Determination of sodium, potassium, magnesium and calcium in urine by inductively coupled plasma atomic emission spectrometry. The study of matrix effects

The complex matrix (of different concentrations) effect in the ICP-AES dete rmination of sodium, potassium, magnesium and calcium was studied. Interfer ence due to individual components (NaCl, KCl, CaCO3, MgCl2, NH4H2PO4, Hcl, H2SO4 and urea) and their concentration levels were evaluated. The develope d method was used as a significant part of an automated complex method for the analysis of trace and matrix elements in urine. Easily ionised elements (sodium, potassium) were determined reliably and directly without any samp le preparation. Sample dilution was not used because it affected the trace element determination due to their low concentrations and the available det ection limits. Suppression of up to 15% of the calcium and magnesium conten t was found due to the main inorganic components Of urine. This effect was overcome by internal standardisation and a matrix-matching technique. The o rganic components of urine had no significant effect. Concentration levels of Na and K ranged from 100 to 3000 in l(-1), Ca from 10 to 300 mg l(-1) an d Mg from 10 to 200 mg l(-1). Precision (RSD) was less than 1% for internal standardisation and less than 2% for direct estimation. Accuracy was evalu ated with a urine control material, Seronom(TM) Trace Element Urine, lot 40 3125 (Nycomed Pharma).