Saris N E
Department of Medical Chemistry, University of Helsinki, Finland.
J Clin Chem Clin Biochem. 1988 Feb;26(2):101-4. doi: 10.1515/cclm.1988.26.2.101.
The protein interference with the determination of ionised Ca2+, Na+ and K+ reported in several studies could be due to effects on liquid/liquid junction potentials or on the ion-selective electrodes, but could also be due to Donnan effects during sample preparation, e.g. ultrafiltration or dialysis. The possible interference of protein was studied by subjecting a bovine serum albumin solution, 100 g/l, to gel-filtration in Sephadex G-25 columns equilibrated with 150 mmol/l NaCl, 5 mmol/l KCl, 20 mmol/l MOPS, pH 7.4 and varying concentrations of Ca2+; 0.75 and 1.25 mmol/l. The albumin was dissolved in the basic electrolyte solution and pH adjusted before the gel-filtration. Samples were taken for measurements before, during and after the elution of the protein peak. In this way it was ensured that the activities were not changed by the presence of albumin. Also the temperature, the ionic strength of the electrolyte and the bridge solution were varied. Ca2+, Na+ and K+ activities were measured with the aid of a Kone Microlyte instrument and Ca2+ in addition with the Radiometer ICA-1 instrument or a measuring system consisting of a Philips IS 561-Ca electrode, a Beckman KCl reference electrode connected to the sample chamber via a 2% agarose bridge containing either 0.15 or 2 mol/l KCl, a pH/voltmeter and a voltage-bucking device. No interference by protein was found.
几项研究报道，蛋白质对离子钙、钠和钾测定的干扰可能是由于对液/液接界电位或离子选择性电极有影响，但也可能是由于样品制备过程中的唐南效应，如超滤或透析。通过将100 g/l的牛血清白蛋白溶液在Sephadex G - 25柱中进行凝胶过滤来研究蛋白质可能的干扰，该柱用150 mmol/l氯化钠、5 mmol/l氯化钾、20 mmol/l MOPS、pH 7.4以及不同浓度的钙（0.75和1.25 mmol/l）平衡。在凝胶过滤前，将白蛋白溶解在碱性电解质溶液中并调节pH。在蛋白质峰洗脱前、洗脱过程中和洗脱后取样进行测量。通过这种方式确保了白蛋白的存在不会改变活性。同时还改变了温度、电解质的离子强度和桥接溶液。借助Kone Microlyte仪器测量钙、钠和钾的活性，此外，使用Radiometer ICA - 1仪器或由飞利浦IS 561 - Ca电极、通过含0.15或2 mol/l氯化钾的2%琼脂糖桥连接到样品室的贝克曼氯化钾参比电极、pH/电压表和电压补偿装置组成的测量系统测量钙的活性。未发现蛋白质的干扰。
