Liquid–liquid extraction in flow injection analysis using an open-phase separator for the spectrophotometric determination of copper in plant digests

Abstract

A flow injection system with an open-phase separation device is presented for the liquid–liquid extraction of the diethyldithiocarbamate–copper complex (DDTC–Cu) using carbon tetrachloride (CCl₄). An open tube enclosed by computer-controlled solenoid valves was installed vertically to promote fast phase separation by differences in density. The solenoid valves were used to introduce the reacted sample zone into the tube, to select a precise volume of the extracted complex to be detected and to pass the remaining solution to waste. A preconcentration factor of 10 was attained, corresponding to the aqueous to organic phase volume ratio. The solenoid valve control allowed the use of a small solvent volume (0.7 ml) per determination. The DDTC–Cu complex was detected at 436 nm. A sample throughput of 30 determinations per hour for Cu ranging from 50 to 400 µg l^–1 in real samples was achieved. A limit of detection of 5 µg l^–1 of Cu was calculated using 3ς. A precision characterised by an RSD of less than 3% was typical for a sample with a copper concentration of 145 µg l^–1. The accuracy was assessed with NIST SRM 1572 and no difference at the 95% confidence level was found.