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Analytical Methods (v.3, #10)

Front cover (pp. 2167-2168).

A rapid, specific and accurate proton nuclear magnetic resonance spectroscopy (¹H-NMR) method was developed to determine Carvedilol antihypertensive drug in pharmaceutical tablet formulation. The method was based on quantitative NMR spectroscopy (qNMR) using Maleic acid as an internal standard and deuterated dimethyl sulfoxide (DMSO-d6) as an NMR solvent. For the quantification of the drug, the ¹H-NMR signals at 8.20 ppm and 6.00 ppm corresponding to the analyte proton of Carvedilol and Maleic acid internal reference standard (IS) respectively were used. The method was validated for the parameters of specificity, precision, intermediate precision, linearity, range, limit of detection (LOD), limit of quantification (LOQ), accuracy, solution stability and robustness. The linearity of the calibration curve for analyte in the desired concentration range was good (R² > 0.9980). The method was accurate and precise with good recoveries. The range study was also performed up to saturation level (338.24 mg/0.60 mL) in DMSO-d6. The advantage of the method is that no reference standard of analyte drug is required for quantification. The method is nondestructive and can be applied for quantification of Carvedilol in commercial formulation products.

Contents (pp. 2169-2180).

Electrochemical techniques provide information of archaeometric interest. An overview on the application and future developments of the voltammetry of microparticles to the study of archaeological metals and their alteration products is presented. A report on the state of the art and future developments of this technique with regard to identification and origin studies of materials, authentication, chronology and dating of archaeological metal is provided.

Tracing, authenticating and dating archaeological metal using the voltammetry of microparticles by Antonio Doménech (pp. 2181-2188).

Monolithic silica with HPLC separation and solid phase extraction materials for determination of drugs in biological materials by Akira Namera; Shota Miyazaki; Takeshi Saito; Akihiro Nakamoto (pp. 2189-2200).

During the last one or two decades, monolithic polymers and silica have been developed for use as a new separation material or as a solid phase extraction sorbent and the applications with monoliths have been dramatically increased to separate the analytes by HPLC and to extract the analytes by solid phase extraction. The structure of monoliths differs from those of conventional particle materials. Specifically, the porosity of monoliths is over 80% and is larger than that of silica particle materials; therefore, columns packed with monoliths provide fast and high throughput analysis. Furthermore, high flow analysis is possible using monoliths because they produce very low back pressure. The applications of HPLC using monoliths for separation of bio-active compounds have gradually increased. In this review, these applications are summarized so that researchers can be introduced to the advantages of using monolithic silica. In addition, monolithic materials have the potential to be used as conventional solid phase extraction sorbents for the extraction of analytes in a sample matrix. The analytes in the sorbent can be eluted with a small volume because the monolith has wider surface area for each unit volume than those in other silicas or polymers and the required volume of the sorbents to extract the analytes is smaller in comparison with the conventional methods. To utilize these advantages of monoliths, new devices have been developed. In this review, the applications of monolithic silica for the extraction of drugs and medicines in biological materials are summarized.

Quantitative polymerase chain reaction: a framework for improving the quality of results and estimating uncertainty of measurement by Kate R. Griffiths; Daniel G. Burke; Kerry R. Emslie (pp. 2201-2211).

International comparability of quantitative polymerase chain reaction (qPCR) measurement results is critical for applied fields within industry, healthcare and forensics and may be achieved through traceability to the International System of Units, the SI. This process requires determining the accuracy of the quantitative result by estimation of the measurement uncertainty (MU). Here we present a relatively simple process for estimating MU for quantitative DNA measurements produced by qPCR. A worked example is given in which the qPCR method has been divided into four parts: DNA extraction; preparation of calibration curves; qPCR set-up and data analysis. A framework is provided in comprehensive tables that allow the identification of most potential sources of variation and bias. We show that each source can be either eliminated from the measurement process or captured in the MU data. The necessary data for MU estimation are relatively easy to gather but the combined uncertainty is only representative if all sources of variation have been incorporated. Although qPCR is given as an example, the principles apply to other nucleic acid measurements.

Phenolics and polysaccharides in major tropical fruits: chemical compositions, analytical methods and bioactivities by Jian Sun; Li Li; Xiangrong You; Changbao Li; Ezhen Zhang; Zhichun Li; Ganlin Chen; Hongxiang Peng (pp. 2212-2220).

Tropical fruits are important sources of phenolics and polysaccharides which are of great benefit to human health and have already been used in foodstuff, drugs and cosmetics. This review attempts to summarize the current research on phenolics and polysaccharides in major tropical fruits with large-scale production. Chemical composition, analytical methods, bioactivities and therapeutic functions of main phenolics and polysaccharides in pericarps, pulps and/or seeds of lychee (Litchi chinensis Sonn.), longan (Dimocarpus longan Lour.), mango (Mangifera indica L.), banana (Musa acuminata L.), pineapple (Ananas comosus L.) and papaya (Carica papaya L.) fruits are elucidated. The future research trends on phenolics and polysaccharides in tropical fruits are also suggested. This review indicates potential applications of phenolics and polysaccharides in tropical fruits, which is an important reference for effectively utilizing these bioactive components in tropical food systems.

Multiclass determination of pesticides and priority organic pollutants in fruit-based soft drinks by headspace solid-phase microextraction/gas chromatography tandem mass spectrometry by José Robles-Molina; Bienvenida Gilbert-López; Juan F. García-Reyes; Natividad Ramos Martos; Antonio Molina-Díaz (pp. 2221-2230).

In this work, a simple, environmentally friendly, rapid and reliable GC-MS/MS method has been developed for the determination of 45 organic contaminants (32 pesticides and 13 PAHs) in fruit-based soft-drinks. The proposed method consists of a solventless sample treatment procedure based on headspace solid-phase microextraction using a fiber of polyacrylate (PA), followed by identification and quantitation of the target pesticides by gas chromatography-tandem mass spectrometry (GC-MS/MS) using a triple quadrupole analyzer in the multiple reaction monitoring (MRM) acquisition mode. Several parameters of the automated extraction were studied including the incubation time, temperature, sample volume and type of SPME fibers. The identification and confirmation of the compounds were based on the retention time matching along with the presence (and relative abundances ratio) of three characteristic MRM transitions (except for PAHs, in which two transitions were used). Fruit-based soft drinks spiked at 100 ng L⁻¹ yielded average recoveries in the range 75–113% with RSD (%) below 15% (n = 8). The obtained limits of detection varied in the range 0.1–180 ng L⁻¹. The proposed method was successfully applied to the analysis of 26 market purchased fruit-based soft drink samples collected mainly in Spain, but also in some other countries, showing its potential applicability and revealing the presence of some of the target species in the ng L⁻¹ range (from 1.5 to 320.8 ng L⁻¹).

Identification of counterfeit medicines from the Internet and the World market using near-infrared spectroscopy by Sulaf Assi; Robert A. Watt; Anthony C. Moffat (pp. 2231-2236).

Pharmaceutical counterfeiting is a life threatening problem affecting all countries. Counterfeit medicines may be encountered anywhere in conventional markets or from the Internet. This paper proposes a rapid and non-destructive near-infrared spectroscopic method for the identification of counterfeit medicines using the minimum number of authentic samples. As little as twenty spectra from ten tablets from a batch are required to compare a test sample to its authentic counterpart. In this respect, tablets are measured as received and the correlation coefficient of the SNV-D2 spectra between the authentic sample and the test sample is determined. A correlation coefficient of lower than 0.95 indicates that the batch fails identification. In this case, if enough authentic samples are available, principal component analysis (PCA) could be applied. The PCA scores plot of the authentic and counterfeit samples with the 95% equal frequency ellipses drawn around the authentic sample set is effective in identifying counterfeits. The method could identify 82 known counterfeit medicines out of 201 medicines supplied from the Internet and the World market. However, it is still a comparative method to identify potential counterfeits and cannot identify products without authentic samples.

Biocompatible self-assembled monolayer platform based on (3-glycidoxypropyl)trimethoxysilane for total cholesterol estimation by Saurabh Kumar; Jay Singh; V. V. Agrawal; Mahboob Ahamad; B. D. Malhotra (pp. 2237-2245).

An electrochemical cholesterol biosensor has been fabricated via covalent immobilization of cholesterol oxidase and cholesterol esterase (ChOx and ChEt) onto a biocompatible self assembled monolayer (SAM) of (3-glycidoxypropyl)trimethoxysilane (GPTMS) fabricated onto an indium tin oxide (ITO) electrode. The ChOx/GPTMS/ITO bioelectrode has been characterized using Fourier transform infrared spectroscopy (FTIR), contact angle measurements (CA), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The results of the electrochemical response studies indicate that the ChOx-ChEt/GPTMS/ITO biosensing electrode can be used to estimate the total cholesterol from 1.5 to 6.1 mM, has sensitivity of 0.351 μA (mg/dl)⁻¹, and can be used more than 10 times with a shelf life of up to 10 weeks. The value of the Michaelis–Menten constant (Km) observed as 0.43 mM reveals a strong binding to the biocompatible GPTMS organic platform and shows low interference effect. Further, this biosensor can be used to estimate the total cholesterol concentration in serum samples.

Application of bimetallic nanoparticles modified screen printed electrode for the detection of organophosphate compounds using an enzyme inhibition approach by Sanjay Upadhyay; Mukesh K. Sharma; G. Rama Rao; Bijoy K. Bhattacharya; Vepa K. Rao; R. Vijayaraghavan (pp. 2246-2253).

A novel, unique gold–platinum bimetallic nanoparticles modified screen printed electrode (SPE) has been developed for the sensitive detection of paraoxon ethyl, carbofuran and simulant of nerve agent diisopropyl fluorophosphate (DFP), based on the enzyme inhibition approach. The gold–platinum nanoparticles were electrochemically deposited on a 3-aminopropyl triethoxy silane modified electrode. Following this acetylcholineesterase (AChE)/choline oxidase (ChOx) bienzymes were immobilized through cross-linking with glutaraldehyde onto a modified electrode. Electrodes were characterized by scanning electron microscopy (SEM), EDX (energy dispersive X-ray analysis) and cyclic voltammetry (CV). The bimetallic alloy nanoparticles have an excellent high surface area and the unique effect of electrocatalytic activity for the oxidation of hydrogen peroxide (H2O2). The IC50 values were determined for the inhibitors using immobilized enzymes on the modified electrode. Paraoxon ethyl, carbofuran, and DFP could be detected up to 0.20 μM, 0.20–0.25 μM, and 0.20–0.25 μM respectively at a 25–30% inhibition level of AChE enzyme (residual enzyme activity) with an incubation time of 10 min.

Determination of nitrobenzenes and nitrochlorobenzenes in water samples using dispersive liquid-liquid microextraction and gas chromatography-mass spectrometry by Delin Zhang; Xiangying Zeng; Zhiqiang Yu; Guoying Sheng; Jiamo Fu (pp. 2254-2260).

A rapid and sensitive method was developed for the determination of eight nitrobenzenes and four nitrochlorobenzenes in water. The method is based on dispersive liquid-liquid microextraction (DLLME) followed by gas chromatography-mass spectrometry (GC-MS). The key factors influencing the extraction efficiencies, including the nature and volume of the extraction and dispersion solvent and the ratios of the extraction solvent and dispersion solvent were examined and optimized. Under the optimized conditions, the method yields a linear correlation at a concentration range of 0.5 μg L⁻¹–500.0 μg L⁻¹ for all the target analytes with correlation coefficients (R²) of 0.9915 to 1.0000, and relative standard deviations (RSD, n = 6) of between 4.9% and 8.2%, depending on the compound analysed. In addition, good pre-concentration factors of 243 to 525 for each specific compound were achieved. These results suggest that the method presented herein is a rapid and powerful microextraction technique that is useful for the detection of these organic pollutants in water samples and is suitable for emergency monitoring.

Determination of 2,4-D in environmental samples by three phases directly suspended LPME combined with HPLC-UV by Vahid Amani; Saeed Roshan; Ali Akbar Asgharinezhad; Ezzatollah Najafi; Hamid Abedi; Najmeh Tavassoli; Hamid Reza Lotfi Zadeh Zhad (pp. 2261-2267).

Experimental design of directly suspended droplet liquid–liquid–liquid microextraction has been used to determine residue of 2,4-D, in environmental water samples. A free suspended droplet of 5.5 μL of receiving phase is delivered to the top-center position of 1-Octanol, which is an immiscible organic solvent, floating on the top of a 2.5 mL aqueous sample while being agitated by a stirring bar to create a mild vortex at the center of the vial. Central composite rotatable design has been used for studying the effect of the parameters, the factors interacting with each other and finding the optimum condition. The chromatographic separation was accomplished on a shim-Pak C18 column using a mixture of 10 mmol L⁻¹ NaH2PO4 (pH = 5.4) : acetonitrile (40 : 60, v/v) as mobile phase at a flow rate 1 mL min⁻¹ with UV detection at λ = 220 nm. In order to achieve the maximum extraction efficiency, different parameters affecting the extraction were optimized. Under the optimized conditions, preconcentration factor of 130 and limit of detection (LOD) of 0.3 μg L⁻¹ were obtained. The calibration graph was linear within the range of 0.8–1500 μg L⁻¹. Finally, the feasibility of the proposed method was successfully confirmed by extraction and determination of 2,4-D in real water samples in the range of microgram per liter and suitable results were obtained (RSDs < 6.4%).

Development of a new method based on scanner electrochemistry: applied for the speciation of Iron(ii) and Iron(iii) by Abdolkarim Abbaspour; Abdolreza Khajehzadeh; Ali Ghaffarinejad (pp. 2268-2272).

A new, simple and inexpensive method was developed based on scanner electrochemistry as an appropriate alternative to visible spectroelectrochemistry. The electrochemical cell containing the sample solution was scanned by a flatbed scanner and color values were analyzed by software in the RGB color system. The validity of this new method was studied by speciation of iron(ii) and (III). The speciation was performed by complexation of iron species with SCN⁻. Parameters, such as time and potential of electrolysis, which affect the system were optimized.

A novel droplet sensor based on liquid-phase microextraction for on-line aluminum analysis by Bo Zhang; Fulian Luo; Yong Guo; Jing Li; Dan Xiao; Martin M. F. Choi (pp. 2273-2278).

A new droplet sensor based on liquid-phase microextraction and fluorescence detection has been developed. This droplet sensor employs a laboratory-made T-tube with a groove as the optical cell, a simple and cheap light-emitting diode (LED) as the excitation source, and a photomultiplier tube as the photodetector. The performance of the droplet sensor is illustrated with the determination of aluminum (Al). A small drop (40 μL) of a water-immiscible organic solvent (chloroform) containing 8-hydroxyquinoline (HQN) is positioned in the groove of the T-tube and is in contact with a flowing stream of Al(iii) solution. Al(iii) ion in the aqueous solution is extracted as aluminum oxinate into the chloroform droplet, resulting in the increase in fluorescence of the organic droplet. The droplet sensor displays a wide linear range (50–800 μg L⁻¹) for Al(iii) at pH 5.5 and the detection limit is 7.6 μg L⁻¹ (S/N = 3). The distinct advantage of our proposed droplet sensor is that it enables both in situ enrichment and on-line determination of Al(iii). By virtue of these valuable features such as low cost, convenience and miniaturization, the droplet sensor is anticipated to have great potential for trace level detection of other metal compounds.

Organic impurities, stable isotopes, or both: A comparison of instrumental and pattern recognition techniques for the profiling of 3,4-methylenedioxymethamphetamine by Hilary A. S. Buchanan; William J. Kerr; Wolfram Meier-Augenstein; Niamh Nic Daéid (pp. 2279-2288).

In this study, we precisely synthesised 61 3,4-methylenedioxymethamphetamine hydrochloride (MDMA.HCl) samples. The synthetic route, reaction conditions, and batch of starting material used were carefully controlled in order to facilitate the assessment of the sample linkage abilities of: (1) GCMS organic impurity profiling using different sets of target impurities recommended from the published literature, and (2) stable isotope ratio mass spectrometry (IRMS) for δ¹³C, δ¹⁵N, δ²H, and δ¹⁸O-values. For GCMS analysis, we utilised the extraction parameters, instrumental conditions, and data analysis techniques recently published. In addition to this, we analysed all MDMA.HCl samples by IRMS for their ¹³C, ¹⁵N, ²H, and ¹⁸O isotopic composition. The resulting data sets were subjected to hierarchical cluster analysis, principal component analysis, and discriminant analysis to identify which type of measurement (i.e. GCMS, IRMS, or both), which set of target impurities for GCMS, and which data pre-treatment method offers meaningful discrimination of the samples according to batch of starting material used, synthetic route used, or both. For our data set, discriminant analysis using a combination of the IRMS data and GCMS data (‘Van Deursen’ impurities pre-treated with the fourth root method) provided the most accurate discrimination of the MDMA.HCl samples. Principal component analysis had the second highest success rate, and hierarchical cluster analysis had only limited success at producing meaningful discrimination of the samples into their known groupings.

Determination of total phenolic content in Prunella L. by horseradish peroxidase immobilized onto chitosan beads by Önder Aybastıer; Saliha Şahin; Esra Işık; Cevdet Demir (pp. 2289-2297).

Horseradish Peroxidase (HRP) was immobilized by covalent binding onto glutaraldehyde cross-linked chitosan beads and these beads were used for determination of total phenolic content in Prunella L. species. Central composite design (CCD) was employed to optimize the conditions for the maximum HRP activity and to understand the significance and interaction of the factors affecting the activity of immobilized HRP. The results indicated that enzyme concentration and immobilization time were significant factors for the immobilization of HRP. The optimum conditions were determined as enzyme concentration 0.25 mg mL⁻¹, pH 8.0 and immobilization time 20h. The recovered activity was obtained as 81% after immobilization under optimal conditions. Total phenol content was determined in four Prunella L. species (Prunella vulgaris L., Prunella laciniata (L.) L., Prunella orientalis Bornm., Prunella grandiflora L.) extracted using methanol, water and methanol/water (4 : 1, v/v). The enzymatic method is based on the spectrophometric measurement of the final quinone-imine colored product, absorbing at 510 nm, by HRP oxidation in presence of hydrogen peroxide. The results were compared with those obtained by applying the Folin method. The highest total phenol content was obtained with the methanol/water (4 : 1, v/v) extract of Prunella vulgaris L. by immobilized HRP method (63.75 mg gallic acid equivalent (GAE) per g dried plant). Operational stability was determined with immobilized HRP and it indicated that a small enzyme deactivation (15%) occurred after 10 consecutive uses.

Techniques for quantifying chemicals concealed behind clothing using near infrared spectroscopy by Aamer Saleem; Céline Canal; David A. Hutchins; Lee A J. Davis; Roger J. Green (pp. 2298-2306).

The detection of specific chemicals when concealed behind a layer of clothing is reported using near infrared (NIR) spectroscopy. It is found that concealment modifies the spectrum of a particular chemical when recorded at stand-off ranges of three meters in a diffuse reflection experiment. Chemometric analysis of the spectra has been performed with neural network-based pattern recognition/classification to deal with this problem. Neural networks help to overcome nonlinearities within the calibration/training dataset, affording more robust modelling. The work has been shown to both allow detection of specific chemicals concealed behind a single intervening layer of fabric material, and to estimate the concentration of hydrogen peroxide using partial least squares regression (PLSR).

Separation and structural characterization of a synthetic cannabinoid found in a herbal product using off-line LC-DAD-NMR by Harri Koskela; Ullastiina Hakala; Leena Loiske; Paula Vanninen; Ilmari Szilvay (pp. 2307-2312).

A herbal product confiscated by the Finnish Customs was analyzed. No illegal compounds were found in the preliminary GC-MS screening against the mass spectral library. The most prominent compounds in the sample, however, could not be identified. These compounds of interest were characterized using an off-line LC-DAD-NMR technique with a mass-sensitive microcoil probehead. The structural analysis, confirmed by GC-MS and LC-MS studies, revealed the presence of a CP 47,497-C8 type compound with a structural modification in the cyclohexyl part of the compound. The structural modification of this potentially psychoactive compound was presumably intended to elude routine screening.

Fe3O4@Au sphere molecular imprinting with self-assembled monolayer for the recognition of parathion-methyl by Xiaoshan Tang; Dan Zhang; Tianshu Zhou; Dongxia Nie; Qinyan Yang; Litong Jin; Guoyue Shi (pp. 2313-2321).

A novel surface molecular imprinting technique is reported based on spherical molecular imprinted monolayer (SMIM) prepared from 3-mercaptopropionic acid self-assembled on core-shell Fe3O4@Au nanoparticles (NPs) with preadsorbed templates of parathion-methyl, which is widely used in agricultural production. The proposed imprinted sensor was characterized by transmission electron microscopy (TEM), FT-IR and UV-visible absorbance spectrum analysis. The result obtained from a series of electrochemical experiments proved that the prepared sorbent had a good adsorption capacity and a fast mass transfer rate for parathion-methyl. The response of the SMIM was linearly proportional to the concentration of parathion-methyl over the range of 2.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with a lower detection limit of 1.0 × 10⁻⁷ M. The selectivity of the sensor was tested by measuring parathion-methyl in the presence of some possible interferent compounds such as imidacloprid, diuron, propanil, parathion and paraoxon and obtained satisfactory results. This imprinted electrochemical sensor was successfully employed to detect parathion-methyl with a simple surface molecular imprinting and self-assembled process which could easily and rapidly remove the template of parathion-methyl by cyclic voltammetry.

Multiphoton ionization/mass spectrometry of polybrominated diphenyl ethers by Osamu Shitamichi; Tomoko Imasaka; Tomohiro Uchimura; Totaro Imasaka (pp. 2322-2327).

Gas chromatography combined with multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) using ultraviolet picosecond and femtosecond lasers was employed to quantitatively analyze a series of polybrominated diphenyl ethers (PBDEs). Congeners from monoBDE to tetraBDEs were analyzed using a picosecond laser emitting at 266 nm. In order to enhance the efficiency of ionization for highly brominated DEs via triplet levels, a different laser emitting at 213 nm was used. It was, however, difficult to quantify such congeners, even at this wavelength. This unexpected result can be explained by the photodecomposition of PBDEs from the triplet levels. On the other hand, all congeners from monoBDE to decaBDE were detected when a femtosecond laser emitting at 267 nm was employed. Interestingly, the isomers having a smaller number of Br atoms at the meta-positions were more efficiently ionized, and provided lower values of detection limit.

Electrocatalysis of epinephrine by TiO2 nanoparticles and 2,2′-[1,7-hepthandiylbis(nitriloethylidyne)]-bis-hydroquinone modified carbon paste electrode by Mohammad Mazloum-Ardakani; Afsaneh Talebi; Hossein Naeimi; Mohammad Ali Sheikh-Mohseni (pp. 2328-2333).

A carbon paste electrode, modified with 2,2′-[1,7-hepthandiylbis(nitriloethylidyne)]-bis-hydroquinone (HBNBH) and TiO2 nanoparticles, was developed and used for the determination of epinephrine (EP). It has been found that oxidation of epinephrine at the surface of such electrodes occurs at potentials less positive than at an unmodified carbon paste electrode. The magnitude of the peak current for HBNBH modified TiO2-nanoparticles CPE (MTNCPE), increased sharply in the presence of EP and was proportional to its concentration. The electrocatalytic oxidation mechanism of epinephrine (EP), at the surface of the (MTNCPE), was studied by the help of cyclic voltammetry (CV), chronoamperometry (CHA), linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV). A dynamic range of 2.0–1600.0 μM, with a detection limit of 0.4 μM for EP, was obtained using DPV technique (pH = 8.0). Parameters such as the electron transfer coefficient, α, heterogeneous rate constant, ks and diffusion coefficient, D for oxidation of EP were also determined. The prepared electrode was successfully applied for the determination of EP in real samples.

Fluorescence polarization as a tool for the detection of a widely used herbicide, butachlor, in polluted waters by Hongtao Lei; Gang Xue; Chunfai Yu; Simon A. Haughey; Sergei A. Eremin; Yuanming Sun; Zhanhui Wang; Zhenlin Xu; Hong Wang; Yudong Shen; Qing Wu (pp. 2334-2340).

A rapid and highly specific fluorescence polarization immunoassay (FPIA) was developed for the detection of a widely used herbicide in rice cultivation, butachlor, in various polluted water samples. Three fluorescent tracers with different spacer arms and structures were synthesized to enhance the FPIA sensitivity. The effects of different fluorescent tracer structure and organic solvent concentration on the performance of the FPIA were investigated. The results showed that the fluorescent tracer 3-(2-((butoxymethyl)(2,6-diethylphenyl)amino)-2-oxoethylthio)-N-(6-(3-(3′,6′-dihydroxy-3-oxo-3H-spiro[isobenzofuran-1,9′-xanthene]-5-yl) thioureido)hexylpropanamide (tracer C) demonstrated the best FPIA sensitivity at pH 8.0, which remained at up to 20% methanol in a tolerance study. The IC50 (50% inhibition concentration) of the FPIA was 207.0 ng mL⁻¹ with the detection of butachlor ranging from 32.0 to 1218.0 ng mL⁻¹ (at 20%–80% inhibition concentration), and the limit of detection (at 10% inhibition concentration) was 11.0 ng mL⁻¹. Recoveries, measured in spiked water samples, ranged from 75.1% to 134.5%. This newly developed FPIA was characterized by high specificity and reproducibility, allowing a rapid, low-cost, and sensitive determination of butachlor in polluted waters.

Quantitative determination and validation of Carvedilol in pharmaceuticals using quantitative nuclear magnetic resonance spectroscopy by Hemant Gadape; Kalpesh Parikh (pp. 2341-2347).

Probing the molecular weight of poly(amidoamine) dendrimers and derivatives using SDS-PAGE by Tongyu Xiao; Xueyan Cao; Shige Wang; Xiangyang Shi (pp. 2348-2353).

As a simple and versatile technique, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to analyze the molecular weight (Mw) of poly(amidoamine) (PAMAM) dendrimers and their derivatives. By optimizing the gel concentration and electrophoretic voltage, we were able to probe the Mw of PAMAM dendrimers of different generations terminated with amine, acetyl, hydroxyl, and carboxyl groups. We show that for acetyl-, hydroxyl-, and carboxyl-terminated dendrimers with neutral, slightly positive, and negative surface charges, the protein standards can be directly used for the determination of their Mws. However, for amine-terminated PAMAM dendrimers, one has to subtract the contribution of SDS molecules adsorbed onto the dendrimer surfaces. Our results clearly indicate that besides the utilization of other techniques, SDS-PAGE could be used as an alternative inexpensive, rapid, and reliable method to determine the Mw of PAMAM dendrimers with different surface functionalities.

Temperature-controlled ionic liquid-based dispersive liquid-phase microextraction, preconcentration and quantification of nano-amounts of silver ion by using disulfiram as complexing agent by Ghodratollah Absalan; Morteza Akhond; Leila Sheikhian; Douglas M. Goltz (pp. 2354-2359).

Microextraction and preconcentration of Ag⁺ by using temperature-controlled ionic liquid-based dispersive liquid-phase microextraction (TCIL-DLPME) method is reported. It was found that tetraethylthiuram disulfide (disulfiram) dissolved in 1-hexyl-3-methylimidazolium hexaflorophosphate, [C6mim][PF6] was useful as extracting media. Graphite furnace atomic absorption spectroscopy was used to quantify Ag⁺. To improve extraction efficiency, different experimental factors, such as volume of ionic liquid phase, pH and volume of aqueous solution, cooling and centrifugation periods, and dissolving temperature were investigated. The calibration curve was linear in the concentration range of 6.0–100.0 ng l⁻¹ of Ag⁺. Relative standard deviation (n = 7), detection limit, and preconcentration factor for determination of Ag⁺ were found to be 4.5%, 5.2 ng l⁻¹, and 120, respectively. The method was successfully applied for determination of Ag⁺ in drinking water and hair samples. Percent recoveries for solutions containing Ag⁺ indicated that chemical interferences by selected anions (NO³⁻, Cl⁻, I⁻, Br⁻ and citrate) or cations (Ni²⁺, Cu²⁺, Mg²⁺, Zn²⁺, Pb²⁺, Ca²⁺, Co²⁺, Hg²⁺, Na⁺ and Mn²⁺) in solution were minimal or non-existent.

High throughput quantitative analysis of melamine and triazines by MALDI-TOF MS by Ajeet Singh; Venkateswarlu Panchagnula (pp. 2360-2366).

Quantitative and high throughput MALDI MS analysis of symmetrical triazines (s-triazines), and milk contaminated with melamine has been demonstrated. s-Triazines from a multi component aqueous test mixture, and melamine, a known adulterant in milk, were quantified at low parts-per-million (ppm) level using 2,5-dihydroxybenzoic acid (2,5-DHB) as a matrix. Mass spectral peak intensity ratios of the analyte and a suitable internal standard were used for the quantitation. Limit of detection at 20 ‘parts-per-billion’ (nano molar concentration) has been achieved for the s-triazines from the aqueous mixture. Quantitation from MALDI MS peak intensities was validated using LC-PDA and LC-ESI-MS analysis using both spectral peak intensities and areas under the chromatographic curves. Excellent linearity in low ppm concentrations along with good precision and accuracy, all of which were comparable to LC-ESI-MS data, were obtained with the advantage of rapid analysis.

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 by Jahan Bakhsh Raoof; Reza Ojani; Mehdi Baghayeri (pp. 2367-2373).

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.

Improved electrocatalytic behavior of ascorbic acid by crosslinked polyaniline with enhanced conductivity by Shaozhu Chen; Lan Xu; Yuanyuan Yang; Bingxin Li; Jingya Hou (pp. 2374-2378).

A newly designed crosslinked polyaniline (CPAN) was developed and preliminarily used to fabricate a sensor for determination of ascorbic acid (AA). The nanostructured copolymer was confirmed through surface morphology studies (SEM). The amperometric response of electrodes toward AA based on crosslinked polyaniline (CPAN) is far more than that of linear polyaniline (LPAN), which exhibits improved electrocatalytic oxidation of AA. The linear range of the promising sensor is from 5.0 × 10⁻⁶ to 1.13 × 10⁻² M with a lower detection limit of 1.67 × 10⁻⁶ M (S/N = 3) as well as good selectivity, stability and reproducibility.

Comparison of Nafion- and overoxidized polypyrrole-carbon nanotube electrodes for neurotransmitter detection by M. Jennifer Peairs; Ashley E. Ross; B. Jill Venton (pp. 2379-2386).

Permselective polymer coatings improve selectivity and sensitivity of microelectrodes for cationic neurotransmitters. Immobilizing carbon nanotubes (CNTs) into these polymers should further improve sensitivity by increasing the electroactive surface area. The goal of this study was to compare the electrochemical properties of overoxidized polypyrrole (oPPY)-CNT and Nafion-CNT coated microelectrodes. Fast-scan cyclic voltammetry was used to test their response to neurochemicals. For dopamine, the average increase in oxidation current compared to bare electrodes was 3.7 ± 0.5 for oPPY-CNT electrodes (limit of detection (LOD) = 3.3 ± 0.6 nM) and 3.3 ± 0.8 for Nafion-CNT electrodes (LOD = 4 ± 1 nM). The selectivity for dopamine over ascorbic acid was better with oPPY-CNT electrodes. oPPY-CNT electrodes also displayed increased electron transfer kinetics for anions while Nafion-CNT electrodes did not, which proves that polymer deposition can affect the electrocatalytic properties of the CNTs. Both oPPY-CNT and Nafion-CNT electrodes were used to detect stimulated dopamine release in the caudate-putamen of anesthetized rats after 2, 4 and 12 pulse stimulation trains. oPPY-CNT electrodes could also detect small amounts of dopamine after 4 and 12 pulse stimulations in the basolateral amygdala (BLA). Although Nafion-CNT electrodes were easier to make, oPPY-CNT electrodes were more advantageous for dopamine detection because they were reproducibly fabricated, measured higher currents in vivo, and maintained selectivity over anions. The addition of CNTs to polymer coatings facilitates measurements of small concentrations of neurotransmitters in vivo.

A novel biosensor based on a gold nanoflowers/hemoglobin/carbon nanotubes modified electrode by Ying-Chun Gao; Kai Xi; Wei-Na Wang; Xu-Dong Jia; Jun-Jie Zhu (pp. 2387-2391).

Well-oriented 3D gold flower-like nanoparticles were successfully synthesized by a facile one-pot method, and the gold nanoflowers (AuNFs) were mixed with hemoglobin (Hb) to form a gold nanoflowers/hemoglobin composite. The composite was further combined with multiwalled carbon nanotubes on a glassy carbon electrode (GCE) to fabricate a novel biosensor. The sensor has high stability and bioactivity, and was studied by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The hemoglobin/gold nanoflowers/multiwalled carbon nanotubes glassy carbon electrode (Hb/AuNFs/CNTs/GCE) either retained the Hb in similar native conformations or promoted direct electron transfer. Moreover, the sensor exhibited remarkable catalytic activity toward H2O2 and trichloroacetic acid (TCA). The linear relationship for the determination is in the range of 1.0–60 μM for H2O2 and 0.06–28 mM for TCA. The detection limits were 0.08 μM and 7.3 μM (S/N = 3), respectively.

Application of an automated multi-pH and multi-temperature platform for accelerated solution stability testing in supporting drug discovery by Yun W. Alelyunas; Luciana Pelosi-Kilby; Russell C. Spreen (pp. 2392-2399).

An automated method for testing the solution stability of drug discovery candidates is described. The method simultaneously tests a compound's stability over 20 h at two temperatures (37 °C and 60 °C) and at as many as six pH values ranging from pH 1 to pH 10. Stability kinetics for each pH and temperature combination are monitored at ∼2 h intervals. Automated liquid handling was used for the sample collection and preparation. Sample analysis was streamlined using an HPLC autosampler and data analysis was automated via proprietary data handling and archival software (AstraZeneca). Scientific validation of the method and application to support drug discovery is also illustrated.

Multi-walled carbon nanotubes/chitosan polymer composite modified glassy carbon electrode for sensitive simultaneous determination of levodopa and morphine by Ali Babaei; Mitra Babazadeh (pp. 2400-2405).

A modified electrode was constructed by coating of the glassy carbon surface with carbon nanotubes/chitosan (CNTs/CS) and used for sensitive and selective determination of levodopa (l-dopa) and morphine (MO) in a 0.1 M phosphate buffer (pH 7.0). The electrochemical response characteristics of the modified electrode toward l-dopa and MO were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) techniques. Under optimum conditions the sensor provided a linear CA response in the range of 1–360 μM with a detection limit of 0.86 μM for l-dopa, and in the range of 1–240 μM, with a detection limit of 0.65 μM for MO. The designed sensor was used for determination of l-dopa and MO in human serum and urine with satisfactory results.

A norepinephrine biosensor based on a glassy carbon electrode modified with carbon nanotubes by Ali Mohammadi; Abdolmajid Bayandori Moghaddam; Samanesadat Hosseini; Mahmood Kazemzad; Rassoul Dinarvand (pp. 2406-2411).

Immobilized enzyme tyrosinase on single-walled carbon nanotubes (SWCNTs) was used to measure the norepinephrine concentration in injections. A simple method was investigated to prepare a modified glassy carbon (GC) electrode with CNTs. First, CNT solution was cast on the electrode surface and dried to form a CNT/GC electrode. Then, tyrosinase (TR) immobilized on the surface of the CNT/GC electrode. The cyclic voltammograms (CVs) in aqueous solution indicated that the CNTs could promote the direct electron transfer of tyrosinase and a pair of stable redox couple appeared. Tyrosinase can catalyze the oxidation of norepinephrine to norepinephrine quinone. When norepinephrine was added to the electrochemical cell, the oxidation peak current of the TR/SWCNT/GC electrode increased and gives a catalytic current. Based on this, a biosensor for determination of norepinephrine has been developed. This method had adequate accuracy, sensitivity and precision; in addition, the biosensor showed good repeatability and stability to assay norepinephrine in bulk form and pharmaceutical dosage forms.

A novel, environmentally friendly procedure for copper extraction using dimethylindodicarbocyanine dye and subsequent graphite furnace atomic absorption spectrometric detection by Jana Škrlíková; Vasiľ Andruch; Ioseph S. Balogh; József Posta; Yaroslav Bazeľ; Alexander Hudák; Veronika Jalčoviková; Lívia Kocúrová (pp. 2412-2415).

A reaction based on ion associate formation between dimethylindodicarbocyanine polymethine dye 1,3,3-trimethyl-2-[5-(1,3,3-trimethyl-1,3-dihydroindol-2-ylidene)-penta-1,3-dienyl]-3H-indolium (DIDC) and Cu(i) in the presence of chloride ions as ligand is used to develop a liquid–liquid extraction procedure for the separation and preconcentration of copper with subsequent graphite furnace atomic absorption spectrometric detection. The optimum reaction conditions for ion associate formation and extraction were found to be: pH 3–5, 0.24–0.36 mol L⁻¹ of chloride, 0.05–0.12 mmol L⁻¹ of DIDC, amyl acetate as extraction solvent, an aqueous to organic phase ratio of 5 : 1 mL : mL. A linear response was obtained in the range 0.4–4.8 μg L⁻¹ of Cu, and the limit of detection, calculated from a regression equation based on three times the standard deviation of the blank, was 0.10 μg L⁻¹. The method was applied to the determination of Cu in real samples. It is important to note that the presented method can also be applied to the determination of Cu(i) in the presence of a 125-fold excess of Cu(ii), thus enabling the speciation analysis.

Quantification of indicator content in silica-based pH solid sensors by diffuse reflectance spectroscopy by Larissa Brentano Capeletti; João Henrique Z. dos Santos; Edwin Moncada (pp. 2416-2420).

The amount of alizarin red, brilliant yellow or acridine encapsulated within silica matrixes as colorimetric pH sensors, produced by three sol–gel routes (acid catalyzed, base catalyzed and non-hydrolytic routes), was investigated using diffuse reflectance spectroscopy in the UV-Vis region. Univariate calibration curves using silica (commercial or sol–gel synthesized) as a blank were linear (R² > 0.99) but did not allow coherent quantification of the pH indicator, likely due to the matrix effect. The standard addition method using the silica blank (produced by the corresponding sol–gel route) to correct background afforded coherent results with standard deviation between 0.017 and 0.59, depending on the sol–gel route and indicator.

Rapid determination of polyphenols in cut tobacco by microwave-assisted extraction-ultrahigh performance liquid chromatography by Zhao Rui-feng; Li Feng; Hu Jing (pp. 2421-2424).

A fast microwave-assisted extraction-ultrahigh performance liquid chromatography (MAE-UPLC) method was developed for the simultaneous determination of chlorogenic acid, scopoletin and rutin in cut tobacco. The extraction conditions of polyphenols were determined by single-factor and orthogonal experiment. The optimal conditions were found to be as follows: methanol concentration of 60% (v/v), extraction solvent temperature of 90 °C, microwave extraction time of 1 min and solid to liquid ratio of 1 : 20 (g mL⁻¹), the recovery rates of polyphenols in cut tobacco were between 96.5% and 105.6%, relative standard deviations were lower than 5%. The total analysis time for a sample was less than 20 min, the results were satisfactory.

Back cover (pp. 2425-2426).

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Analytical Methods (v.3, #10)