Method for measurement of serum copper, zinc and selenium using total reflection X-ray fluorescence spectroscopy on the PICOFOX analyser: Validation and comparison with atomic absorption spectroscopy and inductively coupled plasma mass spectrometry.

Abstract

Total reflection X-ray fluorescence is a comparably new method for the measurement of trace elements in biological samples. Results obtained by total reflection X-ray fluorescence were compared to atomic absorption spectroscopy for Cu and Zn and inductively coupled plasma mass spectrometry for Cu, Zn and Se in patient serum. The total reflection X-ray fluorescence assay was characterized for accuracy; recovery; intra- and inter-assay imprecision (using patients' samples, external quality assurance and quality control materials); limit of blank; limit of detection; linearity; interference and stability of prepared samples. Minimal sample preparation is required for total reflection X-ray fluorescence and simultaneous multi-elemental analysis is possible in clinical samples. There was a small positive bias for Cu and Zn measurements using total reflection X-ray fluorescence compared to atomic absorption spectroscopy and inductively coupled plasma mass spectrometry and a significant negative bias for Se measurements by total reflection X-ray fluorescence relative to inductively coupled plasma mass spectrometry. Recovery, imprecision and linearity were acceptable. The limit of detection was shown to be 1.2  μmol/L for serum Cu, 1.8  μmol/L for serum Zn and 0.2  μmol/L for serum Se. Measurement of Cu and Zn in serum samples using total reflection X-ray fluorescence would be a viable alternative to atomic absorption spectroscopy or inductively coupled plasma mass spectrometry. The volatility of some Se compounds results in lower Se results being reported using total reflection X-ray fluorescence and further work would be necessary to identify whether total reflection X-ray fluorescence has an acceptable clinical sensitivity and specificity for the assessment of Se deficiency. Measurement of copper, zinc and selenium on whole blood samples is possible using total reflection X-ray fluorescence which may provide a more accurate assessment of trace element deficiency for patients with an acute phase response.