DETERMINATION OF LEAD IN SEA-WATER WITH A GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETER AND AN IMPROVED AUTOMATIC ONLINE PRECONCENTRATION SYSTEM

An improved automatic on-line pre concentration system for graphite furnace atomic absorption spectrometry (GFAAS) for the determination of trace metals in sea-water was developed. This system was modified from a Perkin-Elmer AS-40 autosampler by mounting a silica gel C-18 microcolumn near the tip of the autosampler capillary. The pre-concentration procedure was performed by using a four-way distribution valve and controlled by a programmable controller. The pre-concentration system developed previously was improved by using a peristaltic pump to replace the reciprocating pumps, a newly designed tube bed adjuster to release the back-pressure in the pre-concentration system, and a better control program, such that on-line pre-concentration became more reliable and fully automatic. The chelating agent ammonium pyrolidinedithiocarbamate (APDC) and a miniature column packed with 5 mg of C-18 silica gel were used for pre-concentration, This system was tested by analyzing the lead content in reference standard sea-water samples, A sample volume of only 2 ml was required to. determine lead in sea-water. The relative limit of detection of lead was 3.5 pg/ml.