Automated determination of urinary inorganic sulfates with the "AutoAnalyzer".

A turbidimetric method for inorganic sulfates in urine, based on the precipitation of barium sulfate, is adapted to the AutoAnalyzer. Coating of the flowcell with BaSO4is avoided by an inter-sample air rinsing. Sampling rate is 40/h. Inorganic urinary sulfate determinations are of interest for the evaluation of endogenous acid production (1) and in experimental evaluation of the acid-excreting potential of the kidney (2-3). In earlier methods, urinary sulfate was determined gravimetrically as barium sulfate. Precipitation of sulfate, a method first used by Folin (4), is tedious and time-consuming. Subsequently, Rosenheim and Drummond (5) and Fiske (6) used a volumetric benzidine method, but interferences by chloride and phosphate seriously limited the usefulness of this technique (7). Finally, a nephelo-metric method was devised (8-10) and applied to automatic determinations of sulfate (11). This report deals with a modification of this latter technique and its adaptation to the N-methodology of Technicon. Rinsing the system with air prevents BaSO4 from coating the fi owcell. Manifold: (see Figure 1). Dialyzer: a single dialysis is performed at 37#{176}C, with a " C " membrane. Colorimeter: a 15-mm tubular flow cuvet and a 520-nm filter are used. Sampling: the sampling rate is 40/h. Reagents Diluent: Distilled water plus " Brij 35 " (1 ml/-liter water). HC1, iN: To 80 ml of concentrated HC1 in a volumetric flask, add water to 1 liter. BaCl2-gelatin reagent: Add 2 g of gelatin and 0.1 g of thymol to about 500 ml of distilled water and heat while stirring until dissolved. Cool to room temperature, filter through no. 42 Whatman filter paper, and add 20 g of barium chloride slowly with constant stirring. Dilute the mixture to 1 liter with distilled water. Procedure The main difficulty was to prevent the coating of the cuvet walls with BaSO4. Rinsing with DTA or H3P04 aspirated between each sample is inefficient. Instead, air rinsing was found to be quite adequate. As shown in Figure 1, a Technicon three-way valve was inserted in the manifold between the last mixing coil and the colorimeter. At regular intervals, the valve deviates the barium sulfate liquid suspensions from the colorimeter to the waste line (valve-way 2 in Figure 1), while air is aspirated for 22 s through the cuvet by means of an AO glass fitting adapted on the upper part of the T-debubbler. Subsequently, sample and reagent flow resume in the tubular cell while air flow is …