Current Analytical Chemistry - Volume 15, Issue 5, 2019

Background: Ropinirole is a non-ergot dopamine agonist indicated for Parkinson disease and restless leg syndrome. The adverse effects associated with its use are nausea (40-69%) and dizziness, etc. Objective: In order to decrease its dose-dependent adverse effects and monitoring its levels for each individual patient, a more sensitive and cost-effective monitoring techniques were in demand. Methods: Microextraction technique using hollow fiber has been introduced for the analysis of agents at trace levels, which was coupled with HPLC-UV in this study. This sample preparation technique was used to determine the trace level of ropinirole in urine samples. The experiments were designed using Minitab and the results were optimized using MATLAB software. The method was simply and easily implemented by applying a pH gradient of 2 (acceptor phase) and 9 (donor phase) and n-octanol as the organic solvent, entrapped in the pores of the hollow fiber. Other factors affecting the preconcentration and microextraction such as stirring rate, temperature, and salt addition were optimized. Results: Under optimum conditions, the following results were obtained: Preconcentration Factor (PF): 122; Limit of Detection (LOD): 0.0010 mg L-1; Limit of Quantitation (LOQ):0.0031 mg L-1; R2:0.994; RSD: 1.15%(interday) and 1.5% intraday; and R: 12.61%. Conclusion: The advantage of using MATLAB was that it provided the optimum range instead of the optimum points for each parameter, enabling us to predict the conditions required for microextraction of similar drugs, needless to do extra experiments.

Background: The demand for green analytical methods is rising, mainly due its impact on the reduction of waste generation. The official method to assay Doxycycline Hiclate (DOXH) is HPLC, using an unusual column and a multi-component mobile phase. Objective: To develop a capillary electrophoresis method (CZE) to assay DOXH in suppositories and tablets. Methods: Doxycycline was analyzed in a CZE system using a fused silica capillary silica (effective length 40 cm), voltage 25kV, temperature 24°C, detection at 260 nm and hydrodynamic injection of 50mBar/5s. The electrolyte was a mixture of acetonitrile and aqueous solution composed of 25 mM sodium carbonate and 5mM EDTA, pH 10.6. Results: The method was validated according to ICH requirements and DOXH detection was achieved at around 5 min. A linear relationship was observed in the range of 20 to 160 μg.mL-1, the method was precise, showing values of relative standard deviation below 2%. Accuracy was demonstrated by DOXH recovery values ranging from 98.0 to 102.0%, for all the formulations. The specificity was studied by the peak purity evaluation and by the good resolution between peaks of DOXH, degradation products and a related substance intentionally added to the sample solution. Robustness was evaluated by 23 full factorial design, and no effect on DOXH assay was observed under simultaneous variation in significant analytical parameters. Conclusion: This simple and inexpensive method may be used to determine DOXH in suppositories as well tablets, under identical analytical conditions and can be a green alternative to the HPLC official method.

Background: Working with an Evaporative Light Scattering Detector (ELSD), the target components are converted to a suspension of particles in a gas phase by a nebulizer and heated while the mobile phase is evaporated. Then, the incident light is directed at the remaining particles which are scattered and detected. Methods: The signal response of an ELS detector is studied through the correlation of the signal intensity of 65 compounds (at 30, 45 and 80°C) with their structural and physicochemical characteristics. Therefore, 67 physicochemical properties as well as structural features of the analytes were inserted as X variables and they were studied in correlation with their signal intensity (Y variable). Results: The collected data were statistically processed with the use of partial least squares method. The results proved that several properties were those that mainly affected the signal intensity either increasing or decreasing this response. Conclusion: The derived results proved that properties related to vapor pressure, size, density, melting and boiling point of the analytes were responsible for changes in the signal intensity. The light detected was also affected by properties relevant to the ability of a molecule to form hydrogen bonds (HBA and HBD) and its polarizability or refractivity, but at a lower extent.

Background: Formononetin is a common soy isoflavonoid that can be found abundantly in many natural plants. Previous studies have shown that formononetin possesses a variety of activities which can be applied for various medicinal purposes. Certified Reference Materials (CRMs) play a fundamental role in the food, traditional medicine and dietary supplement fields, and can be used for method validation, uncertainty estimation, as well as quality control. Methods: The purity of formononetin was determined by Differential Scanning Calorimetry (DSC), Coulometric Titration (CT) and Mass Balance (MB) methods. Results: This paper reports the sample preparation methodology, homogeneity and stability studies, value assignment, and uncertainty estimation of a new certified reference material of formononetin. DSC, CT and MB methods proved to be sufficiently reliable and accurate for the certification purpose. The purity of the formononetin CRM was therefore found to be 99.40% ± 0.24 % (k = 2) based on the combined value assignments and the expanded uncertainty. Conclusion: This CRM will be a reliable standard for the validation of the analytical methods and for quality assurance/quality control of formononetin and formononetin-related traditional herbs, food products, dietary supplements and pharmaceutical formulations.

Background: Formaldehyde is widely acknowledged as a carcinogen, but as an important organic reagent, it has also been widely employed in the fields of chemical synthesis, industrial production and biomedicine. It is therefore of great practical significance for the detection of formaldehyde in food, clothing, daily necessities, construction materials and environments. Methods: The two silicon QDs, that are, DAMO-Si-QDs (with N-[3-(Trimethoxysilyl) propyl] ethylenediamine as silicon source) and APTMS-Si-QDs (with (3-Aminopropyl) trimethoxysilane as silicon source) as the fluorescence probe to detect formaldehyde in both water and organic phases. Results: Silicon QDs prepared by different silicon sources exhibit an obvious difference in their tolerances to the environment and the responses to formaldehyde. However, APTMS-Si-QDs show better selectivity in both water and organic phases. In Tris-HCl solution (20.00mmol•L-1, pH=5), the formaldehyde concentration maintains an excellent linear relationship with the fluorescence intensity of APTMS-Si-QDs in the range of 3.1250-7-3.1250-5 mol•L-1, with correlation coefficient R2= 0.9998. In methanol, the formaldehyde concentration maintains an excellent linear relationship with the fluorescence intensity of APTMS-Si-QDs in the range of 1.5630-7-3.1250-5 mol•L-1, with correlation coefficient R2= 0.9992. Conclusion: It is found that DAMO-Si-QDs show poor response to the presence of formaldehyde, while APTMS-Si-QDs got a strong, sensitive and selective response to that in both aqueous and organic phases. In the Tris-HCl buffer (20 mmol•L-1, pH=5), the linear range for formaldehyde detection reaches 3.1250-7-3.1250-5 mol•L-1, and for the detection in the organic phase, the linear range reaches 1.5630-7-3.1250-5 mol•L-1, in methanol solution. The paper provides a sensitive, selective and simple means for formaldehyde detection in both aqueous and organic phase.

Background: Tetrodotoxin (TTX) is a biosynthesized neurotoxin that exhibits powerful anticancer and analgesic abilities by inhibiting voltage-gated sodium channels that are crucial for cancer metastasis and pain delivery. However, for the toxin’s future medical applications to come true, accurate, inexpensive, and real-time in vivo detection of TTX remains as a fundamental step. Methods: In this study, highly purified TTX extracted from organs of Takifugu rubripes was injected and detected in vivo of mouse organs (liver, heart, and intestines) using Cyclic Voltammetry (CV) and Square Wave Anodic Stripping Voltammetry (SWASV) for the first time. In vivo detection of TTX was performed with auxiliary, reference, and working herring sperm DNA-immobilized carbon nanotube sensor systems. Results: DNA-immobilization and optimization of amplitude (V), stripping time (sec), increment (mV), and frequency (Hz) parameters for utilized sensors amplified detected peak currents, while highly sensitive in vivo detection limits, 3.43 μg L-1 for CV and 1.21 μg L-1 for SWASV, were attained. Developed sensors herein were confirmed to be more sensitive and selective than conventional graphite rodelectrodes modified likewise. A linear relationship was observed between injected TTX concentration and anodic spike peak height. Microscopic examination displayed coagulation and abnormalities in mouse organs, confirming the powerful neurotoxicity of extracted TTX. Conclusion: These results established the diagnostic measures for TTX detection regarding in vivo application of neurotoxin-deviated anticancer agents and analgesics, as well as TTX from food poisoning and environmental contamination.

Background: The electrochemical behavior of minoxidil on gold (Au), Glassy Carbon (GCEs), and Carbon Paste Electrodes (CPEs) was investigated in an aqueous supporting electrolyte (phosphate buffer [pH 2.0-6.5], acetate buffer [pH 4.3], and Britton and Robinson buffer [pH 2.0-7.4]). Methods: For cyclic voltammetric measurements with suitable methodical parameters, CPEs catalyze electrooxidation of minoxidil more efficiently than do other electrodes. Minoxidil was detected using high-performance liquid chromatography with an electrochemical (carbon paste) detector (HPLCECD). For direct current mode, with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 0.02 to 2.6 mg L-1 was found. The detection limit was approximately 20 ng m L-1. Results: The developed method detected minoxidil samples. Conclusion: Findings using HPLC-ECD and HPLC with an ultraviolet detector were comparable.

Background and Objective: Laser spectroscopy is becoming an increasingly paramount analytical tool. Scientists today have at their disposal many various types of laser-based analytical techniques. In this article, the possibility of using capabilities of a laser to analyze and find the concentration of Serum Total Protein (STP) was studied. Materials and Methods: The laser system includes a diode laser with 532 nm wavelength, with maximum output power being 5 mW. Laser bandwidth ranges around (524 nm – 546 nm) experimentally justified using a monochromator. A simple variable resistance with a range from zero to10Ω for obtaining a range of laser output power, detector, parallel variable resistance with the range from zero to 5 kΩ and meter for measuring the percentage of transmittance. The absorption spectroscopy of STP samples was measured by double beam spectrophotometer. Results: Maximum absorbance of STP is at the range (520-580 nm) and the peak at (500) nm. Laser system measurements included the study of absorbance of STP as a function of cuvet thickness, transmittance as a function of cuvet thickness and absorbance as a function of laser power. In order to ascertain our calculations, the results have been compared with the results of the spectrophotometer. The Relative Standard Deviation (RSD%) values are about (0.67-17.18). Conclusion: The diode laser system is a highly efficient and easy system and allows access to a range of powers. Since the divergence of the laser beam is very low. All results are in good agreement with conventional double beam spectrophotometer.

Background: Conivaptan inhibits two of vasopressin receptor (vasopressin receptor V1a and V2). Conivaptan is used for the treatment of hyponatremia, and in some instances, for the treatment of the heart failure. Methods: The present study aimed to develop a simple, sensitive, and accurate HPLC with ultraviolet detection for the assay of conivaptan (CON) in mouse plasma using bisoprolol as internal standard (IS). A precipitation procedure was used to extract CON and the IS from the mouse plasma. CON was chromatographically separated using a C18 analytical column at 25°C. The separation was carried out using a mixture of phosphate buffer (50 mM): acetonitrile (60: 40, v/v, pH 4.5) with a flow rate of 1.0 mL/min and detection was performed at 240 nm. Results: The assay was validated according to the US Food and Drug (FDA) guidelines. The method demonstrated linearity over a concentration range of 150 - 2000 ng/mL (correlation coefficient: r 2 = 0.9985). The mean recovery of CON from the mouse plasma was 101.13%. All validation parameters for CON were within the acceptable range. Conclusion: The investigated method has been shown to be suitable for estimating the CON in plasma samples, and this method is sensitive and highly selective, allowing the estimation of its concentrations up to the nano-scale. The suggested method was successfully used in a pharmacokinetic study of CON in mouse plasma.

Background: Heparin, it is commercially used as an anticoagulant in surgical procedures for the prevention of blood clotting. However, overdose and prolonged use of heparin often induce potentially fatal bleeding complication. So, it is of crucial importance to monitor closely heparin levels for the sake of health. In this work, a sensitive fluorescence sensing platform to detect heparin was set up based on MPA-CdSe QDs (quantum dots) and protamine enhanced fluorescent system. Methods: The image of CdSe QDs was taken on a JEM-2100 transmission electron microscope (JEOL Ltd.). The fluorescence spectrum was recorded on a FluoroMax-4 fluorescence spectrophotometer (Horiba, USA). UV–vis absorption spectrum was recorded using a Shimadzu UV-2450 Spectrophotometer (Tokyo, Japan). A vortex mixer IKA MS3 digital was selected to mix the solution. Results: Under optimized conditions, the linear response to detect heparin ranges from 0.06 to 14 μg mL-1 with a detection limit of 8 ng mL-1. The approach showed a highly selective response to heparin in the presence of 16 interfered substances. Conclusion: A simple method for the detection of heparin was developed based on MPA-CdSe QDs and protamine enhanced fluorescent system. The electrostatic effect between MPA-CdSe QDs and protamine resulted in strong fluorescence enhancement from the MPA-CdSe QDs. Moreover, the addition of heparin could cause a significant fluorescence decrease due to the strong affinity of protamine and heparin. Under optimal conditions, this method displayed a low detection limit and good selectivity over other substances.