Determination of B in body fluids by isotope dilution inductively coupled mass spectrometry with direct injection nebulization

The determination of B in small volumes of undigested blood plasma and urine by isotope dilution and high efficiency direct injection nebulization (DIN) inductively coupled plasma mass spectrometry (ICP-MS) is proposed. The C interference over ¹¹B was removed by precipitating the samples proteins. Samples aliquots of 1 ml were spiked with an enriched ¹⁰B solution and shaken during 1 h to attain the isotopic equilibrium. Thereafter, the sample proteins were denaturated with nitric acid and the supernatant was analyzed. This procedure was effective to reduce C concentrations in approximately 94%. Sample volumes of 50 μl were introduced into the ICP by the direct injection nebulizer producing transient signals lasting 30 s for B isotopes measurements. Precision of ¹⁰B/¹¹B measurements was characterized by relative standard deviation (RSD) lower than 1%. The instrumental mass discrimination factor was lower than 5%. Total B concentrations from 100 to 135 μg L⁻¹ in plasma and 0.499 to 3.021 mg L⁻¹ in urine samples were found. Reproducibility of triplicate samples was characterized by RSD<2.0% for plasma and lower than 1.3% for urine samples. Limit of detection (3σ) of 0.6 ng ml⁻¹ was calculated from synthetic blood plasma blank. Results of the denatured supernatant and digested plasma and urine samples were comparable at the 95% confidence level.