PURPOSE: To accurately measure ionized calcium in a sample such as blood serum by carrying out the enzymic reaction of calcium in the sample in a buffer solution composed of a nitrogen-containing heterocyclic ring-bound sulfonic acid or its salt within a specific pK range.
CONSTITUTION: A phospholipase (e.g. phospholipase D) is added to react with a sample such as blood serum in a buffer solution composed of a nitrogen- containing heterocyclic ring-bound sulfonic acid or its salt {e.g. N-2- hydroxyethylpiperazine-N'-2-ethanesulfonic acid [HEPES]} having a pK within the range of 6.6-7.6. Furthermore, 4-aminoantipyrine, acetylphosphatidyl-choline, a choline oxidase and a peroxidase are added thereto to develop a color. The extent of the developed color is then obtained by measuring the absorbance at 555nm using a spectrophotometer and the concentration is determined from a calibration curve prepared by using the standard sample. Thereby, ionized calcium in the sample can accurately be measured.
MIIKE AKIRA
KASHIWABARA NORIHIKO
UMEMOTO ATSUSHI
SEIBUTSU KAGAKU KENKYU KAIHATS