A new ultrasonic-assisted cloud-point-extraction procedure for pre-concentration and determination of ultra-trace levels of copper in selected beverages and foods by flame atomic absorption spectrometry

摘要

A new ultrasonic-assisted cloud-point-extraction (UA-CPE) method was developed for the pre-concentration of Cu(Ⅱ) in selected beverage and food samples prior to flame atomic absorption spectrometric (FAAS) analysis. For this purpose, Safranin T was used as an ion-pairing reagent based on charge transfer in the presence of oxalate as the primary chelating agent at pH 10. Non-ionic surfactant, poly(ethyleneglycol-mono-p-nonylphenylether) (PONPE 7.5) was used as an extracting agent in the presence of NH_4Cl as the salting out agent. The variables affecting UA-CPE efficiency were optimised in detail. The linear range for Cu(Ⅱ) at pH 10 was 0.02-70 μg l~(-1) with a very low detection limit of 6.10 ng l~(-1), while the linear range for Cu(Ⅰ) at pH 8.5 was 0.08-125 μg l~(-1) with a detection limit of 24.4 ng l~(-1). The relative standard deviation (RSD %) was in the range of 2.15-4.80% (n = 5). The method was successfully applied to the quantification of Cu(Ⅱ), Cu(Ⅰ) and total Cu in selected beverage and food samples. The accuracy of the developed method was demonstrated by the analysis of two standard reference materials (SRMs) as well as recoveries of spiked samples.