Determination of nonsteroidal anti-inflammatory drugs in biological fluids by automatic on-line integration of solid-phase extraction and capillary electrophoresis

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Abstract
A new, automatic method for the clean‐up, preconcentration, separation, and quantitation of nonsteroidal anti‐inflammatory drugs (NSAIDs) in biological samples (human urine and serum) using solid‐phase extraction coupled on‐line to capillary electrophoresis is proposed. Automatic pretreatment is carried out by using a continuous flow system operating simultaneously with the capillary electrophoresis equipment, to which it is linked via a laboratory‐made mechanical arm. This integrated system is controlled by an electronic interface governed via a program developed in GWBasic. Capillary electrophoresis is conducted by using a separation buffer consisting of 20 mM NaHPO4, 20 mM β‐cyclodextrin and 50 mM SDS at pH 9.0, an applied potential of 20 kV and a temperature of 20°C. The analysis time is 10 min and the detection limits were between 0.88 and 1.71 μg mL−1. Automatic clean‐up and preconcentration is accomplished by using a C‐18 minicolumn and 75% methanol as eluent. The limit of detection of NSAIDs can be up to 400‐fold improved when using sample clean‐up. The extraction efficiency for these compounds is between 71.1 and 109.7 μg mL−1 (RSD 2.0—7.7%) for urine samples and from 77.2 to 107.1 μg mL−1 (RSD 3.5—7.1%) for serum samples.

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