Simultaneous Determination of Nine Quinolones in Pure Milk Using PFSPE-HPLC-MS/MS with PS-PAN Nanofibers as a Sorbent

Rapid Determination of 25-Hydroxyvitamin D3 and 24,25-Dihydroxyvitamin D3 in Human Urine Based on Polystyrene/Graphene Oxide Packed-Fibers Solid-Phase Extraction Coupled With High-Performance Liquid Chromatography and Atmospheric Pressure Chemical Ionization Tandem Mass Spectrometry

Vitamin D plays a crucial role in skeletal metabolism and is implicated in various diseases. Several studies have indicated that human vitamin D status can be evaluated through urine hydroxyvitamin D levels, in addition to plasma hydroxyvitamin D concentrations. In this study, we developed a novel method for the detection of trace amounts of 25-hydroxyvitamin D3 [25(OH)D3] and 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] in urine. This method is based on high-performance liquid chromatography coupled with atmospheric pressure chemical ion source-tandem mass spectrometry, integrated with packed-fibers solid-phase extraction. The composite polystyrene/graphene oxide (PS/GO) nanofibers were synthesized as the sorbent for concentrating 25(OH)D3 and 24,25(OH)2D3, achieving a twentyfold increase in sensitivity when analyzing human urine samples. Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy mapping analysis were employed to characterize GO, PS, and PS/GO. The results indicated that the composite nanofibers were successfully synthesized. In addition, we investigated the relationship between the extraction performance of the fibers and the electrospinning process at varying flow rates of spinning solution through morphological studies and Brunauer-Emmett-Teller surface area analysis. During the extraction process, purification, concentration, and desorption were accomplished within a single step. The established method demonstrated excellent sensitivity and efficiency. Under optimal conditions, limits of detection (signal-to-noise ratio = 3) were found to be 0.33 ng/mL for 25(OH)D3 and 0.19 ng/mL for 24,25(OH)2D3; furthermore, linearity was deemed acceptable across urine samples. Recovery rates ranged from 89.5% to 109.7% for 25(OH)D3 and from 90.3% to 103.1% for 24,25(OH)2D3, respectively.

Preparation of ofloxacin molecularly imprinted polymer Raman sensor based on magnetic graphene oxide

Ofloxacin is a commonly used quinolone antibiotic that is also used as a feed supplement in livestock production and in plant disease prevention and treatment. However, the excessive use and abuse of ofloxacin will accumulate along the food chain and endanger human health. Therefore, the development of a simple, rapid, and sensitive detection method for the determination of ofloxacin is critical. Herein, a detection method combining molecularly imprinted magnetic solid-phase extraction (MISPE) and surface-enhanced Raman spectroscopy (SERS) was developed for the detection of ofloxacin. Graphene oxide supported by magnetic beads was synthesized by a one-pot method, producing what was subsequently referred to as magnetic graphene oxide (MGO), and a molecularly imprinted membrane was synthesized on its surface by exploiting the ability of dopamine to self-polymerize under alkaline conditions. MGO@MIPs were obtained as the adsorbent for magnetic solid-phase extraction, which was used for the extraction and enrichment of ofloxacin in complex sample matrix, and then quantitative analysis was conducted by SERS. The developed method exhibited an excellent linear relationship with respect to ofloxacin concentration (10-5 to 102 μg mL-1), with a detection limit of 9.7 × 10-6 μg mL-1 in ultrapure water. Blank honey, milk, and pork samples spiked with ofloxacin at concentrations of 0.005, 0.1, 1, and 10 μg mL-1 were extracted and determined using the developed method, with recoveries ranging from 93.1% to 105.6%. The results support the strong application prospects for the method, demonstrating simple and time-efficient operation and high accuracy.

Quantum dot-based fluorescence-linked immunosorbent assay for the rapid detection of lomefloxacin in animal-derived foods

Lomefloxacin (LMF), a third-generation fluoroquinolone antibacterial agent, is often used to treat bacterial and mycoplasma infections. However, due to its prolonged half-life and slow metabolism, it is prone to residues in animal-derived foods, posing a potential food safety risk. Therefore, it is particularly urgent and important to establish a method for detecting lomefloxacin. In this study, direct and indirect competitive fluorescence-linked immunosorbent assay (dc-FLISA and ic-FLISA) based on quantum dots (QDs) was established for the detection of LMF. As for dc-FLISA, the half-maximal inhibitory concentration (IC50) and limit of detection (LOD) were 0.84 ng/mL, 0.04 ng/mL, respectively, the detection ranges from 0.08 to 9.11 ng/mL. The IC50 and LOD of ic-FLISA were 0.43 ng/mL and 0.03 ng/mL, respectively, meanwhile the detection ranges from 0.05 to 3.49 ng/mL. The recoveries of dc-FLISA and ic-FLISA in animal-derived foods (milk, fish, chicken, and honey), ranged from 95.8% to 105.2% and from 96.3% to 103.4%, respectively, with the coefficients of variation less than 8%. These results suggest that the dc-FLISA and ic-FLISA methods, which are based on QD labelling, are highly sensitive and cost-effective, and can be effectively used to detect LMF in animal-derived foods.

Sensitive electrochemical detection of enrofloxacin in eggs based on carboxylated multi-walled carbon nanotubes-reduced graphene oxide nanocomposites: Molecularlyimprintedrecognition versus direct electrocatalytic oxidation

A sensitive electrochemical method for detecting enrofloxacin was proposed using carboxylated multi-walled carbon nanotubes-reduced graphene oxide (MWCNT-COOH-RGO) nanocomposites. The MWCNT-COOH-RGO nanocomposites were firstly electrodeposited on a bare electrode, followed by electropolymerization of molecularly imprinted polymers. Enrofloxacin was determined by the mechanisms of direct electrocatalytic oxidation and molecularly imprinted recognition, respectively. Under the optimized conditions, a response range of 5.0×10^-7 M to 5.5×10^-5 M and limit of detection (LOD) of 2.3×10^-7 M were obtained by direct electrocatalytic oxidation of enrofloxacin using chronoamperometry. By contrast, the response range of 1.0×10^-10 M to 5.0×10^-5 M and LOD of 2.5×10^-11 M were achieved by molecularly imprinted recognition of enrofloxacin using square-wave voltammetry. Moreover, the proposed method exhibited good repeatability, stability and selectivity, and could be used for enrofloxacin detection in egg samples with satisfactory results.

Feasible spectrofluorimetric approach for the ultrasensitive determination of lomefloxacin based on synergistic effects of micellization and metal complexation

The purpose of the present work was to establish a fast and convenient strategy for lomefloxacin analysis using a fluorimetric approach. The methodology was based on the complex formation of the drug with aluminum ion to give a product having high fluorescence. Adding sodium dodecyl sulfate led to further boosting the intensity of fluorescence which was recorded at 429 nm after excitation at 332 nm. The relationship of emission intensity with lomefloxacin concentration was linear at 10-130 ng mL^-1 with a correlation coefficient of 0.9996. The quantitation limit was 11.4 ng mL^-1 and detection limit was 3.8 ng mL^-1. The reaction conditions were carefully studied which included the pH, buffer type, its concentration, the type and concentration of surfactant and the diluting solvent. The method was utilized to quantify the aforementioned drug in tablet formulations and in real human plasma with high accuracy and reliability.