Fast kinetic determination of 1-naphthylacetic acid in commercial formulations, soils, and fruit samples using stopped-flow phosphorimetry.

Abstract

A kinetic method has been developed for the determination of 1-naphthylacetic acid by means of micellar-stabilized room temperature phosphorescence (MSRTP) using the stopped-flow mixing technique. The main feature of this system is that it diminishes the time required for the deoxygenation of the micellar medium and for the phosphorescence development. Phosphorescence enhancers such thallium(I) nitrate, sodium dodecyl sulfate (SDS), and sodium sulfite were optimized to obtain maximum sensitivity. The pH was also optimized as it strongly affects the luminescent properties of 1-naphthylacetic acid. A pH of 6.6 was selected as adequate for the phosphorescence development. The kinetic curve of 1-naphthylacetic acid phosphorescence was scanned at lambda(ex) = 278 nm and lambda(em) = 490 nm, and the maximum rate of phosphorescence was taken as the analytical signal. This was obtained by calculating the maximum slope of the curve in an interval of 3.6 s as it provided a good noise-to-signal ratio. This method permitted the determination of 1-naphthylacetic acid throughout a concentration range of 100-1800 ng mL(-1) with high precision (relative standard error = 0.91% and relative standard deviation = 2.30%; 1-naphthylacetic acid concentration = 800 ng mL(-1)). According to the Clayton criterion, the detection limit was 45 ng mL(-1). The same limit resulted in 39.3 ng mL(-1) when the error propagation theory was applied. The applicability of the method was successfully demonstrated by determining 1-naphthylacetic acid in different kind of samples, such as phytosanitary products, soils, pears, and apples. Recovery values not significantly different from the nominal content or the spiked amount were found for these determinations.