SPECTROPHOTOMETRIC DETERMINATION OF LEAD IN TAP WATER WITH 5, 10, 15, 20-TETRA(4-N-SULFOETHYLPYRIDINIUM)PORPHYRIN USING MERGING ZONES FLOW-INJECTION

Determination of lead at concentrations of greater-than-or-equal-to 15 mug l-1 in aqueous samples was achieved by selective reaction with 5,10,15,20-tetra(4-N-sulfoethylpyridinium)porphyrin at pH 9.4 and 30-degrees-C in a merging zones flow injection manifold followed by detection at 480 nm after an elapsed time of 45 s. Interference by aluminium (125-fold excess), cadmium (25-fold excess), copper (25-fold excess), manganese (200-fold excess) and zinc (200-fold excess) was eliminated by the use of 1.0 mol 1-1 NH3-NH4Cl as a buffer/masking agent; interference by iron (10-fold excess) was eliminated by the addition of 1% v/v of acetylacetone to the reagent mixture and use of the method of standard additions for sample analysis. Recoveries from tap water.samples, to which various amounts of lead had been added, ranged from 98 to 109% with a detection limit of 10 mug l-1 when iron was present in the sample matrix and 4.2 mug 1-1 when it was not. Results of analyses of tap water samples using this method were in good agreement with those obtained by electrothermal atomic absorption spectrometry.