LIQUID-LIQUID-EXTRACTION IN FLOW-INJECTION ANALYSIS USING AN OPEN-PHASE SEPARATOR FOR THE SPECTROPHOTOMETRIC DETERMINATION OF COPPER IN PLANT DIGESTS

A flow injection system with an open-phase separation device is presen ted for the liquid-liquid extraction of the diethyldithiocarbamate-cop per complex (DDTC-Cu) using carbon tetrachloride (CCl4), An open tube enclosed by computer-controlled solenoid valves was installed vertical ly to promote fast phase separation by differences in density, The sol enoid valves were used to introduce the reacted sample zone into the t ube, to select a precise volume of the extracted complex to be detecte d and to pass the remaining solution to waste, A preconcentration fact or of 10 was attained, corresponding to the aqueous to organic phase v olume ratio, The solenoid valve control allowed the use of a small sol vent volume (0.7 ml) per determination, The DDTC-Cu complex was detect ed at 436 nm, A sample throughput of 30 determinations per hour for Cu ranging from 50 to 400 mu g l(-1) in real samples was achieved, A lim it of detection of 5 mu g l(-1) of Cu was calculated using 3 sigma. A precision characterised by an RSD of less than 3% was typical for a sa mple with a copper concentration of 145 mu g l(-1). The accuracy was a ssessed with NIST SRM 1572 and no difference at the 95% confidence lev el was found.