FLOW-INJECTION ANALYSIS OF UREA NITROGEN IN SOIL EXTRACTS

Flow injection analysis (FIA) is a relatively new technique with advantages over traditional automated analysis methods in precision and sample throughout. A new procedure has been developed to measure urea in soil extracts using automated FIA. This procedure utilizes the diacetyl monoxime thiosemicarbazide colorimetric method, with a modified acid reagent that increases the rate of color formation and improves the mixing of sample with reagent in narrow-diameter (0.8-mm) tubing. Sixty samples can be analyzed per hour, with a detection limit of 0.01 mg urea-N L-1. Residence time between sample injection and maximum absorbance is 130 s.