Methods of Determination

Abstract

The various electrolytes can be measured by means of electrochemical or spectroscopic methods (Tab. 40). The methods used for determining electrolytes in serum and plasma cannot be used directly for urine because, amongst other things,

• differing concentrations are present

• the ratios of the electrolyte concentrations to each other differ and fluctuate markedly (e.g. sodium and potassium)

• the electrolyte may be present as a poorly soluble salt (e.g. calcium and phosphate)

• interfering factors may exist in other concentration ranges.

This means that, when using the same technique, other calibrators (sodium, potassium determinations) or pretreatment of the sample (calcium and phosphate determinations) may be necessary for urine.