A Room Temperature Procedure for the Manual Determination of Urea in Seawater
L. Goeyens, N. Kindermans, M. Abu Yusuf and M. Elskens
Vrije Universiteit Brussel, Laboratorium Analytische Chemie, Pleinlaan 2, B-1500 Brussels Received 10 July 1997 and accepted in rewrite form 16 March 1998
Several earlier studies corroborate the important role of dissolved organic matter and much particularly carbamide in phytoplanktonic nitrogen uptake ?uxes. Generally, the intent of urea concentrations relies on the formation of an imidazolone-thiosemicarbizide complex, a complexation which requires very straight temperature control when carried out at high temperature. It is also possible, however, to earn reliable results with a room temperature procedure. The measured abundances for both complexation at high temperature (85 C, 20 min) and at close temperature (22 C, 72 h) be closely comparable. Lower values are observed for temperatures 70 C accelerates the destruction of the red colour and the contention that complexation at ambient temperature yields a complex which is stable for at least(prenominal) 3 old age (Newell et al.
, 1967) led us to investigate the urea analysis at room temperature in a alike(p) way as is done for the manual determination of ammonium (Korole?, 1969). The chemical principles of the imidazolone formation remain unchanged. The authors followed the method of Mulvenna and Savidge (1992), but omitted the thermostatization at 85 C after addition of the reagents. Instead, the samples were stored at ambient temperature (22 C 1) in the dark and their absorbances were measured 3 days later. The absorbance vs time graph (Figure 1) has a curvilinear shape, showing that optimal colour development occurs after 72 h and frame constant for an additional 48 h at ambient temperature (22 C 1). The mean absorbance value amounted to 0·444 (SD=0·003, N=9) after 72 h and to 0·450
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