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Carbonate and Bicarbonate -The concentrations of these species are • closely interrelated and are dependent upon pH. Therefore, they are determined together by a single, multiple end-point titration with standard H25O4 using brorncresol green-methyl red mixed indicator. Carbonate and bicarbonate are reported in mg/I. Nitrite -Determined colorimetrically at a wove length of 520 nm after reaction with sulfanilimide and N-(I-naphthyl)-eThylendiamine. Nitrite is reported in mg/I. Nitrate Nitrogen -Deterrnined by reduction of nitrate to nitrite and subsequent colorimetric analysis of nitrite through The formation of areddish-purple azo dye produced by The coupling of diazotized sulfanilic acid with N-(I-naphThyl)- ethylendiarnine dihydrochloride. The reduction is effected by passing the sample through a column of amalgamated cadmium filings. Nitrate is reported in rng/I-NO3. Reference: Standard Methods, page 423. Available Phosphate (Orthophosphate) -Determined by reaction with ammonium molybdate and poTassiurn antimony) tartrate to produce phosphornolybdic acid, which is reduced with oscorbic acid to give molybedenurn blue. This is then determined colorimetrically at 880 nrn. Orthophosphate is reported in rng/I-P. Reference: Standard Methods, page 481. • Total Phosphate -The sample is digested with perchloric acid followed by the ascorbic acid reduction method (colorimetric) described for oriho- phosphote above. Total phosphorus is reported in mg/I. Reference: Standard Methods, page 481. Chloride -Deterrnined titrimetrically with standard mercuric nitrate To a diphenylcarbazone endpoint (yellow -j purple). Chloride is reported in rng/I. Reference: Standard Methods, page 304. Boron -The sample is treated with curcurnin-oxalic acid solution and evaporated to dryness. The residue is taken up in ethyl alcohol and the absorbance determined aT 540 nrn. Boron is reported in mg/I. Reference: Standard Methods, page 287. Fluorides -Determined by use of a fluoride specific ion electrode and millivolt meter. Fluoride is reported in rng/I. Reference: Standard Methods, page 391. Sulfate -Determined turbidirnetrically by ireatrnent with barium chloride to produce insoluble, finely divided barium sulfate. The absorbance of the • turbid solution is measured at 420 nm. Sulfate is reported in mg/1. Reference: Standard Methods, page 496. 2.5-III