Spectrophotometric Nitrate Determination in Natural Waters by Conversion into 4-Nitroguaiacol

Nitrate determination in natural waters by spectrophotometry was described. Nitrate was converted to 4-nitroguaiacol by nitration of guaiacol (2-methoxyphenol) in concentrated sulfuric acid medium. The UV spectrum of nitro product presents a sensitive and reproducible band toward 329 nm with molar absorption coefficient of 2023 L mol(-1) cm(-1). The method gives a linear calibration curve ranging from 0.2 to 24 mg L-1 of NO3- with a reproducibility (RSD) of 1.07% and a limit of detection of 0.05 mg L-1 of NO3-. The application of paired-t-test between the present method and sodium salicylate method, commonly accepted as reference method for nitrate determination, shows there is no significative difference between them and having the same accuracy and exactitude. The method can be used to determine nitrate in ground and surface waters, using less chemicals and requiring less operating procedure time than those of the reference one.