Micro-gel thin film molecularly imprinted polymer coating for extraction of organophosphorus pesticides from water and beverage samples.

Molecularly imprinted polymers (MIPs) have become an important class of materials for selective and efficient adsorption of target analytes. Despite versatility of MIPs for fabrication in numerous formats, these materials have been primarily reported as solid phase extraction packing materials. An effective thin film MIP prepared on stainless steel substrate is reported here for high throughput enrichment of organophosphorus pesticides (OPPs) from water and beverage samples followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. The key factors controlling performance as well as best practices for optimized fabrication of thin film MIPs are presented. A pseudo-phase diagram is introduced to evaluate and predict the effect of the ratio of porogen (solvent, 1-octanol) volume to relative crosslinker mass on the desired polymer features (i.e., porosity, surface area, capacity, and selectivity). At low porogen ratios, a macroporous polymer with insignificant selectivity is formed, whereas at high porogen ratios a micro-gel polymer with superior selectivity towards targets is obtained. The porosity and morphology determined with nitrogen adsorption and scanning electron microscopy were attributed to specific regions in the pseudo-phase diagram. Other factors influencing selectivity and stability of the polymer, such as type of the template and its ratios with monomer (methacrylic acid) and crosslinker (ethylene glycol dimethacrylate) were optimized. The prepared thin film MIPs were characterized using adsorption isotherms and adsorption kinetics, and evaluated for matrix effects (high humic acid content) and cross-reactivity in presence of other pesticides and pharmaceuticals. The optimized method provided limits of quantitation (LOQs) ranged from 0.002 to 0.02 ng mL-1 in water and from 0.095 to 0.48 ng g-1 in apple juice. Regarding inter-device variability (CV∼10% without normalization), excellent linearity (R2 > 0.99), satisfactory accuracies (90-110%) and precisions (<15%) were obtained.

Trace analysis of N-acetyl-L-cysteine using luminol-H2O2 chemiluminescence system catalyzed by silver nanoparticles.

N-Acetyl-L-cysteine (NAC) can inhibit the luminol-H2 O2 , reaction, which is catalyzed by silver nanoparticles. Based on this phenomenon a new method was developed for NAC determination. Under optimum conditions, a linear relationship between chemiluminescence intensity and NAC concentration was found in the range 0.034-0.98 µg/mL. The detection limit was 0.010 µg/mL (S/N =3), and the relative standard deviation (RSD) was <5% for 0.480 µg/mL NAC (n =5). This simple, sensitive and inexpensive method has been applied to measure the concentration of NAC in pharmaceutical tablets.

A highly efficient turn-on fluorescent sensor for determination of water in organic solvents.

2, 3 biphenyl quinoxaline 6-amine is a fluorescent compound in some organic solvents with an excitation wavelength at 435 nm and a fluorescence emission at 518 nm. The fluorescence intensity of 2, 3 biphenyl quinoxaline 6-amine is significantly reduced in the presence of bis-(2, 4, 6-trichlorophenyl) oxalate (TCPO) and Zn(2+) due to the nonfluorescent complex formation. The low stability of the complex in presence of trace amount of water results in decomposing complex, thereby recovering the photoluminescence of 2, 3 biphenyl quinoxaline 6-amine. Based on this fact, a turn-on fluorescence photoluminescence sensor for determination of water content in organic solvents was introduced for the first time.The fluorescence intensity of 2, 3 biphenyl quinoxaline 6-amine as a function of water concentration was used as a simple, sensitive and rapid method for determining trace amount of water in some organic solvents such as ethanol and methanol. The obtained results showed a good linear relationship between fluorescence intensity and the water content with a dynamic range of 0.0094 -1(v/v%), related coefficient of 0.9922 and limit of detection of 0.0026(v/v%). %).

Studies of new peroxyoxalate-H2O2 chemiluminescence system using quinoxaline derivatives as green fluorophores.

Quinoxaline derivatives are a great interest as fluorescent emitters for peroxyoxalate chemiluminescence. Reaction of peroxyoxalates such as bis-(2,4,6-trichlorophenyl) oxalate with H(2)O(2) can transfer energy to fluorophore via formation of dioxetanedione intermediate. Two quinoxaline derivatives used as a fluorophore in this study which produce a green light in the chemiluminescence systems. The relationship between the chemiluminescence intensity and concentrations of fluorophore, peroxyoxalate, sodium salicylate and hydrogen peroxide was investigated. Kinetic parameters for the peroxyoxalate-chemiluminescence were also calculated from the computer fitting of the corresponding chemiluminescence intensity/time profiles. It was found that the biphenylquinoxaline can be used as an efficient green fluorescent emitter.

Studies of visible oscillating chemiluminescence in luminol-H2O2-KSCN-CuSO4 system using (2-hydroxyethyl) trimethylammonium hydroxide.

Visible oscillating chemiluminescence (CL) of luminol-H2O2-KSCN-CuSO4 was studied using the organic base (2-hydroxyethyl)trimethylammonium hydroxide. The effect of concentrations of luminol, H2O2, KSCN, CuSO4 and the base were investigated in a batch reactor. This report shows how the concentration of components involved in the oscillating CL system influenced the oscillation period, light amplitude and total time of light emission. The oscillating CL with different bases was also investigated. Results indicated that using 2-HETMAOH causes regular oscillating CL with nearly the same oscillating period.