Rapid fluorometric estriol determination in pregnancy urine.

curves of precipitation are shown in Figure 1. Ampicillin, carbenicillin, amoxycillin, procaine penicillin, cephalothin, salicylic acid, acetylsalicylic acid, and dexamethasone caused no interference. The presence of methicillin in urine may be differentiated from the turbidity attributable to protein by measuring the absorbance at different intervals during the reaction, such as 0.5 and 5.0 mm. A decreasing absorbance with time indicates that the turbidity is not due to protein, which would show an increase in absorbance with time, reaching an absorbance plateau in approximately 2 to 4 mm. Benzylpenicillin (1 gIL) and cloxacillin (2 g/L) may result in apparent protein concentrations of about 0.3 and 2 gIL, respectively, the curve characteristics being similar to that given by protein. If urine containing either benzylpenicillin or cloxacillin is diluted 10-fold, the curve characteristics remain unchanged, apart from lower absorbance values, while urine containing protein, similarly diluted, shows a characteristic decrease in the slope of the curve, but still reaches an absorbance plateau in 2 to 4 mm. Although these studies were done with a centrifugal analyzer, it clearly is also practicable to apply the principle of measuring absorbance at different time intervals to the manual method. In doing so, it may be possible to differentiate between turbidity owing to the presence of penicillins or other interfering drugs and turbidity owing to protein, by their different precipitation kinetics.