Determination of sodium in blood serum by inductively coupled plasma mass spectrometry

Abstract

Owing to its importance as a serum electrolyte, sodium is determined routinely in clinical laboratories. In the United States, the accuracy of these measurements is assessed through a number of proficiency testing programs. Clinical measurements are supported by the National Institute of Standards and Technology through the production of serum matrix Standard Reference Materials 1 (909 and 956 series). For reference material certification, a gravimetric primary method has traditionally been used, but this method is time consuming. In this work, an alternative method has been developed in which sodium is determined by inductively coupled plasma mass spectrometry (ICP-MS) using a procedure, which is a cross between internal standardization and isotope dilution analysis. Diluted serum is spiked with 26 Mg enriched isotope and the isotope ratio 23 Na/ 26 Mg measured in analog detection mode. The ratios are standardized by measuring a sodium primary standard (SRM 919a) spiked with 26 Mg. As a relatively high concentration of sodium is measured, the sodium background from the ICP-MS instrument is comparatively small. The method has been successfully applied to the determination of sodium in SRM 909b (Human Serum), SRM 956a (Electrolytes in Frozen Human Serum) and serum pools from the College of American Pathologists.

Atomic spectrometry update. Clinical and biological materials, foods and beverages

“…Samples were digested with methanolic KOH, derivatised with sodium tetrapropyl bromate and adsorbed onto a polydimethylsiloxane coated capillary fibre for determination by GC-ICP-MS. Isotope dilution measurements with a laboratory synthesised methylmercury enriched with 198 Hg gave a three-to four-fold improvement in precision compared with standard additions calibration. An LOD of 37 ng g 21 was reported and results from analysis of DOLT-2 and DORM-2 CRMs were in good agreement with certified values.…”

“…Detection was by ICP-MS. Reverse spike ID analysis was performed to determine the accurate concentration of an in-house synthesized 198 Hg-enriched monomethylmercury spike using two natural abundance methylmercury standards. The precision of determination using ID was nearly 4-fold better than using the method of standard additions.…”

“…A high accuracy procedure involving solid phase microextraction, GC separation and ID-ICP-MS was developed for the certification of a fish RM for methylmercury. 121 The RM had been prepared using methylmercury spiked with 198 Hg. The method had an LOD of 2.1 ng g 21 and, at a concentration of 1.54 mg g 21 , the SD was 0.025 mg g 21 .…”

An improved reference method for serum cations measurement by ion chromatography

“…According to the list of reference measurement methods/procedures for electrolytes from Joint Committee for Traceability in Laboratory Medicine (JCLTM), the traditional reference methods were flame atomic emission spectrometry (FAES) for serum sodium and potassium and flame atomic absorption spectrometry (FAAS) for magnesium and calcium, respectively. The primary measurement procedures for sodium, potassium, magnesium, and calcium were inductively coupled plasma mass spectrometry (ICP‐MS) . However, those methods were normally very elaborate and time‐consuming and not suitable for every metrological task.…”

“…The primary measurement procedures for sodium, potassium, magnesium, and calcium were inductively coupled plasma mass spectrometry (ICP-MS). [9][10][11][12] However, those methods were normally very elaborate and timeconsuming and not suitable for every metrological task. Thienpont et al 13 first reported that the ion chromatography could be recommended as reference method for the determination of serum cations in clinical chemistry.…”