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Analytica Chimica Acta (v.666, #1-2)
Multifunctional nanoparticles: Analytical prospects by Alejandro Simón de Dios; Marta Elena Díaz-García (pp. 1-22).
Multifunctional nanoparticles are among the most exciting nanomaterials with promising applications in analytical chemistry. These applications include (bio)sensing, (bio)assays, catalysis and separations. Although most of these applications are based on the magnetic, optical and electrochemical properties of multifunctional nanoparticles, other aspects such as the synergistic effect of the functional groups and the amplification effect associated with the nanoscale dimension have also been observed. Considering not only the nature of the raw material but also the shape, there is a huge variety of nanoparticles. In this review only magnetic, quantum dots, gold nanoparticles, carbon and inorganic nanotubes as well as silica, titania and gadolinium oxide nanoparticles are addressed. This review presents a narrative summary on the use of multifuncional nanoparticles for analytical applications, along with a discussion on some critical challenges existing in the field and possible solutions that have been or are being developed to overcome these challenges.
Keywords: Multifunctional nanoparticles; Analytical applications
Comparison between NIR, MIR, concatenated NIR and MIR analysis and hierarchical PLS model. Application to virgin olive oil analysis by N. Dupuy; O. Galtier; D. Ollivier; P. Vanloot; J. Artaud (pp. 23-31).
This work investigates the potential use of simultaneously near-infrared (NIR) and mid-infrared (MIR) spectroscopies for the quantitative analysis of fatty acids and triacylglycerols and for identifying the Registered Designation of Origin (RDO) of extra virgin olive oils. The two spectral ranges were used separately using PLS and PLS-DA regressions. To combine both information, concatenated matrix was used at the first time, multiblock method using H-PLS models were constructed at the second time. The models were compared in terms of prediction errors. The results obtained with MIR spectroscopy are better than the ones obtained with NIR spectroscopy. The H-PLS methodology seems to be very interesting for quantitative analysis with the use of additional information in the NIR range, which is not present in the MIR one. For RDO identification by discriminant analysis, the use of multiblock method was less efficient.
Keywords: Infrared; Partial least square; Discriminant analysis; Concatenated matrix; Hierarchical partial least square; Virgin olive oils
An improved boosting partial least squares method for near-infrared spectroscopic quantitative analysis by Xueguang Shao; Xihui Bian; Wensheng Cai (pp. 32-37).
Boosting partial least squares (PLS) has been used for regression to improve the predictive accuracy of PLS models, however, there are still problems when the outliers exist in the calibration dataset. To make the method robust and enhance its prediction ability, an improved boosting PLS is proposed and applied in quantitative analysis of near-infrared (NIR) spectral datasets. In the method, a robust step is added to weaken the effect of the outliers on the model. On the other hand, the loss function defined with relative errors is suggested for updating the sampling weight during the boosting procedure. In addition, the ensemble prediction by the weighted mean of the models in the boosting series is found to be more effective than the commonly used weighted median. The performance of the improved method is tested with two large NIR datasets of industrial production. The method was found to have a marked superiority in robustness and prediction ability, particularly when outliers exist.
Keywords: Near-infrared spectroscopy; Partial least squares; Robust; Loss function; Boosting
Determination of five beta-blockers in wastewaters by coupled-column liquid chromatography and fluorescence detection by P. Parrilla Vázquez; M. Martínez Galera; A. Serrano Guirado; M.M. Parrilla Vázquez (pp. 38-44).
A simple multidimensional system for direct injection of large volumes has been developed for the determination of five beta-blockers (atenolol, nadolol, metoprolol, bisoprolol and betaxolol) in wastewater using fluorescence detection. A C18 50mm×4.6mm i.d. column coupled to a RP Amide C16 150mm×4.6mm i.d. column for analyte clean-up and determination were used, respectively. The capability of a first column for eliminating large, interfering molecules, combined with an optimised, coupled-column liquid chromatography separation procedure (LC–LC), large volume injection (LVI) and fluorescence detection (FD), gave excellent sensitivity and selectivity for the target analytes. The LVI-LC–LC-FD method combines analyte isolation, preconcentration and determination into a single step. Detection limits obtained in wastewater were lower than, or equal to, 0.0020μgL−1. Limits of quantification (LOQs) obtained in the matrix according to IUPAC, ranged between 0.0052 and 0.0089μgL−1, whereas LOQs calculated according to EURACHEM Guidance, varied between 0.4 and 0.6μgL−1. Accuracy values ranged from 82 to 107% ( n=3) and relative standard deviation (RSD) values ranged from 0.8 to 9%. The LVI-LC–LC-FD method was applied for determining the target analytes in wastewater samples obtained in Almería (Spain).
Keywords: Liquid chromatography; Coupled columns; Large volume injection; Beta-blockers; Wastewater
Injection port derivatization following sonication-assisted ion-pair liquid–liquid extraction of nonsteroidal anti-inflammatory drugs by Li Xu; Ming Jiang; Gao Li (pp. 45-50).
In this paper, a sonication-assisted ion-pair liquid–liquid extraction approach, combined with injection port derivatization and gas chromatographic (GC) analysis, was developed to extract and detect nonsteroidal anti-inflammatory drugs (NSAIDs). In this procedure, the target analytes in the sample solution were converted into their ion-pair complexes (carboxylate ion-pairs) with tetrabutylammonium hydrogen sulfate. The ion-pairs were then extracted by an organic solvent (ethyl acetate) with the assistance of sonication. The factors influential to extraction, including type of organic solvent, concentration of ion-pair reagent, pH values of sample solution, sonication time duration and salt addition, were investigated in detail. After extraction, the organic phase containing ion-pair complexes was injected to GC sample port. Upon injection, the carboxylate ion-pairs were derivatized promptly under high temperature to yield butyl esters, which were more suitable for GC analysis. The conditions for injection port derivatization, such as injection port temperature and purge off time, were also examined. This newly established approach afforded the limits of detection between 0.44 and 2.75ngL−1 for the tested NSAIDs, with relative standard deviations less than 5.4%.
Keywords: Injection port derivatization; Sonication; Ion-pair; Liquid–liquid extraction; Nonsteroidal anti-inflammatory drug
Derivation of governing equation describing time-dependent penetration length in channel flows driven by non-mechanical forces by Sukalyan Bhattacharya; Dilkumar Gurung (pp. 51-54).
Several past attempts were made to describe the penetration length in microchannels as a function of time for electroosmotic or capillary flow. In all of these studies, a complex governing equation is derived by taking into account the inertial contributions along with other forces. The system being unsteady, this derivation requires the consideration of proper unsteady flow-profile inside the channel. However, the past theories introduced an inconsistency by using parabolic velocity-field valid only for steady systems. This discrepancy creates an error of the same order as the inertial contribution leading to two consequences. Firstly, the inherent inaccuracy makes the past theories inapplicable when Reynolds number is greater than unity. Secondly, it renders the inclusion of inertial terms pointless for low Reynolds number systems—the additional complexity due to inertia does not serve any purpose because error of similar order is already present in the formulation.In this paper, we address this problem by rectifying the mathematical derivation where instead of the parabolic velocity-profile, proper analytical expression for unsteady flow is used. As a result, the correct governing equation is derived for the penetration length for any laminar system with arbitrary Reynolds number. We also simplify the equation for low Reynolds number cases by considering appropriate limiting conditions. The equation for low Reynolds number flow, while being as accurate as the ones obtained in the earlier studies, is much simpler than the previous versions.
Keywords: Microfluidic system; Channel flow; Electroosmotic flow; Capillary flow; Penetration length for propagating fluid front; Unsteady velocity field
A novel dual-valve sequential injection manifold (DV-SIA) for automated liquid–liquid extraction. Application for the determination of picric acid by Jana Škrlíková; Vasil Andruch; Hana Sklenářová; Petr Chocholouš; Petr Solich; Ioseph S. Balogh (pp. 55-61).
A novel dual-valve sequential injection system (DV-SIA) for online liquid–liquid extraction which resolves the main problems of LLE utilization in SIA has been designed. The main idea behind this new design was to construct an SIA system by connecting two independent units, one for aqueous–organic mixture flow and the second specifically for organic phase flow. As a result, the DV-SIA manifold consists of an Extraction unit and a Detection unit. Processing a mixture of aqueous–organic phase in the Extraction unit and a separated organic phase in the Detection unit solves the problems associated with the change of phases having different affinities to the walls of the Teflon tubing used in the SI-system. The developed manifold is a simple, user-friendly and universal system built entirely from commercially available components. The system can be used for a variety of samples and organic solvents and is simple enough to be easily handled by operators less familiar with flow systems. The efficiency of the DV-SIA system is demonstrated by the extraction of picric acid in the form of an ion associate with 2-[2-(4-metoxy-fenylamino)-vinyl]-1,3,3-trimetyl-3 H-indolium reagent, with subsequent spectrophotometric detection. The suggested DV-SIA concept can be expected to stimulate new experiments in analytical laboratories and can be applied to the elaboration of procedures for the determination of other compounds extractable by organic solvents. It could thus form a basis for the design of simple, single-purpose commercial instruments used in LLE procedures.
Keywords: Sequential injection analysis; Dual-valve system; Liquid–liquid extraction; Picric acid
New UPLC coupled to mass spectrometry approaches for screening of non-volatile compounds as potential migrants from adhesives used in food packaging materials by E. Canellas; C. Nerín; R. Moore; P. Silcock (pp. 62-69).
The objective of this study was to identify the non-volatile compounds as potential migrants from adhesives used in food packaging. A number of the current acrylic adhesive formulations were extracted and prepared for analysis. The extracts were screened using ultra-performance liquid chromatography coupled to a time-of-flight mass spectrometer detector (UPLC–TOF-MS). This approach allowed the identification of several components by a combination of exact mass and in-source collision induced dissociation (CID). Due to the lack of freely available information on adhesive formulations further analyses were undertaken using ultra-performance liquid chromatography coupled to high definition mass spectrometry (UPLC–HDMS). Using the MassFragment™ tool to interrogate fragmentation data, a wide series of compounds were identified, demonstrating the usefulness and importance of these tools for difficult problems. Moreover, using several packaging materials containing adhesives, qualitative migration tests were performed with Tenax® as a food simulant. Several non-volatile compounds were identified as well in the Tenax® which emphasizes the importance of this work and demonstrates that even the non-volatile compounds have the potential to migrate into food which is in contact with packaging materials. The main characteristics of the screening study and the results obtained are shown and discussed.
Keywords: Food contact material; Adhesive composition; Screening analysis; Ultra-performance liquid chromatography coupled to a time-of-flight mass spectrometer detector; Ultra-performance liquid chromatography coupled to high definition mass spectrometry; Migration; Tenax; Non-volatile migrants
Molecularly imprinted polymer-based chemiluminescence array sensor for the detection of proline by Pingping Chang; Zhujun Zhang; Chunyan Yang (pp. 70-75).
A new molecularly imprinted polymer (MIP)–chemiluminescence (CL) method has been developed for detection of proline. The molecularly imprinted polymer microspheres were synthesized using precipitation polymerization with hydroxyproline, a structural analogue, as the template. Polymer microspheres were immobilized in microtiter plates (96 wells) which selectively adsorbed the analyte (dansyl-proline). After washing, the bound fraction was quantified based on peroxyoxalate chemiluminescence (PO-CL) reaction enhanced by imidazole. The cavity of MIP synthesized with hydroxyproline as template is smaller, which can avoid non-specific adsorption and lead to enhancement of specificity, response speed and sensitivity when recognizing dansyl-proline. Under the optimum conditions, the relative CL intensity has a linear relationship with the concentration of proline in the range of 1×10−6molL−1 to 4×10−5molL−1, with a limit of detection 3×10−7molL−1 (3 σ). The relative standard deviation (R.S.D.) for proline (1×10−6molL−1, n=7) was 3.7%. The MIP–CL method can become a useful analytical technology for determination of proline in real sample.
Keywords: Molecularly imprinted polymer; Chemiluminescence; Array sensor; Proline; Precipitation polymerization
Development of enzyme linked immunoassay for the simultaneous detection of carbaryl and metolcarb in different agricultural products by Jingwei Sun; Tingting Dong; Yan Zhang; Shuo Wang (pp. 76-82).
A direct competitive enzyme linked immunosorbent assay in multi-enzyme tracers format for the simultaneous analysis of carbaryl and metolcarb in agricultural products is described in this study. The concentrations of coating antibodies and enzyme tracer were studied. Under the optimum conditions, the limits of detection of carbaryl and metolcarb were 0.15μgL−1 and 1.2μgL−1, respectively. Determination of carbaryl and metolcarb in fruit juices and vegetables was accomplished by simple, rapid and efficient extraction methods. Recoveries of spiked samples were great than 70%. Validation of the immunosorbent assay was conducted by comparison of results from high performance liquid chromatography (HPLC). The correlations between the data obtained using multi-enzyme tracers enzyme linked immunosorbent assay and high performance liquid chromatography were good. Results indicated that the new strategy for developing immunoassay for simultaneous quantitative determination of carbaryl and metolcarb residues was suitable in this study.
Keywords: Enzyme linked immunosorbent assay; Simultaneous determination; Carbaryl; Metolcarb; Matrix effects; Agricultural products
Fabrication and performance evaluation of highly sensitive hybrid sol–gel-derived oxygen sensor films based on a fluorinated precursor by Juncal Estella; Dorota Wencel; John P. Moore; Maja Sourdaine; Colette McDonagh (pp. 83-90).
This paper describes the fabrication and performance of a range of highly sensitive luminescence-based oxygen sensor films based on the fluorinated sol–gel precursor 3,3,3-trifluoropropyltrimethoxysilane (TFP-TMOS). The oxygen-sensitive ruthenium complex [Ruthenium(II)-tris(4,7-diphenyl-1,10-phenanthroline)] dichloride, [Ru(dpp)3]2+ was entrapped in a wide range of ORMOSILs (organically modified silicates) matrices composed of alkyl and TFP-TMOS sol–gel precursors in different relative ratios. The influence of TFP-TMOS on sensor sensitivity, humidity-sensitivity and long-term stability was investigated and performance was compared to that of similar but non-fluorinated films. The optimum limit of detection was found to be 0.002% of oxygen for the propyltriethoxysilane (PTEOS)/TFP-TMOS-derived film compared to 0.09% for PTEOS-derived films reported previously. Photobleaching of the luminescent complex in fluorinated and non-fluorinated matrices was also investigated. It was established that photobleaching was reduced but not eliminated in fluorinated films. All films produced in this study exhibit very good reproducibility, reversibility, enhanced sensitivity, humidity-insensitivity and long-term stability.
Keywords: Luminescence; Oxygen sensor; Sol–gel; ORMOSIL; Photobleaching
Luminol/antibody labeled gold nanoparticles for chemiluminescence immunoassay of carcinoembryonic antigen by Xiaoyan Yang; Yingshu Guo; Aiguo Wang (pp. 91-96).
A facile strategy by loading luminol and secondary antibody on gold nanoparticles (Au NPs) was described in the present work. The as-prepared luminol/antibody labeled Au NPs conjugates (LAAu NPs) were used as the chemiluminescent probe for the detection of carcinoembryonic antigen (CEA) in serum. The LAAu NPs were characterized by transmission electron microscopy (TEM), UV–vis spectrophotometry (UV–vis), and chemiluminescent method. Stable and efficient chemiluminescence (CL) was obtained when luminol molecules and secondary antibodies were coimmobilized on the Au NPs by using hydrogen peroxide (H2O2) as an oxidant, horseradish peroxidase (HRP) as a catalyst, and 4-(4′-iodo)phenylphenol (IPP) as an enhancer. The LAAu NPs were further evaluated via a sandwich-type CL immunoassay of CEA in serum. In this protocol, the CEA analyte was captured by the primary antibody immobilized on the surface of magnetic beads, and then was sandwiched by the secondary antibody loaded on luminol-labeled Au NPs. The chemiluminescent intensity was proportional to the concentration of CEA over the range of 5.0×10−10 to 5.0×10−8gmL−1 and 5.0×10−9 to 2.0×10−8gmL−1 by using HRP and Co2+ as catalysts, respectively. The present chemiluminescent immunoassay based on the luminol/antibody labeled Au NPs conjugates has offered great promise for simple, highly biocompatible, and cost-effective analysis of biological samples.
Keywords: Chemiluminescence; Immunoassay; Luminol; Gold nanoparticles; Carcinoembryonic antigen
Gold nanoparticle as an electrochemical label for inherently crosstalk-free multiplexed immunoassay on a disposable chip by Chuan Leng; Guosong Lai; Feng Yan; Huangxian Ju (pp. 97-101).
This work proposed a simple, sensitive and low-cost multiplexed immunoassay by combining a disposable chip with gold nanoparticle (AuNP) as an electrochemical label. The immunosensors array as the disposable chip was firstly prepared by immobilizing capture antibodies on different screen printed carbon working electrodes by passive adsorption. With a sandwich mode, the analytes were then bound to the corresponding capture antibodies for further capture of the gold nanoparticle labeled antibodies. Gold nanoparticles were finally electrooxidized in 0.1M HCl to produce AuCl4− for differential pulse voltammetric detection. Using human IgG and goat IgG as model targets, under optimal conditions this method achieved linear ranges from 5.0 to 500 and 5.0 to 400ngmL−1 with limits of detection of 1.1 and 1.6ngmL−1, respectively. This method eliminated completely electrochemical crosstalk between adjacent immunosensors due to the strong adsorption of the AuCl4− on the printed carbon surfaces. The immunosensors array showed acceptable precision, reproducibility and stability, and could be readily applied to multianalyte determination for clinical diagnostics.
Keywords: Biosensors; Multiplexed immunoassay; Protein; Immunoglobulin; Gold nanoparticle; Amperometry
Capillary electrophoresis determination of antihistamines in serum and pharmaceuticals by Maria Rambla-Alegre; Juan Peris-Vicente; Josep Esteve-Romero; Maria-Elisa Capella-Peiró; Devasish Bose (pp. 102-109).
A capillary electrophoresis (CE) procedure combined with UV detection has proved useful for the quantification of the most frequently prescribed antihistamines corresponding to the ethylendiamine, ethanolamine, propylamine, piperazine and other derivative groups in serum samples and pharmaceuticals. Discussions have focused primarily on the optimisation of the separation conditions by considering the following experimental parameters: pH, pressure injection and voltage; under the criteria of maximum resolution and minimum analysis time. The optimised parameters for the determination of antihistamines were a 24cm capillary (effective length), UV detection at 214nm, 20mM phosphate running buffer at pH 2.0, 2psis−1 injection pressure and 5kV applied voltage. Under these conditions, the analysis time was below 10min. The proposed method was validated according to the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) guidelines. The limits of detection and quantification were in the ranges of 4–28 and 40–250ngL−1, respectively. Intra- and inter-day precision were tested at three different concentrations of the drugs, obtaining RSD values lower than 3% in most cases. The method was robust (RSD<5.6%), simple, specific and suitable for the practical determination of antihistamines in serum samples and pharmaceuticals with high recoveries (95.7–102.9%) without interferences.
Keywords: Antihistamines; Capillary electrophoresis; Pharmaceutical analysis; Serum; UV