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络合竞争光度法用于生物体液中含钙量的测定已有报导,但这些方法中都未涉及到Mg(Ⅱ)等离子共存时所产生的干扰问题。本文选用与钙、镁生成的络合物稳定性差别较大的EGTA(乙二醇二乙醚二胺四乙酸)与锌配制成络合竞争剂,使钙与锌络合竞争,其反应式为:Ca~(2+)+Zn(Ⅱ)-EGTA(?)Ca(Ⅱ)-EGTA+Zn(Ⅱ)然后以PAN(1-[2-吡啶偶氮]-2-萘酚)为显色剂,以吸光度法进行研究。通过实验选定体系显色酸度为pH6.1,波长516nm,钙量在12—120微克/25毫升范围符合比尔定律。铁(Ⅲ)、镁(Ⅱ)、硫酸根、磷酸根存在量分别为64,40,17,10微克时无干扰。
Complexometric competition spectrophotometry for the determination of calcium in biological fluids has been reported, but none of these methods involve the interference caused by the coexistence of Mg (II) ions. In this paper, EGTA (ethylene glycol diethylenediaminetetraacetic acid), which has a great difference in the stability of complexes formed with calcium and magnesium, is formulated into a complexing competition agent with zinc to compete with zinc complexation. The reaction formula is Ca (Ⅱ) -EGTA + Zn (Ⅱ) was then visualized by PAN (1- [2-pyridylazo] -2-naphthol) Agent, to study the absorbance method. Through the experimental system selected color pH6.1, wavelength 516nm, calcium content in the 12-120 micrograms / 25 ml range in line with Bill’s law. Iron (Ⅲ), magnesium (Ⅱ), sulfate, phosphate present at 64, 40, 17, 10 micrograms without interference.