Speciation of mercury by ionic liquid-based single-drop microextraction combined with high-performance liquid chromatography-photodiode array detection

Room temperature ionic liquids can be considered as environmentally benign solvents with unique physicochemical properties. Ionic liquids can be used as extractant phases in SDME, being compatible with chromatographic systems. A single-drop microextraction method was developed for separation and preconcentration of mercury species (MeHg⁺, EtHg⁺, PhHg⁺ and Hg²⁺), which relies on the formation of the corresponding dithizonates and microextraction of these neutral chelates onto a microdrop of an ionic liquid. Afterwards, the separation and determination were carried out by high-performance liquid chromatography with a photodiode array detector. Variables affecting the formation and extraction of mercury dithizonates were optimized. The optimum conditions found were: microextraction time, 20 min; stirring rate, 900 rpm; pH, 11; ionic liquid type, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]); drop volume, 4 μL; and no sodium chloride addition. Limits of detection were between 1.0 and 22.8 μg L⁻¹ for the four species of mercury, while the repeatability of the method, expressed as relative standard deviation, was between 3.7 and 11.6% (n = 8). The method was finally applied to the determination of mercury species in different water samples.     

Determination of senkirkine and senecionine in Tussilago farfara using microwave-assisted extraction and pressurized hot water extraction with liquid chromatography tandem mass spectrometry

Tussilago farfara (Kuan Donghua) is an important Chinese herbal medicine which has been shown to contain many bioactive compounds and widely used to relieve cough and resolve phlegm. However, besides therapeutic bioactive compounds, this herb has been found to contain toxic pyrrolizidine alkaloids (PAs), mainly senkirkine and traces of senecionine. In this report, conditions for microwave-assisted extraction (MAE) and pressurized hot water extraction (PHWE) were optimized for the extraction of the PAs. The results were compared against heating under reflux. It was found that the binary mixture of MeOH:H₂O (1:1) acidified using HCl to pH 2-3 was the optimal solvent for the extraction of the PAs in the plant materials. Liquid chromatography (LC) with ultra-violet (UV) detection and electrospray ionization mass spectrometry (ESI-MS) in the positive mode was used for the determination and quantitation of senkirkine and senecionine in the botanical extract. The proposed extraction methods with LC/MS allow for the rapid detection of the major and the minor alkaloids in T. farfara in the presence of co-eluting peaks. With LC/MS, the quantitative analysis of PAs in the extract was done using internal standard calibration and the precision was found to vary from 0.6% to 5.4% on different days. The limits of detection (LODs) and limits of quantitation (LOQs) for MAE and PHWE were found to vary from 0.26 μg/g to 1.04 μg/g and 1.32 μg/g to 5.29 μg/g, respectively. The method precision of MAE and PHWE were found to vary from 3.7% to 10.4% on different days. The results showed that major and minor alkaloids extracted using MAE and PHWE were comparable to that by heating under reflux. Our data also showed that significant ion suppression was not observed in the analysis of senkirkine and senecionine in the botanical extracts with co-eluting peaks.     

Conformational analysis of bridgehead-substituted bicyclo[m.m.m]alkanes and bicyclo[8.8.n]alkanes

Conformational analyses of bicyclo[m.m.m]alkanes where m=1-10 and of bicyclo[8.8.n]alkanes where n=1-7 bearing methyl groups on the bridgeheads were carried out using a Monte Carlo search strategy. In the bicyclo[m.m.m]alkane series, greater variability was observed for the inter-bridgehead distance for larger values of m. This suggests that properly substituted bicyclo[8.8.8]hexacosanes or larger ring systems might serve as molecular springs.     

Selective hydrogenation of o-chloronitrobenzene (o-CNB) over supported Pt and Pd catalysts obtained by laser vaporization deposition of bulk metals

Carbon nanotubes (CNTs), γ-alumina (γ-Al₂O₃) and silica (SiO₂) supported Pt and Pd catalysts were produced by laser vaporization deposition of respective bulk metals. The catalysts were characterized by inductive coupled plasma emission spectrometer (ICP), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalytic properties of the catalysts were investigated in the liquid phase hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) under 333 K and 1.0 MPa hydrogen pressure. The results show that the catalytic properties are greatly affected by the supports. Pt/CNTs catalyst exhibits the best catalytic performance among the Pt-based catalysts, producing o-CAN with 99.6% selectivity at complete conversion. Pd/CNTs catalyst exhibits the best catalytic performance among the Pd-based catalysts, giving o-CAN with 95.2% selectivity at complete conversion. For Pt-based catalysts, geometric effect and the textures and properties of the supports play important roles on catalytic properties. On the other hand, geometric effect, electronic effect and the textures and properties of the supports simultaneously influence the catalytic properties of the Pd-based catalysts. In addition, hydrogenolysis of the C–Cl bond can be well inhibited over all catalysts prepared by laser vaporization deposition.     

Infrared optical constants, dielectric constants, molar polarizabilities, transition moments, dipole moment derivatives and Raman spectrum of liquid cyclohexane

Previous studies have been done in this laboratory focusing on the optical properties of several liquid aromatic and aliphatic hydrocarbons in the infrared. The current study reports the infrared and absorption Raman spectra of liquid cyclohexane. Infrared spectra were recorded at 25 °C over a wavenumber range of 7400–490 cm⁻¹. Infrared measurements were taken using transmission cells with pathlengths ranging from 3 to 5000 μm. Raman spectra were recorded between 3700 and 100 cm⁻¹ at 25 °C using a 180° reflection geometry. Ab initio calculations of the vibrational wavenumbers at the B3LYP/6311G level of theory were performed and used to help assign the observed IR and Raman spectra. Extensive assignments of the fundamentals and binary combinations observed in the infrared imaginary molar polarizability spectrum are reported. The imaginary molar polarizability spectrum was curve fitted to separate the intensity from the various transitions and used to determine the transition moments and magnitudes of the derivatives of the dipole moment with respect to the normal coordinates for the fundamentals.     

Electroactivity of nitriles on platinum electrodes and its use in chromatographic detection

Acetonitrile yields two oxidative peaks, first at ca. +0.30 and second at ca. +1.15 V vs. Ag/AgCl in cyclic voltammetry with platinum electrodes in 0.10 M methanesulfonic acid (MSA) containing 0.05–5 mM concentrations of acetonitrile. This electroactivity of the nitrile group was used for a direct detection of nitriles after their chromatographic separation. Three organic nitriles (acetonitrile, propionitrile and butanenitrile) were separated with an IonPac ICE-AS 1 column, eluted with 0.10 M MSA and detected on a platinum electrode via pulsed amperometric detection. Analytical performance was evaluated with a three potential waveform (+0.30 V, +1.15 V, −0.30 V vs. Ag/AgCl, current integration at +1.15 V). Numerical values of detection limits, linearity of calibration and reproducibility are reported for all three organic nitriles.     

Application of continual injection liquid‐phase microextraction method coupled with liquid chromatography to the analysis of organophosphorus pesticides

A liquid‐phase microextraction coupled with LC method has been developed for the determination of organophosphorus pesticides (methidation, quinalphos and profenofos) in drinking water samples. In this method, a small amount (3 μL) of isooctane as the acceptor phase was introduced continually to fill‐up the channel of a 1.5 cm polypropylene hollow fiber using a microsyringe while the hollow fiber was immersed in an aqueous donor solution. A portion of the acceptor phase (ca. 0.4 μL) was first introduced into the hollow fiber and additional amounts (ca. 0.2 μL) of the acceptor phase were introduced to replenish at intervals of 3 min until set end of extraction (40 min). After extraction, the acceptor phase was withdrawn and transferred into a 2 mL vial for a drying step prior to injection into a LC system. Parameters that affect the extraction efficiency were studied including the organic solvent, length of fiber, volume of acceptor and donor phase, stirring rate, extraction time, and effect of salting out. The proposed method provided good enrichment factors of up to 189.50, with RSD ranging from 0.10 to 0.29%, analyte recoveries of over 79.80% and good linearity ranging from 10.0 to 1.25 mg/L. The LOD ranged from 2.86 to 82.66 μg/L. This method was applied successfully to the determination of organophosphorus pesticides in selected drinking water samples.     

Potential of combining of liquid membranes and molecularly imprinted polymers in extraction of 17β‐estradiol from aqueous samples

The potential of combination of liquid membranes (microporous membrane liquid–liquid extraction) and molecularly imprinted polymers (MIPs) was performed using 17β‐estradiol (E2) as model compound. The model compound was extracted from aqueous sample through a hydrophobic porous membrane that was impregnated with hexane/ethyl acetate (3:2), which also formed part of the acceptor phase. In the acceptor phase, the compound was bound onto MIP particles that were also part of the organic phase. The potential of such combination was optimised for the type and amount of MIP particles in the organic acceptor phase, the extraction time, and the type of organic acceptor solvent. Ultrasound assisted binding of E2 onto MIP particles was also investigated. MIPs prepared by precipitation polymerization were found to be superior to those prepared by bulk polymerization. Increase in the extraction time and the amount of MIP particles in the acceptor phase led to more E2 binding onto the MIP particles. Hexane/ethyl acetate (3:2) as an organic acceptor was found to give higher E2 binding onto MIP particles compared to toluene, diethyl ether, and hexane. Ultrasound was furthermore found to increase the binding of E2 onto MIP particles. The selectivity of the technique was demonstrated by extracting wastewater and where clean chromatograms were obtained compared to liquid membrane extractions (SLMs) alone.     

Fast and simple method for the determination of urinary 1‐hydroxypyrene

A fast method for the measurement of metabolites of pyrene in urine was improved by HPLC with fluorescence detector using “heart‐cut” technique. This method can quantify the total amount of pyrene metabolites corresponding to glucuronic acid and sulfate conjugates as well as free 1‐OH‐Py. The hydrolyzed biological fluid was directly injected into the chromatographic system, via a column‐switching system. Pre‐treatment and analysis were performed within 0.5 and 9 min, respectively. Enzymatic hydrolysis has been optimized to not exceed 2 h. The best response function, in the 0.2–10 ng/mL range, is the linear regression, bringing simplicity, good accuracy, and low LOQ. The intra‐ and interday precision values were inferior to 1 and 2%, respectively. The proposed method provided a simple, convenient, and practical procedure to determine the level of the main urinary pyrene metabolites in biological samples.     

Electrochemistry meets enzymes: instrumental on-line simulation of oxidative and conjugative metabolism reactions of toremifene

The metabolism of the selective estrogen receptor modulator toremifene was simulated in an on-line electrochemistry/enzyme reactor/liquid chromatography/mass spectrometry system. To simulate the oxidative phase I metabolism, toremifene was oxidized in an electrochemical (EC) flow-through cell at 1,500 mV vs. Pd/H₂ to its phase I metabolites, some of which are reactive quinoid species. In the presence of glutathione-S-transferase (GST), these quinoid compounds react with glutathione, which is also the common detoxification mechanism in the body. While reacting with glutathione, the chlorine atom is eliminated from the toremifene moiety. Due to higher conversion rates, GST supplied in continuous flow proved to be more efficient than using immobilized GST on magnetic microparticles. In the absence of GST, not all GSH adducts are formed, proving the necessity of a phase II enzyme to simulate the complete metabolic pathway of xenobiotics in an on-line EC/LC/MS system. Figure Mass voltammogram of toremifene