INDIRECT DETERMINATION OF NITRATE BY ELECTROTHERMAL ATOMIC-ABSORPTIONSPECTROMETRY USING AN ONLINE CADMIUM MICROCOLUMN

The proposed indirect automatic method is based on the reduction of ni trate to nitrite using a cadmium reductant microcolumn where the flow of the sample through the microcolumn oxidizes the metallic cadmium to Cd-II which is measured by electrothermal atomic absorption spectrome try. The automatic system is achieved simply by replacing the sample t ip of the autosampler arm with the reductant microcolumn. This system results in a powerful integrated system which permits fully automated operation, avoiding time-consuming manual work and enhancing the sensi tivity. The manifold was evaluated with respect to accuracy, precision and sensitivity for nitrate determination in water, the detection lim it achieved being 0.05 mu g ml(-1) (3s) with a sampling rate of about 35 h(-1). A 2.3% relative standard deviation was obtained in a repeata bility study (n = 11) at the 0.2 pg ml-l level of nitrate and 2.6% at the 8.0 mu g ml(-1) level. Some ions which commonly occur with nitrate in mater samples, such as Na+, Ca2+ and Mg2+, interfered to a certain extent, although these interferences were minimized by passing of the sample through an Amberlite cation-exchange resin, The method was app lied to samples of bottled and spring waters with good results, The ma trix effects were minimized by using the standard addition method.