Current Analytical Chemistry - Volume 14, Issue 1, 2018

Background: Heavy metal contamination in natural environment is a serious problem due to increasing industrial activities. Since heavy metal ions are non-biodegradable, they are considered as a serious source to pollute the biosphere throughout the world and cause many healthy and physiological diseases. Therefore, it is imperative to develop simple, sensitive and selective methods for their detection. Methods: This review is based on SCI full-text database, with Web of Science and Google as search tools, using "Photoelectrochemical (PEC)" and "Metal ions" as the theme of the search keywords, selecting the papers published in 2009-2016. Results: It can be seen that a number of PEC sensors for heavy metal ions show an overall increasing trend of this research.The PEC sensors without DNA/DNAzymes were developed relatively earlier, and more related papers were published. The proportions of PEC sensors for Cu2+, Hg2+ and Cr (VI) on the total PEC sensor research for heavy metal ions in research papers are 52.63%, 21.05% and 10.53%, respectively. However, the field of metal ions detection research focused on PEC biosensor in recent years. The proportions of PEC biosensors for Pb2+ and Hg2+ are 46.67% and 40%, respectively. Therefore, the PEC detection of heavy metal ions currently focuses on using DNA/DNAzymes. Conclusion: This paper summarized the mechanisms of PEC biosensors which were developed for heavy metal ions in recent years. In addition, this paper highlights the immobilization and sensing strategies of biosensors with DNAzymes/DNA molecules. The challenges and future directions are also discussed.

Background: The aim of this work was to develop a simple voltammetric method for quantitative determination of the veterinary drug carprofen. To the best of our knowledge there is no literature data on the voltammetric behavior and quantification of carprofen. Methods: Cyclic voltammetry (CV) on a glassy carbon electrode was employed to study the voltammetric behavior of carprofen by investigating the influence of the scan rate and of the supporting electrolyte pH. A differential pulse voltammetric (DPV) method for carprofen quantification was optimized with respect to supporting electrolyte and instrumental parameters. The applicability of the developed method was tested on carprofen’s determination from pharmaceuticals. An HPLC method was used for comparison. Results: CV emphasized that carprofen presents an oxidation wave corresponding to an irreversible and pH –dependent electrode process involving an equal number (n) of protons and electrons (n=1). The linear range and detection limit of the developed DPV method were 7.170-7–8.980-5 M and 2.620-7 M carprofen, respectively. Statistical tests (F, t, Cochran) confirmed that the results obtained by DPV are well correlated with those of the HPLC reference method. Conclusion: This paper reports for the first time a CV study of carprofen and an optimized DPV method for its rapid determination. The method has a linear range of over two orders of magnitude and a submicromolar limit of detection. Statistical analysis proved that the results of carprofen determination by DPV and HPLC from injections were comparable and reliable being in good agreement with the manufacturer claimed amount.

Background: In the present work, two spectrometric methods for determination of formaldehyde were studied and compared. Methods and Results: Both methods are based on the catalytic effect of formaldehyde on the oxidation of Fluorescein natrium by sodium bromate in acid media. In the first method, the decrease in fluorescence intensity of Fluorescein natrium, measured at the emission wavelength of 510 nm (excitation wavelength, 438 nm), was proportional to formaldehyde in the concentration range 0.05-1.2 μg mL-1 and the detection limit was found to be 0.02 μg mL-1. In the second method, the decrease in absorbance of Fluorescein natrium measured at the wavelength of 438 nm was proportional to formaldehyde concentration in the range 0.5-7 μg mL-1 and the detection limit was found to be 0.16 μg mL-1. As preliminary steps, the working parameters (acidity, concentration of reagents, reaction time) were established. Influence of interfering species was also investigated. Conclusion: The proposed methods were applied for the determination of formaldehyde in rainwater samples.

Background: A simple, precise, and inexpensive spectrofluorometric method was developed and validated for the analysis of primaquine (PQ) in tablet formulation. Objective: The objective was to develop low-cost spectrofluorimetric method for the determination of PQ in pharmaceutical formulation. Method: The procedure is based on the reaction of PQ with fluorescamine (FC) in alkaline medium to form fluorescent derivatives measured at 480 nm after excitation at 397 nm. The effects of pH, reaction time, temperature and FC concentrations on the reaction of PQ and FC have been examined. Results: The optimum experimental parameters were investigated. Beer law is obeyed over the range 0.25-1.25 μg/mL. The limit of detection (LOD) and the limit of quantification (LOQ) were measured to be 0.051 and 0.154 μg/mL, respectively, with linear regression correlation coefficient (R2) of 0.9989 which recovered with a range 95-106%. Conclusion: The presented method can be used for the analysis of PQ in pharmaceutical formulation in quality control laboratories.

Background: Mercury in various forms constitute a serious environmental pollutant. Its exposure is still considered a world related risk for individuals in numerous manufacturers. The Context and Purpose of the Study: Because of it serious hazardous effects to human health, there is strong need to develop new tools for mercury ion determination in clinical analysis and environmental monitoring. This investigation describes for the first time the construction of a polyvinyl chloride (PVC) membrane electrode which is exceedingly specific to divalent mercury was formed by utilizing Hg[dimethylglyoxime (phene)]2+ as a suitable carrier. Results: The sensor exhibits a Nernestian response for mercury ions over a wide concentration range (5x10-7-5x10-2 molL-1) with a slope of 29±0.5 mV per decade. It has a reaction time of 30s and can be utilized for 2 months with no quantifiable divergence in potential. The electrode can be used in the pH range from 1.8-4.5.The average recovery obtained is 91.0% with standard deviation of 1.5% (n=8). Conclusion: The proposed sensor demonstrates genuinely great segregating capacity towards mercuric ions in correlation with some heavy metals. This sensor was utilized for the quantitative analysis of mercuric ions in its aqueous solution. Also, was applied in potentiometric titration as an indicator electrodefor Hg2+ in various real samples (e.g.; fluorescent mercury lamp white dust, mercurechrome and dental alloy).

Aim: A novel all solid-state contact PVC-membrane beryllium-selective electrode based on 4-hydroxybenzo-15-crown-5 ether as an ionophore is described. Results: The best performance was obtained with a membrane composition of 4% ionophore, 67% dioctyl sebacate (DOS), 28% poly(vinyl chloride) (PVC), and 1% potassium tetrakis (p-chloro)phenylborate (KTClPB) (w/w). The all solid-state contact PVCmembrane beryllium-selective electrode together with an Ag/AgCl reference electrode exhibited sub-Nernstian response with a slope of 22±1 mV/decade to beryllium ions from 1.0x10-6 to 1.0x10-1 M, and resulted a considerably low detection limit of 6.2x10 7. The electrode had a good performance in selectivity over a wide range of interfering cations tested. It showed a working pH range between 4.0-8.2 with fast response time (<10 s) and a good reproducibility. Conclusion: The all solid-state contact PVC-membrane beryllium-selective electrode developed was successfully applied in potentiometric titration of Be2+ ions with EDTA.

Background: Graphite pencil drawn on paper electrode (PDP) is one of the low cost electrodes due to the good conductivity. Prussian blue (PB) has been widely used in sensors due to its high electrocatalytic activity toward H2O2 reduction at relatively low potential avoiding the interferences of other biological species. The major drawback of PB is their relatively low operational stability since hydroxyl ions causes the collapse of Fe-CN-Fe of PB bonds. Interestingly, a combination of magnetic nanoparticles, Fe3O4 with PB would not only enhance Fe3O4 properties, but also improves the operational stability of PB. In this work, a disposable PDP modified with Fe3O4-PB as sensor was successfully fabricated. Methods: To prepare PDP, lead pencil 4B and Whatman filter paper were used. Briefly, Whatman filter paper was cut into small slides then by hand abrasion of the pencil on the paper surface. Melted candle was used to cover part of the electrode to adjust the working electrode zone. Fe3O4 was prepared by the hydrothermal technique. Transmission electron microscope, scanning electron microscopy, X-ray diffraction, Contact angle (OCA 15 plus) and electrochemical workstation (CHI660e) were used to characterize both PDP and Fe3O4-PB nanoparticles. Results: The PDP possessed excellent electrochemical properties and good reproducibility. Furthermore, the Fe3O4-PB / PDP electrode was quite stable even in neutral and lower alkaline solutions with good electro-catalysis. Conclusion: Both Fe3O4-PB nanoparticles and PDP can be considered as promising candidate materials for fabricating electrochemical sensors, especially in the resource limited condition.

Background: Meat fraud generated a huge outrage amongst customers in 2013 in Europe due to the horsemeat scandal. Portable and hand-held optical near-infrared (NIR, 4,00012,500 cm-1/800-2,500 nm) spectroscopy sensors are traded as promising fast, non-invasive and easy analytical tools that might be applicable at any independent place of inspection. In order to embrace the on-going trend towards instrumental miniaturization, it was the aim of the present feasibility study to evaluate the application of Design of Experiment for frequently applied portable micro-electro-mechanical system (MEMS) based spectrometer by comparing its performance to a bench-top Fourier-Transform polarization near-infrared (FT-NIR) instrument. Methods: 63 samples of different meat types (beef: 9, chicken: 10, mutton: 10, turkey: 10, pork: 10, horse meat: 14) were measured in order to classify the meat-type using a portable micro-electromechanical system (MEMS) based spectrometer and a bench-top Fourier-Transform polarization nearinfrared (FT-NIR) instrument, in order to compare the performance of both systems. In a second step different meat types were minced together in order to investigate the level of adulteration which can be detected using MEMS and FT-NIR. Design of Experiment (DoE) was applied to enhance results. Results: The accuracy of MEMS versus FT-NIR for identifying whole / minced pieces of chicken, pork, turkey, beef and mutton meat (63 samples) against horse meat appeared to be 75.0-100.0% (MEMS) vs. 62.5%-100.0% (FT-NIR) for whole pieces and 75.0-100.0% (MEMS and FT-NIR) for minced meat. When mincing different types of meat together, a maximum of 4 and 1 factors were required for establishing a PLS-R model using again the spectra recorded with MEMS and FT-NIR, respectively. The resulting quality parameters for the MEMS device were: R2=0.06-0.62, Standard Error of Cross Valdiation (SECV)= 17.33-32.91, Ratio of Performance to Deviation (RPD) =0,54-1,70 and for the FTNIR system: R2=0.85-0.94, SECV=7.52-13.83%, RPD=2.2-5.7 (FT-NIR). The limit of detection was found at 10% for the MEMS and at 1% for the FT-NIR device. Conclusion: Meat classification can be performed using the bench-top FT-NIR as well as the hand-held MEMS-NIR. Mincing the meat samples does not necessarily improve classification accuracy as information about the surface structure is lost. NIRS prediction models for adulterations were established for the bench-top system. Prediction models for the hand-held device are inconclusive and have to be improved by a larger sample set and/or further progress in miniaturization technique. Low level adulteration (<10%) may also be predictable with NIRS, but continuative research is necessary.

Background: Danofloxacin is a synthetic antibacterial agent with broad spectrum antibacterial and antimycoplasmal activity which is widely used in aquaculture. Methods: A UPLC (Ultra Performance Liquid Chromatography) method was developed and validated for the determination of danofloxacin (Dano) and its major metabolite N-desmethyl danofloxacin (Ndesmethyl Dano) in muscle plus skin tissue of European seabass (Dicentrarchus labrax) for the first time. For the separation an analytical column UPLC BEH C18 2.1 5 mm (1.7 μm) was used with an isocratic mobile phase consisting of MeOH-water acidified with formic acid (0.01%) (18:82; v/v) and flow rate of 0.3 mL/min within 5.5 min. The detection was performed at 275 nm using a photodiode array detector for both compounds. Examined fluoroquinolones were isolated from seabass muscle and skin tissue by extraction with acidic ACN and further purification with the QuEChERS methodology. Results: Recovery rates from muscle and skin tissue ranged between 90.2 and 101.2% for both compounds. The detection limit of the method was estimated at 13.73 μg/kg for Dano, 18.32 μg/kg for Ndesmethyl Dano, while the limits of quantification were 41.62 and 55.52 μg/kg, respectively. The developed method was fully validated in terms of selectivity, linearity, accuracy, precision, stability and sensitivity according to the European Union Decision 2002/657/EC. Conclusion: The new developed and validated method can be readily applied to aqua cultured fish after dietary administration of danofloxacin.

Background: The high acute toxicity of the organophosphorus pesticides (OPs) imposes the development of simple, rapid, sensitive, and reasonably priced analytical methods for their in situ determination. The electrochemical biosensors-based techniques for OPs determination complete with these requirements. Objective: The objective of this work was the development of an amperometric biosensor with improved analytical performances for the direct organophosphorus pesticides determination, applying a novel chitosan-based bionanocomposite for glassy carbon electrode (GCE) modification. Method: The bionanocomposite sensing platform was created by a simple, one-step electrodeposition onto the surface of the GCE of chitosan-entrapped carbon nanotubes (CS-CNTs), ZrO2 nanoparticles, and organophosphorus hydrolase (OPH). The electrochemical and analytical characterization of the modified electrodes was achieved by recording and analysing their CV, chronoamperometric, and amperometric responses. Results: The electroactive surface area of the CS-CNT-ZrO2-modified GCE (22.66 mm2), and its catalytic activity toward the electrochemical oxidation of p-nitrophenol, which is the product of the OPHcatalyzed hydrolysis of the nitrophenyl substituted OPs (catalytic rate constant 1.84 x103 L mol-1 s-1) were increased. The synergistic action of the CNTs and the ZrO2 nanoparticles also led to the improvement in the biosensor's analytical performances in comparison to the performances of the CS/OPH, CS-ZrO2/OPH, and CS-CNT/OPH modified GCEs; paraoxon was quantified with a sensitivity as high as 33.1 nA L μmol-1, dynamic concentration range extended up to 40 μmol L-1, and LOD as low as 20 nmol L-1. The determination was not affected by the presence of triazine pesticides and OPs without nitrophenyl substituents. The developed biosensor was applied for paraoxon determination in spiked samples of irrigation water with a satisfactory accuracy. Conclusion: An amperometric biosensor for OPs determination was developed using a novel bionanocomposite for GCE modification. The synergistic action of the individual components converted it in a high performant platform for the direct, sensitive, and selective paraoxon determination.

Background: Dexamethasone has been used in ophthalmology for the treatment of different eye diseases and it is a powerful synthetic member of the glucocorticoid class of steroid medicament having anti-inflammatory and immunosuppressant characteristics. The aim of this study is to develop a rapid, sensitive and selective voltammetric method for its determination using polygylcine-multi walled carbon nanotubes (polyglycine-MWCNTs) modified paste electrode. Methods: The electro-activity and the voltammetric behavior of dexamethasone on the polyglycine- MWCNTs electrode were deduced by cyclic voltammetry (CV), square wave stripping voltammetry (SWSV), differential pulse voltammetry (DPV) and linear sweep voltammetry (LSV). The method permits accurate and sensitive detection of the ophthalmic drug dexamethasone in the presence of ascorbic acid, dopamine and uric acid from the generated anodic peaks at +950 mV, +740 mV and +700 mV, respectively. Results: The cyclic voltammetric study indicates that dexamethasone created a single anodic peak at about +1100 mV in pH 3 B-R solution and none of the cathodic peak appeared in the subsequent reverse scan. The detection and quantification limits measured for LSV were 0.087 mg/L and 0.29 mg/L, respectively. The extent of recoveries in the presence of equal amounts (1:1 mass ratio) of ascorbic acid, dopamine and uric acid were calculated as 98.28 ± 0.45, 94.46 ± 1.77 and 98.57 ± 0.60%, respectively. The voltammetric procedure was also applied to dexamethasone spiked urine samples(5.0 mg/L) and the percent recovery was determined as 95.2% with the relative standard deviations of 3.29%. Conclusion: Sensitive and selective voltammetric method was proposed for the direct determination of dexamethasone. The modified polyglycine-MWCNTs paste electrode enabled the direct determination of dexamethasone in the presence of biological molecules such as ascorbic acid, dopamine and uric acid.