Caffeine electrochemical sensor using imprinted film as recognition element based on polypyrrole, sol-gel, and gold nanoparticles hybrid nanocomposite modified pencil graphite electrode.

In the present study, a novel sensitive and selective nanocomposite imprinted electrochemical sensor for the indirect determination of caffeine has been prepared. The imprinted sensor was fabricated on the surface of pencil graphite electrode (PGE) via one-step electropolymerization of the imprinted polymer composed of conductive polymer, sol-gel, gold nanoparticles (AuNPs), and caffeine. Due to such combination like the thin film of molecularly imprinted polymer (MIP) with specific binding sites, the sensor responded quickly to caffeine. AuNPs were introduced for the enhancement of electrical response by facilitating charge transfer processes of [Fe(CN)6](3-)/[Fe(CN)6](4-) which was used as an electrochemical active probe. The fabrication process of the sensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Several important parameters controlling the performance of the sensor were investigated and optimized. The imprinted sensor has the advantages of high porous surface structure, inexpensive, disposable, excellent stability, good reproducibility and repeatability. The linear ranges of the MIP sensor were in the range from 2.0 to 50.0 and 50.0 to 1000.0 nmol L(-1), with the limit of detection (LOD) of 0.9 nmol L(-1) (S/N=3). Furthermore, the proposed method was successfully intended for the determination of caffeine in real samples (urine, plasma, tablet, green tea, energy and soda drink).

Comparison of dispersive liquid-liquid microextraction and hollow fiber liquid-liquid-liquid microextraction for the determination of fentanyl, alfentanil, and sufentanil in water and biological fluids by high-performance liquid chromatography.

Dispersive liquid-liquid microextraction (DLLME) and hollow fiber liquid-liquid-liquid microextraction (HF-LLLME) combined with HPLC-DAD have been applied for the determination of three narcotic drugs (alfentanil, fentanyl, and sufentanil) in biological samples (human plasma and urine). Different DLLME parameters influencing the extraction efficiency such as type and volume of the extraction solvent and the disperser solvent, concentration of NaOH, and salt addition were investigated. In the HF-LLLME, the effects of important parameters including organic solvent type, concentration of NaOH as donor solution, concentration of H(2)SO(4) as acceptor phase, salt addition, stirring rate, temperature, and extraction time were investigated and optimized. The results showed that both extraction methods exhibited good linearity, precision, enrichment factor, and detection limit. Under optimal condition, the limits of detection ranged from 0.4 to 1.9 µg/L and from 1.1 to 2.3 µg/L for DLLME and HF-LLLME, respectively. For DLLME, the intra- and inter-day precisions were 1.7-6.4% and 14.2-15.9%, respectively; and for HF-LLLME were 0.7-5.2% and 3.3-10.1%, respectively. The enrichment factors were from 275 to 325 and 190 to 237 for DLLME and HF-LLLME, respectively. The applicability of the proposed methods was investigated by analyzing biological samples. For analysis of human plasma and urine samples, HF-LLLME showed higher precision, more effective sample clean-up, higher extraction efficiency, lower organic solvent consumption than DLLME.