MULTICOMMUTATION IN FLOW-ANALYSIS EXPLOITING A MULTIZONE TRAPPING APPROACH - SPECTROPHOTOMETRIC DETERMINATION OF BORON IN PLANTS

A flow system based on multicommutation to implement a sequential zone trapping approach to retain multiple sample zone into the analytical path during a previous preset time interval is proposed. This permits an increase of the sample residence time to improve sensitivity of spe ctrophotometric methods based on a relatively slow reaction. The flow network comprises a set of solenoid valves assembled in order to form three analytical pathways with equal length. With this configuration t hree sample zones could be sequentially loaded and trapped into the re action coils to allow the chemical reaction to reach completeness. The flow system was controlled by means of a 486 microcomputer equipped w ith an electronic interface running software written in Quick BASIC 4. 5. Feasibility of the proposed system was ascertained by the spectroph otometric determination of boron in a mineralized plant material using Azomethine-H as chromogenic reagent. The proposed system showed a lin ear response from 0.25 to 6.00 mg B 1(-1) and an analytical throughput of 35 determinations per hour. Other favourable features such as a lo w relative standard deviation of 2.5% (n=9) and a consumption of only 0.5 mg Azomethine-H per determination were also obtained. (C) 1998 Els evier Science B.V. All rights reserved.