Current Analytical Chemistry - Volume 13, Issue 6, 2017

Objective: A simple, economical and rapid RP-HPLC method with PDA detector was developed and validated for the simultaneous determination of simvastatin and caffeine in pure form, in formulation and the method is applied to monitor these drugs in mice plasma. Caffeine containing food and drugs commonly co-administered with statins, there is also a possibility of the caffeine-statins combination as anti-influenza formulation implies a need for a reliable HPLC method for the simultaneous determination of these drugs. Method: In the present work, the separation was carried out using methanol: water (90:10 v/v) as mobile phase at pH of 3.5 adjusted using phosphoric acid. At room temperature, isocratic separation carried out on C18 XBrigde™ column (5 μm, 25x0.46 cm) at a flow rate of 1 mLmin-1 and drugs were detected at 230 nm by using a PDA detector. The established method was validated with respect to linearity, specificity, precision, accuracy and limits of detection and quantification. Results: The method was linear at a concentration range of 5-50 μgmL-1 for both drugs with calculated limit of detection of 0.025 and 0.059 μgmL-1 for simvastatin and caffeine, respectively. This method was also successfully applied for the monitoring of these drugs in mice plasma. Conclusion: The present study suggests that the simultaneous determination of simvastatin and caffeine will be helpful to pharmaceutical manufacturing companies and clinicians checking for drug-drug interactions and could save expenses in case of future combination determination.

Background: Cobalt is one of the most important essential trace metals of human nutrition. Low doses of cobalt are needed for many humans and animals to stay healthy. Cobalamine (named vitamin B12) is a cobalt-containing essential vitamin. The direct detection of metal ions in various matrices by AAS may be difficult due to matrix interferences and extremely low levels of metal ions. Thus, a preconcentration and separation step is normally demanded. In this report, a two-step microextraction technique, combining room temperature ionic liquid based dispersive liquid-liquid microextraction (ILDLLME) and dispersive magnetic solid-phase microextraction (MSPME) was prepared for the flame atomic absorption spectrometric determination (FAAS) of trace cobalt ions in water samples. Methods: In this study, a two-step microextraction technique based on a new combined approach of ILDLLME/ M-SPME was discussed and the proposed method was applied to the rapid determination of trace cobalt ions in various water samples. In this study, room temperature IL-1-ethyl-2,3- dimethylimidazolium bis(trifluoromethyl sulfonyl)imide [EMIM][Tf2N] was employed as an extractant in the first extraction step (i.e. DLLME). This combined technique offers low limits of detection and high preconcentration factors resulting in high sensitivity. The reported method described an amazing and innovative approach of combining different microscope sample preparation methods to solve some analytical problems. Results: In the first microextraction step, room temperature ionic liquid (RTIL) was employed to extract cobalt-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) complexes from aqueous solution with ultrasound. In the second step, magnetic Fe3O4 NPs was added as an adsorbent and employed to collect the analytes in the organic solvent. After magnetic solid phase separation, the concentrated analyte complexes were eluted with 0.1 M HCl. As a consequence, the linear working range was 0.1-250 μg/L, and the detection limit of the method (LOD) was estimated to be 0.05 μg/L. The proposed twostep extraction procedure was employed by analysis of a certified reference and real water samples. Conclusion: In the current study, a simple two-step extraction method, namely ionic liquid DLLME combined with magnetic SPME was developed. The magnetic Citrate-Fe3O4 (Cit-Fe3O4) nanocomposite was synthesized and can be easily separated by a powerful magnet. In addition, this technique does not require clean-up steps and the magnetic sorbent material (i.e. after extraction, IL adsorbed onto the magnetic material) can often be easily regenerated and reused. This new extraction methodology offers various features such as sensitivity, cost-effective, easy to operate, short extraction time, low detection limit, and use less-toxic organic solvents. In fact, the preconcentration method was successfully applied for Co determination in water samples, with good accuracy and good reproducibility. The calibration graph of two-step microextraction method was linear in the range of 0.1-250 μg/L and the percent recovery of Co was in the range of 95-102%. This is an applicable method for cobalt trace assay in various types of matrices in order to diminish its hazardous effects on ecosystem and environment.

Background: A new modified electrode based on the poly(chromotropic acid) (4,5-dihydroxynaphthalene- 2,7-disulfonic acid) film was developed by electrochemical polymerization to explore its voltammetric behavior. The electrochemical synthesis of poly(chromotropic acid) was accomplished by applying an aqueous solution of sodium hydroxide as a supporting electrolyte (0.1 M). The electrochemical behaviors of bisphenol A (BPA) on poly(chromotropic acid) modified glassy carbon electrode (poly(CTA)/GCE) were researched by cyclic voltammetry, square wave voltammetry, and chronoamperometry. Methods: The analytical performances of the developed method were carefully examined. When the concentration of BPA changed from 0.1 μM to 20 μM, the current response of BPA was linearly related to the concentration over the range of 0.1-2 μM and 2.0-20 μM, respectively and the detection limit of the suggested method was found to be 0.06 μM. The feasibility of the detector was successfully demonstrated for BPA detection in various real samples. Results: The suggested methodology was applied for the detection of BPA in different real samples (bottled water, tap water and honey sample). The samples were prepared as described above and these aforesaid samples were analyzed directly. Since no BPA was detected in these samples, standard addition method was employed. The percent recovery tests were also investigated by measuring the current responses to the samples in which the known concentrations of BPA standard solution were spiked. Thus, the spikes are subjected to similar matrix effects. The percent recoveries in the range of 94.0%– 103% were obtained. These consequences indicated that the poly(CTA)/GCE has adequate electroanalytical efficiency and it can be a feasible sensor for detection of BPA in different samples. Conclusion: A new voltammetric sensor for the detection of BPA was developed based on a very simple preparation scheme consisting in the direct electropolymerization of poly(CTA) films on GCE. The proposed poly(CTA)/GCE displays a helpful and easy method for observing of BPA in real aqueous samples exhibiting an adequate electroanalytical performance (linearity, detection limit, sensitivity, and selectivity) due to its stability and reproducibility associated with an effortless and speedy fabrication, and low cost. This new method could offer a charming approach for on-site detection of trace BPA contamination in aqueous samples.

Background: Fusel oil is a mixture of higher alcohols produced as a minor fraction of the fermentation-distillation process in sugar and ethanol industries. It can be used as a fixating agent in cosmetics products, as solvent in the food industry, or recycled as fertilizer. Considering the effects of toxic elements contamination on the quality and safety of these products, and on the environment, an efficient method for elemental fusel oil analysis may find applications in many fields. In this work, we evaluate the application of microwave-induced plasma optical emission spectrometry (MIP OES) for trace element determinations in the fusel oil matrix. Methods: Simple external calibration with standard solutions prepared in either water or 1-propanol is evaluated. Undiluted fusel oil, and 1-propanol solutions containing 5 or 50% v v-1 sample matrix are analyzed. The introduction of air into the plasma prevented potential carbon deposition on the torch and the optics, and contributed to minimizing background signals. Results: No matrix effects were observed for calibration with 1-propanol solutions even for determinations in the undiluted sample (recoveries between 90-109% for a 1.0 mg L-1 spiking level). The MIP stability requires no sample preparation, which allows for lower limits of detection (LODs) and higher sample throughput. The LODs for Cd, Cr, Cu, Ni and Pb in 1-propanol are 0.03, 0.009, 0.01, 0.007 and 0.04 mg L-1, respectively. Conclusion: The MIP OES procedure described here is a simple, accurate and precise approach to trace element analysis of fusel oil.

Background: In biosensors, enzymes play a crucial role in the analyte detection. However, enzyme based sensors suffer from reproducibility, tiresome immobilisation processes, high cost, and loss of enzymatic activity. In order to solve these problems, non-enzymatic detection of analytes is interesting due to the drawbacks described as regards enzymatic detection. Non-enzymatic sensor was presented in this study. Methods: In this study we functionalised a GNP by dip coating technique. Prepared samples were characterized by XRD, SEM, ATR-FTIR, contact angle analysis, UV-VIS and photoluminescence spectroscopy, and electrical measurements. Finally, analytical performance of the designed sensor was tested by cyclic voltammetry and amperometry. Results: By cyclic voltammetry it was demonstrated that by bending the sensor it still works as an analytical tool to detect H2O2. Using amperometry a linear current response as a function of the H2O2 concentration was observed in a wide concentration range. Moreover, the effect of three possible electroactive interfering species, i.e. glucose, ascorbic acid, and ethanol, on the sensor performance while reducing H2O2 was evaluated by amperometric measurement, which showed that these species are not interferences. Conclusion: The designed sensor demonstrated good performance as regards H2O2 response. We confirmed that sensor is selective towards H2O2 and that glucose, ascorbic acid and ethanol are not interferences in this case. The approach we described herein may open new avenues for using flexible graphene bio-nanosensors in a variety of wearable, implantable, real-time applications in medical and environmental monitoring.

Background: Enzyme-linked immunosorbent assay (ELISA) array, a multiplex ELISA format, has significant advantages in comparison with classic ELISA technology, however, caution is necessary when fabricating an ELISA array for a research. Spotting buffer plays a key role in the performance of glass slide based protein microarray, however, such a buffer effect on polystyrene micro-plate has not been studied in detail. In this study, we describe the optimization of spotting buffer for the fabrication of ELISA array. Methods: Antibody against interleukin 6 (IL-6) was selected as a model antibody for the construction of ELISA array. Different types of buffers (0.01 M phosphate buffered saline (PBS), pH7.4; 0.05 M carbonate- bicarbonate buffer saline (CBS), pH9.6) and different concentration of glycerol (2.5%, 5%, 10% and 20%) and Triton X-100 (0.001%, 0.003%, 0.006% and 0.01%) were investigated for improving the quality of spots and the immobilization efficiency on the polystyrene microplate. Different cytokines solutions (IL-1α, IL-1β, IL-10, IFN-α, TNF-α) were applied to determine the specificity. The different concentration of cytokine IL-6 solution ranging from (0.5-200 pg/ml) was applied to determine the dynamic range and sensitivity. The co-efficient of data was determined by repeated experiments. Results: The results showed that the optimized spotting buffer, 0.01 M PBS with 10% glycerol and 0.003% Triton X-100 could produce spots with a homogeneous morphology (full and round) and significantly improve the signal intensities. The performance parameters experiments indicated that no cross reaction was observed, and the dynamic range of IL-6 was from 1 to 150 pg/ml with a sensitivity of 1 pg/ml. The co-efficient of data for repeated tests was less than 10. Conclusion: The optimized spotting buffer could produce spots with a homogeneous morphology (full and round) and significantly improve the signal intensities. The results provide an improved approach to construct high performance ELISA array.

Background: The ability to accurately assess antioxidant activity would help monitor oxidation- reduction balance and the occurrence and progress of disease. Thus, the purpose of this study is to establish a combination serum assay for determination of total antioxidant capacity. It is important and also has potential clinical application. Methods: Exogenous oxidants such as iodine (I2), potassium permanganate (KMnO4) and hydrogen peroxide (H2O2) were evaluated in the assay of total antioxidant capacity of serum by employing various detection methods. These methods include electrode potential, microtitration method, and agar diffusion. Based on the evaluation of repeatability, linearity, relative resolution, and detection conditions from seven methods, we found that the combination of three assay methods were optimal to determine total antioxidant capacity of serum from diabetes patients and healthy participants. Results: Precision of the methods was acceptable and good linear relationships were observed between the measured values and the serum percent concentration. We conducted comparative analysis of assay results, i.e., calculation of relative resolution, and finally selected I2/KI and H2O2 electrode potential, and KMnO4 microtitration in combination as an optimized assay of total antioxidant capacity. Total antioxidant capacity of serum from 30 diabetes patients was lower than that of 30 age- and sex-matched healthy participants (P<0.001). Stratification analysis of assay results through the determination of antioxidant capacity allowed to distinguish diabetes patients from healthy participants. Conclusion: The combined use of three assay methods optimized the determination of total antioxidant capacity of serum. It is better to use a variety of methods in the clinical testing.

Background: The search for new natural or synthetic products with antioxidant activity is commonly based on methods that involve reduction of either 2,2-diphenyl-1-picrylhydrazyl (DPPH) or 2-2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). However, the reported values of the effective concentrations are highly variable, even in controls. Herein, we optimize and validate both methods of determining antiradical activity. Methods: Optimization was carried out using both a fractionated factorial design and a basic sequential simplex method, by monitoring the reduction percentage. Quercetin or Trolox were used as positive control. Furthermore, for each method, linearity, precision, accuracy, robustness, plate uniformity, signal variability, and Z factor, were established. Results: The optimized conditions for the DPPH method were: DPPH 280 μM in ethanol and 15 min of reaction time in the dark. The linear range was between 7 and 140 μM with an R2 value of 0.9987. The optimized conditions for the ABTS method were: ABTS adjusted to 0.7 absorbance units, 70% concentration in ethanol, and a reaction time of 6 min in the dark. The linear range was found to be between 1 and 70% with an R2 = 0.9991. For both methods, the accuracy and precision were within limits and the Z factor value was higher than 0.89. The applicability of each method was assessed by analyzing eight plant extracts. Conclusion: The DPPH and ABTS reduction methods were optimized and validated on a microscale and could be expected to be implemented in any laboratory.

Background: The photo thermal lens microscopy is a technique based on measurement of the temperature rise which is generated in an illuminated matrix because of non-radiative relaxation of absorbed energy from a laser. It is an ideal system for low detection volume measurements in a micro channel. Hence, in this study, a combined microfluidic chip-photo thermal lens microscopy (MFCPTLM) system was assembled for highly sensitive determination of captopril. Captopril is an angiotensin-converting enzyme (ACE) inhibitor used to treat hypertension, congestive heart failure and kidney problem caused by diabetes. Captopril had no absorption in visible range but due to its thiol group, it could interact with Gold nanoparticles (GNPs). So, GNPs act as its labeling agent and the semi-selective measurement of captopril was achieved. Methods: A 3.35 nM GNPs and captopril solution by the same flow rate were introduced to the microchannels by microsyringe pumps. The mixture was detected with an assembled PTLM system. The applicability of optimized method for determination of captopril in human Serum and pharmaceutical sample was investigated as well. Results: The thiol group of captopril bonded to the surface of GNPs, created the core-shell form and reduced the surface plasmon resonance of GNPs; as a consequence, the PTLM signal of GNPs decreased following the increase in captopril concentration. The difference between the PTLM signals of sample and blank was calculated as a ΔPTLM signal. The detection volume of the PTLM was calculated to be 2.68 fL. At the optimum condition this optical view comprised of 5.4 GNPs, surrounded by 65-1049 captopril molecules. Conclusion: In this study, we proposed a sensitive method for the determination of captopril, based on photo thermal lensing of GNPs in a glass microfluidic chip. The S-type form of microchannel and the micro space scale of that enhanced the surface interaction of captopril molecules and GNPs and resulted in more effective reaction. In addition to the fast interaction time and low detection volume, the main features of this method are simplicity, good analytical performance, and low reagent consumption in comparison with batch procedures. The combination of this system with a highly sensitive method such as PTLM reduced the difficulty of sampling which makes it more attractive. The results show the capability of the method for sensitive measurement of captopril in human serum sample and pharmaceutical tablets.

Background: Multivariate statistical analyses were used to investigate the mineral contents of wines from the mid-São Francisco River valley, located between the northeastern Brazilian States of Bahia and Pernambuco, with those of wines from Rio Grande do Sul State. Methods: Ten elements (Al, Ba, Ca, Fe, K, Mg, Mn, Na, P, and Zn) were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The results were applied to Principal Components Analysis PCA) and and Hierarchical Cluster Analysis (HCA). Results: Considering the 28 wine samples analyzed, the elements Ca, Mg, K, and P were found in higher concentrations in the northeastern wines, with average contents of 71.6, 85.5, 632.9, and 191.2 mg L-1, respectively, and concentration ranges of 6.7-132.0, 53.7-120.7, 177.8-1071.9, and 79.5-376.1 mg L-1, respectively. Conversely, the elements Al, Ba, Fe, Mn, Na, and Zn were found in lower concentrations in the northeastern wines, with average contents of 0.53, 0.19, 1.31, 1.47, 0.69, and 0.46 mg L-1, respectively, and concentration ranges of 0.17-1.28, 0.03-0.46, 0.26-2.34, 0.41-2.73, 0.29-1.59, and 0.06-0.95 mg L-1, respectively. Conclusion: Principal component analysis and hierarchical cluster analysis revealed a natural distinction between the wines from the mid-Sao Francisco River valley and Rio Grande do Sul.

Background: The adsorption of volatile estragole vapor by various polymer membranes was determined using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and quartz crystal microbalance (QCM) gas sensor data. Methods: The estragole gas exposure adsorption experiments were selected based on polymer membrane properties: density, double bond saturation, polarity, etc. Results: Correlation coefficients for ATR-FTIR and QCM were 0.9887 at 1510 cm-1, 0.9991 at 1242 cm-1, and 0.9896 at 1035 cm-1. Compared with QCM, ATR-FTIR spectroscopy nondestructive, faster, less expensive, and sufficiently sensitive that it can be used to analyze gas adsorption on a membrane when measuring the estragole content of essential oils; thus, ATR-FTIR is a practical method for assessing fragrance vapor in essential oils. Conclusion: ATR-FTIR and QCM are comparable nondestructive analytical methods for detecting vapor and gas, but ATR-FTIR is faster and less expensive.

Background: Recently, the use of functionalized metal nanoparticles as colorimetric probes for the detection of a variety of compounds including drugs and pesticide have received considerable attention. Highly sensitive, selective, and cost effective method without any pretreatment of analyte for pharmaceutical analysis is of immense research interest to (bio)analytical / pharmaceutical chemist. Objective: Gold and silver nanoparticles having good optical properties are responsible for spectral change between dispersed and aggregated states of nanoparticles (NPs). In this context, 2,4- dinitrophenylhydrazine dithiocarbamate modified silver nanoparticles which serves as a chemical sensor for the colorimetric detection of omeprazole; is the main objective of this current study. Method: The ligand functionalised silver nanoparticles were synthesized, and characterized with confirmation by UV-Vis, proton NMR, FT-IR spectroscopy and AFM technique. It was found that these conjugates are stable upto 48 hours at room temperature. A UV-visible spectroscopy of reaction mixture with omeprazole at optimized pH 8 revealed reduction in the surface plasmon resonance (SPR) Spectroscopy. Results: Peak of Surface Plasmon Resonance (SPR) of 2,4-dinitrophenylhydrazine dithiocarbamate modified silver nanoparticles were appeared around 400 nm. A new peak appeared at 520 nm with a distinct colour change from yellow to orange. Under optimized conditions the linear range was found to be 0.005-0.3 mM, and the detection limit is 5x10-6M. Conclusion: This newly developed method reported here could successively be applied for the determination of omeprazole in pharmaceutical samples with no interference from the matrixes.