HNO solution (3 + 997) 3 5.3Sodium hydroxide solution, NaOH, (10 g/L)5.4Hydrogen peroxide (30%). HO 22 5.5Hydroquinone solution (10 g/liter): Dissolve 1 g of purified hydroquinone inwater in a 100 mL volumetric and dilute to the mark.5.6Mercuric nitrate titrant (0.141 N): Dissolve 25 g Hg(NO) C   HO in 900 mL of  322  distilled water acidified with 5.0 mL conc. HNO in a 1 liter volumetric flask  3 and dilute to the mark with distilled water. Filter if necessary. Standardizeagainst standard sodium chloride solution (5.1) using procedure 6. Adjust toexactly 0.14 1 N and check. Store in a dark bottle. A 1.00 mL aliquot isequivalent to 5.00 mg of chloride.5.7Mercuric nitrate titrant (0.025 N): Dissolve 4.2830 g Hg(NO) C   HO in 50 mL of  322 distilled water acidified with 0.5 mL conc.HNO (sp. gr. 1.42) in a 1 liter 3 volumetric flask and dilute to the mark with distilled water. Filter if necessary.Standardize against standard sodium chloride solution (5.1) using procedure 6.Adjust to exactly 0.025 N and check. Store in a dark bottle.5.8Mercuric nitrate titrant (0.0141 N): Dissolve 2.4200 g Hg(NO) C   HO in 25 mL 322 of distilled water acidified with 0.25 mL of conc. HNO (sp. gr. 1.42) in a 1 liter 3 volumetric flask and dilute to the mark with distilled water,Filter if necessary.Standardize against standard sodium chloride solution (5.1) using procedure 6.Adjust to exactly 0.0141 N and check. Store in a dark bottle. A 1 mL aliquot isequivalent to 500 ug of chloride.5.9Mixed indicator reagent: Dissolve 0.5 g crystalline diphenylcarbazone and 0.05g bromophenol blue powder in 75 mL 95% ethanol in a 100 mL volumetricflask and dilute to the mark with 95% ethanol. Store in brown bottle anddiscard after 6 months.5.10Xylene cyanole FF solution: Dissolve 0.005 g of xylene cyanole FF dye in 95%ethanol or isopropanol in a 100 mL volumetric and dilute to the mark with95% ethanol or isopropanol.6.0Procedure6.1Use 50 mL of sample or an aliquot of sample diluted to 50 mL with distilledwater, so that the concentration of chloride does not exceed 20 mg aliquot. If the sample or aliquot contains more than 2.5 mg of chloride, use 0.025 Nmercuric nitrate titrant (5.7) in step 6.6. If the sample or aliquot contains than2.5 mg of chloride, use 0.0141N mercuric nitrate (5.8) in step 6.6. Determine anindicator blank on 50 mL chloride-free water using step 6.6. If the samplecontains less than 0.1 mg/L of chloride concentrate an appropriate volume to50 mL.6.2Add 5 drops of mixed indicator reagent (5.9), shake or swirl solution.6.3If a blue-violet or red color appears add HNO solution (5.2) dropwise until 3 the color changes to yellow.6.4If a yellow or orange color forms immediately on addition of the mixedindicator, add NaOH solution (5.3) dropwise until the color changes toblue-violet; then add HNO solution (5.2) dropwise until the color changes to 3 yellow.6.5Add 1 mL excess HNO solution (5.2). 3 6.6Titrate with 0.025 N mercuric nitrate titrant (5.7) until a blue-violet colorpersists throughout the solution. See 6.1 for choice of titrant normality. Xylenecyanol FF solution (5.10) may be added with the indicator to sharpen the endpoint. This will change color shades. Practice runs should be made.6.7Additional steps to eliminate particular interferences:6.7.1If chromate is present and iron is not present the end point may bedifficult to detect.6.7.2If chromate is present at > 100 mg/L and iron is not present, add 2 mL  of fresh hydroquinone solution (5.5).6.7.3If ferric ion is present use volume containing no more than 2.5 mg of ferric ion or ferric ion plus chromate ion. Add 2 mL fresh hydroquinonesolution (5.5).6.7.4If sulfite ion is present, add 0.5 mL of HO solution (5.4) to 50 mL 22 sample and mix for 1 minute.7.0Calculationwhere:A=mL titrant for sampleB=mL titrant for blank N=normality mercuric nitrate titrantmg NaCl/L = mg chloride/L x 1.658.0Precision and Accuracy8.1Forty two analysts in eighteen laboratories analyzed synthetic water samplescontaining exact increments of chloride, with the following results:Increment asPrecision asAccuracy asChlorideStandard DeviationBias,Bias,mg/litermg/liter%mg/liter171.54+2.16+0.4181.32+3.50+0.6912.92+0.11+0.1973.16-0.51-0.538211.70-0.61-2.339811.80-1.19-1.7(FWPCA Method Study 1, Mineral and Physical Analyses)8.2In a single laboratory (EMSL), using surface water samples at an averageconcentration of 34 mg Cl/L, the standard deviation was ±1.0.8.3A synthetic unknown sample containing 241 mg/L chloride, 108 mg/L Ca, 82mg/L Mg, 3.1 mg/L K, 19.9 mg/L Na, 1.1 mg/L nitrate N, 0.25 mg/L nitriteN, 259 mg/L sulfate and 42.5 mg/L total alkalinity (contributed by NaHCO) 3 in distilled water was analyzed in 10 laboratories by the mercurimetricmethod, with a relative standard deviation of 3.3% and a relative error of 2.9%. Bibliography 1.Annual Book of ASTM Standards, Part 31, Water , Standard D512-67, Method A,p270 (1976).
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