Current Analytical Chemistry - Volume 14, Issue 6, 2018

Background: Iodide (I-) is a vital micronutrient and its essential roles have been approved in a number of neurological activities. Therefore, there is a growing interest in developing reliable sensitive quantitative methodologies for the determination of the amount of I- in edible salt samples. Methods: First, 2heDTC was synthesized by the mixing of equivalent amounts of pure C2H7NO and CS2 in the presence of NH4OH under vigorous stirring in an ice bath. Then, AuNPs were synthesized; the 250 mL of 1 mM HAuCl4 was put into a round-bottomed flask and was boiled vigorously by stirring for 20 min. Then, 25 mL of 38.8 mM of Na3C6H5O7 was added rapidly into this solution. The solution was heated under reflux for another 15 min. The modification of the AuNPs surface was performed with 2heDTC by proceeding with the ligand exchange reaction. To the quantification of I-, 2 μL (1mM) Hg2+ was added to 0.5 mL (50 mM) of PBS solution with pH = 5.0 containing 500 μL of 2heDTC-AuNPs, which was then maintained at optimized time for the creation of bare AuNPs. Then, the different concentrations of I- were separately added. Finally, the surface plasmon resonance (SPR) absorption bands were taken with UV-Vis spectrophotometer. Results: The presence of Hg2+ induces the destabilization-aggregation of AuNPs due to stronger affinity Hg2+ toward 2heDTC (2heDTC(Hg)) in comparison with AuNPs, and results in the creation of bare AuNPs accompanied by a color change from bright red to blue which can be observed with naked eyes. Moreover, when I- was introduced to the mixture containing 2heDTC(Hg) and bare AuNPs, it inhibited Hg2+-induced aggregation through re-stability obtained by re-binding 2heDTC to AuNPs with abstraction of Hg2+ from 2heDTC due to more affinity of Hg2+ toward I- (HgI2) in comparison with 2heDTC. At optimum conditions, a linear calibration of the A520/A650 values versus I- concentration was obtained within 0.1-4.0 μM with LOD = 20 nM. Conclusion: Taking advantages of excellent sensitivity and selectivity, we employed our proposed nanoprobe for I- assay in the edible salt samples that facilitate the development of affordable and portable UV-Vis chemosensors for I- in food industry applications.

Background: Manganese, Mn, is an essential element that is present in steels, and determines steel's mechanical properties. Traditionally, atomic absorption and X-ray photoelectron spectroscopic methods were used for Mn analysis and complicated instrument operations, sometimes of high cost, are associated, and spectrophotometry/colorimetry is another tool for Mn analysis with simple operations. Nowadays, smartphone is emerging as a new powerful tool with multiple advantages in analytical chemistry. Objective: This project aimed to develop a simple and reliable smartphone-assisted colorimetric method to analyze Mn in steel samples. Method: Steel samples were first dissolved in the mixture of nitric acid and phosphoric acid to convert the elemental form of Mn into Mn(II) ions. The Mn(II) ions were then oxidized into the colored permanganate ions whose color was determined via a smartphone. Quantification of Mn was performed by comparing the unknown signal with the standard calibration curve which was constructed by plotting the green value of the solution as a function of the permanganate concentration with a 2nd polynomial regression fitting. The results from the developed method were then compared with the manufacturer values and another UV/vis spectrophotometry, using the Student t-tests, to validate the method. Results: The concentration of Mn in steel samples was determined by the smartphone-assisted colorimetry to be in the range of 0.56% to 0.97%, which had the same accuracy as the classic spectrophotometry and was in agreement with the manufacturer's values. Conclusion: The experimental results proved that the smartphone-assisted method is a good alternative tool for Mn analysis in steels.

Background: This study was designed to develop a reliable method for simultaneous quantitation of Citalopram (CIT) and its main active metabolite, Desmethylcitalopram (DCIT), in saliva of patients undergoing treatment with CIT. Methods: To compare two procedures of saliva purification, Solid-Phase (SPE) and Liquid-Liquid (LLE) extractions, saliva samples obtained from healthy volunteers were spiked with adequate quantities of CIT and DCIT. Different cartridges were used for SPE, while dichloromethane for LLE. Chromatographic separation and quantitation were carried out by UHPLC with DAD detector using a C-18 column and a mixture of acetonitrile and redistilled water (37:63, v:v) with the addition of formic acid (pH 3.5) as a mobile phase. Results: A comparison of both purification procedures showed that the most satisfactory results were obtained by SPE using Discovery C18 cartridge and redistilled water with formic acid (pH 3.5) as a washing solvent. Dichloromethane proved to be the best extractant in LLE. Both procedures enabled the separation of analytes from human saliva with high precision and recovery. Conclusions: Validation of the developed UHPLC procedure revealed that, regardless of how the sample was purified, the method was characterized by good linearity (between 10 and 1000 ng/mL), sensitivity, reproducibility, specificity and low values of limits of detection and quantitation. The limits of quantitation were 4.0 and 8.0 ng/mL for SPE and LLE, respectively. The efficiency of the method in therapeutic drug monitoring of CIT and DCIT in saliva of patients was confirmed.

Background: Dietary supplements are products that aim to complement the diet of healthy individuals, and may show nutritional, metabolic and physiological effects. The consumption of dietary supplements is increasing every year all over the world and has been accompanied by an increased frequency of adulteration of these products with synthetic pharmaceuticals. Analytical methods that allow testing for the presence of synthetic drugs in dietary supplements are needed to detect such fraudulent practices. Methods: A method was developed for the rapid identification and quantification of diuretics (hydrochlorothiazide, chlorthalidone and furosemide) and stimulants (caffeine and synephrine) by ion-pair chromatography with pulsed amperometric detection in dietary supplements. Dietary supplements were purchased online from randomly chosen websites and from physical stores. The search was restricted to products that advertise and market food supplements with claims of weight loss, fat burning, appetite reduction or metabolism acceleration (thermogenics). Results: A mobile phase composed of 5 mmol L-1 sodium phosphate using 0.3 mmol L-1 sodium dodecyl sulfate as ion-paring reagent and 50% (v/v) methanol as organic additive leads to the efficient separation of hydrochlorothiazide, chlorthalidone, furosemide and amiloride. PAD cycle of the studied drugs involved an oxidation (+1.0 V for 0.4 s) and a reducing potential (-0.2 V for 1.2 s) on the gold electrode surface as a cleaning step. In addition, the drugs were detected by applying an optimized pulse of +0.8 V for 0.4 s, completing the 2 s detection cycle applied to the gold electrode. Caffeine was found to be present in 50% of the studied samples and about 20% of them presented caffeine levels above the quantity considered safe for daily intake. In addition, hydrochlorothiazide and furosemide were found as diuretics in the formulations. Hydrochlorothiazide was found as diuretic in amounts higher than the therapeutic dose in circa 5% of the samples, being that the same incidence found for the stimulant synephrine in the analyzed samples. Conclusion: A new IPC-PAD method using an amperometric cell with a gold disc electrode enabled the simultaneous separation and sensitive detection of the diuretics hydrochlorothiazide, chlorthalidone and furosemide in the presence of the stimulants caffeine and synephrine. Caffeine was found to be present as a stimulant in 50% of the studied samples available as encapsulated or bulk forms from different websites and physical stores. Furthermore, about 20% of the samples presented caffeine levels above the quantity considered safe for daily intake. Beyond caffeine, synephrine was found as stimulant in circa 5% of the studied samples. Lastly, hydrochlorothiazide was found in amounts above the therapeutic dose in 5% of the samples.

Method: A modified quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction method followed by a simple isocratic reversed-phase high-performance liquid chromatography was applied to the simultaneous analysis of Sodium Benzoate (SB) and Potassium Sorbate (PS) preservatives in some dairy products was developed. Results: At first, comparison of the obtained results using original unbuffered and modified buffered QuEChERS versions was done. Then, in order to improve the extraction recovery of SB and PS and clean-up efficiency, some effective parameters were optimized. Satisfactory extraction recoveries (94.0 and 99.8 for SB and PS, respectively) were achieved under optimum conditions. In order to obtain low matrix effect (<20%), quantitation was performed in the presence of an internal standard by referring to a matrix-free calibration curve. The regression coefficient 0.998 and 0.999, and the limit of detection 0.01 and 0.02 μg mL-1 were obtained for SB and PS, respectively. Recoveries for quality control samples prepared by blank real sample fortification were between 95-112% with relative standard deviations (RSD) less than 6%. Finally, SB and PS were determined in various dairy products such as dry milk, milk, yogurt and yogurt drink (Doogh) with relative recoveries in the range of 81-107% and RSDs less than 9%. The obtained results were confirmed using liquid chromatography-mass spectrometry. Conclusion: This methodology, which was successfully applied to dry milk, milk, yogurt and yogurt drink (Doogh) samples, enables the determination of the target analytes in the width concentration ranges.

Background: Substance P and CGRP are neuropeptides that belong to the thachykinin and calcitonin family, respectively. They play an important role in neuropathic pain development and regulation. Methods: In this study, simultaneous analysis of Substance P and CGRP in rat brainstem tissue was conducted by using LC-ESI-MS/MS method. A gradient mobile phase was used with a Zorbax C8 150x2.1 mm, a particle size of 3.5 μm narrow-bore column. Mobile phases consist of 0.2% formic acid in water (A) and 0.2% formic acid in acetonitrile (v/v) (B). Firstly, mass spectrometry parameters were optimized. After achieving chromatographic separation, the method has been validated and applied to rat brainstem samples. Results: SP and CGRP were eluted at 8.7 min and 10.1 min, respectively. Mass spectrum of neuropeptides was obtained in positive polarity and ion transitions of Substance P and CGRP were monitored at m/z 674.4→[600+254.4] and 952.2→1214.200, respectively. Linearity range for quantification was 5.85-438.52 ng/mL for Substance P and 0.21-155.28 ng/mL for CGRP. The limit of quantification was 5.85 ng/mL for Substance P and 0.21 ng/mL for CGRP. According to tissue samples analysis (n=6), basal endogen concentrations of Substance P and CGRP in brainstem tissue were calculated as 260.57±11.24 ng/g and 22.53±0.75 ng/g respectively. Conclusion: A novel LC-ESI-MS/MS method was successfully developed and validated according to the bioanalytical validation guideline published by the EMA including precision, accuracy, specificity and linearity. Acceptable results were achieved. Basal endogen concentrations of Substance P and CGRP in brainstem tissue were determined.

Background: Excessive active oxygen will suppress the antioxidant defense system, resulting in a series of negative effects. Antioxidant substances in the diet can protect important biological molecules by mitigating the harm caused by oxidative stress and reducing the occurrence of chronic diseases related to aging. Therefore, simple, reliable and rapid detection methods for screening potential antioxidants in the diet have become very important. Methods: 1.0 g scented tea was added into 25 mL boiling water, and the extracting solution was filtered through filter paper by normal funnel after 10 min stirring extraction. After cooled to room temperature, the filtrate was diluted with water. Then, 100 μL of the scented tea extract was added into 300 μL of GNR solution, and water was added until the total volume was 900 μL. Subsequently, 900 μL of CTAB solution (0.2 mol/L) and 10 μL of hydrochloric acid (3 mol/L) were added successively. After mixing, 800 μL of H2O2 solution (1.26 mol/L) was added for the reaction. The variation of the GNR absorption spectrum with time was measured to determine the inhibition of oxidation and IC50. Results: The rate of oxidation of GNRs was reduced by the addition of antioxidant substance, such as scented teas. The stronger the antioxidant activity was, the lower the rate of GNR oxidation and the smaller the change in the longitudinal absorption peak. The blue-shift of the longitudinal absorption wavelength was monitored by ultraviolet-visible spectroscopy, enabling evaluation of the antioxidant activity of scented teas. The IC50 values of AA, Lophatherum gracile Brongn, rose, lavender, hawthorn and lotus leaf were 0.0088, 0.0338, 0.0540, 0.0907, 0.2383 and 0.2533 mg/mL, respectively. Conclusion: The relative antioxidant activities from strong to weak for these five scented teas were as follows: Lophatherum gracile Brongn > rose > lavender > hawthorn > lotus leaf. The order was in good accordance with that obtained by the conventional DPPH method. This method is simple and easy to operate, interference-free, and provides a promising solution for filed screening of antioxidant activity of natural products.

Background: Overuse of antibiotics has become a serious ecological problem worldwide. It is necessary to monitor and control the pollution of antibiotics. Kanamycin is a representative antibiotic and has widely been used to treat a wide variety of infections. Although different methods have been established for kanamycin detection, it is still of great significance to develop new sensing approach to kanamycin monitoring. Methods: Graphene and Cadmium Sulphide (GR-CdS) nanocomposites were dispersed in 0.035% chitosan (CHIT) aqueous solution containing 0.52% acetic acid. Then, Glass Carbon Electrode (GCE) surface was coated with 5 μL of 1 mg·mL-1 GR-CdS suspension. The GR-CdS-CHIT modified electrode was immersed in 0.5 mg mL-1 single-stranded DNA (ssDNA) solution and 0.5 V potential was applied for 200 s to immobilize ssDNA on the electrode surface. Results: GR-CdS-CHIT dramatically promoted the electrochemical oxidation response of guanine residue in DNA. ssDNA exhibited higher oxidation peak current than double-stranded DNA (dsDNA). Under optimal conditions, ssDNA/GR-CdS-CHIT/GCE was prepared and used as the sensor to determine kanamycin, which showed a linear response to kanamycin in the concentration range of 0.10 to 1.0 mg mL-1. The proposed sensor was successfully applied to monitoring photodegradation of kanamycin. Conclusion: ssDNA was effectively immobilized on GR-CdS-CHIT modified electrode and exhibited high electrochemical oxidation response. When kanamycin was present in the solution, the electrochemical oxidation peak current of ssDNA on the modified electrode declined due to the interaction between kanamycin and DNA. Thus, a novel electrochemical DNA biosensor for kanamycin was successfully developed.

Background: In order to combat neurocysticercosis, effective and novel Fixed Dose Drug Combinations (FDC) of combination dosage regimens have been always under trial; with Albendazole (ABZ) and Praziquantel (PZQ) combination being one of them. Such outcome is basically dependent on the pharmacokinetic profiling of their metabolites such as Albendazole Sulphoxide (ABZSO, active), Albendazole Sulphone (ABZSO2, inactive) and PZQ-TRANS; followed by their back extrapolations to suggest a safe, however potent dosage regimen. Objective: Development of a novel, rapid yet sensitive column switching RP-HPLC method for routine estimation of the aforementioned drugs and metabolites. The improved dosage version in combination is also targeted. Methods: Pooling rat plasma, with column-switch, parent Albendazole-Praziquantel combination was estimated at 225 nm using Enable C-18G column, whereas Albendazole Sulphone and Sulphoxide were estimated using Phenomenex C-18 Luna column at 290 nm. Results: The method showed high accuracy recovering 92~113% of the metabolite or drugs with LOQ as low as 5~50 ng μL-1. Moreover, administration of ABZ-PZQ combination revealed about 3 times slower elimination of active ABZSO than by solitary administration of ABZ. The former also achieved higher Cmax (77.8078 μg mL-1) compared to the latter (69.685 μg mL-1). Also, ABZSO t1/2 in the former has been estimated as 4.25 h compared to 1.38 h of the latter indicating slower ABZSO metabolism in combination therapy than the solo one. Conclusion: The improved pharmacokinetics data could be attributed to the synergistic effect of ABZ and PZQ with each other. This has led to the designing of a novel safe ABZ-PZQ combination dosage regimen for therapeutic applications.

Background: PBDEs consist of synthetic chemicals frequently employed to help reducing or avoiding flame spread in a fire. As reactive flame retardants, they are covalently bound to the polymeric matrix of various domestic products. These compounds have drawn attention due to their large-scale production and use, and numerous papers have reported their presence as well as persistence in water, soil, sediment and atmospheric air, even in remote areas. The aim of this work was to develop a low cost and environmentally friendly analytical protocol to determine PBDEs in riverine sediment samples. Methods: First step consisted of optimizing instrumental parameters of GC-MS to improve the detectability of the target compounds. Then, factorial experiment designs at two levels, 23 and 24, were applied to evaluate the effects of these parameters on the GC-MS signal responses. The extraction of PBDE from the samples and the clean-up of the extracts were performed in order to ensure efficiency and low consumption of time, power and reagents. Results: GC-MS optimization allowed reduced running time associated with effective PBDE congeners separation and detection, when compared to the official proposed method. Recovery tests of extraction and clean-up steps presented satisfactory values when compared to the costly US EPA methodology. Conclusion: The results allow us to conclude that the proposed methodology is an efficient alternative for the determination of PBDEs from riverine sediments. Its advantage is related to the reduced consumption of time, power and reagents.

Background: Tricyclic Antidepressants (TCAs) can be used for the treatment of depression, psychiatric disorders and insomnia. They are used extensively in all the countries especially in the developed countries and therefore, can enter the aquatic environment mainly through the human excretion. These drugs cannot be completely removed or degraded during the sewage treatment process and their concentrations in the aquatic environment are relatively low; therefore, the development of sensitive analytical methods for determination of their concentrations is very important. In biofluids, the measurements of TCAs are very important to ensure the quality of the preparation and to obtain the optimal therapeutic concentrations, while minimizing the risk of inappropriate dose or overdose. So, the methods for determining these drugs concentrations in human samples for forensic purposes are required. Methods: The aqueous sample solution was transferred into a glass centrifuge tube with flat bottom and 1-octanol as extraction solvent was withdrawn into an HPLC microsyringe and then, rapidly injected into the tube via syringe needle in order to form a mixture of the aqueous sample solution and the organic solvent. Then, this mixture was repeatedly aspirated from the tube and infused into it several times. This caused the solution to become turbid. This operation resulted in the extraction of the target analyte from the sample solution into the fine droplets of 1-octanol. After then, the mixture was centrifuged to gather the drops of low density extractant above the sample solution as a thin film. For sampling, by inserting a PTFE coated stirring bar at the flat bottom of the tube and turning on the stirrer, the thin film of the organic extraction solvent was converted into a conical vortex with enough volume for easy collection by the needle syringe. Results: Several important factors affecting the microextraction efficiency, such as the type and volume of the extraction solvent (180 μL of 1-octanol), the volume of the aqueous sample solution (7 mL), the number of air injected (7 times), pH of the sample solution (pH 10) and the ionic strength (no salt addition) were investigated. Under the optimal extraction conditions, the method exhibited low limit of detection (0.52 ng mL-1) and good linearity (2-1000 ng mL-1) with coefficient of determination (R2) of 0.9979. The relative standard deviation was 4.5 % and the enrichment factor was 32. Finally, the applicability of the proposed method was evaluated by extraction of amitriptyline in the biological and environmental water samples and the calculated relative recoveries were more than 85%. Conclusion: In this research work, a novel microextraction method based on DLLME has been presented for the extraction, preconcentration and determination of amitriptyline in various real samples without using disperser solvents. Also, the developed method was appropriate for the use of low density extraction solvents without any special device and complicated operation which permitted the use of a wider range of the organic extraction solvents. On the other hand, by using an innovative simple method, the internal volume of the quartz UV-Vis microcell decreased and consequently, the volume of the organic extraction solvent reduced as much as possible which led to the proximity to the aspects of green chemistry. In addition, under the optimal extraction condition, the method offers good LOD, as well as good linearity range and repeatability along with acceptable relative recoveries.

Background: Regorafenib is a multikinase inhibitor, indicated for the treatment of metastatic colorectal cancer and locally advanced, unresectable or metastatic gastrointestinal stromal tumor. Objective: A simple and fast, validated bioanalytical method is required for pre-clinical or clinical safety and efficacy investigations and possible pharmacokinetic interaction of regorafenib. Method: Regorafenib and sorafenib were eluted on Acquity UPLC®BEH C18 column. Elution was carried out by pumping mobile phase [methanol (0.1% formic acid): water (85:15%)] at 200μl/min flow rate. Mass detector was operated in multiple-reaction monitoring mode. Deprotonated ions [M-H]^- of regorafenib and sorafenib were fragmented and monitored. Results: Daughter fragments of regorafenib (m/z 481.1 > 194, m/z 481.1 > 260) and sorafenib (m/z 463 > 193.99, m/z 463 > 268.1) were determined in negative electrospray ionization mode. Linear calibration curve of range 50-2500 ng/ml was prepared in plasma. Method was selective, since there was no interfering peak at regorafenib retention time. Coefficients of variation for inter-day precision at three quality control concentrations were 17.6% at lower limit of quantitation, 6.3% at middle limit, and 2.9% at the highest limit of quantitation. Accuracy of the method ranged between 96% to 105.3%. Recovery of drug from blank plasma at quality control concentrations varied between 82.53 to 105.66%. Conclusion: The developed method was successfully validated by adopting US FDA guidance for bioanalytical methods. The method is simple, quick and can be adopted for regorafenib estimation in other biological fluids with necessary modifications.

Background: Among different metal oxides, ferrites play an important role in many fields such as transformers, gas sensors and energy storage and conversion. The magnetic properties of Coferrites are due to the cation distribution among octahedral and tetrahedral sites. Such distribution can be controlled by the preparation method which in its turn depends on the particle size and morphology. Among different synthesis techniques, microwave induced combustion method is rapid and convenient. Methods: Co-Ferrite nanoparticles have been synthesized through a reaction of a mixture of stoichiometric of Co-nitrate hexahydrate, Fe-nitrate nonahydrate, and urea. Different urea to metal nitrates ratio have been used. The mixture is dissolved in an appropriate amount of doubly distilled water then transferred to a commercial microwave oven operating at 800 W for 20 minutes. Results: Sample synthesized at low urea/metal nitrate ratio (1:1) shows undesirable mixed phases namely Co3O4, Fe2O3 together with CoFe2O4. With increasing urea ratio, the detected diffraction peaks are well indexed to CoFe2O4 phase and all other secondary phases are disappeared. It was found that the crystallite size increases with increasing the urea/metal nitrates ratio. The high resolution transmission electron microscope provides a further confirmation for the formation pure Co-ferrite phase. Additionally the magnetic properties such as saturation magnetization and coercivity are measured and found to depend on the urea/metal nitrates ratio. Conclusion: In this study, CoFe2O4 nanoparticles have been successfully fabricated by microwave assisted combustion method. The effect of urea/metal nitrates ratio on the structure and magnetic properties is studied. The XRD results showed that a single CoFe2O4 phase can be obtained at urea/metal nitrates ratio ≥ 2. The crystallite size was estimated to be in the range 10.33-23.29 nm. The studied system shows a high saturation magnetization of about 65 emu/g for the 13.13 nm sized particles. The critical size was found to be about 13 nm with the highest coercivity of about 1200 Oe.

Background: The feasibility of applying methods or the extraction of Allium cepa essential oils using solvent-free microwave extraction (SFME) has been compared to hydro-distillation (HD) process. Parameters of extraction were investigated using a rational design of experiment screening. Objective: To screen the important factors that may influence the quantity and/or quality of the extracts derived from Allium cepa. Method: A no. of 13 experiments were performed based on the screening process. The key parameters, such as power (350/500 W), size of the sample (chopped/sliced), quantity (500/1000 g), time of extraction (25/50 min.) and water ratio (20/50 mL) were selected based on the limitation of the instrument. The essential oils derived from Allium cepa were characterized by GC-MS analysis. Results: The commonly collected constituents via SFME and HD are 3,4-Dimethylthiophene, Disulfide, methyl propyl, Dithiolane, 2,4-Dimethyl-5,6-dithia-2,7-nonadienal, 4,6-Diethyl-1,2,3,5- tetrathiolane, 5,7-Diethyl-1,2,3,4,6-pentathiepane (sulfur-containing compounds) and Methoxyacetic acid, cyclopentyl ester, 2-Propenoic acid, 2-methyl-, octyl ester (fatty acid esters). Conclusion: A pragmatic relationship between the variations of extraction parameters has been studied. Results suggested and verified that among the factors, Power and time of extraction influence the process of extraction significantly.