Showing papers in "Analytical Methods in 2011"

Let there be chip—towards rapid prototyping of microfluidic devices: one-step manufacturing processes

Abstract: Microfluidics is an evolving scientific field with immense commercial potential: analytical applications, such as biochemical assay development, biochemical analysis and biosensors as well as chemical synthesis applications essentially require microfluidics for sample handling, treatment or readout. A number of techniques are available to create microfluidic structures today. On industrial scale replication techniques such as injection molding are the gold standard whereas academic research mostly focuses on replication by casting of soft elastomers such as polydimethylsiloxane (PDMS). Both of these techniques require the creation of a replication master thus creating the microfluidic structure only in the second process step—they can therefore be termed two-(or multi-)step manufacturing techniques. However, very often the number of pieces to be created of one specific microfluidic design is low, sometimes even as low as one. This raises the question if two-step manufacturing is an appropriate choice, particularly if short concept-to-chip times are required. In this case one-step manufacturing techniques that allow the direct creation of microfluidic structures from digital three-dimensional models are preferable. For these processes the number of parts per design is low (sometimes as low as one), but quick adaptation is possible by simply changing digital data. Suitable techniques include, among others, maskless or mask based stereolithography, fused deposition molding and 3D printing. This work intends to discuss the potential and application examples of such processes with a detailed view on applicable materials. It will also point out the advantages and the disadvantages of the respective technique. Furthermore this paper also includes a discussion about non-conventional manufacturing equipment and community projects that can be used in the production of microfluidic devices.

A cost-effective acid digestion method using closed polypropylene tubes for inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of plant essential elements

Abstract: A novel closed-tube nitric acid/hydrogen peroxide digestion method was developed for inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of plant tissue and tested on six botanical reference materials. A suite of 18 mineral elements commonly found in plant tissues as either essential elements (B, Ca, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, S, Se, Zn), potentially toxic metals (Al, Cd, Cr), or soil contaminants (Ti) was analysed by radial view ICP-OES after digestion by the new method and two open-tube methods. Closed-tube method blanks showed less frequent and less severe contamination than the open tube blanks. The closed-tube method was as efficient as the open-tube digestions of reference materials, achieving recoveries of 94–113% of published concentrations for most essential elements, with variability of 2–6%RSD, while the open-tube digests yielded 93–115% recovery and 1–8% RSD. Boron was accurately recovered by the closed-tube method but some loss by volatilization was observed in perchloric acid digests. Concentrations of minor elements (Cd, Cr, Mo, Ni, Ti) in some reference materials were below method reporting limits. High concentrations of Ti (>1 mg kg−1) detected in leafy reference materials was suspected to be derived from soil contamination, potentially also increasing Al and Fe concentrations. Recovery of Al was highly dependant on sample material and digestion method. The closed-tube method uses smaller masses, less reagent, lower digest temperatures and takes less time to complete digestion than existing methods.

A comprehensive review of CUPRAC methodology

Abstract: Measuring the antioxidant activity/capacity levels of food and biological fluids is carried out for the meaningful comparison of the antioxidant content of foodstuffs and for the diagnosis and treatment of oxidative stress-associated diseases in clinical biochemistry. Current literature clearly states that there is no widely adopted/accepted “total antioxidant parameter” as a nutritional index available for the labeling of food and biological fluids due to the lack of standardized quantitation methods. The “parent” CUPRAC (CUPric Reducing Antioxidant Capacity) method of antioxidant measurement, introduced by our research group to world literature, is based on the absorbance measurement of Cu(I)-neocuproine (Nc) chelate formed as a result of the redox reaction of chain-breaking antioxidants with the CUPRAC reagent, Cu(II)-Nc, where absorbance is recorded at the maximal light absorption wavelength of 450 nm; thus this is an electron-transfer (ET)-based method. From the parent CUPRAC method initially applied to food (apricot, herbal teas, wild edible plants, herby cheese etc.) and biological fluids (as hydrophilic and lipophilic antioxidants together or in separate fractions), a number of “daughter” methods have evolved, such as the simultaneous assay of both lipophilic and hydrophilic antioxidants in acetone-water as methyl-β-cyclodextrin inclusion complexes, determination of ascorbic acid alone in the presence of flavonoids (with preliminary extraction of flavonoids as their La(III)-complexes), determination of hydroxyl radical scavenging activity of both water-soluble antioxidants (using benzoate derivatives and salicylate as hydroxylation probes) and of polyphenols using catalase to stop the Fenton reaction so as to prevent redox cycling of antioxidants, measurement of Cu(II)-catalyzed hydrogen peroxide scavenging activity and of xanthine oxidase inhibition activity of polyphenols, TAC measurement of protein thiols in urea buffer, development of a CUPRAC-based antioxidant sensor on a Nafion cation-exchanger membrane, the off-line HPLC-CUPRAC assay and finally the on-line HPLC-CUPRAC assay of antioxidants with post-column detection. The current direction of CUPRAC methodology can be best described as a self-sufficient and integrated train of measurements providing a useful “antioxidant and antiradical assay package”. This review attempts to unify and summarize various methodologies of main and modified CUPRAC procedures that can normally be extracted from quite different literature sources.

Graphene-polymer composite: extraction of polycyclic aromatic hydrocarbons from water samples by stir rod sorptive extraction

Abstract: Due to the excellent mechanical, thermal and electrical properties, graphene/polymer composite is expected to have a variety of applications in analytical chemistry. In this study, a new poly(ethylene glycol dimethacrylate)/graphene composite was prepared by in situpolymerization. The new composite was used for the first time as the extraction coating of stir rod sorptive extraction for the preconcentration of polycyclic aromatic hydrocarbons (PAHs) from water samples. Because of the high specific surface area and π–π electrostatic stacking properties of graphene, the graphene-polymer composite showed higher extraction efficiencies towards most target PAHs from water samples than the neat polymer. Under the optimal conditions, a method for the determination of PAHs in water samples was proposed based on the combination of stir rod sorptive extraction (SRSE) and gas chromatography-mass spectrometry (GC-MS). The limit of detection (LODs) of the developed method for 16 PAHs ranged from 0.005 to 0.429 ng mL−1, depending on the compound. Good reproducibility of method was obtained as intra- and inter-day precisions, the relative standard deviations (RSDs) were less than 12.5% and 12.6%, respectively.

Electrocatalytic oxidation and determination of epinephrine in the presence of uric acid and folic acid at multiwalled carbon nanotubes/molybdenum(VI) complex modified carbon paste electrode

Abstract: A novel modified carbon paste electrode was fabricated by incorporation of carbon nanotubes and a novel molybdenum(VI) complex (MC). The characterization of the modified electrode was carried out by cyclic voltammetry. The apparent charge transfer rate constant, ks, and transfer coefficient, α, for electron transfer between MC and CNT paste electrode were calculated. Furthermore, the modified electrode showed an excellent electrocatalytic effect on the oxidation of epinephrine (EP). Using differential pulse voltammetry (DPV), the peak currents of EP recorded in pH 7.0 solution were linearly dependent on their concentrations in the range of 0.09–750.0 μM. The limit of detection was 49 nM for EP. Then the modified electrode was used to determine EP in an excess of uric acid (UA) and folic acid (FA) by difference pulse voltammetry. Finally, this method was used for the determination of EP in EP ampoule.

The detection of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanol in human dried blood spots

Abstract: Phosphatidylethanol, a series of abnormal phospholipids formed in the presence of ethanol and phospholipase D, has gained popularity as a long-term biomarker of ethanol ingestion. A liquid chromatography tandem mass spectrometric method for a specific, prevalent isomer, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanol, was developed and validated using dried blood spots. Dried blood spots offer numerous advantages over venipuncture including reduced costs, invasiveness and discomfort. Dried blood spots were prepared from authentic whole blood specimens that had been tested using a previously published procedure. Comparison of the results from the two assays demonstrated excellent correlation. The data suggest that dried blood spots may be a useful tool for the detection of alcohol abuse and abstinence monitoring.

Electrochemiluminescence based on quantum dots and their analytical application.

Abstract: This review presents a general description of the electrochemiluminescence (ECL) related to quantum dots (QDs) and their analytical application. It briefly overviews the synthetic route of quantum dots. The basic mechanisms are given for QDs ECL behavior. Finally, new developments and improvements of its application in inorganic substance analysis, organics analysis, immunoassay and aptasensing assay are discussed.

Preparation and evaluation of superparamagnetic surface molecularly imprinted polymer nanoparticles for selective extraction of bisphenol A in packed food

Abstract: Molecularly imprinted polymer (MIP) coated Fe3O4 nanoparticles (Fe3O4@MIP) were synthesized by atom transfer radical polymerization (ATRP) and used as highly selective magnetic solid-phase extraction (MSPE) sorbents for trace bisphenol A (BPA) from packed food. The morphological and polymeric characteristics of the Fe3O4@MIP were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. In this work, competitive recognition compounds (4-n-octylphenol and bisphenol A diglycidyl ether) exhibited lower binding capability to the Fe3O4@MIP than BPA. A high performance liquid chromatography with fluorescence detection (HPLC-FLD) method was developed for the determination of BPA in canned orange and milk samples. The main factors influencing the extraction efficiency, including high specificity, the amount of surfactant, the shaking time and the desorption ability of complex food matrices were investigated and optimized. Various parameters such as the pH of thesample, the amount of Fe3O4@MIP sorbent, the extraction time, and the desorption conditions were optimized. Notably, the extraction can be carried out quickly, and the extraction time for BPA onto Fe3O4@MIP sorbents can be clearly shortened to 5 min. Good linearities (r2 > 0.9965) for all calibration curves were obtained, and the limit of detection (LOD) for BPA was 0.1 and 0.3 ng mL−1 in canned orange and milk samples, respectively. To the best of our knowledge, this is the first time that surface molecularly imprinted polymer nanoparticles have been used for the pretreatment of packed food.

Sample treatments based on dispersive (micro)extraction

Abstract: Sample treatment has evolved in the last few years following basic trends, simplification, automation and miniaturization being the most remarkable ones. Microextraction techniques, including solid phase microextraction (SPME) and liquid phase microextraction (LPME), have emerged in this context showing very competitive features if they are compared with their classic counterparts. Essentially, extraction techniques are surface dependent processes since their kinetics depend directly on the contact surface between the sample and the extractant phase. This aspect, which is important in any extraction procedure, becomes critical when the amount of extractant is reduced to the microscale. In this context, dispersive-based procedures have gained importance as rapid and efficient sample treatment methodologies. This review article deals with the use of dispersion in micro-solid phase extraction (μ-SPE) and LPME. The main techniques as well as their powerful combinations will be described in depth with references to the most relevant applications.

A whole-cell amperometric herbicide biosensor based on magnetically functionalised microalgae and screen-printed electrodes

Abstract: We report the fabrication of an amperometric whole-cell herbicide biosensor based on magnetic retention of living cells functionalised with magnetic nanoparticles (MNPs) on the surface of a screen-printed electrode. We demonstrate that Chlorella pyrenoidosa microalgae cells coated with biocompatible MNPs and retained on the electrode with a permanent magnet act as a sensing element for the fast detection of herbicides. The magnetic functionalisation does not affect the viability and photosynthesis activity-mediated triazine herbicide recognition in microalgae. The current of ferricyanide ion was recorded during alternating illumination periods and biosensor fabricated was used to detect atrazine (from 0.9 to 74 µM) and propazine (from 0.6 to 120 µM) (the limits of detection 0.7 and 0.4 µM, respectively). We believe that the methodology presented here can be widely used in fabrication of a number of whole cell biosensors since it allows for efficient and reversible cells immobilisation and does not affect the cellular metabolism.

Multi-wall carbon nanotubes as a sensor and ferrocene dicarboxylic acid as a mediator for voltammetric determination of glutathione in hemolysed erythrocyte

Abstract: A sensitive and selective electrochemical method was developed for determination of glutathione (GSH) in hemolysed erythrocyte using a ferrocene dicarboxylic acid modified carbon nanotubes paste electrode (FDCCNTPE). Cyclic voltammetry (CV), double potential-step chronoamperometry and differential pulse voltammetric (DPV) were used to investigate the suitability of ferrocene dicarboxylic acid at the surface of a multi-wall carbon nanotubes paste electrode as a mediator for the electrocatalytic oxidation of glutathione in aqueous solutions with various pH. The results showed that FDCCNTPE had high electrocatalytic activity for the electrooxidation of glutathione. Under optimum conditions (pH 7.00), oxidation of GSH occurs at a potential about 230 mV less positive than that at the unmodified carbon nanotubes paste electrode. The catalytic reaction rate constant, kh was calculated (1.98 × 104 M−1 s−1) using chronoamperometry. The electrocatalytic oxidation peak current of GSH showed two linear dynamic ranges with a detection limit of 0.2 μmol L−1 GSH. The linear calibration ranges were obtained between 0.5–24 μmol L−1 and 24–122 μmol L−1 GSH using the DPV method. Finally, the proposed method was also examined as a selective, simple and precise electrochemical sensor for the determination of GSH in real samples such as hemolysed erythrocyte.

Simultaneous determination of ellagic and gallic acid in Punica granatum, Myrtus communis and Itriphal formulation by an electrochemical sensor based on a carbon paste electrode modified with multi-walled carbon nanotubes

Abstract: An electrochemical method for the determination of ellagic acid (EA) and gallic acid (GA) was successfully applied to extracts of Punica granatum, Myrtus communis, and to Itriphal, a herbal formulation. The voltammetric determination of EA and GA was conducted with a novel sensor based on a modified carbon paste electrode with multi-walled carbon nanotubes. The electrochemical behavior of EA and GA at the modified sensor was characterized by cyclic voltammetry, chronocoulometry, linear sweep voltammetry, differential pulse voltammetry and rotating disk electrode voltammetry. Electrochemical parameters such as the diffusion coefficient (D), electron transfer coefficient (α), electron transfer rate constant (k) and ionic exchange current density (Io) were determined for EA and GA oxidation. The detection limit of GA was 0.2 μM and for EA was 0.21 nM over the 180 s accumulation time of the open circuit potential, respectively.

Silver nanoparticles as a cyanide colorimetric sensor in aqueous media

Abstract: The interaction between aqueous colloidal silver nanoparticles (AgNPs) and cyanide ions was studied using UV-Vis absorption and scanning electron microscopy (SEM) techniques. It was found that AgNPs were oxidized by dissolved oxygen in the presence of cyanide ions, resulting in a considerable decrease in the intensity of the surface plasmon resonance (SPR) absorption band of AgNPs. So, we propose a simple, cost effective, rapid, sensitive and selective colorimetric sensor for the detection of cyanide using AgNPs in aqueous media. There is a linear relationship between the absorbance intensity of AgNPs and the concentration of cyanide ions over the range of 16.7 μmol L−1–133.3 μmol L−1 at 394 nm. The proposed method has been successfully used for the determination of cyanide in water samples.

Dispersive liquid–liquid micro extraction of uranium(VI) from groundwater and seawater samples and determination by inductively coupled plasma–optical emission spectrometry and flow injection–inductively coupled plasma mass spectrometry

Abstract: A dispersive liquid–liquid microextraction (DLLME) method was developed for the determination of uranium(VI) in groundwater/seawater by inductively coupled plasma–optical emission spectrometry (ICP–OES) and flow injection–inductively coupled plasma mass spectrometry (FI–ICPMS). This is the first report on the extraction of uranium(VI) by a DLLME method. In this method, uranium(VI) was complexed with ammonium pyrrolidine dithiocarbamate (APDC) in the presence of cetyltrimethyl ammonium bromide (CTAB), which enhanced the hydrophobicity of the ion–association complex resulting in improved extraction into chloroform. The extraction was carried out after adjusting the pH of the water sample to 1. The uranyl ion was back extracted from chloroform layer with nitric acid for determination by ICP–OES/FI–ICPMS. Some effective parameters for complex formation and extraction, such as volume of extraction and disperser solvent, extraction time, pH and concentration of the chelating agent and surfactant have been optimized using ICP–OES. Under optimum conditions, enrichment factors of 11 and 25 were obtained from 10 mL of water sample for determinations by ICP–OES and FI–ICPMS respectively. The calibration graphs were linear in the range of 5–200 μg L−1 and 50–5000 ng L−1 with limits of detection of 2.0 μg L−1 and 30 ng L−1 respectively for ICP–OES and FI–ICPMS. The method has been applied to a few groundwater and seawater samples. The recoveries obtained for uranium(VI) in groundwater and seawater samples spiked to levels of 10 and 5 μg L−1 were 90–105% respectively. The results obtained by the proposed method have been cross validated by laser fluorimetry.

Simultaneous voltammetric determination of Brilliant Blue and Tartrazine in real samples at the surface of a multi-walled carbon nanotube paste electrode

Abstract: A carbon paste electrode (CPE) chemically modified with multi walled carbon nanotubes (MWCNTs) was used for the sensitive and selective determination of Brilliant Blue (BB) and Tartrazine (Tz) by voltammetric methods such as cyclic, differential pulse and square wave voltammetry (CV, DPV, and SWV), and chronoamperometry (CHA). The peak current increased linearly with the BB concentration within the concentration range of 0.05 to 22.0 μmol l−1 for DPV and from 0.05 to 25.0 μmol l−1 for SWV. The detection limits (S/N > 3) for BB by DPV and SWV were found to be 9.0 and 5.0 nmol l−1, respectively. Results of CV showed two well-resolved anodic waves with the peak separation approximately 200 mV for the electrochemical oxidation of BB and Tz, which makes it possible for simultaneous determination of both compounds. The treatment of the CV data showed that the redox of BB and Tz was reversible diffusion-controlled and totally irreversible reactions, respectively. The diffusion coefficient (D/cm2 s−1 = 2.8 × 10−5) for BB was determined using chronoamperometry. DPV method was applied for the quantitative determination of BB and Tz. High sensitivity and selectivity, low detection limit (nanomolar), good reproducibility, easy preparation and regeneration of the electrode make it very suitable for the determination of BB and Tz in soft drinks.

Dummy molecularly imprinted polymer for selective screening of trace bisphenols in river water

Abstract: Bisphenols (BPs) are potential endocrine-disrupting chemicals that may adversely affect human health and wildlife. The complexity of matrix encountered in real-world samples renders screening of trace BPs a formidable challenge. The present study highlighted the potential of molecularly imprinted solid-phase extraction (MISPE) for selective detection of trace bisphenols and their halogenated analogues in surface water. The template bleeding was observed at parts-per-billion levels, deteriorating the accuracy and precision of BPs quantification. To surmount this problem, a dummy MISPE strategy was proposed, in which bisphenol E (BPE) was selected as a dummy template for molecularly imprinted polymer (MIP) synthesis. Coupling this MISPE strategy with chromatographic analysis, a dummy MISPE-HPLC method was established. The linearity, precision, limit of detection (LOD) and recovery were then validated. The linearity of the calibration curve for each BP was observed over the range of 20–2000 ng L−1 (r > 0.998). LOD for each bisphenol was measured as low as 2.5–5.0 ng L−1. This technique was applied to simultaneous screening of BPs in the Qinghe River, and five bisphenols were found within the concentration range of 0–224 ng L−1 in river samples. The designed dummy MIP was superior to the commercial sorbents with regard to the selectivity, cross-reactivity, matrix removal efficiency and reusability. These merits enabled the applications of dummy MISPE for selective extraction and sensitive screening of BPs in environmental water samples. This method also provided a promising tool for monitoring the occurrence, distribution and fate of BPs in surface water.

Trace-Level Automated Mercury Speciation Analysis

Abstract: An automated system for methyl Hg analysis by purge and trap gas chromatography (GC) was evaluated, with comparison of several different instrument configurations including chromatography columns (packed column or capillary), detector (atomic fluorescence, AFS, or inductively coupled plasma mass spectrometry, ICP-MS, using quadrupole and sector field ICP-MS instruments). Method detection limits (MDL) of 0.042 pg and 0.030 pg for CH3Hg+ were achieved with the automated Hg analysis system configured with AFS and ICP-MS detection, respectively. Capillary GC with temperature programming was effective in improving resolution and decreasing retention times of heavier Hg species (in this case C3H7Hg+) although carryover between samples was increased. With capillary GC, the MDL for CH3Hg+ was 0.25 pg for AFS detection and 0.060 pg for ICP-MS detection. The automated system was demonstrated to have high throughput (72 samples analyzed in 8 h) requiring considerably less analyst time than the manual method for CH3Hg+ analysis described in EPA 1630.

Uninformative variable elimination for improvement of successive projections algorithm on spectral multivariable selection with different calibration algorithms for the rapid and non-destructive determination of protein content in dried laver

Abstract: The potential of using partial least square based uninformative variable elimination algorithm (UVEPLS) on successive projections algorithm (SPA) for spectral multivariable selection was evaluated. A case study was done on the visible and shortwave-near infrared (Vis-SNIR) spectroscopy for the rapid and non-destructive determination of protein content in dried laver. Three calibration algorithms, namely multiple linear regression (MLR), partial least square regression (PLS) and least-square support vector machine (LS-SVM), were used for the model establishment based on the selected variables of SPA, UVEPLS and UVEPLS-SPA, respectively. A total of 175 samples were prepared for the calibration (n = 117) and prediction (n = 58) sets. The performances of different pretreatments were compared. Both linear calibration algorithms of MLR and PLS and non-linear calibration algorithms of LS-SVM with linear kernel and RBF kernel obtained similar results based on certain variable selection strategies of SPA, UVEPLS and UVEPLS-SPA. The average improvement percentage of RPD values of four calibration algorithms was 38.66% by calculating SPA on UVEPLS processed variables. Therefore there was much improvement of using UVEPLS on SPA spectral multivariable selection with both linear and nonlinear calibration algorithms in this case. Moreover, the RPD values of both linear and non-linear models based on the thirteen selected variables of UVEPLS-SPA show that coarse quantitative predictions of the protein determination in dried laver is possible based on Vis-SNIR spectra. We hope that the results obtained in this study will help both further chemometric (multivariate selection and calibration analysis) investigations and investigations in the sphere of applied vibrational (Near infrared, Mid-infrared and Raman) spectroscopy of sophisticated multicomponent systems.

Analytical methods used in conjunction with dried blood spots

Abstract: This review covers the wide range of different methods that have been used for the microanalysis of dried blood spots (DBS) from the ones reported in 1914 to the sophisticated processes used, for example, in newborn screening, new drug discovery research and application of PCR based DNA studies of HIV in countries with limited infrastructure. The value of the dried blood spot as a sampling tool and the many advantages it offers in combination with suitable analytical methods is discussed. Current developments in both automating the DBS extraction process and the potential for direct analysis of the sample without prior extraction are reviewed. Possible future directions in the analytical methods used for DBS samples are also highlighted.

Tissue imprint imaging by desorption electrospray ionization mass spectrometry

Abstract: Cross-sections of Myristica malabarica (Lam) seed and mouse brain tissue were imprinted on such ordinary surfaces as printer paper and TLC plates, and successfully imaged by desorption electrospray ionization mass spectrometry (DESI-MS) at 250 μm resolution Chemical images representing the distribution of the alkaloid malabaricone C in the seed substructures and individual lipids in the substructures of the brain were obtained Practical implications include analysis of irregular or soft materials, easy recording, transportation and storage of the latent image, and posterior analysis of the samples by different techniques without the requirement of addition of matrices or use of specific types of surfaces

Novel nanofiber coatings prepared by electrospinning technique for headspace solid-phase microextraction of chlorobenzenes from environmental samples

Abstract: Novel unbreakable solid phase microextraction (SPME) fiber coatings were fabricated by electrospinning method in which the polymeric solution was converted to nanofibers using high voltages. Four different polymers, polyurethane (PU), polycarbonate (PC), polyamide (PA) and polyvinyl chloride (PVC) were prepared as the fiber coatings on thin stainless steel wires. The extraction efficiencies of new coatings were investigated by headspace solid-phase microextraction (HS-SPME) of some environmentally important chlorobenzenes from aqueous samples followed by gas chromatography-mass spectrometry (GC-MS) analysis. Among them, PU showed a prominent efficiency. Effects of coating time and polymer concentration on the PU fiber capability were also optimized. The scanning electron microscopy (SEM) images of the PU coating showed a diameter range of 150–600 nm with a homogeneous and porous surface structure. Effects of different parameters influencing the extraction efficiency including the extraction temperature, extraction time, ionic strength, desorption temperature and time were investigated and optimized. The limits of detection and quantification of the method under optimized conditions were 10 and 50 ng L−1, respectively. The relative standard deviations (RSD) at a concentration level of 0.5 ng mL−1 were obtained between 3 and 8% (n = 3). The calibration curves of CBs showed linearity from 50 to1000 ng L−1. The proposed method was successfully applied to the extraction of CBs from real water samples and relative recoveries were between 94 and 102%.

Electroanalytical determination of carbendazim by square wave adsorptive stripping voltammetry with a multiwalled carbon nanotubes modified electrode

Abstract: A preconcentrating/voltammetric multiwalled carbon nanotube modified glassy carbon electrode (MWCNT–GCE) has been developed for stripping analysis of carbendazim (Methyl Benzimidazol-2-yl Carbamate—MBC), based on dispersing MWCNT in water. The effect of experimental variables, such as the dispersion and loading of MWCNT, was assessed. A quasi-reversible behavior for MBC in acetic acid/acetate buffer 0.1 mol L−1 (pH 4.7) was verified and its high effective pre-concentration was attributed to the high adsorption capability and enormous surface area of the MWCNT. No evidence of carry-over effect, combined with the easiness of electrode preparation, led to the development of a highly sensitive and reliable method with an experimental work range from 0.256 to 3.11 µmol L−1 with a detection limit of 10.5 ppb for a short (60 s) accumulation period. Measurement of MBC in a river water sample was demonstrated. The accuracy of the method for real sample analysis was assessed by estimating the apparent recovery (93 ± 2.9% and 86 ± 4.1% for 4.3 × 10−7 mol L−1) for a MBC spiked river water sample.

Recent advances of enantioseparations in capillary electrophoresis and capillary electrochromatography

Abstract: A comprehensive survey of recent developments and applications of capillary electromigration techniques for enantioseparations from January 2006 to June 2010 is presented. The techniques include capillary electrophoresis, chip capillary electrophoresis and capillary electrochromatography. The separation principles and the chiral recognition mechanisms are discussed. Additionally, on-line preconcentrations in chiral capillary electrophoresis are also reviewed.

Selective detection of nanomolar Cr(VI) in aqueous solution based on 1,4-dithiothreitol functionalized gold nanoparticles

Abstract: The determination of trace Cr(VI) is very important because of its highly carcinogenic and mutagenic effects. In this study, a colorimetric detection method based on 1,4-dithiothreitol functionalized gold nanoparticles (DTT-AuNPs) for nanomolar Cr(VI) in aqueous solution is reported. The method principle was based on the aggregation of DTT-AuNPs induced by Cr(VI), which led to red-shift of the surface plasmon resonance (SPR) peak of DTT-AuNPs. UV-vis absorption spectra, Zeta potentials, and transmission electron microscopy (TEM) images were used to demonstrate the aggregation of DTT-AuNPs. Some parameters affecting the detection including solution pH and DTT concentration were optimized. Under the optimized conditions, a good linear relationship (correlation coefficient r = 0.997 5) was obtained between the ratio (A650/520) of the absorbance at 650 nm to that at 520 nm and the concentration of Cr(VI) over the range of 100–600 nM, and the limit of detection (LOD) for Cr(VI) at a signal-to-noise ratio of 3 was 20 nM. The method showed selective detection toward Cr(VI) against other common metal ions in waters. Furthermore, the method developed was applied for detecting trace Cr(VI) in real water samples, with recoveries of 95%–115%.

Molecularly imprinted-multiwall carbon nanotube paste electrode as a biosensor for voltammetric detection of rutin

Abstract: A new molecularly imprinted polymer–multiwall carbon nanotube paste electrode (MIP–MWNPE) was prepared as a voltammetric sensor for rutin. The electrochemical behavior of rutin at the surface of the modified electrode was studied using cyclic voltammetry (CV) and square wave voltammetry (SWV). Under the optimized conditions, the oxidation peak current of rutin showed two linear dynamic ranges (0.08–1.4 μM and 2.0–160.0 μM) with a detection limit of 0.05 μM, using square wave voltammetric method. The RSD% for 5.0 and 10.0 μM determination of rutin were 2.7% and 2.9%, respectively. The kinetic parameters such as electron transfer coefficient (α) and charge transfer rate constant (ks/s−1) were also determined using the electrochemical approach. The modified electrode showed good sensitivity, special selectivity, and stability for rutin analysis. It was successfully applied for the determination of rutin in real samples such as urine and pharmaceutical formulation with satisfactory results.

An online ionic liquid-based microextraction system coupled to electrothermal atomic absorption spectrometry for cobalt determination in environmental samples and pharmaceutical formulations

Abstract: In the present work, an ionic liquid (IL) lighter than water was employed as extraction solvent in a dispersive liquid-liquid microextraction (DLLME) methodology. An original flow injection system for online microextraction and preconcentration of cobalt (Co) based on the use of tetradecyl(trihexyl)phosphonium chloride (CYPHOS® IL 101) was designed. Cobalt was complexed with 4-(2-pyridylazo)-resorcinol (PAR) reagent at pH 4.8 and then, the IL-DLLME procedure was developed by dispersing CYPHOS® IL 101 with acetone in an aqueous solution containing Co-PAR complex. Different pyridylazo dyes were evaluated for Co preconcentration in terms of their molecular structure, stability and acid-base equilibrium. Online extraction of Co-PAR into the IL and separation of the dispersed IL enriched phase were accomplished with a microcolumn containing Florisil material. Cobalt was removed from the microcolumn with a 10% (v/v) HNO3 acidified-acetone solution and finally measured by electrothermal atomic absorption spectrometry (ETAAS). The detection limit achieved after preconcentration of 2 mL of sample solution was 8 ng L-1. The precision for 10 replicate determinations at the 1 µg L-1 Co level was 5.1% relative standard deviation (RSD), calculated from the peak heights obtained. The method was successfully applied to Co determination in water samples as well as ophthalmic and parenteral solutions. For the first time, an IL-based microextraction technique was applied for metal determination in these complex samples, where Co recovery varied between 97.9 and 103%.

A selective sensor based on a glassy carbon electrode modified with carbon nanotubes and ruthenium oxide/hexacyanoferrate film for simultaneous determination of ascorbic acid, epinephrine and uric acid

Abstract: The development of a highly selective sensor for voltammetric determination of ascorbic acid (AA), epinephrine (EP) and uric acid (UA) in the same solution has been achieved by a glassy carbon electrode modified with multi-walled carbon nanotubes and ruthenium oxide hexacyanoferrate film. The modified electrode showed effective catalytic activity toward the electro-oxidation of AA, EP and UA by separating their oxidation peak potentials and producing larger anodic peak currents than those at unmodified electrodes. The electron transfer efficiency and rate constant of the oxidation process were studied using electrochemical impedance spectroscopy. The electro-catalytic peak currents of differential pulse voltammograms increased linearly with AA, EP and UA concentrations in the ranges of 0.2–15.0 μM, 0.1–10.0 μM and 0.90–250 μM with a detection limit of 0.087, 0.052 and 0.599 μM, respectively. The modified electrode showed good sensitivity, selectivity and stability for the voltammetric determination of these important biological compounds. The modified electrode was satisfactorily used for simultaneous determination of AA, EP and UA in pharmaceutical and biological samples.

Determination of seven commonly used organic UV filters in fresh and saline waters by liquid chromatography-tandem mass spectrometry

Abstract: An analytical method for the simultaneous determination of seven of the most widely used organic UV filter compounds in tap and saline waters was developed and validated. Target compounds included oxybenzone, dioxybenzone, sulisobenzone, avobenzone, octocrylene, octinoxate, and padimate-O. Water samples were adjusted to pH 2 prior to solid-phase extraction (SPE) using Oasis HLB 500 mg cartridges. The detection and quantification were performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with positive electrospray ionization (ESI) using Multiple Reaction Monitoring mode (MRM). Calculated recoveries from fortified samples ranged from 74 to 109% with relative standard deviations of 6–25% for fortified tap water samples and from 71 to 111% with relative standard deviations 2–12% for fortified seawater samples, indicating acceptable method accuracy and precision (n = 5). Method reporting limits ranged from 0.5 to 25 ng L−1 for the seven compounds. Oxybenzone, avobenzone, octocrylene, octinoxate, and padimate-O were detected in seawater samples collected from Folly Beach, South Carolina in the summer of 2010, at concentrations ranging from 10 to 2013 ng L−1, demonstrating the ability of the developed method to measure target compounds in environmental samples. Oxybenzone and octocrylene were found in the highest concentrations, up to 2013 ng L−1 and 1409 ng L−1, respectively. Concentrations for avobenzone, octinoxate, and padimate-O ranged from 62–321 ng L−1, 30–264 ng L−1 and <1–111 ng L−1, respectively, in surface seawater samples (n= 4). Dioxybenzone and sulisobenzone were not detected in any samples from the four sites (method reporting limits 1 ng L−1). To our knowledge, this is the first study reporting sunscreen compounds in the coastal waters of the U.S.A.

Bio-Raman spectroscopy: a potential clinical analytical method assisting in disease diagnosis

Abstract: With the technical progress in lasers, charge coupled device detectors, and fiber-optic probes, Raman spectroscopy (RS) is enjoying a strong resurgence in the field of biomedical science, especially in disease diagnosis. During this time we have witnessed more and more in vitro and in vivo applications of RS, and increasingly frequent reports of its utility. RS enables the extraction of biochemical signatures from biological tissues, and in conjunction with different statistic algorithms, the spectral data with various pathologic attributions can be differentiated and classified depending on their spectral differences, e.g., peak area, peak height or peak shape. This makes RS a potential clinical analytical technique for rapid and non-destructive diagnosis of human diseases. This paper is a review of the biomedical applications of Raman spectroscopic techniques in diagnostics. First, a brief illumination of RS instrumentation and algorithms for data analysis is introduced. Then wide utilization of RS in disease diagnosis is reviewed categorized by different tissues and organs, including brain, eye, body surface organs (breast, skin), abdominal organs (stomach, esophagus, colon, liver), thoracic organs (arteries, lung), reproductive and urinary organs (prostate, cervix, bladder) and hard tissue (bone, teeth). Some other work from our group are also introduced.

Solid-phase microextraction with a novel graphene-coated fiber coupled with high-performance liquid chromatography for the determination of some carbamates in water samples

Abstract: In this study, a novel graphene nanocomposite was synthesized and used as a solid-phase microextraction fiber coating material. The application of the graphene-coated fiber was evaluated through the extraction and determination of the four carbamate pesticides (carbofuran, carbaryl, pirimicarb, diethofencarb) in water samples by high performance liquid chromatography-diode array detection. Parameters that affect the extraction efficiencies, such as the extraction time, stirring rate, extraction temperature, and salt addition, were investigated and optimized. Compared with the two commonly used commercial fibers (CW/TPR, 50 μm; PDMS/DVB, 60 μm), the graphene-coated fiber showed higher extraction efficiency. Under the optimum conditions, the limits of detection (LODs), based on a signal-to-noise ratio (S/N) of 3, were 0.1–0.8 ng mL−1. The limits of quantification (LOQ, S/N = 9) were 0.3–2.4 ng mL−1. The linearity was observed in the range from their corresponding LOQs to 400.0 ng mL−1 with the correlation coefficients (r) ranging from 0.9994 to 0.9998. The recoveries of the carbamate pesticides from water samples at spiking levels of 10.0, 50.0 and 100 ng mL−1 were in the range of 83.8%–95.4%, and the relative standard deviations were between 2.2% and 6.6%.