Fogh-Andersen N, Wimberley P D, Thode J, Siggaard-Andersen O
Clin Chem. 1984 Mar;30(3):433-6.
We compared different sample-handling techniques for measurement of Na+ and K+ with ion-selective electrodes (ISE). Imprecision was less for venous blood (with a minimum of heparin) than for plasma, serum, or capillary blood. The results for K+ were higher for serum than for whole blood, and higher for whole blood than for plasma. The latter difference was apparently due to release of K+ during the analysis. Values were more stable for whole blood stored at 20 degrees C than at 4 degrees C or 37 degrees C. The molality of Na+ in the plasma of mixed whole blood changed by -10.5 mmol/kg per unit change in blood pH. This could be explained by the different H+ buffering capacities of plasma and erythrocyte fluid, because when the pH is changed, the concentration of small anions in erythrocytes changes more than it does in plasma, with a consequent osmotic movement of water across the erythrocyte membrane. When we took into account the residual liquid-junction potential and the mass concentration of water in each of 65 patients' sera, the molality determined for Na+ was 1% lower and that of K+ 3% lower by ISE than by flame photometry--differences that may be related to ionic binding or to a lower molal activity coefficient in serum than in the calibrator.
我们比较了使用离子选择电极（ISE）测量Na⁺和K⁺时不同的样本处理技术。静脉血（添加最少肝素）的不精密度低于血浆、血清或毛细血管血。血清中K⁺的结果高于全血，全血中K⁺的结果高于血浆。后一种差异显然是由于分析过程中K⁺的释放。全血在20℃储存时的值比在4℃或37℃时更稳定。混合全血血浆中Na⁺的质量摩尔浓度随血液pH每单位变化而变化-10.5 mmol/kg。这可以通过血浆和红细胞液不同的H⁺缓冲能力来解释，因为当pH改变时，红细胞中小阴离子的浓度变化比血浆中更大，从而导致水跨红细胞膜的渗透移动。当我们考虑65例患者血清中各自的残余液接电位和水的质量浓度时，ISE测定的Na⁺质量摩尔浓度比火焰光度法低1%，K⁺低3%——这些差异可能与离子结合或血清中比校准液更低的质量活度系数有关。
