The determination of nitrate at different absorbance between 220 nm and 275 nm requires a spectrophotometer functional for measurement at wave-length below 300 nm, which function some spectrophotometer does not have. For Spectrophotometeric determination at larger wave-length like 540nm or 420nm, reduction-based method reduces nitrate to nitrite for azo dye colormetric reaction, which requires different reductase chemicals. The hydrazine sulfate method requires multiple steps and it costs plenty of time, and the sodium salycilate method requires drying samples, which also cause inconvenience in sample preparation. Has anyone tried some other easier and faster spectrophotometeric method for nitrate determination?
One reliable method is the one from Cataldo et al. 1975 which can be applied in both oven-dried and freeze-dried samples. It is an easy and not time consuming method.
Cataldo, D.A., Haroon, M., Schrader, L.E., Youngs, V.L., 1975. Rapid colorimetric determination of nitrate in plant tissue by nitration of salicylic acid. Comm. Soil Sci. Plant Anal. 6, 71-80
The diazotization reactions are used because of high sensitivity, suitability for automation, and small likelihood of background absorbance from the sample. There are numerous nitration reactions. They generally produce yellow chromophores which exposes the risk of background interferences from (yellow) plant pigments and reaction products, unless these are destroyed, and the reactions are susceptible to chemical interferences, e.g. from chloride, unless it too is removed. The UV methods require meticulous attention to broad background absorbance.
There are also options to reduce all the way to ammonia that you may find useful because the ammonia can be distilled off and either titrated or measured colorimetrically
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