Sequential Injection Determination of Nitrate in Vegetables by Spectrophotometry with Inline Cadmium Reduction
2007
Oliveira, S.M. | Lopes, T.I.M.S. | Rangel, A.O.S.S.
A sequential injection system for the determination of nitrate (NO3(-)) in vegetables was developed to automate this determination, allowing for substantially reduced reagent consumption and generated waste using low-cost equipment. After extraction with water and filtration, the extracted nitrate is reduced inline to nitrite in a copperized cadmium (Cd) column and determined as nitrite. According to the Griess-Ilosvay reaction, nitrate is diazotized with sulfanilamide and coupled with N-(1-naphtyl)-ethylenediamine dihydrochloride to form a purple-red azo dye monitored at 538 nm. Nitrate can be determined within a range of 1.35-50.0 mg L(-1) of NO3(-) (corresponding to 0.270-10.0 g of NO3(-) per kg of vegetable), with a conversion rate of nitrate to nitrite of 99.1 +/- 0.8%. The results obtained for 15 vegetable extracts compare well with those provided by the classical procedure, with a sampling throughput of 24 determinations per hour and relative standard deviations better than 1.2%.
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