Development of electrochemically controlled packed-in-tube solid phase microextraction method for sensitive analysis of acidic drugs in biological samples

In the present research, for the first time, a novel packed-in-tube configuration has been applied to electrochemically controlled in-tube solid phase microextraction, followed by high performance liquid chromatography. In order to prepare a mini packed column, small beads of stainless steel were first placed into the stainless steel column. Then, a nanostructured polypyrrole film was prepared on the internal surface of a stainless steel tube and the surface of stainless steel particles through a facile in-situ electrodeposition method. Filling the column with tiny particles of stainless steel effectively reduces the dead volume of the extraction tube and increases the extraction phase volume. The column was used for separation and preconcentration of diclofenac and mefenamic acid as model analytes from biological samples. Several important factors affecting extraction efficiency, such as extraction and desorption times, flow rates of the sample solution and eluent, and extraction and desorption voltages were investigated and optimized. This method showed good linearity for the drugs in the range of 0.3-200.0 mu g L-1, 1.1-200.0 mu g L-1, and 1.8-200.0 mu g L-1 with coefficients of determination better than 0.9986, 0.9973, and 0.9973 in water, urine, and plasma samples, respectively. Intra- and inter-assay precisions (RSD%, n = 3) were in the range of 2.6-4.8% and 2.9-5.1, respectively, at three concentration levels of 10, 25, and 75 mu g L-1. In addition, the limits of detection were in the range of 0.02-0.04 mu g L-1. The validated method was successfully applied to the analysis of diclofenac and mefenamic acid in some biological samples. Finally, it is concluded that this method can be a general and reliable alternative to the analysis of ionic compounds in biological matrices.