A room temperature procedure for the manual determination of urea in seawater

Several earlier studies underpin the important role of dissolved organic matter and more particularly urea in phytoplanktonic nitrogen uptake fluxes. Generally, the determination of urea concentrations relies on the formation of an imidazolone-thiosemicarbizide complex, a complexation which requires very accurate temperature control when carried out at high temperature. It is also possible, however, to obtain reliable results with a room temperature procedure. The measured abundances for both complexation at high temperature (85 degrees C, 20 min) and at ambient temperature (22 degrees C, 72 h) are closely comparable. Lower values are observed for temperatures <10 degrees C though. Moreover, a comparison of both techniques reveals similar precision (coefficient of variation: 2%), sensitivity (slope of calibration line: 0.2) and detection limit (0.14 mM). The room temperature alternative to the earlier described method is therefore a handy tool for urea analyses, when a strict temperature control is difficult or impossible. (C) 1998 Academic Press.