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Analytica Chimica Acta (v.609, #2)
Use of itaconic acid-based polymers for solid-phase extraction of deoxynivalenol and application to pasta analysis by Michelangelo Pascale; Annalisa De Girolamo; Angelo Visconti; Naresh Magan; Iva Chianella; Elena V. Piletska; Sergey A. Piletsky (pp. 131-138).
Molecular modelling and computational design were used to identify itaconic acid (IA) as a functional monomer with high affinity towards deoxynivalenol (DON), a Fusarium-toxin frequently occurring in cereals. IA-based polymers were photochemically synthesised in dimethyl formamide (porogen) using ethylenglycol dimethacrylate as cross-linker and 1,1′-azo-bis(cyclohexane carbonitrile) as initiator, and the relevant binding interactions with DON in solvents with different polarity were investigated. The performances of the non-imprinted IA-based polymer (blank polymer, BP) and the corresponding molecularly imprinted polymer (MIP) were compared using DON as a template. Both BP and MIP were able to bind about 90% DON either in toluene, water or water containing 5% polyethylene glycol. Non-imprinted polymers with different molar ratios of IA to cross-linker were evaluated as adsorbents for solid-phase extraction (SPE) clean-up and pre-concentration of DON from wheat and pasta samples prior to HPLC analysis. Samples were extracted with PBS/0.1M EDTA solution and cleaned up through a cartridge containing blank IA-based polymer. The column was washed with PBS (pH 9.2) and the toxin was eluted with methanol and quantified by reversed-phase HPLC with UV detector ( λ=220nm), using methanol:water:acetic acid (15:85:0.1, v/v/v) as the mobile phase. Effective removal of matrix interferences was observed only for pasta with DON recoveries higher than 70% (RSD<7%, n=3) at levels close to or higher than EU regulatory limit.
Keywords: Deoxynivalenol; Molecular modelling; Itaconic acid; Computational design; Cross-linked sorbent; Solid-phase extraction
Electrochemical and piezoelectric DNA biosensors for hybridisation detection by Fausto Lucarelli; Sara Tombelli; Maria Minunni; Giovanna Marrazza; Marco Mascini (pp. 139-159).
DNA biosensors (or genosensors) are analytical devices that result from the integration of a sequence-specific probe and a signal transducer. Among other techniques, electrochemical and piezoelectric methods have recently emerged as the most attractive due to their simplicity, low instrumentation costs, possibility for real-time and label-free detection and generally high sensitivity.Focusing on the most recent activity of worldwide researchers, the aim of the present review is to give the readers a critical overview of some important aspects that contribute in creating successful genosensing devices. Advantages and disadvantages of different sensing materials, probe immobilisation chemistries, hybridisation conditions, transducing principles and amplification strategies will be discussed in detail. Dedicated sections will also address the issues of probe design and real samples pre-treatment. Special emphasis will be finally given to those protocols that, being implemented into an array format, are already penetrating the molecular diagnostics market.
Keywords: DNA biosensor; Genosensor; Amplicon; Hybridisation; Electrochemical; Piezoelectric transduction
Development of novel and sensitive methods for the determination of sulfide in aqueous samples by hydrogen sulfide generation-inductively coupled plasma-atomic emission spectroscopy by M. Colon; J.L. Todolí; M. Hidalgo; M. Iglesias (pp. 160-168).
Two new, simple and accurate methods for the determination of sulfide (S2−) at low levels (μgL−1) in aqueous samples were developed. The generation of hydrogen sulfide (H2S) took place in a coil where sulfide reacted with hydrochloric acid. The resulting H2S was then introduced as a vapor into an inductively coupled plasma-atomic emission spectrometer (ICP-AES) and sulfur emission intensity was measured at 180.669nm. In comparison to when aqueous sulfide was introduced, the introduction of sulfur as H2S enhanced the sulfur signal emission. By setting a gas separator at the end of the reaction coil, reduced sulfur species in the form of H2S were removed from the water matrix, thus, interferences could be avoided. Alternatively, the gas separator was replaced by a nebulizer/spray chamber combination to introduce the sample matrix and reagents into the plasma. This methodology allowed the determination of both sulfide and sulfate in aqueous samples. For both methods the linear response was found to range from 5μgL−1 to 25mgL−1 of sulfide. Detection limits of 5μgL−1 and 6μgL−1 were obtained with and without the gas separator, respectively. These new methods were evaluated by comparison to the standard potentiometric method and were successfully applied to the analysis of reduced sulfur species in environmental waters.
Keywords: Sulfide; Inductively coupled plasma-atomic emission spectroscopy; Vapor generator; Water analysis
Application of the modelling power approach to variable subset selection for GA-PLS QSAR models by Salvador Sagrado; Mark T.D. Cronin (pp. 169-174).
A previously developed function, the Modelling Power Plot, has been applied to QSARs developed using partial least squares (PLS) following variable selection from a genetic algorithm (GA). Modelling power ( Mp) integrates the predictive and descriptive capabilities of a QSAR. With regard to QSARs for narcotic toxic potency, Mp was able to guide the optimal selection of variables using a GA. The results emphasise the importance of Mp to assess the success of the variable selection and that techniques such as PLS are more robust following variable selection.
Keywords: Genetic Algorithm; QSAR; Variable Selection; Modelling Power Plot
Gas chromatographic determination of carbonyl compounds in biological and oil samples by headspace single-drop microextraction with in-drop derivatisation by Yiannis C. Fiamegos; Constantine D. Stalikas (pp. 175-183).
A suitable method for the gas chromatographic determination of 10 characteristic carbonyls in biological and oil samples based on the in-drop formation of hydrazones by using 2,4,6-trichlorophenylhydrazine (TCPH), has been developed. The derivatisation–extraction procedure was optimized separately for aqueous and oil samples with respect to the appropriate organic drop solvent, drop volume, in-drop TCPH concentration, sample stirring rate, temperature during single-drop microextraction (SDME), reaction time and headspace-to-sample volume ratio. The optimization showed differentiation of optimum values between the studied matrices. The limits of detection were found to range from 0.001 to 0.003μgmL−1 for the aqueous biological samples and from 0.06 to 0.20μgmL−1 for the oil samples. The limits of quantification were in the range of 0.003–0.010μgmL−1 and 0.020–0.059μgmL−1 for aqueous and oil samples, respectively. The overall relative standard deviations of the within-day repeatability and between-day reproducibility were <4.4% and <8.2% for the aqueous biological samples and <3.9% and <7.4% for the oxidized oil samples.
Keywords: Headspace single-drop microextraction; 2,4,6-Trichlorophenylhydrazine; Aldehydes; Oil; Plasma; Urine
Determination of trace metals in urine with an on-line ultrasound-assisted digestion system combined with a flow-injection preconcentration manifold coupled to flame atomic absorption spectrometry by R.M. Cespón-Romero; M.C. Yebra-Biurrun (pp. 184-191).
A flow analysis method with on-line sample digestion/minicolumn preconcentration/flame atomic absorption spectrometry is described for the determination of trace metals in urine. First, urine sample was on-line ultrasound-assisted digested exploiting the stopped-flow mode, and then the metals were preconcentrated passing the pre-treated sample through a minicolumn containing a chelating resin. A home-made minicolumn of commercially available imminodiacetic functional group resin, Chelite Che was used to preconcentrate trace metals (Cu, Fe, Mn and Ni) from urine. The proposed procedure allowed the determination of the metals with detection limits of 0.5, 1.1, 0.8 and 0.8μgL−1, for Cu, Fe, Mn and Ni, respectively. The precision based on replicate analysis was less than ±10.0%, and the enrichment factor obtained was between 21.3 (Mn) and 44.1 (Ni), for sample volumes between 2.5 and 5.0mL, and an eluent volume of 110μL. This procedure was applied for determination of metals in urine of workers exposed to welding fumes and urine of unexposed persons (urine control).
Keywords: Metals; Urine; Flow injection; Flame atomic absorption spectrometry
Analysis of catecholamines and their metabolites in adrenal gland by liquid chromatography tandem mass spectrometry by Qun Gu; Xianzhe Shi; Peiyuan Yin; Peng Gao; Xin Lu; Guowang Xu (pp. 192-200).
Two simple, rapid and specific analytical methods for 13 catecholamines and their metabolites have been developed based on liquid chromatography tandem mass spectrometry in a multiple reaction monitoring mode. Tyrosine, dopamine, dihydroxyphenylalanine, epinephrine, norepinephrine, 3-methoxytyramine, normetanephrine, metanephrine and isoproterenol (internal standard) were separated on a Kromasil™ Cyano analytical column by a mobile phase consisting of 60% (v/v) acetonitrile and 40% (v/v) water adjusted with formic acid to pH 3.0, and detected by positive ionization electrospray tandem mass spectrometry. While vanillymandelic acid, 3,4-dihydroxymandelic acid, homovanillic acid, 3,4-dihydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenylglycol and 5-hydroxy-2-indolecarboxylic acid (internal standard) were separated on a reversed-phase Shim-Pak VP-ODS column with the mobile phase of 60% (v/v) acetonitrile, and 40% (v/v) water adjusted with formic acid to pH 4.5 and detected in the negative ionization electrospray tandem mass spectrometry. The influence of various parameters such as column type and mobile phase composition on separation and sensitivity were investigated. The limits of detection were in the range of 0.5–20ngmL−1. The mean recoveries determined from three different concentrations of each analyte were above 85.4%. The precision of the method calculated as relative standard deviation was lower than 5.3%. Deduced from the results of real sample analysis, adrenal gland synthesizes and stores the catecholamine hormones norepinephrine and epinephrine.
Keywords: Catecholamine; Metabolite; Liquid chromatography; Tandem mass spectrometry; Adrenal gland
Integrated multienzyme electrochemical biosensors for the determination of glycerol in wines by M. Gamella; S. Campuzano; A.J. Reviejo; J.M. Pingarrón (pp. 201-209).
The construction and performance of integrated amperometric biosensors for the determination of glycerol are reported. Two different biosensor configurations have been evaluated: one based on the glycerol dehydrogenase/diaphorase (GDH/DP) bienzyme system, and another using glycerol kinase/glycerol-3-phosphate oxidase/peroxidase (GK/GPOx/HRP). Both enzyme systems were immobilized together with the mediator tetrathiafulvalene (TTF) on a 3-mercaptopropionic acid (MPA) self-assembled monolayer (SAM)-modified gold electrode by using a dialysis membrane. The electrochemical oxidation of TTF at +150mV (vs. Ag/AgCl), and the reduction of TTF+ at 0mV were used for the monitoring of the enzyme reactions for the bienzyme and trienzyme configurations, respectively. Experimental variables concerning both the biosensors composition and the working conditions were optimized for each configuration. A good repeatability of the measurements with no need of cleaning or pretreatment of the biosensors was obtained in both cases. After 51 days of use, the GDH/DP biosensor still exhibited 87% of the original sensitivity, while the GK/GPOx/HRP biosensor yielded a 46% of the original response after 8 days. Calibration graphs for glycerol with linear ranges of 1.0×10−6 to 2.0×10−5 or 1.0×10−6 to 1.0×10−5M glycerol and sensitivities of 1214±21 or 1460±34μAM−1 were obtained with GDH/DP and GK/GPOx/HRP biosensors, respectively. The calculated detection limits were 4.0×10−7 and 3.1×10−7M, respectively. The biosensors exhibited a great sensitivity with no significant interferences in the analysis of wines. The biosensors were applied to the determination of glycerol in 12 different wines and the results advantageously compared with those provided by a commercial enzyme kit.
Keywords: Self-assembled monolayers; Enzyme biosensors; Glycerol; Wines
One-step immobilization of tris(2,2′-bipyridyl)ruthenium(II) via vapor-surface sol–gel deposition towards solid-state electrochemiluminescence detection by Lei Qian; Xiurong Yang (pp. 210-214).
A novel method for immobilization of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)3Cl2) on electrode surfaces based on the vapor-surface sol–gel deposition strategy is first demonstrated in this paper. Ru(bpy)3Cl2 immobilized sol–gel (Ru(bpy)3Cl2/sol–gel) films were characterized by UV–vis spectroscopy and field-emitted scanning electron microscopy (FE-SEM). These results showed that Ru(bpy)3Cl2 was successfully incorporated into the silica sol–gel film. It was found that many irregular Ru(bpy)3Cl2/sol–gel clusters were formed on surfaces through one deposition and thick sol–gel films were observed after further deposition. Electrochemical properties and electrochemiluminescence (ECL) behaviors of Ru(bpy)3Cl2/sol–gel films could be easily adjusted by deposition numbers and time. At last, the Ru(bpy)3Cl2/sol–gel film modified electrode was used for solid-state ECL detection of tripropylamine. The linear range was from 5.8×10−8 to 2.4×10−4M with the detection limit of 5nM, which was three orders of magnitude lower than that from pure Nafion-modified electrodes. The ECL sensor also exhibited high stability, and still remained 92% response after being stored in air for 35 days. This method for immobilization of Ru(bpy)3Cl2 is simple, convenient and low-cost relative to others, so it shows promising applications in solid-state ECL detection.
Keywords: Vapor-surface sol–gel deposition; Tris(2,2′-bipyridyl)ruthenium(II); Electrochemiluminescence
Electrophoresis PDMS/glass chips with continuous on-chip derivatization and analysis of amino acids using naphthalene-2,3-dicarboxaldehyde as fluorogenic agent by O. Yassine; P. Morin; O. Dispagne; L. Renaud; L. Denoroy; P. Kleimann; K. Faure; J.-L. Rocca; N. Ouaini; R. Ferrigno (pp. 215-222).
In this work, we developed a PDMS electrophoresis device able to carry out on-chip derivatization and quantification of amino acids (AAs) using naphthalene-2,3-dicarboxaldehyde (NDA) as a fluorogenic agent. A chemical modification of the PDMS surface was found compulsory to achieve the derivatization of AAs with NDA and a limit of detection (LOD) of 40nM was reached for glycine. Finally, we suggested the applicability of this microdevice for the analysis of real biological samples such as a rat hippocampus microdialysate.
Keywords: Capillary electrophoresis microchip; Microfluidic; Laser-induced fluorescence detection; Derivatization; Amino acids
Dissimilar or orthogonal reversed-phase chromatographic systems: A comparison of selection techniques by M. Dumarey; R. Put; E. Van Gyseghem; Y. Vander Heyden (pp. 223-234).
Developing an analytical separation procedure for an unknown mixture is a challenging issue. An important example is the separation and quantification of a new drug and its impurities. One approach to start method development is the screening of the mixture on dissimilar chromatographic systems, i.e. systems with large selectivity differences. After screening, the most suited system is retained for further method development. In a step prior to such strategy dissimilar chromatographic systems need to be selected. In this paper the performance of different chemometric selection approaches, described in the literature, was visually evaluated and compared. Additionally, orthogonal projection approach (OPA) was tested as another potential selection method. All techniques, including the OPA method, were able to select (a set of) dissimilar chromatographic systems and many similarities between the selections were observed. However, the Kennard and Stone algorithm performed best in selecting the most dissimilar systems in the earliest steps of the selection procedure. The generalized pairwise correlation method (GPCM) and the auto-associative multivariate regression trees (AAMRT) were also performing well. OPA and weighted pair group method using arithmetic averages (WPGMA) are less preferable.
Keywords: Orthogonality; Dissimilarity; Orthogonal projection approach; Reversed-phase liquid chromatography; Drug impurity profiling
Determination of 4-ethylcatechol in wine by high-performance liquid chromatography–coulometric electrochemical array detection by R. Larcher; G. Nicolini; D. Bertoldi; T. Nardin (pp. 235-240).
A HPLC method using a coulometric electrode array detector (CEAD) to analyse 4-ethylcatechol in wine was established. The procedure does not require any sample preparation or analyte derivatisation and performs chromatographic separation in a short time. The assay method is linear up to 1520μgL−1 and precise (R.S.D.<3%), with limits of detection and quantitation of 1.34μgL−1 and 2.2μgL−1, respectively. Recoveries in spiked wine samples ranged from 95% to 104% with a median value of 102% and matrix effects were not observed. The method was applied to the evaluation of the concentration of 4-EC in 250 commercial Italian wines. The red wines analysed had median, 75° percentile and maximum values of 37μgL−1, 89μgL−1 and 1610μgL−1, respectively. For Sangiovese-based wines the mean ratios of 4-EP and 4-EG to 4-EC were 3.7:1 and 0.7:1, respectively. The feasibility of a cheaper fluorimetric approach to 4-EC quantification was investigated.
Keywords: Wine; 4-Ethylcatechol; Volatile phenols; Electrochemical detector; Coulometric electrode array system (CEAS)
Ultrafiltration as alternative purification procedure for the characterization of low and high molecular-mass phenolics from almond skins by Marin Prodanov; Ignacio Garrido; Visitación Vacas; Rosa Lebrón-Aguilar; Montserrat Dueñas; Carmen Gómez-Cordovés; Begoña Bartolomé (pp. 241-251).
A combination of sample preparation (ultrafiltration) and analysis techniques is proposed for the characterization of complex phenolic mixtures such as extracts from almond ( Prunus dulcis (Mill.) D.A. Webb) skins. LC/ESI-MS analysis of the permeates obtained after ultrafiltration on semipermeable membranes (low molecular-mass phenolic fractions) allowed the identification of several benzoic acids and aldehydes, flavan-3-ol monomers and oligomers, and flavonol and flavanone glycosides in almond skins. MALDI-TOF and ESI-MS/MS analysis of the diafiltered concentrates (high molecular-mass phenolic fractions) demonstrated the presence of proanthocyanidin oligomers up to decamers, composed of (epi)afzelechin, (epi)catechin and (epi)gallocatechin units linked by CC bonds (type B) and by both CC and CO bonds (type A). This analytical protocol can be of utility in the study of low and high molecular-mass phenolic compounds in natural products.
Keywords: Almond skins; Polyphenols; Ultrafiltration; Liquid chromatography/electrospray-mass spectrometry; Matrix-assisted laser desorption/ionization time-of-flight