Current Analytical Chemistry - Volume 14, Issue 2, 2018

Background: Atorvastatin calcium belongs to a group of drugs known as statins. It is commonly used to treat a heart disease, so it is used to lower or reduce the fats and bad cholesterol in blood. It has also been used to increase the good cholesterol in blood. Atorvastatin calcium content is commercially known as "Lipitor" tablet. It is available in local pharmacies at different concentrations; 10, 20 and 40mg. Atorvastatin calcium has been previously determined by several analytical techniques such as chromatographic methods, spectrophotometry and electrochemical methods. Methods: Atorvastatin calcium drug was determined in pharmaceuticals using voltammetric techniques, HPLC and UV Vis onto surface of ultra-trace graphite (UT) working electrode. It was also analysed by voltammetric techniques in biological fluids such as plasma and urine. Results: Some analytical parameters were evaluated such as buffer solutions, pH, accumulation time and potential, frequency, scan rate, amplitude voltage step and rate of stirring, using UT electrode vs. Ag/AgCl reference electrode and Pt auxiliary electrode. There are some parameters such as recovery, reproducibility, stability, calibration curve, detection limit, quantification limit and interference, which were also studied. Analytical applications for ATOR were carried out using pharmaceuticals that contained 10, 20 and 40 mg ATOR; and biological samples. Spectrophotometric and HPLC procedures were used for analytical applications to compare their results with anodic stripping voltammetry in terms of accuracy and precision. Conclusion: The developed adsorptive anodic stripping voltammetric method was applied for the determination of ATOR using phosphate buffer at pH3 ATOR at phosphate buffer pH3, 30 s tacc, -0.6 V Eacc, 50 mV amplitude and 3000 rpm in its pharmaceuticals and biological samples. In this research, the determination of ATOR confirmed a high sensitivity of adsorptive anodic stripping voltammetry method comparing other electrochemical methods. The LOD and LOQ also confirmed the sensitivity of the adsorptive anodic stripping voltammetric method. HPLC and UV Vis spectrophotometric methods were used for the comparison of results with adsorptive anodic stripping voltammetry concerning analytical application of ATOR tablets. There are many published articles for the determination of ATOR, but they were lower than adsorptive anodic stripping voltammetry in terms of sensitivity and an ultra - trace graphite working electrode was used in this research as an additional advantage.

Background: Atorvastatin (ATOR) is an antihyperlipoproteinemic drug, (3R, 5R)-7-[2-(4- fluorophenyl)-3-phenyl-4-(phenylcarbamoyl)-5-(propan-2-yl)-1H-pyrrol-1-yl]-3,5-dihydroxyheptanoic acid (Fig. 1a). It is used for the treatment of dyslipidemia and for prevention of different cardiovascular disorders. Methods: A simple and sensitive analytical procedure has been developed, optimized and validated by square wave voltammetry (SWV) using pencil graphite electrode (PGE) for the determination of atorvastatin calcium (ATOR) in both pharmaceutical formulation and biological samples. The voltammetric behavior of ATOR is studied using cyclic and square wave voltammetry in the presence of the ionic liquid-based surfactant, 1-tetradecyl-3-methylimidazolium bromide (C14MImBr). Results: The effect of different factors on the oxidation peak current of ATOR have been studied and optimized such as: pH, scan rate and the concentration of C14MImBr. Under optimized conditions in Britton–Robinson buffer (pH 3.3) containing 28 μmol L-1 C14MImBr, a linear response is obtained within the range of 1.34x10-6 to 10.8x10-6 mol L-1 ATOR, which is adequate for the quantitation of ATOR in real samples. The limit of detection was found to be 3.70x10-8 mol L-1. In addition, the developed method was applied to ATOR analysis in Lipitor tablets and spiked urine samples. Conclusion: This study represents the first report of electrochemical analysis of a pharmaceutical compound using ionic liquid-based surfactant. The analytical signal of ATOR is greatly enhanced in the presence of C14MImBr if compared to that obtained using a traditional cationic surfactant cetyltrimethylammonium bromide (CTAB).

Background: Recently, two-phase flow solvent extraction has been emerged as a promising method for the extraction of radionuclides because it enables minimized radiation exposure and little waste emission. In the field, the coupling of microfluidics-based solvent extraction and stripping with ICP-MS is expected because the combination enables highly sensitive and selective analysis. The previous works have successfully coupled only a single microchip with ICP-MS, leading to lack of selectivity and the need for handling radioactive materials during batch extraction. The study reports for the first time the successful coupling of combined extraction, stripping microchips with ICP-MS. Methods: Extraction of rhenium in 0.1 M HNO3 with Aliquat-336® and stripping of the resulting solvent by 8 M HNO3 were performed on Y-Y shaped microchannel chips. The condition for extraction and stripping in batches and on separate chips were characterized. Then two microchips were connected for extraction and back extraction in series. An external coiled tube (0.1 mm dia., 1 m long) was used to stabilize the pressure. As a result, two-phase flow could be maintained in both the microchips. Additionally, an interface system including a switching valve and a make-up flow was developed for coupling the solvent extraction chip with ICP-MS. The on-line measurement of Re after extraction and stripping was characterized. Results: The condition for extraction and stripping by combined microfluidic chips was found. The two-phase flow could be maintained for hour. The calibration curve of Re was obtained in the 1–20 μg/L range. The detection limit was 0.2 μg/L with a required sample volume of 1 mL. Total process time including extraction, back-extraction, and measurement was less than 1 h. The total efficiency using the combined microsystems was greater than 60%, while the total efficiency of separate extraction and back-extraction on microchips being about 40%. The interference is avoidable with the proposed combined system under the tested conditions. Conclusion: We successfully coupled combined microchips for extraction and stripping with ICP-MS. The two-phase flow can be formed and maintained for a long time through pressure balance by an external flow resistance (we used a coil tube in the study). The developed system promises a highly sensitive and selective elemental analysis with little direct treatment of samples, and thus it is possible to be applied in the field of radiochemical analysis.

Objective: This study uses a novel complexing agent of 2-(2'-benzothiazolylazo)-6- aminophenol impregnated adsorbent multi-walled carbon nanotubes to enrich and separate trace levels of Cd (II), Cu (II), Co (II), Ni (II) and Pb (II) from various samples of food and water collected in Saudi Arabia. Method: Identification of the analyte ions was confirmed by flame atomic absorption spectrometry. The analytical parameters and matrix ions of the solid phase extraction technique were varied to explore optimal analyte recovery. Validation of the procedure was verified by using certified reference materials. Results: The pre-concentration factor was determined to be 100. The following detection limits (LODs) were calculated: Cd (II) 0.6 μg L-1, Cu (II) 0.7 μg L-1, Co (II) 1.0 μg L-1, Ni (II) 0.5 μg L-1 and Pb (II) 1.2 μg L-1. Analyte recovery values ranged from 95-102%, indicating methodological accuracy. Furthermore, precision was demonstrated by the low relative standard deviation (RSD < 2%). Results were consistent with the validating reference materials attesting to the reliability of the method. Conclusion: The method demonstrates high selectivity as it does not experience significant interference from matrix ions. It is also a sensitive method, able to detect ions present in very low quantities. The pre-concentration factor and limit of detection of the proposed method are superior to the other previous solid phase extraction methods.

Background: Reports on the mycotoxin ochratoxin A occurrence in wine and beer indicate that this is a worldwide problem due to the widespread consumption of these beverages. Objective: The existing solid phase extraction methods for the ochratoxin A are usually used in the form of microcolumns, which are generally driven by pumps and take a long time to finish sample pretreatment. It is highly desirable to develop fast, reliable, and low-cost analytical procedures for the monitoring of ochratoxin A in wine and beer. Method: A method comprising magnetic solid-phase extraction (MSPE) followed by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) was developed for the quantification of ochratoxin A in wine and beer. Hexadecyl-immobilized silica-coated magnetic Fe3O4 (C16- Fe3O4@SiO2) nanoparticles were prepared by single-step sol-gel modification of bare Fe3O4 nanoparticles and were used as MSPE adsorbents. Results: Key parameters that affect the MSPE of ochratoxin A in wine and beer, namely, the pH, content of organic components, and desorption solution, were investigated in detail. Under the optimized extraction conditions with gradient chromatographic separation, a limit of detection of 0.02 μg L-1, a precision of 4.4%, and recoveries in the range of 89.7–103.6% were achieved for the determination of ochratoxin A in wine and beer. Conclusion: A MSPE method using C16-Fe3O4@SiO2 nanoparticles as the adsorbent in combination with HPLC-FLD was developed for the determination of ochratoxin A in wine and beer. The validated method is able to provide reliable date at the lower level, displaying satisfactory linearity, precision, accuracy and moderate cost.

Background: The vital importance of trace metal analysis in environmental water samples is widely recognised. In many cases, due to the low levels of trace metals in water samples and the high complexity of the matrixes (i.e. seawater), direct determination of trace metals is not always possible. Atomic absorption spectroscopy (AAS) is a low cost, simple and available technique in many laboratories, but it usually shows saline interferences and insufficient sensitivity for direct Pb determination in water samples. Consequently, a preconcentration and separation step is often necessary prior to lead determination by AAS. Liquid membrane technology is an interesting alternative for separation and enrichment processes, since extraction and stripping processes can be carried out simultaneously and it has been applied in this paper. Method: The processes of transfer, separation and preconcentration of lead ions from saline water samples take place in a bulk liquid membrane using 2-hydroxybenzaldehyde-N-ethylthiosemicarbazone dissolved in toluene as a carrier. The measurements of Pb(II) ions in the stripping phase are performed by AAS. Results: Good recoveries can be obtained using ammonium chloride/ammonia buffer solution at pH 8.5 in the feed phase, carrier concentration of 1.42 x 10-3 mol L-1 in the liquid membrane (using 80 mL of toluene) and 0.3 mol L-1 of HNO3 in the stripping phase. The study has evidenced that chloride anions act as coupled ions, being co-transported with the cationic metal complex. The efficiency of the process at optimal conditions is 83.7±2.5% after 7 hours, with a precision of 3.1% at a confidence level of 95%, being the preconcentration factor of 20.45. The detection limit of the method is 0.391 μg L-1 of Pb(II). The liquid membrane system was successfully applied to the determination of lead in spiked saline samples and real seawater collected from the Algeciras Bay (Cadiz, South Spain). Conclusion: A straightforward method for the preconcentration of trace Pb(II) ions in natural waters with salinity levels (≥10 g L-1) has been developed by a liquid membrane containing 2-HBET in toluene. A lower detection limit of the method in comparison with other liquid membranes for this metal, the use of a cheap commercial organic ligand, as well as the possibility to measure by a common, simple and low cost technique, such as the atomic absorption spectroscopy show the good results obtained. Thus, the separation and preconcentration of lead ions in natural water with saline matrix can be accomplished and the quantitative determination at μg L-1 levels can be achieved by AAS resulting particularly suitable for the analysis of lead ions in seawater samples due to the fact that chloride anions are an active element in the transport process.

Background: Carbamazepine (CBZ) has complex pharmacokinetic properties leading to fluctuation in plasma level, which requires routine therapeutic drug monitoring (TDM) to ensure its efficacy and prevent adverse effects. The objective of this study is directed towards developing and validating a simple, precise, rapid and highly sensitive liquid chromatography-mass spectrometry (LC/MS) technique for measuring CBZ concentration in human plasma of epileptic patients in routine TDM. Methods: The blood samples of 103 epileptic patients were collected for therapeutic monitoring of CBZ with validated LC/MS assay. The analytes from plasma were extracted with methanol by simple protein precipitation method. The Agilent 1100 LC/MS system was used. The ammonium acetate 5mM: methanol (40: 60 v/v) and diamonsil C18 (150mm.6mm, 5μm) were used as mobile phase and analytical column for the separation of analyte, respectively. The temperature of column was 25°C and the rate of flow was set at 0.8 mL/minute. International Conference on Harmonisation (ICH) guidelines were used for the validation of the method. Results: The stated LC/MS assay displayed good linearity in the range of 5-1000ng/ml and linearity equation of calibration curve was y= 2.44516x +0.00348175 with a correlation coefficient (R2) of 0.99881. The lower limit of quantitation (LLOQ) of the stated technique was observed at concentration of 5ng/ml. The linearity, recovery, accuracy and precision, specificity and stability results were within the acceptance limits of ICH guidelines. Conclusion: The simple, precise, rapid and highly sensitive LC/MS technique was developed and validated and successfully applied in TDM of 103 epileptic patients who were using CBZ. Besides TDM, the stated method can also be applied in bioequivalence, pharmacokinetics and pharmacovigilance studies.

Background: Phosphate and silicate are very important in a variety of compounds such as mineral resources, underground water, detergents and cleaners. Phosphate and silicate in water positively influence the metabolism of plants and animals. They have led to an environmental problem. This problem can have serious consequences because phosphate and silicate are widely utilized in water softening, surfactants and a large number of other applications. Methods: Genetic algorithm (GA) is an appropriate method for selecting wavelengths for PLS (partial least squares) calibration of mixtures which have almost identical spectra without losing prediction capacity using spectrophotometric method. In this paper, we have described a simple, sensitive and selective spectrophotometric method for the simultaneous determination of phosphate and silicate based on the formation of phospho- and silicomolybdenum blue complexes in the presence of ascorbic acid. Results: The complexes of phosphate and silicate with a reagent in the presence of ascorbic acid have been simultaneously determined by genetic algorithm- partial least squares (GA-PLS) although they showed a spectral overlap. The calibration curve was linear over a concentration range of 0.01-2.00 and 0.01-3.80 μgmL-1 for phosphate and silicate, respectively. The root mean square error (RMSE) for phosphate and silicate was 0.372 and 0.301, respectively. Conclusion: The present study indicates that the GA can be a good method for feature selection in spectral data sets. Results show that GA-PLS is an excellent calibration method for the determination of phosphate and silicate. In the end the proposed method was successfully applied for the simultaneous determination of phosphate and silicate in synthetic detergents.

Background: Electrochemical DNA sensor is a convenient and sensitive method for the detection of target ssDNA sequence. The developments of nanomaterials modified electrodes provide more opportunity for the enhancement of the analytical performances. Objective: The aim of this paper is to construct a new electrochemical DNA sensor for the detection of Staphylococcus aureus nuc gene sequence with a chitosan-graphene (CTS-GR) and gold nanoparticles (AuNPs) modified electrode. Methods: Electrodeposition was used to synthesize AuNPs directly on carbon ionic liquid electrode (CILE) to obtain AuNPs/CILE. Then CTS-GR nanocomposite was dropped on the surface of AuNPs/CILE to obtain CTS-GR/AuNPs/CILE. The nanocomposite on the electrode was suitable for immobilization of probe ssDNA sequence with electrostatic attraction. Hybridization took place with the complementary ssDNA sequences and assessed with methylene blue (MB) as electrochemical indicator. Results: Due to the synergistic effects of CTS-GR and AuNPs, the modified electrode exhibited excellent electrochemical performances. The reduction peak currents of MB were in line with the concentration of the specific nuc gene sequences from 1.00-13 to 1.00-6 mol L-1 with a detection limit of 3.330-14 mol L-1 (3δ). This electrochemical DNA sensor displayed prominent selectivity to distinct different mismatched ssDNA sequences. Conclusion: This electrochemical DNA biosensor exhibited properties such as higher sensitivity, wider linear range and lower detection limit, which were further applied to the PCR product detection with favorable results.

Background: The acid extraction and enzymatic hydrolysis of starch followed by ion chromatography analysis are the tobacco industry standard methods in China which are very timeconsuming, troublesome, and moreover, there has no structure information of starch. This paper aims to develop an overall method for rapid extraction and simultaneous analysis of the content and structure of starch from flue-cured tobacco leaves by 13C CP/MAS NMR. Methods: The starch from flue-cured tobacco was extracted using pH=10 NaOH solution with the ratio of liquid to solid 30:1 for 90 min and analyzed on the basis of solid state 13C NMR spectroscopy. Its crystalline characteristics, relative crystallinity, proportion of double helices and content were estimated by peak fitting analysis of C-1, C-2,3,5, C-4 and C-6 regions of the spectra. Results: It was found that tobacco starch was B-type crystallinity and had the lowest double helix content and relative crystallinity compared with maize, sweet potato and lotus root starches. The quantitative result of internal standard method showed that the average recovery was 93.0% with the RSD of 3.2%~4.8%. Conclusion: This rapid and accurate NMR method could provide important information about both amount and structure of starch in tobacco.

Background: The majority of non-small cell lung cancer (NSCLC) creates advances in the knowledge of tumor biology and mechanisms of oncogenesis have granted the singling out of several molecular targets for NSCLC treatment. Bevacizumab is an anti-growth factor vascular endothelial growth factor (VEGF) monoclonal antibody, it is the antiangiogenic agent at the most advanced stage of development in the treatment of NSCLC.This drug was selected because of its inter individual differences in clinical response, showing its therapeutic importance in the treatment of NSCLC. The urgent need for proper analytical technique for determination of its concentration in plasma samples for the purpose of therapeutic drug monitoring (TDM) is highlighed. Methods: This study describes the development and validation of a new enzyme-linked immunosorbent assay (ELISA) with high sensitivity and selectivity for bioanalysis of bevacizumab (BEV), a monoclonal antibody used for immunotherapy of different types of cancer. The assay was developed for the purpose of studying the pharmacokinetics (PK), pharmacodynamics (PD), and therapeutic drug monitoring (TDM) of BEV. The assay involved the non-competitive binding reaction of BEV to its specific antigen (human vascular endothelial growth factor protein; VEGF) followed by a chromogenic enzyme reaction for immune detection of the BEV-VEGF complex and color development. Technically, BEV (in the samples) was captured by VEGF antigen protein immobilized onto a 96-well assay plate. The BEV-VEGF complexes formed onto the plate wells were quantified using horseradish peroxidase labeled anti-human IgG (HRP-IgG) and 3,3`,5,5`-tetramethylbenzidine (TMB) as a chromogenic substrate for peroxidase enzyme. The optimum conditions for conducting the proposed ELISA were established and its analytical performance was evaluated as per the guidelines for the validation of immunoassays for bioanalysis. Results: The optimum conditions for conducting the proposed ELISA were established and its analytical performance was validated according to the recommendations for the bioanalytical method validation of ELISA to support PK assessments of macromolecules. The assay limit of detection was 1.01 ng mL-1 and the effective working dynamic range was 1.56-100 ng mL-1 (r2 = 0.9999). The accuracy and precision of the assay were proved. Conclusion: The present study described the development and validation of a highly sensitive and selective ELISA for determination of BEV in plasma samples. The developed ELISA method allowed quantitation limits in human plasma samples at 3.07 ng mL-1 which are 15-fold lower than the reported methods in the literature. The procedures of the proposed ELISA is very convenient to be carried out in a 96-well plate. An analyst can process a batch of ~ 200 samples, in triplicate, per day. This facilitates the processing of a large number of samples in a clinical setting. Because the assay produces color as the analytical signal, only a simple colorimetric plate reader is required. Unlike LC methods, the marked selectivity of the proposed ELISA eliminated the need for pretreatment of plasma samples by affinity chromatography or other sophisticated equipment. For these reasons, the proposed ELISA for BEV is expected to contribute in studying its PK, PD, TDM, and assessing the expected bioavalilability of biosimillars.