An accurate, precise, simple, and efficient spectrophotometric method has been developed for the determination of nitrate concentrations in natural waters by using premixed vanadium and the Griess reagents. We have systematically reassessed and optimized several key parameters influencing nitrate to nitrite reduction and pink azo dye formation, which include the order of reagent addition, reagent concentrations, heating temperatures, and cooling procedures. Samples added with the premixed reagents are heated gradually in a 50 °C water bath for 25−30 min followed by a quick cooling step to fix the final yield. Both nitrite and nitrate produce a stable and equal molar absorptivity of ∼50000 M −1 cm −1 under the optimized condition, without showing a significant salt effect. With a detection limit of 0.2 μM and a precision of 1% (relative standard deviation) for nitrate at 5−50 μM, this simple and reliable protocol provides an alternative to the traditional Cd−Cu reduction method for routine nitrate analysis in natural waters and other aqueous samples.
Abstract:The mass transfer and reaction kinetics of sulfuryl fluoride (SO 2 F 2 ) absorption with aqueous sodium hydroxide (NaOH) solutions were studied in an experimental double-stirred cell. Results showed that SO 2 F 2 absorption with NaOH was followed by a reaction model employing a fast pseudo-first-order. The second-order rate constant for SO 2 F 2 absorption with aqueous NaOH solutions was determined to be 1.44 m 3 /(mol·s) at 298 K. Three models were used in this chemical absorption process, and in each case, the same expression of enhancement factor was obtained. A comparison was made between the experimental enhancement factor and the value calculated from the model, and the maximum relative deviation was less than 4.2%. The proposed model expression gave a reasonable fit with the experimental values, indicating that mass transfer correlations are valid for scaling up design.
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