SPECTROPHOTOMETRIC DETERMINATION OF NITRATE AND NITRITE IN SOIL AND WATER SAMPLES WITH A DIAZOTIZABLE AROMATIC AMINE AND COUPLING AGENT USING COLUMN PRECONCENTRATION ON NAPHTHALENE SUPPORTED WITH ION-PAIR OF TETRADECYLDIMETHYLBENZYLAMMONIUM AND IODIDE

Composite diazotization-coupling reagents containing sulfanilamide (SA M), sulfapyridine (SP) or sulfathiazole (ST) as the diazotizable aroma tic amines and sodium 1-naphthol-4-sulfonate (NS) as the coupling agen t using column preconcentration on lene-tetradecyldimethylbenzylammoni um(TDBA)-iodide adsorbent have been used for the spectrometric determi nation of trace nitrate and nitrite in soil and water samples. Nitrite ion reacts with SAM in the pH range 2.0-5.0, SP in the pH range 2.0-2 .5 and ST in the pH range 2.0-3.3 in HCl medium to form water-soluble colourless diazonium cations. These cations were coupled with NS in th e pH range 9.0-12.0 for the SAM system, 9.6-12.0 for the SP system and 8.5-12.0 for the ST system to be retained on naphthalene-TDBA-I mater ial packed in a column. The solid mass is dissolved from the column wi th 5 mi of dimethylformamide and the absorbance is measured spectromet erically at 543 nm for SAM-NS, 533 nm for SP-NS and 535 nm for ST-NS. Nitrate is reduced to nitrite by a copper-coated cadmium reductor colu mn and the nitrite is then treated with the diazotization-coupling rea gent by column preconcentration. The absorbance due to the sum of nitr ate and nitrite is measured and nitrate is determined by difference. T he calibration graph was linear over the range 2-40 ng NO2--N ml(-1) a nd 1.5-30 ng NO3--N ml(-1) in aqueous samples for the SAM and ST syste ms and 2-48 ng NO2--N ml(-1) and 1.5-36 ng NO3--N ml(-1) in aqueous sa mples for the SP system, respectively. The sensitivity, accuracy and p recision of the systems decreased in the order ST>SAM>SP. The detectio n Limits were 1.4 ng NO2--N ml(-1) and 1.1 ng NO3--N ml(-1) for SAM, 1 .6 ng NO2--N ml(-1) and 1.2 ng NO3--N ml(-1) for SP, and 1.0 ng NO2--N ml(-1) and 0.75 ng NO3--N ml(-1) for ST, respectively. The preconcent ration factors are 8, 5 and 6 for SAM-NS, SP-NS and ST-NS, respectivel y. Interferences from various foreign ions have been studied and the m ethods have been applied to the determination of ng ml(-1) levels of n itrite and nitrate in soil and water samples. The mean recovery was 95 -102% for all three systems.