Liquor Volume by Direct Spectrophotometric Determination of Injected Pah*

Summary Sodium aminohippurate (PAH) has largely replaced dyes in dilution techniques for estimating the volume of amniotic fluid. Until recently this method depended on a diazo reaction for the determination of PAH concentration. A simple and more rapid method, depending upon spectrophotometric measurement of the absorption peak of PAH at 272 nm, is now presented. At this wavelength the calibration graph of extinction against concentration of PAH is linear under the conditions described. To eliminate interference from protein absorption a pre‐injection liquor sample is used for the preparation of a blank and a series of standards. All samples are measured at a concentration where solvent cut‐off effects are minimized. Comparison of the results of the direct and the diazo methods showed good agreement.