X-ray analysis of biological fluids: an update.

X-ray analysis has been used for some twenty years to quantify elements including Na, K, Cl, Ca, Mg and phosphorous in biological fluid samples. The method consists of accurate pipetting of 50-150 pl samples and appropriate drying to form crystalline deposits. Quantitation is obtained by comparison of x-ray intensities with comparable standard crystalline deposits. Electron microprobe analyses have contributed much to our understanding of renal transport function including physiological controls and pathological influences on the tubular handling of the major elements. New approaches to x-ray analysis of solid tissue will further our knowledge concerning transport properties in the kidney and other tissues.