Determination of electrolytes in small biological fluid samples using energy dispersive x-ray microanalysis

A technique is reported for the application of the energy dispersive X-ray microanalysis for the simultaneous determination of electrolytes in picoliter samples of biological fluids. The preparation is characterized by the use of thin films as a specimen support. Using this arrangement, the X-rays generated in the support are kept to a minimum. At an acceleration voltage of 25 kV the specimen preparation can be regarded as 'thin', i.e. the intensity of an emitted characteristic radiation is almost uninfluenced by the gross element composition, and, therefore, is only dependent upon the content of elements. Quantification was achieved by comparing the intensities of the characteristic radiations with that of a standard. Electrolyte concentrations of 1 mM can be detected with an accuracy of 0.1 mM SD.