Which laboratory technique is used for the blood sodium analysis in clinical research? A systematic review

Background Circulating sodium is analyzed by flame spectrometry and indirect or direct potentiometry. The differences between estimates returned by the three techniques are often relevant. It is unknown whether peer-reviewed international publications focusing on this parameter provide information about the technique. Objectives of the study were to ascertain if information about the employed technique is provided. Content A search in the National Library of Medicine for articles whose title contains “hyponatr[a]emia” was performed. We restricted the search to clinical reports including 10 or more humans published in the 2013–2015 and 2017–2019 periods. Authors of papers not reporting the technique were contacted to obtain this information. The study design and journal quartile ranking of each article were also evaluated. Summary For the final analysis, we included 361 articles (2013–2015, n=169; 2017–2019, n=192). Information about the laboratory technique was given in 61(17%) articles. Thanks to our inquiry, we collected this information for 116(32%) further reports. Indirect potentiometry was the most frequently used technique, followed by direct potentiometry. Spectrometry was used in a small minority of studies. Study design, journal ranking and study period did not modulate the mentioned frequency. Outlook Most articles focusing on hyponatremia do not provide information on the laboratory technique. This parameter is nowadays analyzed by indirect or, less frequently, direct potentiometry. The figures are similar for high and low impact factor journals and for the 2013–2015 and the 2017–2019 periods. Many authors, reviewers and editors likely assume that the results of this parameter are not influenced by the technique.

Interferences from titanium and zirconium during calcium determination by flame spectrometry

Titration methods based on an inhibition effect were used to investigate the interferences from Ti and Zr in the determination of Ca by atomic absorption and flame emission spectrometry using an air-acetylene flame. Changes either in the absorption or emission signal of Ca were continuously registered on a computer display and characteristic titration curves were obtained. The mole ratios between Ti or Zr and Ca at characteristic points on titration curves were used to explain the quantitative changes occurring in the solution being titrated and aspirated into the flame. In order to investigate procedures for eliminating these interferences, a method of atomic absorption inhibition release titration was used. For this purpose, a solution of La, as a releasing agent with a very low Ca concentration, used as an indicator, was continuously titrated with the solution of Ti as inhibitor. A comparative study of the activity of Ba, Sr and La as releasing agents was investigated during titration of Ca with Zr solution. Based on the calculated mole ratios between Zr and Ba, Sr or La, the effectiveness of these agents in eliminating the interferences was determined. Possible reactions occurring during evaporation of the aerosol in the air-acetylene flame are represented by chemical equations. .