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Analytica Chimica Acta (v.596, #2)
Analytical applications of glassy carbon electrodes modified with multi-wall carbon nanotubes dispersed in polyethylenimine as detectors in flow systems by Alberto Sánchez Arribas; Esperanza Bermejo; Manuel Chicharro; Antonio Zapardiel; Guillermina L. Luque; Nancy F. Ferreyra; Gustavo A. Rivas (pp. 183-194).
This work reports the advantages of using glassy carbon electrodes (GCEs) modified with multi-wall carbon nanotubes (CNT) dispersed in polyethylenimine (PEI) as detectors in flow injection and capillary electrophoresis. The presence of the dispersion of CNT in PEI at the electrode surface allows the highly sensitive and reproducible determination of hydrogen peroxide, different neurotransmitters (dopamine (D) and its metabolite dopac, epinephrine (E), norepinephrine (NE)), phenolic compounds (phenol (P), 3-chlorophenol (3-CP) and 2,3-dichlorophenol (2,3CP)) and herbicides (amitrol). Sensitivities enhancements of 150 and 140 folds compared to GCE were observed for hydrogen peroxide and amitrol, respectively. One of the most remarkable properties of the resulting electrode is the antifouling effect of the CNT/PEI layer. No passivation was observed either for successive additions (30) or continuous flow (for 30min) of the compounds under investigation, even dopac or phenol. A critical comparison of the amperometric and voltammetric signal of these different analytes at bare- and PEI-modified glassy carbon electrodes and pyrolytic graphite electrodes is also included, demonstrating that the superior performance of CNT is mainly due to their unique electrochemical properties. Glassy carbon electrodes modified with CNT–PEI dispersion also show an excellent performance as amperometric detector in the electrophoretic separation of phenolic compounds and neurotransmitters making possible highly sensitive and reproducible determinations.
Keywords: Carbon nanotubes; Polyethylenimine; Glassy carbon; Neurotransmitters; Phenolic compounds; Herbicides; Catecholamines; Flow injection; Capillary electrophoresis
Absorbance characterization of microsphere-based ion-selective optodes by Nan Ye; Katarzyna Wygladacz; Eric Bakker (pp. 195-200).
Ionophore-based microsphere sensors are characterized here in transmission mode. These sensors contain a lipophilic ionophore for the analyte cation, a chromoionophore for recognizing H+, and a lipophilic cation-exchanger. They function on the basis of an ion-exchange equilibration step where an increased concentration of analyte ion leads to increased level of extraction into the bulk of the microsphere, expelling protons in return and deprotonating the chromoionophore. Since the path length is variable across the microsphere, such bead-based sensors are normally characterized in fluorescence mode. In this paper, the response of the sensing microspheres is calculated from the ratio of transmitted light intensities at the absorbance peak maxima of the protonated and unprotonated forms of the chromoionophore. At a fixed position of the particle, the resulting responses are found to be independent of light scattering, incident light intensity and the shape or size of the microsphere. The responses of potassium-selective microspheres obtained by this method agree quantitatively with corresponding fluorescence-based data.
Keywords: Absorbance; Microsphere; Fluorescence; Ion-selective optical sensor; Chromoionophore
Polymeric membrane electrodes with improved fluoride selectivity and lifetime based on Zr(IV)- and Al(III)-tetraphenylporphyrin derivatives by Mariusz Pietrzak; Mark E. Meyerhoff; Elżbieta Malinowska (pp. 201-209).
Novel aluminum(III)- and zirconium(IV)-tetraphenylporhyrin (TPP) derivatives are examined as fluoride-selective ionophores for preparing polymer membrane-based ion-selective electrodes (ISEs). The influence of t-butyl- or dichloro-phenyl ring substituents as well as the nature of the metal ion center (Al(III) versus Zr(IV)) on the anion complexation constants of TPP derivative ionophores are reported. The anion binding stability constants of the ionophores are characterized by the so-called “sandwich membrane” method. All of the metalloporphyrins examined form their strongest anion complexes with fluoride. The influence of plasticizer as well as the type of lipophilic ionic site additive and their amounts in the sensing membrane are discussed. It is shown that membrane electrodes formulated with the metalloporphyrin derivatives and appropriate anionic or cationic additives exhibit enhanced potentiometric response toward fluoride over all other anions tested. Since selectivity toward fluoride is enhanced in the presence of both anionic and cationic additives, the metalloporphyrins can function as either charged or neutral carriers within the organic membrane phase. In contrast to previously reported fluoride-selective polymeric membrane electrodes based on metalloporphyrins, nernstian or near-nernstian (−51.2 to −60.1mVdecade−1) as well as rapid ( t<80s) and fully reversible potentiometric fluoride responses are observed. Moreover, use of aluminum(III)- t-butyltetraphenylporphyrin as the ionophore provides fluoride sensors with prolonged (7 months) functional lifetime.
Keywords: Al(III)-porphyrins; Zr(IV)-porphyrins; Fluoride-selective electrodes; Ion–ionophore stability constants
Amperometric biosensing of carbamate and organophosphate pesticides utilizing screen-printed tyrosinase-modified electrodes by Yaico D. Tanimoto de Albuquerque; Lucas Franco Ferreira (pp. 210-221).
A tyrosinase (Tyr) screen-printed biosensor based on the electroreduction of enzymatically generated quinoid products was electrochemically characterized and optimized for determination of carbamates and organophosphorus pesticides. A composite electrode prepared by screen-printing a cobalt (II) phthalocyanine (CoPc) modified cellulose–graphite composite on a polycarbonate support was employed as electrochemical transducer. The Tyr biosensor was prepared by immobilization of enzyme on the composite electrode surface by cross-linking with glutaraldehyde and bovine serum albumin. Parameters affecting the biosensor response such as response time, enzyme loading, concentration and pH of the buffer solution were optimized utilizing catechol as substrate. The maximum response for o-quinone enzymatically generated was obtained after 2min of reaction. A good reproducibility and high operational stability were found for Tyr biosensor (60units) at 50mM phosphate buffer, pH 6.50. Under these conditions, the useful lifetime of biosensor was 10days. After 15days, the biosensor could be used with 20% of the initial value. Inhibition studies on the o-quinone steady-state current (at −0.20V versus Ag/AgCl) were performed to investigate the inhibition kinetics of the pesticides in the enzymatic activity of mushroom tyrosinase. The results shown that the methyl parathion and carbofuran can lead to competitive inhibition process of the enzyme, while diazinon and carbaryl act as mixed inhibitors. Linear relationships were found for methyl parathion (6–100ppb), diazinon (19–50ppb), carbofuran (5–90ppb) and carbaryl (10–50ppb). Analysis of natural river water samples spiked with 30ppb of each pesticide showed recoveries between 92.50% and 98.50% and relative standard deviations of 2%.
Keywords: Amperometric biosensor; Tyrosinase electrode; Enzyme inhibitors; Pesticides
Electrodeposition of gold nanoclusters on overoxidized polypyrrole film modified glassy carbon electrode and its application for the simultaneous determination of epinephrine and uric acid under coexistence of ascorbic acid by Jing Li; Xiang-Qin Lin (pp. 222-230).
A novel biosensor was fabricated by electrochemical deposition of gold nanoclusters on ultrathin overoxidized polypyrrole (PPyox) film, formed a nano-Au/PPyox composite on glassy carbon electrode (nano-Au/PPyox/GCE). The properties of the nanocomposite have been characterized by field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and electrochemical investigations. The nano-Au/PPyox/GCE had strongly catalytic activity toward the oxidation of epinephrine (EP), uric acid (UA) and ascorbic acid (AA), and resolved the overlapping voltammetric response of EP, UA and AA into three well-defined peaks with a large anodic peak difference. The catalytic peak currents obtained from differential pulse voltammetry increased linearly with increasing EP and UA concentrations in the range of 3.0×10−7 to 2.1×10−5M and 5.0×10−8 to 2.8×10−5M with a detection limit of 3.0×10−8 and 1.2×10−8M ( s/n=3), respectively. The results showed that the modified electrode can selectively determine EP and UA in the coexistence of a large amount of AA. In addition, the sensor exhibited excellent sensitivity, selectivity and stability. The nano-Au/PPyox/GCE has been applied to determination of EP in epinephrine hydrochloride injection and UA in urine samples with satisfactory results.
Keywords: Overoxidized polypyrrole; Gold nanoclusters; Electrochemical deposition; Epinephrine; Uric acid
Electrochemical and spectroscopic characterisation of amphetamine-like drugs: Application to the screening of 3,4-methylenedioxymethamphetamine (MDMA) and its synthetic precursors by Nuno Milhazes; Pedro Martins; Eugenio Uriarte; Jorge Garrido; Rita Calheiros; M. Paula M. Marques; Fernanda Borges (pp. 231-241).
A complete physicochemical characterisation of MDMA and its synthetic precursors MDA, 3,4-methylenedioxybenzaldehyde (piperonal) and 3,4-methylenedioxy-β-methyl-β-nitrostyrene was carried out through voltammetric assays and Raman spectroscopy combined with theoretical (DFT) calculations. The former provided important analytical redox data, concluding that the oxidative mechanism of the N-demethylation of MDMA involves the removal of an electron from the amino-nitrogen atom, leading to the formation of a primary amine and an aldehyde. The vibrational spectroscopic experiments enable to afford a rapid and reliable detection of this type of compounds, since they yield characteristic spectral patterns that lead to an unequivocal identification.Moreover, the rational synthesis of the drug of abuse 3,4-methylenedioxymethamphetamine (MDMA or “ecstasy”) from one of its most relevant precursors 3,4-methylene-dioxyamphetamine (MDA), is reported. In addition, several approaches for the N-methylation of MDA, a limiting synthetic step, were attempted and the overall yields compared.
Keywords: 3,4-Methylenedioxymethamphetamine; Synthesis; Raman spectroscopy; Voltammetry; Density functional theory calculations
High-performance liquid chromatographic/ion-trap mass spectrometric speciation of aquatic mercury as its pyrrolidinedithiocarbamate complexes by Pavlína Houserová; David Matějíček; Vlastimil Kubáň (pp. 242-250).
Mercury-pyrrolidinedithiocarbamate complexes are first time used for speciation of aquatic mercury with high-performance liquid chromatographic/ion trap-mass spectrometric method utilizing atmospheric pressure chemical ionization (APCI). The separation of the four mercury species was achieved in less than 5min with a linear gradient profile of aqueous methanol from 70 up to 100% (v/v) in 4thmin, isocratic elution at 100% up to 5thmin and followed by a negative gradient to 70% in 6thmin. The best separation was achieved on a reverse phase Zorbax Eclipse XDB C18 column (50mm×2.1mm i.d., 1.8μm particle size). The on-column limits of detection (injection volume 1μL) were 370pg for methylmercury (MeHg+), 280pg for ethylmercury (EtHg+), 250pg for phenylmercury (PhHg+) and 90pg for inorganic mercury (Hg2+) when the data were collected in selective ion monitoring (SIM) mode. A method of isolation and preconcentration of the mercury species using a “home-made” C18 solid phase extraction (SPE) microcolumns was developed to enhance sensitivity of the method. The preconcentration factor as much as 2500 was achieved with on-column complex formation of mercury-pyrrolidinedithiocarbamate. Methanol (100%) was chosen for elution of preconcentrated mercury species. The method was applied for the determination of mercury species in river water samples.
Keywords: Liquid chromatography; Ion trap-mass spectrometry; Electrospray ionization; Atmospheric pressure chemical ionization; Methylmercury; Ethylmercury; Phenylmercury; Ammonium pyrrolidinedithiocarbamate; Mercury-pyrrolidinedithiocarbamate; Solid phase extraction
Selenium transformation studies during Broccoli ( Brassica oleracea) growing process by liquid chromatography–inductively coupled plasma mass spectrometry (LC–ICP-MS) by Zoyne Pedrero; Daniel Elvira; Carmen Cámara; Yolanda Madrid (pp. 251-256).
Selenium uptake and transformation was studied in Se-enriched Broccoli ( Brassica olearacea). Plants were grown in hydroponic culture and exposed during 40 days to Na2SeO3 (1mgL−1). After growing, the plants were harvested and their different parts (roots, stems and fruit) were analyzed by ICP-MS or LC–ICP-MS.Se-species were identified and quantified after enzymatic extraction by using both an anion exchange (PRP-X100), and a size exclusion/ion exchange (Shodex Asahipak) chromatographic columns. Selenium translocation and transformation Se species in plants was studied through the Se-speciation in root, stem and fruit. After 40 days of exposure, selenomethionine was the major species found in roots, however, Se-methylselenocysteine was the main species found in the fruit, suggesting Broccoli as a source of this important selenoamino acid in human diet. However, the degree of meal processing influences the stability of Se-aminoacids. Speciation studies in boiled Broccoli and in the extraction water were also carried out. This experiment revealed a noticeable degradation of Se-methylselenocysteine in the boiled Broccoli fruit.Proteins soluble in Tris–HCl were analyzed by two-dimensional chromatography coupled to ICP-MS.The results obtained contribute not only to a deeper understanding of Se accumulation mechanisms by plants but also to further functional food complements preparation and the effect of food processing on species stability.
Keywords: Selenomethionine; Selenomethylselenocysteine; Plants; Broccoli; Liquid chromatography–inductively coupled plasma mass spectrometry
Determination of quinolone residues in shrimp using liquid chromatography with fluorescence detection and residue confirmation by mass spectrometry by Christine M. Karbiwnyk; Lori E. Carr; Sherri B. Turnipseed; Wendy C. Andersen; Keith E. Miller (pp. 257-263).
The quinolones, oxolinic acid (OXO), flumequine (FLU), and nalidixic acid (NAL), are antibacterial drugs effective against Gram-negative bacteria. Quinolones are used in both human and veterinary medicine, but are currently not approved by the U.S. Food and Drug Administration for use in food fish. A liquid chromatography-fluorescence (LC-FL) method was developed to determine OXO, FLU, and NAL residues in shrimp. An additional liquid chromatography–mass spectrometry (LC–MS n) method was created to confirm these residues using the same sample extract. Samples were prepared with a simple ethyl acetate extraction followed by solvent exchange into 0.2% formic acid and cleaned-up with hexane. Reverse phase chromatography was used to separate the three compounds in both procedures. For the LC-FL determinative method, fluorescence emission was monitored at 369nm with excitation at 327nm. With electrospray ionization, the three most abundant ions from the MS3 product ion spectrum were used to identify OXO, FLU, and NAL in the confirmation procedure. Shrimp samples fortified at levels ranging from 7.5 to 100ngg−1 were used to validate both methods.
Keywords: Quinolones; Residue analysis; Shrimp; Fluorescence; Mass spectrometry; Confirmation
Simultaneous determination of main phytoecdysones and triterpenoids in Radix Achyranthis Bidentatae by high-performance liquid chromatography with diode array-evaporative light scattering detectors and mass spectrometry by Juan Li; Hui Qi; Lian-Wen Qi; Ling Yi; Ping Li (pp. 264-272).
A liquid chromatographic method was developed for simultaneous determination of two main types of bioactive compounds: four phytoecdysones and eight triterpenoids in Radix Achyranthis Bidentatae (RAB), i.e., polypodine B (1), ecdysterone (2), 25- R inokosterone (3), 25- S inokosterone (4), ginsenoside Ro (5), chikusetsusaponin IVa (6), zingibroside R1 (7), chikusetsusaponin IVa ethyl ester (8), 28-deglucosyl-chikusetsusaponin IVa (9), PJS-1 (10), 28-deglucosyl-chikusetsusaponin IVa butyl ester (11), and oleanolic acid (12). Optimum separations were obtained with a Zorbax C18 column, using a gradient elution with 0.08% aqueous formic acid (containing 5% isopropyl alcohol) and acetonitrile as mobile phase. Phytoecdysones were detected by diode array detector (DAD) at 242nm, whereas triterpenoids were monitored by evaporative light scattering detector (ELSD) connected in series with DAD, temperature for the drift tube was 110°C and the nitrogen flow rate was 3.2Lmin−1. The identity of the analytes was confirmed using retention times, ultraviolet absorbance and mass spectral data in comparison with reference compounds. The method was validated for acceptable precision (intra- and inter-day variation ≤ 4.87%), accuracy (recovery≥88.9%) and sensitivity (LOD≤0.43μgmL−1 (DAD) and 26.0μgmL−1 (ELSD), LOQ≤0.97μgmL−1 (DAD) and 46.5μgmL−1 (ELSD), respectively). This rapid and reliable method was applied for the analysis of four cultivated and ten commercial samples. The results demonstrated that the method is suitable for routine analysis and quality control of RAB.
Keywords: Radix Achyranthis Bidentatae; Quality evaluation; High-performance liquid chromatography; Diode array detector; Evaporative light scattering detector; Mass spectrometry
Determination of four major saponins in the seeds of Aesculus chinensis Bunge using accelerated solvent extraction followed by high-performance liquid chromatography and electrospray-time of flight mass spectrometry by Junhui Chen; Wenlong Li; Baijuan Yang; Xiuchun Guo; Frank Sen-Chun Lee; Xiaoru Wang (pp. 273-280).
A new method based on accelerated solvent extraction (ASE) followed by a reliable high-performance liquid chromatography-diode array detector (HPLC-DAD) and positive ion electrospray-time of flight mass spectrometry (ESI-TOF/MS) analysis has been developed for the characterization and quantification of four major saponins in extracts of the seeds of Aesculus chinensis Bunge (Semen Aesculi). The saponins escin Ia, escin Ib, isoescin Ia and isoescin Ib were extracted from seeds of A. chinesis Bunge via ASE, and the operational parameters of ASE were optimized, such as extraction solvent, extraction temperature, static extraction time and extraction cycles. The optimized procedure employed 70% MeOH as extraction solvent, 120°C of extraction temperature, 7min of static extraction time, 60% flush volume and the extraction recoveries of the four compounds were nearly to 100% for two cycles. The HPLC conditions are as follows: SinoChrom ODS BP C18 (4.6mm×200mm, 5μm) column, acetonitrile and 0.10% phosphoric acid solution as mobile phase, flow rate is 1.0mLmin−1, detection length of UV is 203nm, injection volume is 10μL. The results indicated that the developed HPLC method is simple, sensitive and reliable for the determination of four major saponins in seeds of A. chinesis Bunge with a good linearity ( r2>0.9994), precision (relative standard deviation (R.S.D.) <1.5%) and the recovery ranges of 95.2–97.3%. The limits of detection (LOD) of the four compounds were in the range of 0.40–0.75μgmL−1. This assay can be readily utilized as a quality control method for Semen Aesculi and other related medicinal plants.
Keywords: Semen Aesculi; Saponins; Accelerated solvent extraction; High-performance liquid chromatography; Electrospray-time of flight mass spectrometry
Determination of trace amounts of nitrogen in uranium based samples by ion chromatography (IC) without Kjeldahl distillation by Poonam Verma; Ramakant K. Rastogi; Karanam L. Ramakumar (pp. 281-284).
A simple, sensitive and fast ion chromatographic (IC) method with suppressed conductivity detection is described for the determination of traces of nitrogen in uranium based fuel materials. Initially a method was developed to determine nitrogen as NH4+ using cation exchange column after matrix separation by Kjeldahl distillation. The method was then improved by eliminating this distillation. Matrix separation after sample dissolution was done by hydrolyzing and filtering off the polyvalent cations. This had helped in reducing both the sample size and analysis time. Optimization of dissolution conditions for various kinds of uranium based samples was done to keep acid content minimum; a prerequisite chromatographic condition. The calibration plot for nitrogen was linear in the concentration range of 0.02–1mgL−1 with regression coefficient of 0.9999. The relative standard deviation (R.S.D.) obtained in this method (100μL injected) was 3% and 2% in 9 replicates at nitrogen level of 28 and 55ngg−1, respectively. Detection limit based on S/N=3 (100μL injected) as well as three times of variation in blank value was 4ngg−1. The developed method was authenticated by comparison with certified uranium-alloy standard as well as with independent indophenol photometry method. The developed method was applied to uranium-alloy, uranium-metal, sintered UO2 pellets and sintered UO2 microspheres samples.
Keywords: Nitrogen determination; Uranium based nuclear samples; Ion chromatography; Kjeldahl elimination
Determination of 16 polycyclic aromatic hydrocarbons in milk and related products using solid-phase microextraction coupled to gas chromatography–mass spectrometry by Nerea Aguinaga; Natalia Campillo; Pilar Viñas; Manuel Hernández-Córdoba (pp. 285-290).
A method for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in milk and related products based on direct immersion-solid phase microextraction (DI-SPME) followed by gas chromatography–mass spectrometry detection (GC–MS) has been developed. The influence of various parameters on PAH extraction efficiency was carefully monitored. Good performance (recovery, precision and quantitation limits) was attained when a PDMS/DVB fiber was immersed in the sample for 60min at 55°C. Detection limits ranged from 0.003 to 1.5μgL−1 at a signal-to-noise ratio of 3, depending on the compound and the sample. The proposed method was successfully applied to infant formulas, milk and related products and the presence of both fluoranthene and pyrene in two samples was confirmed.
Keywords: Solid-phase microextraction; Gas chromatography; Mass spectrometry; Polycyclic aromatic hydrocarbons; Milk
Gas chromatography–mass spectrometry determination of 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate in wine by Bruno Fedrizzi; Giuseppe Versini; Irma Lavagnini; Giorgio Nicolini; Franco Magno (pp. 291-297).
A gas chromatography–mass spectrometry method was established using headspace solid phase microextraction (HS-SPME) as the sampling procedure to analyse 3-mercaptohexan-1-ol (3-MH) and 3-mercaptohexyl acetate (3-MHA), two molecules with a tropical fruit aroma, in wine at trace level. This method offers important advantages, as it neither requires time-consuming sample preparation nor uses dangerous organic compounds, thus making control of wine aroma easier and suitable for routine analysis. As a comparison, a solid phase extraction (SPE) method, already described elsewhere for aroma analysis, was applied to quantify these analytes, extending this exhaustive enrichment to two important thiols. Detection limits for both the approaches were close to the sensory threshold value, resulting lower for the HS-SPME procedure and suitable for requirements in the oenological field. The application of the two proposed methods to 52 wines of different varieties gave similar results.
Keywords: Sulphur compounds; Head space solid phase microextraction/gas chromatography–mass spectrometry; Solid phase extraction; Wine; Aroma
Determination of protein by hydroxypropyl-β-cyclodextrin sensitized fluorescence quenching method with erythrosine sodium as a fluorescence probe by Xiashi Zhu; Jing Sun; Yanyan Hu (pp. 298-302).
The fluorescence spectral behavior of interaction of erythrosine sodium (ES) and bovine serum albumin (BSA) was investigated in hydroxypropyl-β-cyclodextrin (HP-β-CD) medium at pH 5.8. The excitation and emission wavelengths were 527nm and 549nm, respectively. The fluorescence intensity of ES increased due to the formed inclusion complex of HP-β-CD and ES. But the fluorescence intensity of ES–HP-β-CD diminished when BSA was added, and there was a linear relationship between the fluorescence quenching value of the system (Δ F= FES–HP-β-CD− FBSA–ES–HP-β-CD) and the concentration of BSA. Based on this, a novel fluorescence quenching method for the determination of protein with ES as a fluorescence probe has been developed. Under the optimal conditions, the linear range of calibration curve for the determination of BSA was 0.5–32.0μgmL−1, and the detection limit was 49.2ngmL−1. It has been applied to the determination of serum in serum samples with satisfactory results.
Keywords: Protein; Hydroxypropyl-β-cyclodextrin; Erythrosine sodium; Fluorescence probe
Hapten heterology for a specific and sensitive indirect enzyme-linked immunosorbent assay for organophosphorus insecticide fenthion by Qi Zhang; Laibao Wang; Ki Chang Ahn; Qin Sun; Baishi Hu; Jie Wang; Fengquan Liu (pp. 303-311).
Five haptens with different spacer-arm attachment sites on the structure of the organophosphorus insecticide fenthion were designed and synthesized. All of the haptens were conjugated with ovalbumin (OVA) for the coating antigen, and three haptens containing all or most of the structure of fenthion were conjugated with bovine serum albumin (BSA) for the immunogen. Six polyclonal antisera were raised against the three BSA conjugates, and 30 antibody/coating conjugate combinations were selected for studies of assay sensitivity and specificity for fenthion. The study revealed the best combination with high sensitivity ( I50 of 0.08ngmL−1) and high assay specificity, which indicated that when structural difference between the analyte and an immunizing hapten is less than that between a coating hapten and the immunizing hapten, a high sensitive enzyme-linked immunosorbent assay (ELISA) in the heterologous system may stand a good chance to be developed. The immunity results showed that heterology in the hapten spacer-arm attachment site of the immunogen could achieve a remarkable improvement in the quantity, sensitivity, and/or specificity of antibody, and that the moiety of an analyte, which is the same as the moiety near/on the immunizing spacer-arm hapten attachment site, contributes greatly to the interaction of antibody and hapten.
Keywords: Abbreviations; NHS; N; -hydroxysuccinimide; DCC; N; ,; N; -dicyclohexylcarbodiimide; BSA; bovine serum albumin; OVA; ovalbumin; CR; cross-reactivity; ELISA; enzyme-linked immunosorbent assay; TMB; tetramethylbenzidine; GAM-HRP; peroxidase-labeled goat anti-mouse immunoglobulins; I; 50; concentration giving 50% inhibition of maximum response; LOD; limit of detection; PBS; 150; mM phosphate buffer, pH 7.4; PBST; PBS containing 0.05% (v/v) Tween 20Hapten; Spacer-arm attachment site; Antibody; Sensitivity; Specificity; Enzyme-linked immunosorbent assay (ELISA); Organophosphorus insecticide; Fenthion
Application of surfactants and microemulsions to the extraction of pyrene and phenanthrene from soil with three different extraction methods by Guanqun Song; Chao Lu; Jin-Ming Lin (pp. 312-318).
In the present work, the use of surfactants and oil-in-water (O/W) microemulsions as alternative extractants in accelerated solvent extraction (ASE) for the extraction of polycyclic aromatic hydrocarbons (pyrene and phenanthrene) from soils was investigated. In particular, the effect of each individual component within the microemulsions, i.e., oil phase, surfactant and co-surfactatnt, and extraction conditions on the percentage recovery was systematically studied. When compared to the water and organic solvent, the important findings were that the common surfactant solutions at the concentrations above their critical micelle concentrations (CMC) were shown to enhance the percentage recovery at the lower extraction temperature. Moreover, the highest percentage recovery can be obtained using microemulsion as the extractant. The chemical component within the microemulsions and relative amounts of the oil phase appeared to play a much more significant role in ensuring high percentage recovery. Finally, an overall comparison between the percentage recoveries obtained with ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and ASE using organic solvents, surfactants and microemulsions as extractants was exhibited.
Keywords: Surfactant; Microemulsion; Polycyclic aromatic hydrocarbons; Accelerated solvent extraction; Ultrasound-assisted extraction; Microwave-assisted extraction
Authentication of fattening diet of Iberian pig according to their triacylglycerols profile from subcutaneous fat by Isabel Viera-Alcaide; Isabel M. Vicario; E. Graciani Constante; M. León-Camacho (pp. 319-324).
Triacylglycerols of 50 samples of subcutaneous fat of Iberian pigs reared extensively on two different feeding systems: montanera (M) and cebo (C) have been analysed by gas chromatography flame ionization detector. The lipids were extracted by melting from subcutaneous fat into microwave oven. The fat was then filtered and dissolved in hexane. This analysis was performed on a column (30m×0.25mm i.d.) coated with a bonded stationary phase DB-17HT (50% phenyl–50% methylpolysiloxane; 0.15μm film thickness) with hydrogen (2.1mLmin−1) as a carrier gas, programmed temperature was kept at 320°C, and was then raised to 350°C at a rate of 2.0°Cmin−1 and flame ionization detector. By using the triacylglycerols as chemical descriptors, pattern recognition techniques were applied to differentiate between montanera and cebo fattening diet of Iberian pig. Triolein, palmitoyl-stearyl-oleoyl glycerol and di-oleoyl-linoleoyl glycerol were found to be the most differentiating variables.
Keywords: Iberian pig; Triacylglycerols; Gas chromatography; Pattern recognition
A rapid and automated low resolution NMR method to analyze oil quality in intact oilseeds by Rosilene Aparecida Prestes; Luiz Alberto Colnago; Lucimara Aparecida Forato; Lucinéia Vizzotto; Etelvino Henrique Novotny; Emanuel Carrilho (pp. 325-329).
Oilseeds with modified fatty acid profiles have been the genetic alternative for high quality vegetable oil for food and biodiesel applications. They can provide stable, functional oils for the food industry, without the hydrogenation process that produces trans-fatty acid, which has been linked to cardiovascular disease. High yield and high quality oilseeds are also necessary for the success of biodiesel programs, as polyunsatured or saturated fatty acid oil produces biofuel with undesirable properties. In this paper, a rapid and automated low resolution NMR method to select intact oilseeds with a modified fatty acid profile is introduced, based on1H transverse relaxation time ( T2). The T2 weighted NMR signal, obtained by a CPMG pulse sequence and processed by chemometric methods was able to determine the oil quality in intact seeds by its fatty composition, cetane number, iodine value and kinematic viscosity with a correlation coefficient r>0.9. The automated system has the potential to analyze more than 1000 samples per hour and is a powerful tool to speed up the selection of high quality oilseeds for food and biodiesel applications.
Keywords: Nuclear magnetic resonance; Carr–Purcell–Meiboom–Gill pulse sequence; Biodiesel; Trans-fatty acid; Oilseeds
Determination of edible oil parameters by near infrared spectrometry by S. Armenta; S. Garrigues; M. de la Guardia (pp. 330-337).
A chemometric method has been developed for the determination of acidity and peroxide index in edible oils of different types and origins by using near infrared spectroscopy (NIR) measurements. Different methods for selecting the calibration set, after an hierarchical cluster analysis, were applied. After discrimination of olive oils from maize, seed and sunflower, the prediction capabilities of partial least squares (PLS) multivariate calibration of NIR data were evaluated. Several preprocessing alternatives (first derivative, multiplicative scatter correction, vector normalization, constant offset elimination, mean centering and standard normal variate) were investigated by using the root mean square error of validation (RMSEV) and prediction (RMSEP), as control parameters. Under the best conditions studied, the validation set provides RMSEP values of 0.034 and 0.037% (w/w) for acidity in (I) olive oil group and (II) sunflower, seed and maize oils group. RMSEP values for peroxide in both sample groups, expressed as mequiv.O2kg−1, were, respectively 1.87 and 0.79. The limit of detection of the methodology developed was 0.03% for acidity in both groups of edible oils (I and II), and 0.9 and 0.8mequiv.O2kg−1 for peroxide in the olive oil and other edible oils groups, respectively. In fact, the methodology developed is proposed for direct acidity quantification and for the screening of peroxide index in edible oils, requiring less than 30s per sample without any previous treatment.
Keywords: Edible oil; Near infrared; Chemometrics; Acidity; Peroxide value