Development of a new measurement method for serum calcium with chlorophosphonazo-III

Eisaku Hokazono, Susumu Osawa, Tomota Nakano, Yukari Kawamoto, Yuji Oguchi, Taeko Hotta, Yuzo Kayamori, Dongchon Kang, Yuichiro Cho, Kiyoko Shiba, Kenji Sato

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11 Citations (Scopus)


Background: Although serum calcium has been measured using the o-cresolphthalein complexone (oCPC) method in the clinical laboratory, this method still has some problems regarding linearity and reagent stability. We developed a new measurement procedure using chlorophosphonazo-III (CPZ-III: 2,7-bis (4-chloro-2-phosphonophenylazo) -1,8- dihydroxy-3, 6- naphthalenedisulphonic acid, disodium salt) as a chelator with an acid medium for serum calcium measurement. The present method showed better linearity and reagent stability compared with the oCPC method. Methods: Characteristics were studied in optimized conditions measuring wavelength by absorption spectra analysis, and interference of protein and metals with Mg2+, Fe 2+, Cu2+ and Zn2+. The method was applied to an automated analyser (7170; Hitachi High Technologies Corp). The measurement performance was evaluated for accuracy, precision, recovery rate, linearity and reagent stability with a comparison study against atomic absorption spectrophotometry (AAS). Results: The within-run and between-run variations (coefficient of variation [CV]) were 0.92-1.01% and 0.75-1.43%, respectively. The linearity was 0-7.0 mmol/L. The comparison study obtained y = 1.002x (AAS) - 0.10, Sy/x = 0.18 mmol/L, n = 50. Reagent stability was at least 20 d at 48C without daily calibration. Conclusion: The new calcium measurement method in serum was demonstrated to have reliable and acceptable performances as a routine test in clinical laboratory.

Original languageEnglish
Pages (from-to)296-301
Number of pages6
JournalAnnals of Clinical Biochemistry
Issue number4
Publication statusPublished - Jul 2009

All Science Journal Classification (ASJC) codes

  • Clinical Biochemistry


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