Reference measurement procedure for the determination of electrolytes in human blood via ICP-OES measurement

The determination of electrolytes in human body fluids is one of the most frequently performed analyses in clinical routine laboratories. Metrological traceability of measurement results in patient samples is essential and requires the involvement of higher order reference measurement procedures wherever available. Here, the authors present the evaluation of a higher order reference system for the simultaneous determination of K+, Li+, Na+, Ca2+ and Mg2+ in blood serum and plasma. In the same order, the determined measurement performances were as follows: measurement ranges: 0.75 mmol l−1-75.0 mmol l−1, 0.05 mmol l−1-5.00 mmol l−1, 5 mmol l−1-200 mmol l−1, 0.4 mmol l−1-8.0 mmol l−1 and 0.1 mmol l−1-4.0 mmol l−1. Measurement imprecision: CVs were 1.1% for intra assay investigations and 1.8% for long term inter assay investigations for all measurands. Excellent accuracy was found testing certified Standard Reference Materials from NIST: SRM 909 (deviations from 0.0% to 1.1%) and SRM 956 (deviations from 0.0% to 1.5%). Intercomparisons with the German Metrology Institute (PTB) revealed differences from 0.1% to 0.8%. Matrix influences and carry over were not detectable. The expanded combined measurement uncertainties for the determination of the reference method values were estimated as 1.5% (k = 2) for each measurand. The reference measurement procedure is accredited by the German accreditation body (DAkkS) in association with the German calibration service (DKD) according to ISO 17025 and ISO 15195. Services comprise the certification of calibrators, control materials and samples used in proficiency testing schemes.