SPECTROPHOTOMETRIC DETERMINATION OF NITRATE AND NITRITE IN WATER AND SOME FRUIT SAMPLES USING COLUMN PRECONCENTRATION

A sensitive analytical method for the simultaneous assay of nitrate an d nitrite in water and some fruit samples is presented. The method is based on nitrite determination using the diazotization-coupling reacti on by column preconcentration and on the reduction of nitrate to nitri te using the Cd-Cu reductor column. Nitrite is diazotized with sulfani lamide (SAM) in the pH range 2.0-5.0, sulfamethizole (SM) in pH 1.8-5. 6 and sulfadimidine (SD) in pH 1.8-4.0 in a hydrochloric acid medium t o form water-soluble colourless diazonium cations. These cations were coupled with sodium 1-naphthol-4-sulfonate (NS) in the pH range 9.0-12 .0 for the SAM-NS system, pH 8.6-12.0 for the SM-NS system and pH 9.4- 12.0 for the SD-NS system to be retained on naphthalene-tetradecyldime thyl-benzylammonium (TDBA)-iodide (I) adsorbent packed in a column. Th e solid mass is dissolved out from the column with 5 ml of dimethylfor mamide (DMF) and the absorbance is measured by a spectrophotometer at 543 nm for SAM-NS, 537 nm for SM-NS and 530 nm for SD-NS. The calibrat ion graph was linear over 30-600 ng NO2-N and 22-450 ng NO2-N in 15 ml of final aqueous solution (i.e. 2-40 ng NO2-N ml(-1) and 1.5-30 ng NO 3-N ml(-1) in aqueous sample) for three systems. The detection limits were 1.4 ng NO2-N ml(-1) and 1.1 ng NO3-N ml(-1) for SAM-NS, 1.2 ng NO 2-N ml(-1) and 0.89 ng NO3-N ml(-1) for SM-NS, 1.0 ng NO2-N ml(-1) and 0.75 ng NO3-N ml(-1) for SD-NS, respectively. The concentration facto r is eight for SAM-NS and SM-NS, and 12 for SD-NS. Interferences from various foreign ions have been examined and the method was successfull y applied to the determination of low levels of nitrate and nitrite in water and some fruit samples. (C) 1998 Elsevier Science B.V. All righ ts reserved.