A ROOM-TEMPERATURE PROCEDURE FOR THE MANUAL DETERMINATION OF UREA IN SEAWATER

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