A Clotrimazole-Selective Electrode and its Application to Pharmaceutical Analysis

The effect of measurement conditions and the nature of the plasticizer of an ion-selective electrode membrane (ortho-nitrophenyloctyl ether, dinonyl adipate, dibutyl phthalate) on the main performance characteristics of clotrimazole-selective electrodes with polyvinyl chloride ion-exchange membranes containing potassium tetrakis(4-chlorophenyl)borate as an ion exchanger was studied. The introduction of small (up to 20%) ethanol additives into the aqueous solution leads to a significant improvement of the potential stability and expands the working range of the electrodes. All of the studied electrodes have high selectivity to clotrimazole with respect to both inorganic and organic cations, slope of the electrode function close to the theoretical value, and low limits of detection (5.0 × 10^–8–7.5 × 10^–8 M). An electrode with a membrane plasticized with ortho-nitrophenyloctyl ether was the best for the combination of characteristics. It was demonstrated that clotrimazole can be determined in model solutions and various dosage forms (spray, cream, suppositories, tablets) using direct potentiometry and potentiometric titration with sodium tetraphenylborate. The proposed procedures are rapid (10–15 min) and characterized by excellent reproducibility (the relative standard deviation does not exceed 1.2%).     

Potentiometric sensors based on new active components in the multisensor determination of homologues anionic surfactants

Potentiometric sensors are proposed on the basis of alkyl sulfates and cationic copper(II) complexes with organic reagents selective to anionic surfactants. Physical and chemical properties of the ionophores (composition, thermal stability, solubility) are determined in aqueous solutions and in the membrane phase. The studied compounds are poorly soluble (K _s = n × 10^–22–n × 10^–20) and thermally stable at 80?90°C. The main electroanalytical properties of sensors are estimated, i.e., analytical range in solutions of sodium alkyl sulfates 2 × 10^–7–1 × 10^–2 M; 46 <α < 66 mV/рc; LOD = 1 × 10^–7 M; response time 8–9 s in a solution of sodium dodecyl sulfate with the concentration not lower than 1 × 10^–4 M; potential drift 2–3 mV/day; and lifetime 12 months. The multisensor determination of homologues sodium alkyl sulfates in model mixtures and natural waters is performed using the proposed sensors.     

Physicochemical properties of compounds of alkyl sulfates and cationic copper(II) complexes with some organic reagents

Compounds of alkyl sulfates and cationic copper(II) complexes with some organic reagents (pyridine, 1,10-phenanthroline, 2,2'-dipyridyl) were prepared, and their physicochemical characteristics (composition, thermal stability, solubility) were determined. The synthesized compounds are poorly soluble (solubility product K_S = n×10^–20–n×10^–22) and thermally stable (90–260°С). An effect of the hydrophobilicity of alkyl sulfates on the UV characteristics of the copper(II)–organic reagent systems and on the solubility of the studied compounds was evaluated.     

Detoxification of lignocellulose hydrolysates with ion-exchange resins

Lignocellulose hydrolysates contain fermentation inhibitors causing decreased ethanol production. The inhibitors include phenolic compounds, furan aldehydes, and aliphatic acids. One of the most efficient methods for removing inhibiting compounds prior to fermentation is treatment of the hydrolysate with ion-exchange resins. The performance and detoxification mechanism of three different resins were examined: an anion exchanger, a cation exchanger, and a resin without charged groups (XAD8). A dilute acid hydrolysate of spruce was treated with the resins at pH 5.5 and 10.0 prior to ethanolic fermentation with Saccharomyces cerevisiae. In addition to the experiments with hydrolysate, the effect of the resins on selected model compounds, three phenolics (vanillin, guaiacol, and coniferyl aldehyde) and two furan aldehydes (furfural and hydroxymethyl furfural), was determined. The cation exchanger increased ethanol production, but to a lesser extent than XAD-8, which in turn was less effective than the an ion exchanger. Treatment at pH 10.0 was more effective than at pH 5.5. At pH 10.0, the anion exchanger efficiently removed both anionic and uncharged inhibitors, the latter by hydrophobic interactions. The importance of hydrophobic interactions was further indicated by a substantial decrease in the concentration of model compounds, such as guaiacol and furfural, after treatment with XAD-8.     

Electrophoretic and spectrophotometric determination of triiodides of sulfur-containing organic cations

Trimethylsulfonium triiodide (I) and p-xylylene-bis-(tetrahydrothiophenium) triiodide (II) were identified and determined by capillary electrophoresis with the resolution R _s = 4.86 using an unmodified quartz capillary. The procedure ensures the determination of sulfur-containing organic compounds in a concentration range of 1.0 × 10^?5–5.0 × 10^?4 M RSD ≤ 5%). The high stability of trimethylsulfonium triiodide and p-xylylene-bis-(tetrahydrothiophenium) triiodide in chloroform and acetonitrile solutions was found by spectrophotometry. A procedure was proposed for the spectrophotometric determination of compounds I and II as ion associates of sulfur-containing cations with a sulfophthalein dye, Bromocresol Purple (c _min (I) = 1.32 × 10^?5 M, c _min (II) = 7.1 × 10^?6 M, RSD = 5%), and by the characteristic absorption of the triiodide anion in acetonitrile (c _min (I) = 3.18 × 10^?6 M, c _min (II) = 2.76 × 10^?6 M, RSD <-3%).     

Simultaneous screening of homotaurine and taurine in marine macro-algae using liquid chromatography–fluorescence detection

Simultaneous analysis of homotaurine and its homologous, taurine, is a highly challenging issue, especially in matrices they exist simultaneously. A simple precolumn derivatization procedure combined with high-performance liquid chromatography–fluorescence detection was developed for simultaneous determination of homotaurine and taurine in marine macro-algae. The analytes were derivated with o-phthalaldehyde at an ambient temperature and alkaline medium. Calibration curves were linear in the ranges of 50–2500 µg L^?1 for homotaurine and 100–2500 µg L^?1 for taurine with the coefficients of determination higher than 0.998. Limits of detection of homotaurine and taurine were 15 and 30 µg L^?1, respectively. Intraday (n = 6) and inter-day (n = 4) precisions of the method were satisfactory with relative standard deviations less than 6.0%. Good recoveries (>94%) were acquired by the method for extraction of homotaurine and taurine from algae matrices. Liquid chromatography–mass spectrometry was also used to confirm detection of the analytes in algae samples. The data suggest that the method was successfully applied to simultaneous determination of homotaurine and taurine in algae samples.     

Magnetic Multi-Walled Carbon Nanotubes Matrix Solid-Phase Dispersion with Dispersive Liquid–Liquid Microextraction for the Determination of Ultra Trace Bisphenol A in Water Samples

Magnetic nanoparticle-assisted solid-phase dispersion (MMSPD) combined with dispersive liquid–liquid microextraction (DLLME) prior to high performance liquid chromatography with fluorescence detector (HPLC–FLU) is presented for determination of ultra trace Bisphenol A (BPA) in water. Magnetic multi-walled carbon nanotubes (MMWCNTs) were synthesized for the adsorption of BPA in water. Ultra trace BPA in water was transferred into the elute solvent by the MMSPD and further concentrated into trace volume extraction solvent by the DLLME. The limit of detection and limit of quantitation were 0.003 and 0.01 µg L^?1, respectively. Good linearity of BPA was found, ranging from 0.01 to 10 µg L^?1, with good squared regression coefficient (R ²) of 0.9999. Additionally, relative recoveries were 83.1 and 95.9% for two environmental water samples spiked with 0.20 µg L^?1 BPA, respectively. All results showed that the MMWCNTs nanoparticle-assisted MMSPD–DLLME–HPLC–FLU method was simple and reliable for the determination of ultra trace BPA in environmental water.     

Trace determination of cadmium in rice samples using solidified floating organic drop microextraction based on vesicular supramolecular solvent followed by flow-injection analysis–flame atomic absorption spectrometry

In this work, a solidified floating organic drop microextraction was developed based on a vesicular supramolecular solvent consisting of decanoic acid and quaternary ammonium. The method was used for preconcentration of trace amount of cadmium in different rice samples followed by flow-injection analysis–flame atomic absorption spectrometry. Several parameters affecting the extraction efficiency including pH, concentration of 1-(2-pyridylazo)-2-naphthol as the chelating agent, sample and extraction solvent volume, stirring rate, extraction time, salt effect, and interfering ions were investigated and optimized. Under the optimum conditions, a preconcentration factor of 84 was achieved. LOD and LOQ were found to be 0.09 and 0.31 µg L^?1, respectively. The calibration curve was linear within the range of 5.0–700 µg L^?1 (r²?>?0.9978). Intra- and inter-day precisions (RSD% n?=?3) were estimated 2.7 and 3.9% at the concentration of 20 µg L^?1, respectively. The accuracy of the method was successfully validated by analysis of an SRM-1643f standard reference material. Relative recoveries were achieved within the range of 93–107% elucidating suitability of the method for determination of cadmium in rice samples.     

Labile metal content of sediments-fractionation scheme based on ion-exchange resins

The labile metal content of sediments can be evaluated by equilibrating sediment suspensions with ion-exchange resins. By use of a sequence of strong-acid and weak-acid cation-exchangers (H(+)- and Na(+)-form) and chelating resins, extraction can be performed at pH values ranging from 2 to 10. The results allow the total metal content to be subdivided into seven categories designated as (i) low-pH labile, (ii) weak-acid labile, (iii) exchangeable and readily desorbed at sediment-suspension pH, (iv) weak-base labile, (v) high-pH labile, (vi) non-labile soluble forms and (vii) detrital metal content. The sediment suspensions are mixed overnight with the different types of exchanger (held in porous containers) and the cations transferred from the sediment are subsequently back-extracted from the resins into 0.05M EDTA (pH 7.5). The EDTA extracts are analysed for Cu, Pb, Zn, Cd, Ca, Mg, Fe and Al. Analysis of the aqueous phase left in contact with the sediment residue gives the amount of non-labile species released. Eighteen sediments, containing various levels of metal contamination, and an effluent dam sludge have been examined by this technique. All the exchangers released Ca and Mg from the sediments, and the H(+)-form exchangers also released Fe and Al. Some of the Fe, Al and to a lesser extent Zn released by the sediment/exchanger interactions was present as non-labile "soluble" species. The advantages and limitations of this "labile metal" fractionation scheme have been considered.     

Determination of <Emphasis Type="Italic">o</Emphasis>-phthalic acid esters in water by chromatography–mass spectrometry with emulsion dispersive liquid–liquid microextraction preconcentration

Using emulsion dispersive liquid–liquid microextraction preconcentration and injection of a large volume of an extract (10 μL), the limits of chromatographic–mass spectrometric detection of o-phthalic acid esters in water have been attained at the level 4 × 10^–6–1 × 10^–5 mg/L. The main source of the systemic error of the determination of impurities was found to be the release of o-phthalates from microparticles of chromatographic septum to the carrier gas. The extractant (n-octane) was purified by Rayleigh distillation. The independence of the concentration coefficient of the studied o-phthalates of concentration in the range (0.4–30) × 10^–4 mg/L has been demonstrated. The relative expanded uncertainty of the determination of o-phthalates has been calculated and equals 12–39%.     

Calculating the Ionization Constant of Functional Groups of Carboxyl Ion Exchangers

The potentiometric titration of a weakly basic carboxyl cation exchanger, obtained via alkaline hydrolysis of an acrylonitrile copolymer with divinyl benzene (degree of crosslinking, 12%) in a wide range of variation in a solution of рН (2–12) and NaCl (concentration 0.01, 0.1, 0.5, 1 М), is considered. The maximum ion-exchange capacity of the ion exchanger for Na⁺ is determined (10.10 ± 0.088 mmol/g of the dry mass) and found to be independent of the solution’s ionic strength. It is established that in the investigated range of NaCl concentrations and рН, the acid–base balance is adequately described by Gregor’s equation. The parameters of this equation are calculated as a function of the NaCl concentration: рK_а = 8.13 ± 0.04, n = 1.50 ± 0.02 for 0.01 М; рK_а = 6.56 ± 0.04, n = 2.60 ± 0.07 for 0.1 М; and рK_а = 5.66 ± 0.6, n = 2.62 ± 0.06 for 0.5 and 1 М. It is shown that to describe the acid–base balance correctly within the proposed model we must estimate the adequacy of the experimental and calculated values of the ion exchanger’s capacity at each рН value according to the calculated parameters of Gregor’s equation.     

Simultaneous spectrophotometric determination of iron species using orthogonal signal correction–generalized partial least squares calibration method after vortex-assisted dispersive liquid–liquid microextraction

A vortex-assisted dispersive liquid–liquid microextraction method in combination with UV–Vis spectrophotometry was developed for the simultaneous extraction and determination of iron species. In this method, Fe²⁺ and Fe³⁺ were complexed with pyridine-2-amidoxime, neutralized through ion pair formation with sodium dodecyl sulfate, and extracted into the fine droplets of chloroform. After centrifugation, the absorbance of the extracted complexes was recorded in the wavelength range of 360–700 nm. The parameters affecting the extraction efficiency such as the pH, the type and volume of the extraction solvent, ligand concentration, and sample volume were optimized. The individual iron species was then determined by means of the orthogonal signal correction–generalized partial least squares method. Under the optimized conditions, the calibration curves were linear over the range of 2.0–100 and 3.0–200 µg L^?1 with detection limits of 0.4 µg L^?1 for Fe²⁺ and 0.8 µg L^?1 for Fe³⁺, respectively. The relative standard deviations for intra- and inter-day assays (n = 5) were 2.3 and 4.0 for Fe²⁺ at 50 µg L^?1 and 2.7 and 4.3 for Fe³⁺ at 30 µg L^?1, respectively. The enhancement factors of 77 and 69 were achieved for Fe²⁺ and Fe³⁺, respectively. The proposed method was successfully applied to the determination of iron species in water samples.     

Physicochemical basis of the ion-exchange separation of gold cyanide complexes

The mechanism of the separation of gold cyanide complexes is discussed, along with ion exchanger selection, selectivity, elution, and industrial applications. The ion-exchange mechanism for the sorption of gold cyanide complexes is established, and a criterion is suggested for selecting the anion exchanger for their extraction (specifically, the pK _a of the anion exchanger). The selectivity of the sorption of gold cyanide complexes by anion exchangers with rarely distributed ionogenic groups is demonstrated. A procedure for the elution of gold cyanide complexes using alkaline solutions is developed.     

Application of bar adsorptive microextraction to determine trace organic micro-pollutants in environmental water matrices

The present work proposes the application of bar adsorptive micro-extraction (BAµE) coated with an N-vinylpyrrolidone polymer (NVP) combined with micro-liquid desorption (200 µL) followed by high-performance liquid chromatography with diode array detection (BAµE(NVP)-µLD/HPLC-DAD) for the determination of trace levels of emerging organic micro-pollutants in environmental water matrices. The model compounds selected include an antibacterial/antifungal agent (triclosan), two pharmaceuticals (carbamazepine and diclofenac) and two steroid hormones (17α-ethinylestradiol and 17β-estradiol), in which the latter three were recently included in the European Union watch list of substances to be monitored in the field of water policy. Assays performed on 25 mL of ultrapure water samples spiked at the 8.0 µg L^?1 level yielded average recoveries ranging from 81.9 to 102.4% for the compounds studied using optimised experimental conditions. The proposed analytical methodology demonstrated suitable detection limits (0.02–0.10 µg L^?1) and good linear dynamic ranges (0.1–20.0 µg L^?1) with determination coefficients higher than 0.9909. Using the standard addition method (SAM), the present analytical approach was applied on environmental water matrices, including surface, sea, river and groundwaters. The proposed method proved to be a suitable and alternative sorption-based static micro-extraction technique for monitoring trace levels of organic micro-pollutants in environmental water matrices.     

Flow injection-based cloud point extraction of phosalone and ethion in seawater of Chabahar Bay and determination by high-performance liquid chromatography: study of use of carbon nanotube and nanofibers as a column filler in flow system

This study presents an easy and cost-effective flow-based cloud point extraction (CPE) method for determining partial amounts of two organophosphorus pesticides (phosalone and ethion) in seawater by HPLC–UV–Vis. In continues CPE methodology, the effect of the different column packing type such as carbon nanotube, polyacrylonitrile nanofiber and fiberglass on pesticide extraction was investigated. The Triton X-100 was utilized as nonionic surfactant, and moreover, effect of different parameters such as pH, temperature, extraction time, surfactant concentration, type and volume of the eluent solution on the extraction efficiency was optimized. Under optimum conditions, the figures of merit of the method for phosalone and ethion were obtained as: the enrichment factor (172 and 166), line range (0.8–300 and 0.5–300 µg L^?1, R ² = 0.9973 and 0.9982), relative standard deviation in concentration of 200 µg L^?1 (%RSD = %5.4 and %7.99, N = 5) and limit of detection (LOD = 0.24 and 0.14 µg L^?1). The suggested method was successfully used for determination of phosalone and ethion in Chabahar Bay seawaters with satisfactory results.     

Sensitive and selective determination of peptides,PG and PGP,using a novel fluorogenic reagent 4-chlorobenzene-1,2-diol

A novel fluorometric method was developed for the sensitive and selective detection of Pro-Gly (PG) and Pro-Gly-Pro (PGP) using 4-chlorobenzene-1,2-diol (4-CBD) as a fluorogenic reagent. The reaction was performed at 37°C for 30 min in the presence of a borate buffer (pH 7.0) and sodium periodate. The resulting fluorescence intensity was measured using a spectrofluorometer with excitation and emission wavelengths of 450 nm and 535 nm. To obtain a stable fluorescent signal and maximise its intensity, different reaction conditions such as the concentrations of the reagents, the reaction time, and the pH were optimised. Under the optimised conditions, a linear relationship was obtained between fluorescence intensity and peptide concentrations from 1.0–40.0 µmol L^?1 with a limit of detection of 1.0 µmol L^?1 (S/N = 3). Both PG and PGP generated a strong signal out of all the peptides tested and no other biogenic substances such as amino acids or proteins produced any fluorescence. The reaction thus developed is simple, rapid, selective, and sensitive. It can be applied to the determination of peptides as biomarkers or substrates.     

Rapid Ultrasound-Assisted Emulsification Microextraction Combined with COU-2 Dispersive Micro-solid Phase Extraction for the Determination of Azole Antifungals in Milk Samples by HPLC-DAD

A rapid, simple, and efficient method using ultrasound-assisted emulsification microextraction combined with dispersive micro-solid phase extraction (USAE-D-µ-SPE) was developed for detection and quantification of three azole antifungals in milk samples by high-performance liquid chromatography diode array detector. In this study, mesoporous carbon, COU-2, was used as sorbent in USAE-D-µ-SPE for the extraction and preconcentration of analytes. Several important experimental parameters, including type of deproteinized solvents, desorption time, type of extraction solvents, volume of extraction solvent, extraction time, emulsification time, sample pH, salt addition, and mass of COU-2 sorbent, were optimized using spiked milk samples. Under the optimum extraction and detection conditions, three azole antifungals, namely ketoconazole, clotrimazole, and miconazole, were determined within 20 min, with good linearity of matrix-matched calibration in the range of 0.5–5000.0 µg L^?1 with coefficient of determination, r ² ≥ 0.9943. The method showed limits of detection and limits of quantification of all analytes in the range of 0.15–3.0 and 0.5–10.0 µg L^?1, respectively. Good repeatability with RSDs <15% (n = 3) and satisfactory relative recoveries (83.3–111.1%) were obtained for spiked azole antifungal drugs in milk. The results reveal that the developed USAE-D-µ-SPE method was a simple, rapid, efficient, environmentally friendly, and practicable method for the determination of azole antifungals in milk samples.     

Simultaneous Spectrophotometric Determination of Paracetamol and <Emphasis Type="Italic">p</Emphasis>-Aminophenol in Pharmaceutical Products with Tiron Using Dissolved Oxygen as Oxidant

A simple, rapid, and specific method was developed for the determination of paracetamol and p-aminophenol. The method is based on the hydrolysis of paracetamol to p-aminophenol, which, using dissolved oxygen as an oxidant in the alkaline region, was further transformed into benzoquinoneimine, capable of reacting with tiron to produce a green indophenol dye. The stabilization of indophenol dye was achieved by the addition of copper(II) solution. The absorbance was measured at 601 nm in alkaline medium, and the molar absorptivity was found to be 1.1 × 10⁴ L/(mol cm). Paracetamol (PCT) and p-aminophenol (PAP) were determined in pharmaceutical products in the 1.5–15 mg/L PAP concentration range with a detection limit of 1.2 × 10⁻⁶ M or 0.13 μg/mL PAP. The developed method can be applied to the determination of p-aminophenol in the presence of paracetamol without prior separation. The proposed method is successfully employed for determination of paracetamol and p-aminophenol in various synthetic mixtures and pharmaceutical preparations. The obtained results were statistically compared with those given by the official method and the procedures evaluated as regards to both figures of merit and ease of applicability. __________ From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 11, 2005, pp. 1147–1151. Original English Text Copyright ? 2005 by Cekic, Filik, Apak. This article was submitted by the authors in English.     

Determination of Pt and Pd in particles emitted from automobile exhaust catalysts using ion-exchange matrix separation and voltammetric detection

We report on the ion-exchange separation of Pt and Pd from the main elements emitted from catalysts of gasoline-fueled cars by exploiting the selective chelating ion exchanger Lewatit MonoPlus TP-214. Pt and Pd were then eluted with a recovery of 92% and 96%, respectively, using an acidified solution of thiourea, and the eluent was analyzed by sequential voltammetry. The detection limits are 0.04 μg L^?1 and 1 μg L^?1 for Pt and Pd, respectively, and the relative standard deviation is about 4.0% (for n?=?10). The procedure was successfully applied to particles emitted from automobile exhaust catalysts of four capacity engine vehicles. Graphite furnace atomic absorption spectrometry was also employed for reasons of comparison. Emission by four vehicles with 1400, 2600, 3200, and 4800 cc engines, respectively, ranged from 19 to 28 ng km^?1 for Pt, and from 102 to 150 ng km^?1 for Pd.

The separation–preconcentration and determination of ultra-trace gold in water and solid samples by dispersive liquid–liquid microextraction using 4-ethyl-1(2-(4-(4-nitrophenyl)piperazin-1-yl)acetyl)thiosemicarbazide) as chelating agent and flame atomic absorption spectrometry

A selective separation and preconcentration method for the determination of gold ions in water and ore samples has been developed using dispersive liquid–liquid microextraction, followed by flame atomic absorption spectrometry. 4-Ethyl-1(2-(4-(4-nitrophenyl)piperazin-1-yl)acetyl)thiosemicarbazide) (NPPTSC) has been used for the first time as new chelating reagent. A mixture of ethanol (dispersive solvent) and carbon tetrachloride (extraction solvent) was used. Some parameters affecting the extraction procedure including the type and volume of the extracting and dispersive solvents, HNO₃ concentration, the chelating agent amount, volume of sample, and foreign ions have optimized. Also, the complex formation between gold ions and the ligand has been investigated in a methanol–water solution (1:1) using UV–visible spectrometry. The spectrophotometric titration data showed that of Au–NPPTSC complex composition was found to be 3:2. After optimizing the instrumental and experimental parameters, we achieved a detection limit of 1.5 µg L^?1, a preconcentration factor of 50, and a linear dynamic range of 10.0–400.0 µg L^?1. The relative standard deviation obtained 2.1% at 50 µg L^?1 for gold ions (n = 10). The proposed method was successfully performed for the determination of gold in certified reference material, environmental water, and ore samples.