Current Analytical Chemistry - Volume 16, Issue 4, 2020

Background: Nano level chiral separation is necessary and demanding in the development of the drug, genomic, proteomic, and other chemical and the environmental sciences. Few drugs exist in human body cells for some days at nano level concentrations, that are out of the jurisdiction of the detection by standard separation techniques. Likewise, the separation and identification of xenobiotics and other environmental contaminants (at nano or low levels) are necessary for our healthiness. Discussion: This review article reports the state-of-the-art of nano level chiral analyses by nano liquid chromatography (NLC) and nano capillary electrophoresis (NCE). The optimization procedure of the enantiomeric resolution is also deliberated. Also, the efforts are made to describe the chiral resolution mechanisms of in NLC and NCE. Finally, the future perspectives are also emphasized. Conclusion: This article will be beneficial for chiral chromatographers, academicians, pharmaceutical industries, environmental researchers and Government regulation authorities.

Background: Today, “drugs of abuse” pose serious social problems such as many crimes, medical treatment costs, and economic repercussions. Several worldwide clinical laboratories use analytical separation methods to analyze their patient samples for drugs and poisons. In this way, they provide qualitative and quantitative data on the substances in various biological matrices (e.g., urine, plasma or serum, saliva, and breath). Methods: An extensive review of the published articles indicates that the use of Capillary Electrophoresis (CE) coupled with sensitivity enhancing methods is a very attractive area of interest in the assay of drugs of abuse. Results: This review was prepared to have a comprehensive study on applications of sensitivity enhancing methods on the determination of drugs of abuse especially from 2007 to present. The sample preconcentration approaches almost address all methods from online preconcentration (both electrophoretic and chromatographic-based methods) to offline preconcentration. Furthermore, detection system modification and capillary column fabrications were investigated in order to increase the detection sensitivity of complex samples in CE. Conclusion: The present review summarizes the most recent developments in the detection of drugs of abuse using CE. Although CE still has a limitation in sensitive detection, several publications in recent years have proposed valuable methods to overcome this problem.

Background: Cadmium (Cd2+) and lead (Pb2+) have acute and chronic effects on humans and other living organisms. In the present work, new, green and accurate dispersive micro solid-phase extraction (DμSPE) method for the separation and preconcentration of trace amounts of cadmium (Cd2+) and lead (Pb2+) ions in various food, water and tobacco samples collected from Saudi Arabia prior to its Flame Atomic Absorption Spectrometric (FAAS) determinations was developed. Methods: The proposed method was based on a combination of oxidized multiwalled carbon nanotubes (O-MWCNTs) with a new chelating agent 5-benzyl-4-[4-methoxybenzylideneamino)-4H- 1,2,4-triazole-3-thiol (BMBATT) to enrich and separate trace levels of Cd2+ and Pb2+. The effect of separation parameters was investigated. The validation of the proposed preconcentration procedure was performed using certified reference materials. Results: Analyte recovery values ranged from 95-102%, indicating that the method is highly accurate. Furthermore, precision was demonstrated by the relative standard deviation (RSD < 3.0%). The limits of detection were 0.08 and 0.1 μg L−1 for Cd2+ and Pb2+ ions, respectively. The preconcentration factor was 200. Conclusion: The proposed method was used for the estimation of Cd2+ and Pb2+ ion content in various real samples, and satisfactory results were obtained. The proposed method has high adsorption capacity, rapid adsorption equilibrium, extremely low LODs, high preconcentration factors and shortens the time of sample preparation in comparison to classical SPE.

Introduction: In this study, solar exfoliated graphite oxide modified glassy carbon electrode was used for the anodic oxidation of epinephrine in a phosphate buffer medium at pH7. The modified electrode showed fast response and sensitivity towards Epinephrine Molecule (EP). The electrode was characterized electrochemically through Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV). Area of the electrode enhanced three times during modification and studies reveal that the oxidation process of EP occurs by an adsorption controlled process involving two electrons. The results showed a detection limit of 0.50 ± 0.01μM with a linear range up to 100 μM. The rate constant calculated for the electron transfer reaction is 1.35 s-1. The electrode was effective for simultaneous detection of EP in the presence of Ascorbic Acid (AA) and Uric Acid (UA) with well-resolved signals. The sensitivity, selectivity and stability of the sensor were also confirmed. Methods: Glassy carbon electrode modified by reduced graphene oxide was used for the detection and quantification of epinephrine using cyclic voltammetry and differential pulse voltammetry. Results: The results showed an enhancement in the electrocatalytic oxidation of epinephrine due to the increase in the effective surface area of the modified electrode. The anodic transfer coefficient, detection limit and electron transfer rate constant of the reaction were also calculated. Conclusion: The paper reports the determination of epinephrine using reduced graphene oxide modified glassy carbon electrode through CV and DPV. The sensor exhibited excellent reproducibility and repeatability for the detection of epinephrine and also its simultaneous detection of ascorbic acid and uric acid, which coexist in the biological system.

Background: The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is one of the world’s most serious stored grain insect pests. A method of early and rapid identification of red flour beetle in stored products is urgently required to improve control options. Specific chemical signals identified as Volatile Organic Compounds (VOCs) that are released by the beetle can serve as biomarkers. Methods: The Headspace Solid Phase Microextraction (HS-SPME) technique and the analytical conditions with GC and GCMS were optimised and validated for the determination of VOCs released from T. castaneum. Results: The 50/30 μm DVB/CAR/PDMS SPME fibre was selected for extraction of VOCs from T. castaneum. The efficiency of extraction of VOCs was significantly affected by the extraction time, temperature, insect density and type of SPME fibre. Twenty-three VOCs were extracted from insects in 4 mL flask at 35 ± 1°C for four hours of extraction and separated and identified with gas chromatography-mass spectroscopy. The major VOCs or chemical signals from T. castaneum were 1-pentadecene, p-Benzoquinone, 2-methyl- and p-Benzoquinone, 2-ethyl. Conclusion: This study showed that HS-SPME GC technology is a robust and cost-effective method for extraction and identification of the unique VOCs produced by T. castaneum. Therefore, this technology could lead to a new approach in the timely detection of T. castaneum and its subsequent treatment.

Background: As a broad-spectrum antibiotic of the sulfonamide family, Sulfadimethoxine (SDM) has been widely utilized for therapeutic and growth-promoting purposes in animals. However, the use of SDM can cause residual problems. Even a low concentration of SDM in the aquatic system can exert toxic effects on target organisms and green algae. Therefore, the quantitation of SDM residues has become an important task. Methods: The present work describes the development of a sensitive and selective electrochemical sensor for sulfadimethoxine based on molecularly imprinted poly(o-aminophenol) film. The molecular imprinted polymer film was fabricated by electropolymerizing o-aminophenol in the presence of SDM after depositing carboxylfunctionalized multi-walled carbon nanotubes onto a glassy carbon electrode surface. SDM can be quickly removed by electrochemical methods. The imprinted polymer film was characterized by cyclic voltammetry, differential pulse voltammetry and scanning electron microscopy. Results: Under the selected optimal conditions, the molecularly imprinted sensor shows a linear range from 1.0 x 10-7 to 2.0 x 10-5 mol L-1 for SDM, with a detection limit of 4.0 x 10-8 mol L-1. The sensor was applied to the determination of SDM in aquaculture water samples successfully, with the recoveries ranging from 95% to 106%. Conclusion: The proposed sensor exhibited a high degree of selectivity for SDM in comparison to other structurally similar molecules, along with long-term stability, good reproducibility and excellent regeneration capacity. The sensor may offer a feasible strategy for the analysis of SDM in aquaculture water samples.

Background: Nowadays, polymeric composites modified with carbonaceous nanomaterials have been popular due to their greater application potentials in many application fields. However, the structural consistency of the composite prepared by electropolymerization suffers from agglomeration of Carbon Nanotubes (CNTs) probably due to their poor dispersion in the coating solution. Present study describes a new synthesis route for the preparation of polypyrrole/CNT composite film on a Glassy Carbon Electrode (GCE) via combining the ultrasonication and electrochemical pulsed deposition for the first time. The performance of the composite film was tested by monitoring the electrochemical oxidation of droxidopa which is used as a new psychoactive drug and synthetic amino acid precursor which acts as a prodrug to the neurotransmitters. Methods: The polypyrrole/CNT composite film was deposited onto a glassy carbon electrode via combining the ultrasonication and electrochemical pulsed deposition. The composite film was characterized by Scanning Electron Microscopy (SEM), Fourier Transfer Infrared Spectroscopy (FTIR), Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV). Then after, the electrochemical behavior of droxidopa was investigated on the GCE/PPy-CNT electrode. Results: SEM images of the surface morphology have revealed a more ordered film formation and enhanced conductivity of the surface has been confirmed by EIS measurements. The synergetic effect of this composite film was tested by monitoring the electrochemical oxidation of a new psychoactive drug; droxidopa at 0.45 V. The influence of solution parameters such as medium pH, pyrrole concentration and amount of CNT along with the instrumental parameters including applied pulse number on the peak formation was investigated by aid of cyclic voltammetry. Under the optimal conditions, by monitoring the oxidation peak in dp mode, two linear ranges have been observed in 4 - 20 μM which is well suited for droxidopa analysis in pharmaceutical preparations. The limit of detection (S/N=3) was calculated as 1.3 μM. Conclusion: Present study offers a fast, easy and sensitive method for the determination of droxidopa by providing a novel route for the preparation of PPy-CNT composite films for any further studies.

Background: Simeprevir is one of the recently discovered drugs for treating hepatitis C which is one of the major diseases across the globe. Objective: The present study involves the development of a new and unique High-Performance Liquid Chromatography (HPLC) method using fluorescence detection for the determination of simeprevir (SIM) in human plasma. Methods: Two methods of extractions were tested, protein precipitation using acetonitrile and liquidliquid extraction. A 25 mM dipotassium hydrogen orthophosphate (pH 7.0)/ACN (50/50; v/v), was used as mobile phase and C18 reversed phase column as the stationary phase. The chromatographic conditions were optimized and the concentration of simeprevir was determined by using the fluorescence detector. Cyclobenzaprine was used as an internal standard. Results: Recovery of the assay method based on protein precipitation was up to 100%. Intra-day and inter-day accuracies range from 92.30 to 107.80%, with Relative Standard Deviation (RSD) range 1.65-8.02%. The present method was successfully applied to a pharmacokinetic study where SIM was administered as a single dose of 150 mg SIM/capsule (Olysio®) to healthy individuals. Conclusion: This method exhibits high sensitivity with a low limit of quantification 10 ng mL-1, good selectivity using fluorescence detection, wide linear application range 10-3000 ng mL-1, good recovery and highly precise and validation results. The developed method can be applied in routine analysis for real samples.

Background: Parabens are synthetic esters used extensively as preservatives and/or bactericides in personal care personal products. Objective: Development and validation of a novel robust chemometric assisted analytical technique with superior analytical performances for the determination of ethylparaben, methylparaben and propylparaben, using simulated wastewater matrix. Methods: An automated Solid Phase Extraction (SPE) method coupled with liquid chromatographymass spectrometry was applied in this study. A gradient elution programme comprising of 0.1% formic acid in deionised water (A) and 0.1% formic acid in Methanol (B) was employed on a 100 x 2.1 mm, 3.0 μm a particle size biphenyl column. Two-level (2k) full factorial design coupled with response surface methodology was used for optimisation and investigation of SPE experimental variables that had the most significant outcome of the analytical response. Results: According to the analysis of variance (ANOVA), sample pH and eluent volume were statistically the most significant parameters. The method developed was validated for accuracy, precision, Limits of Detection (LOD) and Limit of Quantification (LOQ) and linearity. The LOD and LOQ established under those optimised conditions varied between 0.04-0.12 μgL−1 and 0.14-0.40 μgL−1 respectively. The use of matrix-matched external calibration provided extraction recoveries between 78-128% with relative standard deviations at 2-11% for two spike levels (10 and 100 μgL-1) in three different water matrices (simulated wastewater, influent and effluent water). Conclusion: The newly developed method was applied successfully to the analyses of parabens in wastewater samples at different sampling points of a wastewater treatment plant, revealing concentrations of up to 3 μgL−1.

Background: Quetiapine Fumarate (QTF) is an atypical antipsychotic drug used to treat mental disorders as depression and schizophrenia. The analysis of the dug in the presence of its precursors, degradants and impurities without interference represents a challenge for the analysts. The regulatory requirements recommended by ICH stated that the impurities above or equal to 0.1% must be identified, characterized and determined. The aim of this work was to introduce three smart and selective spectrophotometric methods that could resolve the complete overlapping of QTF drug with its three related compounds; namely lactam (LAC), N-oxide (OXD) and des-ethanol (DES) without prior separation or extraction step. Methods: So far there is no spectrophotometric method reported in the literature for the analysis of QTF drug with its three related compounds without interference. The First derivative zero crossing (1D-ZC), Spectrum subtraction (SS), and Simultaneous derivative ratio (S1DD) are well-developed methods used for determination and resolution of multicomponent mixtures. While Ratio difference isosbestic point method is a new method that needs two isoabsorptive points for its application and was successfully adopted for simultaneous estimation of ternary mixtures. Results: The linearity range was found in the range of (6-50 μg/mL) for Quetiapine fumarate, (6-110 μg/mL) for lactam, (4-28 μg/mL) for N-oxide and (6-32 μg/mL) for Des-ethanol. The method validation was performed according to ICH guidelines. The results were statistically compared with a reported HPLC method and no significant difference was obtained. Conclusion: The presented spectrophotometric technique highlighted the significance of different tools such as normalized spectra and isoabsorptive points, especially when combined together for the determination and resolution of complex quaternary mixtures as that of QTF and its three major impurities. The proposed methods were smart, accurate and sensitive and were able to determine the four components showing sever overlap without prior separation. The proposed methods are rapid, cheap ecofriendly (green method) and didn’t require any sophisticated programs and could be easily adopted for the routine determination of complex multicomponent mixtures with minimum sample preparation.

Background: A simple, eco-friendly and low-cost Infrared (IR) method was developed and validated for the analysis of Cefepime Hydrochloride (CEF) in injectable formulation. Different from some other methods, which employ organic solvents in the analyses, this technique does not use these types of solvents, removing large impacts on the environment and risks to operators. Objective: This study aimed at developing and validating a green analytical method using IR spectroscopy for the determination of CEF in pharmaceutical preparations. Methods: The method was validated according to ICH guidelines and the quantification of CEF was performed in the spectral region absorbed at 1815-1745 cm-1 (stretching of the carbonyl group of β- lactam ring). Results: The validated method showed to be linear (r = 0.9999) in the range of 0.2 to 0.6 mg/pellet of potassium bromide, as well as for the parameters of selectivity, precision, accuracy, robustness and Limits of Detection (LOD) and Quantification (LOQ), being able to quantify the CEF in pharmaceutical preparations. The CEF content obtained by the IR method was 103.86%. Conclusion: Thus, the method developed may be an alternative in the quality control of CEF sample in lyophilized powder for injectable solution, as it presented important characteristics in the determination of the pharmaceutical products, with low analysis time and a decrease in the generation of toxic wastes to the environment.

Background: Cyclic voltammetry is widely employed in electroanalytical studies because it provides fast information about the redox potentials of the electroactive species and the influence of the medium on the redox processes. Azole compounds have been found to be effective corrosion inhibitors for copper in chloride-containing solutions. The aim of this work was to investigate in detail the influence of the addition of various azole compounds on the oxidation mechanism of copper in chloride-containing solutions, using cyclic voltammetry. Methods: The influence of thirteen azole compounds, at three different concentrations on the electrochemical/ chemical reactions of pure copper immersed in 3 wt.% NaCl solution was studied using cyclic voltammetry at different scan rates. The change of the peak current and potential with the scan rate were investigated. The possible linearity was compared with the theoretically derived mechanism. The possible reaction mechanisms were discussed based on the linearity of these parameters (peak current and potential) with the scan rate compared to theoretically derived models. Results: Both the peak current and peak potential of the copper samples immersed in chloridecontaining solutions with additions of the majority of azole compounds showed linearity with the square root of the scan rate, suggesting that copper follows the Müller-Calandra passivation model. The same behavior was also found for copper in chloride-containing solutions without additions of azole compounds. A linear variation of the peak potential with the natural logarithm of the scan rate and linear variation of the peak potential with the square root of the scan rate was observed for the copper samples immersed in chloride-containing solutions with the addition of 10 mM of 2-mercapto-1- methylimidazole, imidazole, or 2-aminobenzimidazole. This suggests that copper follows irreversible redox reactions under a diffusion controlled process. No other linear relations of the peak current and peak potential with the scan rate were found. Conclusion: Copper oxidation in chloride-containing solutions is controlled by passivation (following the Müller-Calandra passivation model) upon the addition of the majority of the selected azoles. In the minority of cases, irreversible redox reactions that follow a diffusion-controlled process were identified. None of the systems followed an adsorption-controlled process. Moreover, none of the tested systems underwent reversible redox reactions that followed a diffusion controlled process.

Background: Sarin is a nerve agent which is lethal to people due to its high toxicity. According to its extreme toxicity, sarin, relatively lack of color, highly toxic, miscible in water, poses viable threats to potable water sources. Therefore, there is an urgent need for portable, rapid and yet reliable methods to monitor for adulteration of potable water sources by sarin on spot. Methods: A stock solution of 30 mg/L sarin was prepared daily by dissolving 300 μg of sarin in 10 mL isopropanol. A certain amount of sarin was added to the glass tube, and then o-dianisidine and hydrogen peroxide were added. The pH value of the solution was adjusted to 9.8. The solution was transferred to the test tube after 10 minutes. A test tube of 2 mL was placed between the light source and the RGB color sensor. The LED light source illuminates directly over the test tube while the RGB sensor obtained the generated spectral response. This RGB voltage output is connected to the ADC and microcontroller to convert these analog voltages to three digital data. This RGB digital data is linked to the microcomputer through the serial port that is interfaced with the user interface. The data thus obtained in the sensor can be processed to display the sarin concentration. Results: Under the optimum conditions as described above, the calibration curve of chromaticity value versus sarin concentration was linear in the range of 0.15 mg/L to 7.8 mg/L. According to the IUPAC definition, theoretical detection limits of this method were 0.147 mg/L and 0.140 mg/L for R and B values, respectively. The practical detection limit was 0.15 mg/L. The sensor was successfully applied to the determination of sarin in artificial water samples and the recoveries were between 86.0% to 95.9%. Conclusion: The results in the present work have demonstrated the feasibility to design a new portable colorimetric sensor based on the RGB chromaticity method for quantitative determination of sarin in water. The influences of chromogenic reagent, oxidant, reaction time, o-dianisidine concentration, hydrogen peroxide concentration, reaction temperature, pH on the chromaticity values were investigated. The results showed that the sensor possessed high selectivity, sensitivity and good repeatability. The method would be potentially applied to the analysis of other toxic compounds in environment, such as other chemical warfare agents.

Background: Owing to the strong oxidizing and reducing properties of hydrogen peroxide (H2O2), it has been widely used in many fields. In particular, H2O2 is widely used in the aseptic packaging of drinks and milk. The residue of H2O2 in food is harmful to human health. Therefore, the quantitative detection of H2O2 is of great practical significance. Methods: The Ag-Au/RGO/TiO2 nanocomposites were facilely synthesized by photo-reduction approach. Transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize the synthesized Ag-Au/RGO/TiO2 nanocomposites. Cyclic voltammetry was used to analyze the electrochemical behavior of H2O2 on the Ag-Au/RGO/TiO2/GCE. Amperometry was applied for quantitative determination of the concentration of H2O2. Results: A novel Ag-Au/RGO/TiO2/GCE was prepared. The Ag-Au/RGO/TiO2/GCE displayed high electrocatalytic activity towards H2O2 reduction. An electrochemical reduction peak of H2O2 was achieved on the Ag-Au/RGO/TiO2/GCE. The current responses were linear with the concentrations of H2O2 in the range of 0.01-30 mM with the detection limit of 3.0 μM (S/N = 3). Conclusion: An amperometric sensor has been prepared for H2O2 detection using Ag- Au/RGO/TiO2/GCE. The Ag-Au/RGO/TiO2/GCE shows good performance for the determination of H2O2. The proposed sensor exhibits good selectivity and stability.

Background: Formaldehyde has been recognized as the important liquid environmental pollutant which can cause health risk. Great effort has been devoted to detecting formaldehyde in liquid environment. It is of important significance to develop a sensitive method for measuring formaldehyde from the environmental and health viewpoints. Methods: Polyaniline/graphene nanocomposites have been prepared by a simple in-situ polymerization process using graphene and aniline as the raw materials. The nanocomposites were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) and high-resolution TEM (HRTEM). The polyaniline/graphene nanocomposites were applied to modify the glassy carbon electrode for the detection of formaldehyde by cyclic voltammetry (CV) method. Results: The polyaniline/graphene nanocomposites consist of hexagonal graphite phase. The polyaniline particles are dispersed and attached to the surface of the graphene nanosheet-shaped morphology. The thickness of the graphene nanosheets is less than 50 nm. The electrocatalytic performance of the polyaniline/graphene nanocomposites modified glassy carbon electrode towards formaldehyde was obtained. The potential of the irreversible oxidation peak is located at +0.19 V. The polyaniline/graphene nanocomposites modified glassy carbon electrode shows a wide linear range of 0.0001-2 mM and low detection limit of 0.085 μM. Conclusion: The nanocomposites modified glassy carbon electrode possesses good reproducibility and stability. The polyaniline/graphene nanocomposites show great application potential for the electrochemical sensors to detect formaldehyde in liquid environments.