Thin-layer chromatographic determination of furosemide and 4-chloro-5-sulfamoyl anthranilic acid in plasma and urine

A method is described for the assay of furosemide based on thin-layer chromatography and measurement of fluorescence directly on the plates. Conditions are specified for stabilizing fluorescence over the time of measurement. As little as 10 ng can be accurately measured and fluorescence is linear up to 160 ng. The metabolite or decomposition product 4-chloro-5-sulfamoyl anthranilic acid is well separated and measured quantitatively in the procedure. Application of the method to human plasma and urine is demonstrated.