TITLE: Chlorine, Total Residual …

1 METHOD #: for NPDES (Issued 1978) TITLE: chlorine , Total Residual ( spectrophotometric ,DPD) analyte :CAS # Cl chlorine 7782-50-5 instrumentation :SpectrophotometerSTORET and DPD-Colorimetric method is applicable to natural and treated waters atconcentrations from mg/L. of (hypochlorite ion, hypochlorous acid) and chloraminesstoichiometrically liberate iodine from potassium iodide at pH 4 or less. liberated iodine reacts with N,N-diethyl-p-phenylene diamine (DPD) toproduce a red colored solution. solution is spectrophotometrically compared to a series of standards, usinga graph or a regression analysis calculation.

2 Results are read or calculated into mg/L Cl. oxidizing agents; these are usually present at insignificant concentrationscompared to the Residual chlorine concentrations. and color will essentially prevent the colorimetric analysis. for use at 515 nm and cells of light path 1 cm or longer. buffer solution: Dissolve 24 g anhydrous disodium hydrogenphosphate, Na HPO , and 46 g anhydrous potassium dihydrogen phosphate,24KH PO , in distilled water. Dissolve 800 mg disodium ethylenediamine24tetraacetate dihydrate in 100 mL distilled water.

3 Combine these two solutionsand dilute to 1 liter with distilled water. Add 20 mg Hg Cl2 as a preservative. ,N-Diethyl-p-phenylenediamine (DPD) indicator solution: Dissolve 1 g DPDoxalate or g p-amino-N,N-diethylaniline sulfate in chlorine free distilledwater containing 8 mL of 1+3 H SO ( ) and 200 mg disodium24ethylenediamine tetraacetate dihydrate. Dilute to 1 liter, store in a colored,glass-stoppered bottle. Discard when discolored. The buffer and indicatorsulfate are available as a combined reagent in stable powder form.

4 CAUTION:The oxalate is toxic, avoid ingestion. acid solution (1 + 3): Slowly add one part of H SO (sp. gr. ) to24three parts of distilled water. Iodide, KI crystals. Potassium Permanganate Solution: Place g KMnO in a volumetric4flask and dilute to 1 Potassium Permanganate Solution: Dilute mL of stockpotassium permanganate solution ( ) to 100 mL with distilled water in avolumetric flask. One milliliter of this solution diluted to 100 mL with distilledwater is equivalent to mg/L a series of permanganate standards covering the chlorineequivalent range of to 4 mg/L.

5 5 mL phosphate buffer ( ) in a flask. 5 mL DPD reagent ( ). 100 mL permanganate standard ( ). at 515 nm on a spectrophotometer and record the absorbance. the contents of the cell to the the contents of the flask with standard ferrous ammoniumsulfate (DPD- FAS Method), until the red color is discharged. Recordthe result. mL phosphate buffer ( ) in flask. mL DPD reagent ( ). approximately g KI ( ). 10 mL of sample. stand 2 minutes. at 515 nm on a spectrophotometer, and record the absorbance.

6 Curve the absorbance of the standard permanganate solutions ( ) onthe vertical axis versus the titrated concentration ( ) on thehorizontal axis. the line of best fit through the points. the absorbance ( ) of the sample on the vertical the concentration on the horizontal axis at the intersect of theabsorbance and the calibration line. Analysis the absorbance data of the standard permanganate solutions( ) and the respective titrated concentrations ( ) in theappropriate places in the program.

7 The absorbance data of the sample. computer will then display the concentration in mg/L Cl. and laboratories analyzed prepared samples of mg/L Cl. Therelative standard deviation was and the relative error was In a single laboratory, single operator situation the following results DevRel. Std. mg/L%Distilled Water(a) (a)Three replicates for distilled water. Seven replicates for other three samples the results were compared to the iodometric titration as a means ofobtaining a relative RecoveryMatrixTitrationColorime-mg/Ltric mg/LDrinking Methods for the Examination of Water and Wastewater, 14th Ed.

8 , Pg. 332,Method 409F, "DPD Colorimetric Method", (1975). , D. F., "Comparison of Methods for the Determination of Total AvailableResidual chlorine in Various Sample Matrices", EPA Report-600/4-78-019.