title: Development of a new measurement method for serum calcium with chlorophosphonazo-III.
abstract: 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 Mg(2+), Fe(2+), Cu(2+) and Zn(2+). 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 4 degrees C without daily calibration.
  
  
  CONCLUSIONS
  The new calcium measurement method in serum was demonstrated to have reliable and acceptable performances as a routine test in clinical laboratory.
authors.affiliation: Department of Health Sciences, Division of Biological Science and Technology, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. hokazono@shs.kyushu-u.ac.jp
authors.forename: Eisaku
authors.initials: E
authors.lastname: Hokazono
authors.forename: Susumu
authors.initials: S
authors.lastname: Osawa
authors.forename: Tomota
authors.initials: T
authors.lastname: Nakano
authors.forename: Yukari
authors.initials: Y
authors.lastname: Kawamoto
authors.forename: Yuji
authors.initials: Y
authors.lastname: Oguchi
authors.forename: Taeko
authors.initials: T
authors.lastname: Hotta
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Kayamori
authors.forename: Dongchon
authors.initials: D
authors.lastname: Kang
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Cho
authors.forename: Kiyoko
authors.initials: K
authors.lastname: Shiba
authors.forename: Kenji
authors.initials: K
authors.lastname: Sato
mesh_terms: D002118:Calcium / Q000097:blood* / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D006801:Humans; D007202:Indicators and Reagents / Q000737:chemistry*; D015394:Molecular Structure; D013054:Spectrophotometry, Atomic
chemical_list: D002614:Chelating Agents; D007202:Indicators and Reagents; D002118:Calcium