A nanocomposite prepared from a polypyrrole deep eutectic solvent and coated onto the inner surface of a steel capillary for electrochemically controlled microextraction of acidic drugs such as losartan.

The authors describe a new coating for use in electrochemically controlled in-tube solid phase microextraction (EC-IT-SPME). It consists of a nanocomposite that was prepared from polypyrrole and deep eutectic solvent (DES) by electrochemical deposition on the inner walls of a stainless steel capillary that serves as a working electrode. The hypertension drug losartan acts as an acidic model analyte. The extraction efficiency, mechanical stability, chemical stability and lifetime of the coating were investigated. It is found to be quite stable in relatively acidic and basic media and to be re-usable >450 times without decrease in extraction efficiency. Its extraction capability in comparison to the commercial polypyrrole coating is better by a factor of 1.5. The coated steel capillary was used as the anode (anion-exchanger), and a platinum electrode was used as the cathode. By passing a sample solution through the electrode, losartan can be extracted by applying a positive potential to the flow. In the next step, losartan is electrochemically desorbed and subjected to HPLC analysis with UV detection. Under optimal conditions, losartan can be quantified with limits of detection that range from 50 to 500 ng L-1 depending on the sample matrix. Response is linear in the 0.1-500 μg L-1 concentration range. The inter- and intra-assay precisions (RSDs; in %, for n = 3) are in the range from 2.4-4.6% and from 1.9-3.9%, respectively. Graphical abstract Schematic of the preparation of a nano-structured polypyrrole-deep eutectic solvent nanocomposite coating placed on the inner surface of a stainless steel capillary and used for electrochemically controlled in-tube solid phase microextraction of losartan from biological samples.