MULTICOMMUTATION IN FLOW-ANALYSIS .1. BINARY SAMPLING - CONCEPTS, INSTRUMENTATION AND SPECTROPHOTOMETRIC DETERMINATION OF IRON IN PLANT DIGESTS

A novel strategy to handle sample and reagent introduction in continuo us flow systems is proposed. Basic features such as the effect of flow cell volume, analytical pathlength and peristaltic pump pulsation on the precision of measurement were studied. The manifold was based on a set of three-way solenoid valves controlled by a microcomputer using software written in QuickBASIC. It could also control the rotation spe ed of the peristaltic pump. By sampling slugs of sample and reagent so lutions synchronized with pulsation of the peristaltic pump, aliquots with volumes as low as 2 mu l could be sampled with a relative standar d deviation <3%. Characteristics and performance of the system were st udied by using a dye solution to simulate the samples. The feasibility was assessed by spectrophotometric determination of iron in acid plan t digests using potassium thiocyanate. Results were in agreement with inductively-coupled argon plasma atomic emission spectrometric determi nations. A throughput of 220 samples per hour was achieved and reagent consumption was only 0.7 mg per determination.