Current Analytical Chemistry - Volume 16, Issue 6, 2020

Background: Potassium permanganate is a green and versatile industrial oxidizing agent. Due to its high oxidizing ability, it has received considerable attention and has been extensively used for many years for the synthesis, identification, and determination of inorganic and organic compounds. Objective: Potassium permanganate is one of the most applicable oxidants, which has been applied in a number of processes in several industries. Furthermore, it has been widely used in analytical pharmacy to develop analytical methods for pharmaceutically active compounds using chemiluminescence and spectrophotometric techniques. Results: This review covers the importance of potassium permanganate over other common oxidants used in pharmaceuticals and reported its extensive use and analytical applications using direct, indirect and kinetic spectrophotometric methods in different pharmaceutical formulations and biological samples. Chemiluminescent applications of potassium permanganate in the analyses of pharmaceuticals using flow and sequential injection techniques are also discussed. Conclusion: This review summarizes the extensive use of potassium permanganate as a chromogenic and chemiluminescent reagent in the analyses of pharmaceutically active compounds to develop spectrophotometric and chemiluminescence methods since 2000.

Background: Uremia is the outcome of the remaining of nitrogenous waste products that are normally removed by the kidneys. Para-cresol (4-methylphenol) can be regarded as a proteinbound uremic toxin. The p-cresol determination in sera is necessary since it is a marker of cardiovascular risk and overall mortality in hemodialysis patients. Among the reported methods, chromatographic ones especially HPLC techniques due to the high sensitivity, selectivity and reproducibility have been extensively exploited in analysis of p-cresol in complex mixtures. However, an appropriate sample preparation prior to analysis is necessary for obtaining accurate and precise results. Methods: In this study, the appropriate precipitating agent for p-cresol determination in plasma samples was investigated. Then, in situ surfactant-based solid phase microextraction followed by HPLCFL detection was developed and validated for the quantification of p-cresol in plasma samples. Results: According to the results, HCl/heat precipitation method was used for p-cresol microextraction from from plasma samples. In situ surfactant-based solid phase microextraction using cetyltrimethylammonium bromide as extraction medium was proposed for pretreatment of plasma samples prior to analysis. The separation was achieved by isocratic elution with sodium acetate buffer (pH 3.8) and acetonitrile (20:80, v/v). Linearity was found to be acceptable over the concentration ranges of 0.5 to 8 μg mL-1 with the limit of detection and quantification of 0.324 and 0.422 μg mL-1, respectively. The variations for intra-day and inter-day precisions were both less than 8.2% and the extraction recoveries were more than 97%. Conclusion: A validated ISS-SPME followed by HPLC-FL detection reported to determine the total p-cresol concentration of human plasma samples. The traditional liquid-liquid extraction techniques are normally time consuming and require the use of large amounts of toxic organic solvents. In addition, the evaporation of extraction solvent and dissolving the analyte in the mobile phase is commonly used before HPLC analysis. Such a requirement makes the sample preparation process even more tedious and time consuming. ISS-SPME that is the developed ISS-SPE in micro scale, is a simple, rapid and effective sample preparation technique that is appropriate for HPLC-FL analysis.

Background: Ginger oil poses various pharmacological properties corresponding to its terpene composition which depends upon the preparation method along with the sample variety. Objective: This work aims to explore the variability in the derived oil associated with the hydrodistillation settings i.e. sample freshness/dryness, size reduction process, and heating duration using chemometric approaches. Methods: The extraction process was evaluated with a two-level full factorial design where the volatile oils were hydrodistillated and characterized by gas chromatographic-mass spectrometry. The multivariate dataset ascertained was further explored with principal component analysis. Results: According to the outcomes from the design, the yield could be quantitatively improved by using fresh sample, with reduced particle thickness and longer extraction cycle. The clastering patterns from principal component analysis revealed the domination of monoterpenes in the extracts from fresh samples; sesquiterpenes in the grated samples; whereas heating duration demonstrated antagonistic effect between monoterpenes and sesquiterpenes. Conclusion: These findings suggest the importance of experimental conditions in driving the yield and quality of ginger extracts according to the requirement of the industries.

Background: Carbon-based nanomaterials, especially carbon nitride (C3N4) has attracted tremendous interest in biosensor applications. Meanwhile, the mechanism of redox protein sensing and related electrocatalytic reactions can provide a valid basis for understanding the process of biological redox reaction. Objective: The aim of this paper is to construct a new electrochemical enzyme sensor to achieve direct electron transfer of myoglobin (Mb) on CILE surface and display electrocatalytic reduction activity to catalyze trichloroacetic acid (TCA) and H2O2. Methods: The working electrode was fabricated based on ionic liquid modified Carbon Paste Electrode (CILE) and C3N4 nanosheets were modified on the CILE surface, then Mb solution was fixed on C3N4/CILE surface and immobilized by using Nafion film. The as-prepared biosensor displayed satisfactory electrocatalytic ability towards the reduction of TCA and H2O2 in an optimum pH 7.0 buffer solution. Results: The results indicated that C3N4 modified electrode retained the activity of the enzyme and displayed quasi-reversible redox behavior in an optimum pH 7.0 buffer solution. The electrochemical parameters of the immobilized Mb on the electrode surface were further calculated with the results of the electron transfer number (n) as 1.27, the charge transfer coefficient (α) as 0.53 and the electrontransfer rate constant (ks) as 3.32 s-1, respectively. The Nafion/Mb/C3N4/CILE displayed outstanding electrocatalytic reduction activity to catalyze trichloroacetic acid and H2O2. Conclusion: The Nafion/Mb/C3N4/CILE displayed outstanding electrocatalytic reduction, which demonstrated the promising applications of C3N4 nanosheet in the field electrochemical biosensing.

Background: Burning temperature is one of the most important factors affecting the chemical structure of the smoke and the addition of reconstituted tobacco sheet to cut tobacco has been widely used by the tobacco industry to reduce the cost of cigarettes and the health risks of smoking. Methods: A flame retardant film, made from chitosan and ammonium polyphosphate, has been coated on the surface of the reconstituted tobacco sheet substrate by Layer-by-Layer and spray coating techniques. The thermal degradation properties and flame retardancy of these reconstituted tobacco sheets were analyzed by TG-FTIR and micro-scale combustion calorimetry. Results: It was found that the reconstituted tobacco sheet with the ratio of chitosan (5%) and ammonium polyphosphate (3%) film coating showed significant reductions in the peak heat release rate (50.7%), total heat release (35.8%) and the highest temperature in the temperature distribution diagram (77°C). The main gases released during the pyrolysis of these reconstituted tobacco sheet samples were H2O, CO2, CO, NH3, carbonyl compounds and the presence of film coating changed the formation of evolved volatile products and formed less gaseous products except NH3 during the thermal decomposition process. Conclusion: The coating film can greatly enhance the char forming ability and reduce the flammability of reconstituted tobacco sheet, and therefore, reduce the health risks of smoking with the addition of these reconstituted tobacco sheets.

Background: Reverse İontophoresis (RI) is one of the promising non-invasive technologies. It relies on the transition of low magnitude current through the skin and thus glucose measurement becomes possible as it is extracted from the surface during this porter current flow. Objective: This paper deals with the development and optimization of an RI determination method for glucose. CE dialysis membrane based artificial skin model was developed and the dependence of RI extraction on various experimental parameters was investigated. Methods: Dependence of RI extraction performance on noble electrodes (platinum, silver, palladium, ruthenium, rhodium) was checked with CA, CV and DPV, in a wide pH and ionic strength range. Optimizations on inter-electrode distance, potential type and magnitude, extraction time, gel type, membrane MWCO, usage frequency, pretreatment, artificial body fluids were performed. Results: According to the optimized results, the inter-electrode distance was 7.0 mm and silver was the optimum noble metal. Optimum pH and ionic strength were achieved with 0.05M PBS at pH 7.4. Higher glucose yields were obtained with DPV, while CA and CV achieved almost the same levels. During CA, +0.5V achieved the highest glucose yield and higher potential even caused a decrease. Glucose levels could be monitored for 24 hours. CMC gel was the optimum collection media. Pretreated CE membrane with 12kD MWCO was the artificial skin model. Pretreatment affected the yields while its condition caused no significant difference. Except PBS solution (simulated as artificial plasma), among the various artificial simulated body fluids, intestinal juice formulation (AI) and urine formulation U2 were the optimum extraction media, respectively. Conclusion: In this study, various experimental parameters (pretereatment procedure, type and MWCO values of membranes, inter-electrode distance, electrode material, extraction medium solvents, ionic strength and pH, collection medium gel type, extraction potential type and magnitude, extraction time and etc) were optimized for the non-invasive RI determination of glucose in a CE dialysis membrane-based artificial skin model and various simulated artificial body fluids.

Background: The synthesis of small organic molecules based Hg2+ ions receptors have gained considerable attention because it is one of the most prevalent toxic metals which is continuously discharged into the environment by different natural and industrial activities. 1,4-Disubstituted 1,2,3-triazoles have been reported as good chemosensors for the detection of various metal ions including Hg2+ ions. Methods: The synthesis of 1,2,3-triazoles (4a-4c) was achieved by Cu(I)-catalyzed azide-alkyne cycloaddition, and their binding affinity towards various metal ions and anions were studied by UVVisible titration experiments. The perchlorate salts of metal ions and tetrabutylammonium salts of anions were utilized for the UV-Visible experiments. DFT studies were performed to understand the binding and mechanism on the sensing of 4a toward Hg2+ using the B3LYP/6-311G(d,p) method for 4a and B3LYP/LANL2DZ for 4a-Hg2+ species on the Gaussian 09W program. Results: The UV-visible experiments indicated that the compounds 4a-4c show a selective response towards Hg2+ ion in UV-Visible spectra, while other ions did not display such changes in the absorption spectra. The binding stoichiometry was evaluated by Job’s plot which indicated the 1:1 binding stoichiometry between receptors (4a-4c) and Hg2+ ion. The detection limit of 4a, 4b and 4c for the Hg2+ ions was found to be 29.1 nM, 3.5 μM and 1.34 μM, respectively. Conclusion: Some 1,2,3-triazole derivatives were synthesized (4a-4c) exhibiting high selectively and sensitivity towards Hg2+ ions in preference to other ions. Compound 4a has a low detection limit of 29.1 nM and the binding constant of 2.3x106 M-1. Similarly, 4b and 4c also showed selective sensing towards Hg2+ ions in the μM range. The observed experimental results were corroborated by density functional theory (DFT) calculations.

Background: Diabetes Mellitus (DM) is a major public metabolic disease that influences 366 million people in the world in 2011, and this number is predicted to rise to 552 million in 2030. DM is clinically diagnosed by a fasting blood glucose that is equal or greater than 7 mM. Therefore, the development of effective glucose biosensor has attracted extensive attention worldwide. Fluorescence- based strategies have sparked tremendous interest due to their rapid response, facile operation, and excellent sensitivity. Many fluorescent compounds have been employed for precise analysis of glucose, including quantum dots, noble metal nanoclusters, up-converting nanoparticles, organic dyes, and composite fluorescent microspheres. Silicon dot as promising quantum dots materials have received extensive attention, owing to their distinct advantages such as biocompatibility, low toxicity and high photostability. Methods: MnO2 nanosheets on the Si nanoparticles (NPs) surface serve as a quencher. Si NPs fluorescence can make a recovery by the addition of H2O2, which can reduce MnO2 to Mn2+, and the glucose can thus be monitored based on the enzymatic conversion of glucose by glucose oxidase to generate H2O2. Therefore, the glucose concentration can be derived by recording the fluorescence recovery spectra of the Si NPs. Results: This probe enabled selective detection of glucose with a linear range of 1-100 μg/mL and a limit of detection of 0.98 μg/mL. Compared with the commercial glucometer, this method showed favorable results and convincing reliability. Conclusion: We have developed a novel method based on MnO2 -nanosheet-modified Si NPs for rapid monitoring of blood glucose levels. By combining the highly sensitive H2O2/MnO2 reaction with the excellent photostability of Si NPs, a highly sensitive, selective, and cost-efficient sensing approach for glucose detection has been designed and applied to monitor glucose levels in human serum with satisfactory results.

Introduction: Verapamil (Verap) is an antidysrhythmic agent and a calcium channel blocker, indicated for angina, hypertension, supraventricular arrhythmias, and migraine. Objective: Drug monitoring plays a critical role in patient survival. In order to prevent the onset of drug toxicity, trace levels of this drug should be determined. Methods: For this reason, solvent bar microextraction technique coupled with high-performance liquid chromatography was implemented. Results: Under optimum condition, verapamil was micro-extracted from a donor solution (pH=11) to an acceptor solution (pH=3.2). It was transferred through n-octanol as the organic solvent, which was impregnated in the pores of the hollow fiber. Salt addition (30%) had the major effect on the efficiency of the method. Interaction of time (65 min), temperature (25°C), and stirring rate (818 rpm) had a significant effect too. It all resulted in a limit of detection and quantification of 15 ng mL-1 and 50 ng mL-1, respectively. The relative standard deviations of analysis were 4.9% within a day (n=3) and 5.7% between days (n=9). The calibration curves represented good linearity for urine and plasma samples with coefficient estimations higher than 0.99 with a linearity range of 50-5000 ng mL-1. The relative standard deviation for intra- (n=3) and inter-(n=9) day was 4.2% and 5.7%, respectively. Conclusion: It could be concluded that the application of this method for dose monitoring can be done at hospital and healthcare facilities.

Background: Drug Enforcement Administration confirmed that many manufacturers began adding tetramisole or its individual isomers to cocaine as an adulterant, and believed that tetramisole may augment cocaine’s effects. In recent times, there is an increasing trend in the usage of tetramisole and its individual enantiomer in race sports especially in horse and camel races. So it’s is very much required to confirm the stereochemistry of this illicit drug in the routine race day samples coming to the anti-doping labs in order to avoid legal arguments and challenges to the analytical findings. Methods: The aim of the study was to develop a simple, rapid and accurate method for the chiral separation and determination of enantiomeric mixtures of levamisole and dexamisole using Thermo Q-Exactive High-Resolution Mass Spectrometer. In order to evaluate the suitability of the method for determining the enantiomeric purity of tetramisole, validation studies were also carried out by using equine plasma. Results: The enantio-separation was achieved using the Lux i-cellulose-5 column. Isocratic flow was used with a 1:1 mixture of mobile phase A (10 mM ammonium acetate in water) and mobile phase B (acetonitrile), at a flow rate of 0.6 mL/min. The run time was 8.0 min, and the column temperature was 50°C. Dexamisole eluted at 5.94 min, and levamisole eluted at 6.62 min, giving the R-value of 1.50. The obtained inter-day precisions of dexamisole, levamisole were 3.16% and 2.85%, respectively. The accuracy of dexamisole was in the range of 97.78 to 102.44%, and that for levamisole was 99.16 to 102.82%. The limit of quantification value for both isomers in this method was 0.1 ng/ mL. The method was linear in the range of 0 to 50 ng/mL. Conclusion: Chromatographic separation was achieved using the polysaccharide cellulose chiral column, and the reverse-phase separation approach was found to have the highest potential for successful chiral resolution in LC-MS. Linearity, precision, accuracy, detection limit, recovery, and the matrix effect in equine plasma were determined. Under the optimized conditions, the validated method can be applied for the identification and detection of the tetramisole enantiomers in different sources of illicit drugs of abuse.

Background: Vanillin is a key constituent of natural vanilla. Usage of natural vanilla is affected due to its high price and limited supply, which leads to the use of artificial vanilla flavoring substances. Coumarin is a commonly encountered adulterant in beverage, food, and cosmetics as a flavoring and fragrance enhancer. However, coumarin has been banned for use as a food additive due to its toxic effects. To comply with the quality of vanillin in food and food products needs to be ensured. Methods: A rapid, simple and selective analytical method has been developed and validated using ultra-high performance liquid chromatography-tandem mass spectrometry for quantitative analysis of vanillin and coumarin. We also optimized fragmentation pattern of these metabolites while increasing collision energy to elucidate its structural information. The suitability and robustness of the method was checked by Zorbax Eclipse XDB C8 column (4.6 × 150 mm, 5 μm) using mobile phase comprising of methanol (A) and water with 0.1% formic acid (B) (90:10) with a flow rate 200 μL/min. The separation was achieved within 4.2 min with total run time of 5.0 min. The analysis was done by multiple reaction monitoring using 153/93 and 147/91 pair transition in positive electrospray ionization for vanillin and coumarin respectively. Results: The lower limit of quantification of vanillin and coumarin was 0.39 ng/mL and 3.9 ng/mL respectively. The intra and inter-day precisions for vanillin and coumarin were lower than 8.87 and 8.62 whereas, accuracy was within ± 2.13 and ± 1.53 respectively. The vanillin and coumarin was found to be stable under the examined conditions. This method was successfully applied for quantification of vanillin and coumarin in mangrove species and commercial food products. Conclusion: The described method and fragmentation pattern could be useful to direct confirmation and quality monitoring of a commercial food products assimilated with vanillin.

Background: Bougainvillea x buttiana has long been used as a Mexican conventional medicinal drug to cure different sicknesses. Objective: In this work, the consequences of ethanol combination and temperature extraction for phenolic compound recovery with the biological activity in Bougainvillea x buttiana extracts were investigated. Materials and Methods: The phenolic recovery from Bougainvillea x buttiana was determined by comparing the effects of ethanol 0%, 50-100% (v/v) and extraction temperature (26, 45 and 64°C). The total phenolic content was investigated using spectrophotometric methods. Antioxidant activity from different Bougainvillea x buttiana extracts was evaluated by determining their potential to scavenge the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical. The chemical compositions and cytotoxic effect of extracts were determined using GC-MS techniques and the crystal violet technique, respectively. Results: Our results confirmed that all extractions with different concentrations and temperatures had significant effects over the total phenolic contents and antioxidant activity (DPPH) of the extracts. The best recuperation of the total phenol content was observed in extracts with 60% ethanol at 26°C (201.08 mgEGA/g dry extract). Extracts with 100% ethanol at 26°C showed the highest antioxidant activity (IC50 was 286.75 μg/mL). GC-MS revealed the presence of various phytochemical contents with polar and non-polar properties. The phenolic compounds were investigated as to the structure, quantity and position of the hydroxyl groups on the benzene ring. Conclusion: The ethanolic extract of Bougainvillea x buttiana was confirmed to have high phenolic content and contain pharmacologically active compounds, with potent antioxidant effects and low cytotoxic effects.

Objective: Molecularly Imprinted Polymer (MIP)-modified potentiometric sensors for histamine (HIS) (as denoted as HIS sensor) have been developed. Methods: The MIPs comprise HIS, Methacrylic Acid (MAA) and ethylene glycol dimethacrylate as the template molecule, functional monomer and cross-linker, respectively. To examine the specificity of the MIP to HIS, the MIP particles were prepared with varying ratios of HIS: MAA and the HIS binding amount toward the MIP particles was determined by UV spectrophotometry. Furthermore, to quantitatively determine the ability of MIP (H2M20) to HIS, a HIS sensor was measured using Ag/AgCl as a reference electrode. Results: MIP particles having a HIS:MAA of 2 mmol:20 mmol (MIP (H2M20)) had the largest HIS binding amount among the MIP particles prepared. Additionally, MIP (H2M20) displayed a HIS binding amount approximately two times larger than the corresponding non-imprinted polymer (NIP) particles in the absence of template. The HIS sensor potential change increased as a function of HIS concentration and exhibited a near-Nernstian response of −25.7 mV decade−1 over the HIS concentration range of 1x10−5 to 1x10−4 mol L−1 with a limit of detection of 9.6x10−6 mol L−1. From the Nernstian response value, it was observed that the HIS sensor could detect the di-protonated HIS binding to the MIP. Conversely, when comparing at the same HIS concentration, the potential response value of the sensors fabricated using NIP particles were significantly smaller than the values of the corresponding HIS sensor. Conclusion: The MIP-modified potentiometric sensors can potentially be employed as an analytical method to quantitatively determine various analytes.

Background: A simple, fast and economic analytical method for the determination of ethanol is important for clinical, biological, forensic and physico-legal purposes. Methods: Ni2+-NTA resin was used as an immobilization matrix for the simple one-step purification/ immobilization of his6-tagged ADH. Different alcohols with a concentration range of 0.5-50% V/V, namely methanol, ethanol and propanol were measured using prepared ADH enzyme thermistor. The ethanol content of Tsingtao beer was tested as a real sample containing alcohol. Reproducibility and stability of prepared ADH enzyme thermistor were also investigated by repeated measurements. Results: In comparison to the controlled pore glass (a common used support for the immobilization of enzyme) used in thermal biosensor, the use of Ni2+-NTA resin not only led to simple one-step purification/ immobilization by his6-tagged ADH binding to Ni2+-NTA resin, but also made the immobilizing supports reusable. The prepared biosensor can be used to determine ethanol and methanol by the calorimetric measurement. A linear range of 1 -32% (V/V) and 2-20% (V/V) was observed for ethanol and methanol, respectively. The detection limits were 0.3% (V/V) and 1% (V/V) for ethanol and methanol, respectively. The tested ethanol concentration of Tsingtao beer was 4.5% V/V, which is comparable with the labeled alcohol by volume (ABV) 4.80%. Conclusion: Ni2+-NTA resin, as an immobilization matrix in ET sensor, provides a simple one-step purification/immobilization for His6-tagged recombinase and a reusable immobilization matrix. The prepared biosensor exhibits good repeatability and stability. Such a new biosensor shows great promise for rapid, simple, and cost-effective analysis of ethanol and methanol, both in qualitative and in quantitative tests.

Background: Molecular imprinting is a technology used to produce artificial receptors that simulate the molecular recognition in the nature and prepare the polymer network structure in the presence of template molecule. Molecularly imprinted visual sensor combines the advantages of specific recognition via molecular imprinting and fast response speed via visualization. The aims of this paper are to prepare a portable visual sensor for Horseradish Peroxidase (HRP) recognition based on molecularly imprinted hydrogel. Methods: At first, HRP-imprinted polyacrylamide hydrogels with 1 mm thickness were obtained by one-step synthesis via radical induced in-situ polymerization of acrylamide using acrylamide (AAm) as the functional monomer, N,N'-Methylenebisacrylamide (MBA) as the crosslink agent and HRP as the template molecule. Results: Compared with nonimprinted hydrogels, the HRP-imprinted hydrogel sensor showed significant color changes in response to the target HRP. This visual sensor was constructed based on 3, 3', 5, 5'- tetramethyl benzidine (TMB) - H2O2 color reaction system by HRP catalyzing to produce color change through digital photography and image analysis (RGB system). The HRP-imprinted hydrogel showed good response in the range of 0.001-0.5 mg/mL and had a significant specific recognition compared to other proteins via selective test. Conclusion: The proposed portable visual sensor could be used for qualitative and semi-quantitative analysis of HRP with high selectivity and reasonable regeneration. The sensor has the advantages of simple operation, low cost, no special equipment, and can be applied to serum sample with less sample consumption and no need of sample preparation. It has wide application prospects in microfluidic devices, biomimetic sensors, flexible biosensor and membrane separation technology.