MULTICOMMUTATION IN FLOW-ANALYSIS .5. BINARY SAMPLING FOR SEQUENTIAL SPECTROPHOTOMETRIC DETERMINATION OF AMMONIUM AND PHOSPHATE IN PLANT DIGESTS

A flow set up for the spectrophotometric determination of ammonium and orthophosphate in acidic digests of plant materials is described. The flow network comprises solenoid valves assembled so that multicommuta tion and binary sampling can be implemented, providing facilities to d etermine sequentially these two analytes. Determinations are based on the molybdenum blue and indophenol blue methods. The flow network pres ents an active hardware, controlled by a microcomputer running a softw are written in Quick BASIC 4.5, and affords facilities to determine th e analytes employing a single pumping channel. The volumes of sample a nd reagents, and the flow rates are settled previously as entry data, Profitable features such as a throughput of 80 determinations per hour , and low reagents consumption (180 mu l salicylic acid, 120 mu l sodi um hypochloride, 120 mu l ammonium molybdate and 80 mu l ascorbic acid per determination) were achieved. A 2.0% relative standard deviation for ammonium and 1.5% for orthophosphate (n=8), using a typical sample with 73.1 mg/l nitrogen and 8.3 mg/l phosphorus were estimated, Accur acy was ascertained by comparing data obtained for phosphorus by induc tively coupled plasma atomic emission spectrometry and for nitrogen by titration as ammonium with sodium hydroxide, On applying the paired t -test between results, no significant difference at the 95% confidence level was observed.