Zoppi F, Guagnellini E, Manzoni A
Clinical Biochemistry and Haematology Laboratory, Niguard a Ca' Granda Hospital, Milan, Italy.
Scand J Clin Lab Invest. 1993 Aug;53(5):521-7. doi: 10.1080/00365519309092549.
In some instruments that measure sodium directly in whole blood, plasma, or serum using ion selective electrodes (direct potentiometry), the higher the ionic strength of the solution, the lower is the sodium recovery in serum, as predicted by theory. The same could be expected for ionized calcium. When measuring the recovery of serum sodium on indirect potentiometric instrument and by flame photometry, which determine concentration in prediluted samples, and on direct potentiometric instruments, we observed that two out of the three direct potentiometry instruments showed a decreased recovery of sodium, as the ionic strength was increased, while on all the other instruments the recovery was complete. No effect of increased ionic strength was noted on the ionized calcium measurements in serum on all the instruments tested. Analysing pure aqueous solutions of sodium and calcium chloride with increased ionic strength on the same instruments, the sodium recovery was always complete or positive, and the same was true for ionized calcium. We postulate some effect of ionic strength on the salt bridge of the measuring systems, which is different when analysing serum or pure aqueous solutions.
在一些使用离子选择电极（直接电位法）直接测量全血、血浆或血清中钠的仪器中，正如理论所预测的那样，溶液的离子强度越高，血清中钠的回收率越低。对于离子钙也可作同样预期。在通过间接电位法仪器和火焰光度法（它们测定预稀释样品中的浓度）以及直接电位法仪器测量血清钠回收率时，我们观察到，随着离子强度增加，三台直接电位法仪器中有两台钠回收率降低，而在所有其他仪器上回收率是完全的。在所有测试仪器上，血清中离子钙测量均未发现离子强度增加有影响。在同一仪器上分析离子强度增加的氯化钠和氯化钙纯水溶液时，钠回收率始终是完全的或呈正值，离子钙也是如此。我们推测离子强度对测量系统的盐桥有某种影响，在分析血清或纯水溶液时这种影响有所不同。
