Zeolitic imidazolate framework-8 decorated with gold nanoparticles for solid-phase extraction of neonicotinoids in agricultural samples.

A composite built with aminated zeolitic imidazolate framework and gold nanoparticles (AuNPs) for solid-phase extraction (SPE) of neonicotinoids in agricultural samples is presented. The composite was prepared through the assembly of AuNPs onto the surface of metal-organic framework based on the strong interaction between the amino group and AuNP. These metallic surfaces provided additional interactions based on the affinity of amino and cyano groups present in the target compounds. The composite was characterized by scanning electron microscopy, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and surface area measurements. Regarding the SPE protocol, several parameters that can influence the extraction performance were optimized, such as sample volume or composition of elution solvent, among others. After elution, the analytes were determined via HPLC with diode-array detection. Under the selected conditions, satisfactory recoveries of five pesticides (thiamethoxan, clothianidin, imidacloprid, acetamiprid, and thiacloprid) were obtained (between 80 and 110%) in real samples, whereas the limits of detection ranged from 0.019 to 0.041 µg L-1 in aqueous samples and 0.3 to 0.8 µg g-1 in solid samples.

Rapid monitoring of fungicide fenhexamid residues in selected berries and wine grapes by square-wave voltammetry at carbon-based electrodes.

A completely new electroanalytical method for the determination of fenhexamid (FNX) residues in fruit samples has been developed. This method is based on anodic oxidation of fungicide in Britton-Robinson buffer (pH 4) containing 10% (v/v) methanol using square-wave voltammetry when five different carbon-based electrodes were tested. An electrochemical behaviour of FNX was studied on a glassy carbon electrode using cyclic voltammetry, while glassy carbon paste electrode was selected for analytical purposes. Linear range for FNX from 3.96 to 49.50 µmol L-1 characterized by coefficient of determination of 0.9964, sensitivity of 0.176 µA L µmol-1, and detection limit of 1.32 µmol L-1 were calculated. Results acquired from analyses of blueberries and wine grapes were compared to those obtained by a reference chromatographic method, and a satisfactory agreement has been reached. Finally, it seems that the present voltammetric approach could find its application in food quality control as screening assay.

Flow injection tyrosinase biosensor for direct determination of acetaminophen in human urine.

An amperometric biosensor compatible with a flow injection analysis (FIA) for highly selective determination of acetaminophen (APAP) in a sample of human urine was developed. This biosensor is also suitable for use in the routine pharmaceutical practice. To prove this statement, two different commercially available pharmaceutical formulations were analyzed. This nano-(bio)electroanalytical device was made from a commercially available screen-printed carbon electrode covered by a thin layer of non-functionalized graphene (NFG) as amperometric transducer. A biorecognition layer was prepared from mushroom (Agaricus bisporus) tyrosinase (EC 1.14.18.1) cross-linked using glutaraldehyde, where resulting aggregates were covered by Nafion®, a known ion exchange membrane. Owing to the use of tyrosinase and presence of NFG, the developed analytical instrument is able to measure even at potentials of 0 V. Linear ranges differ according to choice of detection potential, namely up to 130 µmol L-1 at 0 V, up to 90 µmol L-1 at -0.1 V, and up to 70 µmol L-1 at -0.15 V. The first mentioned linear range is described by the equation Ip [µA] = 0.236 - 0.1984c [µmol L-1] and correlation coefficient r = 0.9987; this equation was used to quantify the content of APAP in each sample. The limit of detection of APAP was estimated to be 1.1 µmol L-1. A recovery of 96.8% (c = 25 µmol L-1, n = 5 measurements) was calculated. The obtained results show that FIA is a very selective method for APAP determination, being comparable to the chosen reference method of reversed-phase high-performance liquid chromatography.