PROGRAMS AND PLANS--Analytical Methods: Sulfate determinations In Reply Refer To: February 25, 1983 EGS-Mail Stop 412 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM 83.07 PROGRAMS AND PLANS--Analytical Methods: Sulfate determinations Beginning March 1, 1983, sulfate concentrations will be measured by the "turbidimetric, barium sulfate, automated- discrete" method. The procedure is more precise and has a lower detection limit than the methylthymol blue (MTB) procedure currently used. Samples collected for the NASQAN and Bench-Mark Networks after October 1, 1982, have been analyzed by the turbidimetric procedure as a special analysis. All schedules containing Lab Code (LC) 63, sulfate, mg/L as S04, MTB procedure, will automatically be changed to Lab Code 1200, which has been assigned to the new turbidimetric procedure. If continuity of data is judged essential to complete long-term commitments, LC 63 can be requested for the remainder of FY 1983 as a regular determination. Thereafter, LC 63 may be requested as a special analysis and turnaround time and cost will be negotiated. The turbidimetric method may be used to measure the concentration of sulfate in natural water and waste effluents. Samples with color in excess of 50 platinumcobalt units, and silica in excess of 200 mg/L, may require correction. The detection limit by the turbidimetric procedure is 0.2 mg/L versus 5 mg/L by the methylthymol blue procedure. The instrumentation employed in the turbidimetric procedure is an American Monitor discrete analyzer system, and measurements are made in 3 ranges: 0.2 to 10 mg/L, 10 to 200 mg/L, and 200 to 1,000 mg/L. Sulfate ion is reacted with barium chloride under acidic conditions to form barium sulfate. The absorbance of the resulting suspension is measured photometrically and is proportional to the sulfate concentration present in the original sample. Test results in the low range compare favorably with results by ion chromatography; results in the mid-range compare with results obtained by the MTB automated Technicon procedure; and results in the high range are comparable to results obtained by gravimetric analysis. Support data obtained by the Atlanta and Denver Central Laboratories, representing many months of intense effort, are on file with the Methods Evaluation/TWRI Project (Marvin Fishman, Arvada, CO). The Central Laboratories System is pleased to provide this improvement in analytical service through advances in technology at no increase in cost. R.J. Pickering Chief, Quality of Water Branch WRD Distribution: A, B, S, FO, PO Key Words: water quality, analytical methods, laboratories, sulfate This memorandum does not supersede any other memorandum.