With the objective to get new analytical methods for the determination of oxygen in sea water [1] and/or pollutants in the environment water (nitrate, nitrite, etc.) [2], we developed technologies based on fluorimetry with the use of optical fibers. Fluorimetric methods were selected for their great sensitivity and also for their possible remote measurement. Concerning the nitrate determination, the generally required drastic conditions (in the major cases highly acidic media [3]), led us to study an indirect method of nitrate analysis, i.e. reduction to nitrite [see reference 4 for a review].Among the described methods for the nitrite determination, the one using 2,3-diaminonaphthalene (DAN) was chosen ( Fig. 1). The method based on the reaction of nitrite with DAN (slightly fluorescent) which affords 1-[H]-naphthotriazole (highly fluorescent) was first described by Wiersma [5] and later improved by others [6][7][8][9][10] and more particularly by Damiani and Burini [11].The major drawback of the method is the use in a large excess of the reagent DAN, which is a carcinogenic compound. Indeed, in the procedure described by Damiani and Burini, DAN was used exceedingly large if compared to the nitrite concentration to be determined: for the maximal nitrite concentration of 50 µg NO 2 -.L -1 , DAN remaining in solution represented approximatively 60 times the quantity involved in the stoechiometric reaction. In order to diminish the required DAN quantity, it would be of interest to study if a stoechiometric reaction between DAN and nitrite might be still feasible. It is the purpose of the present paper, in which an improvement of the procedure is described.
Experimental section ReagentsSodium nitrite (99 %) was from Merck (D -Darmstadt) and dried at 100 °C before using. 2,3-diaminonaphthalene (97 %) was from Aldrich (St Quentin Fallavier, France). 37 % minimum chlorhydric acid (R.P. Normapur TM ) was from Prolabo (Paris, France) and sodium hydroxide (puriss p.a. > 98 %) from Fluka (St Quentin Fallavier, France). The water used was demineralized.
ApparatusFluorescence measurements were made with a SPEX 1681 Fluorolog spectrofluorimeter equipped with a continuousspectrum Xenon lamp source (450 watt). The excitation wavelength was set at 365 nm and the emission was measured at 405 nm. The fluorescence intensities are only Groupe ENSIC,1, rue Grandville, 54000 Nancy, France Abstract. One of the fluorimetric methods for nitrite determination is based on the reaction of nitrite ions with 2,3-diaminonaphthalene (DAN) to form fluorescent 1-[H]-naphthotriazole. The procedure is sensitive, simple and rapid. However, the DAN reagent is carcinogenic and its use in a large excess for the reaction might be a drawback for an extensive application. In particular to know if a stoechiometric quantity of the reagent might be sufficient to run the reaction, the method was re-examined. In fact, using the latter condition, it was still possible to get nitrite determination in the range 0 to 50 µg NO 2 -.L -1 , with a rather smal...
