Most flow injection analysis methods for the determination of nitrate determination are based on either homogeneous or heterogeneous reduction of nitrate to nitrite and subsequent colorimetric determination of the nitrite by Griess reaction, in which diazotization with sulfanilamide is followed by coupling with N-(1-naphthyl)-ethylenediamine dihydrochloride (NED) to form a pink azo dye [18]. Titanium (III) and hydrazine have been used as soluble reductants for nitrate reduction (c.f. Table 1). Both approaches have limitations: the hydrazine method requires lengthy reaction times for reduction and color development in order to achieve adequate sensitivity [19], while titanium (III) chloride solution is violet and absorbs light in the same range as the pink azo dye [20]. A photo-reduction method has also been reported for nitrate determination in flow injection analysis systems (c.f. Table 1).