Ultrasonic oscillation dialysis-graphite furnace atomic absorption spectrometer method for determination of "free" copper and exchangeable copper in serum.

Background: The determination of copper (Cu) in human blood is important in medical diagnosis. However, its biological activities strongly depend on the chemical forms, and thus data for total Cu concentration is not sufficient for medical diagnosis or mechanism study. Therefore, analyses of copper species in serum have much more physiologically meaningful.

Methods: Ultrasonic oscillation dialysis procedure was introduced in the determination of "free" Cu, more precisely PBS dialysis Cu (DiaCu), and exchangeable Cu (EXCu) by graphite furnace atomic absorption spectrometry (GFAAS). Then the levels of serum "free" Cu and EXCu from hepatitis, liver cancer, and cervical cancer patients were determined.

Results: The accuracy of the method ranged from 92% - 97% for PBS DiaCu and 90% - 107% for EXCu when using a dialysis membrane pore size of 25 kDa. The regression equation of the calibration curve was expressed as y = bChi + a, with linear regression coefficients (r2) of 0.9999 for ultrapure water and 0.9998 for PBS buffer and EDTA buffer. The limit of detection is 0.76 microg/L. Application of this method to serum samples showed that the levels of"free" Cu and EXCu in serum changed in various pathophysiological conditions.

Conclusions: Ultrasonic oscillation dialysis-GFAAS method described here for the speciation of "free" Cu and EXCu in serum is simple with good reproducibility and small sample volume.