SAMPLING STRATEGIES IN SEQUENTIAL INJECTION-ANALYSIS - EXPLOITING THEMONOSEGMENTED-FLOW APPROACH

An evaluation of different sampling techniques employing sequential in jection analysis (SIA) is described. The reaction between Fe(II) and 1 ,10-phenanthroline, which needs a pH adjustment with acetate buffer an d a prior reduction with hydroxylamine solution, was employed. As a ge neral rule, sensitivity, compared to that of the usual SIA technique, can be enhanced with binary sampling, sandwich sampling and monosegmen ted flow, in that order. Under the employed conditions, signals 13, 31 and 58% higher than those provided by conventional SIA can be obtaine d with the binary, sandwich and monosegmented sampling, respectively. The monosegmented-flow approach was applied in determining iron in nat ural waters and results do not differ significantly from those obtaine d by ICP/AES at the 95% confidence level. The precision was 1.1%, expr essed as relative standard deviation obtained by the measurement of ni ne replicates of 1.0 mg l(-1) Fe(III) reference solution. (C) 1998 Els evier Science B.V.