Qualitative and quantitative trace-metal analysis in physiological fluids of multiple sclerosis patients by field desorption mass spectrometry

Abstract

Trace metals such as aluminium, barium, cesium, chromium, cobalt, copper, and rubidium have been identified in microlitre samples of urine, serum, and cerebrospinal fluid of patients suffering from multiple selerosis. Quantitative determinations of rubidium in the urine of seven patients were performed and gave an average concentration of 1.20 ± 0.02 mg I −1 (14.0 μmol I −1). As a control, the rubidium levels in the urine of twelve healthy volunteers were determined, averaged and found to be approximately twice as high, namely 2.52 ± 0.07 mg I −1 (29.5 μmol I −1). The time-dependence for the excretion of rubidium in the urine from one patient was established for a period of 24 h and correlated with the renal function. Further, initial values for the concentration of Rb + ions in serum (2.2 μmol I −1) and cerebrospinal fluid (0.15 μmol I −1) could be established. The novel method for trace analysis of metals in microlitre samples of human material using stable-isotope dilution and field desorption mass spectrometry allows direct, fast and reliable estimation of nanogram to picogram amounts of metals. The typical analysis time is 15–20 min and the precision and accuracy obtained within a few tenths of a percent. The sensitivity of the technique for rubidium is extraordinarily high, between 1.1 and 9 × 10 −7 C μg −1. The detection limit for Rb + ions lies below 10 −15 g. A newly developed technique using electrolytical deposition of trace metals such as chromium, manganese, iron, nickel, copper, gallium, silver, gold, thallium and uranium on the emitter surface from a complex, biological matrix showed improvements in sensitivity by a factor of approximately 20.