On-line solid phase extraction of the 5,7-dichloroquinoline-8-ol complex onto C18 bonded silica gel and flame AAS determination of Cu in seawater samples

A flow injection on-line adsorption preconcentration system coupled to flame atomic adsorption spectrometry (FAAS) was developed for the determination of copper at the mug L-1 level. Copper is complexed with 5,7-dichloroquinoline-8-ol in the pH range of 7.0-9.0 in the flow injection system and adsorbed onto the C-18 bonded silica gel column. The preconcentrated chelate complex was eluted with acidified methanol (pH > 2) and injected directly into the nebulizer for atomisation in an air-acetylene flame for measurement. With a 1-minute preconcentration and sample frequency of 30 h(-1), the enrichment factor was 100 which can be further improved by increasing the preconcentration time. The detection limit was 0.05 mug L-1 and the precision 1.4% at the 2 mug L-1 Cu level. Variation of the developed method was carried out by analyzing certified seawater reference material (CASS 4) and determining copper at a concentration of 0.60+/-0.06 compared to a certified value of 0.592+/-0.05 mug L-1. The method was also applied successfully to the analysis of seawater samples and the accuracy was tested by recovery measurements on spiked samples. No significant interferences from other substances usually occurring in seawater were found.