Optimization of Square Wave Voltammetry (SWV) Parameters by Design of Experiment (DoE) Methodologies for the Determination of Mifepristone at Glassy Carbon Electrode (GCE)

In the present study, an electroanalytical method that permits the optimization of factors affecting SWV for sensitive detection of mifepristone at glassy carbon electrode (GCE) using response surface methodology (RSM) with desirability function (DF) is presented. Factors selected for optimization after screening using full factorial design were frequency (X₁), amplitude (X₂), and pH (X₃). The central composite design as a response surface methodology with desirability function (DF) was applied for obtaining the optimum level. The optimum conditions were obtained as follows: Frequency (X₁=50 Hz), amplitude (X₂=33.4 mV), and pH (X₃=9.4), with an overall desirability function of 0.97. Subsequently, confirmatory experiments were performed in triplicates to validate the optimum conditions. The results obtained were satisfactory and agreed well with less only 11.9 % deviation from the values predicted by the model. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.54 and 1.80 ppm, respectively. The proposed method was applied for a quantitative determination of mifepristone in spiked tap water samples. The recovery tests showed that the detection of mifepristone at GC could be evaluated on environmental samples.     

Critical parameters in a supported liquid membrane extraction technique for ionizable organic compounds with a stagnant acceptor phase

The reviews cover important critical parameters that are often optimized in a supported liquid membrane extraction technique in both flat sheet and hollow fibre designs for ionizable organic molecules. Understanding of these parameters can enable one to predict the behavior of the compound before hand and thus reduce the number of optimization experiments. Moreover, less number of experiments can be also generated using statistical techniques which are now becoming more commonly used. Supported liquid membrane extraction optimal parameters such as the conditions of the pH of the acceptor and donor phases should easily be fixed from the pKa values of the compounds. Other parameters, including the polarity of the compound can help to predict the partitioning into the membrane and the behavior of the compound. The influence of parameters such as temperature on the mass transfer in supported liquid membrane depends on the design of the module, experimental design and type of mass transfer controlling the extraction process.     

Preparation, characterization, and application of polypropylene-clinoptilolite composites for the selective adsorption of lead from aqueous media

The miscibility, mechanical and morphological properties of mixed Langmuir and Langmuir-Blodgett monolayers prepared from the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and the perfluorinated fatty acid perfluorooctadecanoic acid have been studied as a function of film composition and subphase salinity. It was demonstrated here, for the first time, that the extent of surfactant miscibility in mixed phospholipid-perfluoroacid monolayers, and hence the resulting mechanical properties of the monolayer film, can be controlled by altering the concentration of sodium ions in the underlying subphase. Elevated Na(+) concentrations resulted in lower net attractive interactions between film components, likely through specific ion adsorption to the negatively-charged perfluoroacid, along with decreased film elasticities. These results differ significantly from conventional fatty-acid-carboxylate monolayer systems in which film cohesion is typically enhanced through adsorption of cations to surfactant headgroups. Atomic force microscope images of films deposited onto solid mica substrates revealed that the films deposited from pure water formed multimolecular aggregates of surfactant, which could be attributed to the highly cohesive nature of the films, but the use of salt in the subphase diminished aggregate formation and resulted in the production of homogeneous monolayer films.     

Ionic Liquid–Liquid Extraction and Supported Liquid Membrane Analysis of Lipophilic Wood Extractives from Dissolving-Grade Pulp

In this study, the extraction of lipophilic wood extractives from dissolving pulp samples using ionic liquid–liquid extraction and a two phase hollow fibre supported liquid membrane was investigated. Ionic liquids are capable of dissolving a range of organic and polymeric compounds and are biodegradable, with a negligible vapour pressure. Pulp samples were dissolved in a suitable amount of molten 1-butyl-3-methylimidazolium chloride to give 5 % cellulose solution. Pure cellulose was regenerated by adding water and filtered off. The ionic liquid-aqueous filtrate was first extracted for lipophilic extractives using liquid–liquid extraction. Then, a two phase hollow fibre supported liquid membrane extraction of lipophilic extractives was performed to extract the derivatized compounds prior to analysis by gas chromatography mass spectrometry. The operational parameters of this sample preparation approach were optimised using sterols and fatty acid methyl esters. The variation of enrichment factors and extraction efficiency with respect to liquid membrane, extraction time, stirring speed and sample pH were observed and used to get the optimal parameters. The approach was used in the analysis of oxygen bleached dissolving pulp samples in which main compounds identified were fatty acids, sterols, fatty alcohols, steroid hydrocarbons and ketones. These compounds were similar to those obtained using molecular solvent extraction method, which indicated the absence of chemical reaction between extractives and ionic liquid used.

     

Comparative study of sample preparation methods; supported liquid membrane and solid phase extraction in the determination of benzimidazole anthelmintics in biological matrices by liquid chromatography-electrospray-mass spectrometry

Supported liquid membrane (SLM) and solid phase extraction (SPE) have been applied as clean-up and/or enrichment techniques for a mixture of five benzimidazole anthelmintics compounds, namely albendazole, fenbendazole, mebendazole, oxibendazole, and thiabendazole. Two biological matrices, mainly urine and milk, and ultra high purity (UHP) water were spiked with a mixture of these five compounds. Waters Oasis^® MCX and International Sorbent Technology (IST) HCX SPE sorbents were used. The liquid membrane used for clean-up and/or enrichment of these compounds was 5% tri-n-octylphosphine oxide (TOPO) dissolved in n-undecane/di-n-hexyl ether (1:1). The SLM extraction efficiencies and SPE percentage recoveries ranged between 60 and 100%. The detection limits (DLs) for different benzimidazole compounds by SPE/LC-ES-MS for thiabendazole, oxibendazole, and albendazole was 0.1 ng/L, for fenbendazole and mebendazole was 1 and 10 ng/L, respectively. Similarly, the detection limits of SLM/LC-ES-MS for thiabendazole, oxibendazole, and albendazole was 0.1 ng/L and for fenbendazole and mebendazole was 1 ng/L. The results of optimization of various parameters of the SLM method are reported.     

Pre-concentration of trace elements in short chain alcohols using different commercial cation exchange resins prior to inductively coupled plasma-optical emission spectrometric detection

Chelex-100, Dowex 50W-x8 and Dowex MAC-3 exchange resins were investigated for separation and pre-concentration of trace amounts of Cd, Cr, Cu, Fe, Mn, Pb, Ti and Zn in alcohols with respect to retention and desorption characteristics. Dowex 50W-x8 was found to be the best sorbent with percentages recoveries >95%. In addition, Chelex-100 appeared to be suitable for the pre-concentration of Cu, Fe and Zn, whereas Dowex MAC-3 was selective for Cu and Fe. Therefore, Dowex 50W-x8 was used for further investigations. The relative standard deviations <4% (n = 20), limits of detection and quantification were 0.1–1.2 μg L⁻¹ and 0.3–1.5 μg L⁻¹, respectively. The SPE method was validated against a certified reference material and the results were in agreement with certified values. The accuracy of the optimized method was verified by the recovery test in the spiked alcohol samples. The accuracy and spike recovery test for different metal ions were in the range 98–102% and 95–105%, respectively. The optimized method was applied to the separation and pre-concentration of metal ions in different commercial alcohol samples.     

Ionic Liquid-Based Extraction of Fatty Acids from Blue-Green Algal Cells Enhanced by Direct Transesterification and Determination Using GC × GC-TOFMS

Blue-green algae commonly referred to as cyanobacteria are known to grow in freshwater bodies when they are provided with suitable growth conditions such as nutrients, temperature and light. Algae biomass is known to contain a large amount of lipids, such as saturated and unsaturated fatty acids. In this study, fatty acids from algal cells were extracted using a newly developed extraction protocol using ionic liquid enhanced by direct transesterification at an elevated temperature. The identification and quantification of fatty acids was performed using gas chromatography coupled to a time-of-flight mass spectrometer (GC × GC-TOFMS). The extracted fatty acids were dominated by those with carbon chain of C16 and C18; [i.e. 7-hexadecenoic acid (C16:1) and hexadecanoic acid (C16:0) for C16, whereas C18 includes γ-linolenic acid (γ-C18:3); linoleic acid (C18:2); linolenic acid (C18:3); 6,9,12,15-octadecatetraenoic acid (C18:4); oleic acid (C18:1) and octadecanoic acid (C18:0)]. The obtained fatty acid composition was then compared with that obtained by organic solvent extraction using a mixture of chloroform and methanol. Statistical evaluation was performed using one-way ANOVA and found that there was no statistically significant difference (P = 0.908) between the two extraction methods, a finding which indicates the usefulness of ionic liquid as a solvent to replace volatile organic solvent to minimize environmental pollution.     

The Use of Supported Liquid Membranes in the Extraction of Macrolides in Biomatrices

Supported liquid membranes (SLMs) have been used in a sample pre-treatment and/or clean-up technique for the continuous extraction of a mixture of three macrolide compounds, namely tylosin tartrate, erythromycin and spiramycin from different biomatrices. The matrices from which extraction was done include cows milk, bovine kidney, and liver tissues. The supported liquid membrane used to trap these compounds was made up of 1-decanol:n-undecane (1:1). Several factors affecting the extraction efficiency during SLM enrichment, such as donor pH, acceptor buffer pH, and enrichment time were studied. High performance liquid chromatography coupled to a mass spectrometer operating in electrospray mode was used as a detection method for these antibiotic compounds with their minor structural components. Fragmentation behavior in ESI-MS (full scan) and ESI-MS/MS modes for these compounds has been studied, and the data obtained was used in selected ion monitoring after LC/MS. The detection limits obtained were 0.01ppb for tylosin tartrate, 0.03ppb for erythromycin and 0.08ppb for spiramycin.     

Voltammetric detection of sulfonamides at a poly(3-methylthiophene) electrode

Detection of sulfonamide compounds in a mixture of standards at a poly(3-methylthiophene) coated on glassy carbon (GC) electrode is reported. The polymer, poly(3-methylthiophene), was electrochemically synthesized at a GC rotating disk-working electrode versus Ag/AgCl using cyclic voltammetry (+0.5 to +2.0 V). Square wave voltammetry (SQWV) with cathodic reduction (0 to -4.0 V) was used for the detection of seven sulfonamide compounds in a mixture. The working concentration ranges (curvilinear) established for different compounds in Britton-Robinson (BR) buffer (pH 6.26), were: 5.0x10(-6)-3.2x10(-3) M sulfamerazine, 5.0x10(-6)-3.2x10(-3) M sulfadiazine, 7.5x10(-7)-3.2x10(-4) M sulfasalazine, 9.0x10(-7)-5.0x10(-4) M sulfamethazine, 6.5x10(-8)-3.5.0x10(-5) M sulfamethoxazole, 9.7x10(-8)-5.0x10(-5) M sulfathiazole, and 9.0x10(-8)-3.2x10(-5) M 5-sulfaminouracil. Detection limits were calculated as: 3.9x10(-6) M for sulfamerazine; 4.0x10(-6) M sulfadiazine; 2.5x10(-7) M sulfasalazine; 3.7x10(-7) M sulfamethazine; 4.0x10(-8) M sulfamethoxazole; 6.4x10(-8) M sulfathiazole and 6.0x10(-9) M 5-sulfaminouracil. The data suggests a potential application of the poly(3-methylthiophene) (P3MT) electrode for determination of sulfonamides in veterinary and other applications.