Determination of nitrate in environmental water samples by conversion into nitrophenols and solid phase extraction-spectrophotometry, liquid chromatography or gas chromatography–mass spectrometry

Conversion of nitrate into a nitro-phenol derivative by reaction with 2-methylphenol or 2,6-dimethylphenol allowed at least 100-fold enrichment of the derivative on Lichrolut EN polymeric cartridge, and it is stable for up to 1 month on the cartridge. The derivative could be eluted with ammonia–methanol mixture. This reaction for nitrate determination has permitted a choice of final measurement by UV-Vis spectrophotometry, liquid chromatography or gas chromatography–mass spectrometry when the limits of detection were 10, 6 and 3 (mu)g l^-1, respectively, and the calibration range 20 (mu)g to 10 mg l^-1 nitrate. The method has been validated by spiking natural water samples, when the recovery of nitrate was 98.5–108.4% (relative standard deviation 2.5–6.1%).