Measurement of extracellular water volume by bromide ion chromatography

Extracellular body water can be determined from plasma bromide dilution. Plasma Br is separated from other anions by ion chromatography and is detected at an ultraviolet wavelength of 210 nm. Plasma proteins are removed by ultrafiltration, and interference by plasma chloride is minimized by dilution and the use of 5 mmol NaCl/L as the eluant. Human plasma samples were spiked with known quantities of Br (between 37.54 and 125.14 mumol/L) and were measured by ion chromatography. The results were reproducible to within 0.72 mumol/L (SD) and differed from the gravimetric values by -1.88 +/- 4.27 mumol/L (mean +/- SD). The difference, however, was not significantly different from 0 (p = 0.19). Extracellular water volumes of 10 newborn minipigs measured by Br dilution by using the chromatographic technique (400 +/- 63 mL/kg) were comparable with literature values reported for premature infants.