Column preconcentration analysis-spectrophotometric determination of nitrate and nitrite by a diazotization-coupling reaction

Composite diazotization-coupling reagents containing sulfanilic acid (SA) as the diazotisable aromatic amine and sodium 1-naphthol-4-sulfonate (NS), 1-naphthol or phenol as the coupling agent were used for the spectrophotometric determination of trace amounts of nitrate and nitrite, Column preconcentration on a naphthalene-tetradecyldimethylbenzylammonium (TDBA)-iodide (I) or biphenyl-trioctylmethylammonium chloride (TOMA)-bromate (BrO3) adsorbent was used, Nitrate was determined by use of a Cd-Cu column which concerts nitrate into nitrite, Nitrite ion reacted with SA in the pH range 2.1-2.8 for the SA-NS system, 2.0-2.75 for the SA-1-naphthol system and 2.2-2.6 for the SA-phenol system in hydrochloric acid medium to form water-soluble, colourless diazonium cations, These cations were coupled with NS in the pH range 10.0-13.0, 1-naphthol in the pH range 1.6-4.6 and phenol in the pH range 9.05-13.0 to be retained on naphthalene-TDBA-I for SA-NS and SA-1-naphthol and on biphenyl-TOMA-BrO3 for SA-phenol. The solid mass was dissolved from the column with 5 ml of the final dimethylformamide (DMF) solution and the absorbance was measured with a spectrophotometer at 526 nm for SA-NS, 418 nm for SA-1-naphthol and 480 nm for SA-phenol, The calibration curves were linear over the concentration ranges 0.14-2.86 x 10(-6) mol l(-1) NO2-N and 0.11-2.14 x 10(-6) mol l(-1) NO3-N for SA-NS, 0.71-18.86 x 10(-6) mol l(-1) NO2-N and 0.54-14.00 x 10(-6) mol l(-1) NO3-N for SA-1-naphthol and 0.21-7.21 x 10(-6) mol l(-1) NO2-N and 0.16-5.36 x 10(-6) mol l(-1) NO3-N for SA-phenol in aqueous samples, The molar absorptivity decreased in the order SA-NS > SA-phenol > SA-1-naphthol. In SA-NS, an unexpectedly high sensitivity was obtained because of the increased molar absorptivity in adsorption-DMF (9.75 x 10(4) l mol(-1) cm(-1), lambda(max) = 526 nm), approximately five times larger than that in water (1.82 x 10(4) l mol(-1) cm(-1), lambda(max) = 492 nm). The concentration factor decreased in the order SA-phenol > SA-NS > SA-1-naphthol, Interferences by various foreign ions were studied and the method was applied to the determination of low levels of nitrite and nitrate in water samples.