Ultrafiltration-light absorption spectrophotometric determination of silicon in blood

Abstract

An ultrafiltration-light absorption spectrometric method for soluble molybdate-reactive silicon was assessed and applied to bovine and ovine blood plasma and sera, giving precise analytical results. Interfering protein above molecular weight 10,000–25,000 was removed by ultrafiltration, and silicon in ultrafiltrates was quantitated by measuring light absorption at 810 nm of the 1,2,4-aminonaphthol sulfonic acid/ascorbic acid-reduced silicomolybdate. Chemical interferences on the color-forming reaction of remaining blood components were tested by measuring recoveries of silicon added to real blood plasma samples and to synthetic blood plasma solutions, the latter containing typical levels of the major ions Na +, K +, Ca 2+, HCO 3 −, and Cl −, together with varying quantities of the potential interferants (amount per analytical reaction): phosphate (0–0.5 mg P), ferric ion (0–3 mg), fluoride (0–1.25 mg), vanadate (0–0.5 mg V), arsenate (0–10 μg As), and germanate (0–0.5 μg Ge). The mean recovery of added 0.8–9 μg silicon/g of bovine and ovine plasma was 97.7% (SE = 1.0, n = 17); the mean recovery of 1 and 5 μg silicon from synthetic blood plasma solutions with interferant levels up to 50-fold that in normal plasma was 99.2% (SE = 0.3, n = 47). Silicon concentrations found in bovine and ovine blood plasma and sera were typically around 7 μg/ml with procedural reagent blanks consistently low at a mean of 0.12 μg/test (SD = 0.011, n = 20). The silicon level in Center for Disease Control bovine serum (reference specimen Lot R-2274) was found to be (mean ± SE, n = 10) 1.147 ± 0.013 μg/g or 1.172 ± 0.013 μg/ml (25°C). The method detectivity (detection limit) was estimated at 0.03 μg.