Chromatographic Determination of Nanomolar Cyanate Concentrations in Estuarine and Sea Waters by Precolumn Fluorescence Derivatization

Recent studies suggest that cyanate (OCN-) is a potentially important source of reduced nitrogen (N) available to support the growth of aquatic microbes and, thus, may play a role in aquatic N cycling. However, aquatic OCN- distributions have not been previously described because of the lack of a suitable assay for measuring OCN- concentrations in natural waters. Previous methods were designed to quantify OCN- in aqueous samples with much higher reduced N concentrations (micromolar levels) than those likely to be found in natural waters (nanomolar levels). We have developed a method to quantify OCN- in dilute, saline environments. In the method described here, OCN- in aqueous solution reacts with 2-aminobenzoic acid to produce a highly fluorescent derivative, 2,4-quinazolinedione, which is then quantified using high performance liquid chromatography. Derivatization conditions were optimized to simultaneously minimize the reagent blank and maximize 2,4-quinazolinedione formation (>90% reaction yield) in estuarine and seawater matrices. A limit of detection (LOD) of 0.4 nM was achieved with only minor matrix effects. We applied this method to measure OCN- concentrations in estuarine and seawater samples from the Chesapeake Bay and coastal waters from the mid-Atlantic region. OCN- concentrations ranged from 0.9 to 41 nM. We determined that OCN- concentrations were stable in 0.2 mu m filtered seawater samples stored at -80 degrees C for up to nine months.