An integrated on-line method for the preconcentration and simultaneous determination of metsulfuron methyl and chlorsulfuron using oxidized carbon nanotubes and second order fluorescent data

Abstract

Trace amounts of two sulfonylurea herbicides widely used for crops protection, metsulfuron methyl (MSM) and chlorsulfuron (CSF) were simultaneously determined taking into account the different kinetic photodegradation behavior of their photoproducts in alkaline medium. As the analytes are present at trace concentration levels, a preconcentration by sorption on a mini-column packed with oxidized multiwall carbon nanotubes (ox-MWCNTs) at pH 3.0 was performed. The retained analytes were removed from the ox-MWCNTs mini-column with a mixture of ACN contained 10% (v/v) of NaOH pH 12.5. A total enrichment factor of 26-fold for a 14.50 mL sample volume was obtained. The eluate was photodegraded by UV radiation during 126 s and the fluorescent spectra corresponding to the analytes photoproducts were registered overtime between 300 and 500 nm. The kinetic second order data were analyzed by unfolded-partial least squares-residual bilinearization (U-PLS/RBL) and multidimensional-partial least squares-residual bilinearization (N-PLS/RBL) algorithms. The relative error of prediction (REP %) for N-PLS/RBL was 7.73% for MSM and 6.37% for CSF. In the case of U-PLS/RBL, this statistical parameter was 7.75% for MSM and 7.23% for CSF, respectively. The limits of detection (LOD) were 0.19 μg L-1 for MSM and 1.14 μg L-1 for CSF using N-PLS/RBL and 0.21 μg L-1 for MSM and 1.03 μg L-1 for CSF when U-PLS/RBL was applied. The entire procedure was performed in an on-line integrated fully automated flow system coupled to a low mercury UV lamp (15 W, 254 nm) and a spectrofluorometer. In this manner, the preconcentration, photodegradation and detection steps were performed in a reproducible way. After optimization, the method was successfully applied to the analysis of real water samples obtained in the south part of Buenos Aires province and used for irrigation and consumption.