SPECTROPHOTOMETRIC DETERMINATION OF NITRITE IN ENVIRONMENTAL WATERS USING COLUMN PRECONCENTRATION ON BIPHENYL

Column preconcentration methods have been established for the spectrop hotometric determination of trace nitrite with sulfanilic acid (SA) or p-aminoacetophenone (AAP) as the diazotizable aromatic amine and N,N- dimethylaniline (DMA) or 1-aminonaphthalene (AN) as the coupling agent , using different ion-pairs co-precipitated with biphenyl. Nitrite ion reacts with SA in the pH range 2.0-3.0 and AAP in the pH range 1.7-3. 0 in HCl medium to form water-soluble colourless diazonium cations. Th ese cations are subsequently coupled with DMA in the pH range 3.7-6.1 for the SA-DMA system and AN in the pH range 1.7-2.3 for the AAP-AN sy stem to be retained on microcrystalline biphenyl packed in a column. T he solid mass is dissolved out from the column with 5 ml of DMF and th e absorbance is measured by a spectrophotometer at 420 nm for the SA-D MA system and at 517 nm for the AAP-AN system. The calibration was lin ear over the concentration ranges 0.3-6.0 mu g of nitrite in 5 ml of D MF solution (i.e., 0.02-0.40 mu g/ml in the sample solution) for the S A-DMA system and 0.5-7.0 mu g of nitrite in 5 ml of DMF solution (i.e. , 0.03-0.47 mu g/ml in the sample solution) for the AAP-AN system. The molar absorptivity and Sandell's sensitivity were respectively 2.63 x 10(4) l mol(-1) cm(-1) and 1.75 x 10(-3) mu g cm(-2) for SA-DMA and 3 .28 x 10(4) l mol(-1) cm(-1) and 1.40 x 10(-3) mu g cm(-2) for AAP-AN. The concentration factors were 4 and 16 for SA-DMA and AAP-AN, respec tively. The detection limits were 0.0138 and 0.0175 mu g/ml NO; for SA -DMA and AAP-AN, respectively. Seven replicate determinations of a sol ution containing 3.5 mu g of nitrite gave mean absorbances of 0.410 an d 0.500 with relative standard deviations of 0.51 and 0.55% for SA-DMA and AAP-AN, respectively. Interference from various foreign ions has been studied and the methods have been applied to the determination of nitrite in environmental samples.