Comparison of sample preservation methods for clinical trace element analysis by inductively coupled plasma mass spectrometry

The effects of chemical additives and storage temperatures on measurement of 16 trace elements in urine by inductively coupled plasma mass spectrometry (ICP-MS) were evaluated. A 24-hour urine specimen was supplemented with concentrations of the elements. Aliquots containing I of 4 chemical additives were stored at 3 different temperatures in sealed polypropylene containers. Elemental concentrations were determined by ICP-MS for the resulting samples after 1, 2, 8, and 65 days of storage. Initial element concentrations measured within 8 hours of specimen preparation were consistent with expected concentrations (except for aluminum). For most elements, preservation and storage conditions yielded consistent measured concentrations throughout the experiment. Notable exceptions were for aluminum (general rise over time) and mercury (general decrease over time). Adding boric acid and potassium pyrosulfate resulted in sample contamination; elemental contamination was concentration-dependent for both. Although little microbial contamination was observed during the experiment, refrigeration of samples is recommended to curtail bacterial growth in nonsterile specimens. In light of these results, refrigerated urine storage without the use of chemical additives is an effective preservation method for ICP-MS analysis of many trace elements.