Current Analytical Chemistry - Volume 10, Issue 4, 2014

The ICP-AES technique was developed for rhenium determination in the range of 0.00002 - 0.05 % in copper and molybdenum ores along with their concentrates. The sample pretreatment method by sintering with magnesium oxide and oxidizing agents was offered for analysis; optimum conditions for samples digestion were established. These conditions enabled to pass rhenium into solution with no losses. Matrix influence on rhenium emission spectral lines was studied and methods were investigated to eliminate matrix effects. The analysis results of rhenium-containing ores and concentrates certificated reference materials and mixtures on their basis, obtained by the developed procedure, agreed well with the certified rhenium content values.

Ornidazole is an antibacterial drug active compound. A glassy carbon electrode (GCE) was modified with an electropolymerized film of p-aminobenzene sulfonic acid (p-ABSA) in pH 7.0 phosphate buffer solution (PBS). The electrochemical properties of the polymer film were studied using cyclic voltammetry (CV) and different pulse voltammetry (DPV) techniques. The polymer film-modified electrode was used to electrochemically detect ornidazole. The polymer film showed excellent electrocatalytic activity for the reduction of ornidazole. The cathodic peak potential value of the ornidazole at the p-ABSA modified glasy carbon electrode was -513 mV obtained by DPV. A linear calibration curve for DPV analysis was constructed in the ornidazole concentration range 8x10-7-5x10-5 M. Limit of detection (LOD) and limit of quantification (LOQ) were 1.00x10-7 and 3.32x10-7 M respectively. The DPV technique proposed was successfully applied to the detection of ornidazole in tablet dosage forms. Precision and accuracy of the developed technique were checked by recovery studies. The proposed method exhibits good recovery and reproducibility. The mechanisms of electropolymerization of p-ABSA and reduction of ornidazole at p-ABSA- modified GCE are also suggested.

This work presents the development and validation of a capillary zone electrophoresis method for calcium ions release quantitation from composite biomaterials with potential application in bone tissue engineering. Calcium ions quantitation was made using a fused silica capillary (40 cm, 75 m ID) and background electrolyte containing 5 mM imidazole, 6 mM α-hydroxyisobutyric acid, 1 mM 1,4,7,10,13,16-hexaoxacyclo-octadecane and 20 % w/v methanol, at pH 4.5. Indirect UV-detection mode at 214 nm was performed. The separations were achieved using normal polarity at 6 kV, a cartridge temperature of 25 °C and 0.5 psi for 5 s for sample introduction. Parameters of validation such as specificity, linearity, limit of detection and quantitation, accuracy, precision and robustness were evaluated according to the International Conference on Harmonization guidelines. The new developed method resulted to be suitable for calcium determination from composite biomaterials for potential application in bone tissue engineering.

A selective and sensitive cloud point extraction procedure for the preconcentration of trace amounts of gold prior to their determination by flame atomic absorption spectrometry has been developed. The cloud point extraction method is based on the formation AuI3 and then entrapped in non-ionic surfactant Triton X-114. The main factors affecting cloud point extraction efficiency, such as pH of sample solution, concentration of iodide ion and Triton X-114, equilibration temperature and time, were investigated in detail. Under the optimized conditions, calibration curves were constructed for the determination of gold according to the general procedure. Linearity was maintained between 3.0 ng mL-1 to 1.5 μg mL-1. Detection limits based on three times the standard deviation of the blank divided by the slope of analytical curve (3Sbm) for Au (III) ion was 1.3 ng mL1. Eight replicate determination of a solution of 0.1 μg mL-1 gold gave a relative standard deviation 1.9%. The high efficiency of cloud point extraction to carry out the determination of analyte in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of gold in certified reference material, Silica ore and wastewater samples with satisfactory results.

Graphene, a monolayer of carbon atoms densely packed into a two-dimensional honeycomb crystal lattice, has recently attracted much attention. It possesses an ultrahigh specific surface area, and thus has great potentials for the use as sorbent materials. In this article, we have developed a new method for the preconcentration and determination of trace amounts of cadmium (Cd) prior to its determination by flame atomic absorption spectrometry. It is based on the use of a column packed with graphene as the sorbent. Several effective parameters on the extraction and complex formation were selected and optimized. Under optimum conditions, an enrichment factor of 125 was obtained. The calibration function was linear in the concentration range of 10.0-120.0 μg L-1 with a detection limit of 0.54 μg L-1. The relative standard deviation for ten replicate measurements of 10.0 and 80.0 μg L-1 of Cd were 3.57 and 2.63%, respectively. Comparative studies showed that graphene is superior to other adsorbents including C18 silica, graphitic carbon, and single- and multiwalled carbon nanotubes for the extraction of Cd. The proposed method was successfully applied in the analysis of four real environmental water samples. Good spiked recoveries over the range of 95.4%-100.5% were obtained. This method reveals the large potential of graphene as a sorbent material in separation and preconcentration processes.

In an attempt to discriminate and identify several bacterial species, headspace air samples above a series of bacterial cultures were interrogated using a TD-GC/MS system. Three microorganism strains with relatively low pathogenic character – Escherichia coli, Bacillus subtilis and Staphylococcus aureus – were investigated during a period of 72 hours from the inoculation. Air samples with a volume of 1 L each were collected from the headspace above the bacterial cultures in agar growth medium of a 5 cm3 volume kept in 30 cm3 glass vials, in Tenax-Carbograph desorption tubes, by using a custom-built sampling unit based upon a portable air sampling pump. One sample was taken for each of the 10 different cultures of a bacterial strain, at 24, 48 and 72 hours from the incubation. The adsorption tubes were analyzed using the TD-GC/MS system and the resulting datasets – chromatograms and associated mass spectra – were used to produce a qualitative insight into the chemical profile of the headspace air above the bacterial cultures. Analysis by TD-GC/MS indicated that the chemical profile of the headspace air samples was complex and changed during the three days monitoring period; also, there appeared to be a series of chemicals specific to individual species of microorganisms.

An improved procedure is presented to determine Pb(II) and Cu(II) in gasoline using a mercury film electrode generated in situ. The method is based on the reduction of the metal ions at adequate potentials on the glassy carbon electrode, in whose optimized microemulsion medium composition, the ions can be determined directly and simultaneously by differential pulse anodic stripping voltammetry. Good results were obtained in terms of analytical performance and voltammetric wave forms, with two stripping peaks near to -0.420 V and -0.13 V, attributed to Pb(II) and Cu(II), respectively. Linear responses for both metal ions indicated quite low detection limits (2.1x 10s-9 mol L-1 for Pb(II) and 2.4 x 10-9 mol L-1 for Cu(II)). The method was applied successfully to real gasoline samples, presenting good results for precision (variation coefficients of 12.4% and 10.2%) and accuracy (recoveries ranging from 96.7 to 99.33% and 101.33 to 102.67%), for Pb(II) and Cu(II), respectively.

The influence of different protic and aprotic solvents on the conductometric titrations of cerium(III) with EDTA has been studied. The results are explained for mixed solvent systems using 1,4-dioxane (DA), acetonitrile (ACN), Dimethylsulphoxide (DMSO), N,N’-dimethylformamide (DMF), Tetrahydrofuran (THF) and Methanol (MA) as cosolvents. End points of conductometric titrations improved in presence of 1,4 dioxane as a co-solvent (in comparison to that in aqueous medium) for binary mixtures of Ce(III) with Al(III), Cu(II), Mn(II) and Pb(II), respectively. Composition of co-solvent-solvent medium has been optimized for best conductometric titration results. On the basis of synergic effect of dielectric constant, proton affinity and extent of solvation relative order of co-solvents showing increasing effect has also been proposed. It is now possible to determine Ce(III) in presence of Al(III) without interference in aqueous medium in presence of 20% 1,4 dioxane.

A novel sorbent was synthesized by modification of graphene nano-sheets by pyridine group and characterized by transmission electron microscopy (TEM), thermal analysis (TG/DTA), elemental analysis (CHN) and infrared spectroscopy (IR). The application of this sorbent in determination of lead ions in environmental samples was investigated. Some parameters such as pH and time on adsorption process were optimized and introduced . The other parameters including eluent concentration, eluent volume and elution time which are important factors in desorption process were optimized by using a three-level three variables Box-Behnken experimental design. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 3.5 ng mL-1, 2.2% and 98%, respectively. Finally the method was validated using several standard reference materials.

Enantioseparation of 2-chloromandelic acid enantiomers by ligand exchange chromatography was successfully carried out using chiral ionic liquids (CILs) containing imidazolium cation and L-Proline anion as chiral selectors. The main factors influencing resolution, such as alkyl chain length of CILs, concentrations of Cu2+ and CILs, pH of the mobile phase and temperature, were investigated. To better understand the enantioseparation process, some thermodynamical parameters were evaluated, and the results indicated that the chiral separation of 2-chloromandelic acid enantiomers was an enthalpy-controlled process.

A simple, novel and sensitive assay method was developed and validated for the estimation of febuxostat, an anti-gout agent, in human plasma using high-performance liquid chromatography coupled to tandem mass spectrometry. The bioanalytical method is involved in liquid–liquid extraction of febuxostat and rosiglitazone (internal standard: IS) using micro volume (100 μL) human plasma and quantitation by triple quadrupole mass spectrometry with the help of electrospray ionization technique, operating in multiple reaction monitoring and positive ion modes. Chromatographic separation was achieved using an isocratic mobile phase (0.2% formic acid solution in water : methanol, 10:90, v/v) at a flowrate of 0.5 mL/min on a ZORBAX SB-CN column (50x4.6 mm, 3.5 m) with a total run time of 2.2 minutes. The MS/MS ion transitions were monitored as 317.3→261.1 for febuxostat and 358.3→135.2 for IS. Method validation was examined as per FDA guidelines and the results obtained were quite satisfactory. The lower limit of quantitation obtained was 0.005 μg/mL and the linearity range reported an extension from 0.005 to 10 μg/mL. Febuxostat was found to be stable in a battery of stability studies viz. bench-top, auto-sampler, freeze thaw cycle and long-term. The method was proved highly reproducible with low chromatographic retention cycle and was successfully applied to quantitatively assess febuxostat in human plasma obtained from the pharmacokinetic study.

Propolis – in the form of alcoholic extract – is one of the most produced and commercialized bee products in the world due to its many pharmacological properties hence several chemical compositions which vary according to their producing regions, botanical source, type of bee, climate amongst other factors are there. In this manner, this study has the objective of finding a relation among the Brazilian commercial propolis extracts to each of their respective producing regions by applying a supervised classification method as the partial least squares discriminant analysis (PLS-DA). Thusly, it was possible to discriminate between the samples from the South and Southeast regions of the country with 100% accuracy in the prediction of new samples from both regions studied. In this sense, the proposed methodology can be used to perform a rapid distinction between geographical origins of the propolis extracts due to its fast capability to do so, as well as, its low cost, in order to attain a superior quality control of these products.

In this study, the simultaneous determination of verapamil hydrochloride, gliclazide and simvastatin in pharmaceuticals by chemometric approaches using UV spectrophotometry has been reported. Spectra of verapamil hydrochloride, gliclazide and simvastatin were recorded at several concentrations within their linear ranges and were used to compute the calibration mixture between wavelength range of 200 and 400 nm at an interval of 3 nm in pH 6.8 phosphate buffer containing 0.5% sodium lauryl sulphate (SLS). Partial least squares regression (PLS) and principle component regression (PCR) were used for chemometric analysis of the data. The analytical performances of these chemometric methods were characterized by relative prediction errors and recoveries (%) and were compared with each other. These two methods were successfully applied to pharmaceutical formulation, tablet, with no interference from excipients as indicated by the recovery study results. The proposed methods are simple, rapid and can be easily used as an alternative analysis tool in the quality control of drugs and formulation.

In this work, a new version of RAFA was developed for simultaneous determination of the stepwise dissociation constants along with concentration of multiprotic acids based on pH gradual change-UV spectral data. The main aim of this study was to introduce an improved version of the model based RAFA for quantification of analytes and also calculation of model parameters without knowing the pure spectra. The proposed method was validated by analyzing simulated data at the first stage. Then, the binary mixtures of ascorbic and sorbic acids were selected as the model compounds and good analytical results were obtained using the proposed procedure. Finally, the method was successfully applied to simultaneous determination of ascorbic acid and sorbic acid in sour cherry juice as a real sample.

A stability-indicating reversed-phase high-performance liquid chromatography (RP-HPLC) method has been developed which can separate and accurately quantitate Mebeverine hydrochloride (MEB) and Chlordiazepoxide (CPZ) in commercial tablets. The method has shown adequate separation for MEB and CPZ from their degradation products and main impurities of CPZ whether in pure forms or in commercial tablets. A gradient mobile phase system consisting of (A) water and (B) methanol was used with Phenomenex&® Luna C18 analytical column (250mm x 4.6mm i.d., 5μm ps). Quantitation was achieved with UV detection at 254 nm, based on peak area. MEB and CPZ were subjected to acidic, basic hydrolysis and oxidative degradation to apply stress conditions. The linearity of the proposed method was investigated in the range of 40-130 μg ml-1 (r = 0.9987) for MEB and 8-22 μg ml-1 (r = 0.9991) for CPZ. The limits of detection were 4.77μg ml-1 and 0.71μg ml-1 for MEB and CPZ, respectively. The limits of quantitation were 14.44 μg ml-1 and 2.14 μg ml-1 for MEB and CPZ, respectively. Degradation products of MEB, CPZ and impurities of CPZ did not interfere with the detection of MEB and CPZ. The proposed method can thus be considered as a stability indicating assay.

Resolution of complex binary mixtures of Ethinylestradiol (ST) and Levonorgestrel (LEV) was successfully achieved with minimum sample pre-treatment and without analyte separation. The work is based on the radial basis functions- partial least squares (RBF-PLS) analysis of UV spectral data. For calibration and external test sets, binary mixtures were rationally designed. The results for modeling and subsequent prediction in external test set samples resulted in Q2 values of 94.1 and 99.4% for ST and LEV, respectively. The RBF-PLS models were then successfully applied to determine the analytes in real samples consisting of pharmaceutical preparations. In the analysis of the real samples, we excluded the spectral regions where the unknown interferences are absorbed and matrix effect exists. The mean recoveries for the real samples were between 90.6 and 106.8%. The estimated precisions of the method in terms of RSD% were in most cases below 4%.

In this study emulsification based liquid microextraction (EBLME) was developed for preconcentration of Cu(II) using a redesigned dispersive liquid - liquid microextraction (DLLME). The procedure is based on an organic extraction solvent and aqueous solution of surfactant system where a mixture contains appropriate amounts of the extraction solvent (25.6 μg mL-1 dithizone chloroformic solution) and aqueous solution of sodium dodecyl sulfate (SDS) as a disperser. Immediately after the injection, a cloudy media is formed containing oil in water microemulsions; into which the analyte ions could be extracted. After centrifugation, the copper is determined in the enriched phase by flame atomic absorption spectrometer. Some factors influencing the extraction efficiency of copper ion determination were studied and optimized. Under the optimized conditions, the relative standard deviation (RSD) for seven repeated determinations, at a concentration of 0.2 μg mL-1 was obtained to be 3.9 %. The limit of detection and enrichment factor were 0.32 ng mL-1 (S/N = 3) and 147, respectively. A comparison between the employed method and dispersive liquid–liquid microextraction indicates that emulsification based liquid microextraction (EBLME) has simplicity, rapidity, reproducibility, and possesses lower limit of detection and higher enrichment factor for determination of copper ion in natural waters.

In this work solid phase extraction had been implemented with fiber optic-linear array detection spectrometry and partial least squares (PLS) multivariate calibration approach for simultaneous determination of ultra trace amounts of metals with complexes which have overlapping spectra. An octadecyl silica membrane disk modified with N-benzoyl-Nphenylhydroxylamine (BPHA) in combination with partial least squares regression (PLS) was used for simultaneous preconcentration and spectrophotometric determination of iron and vanadium in water samples. The method was based on the retention of V(V) and Fe(III) on the disks modified by BPHA in the pH range of 2.0-4.5. The retained ions were eluted with 3 mL of methyl isobutyl ketone and were measured spectrophotometrically. The data obtained from the experiments were processed by partial least squares chemometric method. PLS was applied for multivariate calibration and noise reduction through eliminating of the less important latent variables. Under the optimum conditions, for preconcentrating the analytes from 100 mL sample, the linear dynamic ranges were 14–320 μg L-1 and 10–530 μg L-1 and the detection limits were 4.2 μg L-1 and 2.5 μg L-1 for V(V) and Fe(III), respectively. The method was successfully applied to the determination of analytes in several categories of water samples. The accuracy was assessed through the recovery experiments, independent analysis by graphite furnace atomic absorption spectrometry and the analysis of a certified reference water sample.

Nucleic acid-based biosensors are typically used to detect DNA or RNA fragments of genetic importance. However, nucleic acids can also serve as binding partners for other molecules, including metal ions. This binding occurs through electrostatic interactions between metal cations and negatively charged DNA strands and through the specific binding of metal cations by donor atoms from the phosphate groups and nucleobases. Additionally, the ability of nucleic acids to form secondary structures is of particular importance, as the formation of secondary structures can modify the interactions with metal ions through shape-recognition effects. This article reviews electrochemical DNA sensors used for metal ion quantification. These devices are divided into three categories: sensors with receptor layers composed of double- stranded DNA (dsDNA), single-stranded DNA (ssDNA) or random-sequence oligonucleotides; sensors based on oligonucleotide sequences that show high selectivity toward particular metal ions; and sensors that employ DNAzymes with metal ion cofactors.

Nitric oxide (NO), a reactive free radical, is an important messenger molecule in biological cells. It plays a critical role in regulating vascular tone, host immunity, neurotransmission, nutrient metabolism and the whole-body homeostasis. NO is metabolized into various products, including plentiful nitrite and nitrate in the circulatory and excretory in vivo, others such as peroxynitrite, nitronium ions, nitroxide ions, and S-nitroso/nitro compounds are unstable and degraded to nitrite and nitrate. The direct measurement of NO is difficult for its reactive chemical properties and short half life. The determinations of nitrite and nitrate could be used to evaluate NO level. Numerous methods are available for measurement of nitrite and nitrate, such as high performance liquid chromatography (HPLC), gas chromatography (GC), ion chromatography (IC), Griess, spectrophotometry, chemiluminescence, fluorescence, catalytic kinetic, infrared spectrophotometry and electron paramagnetic resonance. Of note, chromatography analysis is a common and sensitive method. Based on the reaction of nitrite with 2,3-diaminonaphthalene (DAN) to form N-naphthotriazole (NAT), HPLC coupled with fluorescence detector could lower the limit of detection of nitrite and nitrate, and has no interference of impurities in biological samples. Furthermore, the method involves the GC/LC-MS with the use of 15N as a stable-isotope label. GC-MS can determine the PFB-NO2 and PFB-NO3 derived from nitrite and nitrate with PFB-Br, while LC-MS can determine NAT derived from nitrite with DAN. GC/LC-MS could not only enable specific assessment for low nitrite and nitrate, but also enable reliable investigations on the metabolic fate and reactions of NO and its metabolites S-nitro compounds in vitro and in vivo. Here, we reviewed the applications of HPLC, GC and IC on the analysis of nitrite and nitrate in various biological fluids. It will provide some suggestions for the study of NO in biochemistry, physiology, and pharmacology researches in the future.

The review presents a brief description of electrogenerated chemiluminescence (ECL) and an overview of luminophores focusing on semiconductor nanocrystals elucidating their fundamental principles and development. It also presents the immobilization of Ru(bpy)3 2+ on electrode surface and its merging chemistry with separation techniques. Finally, the conclusion part highlights future challenges and prospects of the development of solid-state ECL sensors.