Liquor Volume by Direct Spectrophotometric Determination of Injected Pah*

Abstract

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.

Rhesus haemolytic disease

“…With regard to the possible effect of amniotic fluid volume upon bilirubin values, a simplified accurate amniotic fluid volume test using a para-aminohippurate (PAH) dilution test, with measurement by spectrophotometry rather than by the diazo reaction, was developed by Thompson et al (1971).…”

Factors Influencing the Measurement of the Lecithin/Sphingomyelin Ratio in Amniotic Fluid

“…Specimens of amniotic fluid are often required for a number of tests. For example, para-amniohippuric acid (PAH) may be introduced into the amniotic cavity for the measurement of the amniotic fluid volume (Thompson et al, 1971) and it would be convenient if the same samples used for this estimation could also be used for the L/S ratio or shake test. The effects of PAH on such measurements are, however, unknown.…”