Burns R F, Russell L J
Contemp Issues Clin Biochem. 1985;2:121-30.
Diluting a sample before analysis, as is required by both flame photometry and indirect reading ISE analysers, gives less relevant analytical results than measuring an undiluted sample directly. This is because dilution masks the impact that protein and lipids exert on the true activity of an ion in a clinical sample. Measuring a sample directly without dilution enables only those ions which are not bound to other materials, e.g. other ions or proteins, to be detected. The levels of these free ions are more likely to reflect true physiological status than analysis of both free and bound ions. Measuring a sample of whole blood directly without dilution can only be performed accurately if the ISE analyser reference junction is unaffected by changes in haematocrit. Calibrant compositions should be of an ionic strength similar to that of physiological samples. Residual liquid junction potentials between calibrants and samples should be minimised by careful design of the reference electrode.
正如火焰光度法和间接读数离子选择性电极（ISE）分析仪所要求的那样，在分析前对样品进行稀释，其分析结果的相关性低于直接测量未稀释的样品。这是因为稀释掩盖了蛋白质和脂质对临床样品中离子真实活性的影响。直接测量未稀释的样品只能检测到那些未与其他物质（如其他离子或蛋白质）结合的离子。与同时分析游离离子和结合离子相比，这些游离离子的水平更有可能反映真实的生理状态。只有当ISE分析仪的参比电极不受血细胞比容变化影响时，才能准确地直接测量未稀释的全血样品。校准液的成分应具有与生理样品相似的离子强度。通过精心设计参比电极，应尽量减少校准液与样品之间的残余液接电位。
