Analytical Sciences

Micro-Phase Sorbent Extraction for Trace Analysis via in situ Sorbent Formation: Application to the Spectrophotometric Determination of Nitrite in Environmental Waters

Noriko HATA,  Misaki KAWASHIMA, Issei KASAHARA, and Shigeru TAGUCHI

Department of Environmental Biology and Chemistry, Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

A micro-phase sorbent in situ formation from an aqueous solution was proposed for the sensitive spectrophotometric determination of nitrite in environmental waters. Nitrite in a 10 mL sample solution was converted into a cationic azo dye by the reaction with 4-trifluoromethylanilinium ion and N-1-naphthylethylenediammonium ion in an acidic medium. Addition of dodecylbenzenesulfonate ion caused the formation of a suspension of ion associate in the solution. Centrifugation of the solution led to the isolation of a liquid organic phase that extracted the azo dye at the bottom of the centrifuge tube. The volume of the new phase was ca. 5 uL. After the aqueous phase was discarded, the organic phase was dissolved with 1 mL of 2-methoxyethanol to measure the absorbance. Nitrogen as NO₂^- at concentrations from 1.5 to 30 ug L^-1 was determined with sufficient precision. When 0.2 mL of 2-methoxyethanol was applied to dissolve the organic phase, 0.3 - 4.8 ug NO₂^--N L^-1 was determined. The recovery tests for nitrite added to some river water and seawater were satisfactory. This method is very simple and rapid. It takes only 30 min from the dye formation to the measurement of the absorbance.

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