Cold-vapour atomic absorption spectrometry underestimates total mercury in blood and urine compared to inductively-coupled plasma mass spectrometry: an important factor for determining mercury reference intervals

Summary Aim In recent years, the application of inductively-coupled plasma mass spectrometry (ICP-MS) has been used increasingly in clinical laboratories for the measurement of various trace elements and heavy metals. However, full evaluation of this technique has not been conducted to ensure the transfer of comparable results from conventional cold-vapour atomic absorption spectrophotometry (CVAAS) for blood and urine total mercury (Hg) analysis. Methods A total of 131 blood and 223 urine samples from both patients and normal healthy subjects were collected from a university-based trace element laboratory and a population survey of healthy school adolescents. Correlation study was conducted for total Hg concentration measured by the traditional on-line digestion with flow injection CVAAS and the newly installed ICP-MS. Reference materials were used for method validation and quality control. Standard addition of fixed amounts of inorganic and methyl Hg standards into blood and urine were performed for recovery study. Bias in total Hg measurement was investigated by re-calibrating both instruments using methyl Hg standards. Results The intra- and inter-assay coefficients of variation in the ICP-MS were r  = 0.84, p r  = 0.93, p Conclusions Analysis of total Hg was underestimated at about 69% in blood and 14% in urine using the traditional CVAAS method compared to ICP-MS, plausibly due to incomplete oxidation and reduction of methyl Hg species in CVAAS method. The normal limit of blood total Hg concentration has been targeted at in vivo proportion of methyl Hg of individuals mainly depends on the dietary intake of seafood. Therefore, for clinical laboratories preparing to change over to ICP-MS method for total Hg analysis, the local reference interval for blood total Hg should be re-determined using a non-occupationally exposed population. Otherwise, over-diagnosis of Hg intoxication can result. We have found that by using ICP-MS for total Hg analysis, the local reference range in blood was