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Analytica Chimica Acta (v.528, #1)
Development of a tyrosinase biosensor based on gold nanoparticles-modified glassy carbon electrodes by V. Carralero Sanz; M Luz Mena; A. González-Cortés; P. Yáñez-Sedeño; J.M. Pingarrón (pp. 1-8).
The preparation of a tyrosinase biosensor based on the immobilization of the enzyme onto a glassy carbon electrode modified with electrodeposited gold nanoparticles (Tyr-nAu-GCE) is reported. The enzyme immobilized by cross-linking with glutaraldehyde retains a high bioactivity on this electrode material. Under the optimized working variables (a Au electrodeposition potential of −200mV for 60s, an enzyme loading of 457U, a detection potential of −0.10V and a 0.1moll−1 phosphate buffer solution of pH 7.4 as working medium) the biosensor exhibited a rapid response to the changes in the substrate concentration for all the phenolic compounds tested: phenol, catechol, caffeic acid, chlorogenic acid, gallic acid and protocatechualdehyde. A R.S.D. of 3.6% ( n=6) was obtained from the slope values of successive calibration plots for catechol with the same Tyr-nAu-GCE with no need to apply a cleaning procedure to the biosensor. The useful lifetime of one single biosensor was of at least 18 days, and a R.S.D. of 4.8% was obtained for the slope values of catechol calibration plots obtained with five different biosensors. The kinetic constants and the analytical characteristics were calculated for all the phenolic compounds tested. The Tyr-nAu-GCE was applied for the estimation of the phenolic compounds content in red and white wines. A good correlation of the results ( r=0.990) was found when they were plotted versus those obtained by using the spectrophotometric method involving the Folin–Ciocalteau reagent.
Keywords: Gold nanocrystal-modified glassy carbon electrodes; Tyrosinase biosensors; Phenolic compounds; Wines
Amperometric screen-printed biosensor arrays with co-immobilised oxidoreductases and cholinesterases by R. Solná; E. Dock; A. Christenson; M. Winther-Nielsen; C. Carlsson; J. Emnéus; T. Ruzgas; P. Skládal (pp. 9-19).
Amperometric screen-printed biosensor arrays for detection of pesticides (organophosphates and carbamates) and phenols have been developed. Cholinesterases (AChE and BChE), tyrosinase (TYR), peroxidases (SBP, soybean and HRP, horseradish) and cellobiose dehydrogenase (CDH) were combined on the same array consisting of one Ag/AgCl reference electrode surrounded by eight radially distributed working electrodes of either carbon or platinum. Mainly cross-linking with glutaraldehyde was employed for enzyme immobilisation. The substrates for the enzymes were acetylthiocholine for cholinesterases (ChEs), cellobiose for CDH and hydrogen peroxide for peroxidases. Hydrogen peroxide was generated in the presence of glucose by co-immobilised glucose oxidase (GOx). All measurements were performed in an electrochemical steady state system specially constructed for eight channel screen-printed electrode arrays. The achieved relative standard deviation values calculated for different enzyme substrates (10 measurements) were typically below 7% and one assay was completed within less than 10min. The detection limits for pesticides and phenols were in the nanomolar and micromolar ranges, respectively. The developed biosensor array was evaluated on wastewater samples. To simplify interpretation of results, the measured data were treated with multivariate analysis–principal component analysis (PCA).
Keywords: Amperometric multienzyme sensor; Steady state system; Cholinesterase; Oxidoreductase; Phenols; Pesticides; Wastewater; Multivariate analysis
Developing a sequential injection-square wave voltammetry (SI-SWV) method for determination of atrazine using a hanging mercury drop electrode by Luciana B.O. dos Santos; Marcelo S.P. Silva; Jorge C. Masini (pp. 21-27).
This paper describes the development of a sequential injection analysis method to automate the determination of atrazine by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800μL monosegment is formed, composed by 400μL of sample and 400μL of buffer/standard solution. To obtain an efficient homogenization, the sample solution is divided in five zones intercalated by four zones of the Britton–Robinson buffer (pH 2.0) in presence of appropriate concentration of NaNO3 and varying atrazine standard concentrations. This mixture zone is isolated from the carrier solution by two 100μL air bubbles. After homogenization in an auxiliary reaction coil the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50μLs−1. After a suitable delay time, the potential is scanned from −0.5 to −1.2V versus Ag/AgCl using a frequency of 300Hz and pulse height of 25mV. The linear dynamic range is observed for atrazine concentrations between 1.16×10−7 and 2.32×10−6molL−1, obeying the linear equation ip=(−6.91±0.07)×108[atrazine]+(4±8), with r2=0.9996, for which the slope is given in nALmol−1. The detection and quantification limits of the method are 2.1×10−8 and 7.0×10−8molL−1, respectively. The sampling frequency is 37h−1, when the standard addition protocol is followed. This frequency can be increased to 42h−1 if the protocol to obtain in-line calibration curve is used for quantification. The method was applied for determination of atrazine in spiked river water samples and its accuracy was evaluated by comparison with the batch standard addition approach, which revealed that there is no evidence of statistically significant differences between the two methods.
Keywords: Sequential injection analysis; Square wave voltammetry; Atrazine; In-line standard addition; In-line sample conditioning; Water
Determination of human IgG by solid substrate room temperature phosphorescence immunoassay based on an antibody labeled with nanoparticles containing dibromofluorescein luminescent molecules by Jia-Ming Liu; Guo-Hui Zhu; Zhi-Ming Rao; Chang-Jin Wei; Long-Di Li; Cui-Lian Chen; Zhi-Ming Li (pp. 29-35).
Luminescent silicon dioxide nano-particles with size of 20nm, which containing dibromofluorescein (D) were synthesized by sol–gel method (symbolized by D–SiO2).The particles can emit intense and stable room temperature phosphorescence signal on polyamide membrane when Pb(Ac)2 was used as a heavy atom perturber. The λexmax/ λemmax was 457/622nm. Our research indicated that the specific immune reaction between goat-anti-human IgG antibody labeled with D–SiO2 and human IgG could be carried out on polyamide membrane quantitatively, and the phosphorescence intensity of the particle was enhanced after the immunoreactions. Thus a new method of solid substrate room temperature phosphorescence immunoassay (SS-RTP-IA) for the determination of human IgG was established basing on antibody labeled with the D–SiO2 nanoparticles. The linear range of this method was 0.0624–20.0pg human IgG spot−1 (corresponding concentration: 0.156–50.0ngml−1, the sample volume: 0.40μlspot−1) with a limit of detection (LD) as 0.018pgspot−1, and the regression equation of working curve was Δ Ip = 7.201mIgG (pgspot−1) + 82.57. Samples containing 0.156 and 50.0ngml−1 of IgG were measured repeatedly for 11 times and R.S.D.s were 4.1 and 3.4%, respectively. Results showed that this method had the merits as sensitive, accurate and precise.
Keywords: Luminescent nanoparticle; Solid substrate room temperature phosphorescence immunoassay; Human IgG; Dibromofluorescein
Biosensor immunoassays for the detection of bisphenol A by Gerardo R. Marchesini; Eline Meulenberg; Willem Haasnoot; Hubertus Irth (pp. 37-45).
Bisphenol A (BPA) is a xenoestrogen found in the environment, in consequence, for the biosensor detection of BPA we raised antibodies (polyclonal (PAbs) and monoclonal (MAbs)) against a structural analogue of BPA, 4,4 bis-(4-hydroxyphenyl) valeric acid (BVA). The kinetics of the MAb–BPA interaction were evaluated and the MAb providing the highest affinity was directly immobilized onto the sensor chip surface to evaluate a direct assay. Afterwards, the performance of the MAbs and the PAbs was compared in an inhibition assay using a BVA-coated chip.The highest sensitivity (limit of detection (LOD) of 0.4μgL−1) was obtained with MAb 12 in the direct assay. However, the inhibition assay was the most robust and the PAbs showed the highest sensitivity (LOD of 0.5–1μgL−1). The antibodies were specific for BVA and BPA as only minor cross-reactivities were found toward structurally related compounds or other endocrine disruptors. In the inhibition assay (with a run time of 6min), water samples spiked with BPA at different levels (0.5–50μgL−1) resulted in recoveries varying between 68% and 121%. The sensitivity of the inhibition assay could be improved 40 times (LOD of 0.03μgL−1 with the Mab 12-based assay) using solid phase extraction (SPE).
Keywords: Bisphenol A; Biosensor immunoassays; BIACORE 3000; Polyclonal antibodies; Monoclonal antibodies
Production of a monoclonal antibody and development of enzyme-linked immunosorbent assay for alkyl ethoxylates by Yasuhiro Goda; Masato Hirobe; Ayako Kobayashi; Shigeru Fujimoto; Michihiko Ike; Masanori Fujita (pp. 47-54).
A monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) has been developed for the determination of alkyl ethoxylates (AEs) that are the most widely used nonionic surfactants in the world. Three types of hapten, hemi-succinated AEs (C12EO7suc, C16EO23suc, and C18EO10suc), were synthesized and conjugated to bovine serum albumin (BSA) for mouse immunization. The mice immunized with the C12EO7suc-BSA that showed the high immune responses were used for cell fusion. The obtained monoclonal antibody (TFG2-76) was specific to AEs, which had alkyl (C) and ethoxy (EO) chain lengths of C10-12 and EO5-15, respectively. Two types of solid support, namely, a polystyrene tube and a 96-well microplate, were used for antibody immobilization. The working ranges of the tube-type and plate-type ELISAs were 2–100 and 20–1000μg/L with IC50 values of 12 and 71μg/L AE (C12EO7), respectively. Moreover, the lowest quantification limit of plate-type ELISA could be lowered to 5μg/L by decreasing the coated antibody concentration. Cross-reactivities with non-AE surfactants were determined, and the assay proved highly selective for AEs. The application of plate-type ELISA to determine spiked AEs in distilled water, tap water and river water provided good recoveries without matrix effects.
Keywords: ELISA; Alkyl ethoxylates; Nonionic surfactants; Monoclonal antibody; Analysis; Environment
Artificial neural network for simultaneous determination of two components of compound paracetamol and diphenhydramine hydrochloride powder on NIR spectroscopy by Ying Dou; Ying Sun; Yuqiu Ren; Yulin Ren (pp. 55-61).
Diffuse reflectance near-infrared (NIR) spectroscopy is a technique widely used for rapid and non-destructive analysis of solid samples. A method for simultaneous analysis of the two components of compound paracetamol and diphenhydramine hydrochloride powdered drug has been developed by using artificial neural network (ANN) on near-infrared (NIR) spectroscopy. An ANN containing three layers of nodes was trained. Various ANN models based on pretreated spectra (first-derivative, second-derivative and standard normal variate; SNV) were tested and compared, respectively. In the models the concentration of paracetamol and caffeine as active principles of compound paracetamol and diphenhydramine hydrochloride powder was determined simultaneously. Partial least squares regression (PLS) multivariate calibrations were also used, which were compared with ANN. The best model was obtained at first-derivative spectra. We have also discussed the parameters that affected the networks and predicted the test set (unknown) specimens. The degree of approximation, a new evaluation criteria of the network were employed, which proved the accuracy of the predicted results.
Keywords: Artificial neural networks; NIR spectroscopy; Degree of approximation; Compound paracetamol and diphenhydramine hydrochloride powder
Simplex optimization and kinetic determination of nabumetone in pharmaceutical preparations by micellar—stabilized room temperature phosphorescence by J.A. Murillo Pulgarín; A. Alañón Molina; M.T. Alañón Pardo (pp. 77-82).
The present method described the kinetic determination of nabumetone, a non-steroidal anti-inflammatory drug, by means of micellar-stabilized room temperature phosphorescence (MS-RTP), using the stopped-flow mixing technique. This methodology enables us to determine analytes in complex matrices without the need for a tedious separation process, as well as greatly diminishes the time for the analysis.Firstly, chemical and instrumental variables affecting the rate of phosphorescent development and the intensity of the signal, were found using a simplex optimization procedure. As application, nabumetone was determined in commercial Spanish pharmaceutical preparations.With the proposed method, the maximum signal of phosphorescence appears in only 10s once the sample has been prepared, and the maximum slope of the kinetic curve, corresponding with the maximum rate of the phosphorescence development, was measured at λex=271nm and λem=520nm. The overall least-squares regression to find the straight line that fitted the experimental data, the detection limit, the repeatability and the standard deviation for replicate sample, were also determined.The proposed method was validated versus a HPLC method with satisfactoty results.
Keywords: Nabumetone; Room temperature phosphorescence; Simplex; Stopped-flow; Kinetics
Optimization of preconcentration and isolation for the determination of 15 phenols by supercritical-fluid extraction and gas chromatography with metallomesogenic stationary phase by Jian-Lian Chen; Chuen-Ying Liu (pp. 83-88).
Based on the merits of well-established capillary gas chromatography (GC), metallomesogenic polymer was used as the stationary phase and flame ionization detector (FID) was used as the detector, the analysis of phenolic compounds explored the possibility of application in complex matrices. We proposed the method combined supercritical-fluid extraction (SFE) of phenolic compounds, which had been enriched on the solid supports of XAD-4 resins, and then with their determinations by capillary GC-FID. The SFE parameters suitable for 15 phenols simultaneously adsorbed onto XAD-4 resins in aqueous solution were assessed by a 45 factorial design method. The best results were 5min static time, 10min dynamic time, 0.25ml methanol spiked, 80°C oven temperature and 410 atm CO2 pressure. Also, other parametric conditions for specific phenols were revealed and analyzed. In the comparison with Soxhlet extraction with regard to the recoveries and reproducibility, the developed SFE was quite superior and helped to reduce the detection limit of aqueous samples to 10−2-fold. Eventually, the polluted soils near a pharmaceutical factory were primarily tested and given the probable distribution.
Keywords: Phenols; XAD-4; SFE; Factorial design; Metallomesogen; Capillary; GC; Soil
Determination of the antifouling booster biocides irgarol 1051 and diuron and their metabolites in seawater by high performance liquid chromatography–diode array detector by Georgia Gatidou; Anna Kotrikla; Nikolaos S. Thomaidis; Themistokles D. Lekkas (pp. 89-99).
A method for the simultaneous determination of two antifouling booster biocides, diuron (1-(3,4 dichlorophenyl) 3,3 dimethyl urea) and irgarol 1051 (2-methylthio-4- tert-butylamino-6-cyclopropylamino- s-triazine), and their metabolites, DCPMU (1-(3,4 dichlorophenyl)-3 methyl urea), DCPU (1-(3,4 dichlorophenyl) urea), DCA (3,4 dichloroaniline) and M1 (2-methylthio-4- tert-butylamino- s-triazine) in seawater by high performance liquid chromatography–diode array detector (HPLC–DAD) was developed. The optimization of the extraction procedure included the type of sorbent and the type of the organic solvent for the elution. Optimization of the liquid chromatography (LC) separation was also performed and the robustness of the developed separation was tested, in respect to the effect of three factors (column temperature, flow rate and initial strength of acetonitrile) on the retention times, peak resolution and peak area of the six compounds. The optimized procedure included off-line extraction of these compounds from seawater samples using C18 solid phase extraction (SPE) cartridges. The inter-day precision of the developed procedure was less than 14% (as R.S.D.s) for all the tested compounds. Satisfactory recoveries (higher than 82%) were obtained for all substances, except for DCA, for which low recovery was obtained (30.5%). The limits of detection (LODs) of the substances varied between 0.005 (DCPMU) and 0.026 (M1) μgL−1.
Keywords: Irgarol 1051; Diuron; Degradation products; Antifouling paints; Seawater; Robustness
Detection ofd-serine in neural samples by saccharide enhanced chiral capillary electrophoresis by Zhe Quan; Yaru Song; Yangzheng Feng; Michael H. LeBlanc; Yi-Ming Liu (pp. 101-106).
Highly fluorescent enantiomeric derivatives ofd/l-serine from naphthalene-2,3-dicarboxaldehyde were resolved by hydroxypropyl-γ-cyclodextrin modified capillary electrophoresis using a saccharide as an enhancing chiral selector. Four saccharides, i.e.d-(+)-glucose,d-(−)-fructose, β-lactose, and sucrose were tested. Similar enhancing effects were observed. Coupled with laser induced fluorescence detection, this separation was applied to the determination ofd-serine in neural samples including rat brain tissues, Aplysia ganglia, microdialysates from rat brain, and Aplysia individual neurons. High levels ofd-serine were found in certain rat brain sections including hippocampus and striatum.d-Serine was also found to occur in Aplysia ganglia, but interestingly, it was not detected in single neurons isolated from Aplysia ganglia.
Keywords: d; -Serine; Capillary electrophoresis; Enantiomeric separation; Rat brain tissue; Microdialysates; Aplysia; ganglia
A critical examination of the use of the Freundlich isotherm in characterizing molecularly imprinted polymers (MIPs) by Gregory T. Rushton; Chelsey L. Karns; Ken D. Shimizu (pp. 107-113).
The Freundlich isotherm (FI) has previously been shown to be useful in modeling the binding properties of non-covalent molecularly imprinted polymers (MIPs). The advantage of the FI is that it is a heterogeneous binding model that can accommodate and measure the heterogeneity inherent in MIPs. However, it is often difficult to verify whether the FI is an appropriate binding model for a particular MIP because only a narrow portion of the binding isotherm is experimentally measurable. This study takes a critical examination of whether the FI is an appropriate binding model for MIPs and explores its limitations in characterizing a (+)-cinchonine (CN) imprinted polymer and a non-imprinted polymer (NIP). A wider portion of the binding isotherm can be examined by systematically measuring a series of isotherms at different polymer concentrations. This strategy verified that FI can yield an accurate measure of the heterogeneity in the cinchonine MIP and the NIP. However, in cases of extremely high polymer loading, saturation behavior was observed, and the FI yielded inaccurate measures of the binding properties even though the experimental isotherm appears to be well modeled by the FI. Further, these studies indicate that the FI accurately predicts the heterogeneity index for more homogeneous compared to heterogeneous polymers over a wider concentration range but is subject to considerable error as saturation conditions are approached. These studies demonstrate the importance of correctly applying the FI to the lowest concentration portion of the binding isotherm that is experimentally measurable.
Keywords: Molecular imprinting; Freundlich isotherm; Polymers; Cinchonine; Analytical methods; Adsorption isotherms
Determination of bromide ions in seawater using flow system with chemiluminescence detection by Eduardo P. Borges; André F. Lavorante; Boaventura Freire dos Reis (pp. 115-119).
A simple flow-based procedure with chemiluminescence (CL) detection is proposed for bromide ion determination in seawater. The procedure was based on the oxidation of bromide to bromine by chloramine-T followed by the reaction of bromine with luminol resulting in CL emission. Since no significant reaction within chloramine-T and luminol was observed, the detection was carried out without bromine extraction from the oxidant medium. The proposed flow system had a sampling rate of 40 determinations per hour, reagents consumption of 100μg luminol and 60μg chloramine-T per determination, a limit of detection of 0.5mgl−1 bromide ions, a linear concentration range ( r = 0.999 and n = 7) between 0 and 100mgl−1, and a coefficient of variance better than 2.5% (for 10 measurements of a 10mgl−1 Br− solution) were achieved. The analytical system was applied for the determination of bromide in seawater and estuarine-water samples, obtaining an analyte recovery ranging from 94 to 102% and comparing the results with a reference spectrophotometric method no significant difference was observed in 95% confidence level.
Keywords: Flow analysis; Chemiluminescence; Bromide; Seawater; Estuarine-water; Chloramine-T
Determination of cosmochemically volatile trace elements in chondritic meteorites by inductively coupled plasma mass spectrometry by Stephen F. Wolf; Derick L. Unger; Jon M. Friedrich (pp. 121-128).
We have developed a method for the quantification of 14 cosmochemically moderately volatile to highly volatile trace elements (Cu, Zn, Ga, Se, Rb, Ag, Cd, In, Sn, Sb, Te, Cs, Tl, and Bi) in chondritic meteorites by ICPMS. The method utilizes internal standardization via addition of Be, Rh, Re, and U and multiple single point matrix-matched external calibrations with Allende standard reference meteorite to provide drift corrected calibration within an ICPMS procedure. We have demonstrated our method's precision and accuracy by performing replicate dissolutions and analyses of 0.05–0.10g samples of a homogenized sample of the CM2 Murchison meteorite and compared our results to literature values for this meteorite. Our procedure allows for a rapid and accurate determination of the cosmochemically important VTEs in chondritic meteorites providing the means for an even more comprehensive elemental analysis of a single sample of chondritic material.
Keywords: Trace elements; Chondritic meteorites; Plasma mass spectrometry
Use of spectroscopic techniques for the chemical analysis of biomorphic silicon carbide ceramics by J.M. Cano Pavón; E. Vereda Alonso; M.T. Siles Cordero; A. García de Torres; J.M. López-Cepero (pp. 129-134).
Biomorphic silicon carbide ceramics are a new class of materials prepared by several complex processing steps including pre-processing (shaping, drying, high-temperature pyrolysis in an inert atmosphere) and reaction with liquid silicon to obtain silicon-carbide. The results of industrial process of synthesis (measured by the SiC content) must be evaluated by means of fast analytical methods. In the present work, diverse samples of biomorphic ceramics derived from wood are studied for to evaluate the capability of the different analytical techniques (XPS, LIBS, FT-IR and also atomic spectroscopy applied to previously dissolved samples) for the analysis of these materials. XPS and LIBS gives information about the major components, whereas XPS and FT-IR can be used to evaluate the content of SiC. On the other hand, .the use of atomic techniques (as ICP–MS and ETA–AAS) is more adequate for the analysis of metal ions, specially at trace level. The properties of ceramics depend decisively of the content of chemical elements. Major components found were C, Si, Al, S, B and Na in all cases. Previous dissolution of the samples was optimised by acid attack in an oven under microwave irradiation.
Keywords: Spectroscopy; Silicon carbide; Ceramics; Biomorphic materials; Metal ions