Establishment of a candidate reference method for serum calcium determination based on inductively coupled plasma mass spectrometry

Abstract

Objective To establish a candidate reference method for serum calcium determination based on inductively coupled plasma mass spectrometry(ICP-MS). Methods Establishment of methodology: serum samples collected from the hospital were diluted 100 times by 0.3% ultrapure nitric acid. Calcium standard solutions with different concentrations were added to serum samples matrix solutions. Serum calcium concentration was calculated according to the standard addition method using germanium (Ge) as internal standard. The linearity, precision, trueness of the performance of the established candidate reference method were evaluated, and a comparison with the reference method was made. Results The linearity was good in serum calcium concentrations from 0.000 mmol/L to 20.400 mmol/L (the concentration after dilution from 0.000 mmol/L to 0.204 mmol/L) (R2>0.999 9);the within-run precision was from 0.22% to 0.47%, and the between-run precision was from 0.64% to 0.77%; the total precision was from 0.98% to 1.09%. The determination results of 3 concentrations of SRM 956d were all in the uncertainty range required bythe certificate. The biases were -0.16%, 0.04% and 0.23%, respectively. The established candidate reference method participated in and passed the 2017 External Quality Assessment Scheme for Reference Laboratories in Laboratory Medicine (RELA) comparison. The results of the established candidate reference method were consistent well with those of the reference method in the Joint Committee for Traceability in Laboratory Medicine (JCTLM) list. There was a good correlation between the established candidate reference method and the clinical routine electrode method. Conclusions The established candidate reference method for serum calcium determination based on ICP-MS is precise, accurate, with wide range of linearity.It is expected to play a role in tracing the quantities of serum calcium in clinical laboratories. Key words: Calcium; Mass spectrometry; Reference standards