Determination of Abundances of Fifty-Two Elements in Natural Waters by ICP-MS with Freeze-Drying Pre-concentration

To precisely determine the abundances of fifty-two elements found within natural water samples, with mass fractions down to fg g⁻¹ level, we have developed a method which combines freeze-drying pre-concentration (FDC) and isotope dilution internal standardisation (ID-IS). By sublimation of H₂O, the sample solution was reduced to < 1/50 of the original volume. To determine element abundance with accuracy better than 10%, we found that for solutions being analysed by mass spectrometry the HNO₃ concentration should be > 0.3 mol l⁻¹ to avoid hydrolysis. Matrix-affected signal suppression was not significant for the solutions with NaCl concentrations lower than 0.2 and 0.1 cg g⁻¹ for quadrupole ICP-MS and sector field ICP-MS, respectively. The recovery yields of elements after FDC were 97–105%. The detection limits for the sample solutions prepared by FDC were ≤ 10 pg g⁻¹, except for Na, K and Ca. Blanks prepared using FDC were at pg-levels, except for eleven elements (Na, Mg, Al, P, Ca, Mn, Fe, Co, Ni, Cu and Zn). The abundances of fifty-two elements in bottled drinking water were determined from five different geological sources with mass fractions ranging from the fg g⁻¹ to μg g⁻¹ level with high accuracy.