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Analytica Chimica Acta (v.655, #1-2)
Spiropyran-based optical approaches for mercury ion sensing: Improving sensitivity and selectivity via cooperative ligation interactions using cysteine by Na Shao; Xiadi Gao; Hao Wang; Ronghua Yang; Winghong Chan (pp. 1-7).
Spiropyrans are an attractive starting point in design of optical approaches for metal ions sensing. However, the high background in aqueous solution and non-specific chelation of the spiropyran with heavy metal ions has hindered their application as reliable sensors for environmental and biological species. Here, we report on a new spiropyran-based approach for sensitive and selective sensing of Hg2+ in aqueous solution, based on cooperative ligation interactions among the spiropyran probe, an intermediate, cysteine, and the metal ion. To test the feasibility of this design, three spiropyran scaffolds, L1–L3, with different ligation functions at the 8′-position were examined as model systems. The results demonstrate that by using cysteine, a potential ligand of Hg2+, the spiropyran could detect 1.0×10−7M Hg2+ in aqueous solution. Due to the specific metal–amino acid interaction, the approach exhibits selective response toward Hg2+ over other metal ions and anions, although possible interference from Cu2+ has to be considered at the high level of the metal ion. This approach has been used for the determination of Hg2+ in water samples containing potential interferents with satisfactory recovery.
Keywords: Spiropyran; Metal ions; Probe; Cooperative interaction
Developments and applications of capillary microextraction techniques: A review by Hiroyuki Kataoka; Atsushi Ishizaki; Yuko Nonaka; Keita Saito (pp. 8-29).
Sample preparation is important for isolating desired components from complex matrices and greatly influences their reliable and accurate analysis. Recent trends in sample preparation include miniaturization, automation, high-throughput performance, and reduction in solvent consumption and operation time. This review focuses on novel microextraction techniques using capillaries for off-line and on-line sample preparation. Open-tubular trapping (OTT), in-tube solid-phase microextraction (SPME), wire-in-tube SPME, fiber-in-tube solid-phase extraction (SPE), sorbent-packed capillary in-tube SPME and monolithic capillary in-tube SPME are critically evaluated and applications of these techniques in biological, pharmaceutical, environmental and food analyses are summarized.
Keywords: Sample preparation; Capillary microextraction; Open-tubular trapping; In-tube solid-phase microextraction; On-line analysis; Automated analysis
About estimating the limit of detection of heteroscedastic analytical systems by Elio Desimoni; Barbara Brunetti (pp. 30-37).
The limit of detection is a fundamental figure of merit in chemical analysis. Many different approaches are available for its estimation, but only few allow analysing data characterized by a significant change of precision with concentration. Among these, the ISO 11843-2 approach is certainly the most suitable. However, its implementation may not look easy to operators needing to develop the necessary spreadsheets by commercial software packages. This paper is aimed to verifying if alternative approaches are available for getting acceptably approximate estimates of the limit of detection (LOD). Pragmatically, they were set-up by simply adapting some of the approaches already available in the literature, but compatible only with homoscedastic analytical systems. The results obtained by these alternative approaches when analysing a series of calibrations relevant to the electroanalytical determination of hexavalent chromium in some water samples were compared to those furnished by the ISO approach. The results allowed confirming the critical role of the numerosity of the available data on the consistency of any estimate. Even when using the ISO approach, reliable estimates were only obtained by performing a number of calibrations usually uncommon under standard routine conditions. In such a situation, the differences between the results obtained by all the examined approaches appear less important.
Keywords: Limit of detection; Heteroscedasticity; International Organization for Standardization 11843; Weighted regression; Hexavalent chromium; Adsorptive stripping voltammetry
Second order advantage in the determination of amaranth, sunset yellow FCF and tartrazine by UV–vis and multivariate curve resolution-alternating least squares by Natalia Elizabeth Llamas; Mariano Garrido; María Susana Di Nezio; Beatriz Susana Fernández Band (pp. 38-42).
A direct spectrophotometric method for the determination of three artificial colors – amaranth, sunset yellow FCF and tartrazine – in beverages samples is proposed. The spectra were recorded between 359 and 600nm. The spectra of the samples (just filtrated), pure dyes (concentrations ranged between 0.01 and 1.8mgL−1 for amaranth, 0.08 and 4.4mgL−1 for sunset yellow and 0.04 and 1.8mgL−1 for tartrazine) and synthetic mixtures were disposed in a column-wise augmented data matrix. This kind of data structure, analyzed by multivariate curve resolution-alternating least squares (MCR-ALS) makes it possible to exploit the so called ‘second order advantage’. MCR-ALS algorithm was applied to the experimental data under the non-negativity and equality constraints. As a result, the concentration of each dye in the samples and their corresponding pure spectra were obtained.The results were validated using internal reference materials and no significant differences were found ( α=5%) between the reference values and the ones obtained with the proposed method. The second order advantage made it possible to obtain unbiased results even in the presence of interferences.
Keywords: Multivariate curve resolution; Alternating least squares; Second order advantage; Dyes; Beverages samples
Recognizing paracetamol formulations with the same synthesis pathway based on their trace-enriched chromatographic impurity profiles by M. Dumarey; A.M. van Nederkassel; I. Stanimirova; M. Daszykowski; F. Bensaid; M. Lees; G.J. Martin; J.R. Desmurs; J. Smeyers-Verbeke; Y. Vander Heyden (pp. 43-51).
The development of a new drug substance is an expensive and time-consuming process. Therefore, the developers want to maximize the profit from the drug by patenting the concerned molecule as well as its synthesis pathway. In a later stage a faster or cheaper manufacturing process can be developed and patented. The aim of this study is to recognize paracetamol-containing drug formulations in relation to their synthesis pathways, in order to demonstrate the possibility to reveal fraudulently synthesized paracetamol. Since different synthesis pathways require different starting materials, solvents, reagents and catalysts and since they can produce different intermediates, it is expected that drug products originating from a different synthesis pathway will exhibit a different impurity profile. Therefore, in this study several paracetamol samples, synthesized in four different ways, are analyzed using trace-enrichment high-performance liquid chromatography (HPLC). The resulting chromatographic data were chemometrically treated in order to reveal clustering tendencies in the hope of distinguishing the different pathways. When performing principal component analysis (PCA) only 3 vaguely outlined clusters appeared. Projection pursuit (PP) was able to reveal 4 clusters and the samples with known synthesis pathway, except one, were classified in the different clusters. When hierarchical clustering and auto-associative multivariate regression trees (AAMRT) were applied, the samples of the four synthesis pathways could also be distinguished. AAMRT has an added value, since it can indicate the variables (peaks and thus also the impurities) that are responsible for the differences between the samples synthesized differently.
Keywords: Synthesis pathway; Impurity profiling; Trace-enrichment chromatography; Chemometric exploration; Paracetamol
Ionic liquid-based dispersive liquid–liquid microextraction followed high-performance liquid chromatography for the determination of organophosphorus pesticides in water sample by Lijun He; Xianli Luo; Hongxue Xie; Chunjian Wang; Xiuming Jiang; Kui Lu (pp. 52-59).
Using 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) ionic liquid as extraction solvent, organophosphorus pesticides (OPPs) (parathion, phoxim, phorate and chlorpyifos) in water were determined by dispersive liquid–liquid microextraction (DLLME) combined with high-performance liquid chromatography (HPLC). The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of [C8MIM][PF6] dispersed entirely into sample solution with the help of disperser solvent (methanol). Parameters including extraction solvent and its volume, disperser solvent and its volume, extraction time, centrifugal time, salt addition, extraction temperature and sample pH were investigated and optimized. Under the optimized conditions, up to 200-fold enrichment factor of analytes and acceptable extraction recovery (>70%) were obtained. The calibration curves were linear in the concentration range of 10.5–1045.0μgL−1 for parathion, 10.2–1020.0μgL−1 for phoxim, 54.5–1089.0μgL−1 for phorate and 27.2–1089.0μgL−1 for chlorpyifos, respectively. The limits of detection calculated at a signal-to-noise ratio of 3 were in the range of 0.1–5.0μgL−1. The relative standard deviations for seven replicate experiments at 200μgL−1 concentration level were less than 4.7%. The proposed method was applied to the analysis of four different sources water samples (tap, well, rain and Yellow River water) and the relative recoveries of spiked water samples are 99.9–115.4%, 101.8–113.7% and 87.3–117.6% at three different concentration levels of 75, 200 and 1000μgL−1, respectively.
Keywords: Ionic liquid; Dispersive liquid–liquid microextraction; Organophosphorus pesticide; High-performance liquid chromatography
Development of a simple device for dispersive liquid–liquid microextraction with lighter than water organic solvents: Isolation and enrichment of glycyrrhizic acid from licorice by Payman Hashemi; Somayeh Beyranvand; Reza Siah Mansur; Ali Reza Ghiasvand (pp. 60-65).
A simple device was developed that makes the use of lighter than water organic solvents feasible in dispersive liquid–liquid microextraction (DLLME) method. In the ordinary DLLME, the fact that a heavier than water organic solvent must be used, to be sedimented at the conical bottom of a centrifuge tube, limits the applications of this method in some extent. In the developed method, a glass tube with a narrow neck is inserted inside the centrifuge tube. After phase separation, the organic solvent is accumulated in the narrow neck of the device and therefore, can be simply collected by a micro-syringe. The DLLME method with the proposed device was tested for the enrichment of glycyrrhizic acid from aqueous extracts of licorice before analysis by a HPLC method. n-Hexanol and acetone were used as the organic and disperser phases, respectively. Effects of pH, salt concentration and phase volumes on the extraction of the analyte were optimized using a central composite (response surface) design. Under the optimized conditions (i.e. pH 1.3, ionic strength 0.2molL−1, n-hexanol 140μL and acetone 0.8mL) an extraction recovery of 104.1 (±5.1)% and an enrichment factor of 54 were obtained. The proposed method was successfully applied for the study of glycyrrhizic acid's level of licorice roots grown in three regions of Lorestan province, Iran, with different climate conditions.
Keywords: Dispersive liquid–liquid microextraction; Lighter than water organic solvents; Glycyrrhizic acid; High performance liquid chromatography; Multivariate optimization
Phosphorescent sensing of carbon dioxide based on secondary inner-filter quenching by I.M. Pérez de Vargas-Sansalvador; M.A. Carvajal; O.M. Roldán-Muñoz; J. Banqueri; M.D. Fernández-Ramos; L.F. Capitán-Vallvey (pp. 66-74).
A study of different strategies to prepare phosphorescence-based sensors for gaseous CO2 determination has been performed. It includes the characterization of different configurations tested, a discussion of the results obtained and possibilities for the future. The optical sensor for gaseous CO2 is based on changes in the phosphorescence intensity of the platinum octaethylporphyrin (PtOEP) complex trapped both on oxygen-insensitive poly(vinylidene chloride-co-vinyl chloride) (PVCD) membranes and PVCD microparticles, due to the displacement of the α-naphtholphthalein acid–base equilibrium with CO2 concentration. A secondary inner-filter mechanism was tested for the sensor and a full range linearized calibration was obtained by plotting ( I100− I0)/( I− I0) versus the inverse of the CO2 concentration, where I0 and I100 are the detected luminescence intensities from a membrane exposed to 100% nitrogen and 100% CO2, respectively, and I at a defined CO2 concentration. The different configurations tested included the use of membranes containing luminophore and pH-sensitive dye placed on two opposite sides of a transparent support to prevent the observed degradation of the PtOEP complex in the presence of the tetraoctylammonium hydroxide (TOAOH) phase transfer agent, which produced better results regarding stability and sensitivity. The CO2 gas sensor based on PtOEP homogeneous membranes presented better properties in terms of response time and sensitivity than that based on PtOEP microparticles. With a detection limit of 0.02%, the response time (10–90% maximum signal) is 9s and the recovery time (90–10%) is 115s. The lifetime of the membranes for CO2 sensing preserved in a 94% RH atmosphere and dark conditions is longer than at least 4 months.
Keywords: Carbon dioxide; Gas sensor; Phosphorescence; Secondary inner-filter quenching; Microparticles
Selective chemosensor for Hg(II) ions based on tris[2-(4-phenyldiazenyl)phenylaminoethoxy]cyclotriveratrylene in aqueous samples by Nuriman; Bambang Kuswandi; Willem Verboom (pp. 75-79).
A novel chemosensor, based on tris[2-(4-phenyldiazenyl)phenylaminoethoxy]cyclotriveratrylene (TPPECTV) as chromophore, has been developed for the colorimetric determination and visual detection of Hg(II) ions. TPPECTV exhibits a pronounced chromogenic behavior toward Hg(II) ions by changing the color of the solution from yellow to red-orange upon its addition, which can be easily detected with the naked-eye. Based on this sensing scheme a colorimetric method was developed, where the absorbance linearly increases as a function of the Hg(II) concentration up to 2.0×10−4M, with a detection limit of 0.5μM. The visual detection, using TPPECTV absorbed on silica, provides a simple, rapid and sensitive method and was used for the detection of Hg(II) ions in water samples with a detection limit of 5.0μM. The colorimetric results of the detection of Hg(II) ions in environmental water samples (river water) are in good agreement with those obtained by cold vapor atomic absorption spectrometry (CVAAS).
Keywords: Chemosensor; Visual detection; Colorimetric method; Hg(II); Water samples
Development of a miniaturized diffusive gradients in thin films (DGT) device by Nadia Alexa; Hao Zhang; Jamie R. Lead (pp. 80-85).
A miniaturized diffusive gradients in thin films (DGT) device with a sampling window which is 16 times smaller than the conventional DGT device was developed. Its main advantage is the reduced volume of solution necessary for deployment, which extends its potential applications. The design of the miniaturized DGT device was also improved compared with the conventional DGT device, such that the area of the diffusive gel layer that allows the diffusion of metal towards the binding gel layer has the same diameter as the opening in the cap of the device and no additional metal is accumulated due to lateral diffusion as is the case for the conventional device. A good correlation between the metal concentration directly measured and the concentration estimated with the help of the DGT equation was obtained using this device in synthetic solutions (10μgL−1 Cd, 0.01M NaNO3, pH 6). The capacity of the device for Cd was ∼20μg, potentially allowing long term measurements to be performed. Metal accumulation increased linearly with deployment time up to 28h and showed the theoretically expected dependence on diffusive layer thickness. The diffusive boundary layer thickness of ∼0.2mm in stirred solution was considered for accurate quantification of concentration. There was no difference between concentrations of labile metal measured in natural waters using the new miniaturised devices and the conventional devices.
Keywords: DGT; Dynamic speciation; Trace metals; In-situ; Miniaturization
An integrative approach for the isolation, screening and analysis of antitumor agents by liquid chromatography combined with mass spectrometry by Cuirong Sun; Jindi Fu; Shan He; Yuanjiang Pan (pp. 86-91).
A rapid approach has been developed for screening trace level compounds with antitumor activities based on their interactions with microtubules. This interaction can be quantified with liquid chromatography (LC) by measuring the difference of bioactive compound's concentration before and after the formation of compound–microtubule complexes in the fast dialyzers. To test the effectiveness of this approach, several antitumor drugs such as colchicine, taxol, daunorubicin, and a non-antitumor reagent ketoprofen were used. Results indicate that the antitumor constituents can be identified without any disturbance, and the inactive components can be excluded. This screening method was then successfully applied to some potential antitumor compound mixtures, and the active compounds could be separated and screened rapidly. The binding activities measured were consistent with their cytotoxicity assays. This integrative approach is rapid and convenient for screening, isolating, and analyzing potential antitumor active compounds from a mixture.
Keywords: Screening; Microtubule; Antitumor compounds mixture; Liquid chromatography
Corrigendum to “A biofunctional polymeric coating for microcantilever molecular recognition” [Anal. Chim. Acta 630 (2008) 161–167]
by Giulio Oliviero; Paolo Bergese; Giancarlo Canavese; Marcella Chiari; Paolo Colombi; Marina Cretich; Francesco Damin; Sonia Fiorilli; Simone L. Marasso; Carlo Ricciardi; Paola Rivolo; Laura E. Depero (pp. 92-92).