Determination of silicon in biological fluids using metal carbide-coated graphite tubes

Abstract

A method is described for the determination of silicon in serum and urine at physiological levels using electrothermal atomic absorption spectrometry. Except for a 1 + 3 dilution of serum and 1 + 49 dilution of urine, no other sample pre-treatment was necessary. Interferences arising from the volatilization of silicon have been studied in detail. The use of different carbide-forming elements (including zirconium, tantalum, molybdenum and tungsten) for the treatment of pyrolitic L'vov platforms and graphite tubes has been investigated. Different chemical modifiers have been studied for each metal coating. Comparison of the results obtained proved that amongst the different carbide-forming elements studied, tungsten gave the best results. In aqueous solution, the detection limit (3s), using tungsten coated graphite tubes and platforms, was 3.5 µg l^–1, and a precision of 2.0% for ten replicates on 90 µg l^–1 of Si was observed. The use of chemical modifiers in serum and urine proved to be unnecessary using the proposed method. Results of silicon levels in serum and urine of patients suffering from chronic renal failure are presented. The results obtained did not correlate with the corresponding aluminium concentrations in serum or in urine, except for very high levels of aluminium (i.e., above 100 µg l^–1).