DESIGN OF A CONTINUOUS-FLOW 2-STEP EXTRACTION SAMPLE WORK-UP SYSTEM FOR GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

Heavy metals in aqueous samples are concentrated 50-100--fold and are separated from the matrix. In the first extraction step the metals are extracted as dithiocarbamates into Freon 113 and in the second step they are stripped into a dilute aqueous mercury(II) solution. The system is studied with respect to pH, extraction rate, materials for the extraction coils and segment stability. A new segmentor suitable for use in extractive sample concentration from an aqueous to an organic phase is presented. The system is connected on-line with a graphite furnace atomic absorption spectrometer. The sample throughput is 30 h-1, giving a sample carryover of 1.2% when concentrating the samples 50-fold. Extraction yields are in the range 80-107% for Cd, Co, Cu, Fe, Ni and Pb, the coefficient of variation on repeated analyses is 1.5-2.7% and the detection limits are below 10 ng 1-1. © 1990.