Electroplating of nanostructured polyaniline–polypyrrole composite coating in a stainless-steel tube for on-line in-tube solid phase microextraction

• Polyaniline (PAN) and polypyrrole (PPY) can be suitable coatings for SPME fibers.
• PAN–PPY nano composite was electrochemically deposited on inner surface of stainless steel tube.
• On-line in-tube SPME followed by HPLC was developed for extraction of parabens.
• Several important factors affecting extraction efficiency were investigated and optimized.
• The method was applied for analysis of the parabens in water, milk, and juice samples.

In this work, a novel and efficient on-line in-tube solid phase microextraction method followed by high performance liquid chromatography was developed for preconcentration and determination of trace amounts of parabens. A nanostructured polyaniline–polypyrrole composite was electrochemically deposited on the inner surface of a stainless steel tube and used as the extraction phase. Several important factors that influence the extraction efficiency, including type of solid-phase coating, extraction and desorption times, flow rates of the sample solution and eluent, pH, and ionic strength of the sample solution were investigated and optimized. Under the optimal conditions, the limits of detection were in the range of 0.02–0.04 μg L−1. This method showed good linearity for parabens in the range of 0.07–50 μg L−1, with coefficients of determination better than 0.998. The intra- and inter-assay precisions (RSD%, n = 3) were in the range of 5.9–7.0% and 4.4–5.7% at three concentration levels of 2, 10, and 20 μg L−1, respectively. The extraction recovery values for the spiked samples were in the acceptable range of 80.3–90.2%. The validated method was successfully applied for analysis of methyl-, ethyl-, and propyl parabens in some water, milk, and juice samples.