Separation and quantitative analysis of furosemide and 4-chloro-5-sulfamoylanthranilic adid (CSA) by high pressure liquid chromatography.

After extraction by ether from acidified plasma or urine and concentration into basic phosphate buffer, furosemide and 4-chloro-5-sulfamoylanthranilic acid (CSA) were separated on a high pressure liquid ion-exchange system and measured fluorometrically. Sensitivity is 0.2 mug/ml of ether compound in plasma and 0.1 mug/ml in urine with an 8% coefficient of variation. Interference by porphyrins in urine was eliminated by subtracting a second fluorometric measurement at a different wave-length from that used for furosemide. No quenching at this wave-length is seen with concentrations of furosemide up to 50 mug/ml. Standard curves of furosemide and CSA are linear from 0.2 mug/ml to 50 mug/ml.