Jorge J. Soto-Chinchilla

On-line preconcentration for the determination of aflatoxins in rice samples by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection.

MEKC coupling with LIF detection has been used for the determination of four aflatoxins (B1, B2, G1 and G2). Separations were performed in an uncoated fused‐silica capillary (70 cm×75 μm id, 55 cm effective length), using 20 mM borate buffer with 30 mM SDS (pH 8.5) and 7% ACN. In order to increase sensitivity, an on‐line preconcentration procedure was applied, based on sweeping, using the same separation buffer without SDS as solvent of the sample. The precision of the method was evaluated in terms of repeatability and intermediate precision and the results were acceptable in all cases (RSD<12%). With the on‐line preconcentration LODs (obtained as 3×S/N) were as low as 0.11, 0.52, 0.04 and 0.10 μg/L for G2, G1, B2 and B1, respectively. Recovery studies were developed with extracts of rice samples spiked with aflatoxins, being in the range between 93.0 and 105.4%. The method has also been applied to the determination of aflatoxins in rice samples, and the results compared with those obtained by a standard method, being in good agreement.

Use of highly efficient Draper/Lin small composite designs in the formal optimisation of both operational and chemical crucial variables affecting a FIA-chemiluminescence detection system

A new formal strategy in the multidimensional optimisation of the experimental variables affecting the chemiluminescence (CL) detection in flow injection analysis (FIA) is proposed here. The strategy implies several steps, being the most significant: selection of the variables to be studied and their experimental domain; use of a screening design to detect significant variables and interactions into the experimental region; study of the main effect of variables and second-order interactions; and finally application of a Draper-Lin small composite design (orthogonal) to obtain the optimum values of the significant variables. The methodology is applied to the determination of methylamine by FIA based on the use of the peroxyoxalate CL (PO-CL) reaction. Considering the high number of experiments required due to the different chemical and instrumental variables to be taken account and their adequate compatibility to obtain maximum sensitivity, the methodology offers a rigorous study of the main effects and interactions, achieving a reduction of experimental work.