Current Analytical Chemistry - Volume 12, Issue 6, 2016

Prussian blue (PB) is one of the most commonly used electrochemical mediators for analytical applications during the last decades. Its redox properties of electro-catalyzing hydrogen peroxide qualify it to be used in construction of various sensors for environmental, clinical and food analysis. In this review, the significant characteristic of PB was extensively discussed. Several methods for synthesizing Prussian blue nanoparticles (PBNPs) were also involved. A comprehensive review was given to the electrochemical sensors based on PB composite modified electrodes to monitor hydrogen peroxide and organic peroxides. Furthermore, both pH effect and stability of PB film in sensing applications were highlighted.

Background & Objective: The presence of Lewis acid sites on the metal oxides is responsible for a problematic elution of Lewis bases from these stationary phases due to the ligand exchange. The interactions are quite strong and the kinetics is relatively slow which is chromatographically undesirable. On the other hand, the interactions based on ligand-exchange could be employed in the solid-phase extraction. We newly tested these presumptions in the extraction process of ibuprofen (Lewis base) from hydrophobic suppositories as well as a hydrophilic oral suspension. Method & Results: The pharmaceutical formulation was dissolved in hexane (suppositories) or 50 % methanol (oral suspension) and 0.5 mL of the appropriate solution was loaded on a cartridge containing bare zirconia. After washing with methanol and water, ibuprofen was eluted by 1% ammonia in methanol. It was shown that only zirconia (in contrast to titania) was capable to extract ibuprofen from pharmaceuticals thanks to the stronger ligand exchange properties. A novel method for ibuprofen extraction using zirconia was proposed. The recoveries of ibuprofen were 95 % and 94 % from suppositories and an oral suspension, respectively. Conclusion: This paper describes the first successful utilization of ligand exchange process on zirconia in the extraction of ibuprofen from two different pharmaceuticals. It was shown the pivotal role of interactions between the carboxylic moiety and the Lewis acid sites on the zirconia surface. The procedure can be applied in case that the vehicle is not compatible with the chromatographic conditions used for the subsequent analysis of the active compound.

Background: Supercritical Fluid Chromatography (SFC) is an eco-friendly and sensitive method for the determination of various polar and non-polar analytes. SFC is offering advantage of low solvent consumption. The aim of this paper is to describe a novel SFC method for determination of montelukast in formulation and exploring the possibility of the method for the degradation study of montelukast. Methods: Methanol was used as solvent for analyte. Supercritical carbon dioxide (SC-CO2) was used as a mobile phase at a flow rate of 1.9 mL/min with 5% v/v methanol as co-solvent. Chromatographic separation was achieved on Zorbax SB Phenyl column (150 mm X 4.6 mm, 5 μm) with monitoring of the eluent at 238 nm using UV detector. The column temperature and back pressure of the system were 400C and 200 bar respectively. The physical properties like densities and polarities of the mobile phase were optimized from the effect of pressure, temperature and co-solvent concentration on chromatographic parameters. Validation of the developed method was carried out as per ICH guidelines in terms of selectivity, linearity, precision, recovery, robustness and solution stability. Results: The retention time for montelukast was 8.71 ± 0.14 min. Beer-Lambert’s law was found to obey in the concentration range 10-250 μg/mL with correlation coefficient 0.999. The method was found to be precise, accurate and robust with % RSD of less than 2%. Assay of montelukast was found to be 100.43 and 96.17% in formulations containing 10 mg and 5 mg of montelukast respectively. Montelukast was found to get degraded in acid, photo and peroxide stress conditions, while no degradation was observed in base and thermal stress conditions. Conclusion: The method was successfully applied for the assay and content uniformity of different marketed formulations having a dose of 10 or less than 10 mg of montelukast. The developed method proved its potential for the separation of degradation products of montelukast in various degradation conditions.

Background: Quantitative structure-activity relationship studies of long chain arylpiperazines demonstrated that 5-HT1A affinity is influenced by the nature of the aryl group at N1 of the piperazine ring and the length of the alkyl chain at N4 position linked to terminal amide or imide part, but still the function of terminal amide/imide moieties is less clear. Objective: The aim of the study is building analytical models useful in predicting the biological activity of potential 5-HT1A ligands. Pyrimido[5,4-c]quinolin-4(3H)-ones differ from previously analyzed compounds in the volume of the no-pharmacophoric part of the molecule which can be located in the large pocket of the receptor. Method: The multiple linear regression (MLR) analysis was carried out to study the quantitative structure- activity relationship. Models were developed on the basis of biological in vitro study, chromatographic data and molecular descriptors. The thin layer chromatography was performed on normal-phase plates impregnated with solution of L-amino acids residues determined as essential for ligand-binding to the 5-HT1A receptor. Results: The satisfactory result of statistical analyses expressed by the final structure-activity relationship models explain 87% and 93% of the variance and simultaneously describe the potential interactions between the ligand and amino acid residues. Additionally, the effect of electronic properties of compounds on 5-HT1A receptor binding affinity can be observed. Conclusion: The predictive ability of analytical models was demonstrated using Leave-One-Out and Leave-N-Out cross-validation procedures. Obtained results confirmed that they can be used for prediction of the potential biological activity of new entities in drug discovery process.

Background: Tons of pharmaceutical compounds are used every year around the world in human and veterinary medicine, and these can reach wastewater treatment plants by metabolic excretion and/or improper disposal. Some compounds are not completely eliminated during the wastewater purification processes and are introduced into the environment through a variety of sources and pathways. Pharmaceuticals can have large toxicological effects on the marine biota. It is necessary to develop sensitive and selective analytical methodologies in order to determine these compounds at the low requiered levels. Methods: Development of procedures for the determination of four pharmaceuticals (acetylsalicylic acid, naproxen, ibuprofen and gemfibrozil) in both water and sludge samples, based on solid phase extraction (SPE) and microwave assisted extraction (MAE) followed by ultra-high performance liquid chromatography with fluorescence detection (UHPLC-FD). Results: The optimum conditions for the SPE procedure were extraction with an Oasis HLB cartridge, 250 mL of sample at pH 9 without salt addition, 5 mL of Milli-Q water for the wash step and 3 mL of methanol for the elution. For the MAE procedure, the following conditions were used: power of 500 W, an extraction time of 6 min and 5 mL of methanol as the extractant. Limits of detection between 13.20 and 1338 ng·L-1 for liquid samples and between 1.16 and 86.4 ng·g-1 for solid samples were obtained. Recoveries were over 79% and 69% for liquid and solid samples, respectively. The application of the optimized methodology to sewage samples from different elimination treatments allows for the detection of gemfibrozil at a concentration of 2.52 μg·L-1. Sludge samples were also analyzed, but any compound was detected. Conclusion: The optimized methods for the analysis of liquid and solid products from WWTPs were satisfactorily validated for most of the target pharmaceutical compounds. Although the use of mass spectrometry detection provides higher sensitivity and is suitable for the detection of the trace levels, optical detectors continue to be very useful because of the low cost of their acquisition and maintenance.

MC-ICP-MS analysis is conducted on seven Han dynasty bronze artifacts from Liangshan Yi Autonomous Prefecture Museum, Sichuan Province, Southwest China. The lead isotope ratios conform to the characteristics of the common lead. The lead ore sources are mainly located in Mengzi-Gejiu and Qiaojia-Huize area, Yunnan Province. Some lead ore was from Geochemical Province of Southern China. A further study shows the lead ores used by Ba State in the Eastern Zhou dynasty (476 BC-221 BC) were used in the Han dynasty (202 BC-221 AD). The lead ingot products were utilized in Liangshan bronze industry. Moreover, in the Han dynasty, the ancient cultures of Liangshan, Dian, Ba and Yelang were exchanged. By contrast, communications among Liangshan, Dian and Ba were closer.

Background: Mixed anxiety depressive disorder is commonly treated with a mixture of an antidepressant and a benzodiazepine drug. Quality control to ensure that these products comply with the specifications is required. To improve the quality control of pharmaceutical products throughout the world, accessible analytical methods are needed. Objective: The aim was to develop fast, simple, cheap, accurate and easily accessible analytical methods for the simultaneous determination of selected antidepressant mixtures by high performance liquid chromatography. The first mixture contained amitriptyline, chlordiazepoxide and nortriptyline as an impurity of amitriptyline, while the second one was imipramine and alprazolam in a challenging component ratio. Method: Both chromatographic methods used a 5 cm length Phenomenex C18 column. The mobile phase was acetonitrile - 0.05 M phosphate buffer pH 3 (25:75, v/v) for the first mixture, and acetonitrile - 0.05 M phosphate buffer pH 2.8 (30:70, v/v) for the second mixture. The UV- detector was set at 240 nm. Results: The methods show good linearity in the range 0.1 - 100 μg mL-1 for both amitriptyline and chlordiazepoxide and 0.1 - 20 μg mL-1 for nortriptyline in the first mixture. The second mixture shows linearity over 1 - 400 μg mL-1 for imipramine while alprazolam was linear from 0.1 to 10 μg mL-1. The accuracy and precision of the methods have been determined by analyzing laboratory prepared pharmaceutical mixtures. Both methods proved to be specific, robust and accurate according to the International Conference on Harmonization guidelines and can be applied in quality control of these drugs. Conclusion: Short reversed phase columns provided separation in a few minutes for the mixture of amitriptyline and chlordiazepoxide (containing nortriptyline) as well as imipramine and alprazolam.

Cyclovirobuxine D is an active steroid alkaloid distributed in Buxus microphylla and applied in therapeutic practice of cardiovascular disease. This study describes the development of a new CRM, which includes the homogeneity assessment, stability assessment, purity determination, and uncertainty evaluation. DSC method was applied to the value assignment of cyclovirobuxine D for the first time. The certified purity value for the CRM of cyclovirobuxine D is 996.6 mg•g-1 with an extended uncertainty of 0.6 mg•g-1 (k = 2, P = 0.95) by DSC method. The CRM of cyclovirobuxine D can be widely used to quantitative analyses of cyclovirobuxine D and other related pharmaceutical formulations.

Background: Hair provides important information that helps medicine with an early diagnosis of physiological disorders associated with metabolic alterations of essential and toxic elements. However, some metals are present in the hair sample in very low concentrations for some analytical techniques, such as flame atomic absorption spectrometry. This work aims to develop an on-line pre-concentration system for copper determination in trace levels from hair samples. Methods: A basic simplex algorithm was applied to the optimization of the on-line preconcentration system. The system is based on the solid phase extraction of copper in a mini-column packed with Amberlite XAD-4, functionalized with 3,4-dihydroxybenzoic acid, and metal elution with hydrochloric acid solution. The optimized variables were: pH, sample flow rate and HCl concentration. Results: The developed system presents limits of detection, quantification and enrichment factor of 1.1 μg L-1, 3.7 μg L-1 and 23.8, respectively, with a pre-concentration time of 120 s. The accuracy of the method expressed as relative standard deviation was 9.4% at the concentration of 10.0 μg L-1 and 8.5% for 40.0 μg L-1. The accuracy of the method was accessed by copper determinations in real hair samples, comparing the results of two analytical techniques, and there were no significant differences between the results at 95% confidence level. Conclusion: Simplex has been shown a simple, fast and efficient optimization method in the establishment of the optimum conditions for the developed of an on-line pre-concentration system for copper determination. Validation procedures has proved that, it presents analytical characteristics to allow trace levels determination from human hair.

Background: Epinephrine (EP), ascorbic acid (AA) and tyrosine (TY) usually coexist together in human blood and are considered as important molecules for physiological processes in human metabolism. Thus, to determine these compounds in biological fluids, we need to develop sensitive, simple and rapid methods. Method: The simultaneous spectrophotometric determination of AA, EP and TY, at pH=7.0 using multivariate calibration techniques such as principal component regression (PCR), partial least squares (PLS) and their first derivative methods have been carried out. Results: Satisfactory results were achieved using first derivative-partial least squares. After optimization of all variables, the linear ranges for AA, EP and TY were 0.8-35.0, 1.0-72.01 and 1.0-145.0 μgmL-1, respectively. The detection limits for AA, EP and TY obtained 0.1, 0.35 and 0.28 μgmL-1, respectively. Principal component (NPC) for AA, EP and TY were 2, 3 and 3. Prediction error sum of squares (PRESS) for AA, EP and TY were 2.37, 0.91 and 2.57, respectively. The root mean square errors of Prediction (RMSEP) for AA, EP and TY were 0.35, 0.16 and 0.60 respectively. Conclusion: Good agreement between prediction and actual concentrations clearly indicates the utilization of this procedure for the simultaneous determination of AA, EP and TY in serum, plasma and urine samples and also for the determination of AA in vitamin c tablet and EP in epinephrine injection.

Background: Solifenacin is used for the treatment of overactive bladder. At present, a number of separation and determination techniques, including high-performance liquid chromatography, Liquid chromatography–tandem mass spectrometry and spectrophotometric techniques have been used for the analysis of solifenacin in different samples. Objective: In the present work, for the first time, a Hollow fiber based liquid phase microextraction (HFLPME) followed by high performance liquid chromatography (HPLC-UV) was used for extraction of solifenacin from biological samples. Method: Chemometric method was used for optimization of the effects of different parameters influencing the extraction efficiency of the proposed method. The organic liquid membrane consists of 1-Octanol immobilized in the pores of a hollow fiber wall. A pH gradient was applied to migrate analytes from alkaline sample solution with pH 10.9, through the organic liquid membrane into an acidic acceptor solution with pH 2.9. which was located inside the lumen of hollow fiber. Results: Under optimized experimental conditions, extraction recoveries higher than 85% were obtained in different biological matrices which resulted in preconcentration factors higher than 163 and acceptable repeatability(RSD% within day:3.47%..RSD% between day: 4.12%). Conclusion: The method offers good linearity with estimation of coefficient higher than 0.9900. Finally, it was applied to the detection and determination of solifenacin in human plasma and urine samples.

Background: Hot corrosion is a phenomenon seen in gas turbines using residual fuel oils, which contains vanadium. Austenitic stainless steels are ones of the most used materials in components and devices of boilers, gas turbines and furnaces burning contaminated fuel oil. The materials selection is made in great extend due to a good corrosion resistance and low cost. Some works have been done in order to determine the performance of stainless steels under molten salts at high temperatures, obtaining good corrosion resistance, that is why the evaluation of the corrosion rate and the type of corrosion suffered by two austenitic stainless steels is important in order to determine their possible selection under hot corrosion conditions. Methods: The corrosion resistance of the materials was obtained applying the linear polarization resistance and the electrochemical impedance spectroscopy during 100 hours. In order to determine some aspects of the corrosion mechanism, potentiodynamic polarization measurements were also obtained. Physical and Chemical analyses were carried out utilizing the Scanning Electron Spectroscopy and the Xray Diffraction technique. Results: It was determined that AISI-316H developed a Cr2O3 layer, which was dissolved by the electrolyte, so that, this alloy suffered intergranular corrosion due to the precipitation of Cr23C6, such as it has been reported extensively. AISI-347H presented the Kirkendall effect, suffering an important depletion of Fe and in a less extent of Cr, leading to a mixed corrosion process. These behaviors were corroborated with the electrochemical techniques. Conclusion: AISI-316H presented intergranular corrosion, whereas AISI-347H suffered a mixed corrosion type, observing areas indistinctively localized and uniformly corroded. The electrochemical techniques indicated that AISI-316H is more corrosion resistance and both alloys were diffusion controlled systems.

A sequential injection analysis (SIA) was developed for the determination of ferrous ion (Fe(II)). The detection method was based on monitoring of surface plasmon resonance at 446 nm of the product obtained by on-line reaction of silver nanoclusters (AgNCs) with Fe(II). The experimental parameters affecting the sensitivity were investigated, including sequence order of operation, volume of sample and reagent zones, flow rate for detection, and concentration of the reagents involved. Under the selected conditions, a linear calibration for Fe(II) determination was obtained in the range of 1–30 mg L-1. The limit of detection was found at 0.3 mg L-1. A sampling frequency of 25 h-1 was obtained. The proposed method was applied for the determination of Fe(II) in supplement products with percentage recoveries obtained in the range of 87–105%. The results showed no significant difference with colorimetry and FAAS standard methods.

Background: Microbiological assay is the gold-standard method for analyzing antibiotics, since it ensures the success of antimicrobial therapy. However, this method may be time-consuming and it remains almost unaltered since it was first developed. Here, we present the design space of a rapid microplate bioassay for bacitracin. Methods: Triphenyltetrazolium chloride was used in the bioassay to provide faster response. Factorial design and response surface methodologies were used to optimize microorganism, inoculum proportion, culture medium composition, bacitracin concentration, and triphenyltetrazolium chloride concentration. Results: Yeast extract amount in culture medium was a key factor in reducing incubation time and it allowed the development of a faster bioassay. In addition, inoculum proportion was a critical parameter. On the other hand, triphenyltetrazolium chloride concentration did not affect the bioassay response. The bioassay was linear, accurate, precise and robust. Conclusion: Besides being equivalent to an agar diffusion assay according to statistical analysis, the colorimetric bioassay requires less culture medium and solutions, and provides faster results.

Background: Nitrite is a carcinogenic compound and can be found in water, soil, and food products. Determining the presence of nitrite has become very important in monitoring water quality and food safety. Methods: A highly sensitive optical chemical sensor based on sol-gel film for trace amounts of nitrite was developed. The Xylene cyanol FF dye doped organic-inorganic silica hybrid film was obtained by copolymerization of tetraethoxysilane (TEOS) with methyltriethoxysilane (MTEOS) as an organically modified sol-gel precursor, and deposited onto glass substrates using spin-coating techniques. Results: The organically modified silicate thin film prepared with a 2:1 TEOS: MTEOS volume ratio was found to be the best in terms of transparency, uniformity, and stability. The organically modified silicate thin film changes from blue to yellow when added to a nitrite aqueous solution, causing decreased absorbance of the film at 618 nm. The experimental results show that the film has a good linear response (R2 = 0.9833) to nitrite in the range of 10 to 0.1 μg. L-1. Conclusion: The XCFF dye doped sol-gel film has high sensitivity, selectivity for nitrite in the water samples. The detection limit of film for nitrite was found to be 0.011 μg. L-1 (0.24 nmol.L-1). This sol-gel film is stable, inexpensive, and easily fabricated. It could be practical used for the determination of nitrite in most real water samples.

Background: The biosensors are analytical devices combining a bioreceptor and a physicochemical transducer to translate the signal resulting from the interaction of the analyte with the biological element into an electrical reading. The technological attractiveness of the biosensors resides in their high sensitivity, continuous measuring capabilities, low cost, and precision. An important and promising area of biosensors application is the associated with blood glucose levels monitoring in diabetic patients. However, accuracy and stability issues are still under development, impeding the more widespread offering of glucose biosensors in the market. Thus, this work aims to contribute to the biosensors technology by analyzing the amperometric response to glucose of a typical glucose oxidase-based sensor of second generation, applying mathematical models. Methods: The amperometric response of the glucose oxidase-based electrochemical sensor of second generation was analyzed under different conditions such as temperature, pH, mediators’ and substrate’s concentrations through statistical learning methods from a regression perspective. Artificial Neural Networks (ANN), LASSO and RIDGE Regression and Classification and Regression (CART) were the algorithms selected to achieve the regression task. Results: The reported experimental results show a promising very low prediction error of the biosensor output by using Neural Networks and Classification and Regression Trees. It is also shown that the relationship between predictors, i.e. features or variables- and response-target variable- corresponds to a nonlinear behavior. Conclusion: A final CART and a Neural Network models are presented as a simple solutions that can be solidly constructed in order to predict the amperometric response of a glucose oxidase sensor. The experimental proposal and conditions offered in this paper could be applied for other scenarios in the wide spectrum of biosensing technology.

A sensitive, accurate and simple method for the simultaneous preconcentration of Cu(II), Ni(II), Cd(II), Mn(II), Cr(III) and Pb(II) in milk samples has been reported in this study. Target metal ions were determined by flame atomic absorption spectrometry (FAAS) after preconcentration on Aspergillus niger (A. niger) loaded on TiO2 nanoparticles. The dead biomass of A. niger was first loaded on TiO2 nanoparticles and bioadsorbent obtained was characterized by SEM. The effect of pH, amount of bioadsorbent, elution conditions, maximum sample volume and flow rate on the recovery of trace metal ions studied were investigated. Trace metals were quantitatively sorbed on the bioadsorbent at pH 6.0, at a flow rate of 3.0 mL min-1 and subsequently eluted from the mini column with 2.0 mL of 0.5 mol L-1 HNO3. The preconcentration factor of the proposed method was 600. Detection limits (3s) of the method were 0.21 μg L-1 for Cu(II), 0.34 μg L-1 for Ni(II), 0.18 μg L-1 for Cd(II), 0.08 μg L-1 for Mn(II), 0.53 μg L-1 for Cr(III) and for 0.61 μg L-1 Pb(II). Relative standard deviations (RSDs) of the method are lower than 3% indicating that the precision of method is very good. The accuracy was evaluated by means of the analysis of the standard reference material (NIST SRM 8435, whole milk powder). Finally, the developed preconcentration method was applied to the quantification of Cu(II), Ni(II), Cd(II), Mn(II), Cr(III) and Pb(II) in different milk samples by FAAS.