Application of internal standard for micro extraction-spectrophotometric determination of copper in serum and in natural waters

Abstract

The well-known limitation of separation/preconcentration procedures is the increasing risk of analytical errors. Such source of errors can be controlled by using a method of internal standard (IS), which is common in chromatographic and in some spectrometric techniques. Recently, IS was also applied in spectrophotometry UV/Vis and the improved analytical performance was achieved both for many-fold dilution and for preconcentration procedures. In this work, bromophenol blue was used as IS in the extraction-spectrophotometric determination of copper with bathocuproine disulphonate in serum and in ground water. The ratio between the absorbances measured at 477 (copper complex) and at 602 nm (IS) was taken as the analytical signal. In serum analysis, after extraction to chloroform (150 μl), copper was determined directly in the organic phase (sample volume 300 μl, calibration range 0–2 mg l −1, DL 0.03 mg l −1, CV for 0.5 mg l −1 Cu 2.2%, n=6), while for water analysis the organic phase was evaporated and the obtained residue was dissolved in a micro volume (150 μl) of methylene chloride (sample volume 10 ml, calibration 0–40 μg l −1, DL 0.4 μg l −1, CV for 8.0 μg l −1 Cu 4.8%, n=6). The analytical performances of the two procedures were significantly improved as compared with the parameters obtained without IS.