Determination of cadmium in seawater using automated on-line preconcentration and direct injection graphite furnace atomic absorption spectrometry

An on-line preconcentration method for the determination of cadmium in seawater was developed for graphite furnace atomic absorption spectrometry (GFAAS) using deuterium lamp background correction. The technique was adapted from a previously reported technique and was fully automated. Automated preconcentration of cadmium reduced the concentrations of matrix elements in samples to levels that did not interfere with the determination of cadmium at ultratrace levels. The soluble ligand, 1-pyrrolidinecarbodithioic acid (APDC), was mixed with the sample in a continuous flow system to form a non-polar metal complex which was absorbed onto a C-18 column. The metal complex was then eluted from the column directly into the graphite furnace. The addition of an in-line nitric acid rinse step between sample load cycles allowed for the determination of cadmium with one elute cycle. Other modifications included laboratory purification of the ammonium acetate rinse solution, a non-buffered APDC ligand solution, and a computer-activated load cycle to reduce sample consumption. The average column recovery was 73% with a sample loading flow rate of 2.2 ml/min and 55 s preconcentration time. Sample throughput was approximately 15 samples/h with 2 ml of sample preconcentrated and analyzed every 4 min. The small sample volume required made this method useful where sample volumes are limited. The 3 sigma limit of detection for replicate blanks was 42 pM Cd (n=5) for a 2 ml sample. The effectiveness of the method was demonstrated for the determination of Cd in certified open ocean reference materials NASS-3 and NASS-4, Analysis of Cd in equatorial Pacific seawater demonstrated that the system produces oceanographically consistent results. (C) 1998 Elsevier Science B.V. All rights reserved.