Determination Of Serum Sodium By Inductively Coupled Plasma Mass Spectrometry

Sodium is an important metal ion in human body,which plays a pivotal role in the regulation of osmotic pressure and the distribution of water within the extra-cellular fluid compartments of the body.Several analytical techniques have been employed for the determination of sodium in blood serum.In routine use for clinical diagnostics,the most commonly used techniques are potentiometry using ion selective elective eletrodes(ISE), enzymatic spectrophotometry,dry chemistry and flame atomic emission spectrometry(FAES). These methods offer rapid sample throughput,the capability for total automation and simplicity of use.But the calibration and nonspecificity problems lead to great variation between methods.There is a need for critically evaluated reference measurement procedure for serum sodium.Isotope dilution inductively coupled plasma mass spectrometry(ID/ICP-MS) method is a definitive,approach with high accuracy and precision.Compare to traditional gravimetric primary method,ID/ICP-MS is less time consuming and less technique demanding;and compared with other reference measurement principles,such as FAES and ion chromatography, ID/ICP-MS is more accurate and precise.This work aims to develop a measurement method which is based on the ID/ICP-MS principle and gives the required accuracy and precision for use as a reference method for serum sodium.Due to the fact that sodium is a single isotope element,aluminum was selected as surrogate isotope internal standard of sodium and spiked gravimetrically into undiluted serum samples and two levels of sodium standard solutions.The serum samples are digested by purified HNO₃ and diluted with 2%HNO₃.The ²³Na/²⁷Al isotope ratios of the calibrators and the samples were measured by ICP-MS,the sodium concentrations were quantified with a bracketing calibration.The analytical precision is 0.04%and 0.06%respectively for 2 different serum samples, and recoveries is 99.88%,100.17%,99.89%and 100.01%respectively for 4 different serum samples.The results of measuring sodium in serum of Standard Reference Material(SRM) gave the coefficients of variation(CVs) of 0.13%and 0.12%for 2 levels of 909b and 0.28%, 0.29%and 0.27%for 3 levels of 956b during 3 days 15 measurements.The results is agree with the certified value and the CV is +0,17%and +0.14%for 909b and -0.09%,-1.05%, -0.48%for 956b respectively.In conclusion,an ICP-MS method for the measurement of serum sodium has been established.The method is simple,precise and accurate,and maybe used as reference method for serum sodium.