Newly developed flow-through coulometric detector with renewable working material of glassy carbon microbeads was fabricated and its basic electrochemical parameters were studied by flow injection analysis using potassium ferrocyanide and hydroquinone as probes. Main advantage of the detector is its simple construction while maintaining good electrochemical parameters and high conversion degree. Practical application of the detector was proved by the development of new HPLC and FIA method of thymol and sulfamethizole determination in pharmaceutical preparations. Optimal determination conditions were found and calibration dependences were measured. A value of quantification limit 0.97 mu mol L (1) for thymol and 0.040 mu mol L (1) for sulfamethizole were obtained. Newly developed methods were used for determination of the studied compounds in pharmaceutical preparations. HPLC with spectrophotometric detection was used as a comparative method; results from both methods were in good agreement. (C) 2014 Elsevier Ltd. All rights reserved.