Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.587, #1)

Editorial Board (pp. co1).

Contents (pp. v-vi).

Calendar of forthcoming meetings (pp. n1).

Contents (pp. v-vi).

Editorial Board (pp. co1).

Plastic enzyme-linked immunosorbent assays (ELISA)-on-a-chip biosensor for botulinum neurotoxin A by Seung-Mok Han; Joung-Hwan Cho; Il-Hoon Cho; Eui-Hwan Paek; Hee-Bok Oh; Bong-Su Kim; Chunsun Ryu; Kyunghee Lee; Young-Kee Kim; Se-Hwan Paek (pp. 1-8).

A plastic ELISA-on-a-chip (EOC) employing the concept of cross-flow immuno-chromatographic analysis was applied to the measurement of botulinum neurotoxin A (BoNT/A) as agent for bio-terrorism. Two monoclonal antibodies specific to the heavy chain of the toxin were raised and identified to form sandwich binding complexes as the pair with the analyte. For the construction of an immuno-strip, one was utilized as the capture antibody immobilized onto nitrocellulose membrane and the other as the detection coupled to an enzyme, horseradish peroxidase. The two plates of EOC used in this study were fabricated by injection molding of polycarbonate to improve the reproducibility of manufacture and, after inclusion of the immuno-strip, bonded using a UV-sensitive adhesive. Under optimal conditions of analysis, the chip produced a color signal in proportion to the analyte dose and the signal was quantified using a detector equipped with a digital camera. From the dose–response curve, the detection limit of BoNT/A was 2.0ngmL⁻¹, approximately five times more sensitive than a commercial-version detection kit employing colloidal gold tracer.

Keywords: Cross-flow immuno-chromatography; Enzyme label; Injection-molded plastic chip; Colorimetric detector; Bio-defense

A novel sandwich assay with molecular beacon as report probe for nucleic acids detection on one-dimensional microfluidic beads array by Xinbing Zuo; Xiaohai Yang; Kemin Wang; Weihong Tan; Jianhui Wen (pp. 9-13).

A novel sandwich assay with molecular beacons as report probes has been developed and integrated into one-dimensional microfluidic beads array (1-D chip) to pursue a label-free and elution-free detection of DNA/mRNA targets. In contrast with the immobilized molecular beacons, this sandwich assay can offer lower fluorescence background and correspondingly higher sensitivity. Furthermore, this sandwich assay on 1-D chip operating in conjunction with molecular beacon technique allows multiple targets detection without the need of laborious and time-consuming elution, which makes the experiment process simple, easy to handle, and reproducible results. In the experiment, the synthesized DNA targets with different concentrations were detected with a detection limit of ∼0.05nM. Moreover, the mRNA expression changes in A549 cells before and after anticancer drug 5-flouorouracil treatments were detected and the results were validated by the conventional RT-PCR method.

Keywords: Molecular beacon; Sandwich assay; Microfluidic; One-dimensional beads array

Optimization of zeta potential profile for low-dispersion flows in microchannel turns by H.M. Park; S.M. Hong; J.S. Lee (pp. 14-21).

A method is developed to determine the optimal profile of zeta potential around U turns such that the turn-induced spreading of a solute band is minimized. After proposing a velocity profile that eliminates the racetrack effect, a conjugate gradient method is adopted to find the zeta potential profile to induce the required velocity. The optimal profiles of zeta potential seem to be insensitive to the relevant parameters of electroosmotic flows. It is shown that a reduction of variance two orders of magnitude below that of a comparable turn with uniform zeta potential is easily attained by adopting the optimal profile of zeta potential, which can be realized using a UV excimer laser or external voltage control.

Keywords: Microchip electrophoresis; Dispersion minimization; Conjugate gradient method

Optimization of zeta potential profile for low-dispersion flows in microchannel turns by H.M. Park; S.M. Hong; J.S. Lee (pp. 14-21).

Keywords: Microchip electrophoresis; Dispersion minimization; Conjugate gradient method

Organophosphorus and carbamate pesticide analysis using an inhibition tyrosinase organic phase enzyme sensor; comparison by butyrylcholinesterase+choline oxidase opee and application to natural waters by L. Campanella; D. Lelo; E. Martini; M. Tomassetti (pp. 22-32).

Recent research performed in our laboratory (using a butyrylcholinesterase+choline oxidase enzyme electrode) suggested the validity of the biosensor approach using enzyme inhibition OPEEs (i.e. enzyme electrodes working in organic phase) in the case of organophosphorus and carbamate pesticides, which are poorly soluble in aqueous solutions. Since these pesticides are generally much more soluble in chloroform than in water, the present research aimed at analysing this class of pesticides using a tyrosinase inhibition OPEE operating in water-saturated chloroform medium. The tyrosinase biosensor was assembled using an oxygen amperometric transducer coupled to the tyrosinase enzyme, immobilized in kappa-carrageenan gel. Lastly a detailed comparison between the inhibition monoenzymatic tyrosinase and inhibition bienzymatic (butyrylcholinesterase+choline oxidase) OPEEs was performed and discussed in this work.

Keywords: Biosensor pesticide analysis; Carbamate; Organophosphorus; Tyrosinase inhibition

Direct electrochemistry of glucose oxidase entrapped in nano gold particles-ionic liquid- N, N-dimethylformamide composite film on glassy carbon electrode and glucose sensing by Jiangwen Li; Jingjing Yu; Faqiong Zhao; Baizhao Zeng (pp. 33-40).

The direct electrochemistry of glucose oxidase (GOD) entrapped in nano gold particles (NAs)- N, N-dimethylformamide (DMF)-1-butyl-3-methylimidazolium hexafluophosphate (BMIMPF₆) composite film on a glassy carbon electrode (NAs-DMF-GOD (BMIMPF₆)/GC) has been investigated for first time. The immobilized GOD exhibits a pair of well-defined reversible peaks in 0.050M pH 5 phosphate solutions (PS), resulting from the redox of flavin adenine dinucleotide (FAD) in GOD. The peak currents are three times as large as those of GOD-NAs-DMF film coated GC electrode (i.e. NAs-DMF-GOD (water)/GC). In addition, the NAs-DMF-GOD (BMIMPF₆) composite material has higher thermal stability than NAs-DMF-GOD (water). Results show that ionic liquid BMIMPF₆, DMF and NAs are requisite for GOD to exhibit a pair of stable and reversible peaks. Without any of them, the peaks of GOD become small and unstable. Upon the addition of glucose, the peak currents of GOD decrease and a new cathodic peak occurs at −0.8V (versus SCE), which corresponds to the reduction of hydrogen peroxide (H₂O₂) generated by the catalytic oxidation of glucose. The peak current of the new cathodic peak and the glucose concentration show a linear relationship in the ranges of 1.0×10⁻⁷ to 1.0×10⁻⁶M and 2.0×10⁻⁶ to 2.0×10⁻⁵M. The kinetic parameter I_max of H₂O₂ is estimated to be 1.19×10⁻⁶A and the apparent K_m (Michaelis–Menten constant) for the enzymatic reaction is 3.49μM. This method has been successfully applied to the determination of glucose in human plasma and beer samples, and the average recoveries are 97.2% and 99%, respectively.

Keywords: Direct electrochemistry; Glucose oxidase; Nano gold particles; Room-temperature ionic liquid; Glucose sensor

Immobilization of uricase within polystyrene using polymaleimidostyrene as a stabilizer and its application to uric acid sensor by Xiuyun Wang; Tokio Hagiwara; Shunichi Uchiyama (pp. 41-46).

A novel amperometric uric acid (UA) sensor has been developed by coating the surface of a gold electrode with a polystyrene (PS) membrane formed by 30μL of a 30mgmL⁻¹ PS chloroform solution combined with 30μL of a 5mgmL⁻¹ polymaleimidostyrene (PMS) solution as a dispersant for enzyme, uricase; this membrane has been successfully employed as an immobilization support for uricase. In the PS membrane, PMS forms micelle-like structures containing uricase in an active state. This immobilized uricase membrane permits the permeation of oxygen, which is consumed by the uricase reaction. A good linear relationship is obtained over the concentration range of 5–105μM. The concentration of uric acid was determined at a negative potential based on the decrease in the reduction current of oxygen and the interference ofl-ascorbic acid can be completely eliminated.

Keywords: Polymaleimidostyrene; Polystyrene; Immobilization; Uric acid; Uricase; Biosensor

Immobilization of uricase within polystyrene using polymaleimidostyrene as a stabilizer and its application to uric acid sensor by Xiuyun Wang; Tokio Hagiwara; Shunichi Uchiyama (pp. 41-46).

Keywords: Polymaleimidostyrene; Polystyrene; Immobilization; Uric acid; Uricase; Biosensor

Rapid high throughput assay for fluorimetric detection of doxorubicin—Application of nucleic acid–dye bioprobe by Yang Liu; Bengt Danielsson (pp. 47-51).

A double stranded DNA based fluorescence bioprobe for anticancer agent (doxorubicin) detection is described. This method provides a new way for sensitive DNA/drug interaction study by a homogeneous assay. The probe employs the long-wavelength intercalating fluorophore TOTO-3^® (TT3). The anticancer agent, doxorubicin, which interacts with the DNA-TT3 complex, was indirectly measured by the decrease in the fluorescence intensity. Various oligonucleotides with different sequences were examined. Doxorubicin has preference for the oligonucleotide 5′AGCACG3′. Enhanced fluorescence observed for the TT3 intercalation with this oligonucleotide makes the DNA–dye complex a suitable bioprobe for doxorubicin detection by competitive assay. A home-built CCD camera setup was applied along with 384 well plate assay format for high throughput fluorescence imaging. The detection limit can be as low as 25ngmL⁻¹ with an upper limit of 100μgmL⁻¹. The recovery test with spiked serum sample shows that this method can be a potential routine method for therapeutic drug monitoring (TDM).

Keywords: Doxorubicin; Fluorescence; Deoxyribonucleic acid; High throughput

Rapid high throughput assay for fluorimetric detection of doxorubicin—Application of nucleic acid–dye bioprobe by Yang Liu; Bengt Danielsson (pp. 47-51).

Keywords: Doxorubicin; Fluorescence; Deoxyribonucleic acid; High throughput

A novel detection approach based on chromophore-decolorizing with free radical and application to photometric determination of copper with acid chrome dark blue by Hong-Wen Gao; Fang-Fang Chen; Ling Chen; Teng Zeng; Lu-Ting Pan; Jian-Hua Li; Hua-Fei Luo (pp. 52-59).

A novel detection approach named chromophore-decolorizing with free radicals is developed for determination of trace heavy metal. The hydroxyl radicals (HO) generated from Fe(III) and hydrogen peroxide will oxidize the free chromophore into almost colorless products. The copper–acid chrome dark blue (ACDB) complexation was investigated at pH 5.07. In the presence of Fe(III) and hydrogen peroxide, the excess ACDB was decolorized in the Cu–ACDB reaction solution, and the final solution contained only one color compound, the Cu–ACDB complex. After oxidation of free hydroxyl radicals, the complexation becomes sensitive and selective and it has been used for the quantitation of trace amounts of Cu(II) dissolved in natural water. Beer's law is obeyed in the range from 0 to 0.500μgmL⁻¹ Cu(II) and the limit of detection is only 6μgL⁻¹ Cu(II). Besides, the Cu–ACDB complex formed was characterized.

Keywords: Chromophore-decolorizing; Hydroxyl radicals; Determination of copper; Acid chrome dark blue; Spectral correction technique; Spectrophotometry

Development of a column-switching high-performance liquid chromatography for kynurenine enantiomers and its application to a pharmacokinetic study in rat plasma by Shogo Mitsuhashi; Takeshi Fukushima; Kotaro Arai; Masayuki Tomiya; Tomofumi Santa; Kazuhiro Imai; Toshimasa Toyo’oka (pp. 60-66).

Kynurenine (KYN), a tryptophan metabolite, is a precursor of kynurenic acid, which is an antagonist of N-methyl-d-aspartate receptor. In this study, an enantiomeric separation ofd,l-KYN derivatized with the benzofurazan fluorescence reagent 4- N,N-dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (DBD-F) (DBD-d,l-KYN) was first investigated by using a high-performance liquid chromatography (HPLC) with several chiral columns. As a consequence, DBD-d,l-KYN was enantiomerically separated on a cellulose-type chiral column (CHIRALCEL OJ-RH) with a mobile phase of H₂O/CH₃CN/MeOH (40/50/10) containing 0.1% acetic acid. Under this condition, the separation factor and resolution were 1.48 and 1.28, respectively. Next, a column-switching HPLC consisting of both octadecylsilica and chiral columns was developed and used to determine bothd- andl-KYN enantiomers in 10μL of rat plasma following the intraperitoneal administration ofd,l-KYN to rats (10mgkg⁻¹). The result revealed that the concentration ofl-KYN was higher than that ofd-KYN, suggesting thatd-KYN was eliminated faster thanl-KYN.

Keywords: d,l; -Kynurenine; 4-; N,N; -Dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole; CHIRALCEL OJ-RH; Rat plasma; Column-switching high-performance liquid chromatography

Purification of clenbuterol-like β₂-agonist drugs of new generation from bovine urine and hair by α₁-acid glycoprotein affinity chromatography and determination by gas chromatography–mass spectrometry by Pasquale Gallo; Gianfranco Brambilla; Bruno Neri; Maurizio Fiori; Cecilia Testa; Luigi Serpe (pp. 67-74).

The control of illegal use of clenbuterol and other β₂-agonist drugs as growth promoters in the European Union countries has led to outlaw practices for synthesizing new concept molecules, showing similar biological activity but not detectable by test methods usually employed to perform the official monitoring programmes. The synthesis schemes of some β₂-agonist compounds, formally derived from clenbuterol, were found out by Italian detective authorities. These compounds were synthesised ex novo in our laboratories: then, both their molecular structures and biological activities were characterised. In this paper, we describe different strategies for purifying some β₂-agonist drugs of new concept, more hydrophobic than clenbuterol. A two-step clean up procedure, prior to gas chromatography–mass spectrometry analysis, was developed for the multi-residue determination of these β₂-agonists from bovine hair and urine. The purification strategy we chose was based on adsorption solid phase extraction and, subsequently, on specific molecular recognition by affinity chromatography. The affinity columns were homemade by coupling bovine α₁-acid glycoprotein, a plasmatic acceptor for basic drugs, to a chromatographic support; their effectiveness for purifying new β₂-agonists was discussed. The data about method recoveries and repeatability were also reported.

Keywords: α; ₁; -Acid glycoprotein; Affinity chromatography; Adrenergic drugs; Clenbuterol

The investigation of electrospun polymer nanofibers as a solid-phase extraction sorbent for the determination of trazodone in human plasma by Xuejun Kang; Cao Pan; Qian Xu; Yingfang Yao; Yian Wang; Dongjin Qi; Zhongze Gu (pp. 75-81).

A novel micro-extraction procedure was developed through the use of an electrospun polymer nanofiber as a solid-phase extraction (SPE) sorbent to directly extract trazodone from human plasma. The target compound was then monitored by a high performance liquid chromatography with ultraviolet detector (HPLC-UV) system. Parameters of influencing the extraction efficiency, such as fiber diameter, fiber packing amount, eluted solvent, pH and ionic strength were investigated. Under the optimized conditions, a linear response for trazodone over the range of 20–2000ngmL⁻¹ was achieved with a γ² value of 0.9996. The precision of the method was examined with relative standard deviations of 5.7, 2.7, 2.2% corresponding to 50, 200, and 500ngmL⁻¹, respectively, of trazodone spiked into 0.1mL of plasma samples. The extraction recoveries of 58.3–75.2% and the relative recoveries of 94.6–105.5% were obtained. The limit of detection (LOD) was determined to be 8ngmL⁻¹. A 15min of HPLC gradient was successfully applied to determine trazodone from human plasma. Due to its simplicity, selectivity and sensitivity, the method may be applied to pharmacokinetic and pharmacodynamic studies of drugs.

Keywords: Solid-phase extraction; Preconcentration; Electrospinning; Plasma; Trazodone; High performance liquid chromatography with ultraviolet detector

Determination of N-vinyl-2-pyrrolidone and N-methyl-2-pyrrolidone in drugs using polypyrrole-based headspace solid-phase microextraction and gas chromatography–nitrogen-phosphorous detection by Ali Mehdinia; Alireza Ghassempour; Hasan Rafati; Rouhollah Heydari (pp. 82-88).

A headspace solid-phase microextraction and gas chromatography–nitrogen-phosphorous detection (HS-SPME–GC–NPD) method using polypyrrole (PPy) fibers has been introduced to determine two derivatives of pyrrolidone; N-vinyl-2-pyrrolidone (NVP) and N-methyl-2-pyrrolidone (NMP). Two types of PPy fibers, prepared using organic and aqueous media, were compared in terms of extraction efficiency and thermal stability. It was found that PPy film prepared using organic medium (i.e. acetonitrile) had higher extraction efficiency and more thermal stability compared to the film prepared in aqueous medium. To enhance the sensitivity of HS-SPME, the effects of pH, ionic strength, extraction time, extraction temperature and the headspace volume on the extraction efficiency were optimized. Using the results of this research, high sensitivity and selectivity had been achieved due to the combination of the high extraction efficiency of PPy film prepared in organic medium and the high sensitivity and selectivity of nitrogen-phosphorous detection. Linear range of the analytes was found to be between 1.0 and 1000μgL⁻¹ with regression coefficients ( R²) of 0.998 and 0.997 for NVP and NMP, consequently. Limits of detection (LODs) were 0.074 and 0.081μgL⁻¹ for NVP and NMP, respectively. Relative standard deviation (R.S.D.) for five replications of analyses was found to be less than 6.0%. In real samples the mean recoveries were 94.81% and 94.15% for NVP and NMP, respectively. The results demonstrated the suitability of the HS-SPME technique for analyzing NVP and NMP in two different pharmaceutical matrices. In addition, the method was used for simultaneous detection of NVP, 2-pyrrolidone (2-Pyr), γ-butyrolactone (GBL) and ethanolamine (EA) compounds.

Keywords: Headspace solid-phase microextraction; Gas chromatography–nitrogen-phosphorous detection; Polypyrrole; N; -Vinyl-2-pyrrolidone; N; -Methyl-2-pyrrolidone

Headspace–mass spectrometry determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers in soil samples using chemometrics by F.A. Esteve-Turrillas; S. Armenta; S. Garrigues; A. Pastor; M. de la Guardia (pp. 89-96).

A simple and fast method has been developed for the determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers (BTEX) in soils. Samples were introduced in 10mL standard glass vials of a headspace (HS) autosampler together with 150μL of 2,6,10,14-tetramethylpentadecane, heated at 90°C for 10min and introduced in the mass spectrometer by using a transfer line heated at 250°C as interface. The volatile fraction of samples was directly introduced into the source of the mass spectrometer which was scanned from m/ z 75 to 110. A partial least squares (PLS) multivariate calibration approach based on a classical 3³ calibration model was build with mixtures of benzene, toluene and o-xylene in 2,6,10,14-tetramethylpentadecane for BTEX determination. Results obtained for BTEX analysis by HS–MS in different types of soil samples were comparables to those obtained by the reference HS–GC–MS procedure. So, the developed procedure allowed a fast identification and prediction of BTEX present in the samples without a prior chromatographic separation.

Keywords: Benzene; Toluene; Ethylbenzene; Xylene isomers; Headspace-mass spectrometry; Chemometric analysis

Direct determination of chlorophenols present in liquid samples by using a supported liquid membrane coupled in-line with capillary electrophoresis equipment by S. Almeda; L. Nozal; L. Arce; M. Valcárcel (pp. 97-103).

Actually there is a great trend on the development of effective analytical methods for monitoring trace levels of various phenols which can indicate, among others compounds, the water quality. A simple, inexpensive supported liquid membrane (SLM) device was used in combination with commercially available capillary electrophoresis (CE) equipment for the direct determination of chlorophenols in surface water samples. The manifold was used simultaneously to extract and preconcentrate the analytes from liquid samples. In the extraction set-up, the donor phase (4mL) was placed in the CE vial, where a micro-membrane extraction unit (MMEU) accommodating the acceptor phase (100μL) in its lumen was immersed. The supported liquid membrane was constructed by impregnating a porous Fluoropore Teflon (PTFE) membrane with a water-immiscible organic solvent (dihexyl ether). The extraction process was optimized with regard to the pH of the donor and acceptor phases, membrane liquid, extraction time and voltage applied to the inlet or outlet vial during extraction. The chlorinated phenols pentachlorophenol (PCP), 2,3,6 trichlorophenol (TCP) and 2,6 dichlorophenol (DCP) were thus efficiently separated by CE, using tris(hydroxymethyl)aminomethane (Tris) and an NaH₂PO₄ solution containing 1% (v/v) methanol at pH 10.5 as running buffer.

Keywords: Supported liquid membrane; Capillary electrophoresis; Chlorophenols

Determination of sinomenine in Sinomenium acutum by capillary electrophoresis with electrochemiluminescence detection by Min Zhou; Yong-Jun Ma; Xiao-Na Ren; Xiu-Ying Zhou; Li Li; Hui Chen (pp. 104-109).

A Ru(bpy)₃²⁺-based electrochemiluminescence (ECL) detection coupled with capillary electrophoresis (CE) has been established for the determination of sinomenine for the first time. Optimum separation was achieved with a fused-silica capillary column (50cm×25μm i.d.) and a background electrolyte of 50mM sodium phosphate (pH 5.0) at a separation voltage of 15kV. The content of sinomenine was detected by ECL at the detection voltage of 1.15V (versus Ag/AgCl) with 5mM Ru(bpy)₃²⁺ in 75mM phosphate solution (pH 8.0) when a chemically modified platinum electrode by europium(III)-doped prussian blue analogue (Eu-PB) was used as a working electrode. Under the optimized conditions, the ECL intensity was in proportion to sinomenine concentration in the range from 0.01 to 1.0μgmL⁻¹ with a detection limit of 2.0ngmL⁻¹ (3 σ). The relative standard derivations of migration time and ECL intensity were 0.93 and 1.11%, respectively. The level of sinomenine in Sinomenium acutum Rehd. et Wils was easily determined with recoveries between 98.6 and 102.7%.

Keywords: Electrochemiluminescence; Capillary electrophoresis; Sinomenine

Selective response of dopamine in the presence of ascorbic acid on carbon paste electrode modified with titanium phosphated silica gel by Mojtaba Kooshki; Esmaeil Shams (pp. 110-115).

Titanium phosphate grafted on the surface of silica gel (devoted briefly as Si-TiPH) was synthesized and used as bulk modifier to fabricate a renewable three-dimensional chemically modified electrode. The Si-TiPH bulk modified carbon paste electrode was used for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA). The modified electrode offers an excellent and stable response for the determination of DA in the presence of AA. The differential pulse voltammetry peak current was found to be linear with the DA concentration in the range 2×10⁻⁷ to 1×10⁻⁶ and 2×10⁻⁶ to 6×10⁻⁵molL⁻¹. The detection limit of the proposed method in the presence of 2.0×10⁻⁵M of AA was found to be 4.3×10⁻⁸molL⁻¹ for DA determination. The proposed method was successfully applied for the determination of DA in injections.

Keywords: Titanium phosphate; Silica gel; Carbon paste electrode; Dopamine; Ascorbic acid

Selective response of dopamine in the presence of ascorbic acid on carbon paste electrode modified with titanium phosphated silica gel by Mojtaba Kooshki; Esmaeil Shams (pp. 110-115).

Keywords: Titanium phosphate; Silica gel; Carbon paste electrode; Dopamine; Ascorbic acid

Comparative electrooxidation of nitrite by electrodeposited Co(II), Fe(II) and Mn(III) tetrakis (benzylmercapto) and tetrakis (dodecylmercapto) phthalocyanines on gold electrodes by Bolade Agboola; Tebello Nyokong (pp. 116-123).

This work reports on the electrooxidation of nitrite using Co(II), Fe(II) and Mn(III) tetrakis (benzylmercapto) and tetrakis (dodecylmercapto) phthalocyanines electrodeposited onto a gold electrode. Good catalytic activity (in terms of lowering overpotential) was obtained for these molecules when compared to previously reported MPc catalysts. The catalytic current was found to vary linearly with nitrite concentration in the range employed in this work (0.1–1mM) and high sensitivities ranging from 6.9 to 9.9μAmM⁻¹ were observed for all the modified electrodes.

Keywords: Metallophthalocyanines complexes; Cyclic voltammetry; Electrodeposition; Electrocatalysis; Nitrite oxidation

Electrochemistry and electrocatalysis of polyoxometalate-ordered mesoporous carbon modified electrode by Ming Zhou; Li-ping Guo; Fan-yun Lin; Hai-xia Liu (pp. 124-131).

In this work, we have developed a convenient and efficient method for the functionalization of ordered mesoporous carbon (OMC) using polyoxometalate H₆P₂Mo₁₈O₆₂· xH₂O (P₂Mo₁₈). By the method, glassy carbon (GC) electrode modified with P₂Mo₁₈ which was immobilized on the channel surface of OMC was prepared and characterized for the first time. The large specific surface area and porous structure of the modified OMC particles result in high heteropolyacid loading, and the P₂Mo₁₈ entrapped in this order matrix is stable. Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption–desorption isotherm and X-ray diffraction (XRD) were employed to give insight into the intermolecular interaction between OMC and P₂Mo₁₈. The electrochemical behavior of the modified electrode was studied in detail, including pH-dependence, stability and so on. The cyclic voltammetry (CV) and amperometry studies demonstrated that P₂Mo₁₈/OMC/GC electrode has high stability, fast response and good electrocatalytic activity for the reduction of nitrite, bromate, idonate, and hydrogen peroxide. The mechanism of catalysis on P₂Mo₁₈/OMC/GC electrode was discussed. Moreover, the development of our approach for OMC functionalization suggests the potential applications in catalysis, molecular electronics and sensors.

Keywords: P; ₂; Mo; ₁₈; Ordered mesoporous carbon; Cyclic voltammetry; Electrocatalysis

Electrochemistry and electrocatalysis of polyoxometalate-ordered mesoporous carbon modified electrode by Ming Zhou; Li-ping Guo; Fan-yun Lin; Hai-xia Liu (pp. 124-131).

Keywords: P; ₂; Mo; ₁₈; Ordered mesoporous carbon; Cyclic voltammetry; Electrocatalysis

Ex vivo evaluation of the percutaneous penetration of proanthocyanidin extracts from Guazuma ulmifolia using photoacoustic spectroscopy by J.C.B. Rocha; F. Pedrochi; L. Hernandes; J.C.P. de Mello; M.L. Baesso (pp. 132-136).

In this work photoacoustic spectroscopy has been applied to determine ex vivo the percutaneous penetration of proanthocyanidins present in extracts obtained from Guazuma ulmifolia, in rats. Lotion formulations containing 0.0663mg of procyanidin B2day⁻¹animal⁻¹ were topically applied during 7, 10 and 13 days in each group of the animals. After the end of treatment the animals were killed, the skin dissected to remove the basal content, and the measurements were carried out as a function of the period of time of treatment. The results showed that despite the very low concentration of the active principle (procyanidin B2) in the lotion, the photoacoustic method was able to show the presence of optical absorption bands from this substance in the dermis region, evidencing once again that this method may be useful for studies of topically applied formulations of interest in the pharmacokinetic area.

Keywords: Photoacoustic spectroscopy; Percutaneous penetration; Natural substances; Ex vivo measurements

A novel surface ionization source for ion mobility spectrometer by Guo Hui-yong; He Xiu-li; Gao Xiao-guang; Jia Jian; Li Jian-ping (pp. 137-141).

A surface ionization (SI) source is designed and prepared for ion mobility spectrometer (IMS). The source acts not only as an emitter but also an ion injector which can inject ions periodically into the drift region of drift tube. Using the dual-role source, the dimension of the drift tube can be decreased and the circuit for high voltage can be simplified efficiently. The IMS with the SI source has a response range of ∼4 orders of magnitude and a good reproducibility to tri-ethylamine. Compared with radioactive ionization (RI), the ultra-short time for ion injection and the zero level base line of ion mobility spectrum are characteristics of the surface ionization.

Keywords: Surface ionization; Ion mobility spectrometer; Tri-ethylamine

A novel surface ionization source for ion mobility spectrometer by Guo Hui-yong; He Xiu-li; Gao Xiao-guang; Jia Jian; Li Jian-ping (pp. 137-141).

Keywords: Surface ionization; Ion mobility spectrometer; Tri-ethylamine

A quantitative method for determination of Co(II) based on the inner filter effect of reagents on the Raman scattering signals of water by Hui Ying Wang; Cheng Zhi Huang (pp. 142-148).

It is known that Raman scattering signals are one of main interference sources leading up to determination errors in spectrofluorometry, and thus the signals can be easily detected with a common spectrofluorometer. In this contribution, we propose a quantitative method based on the inner filter effect (IFE) of reagents on the Raman scattering signals of solvent by taking the complexation of divalent cobalt ion with 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB) as a model system. By adjusting the excitation wavelength of the spectrofluorometer, we could easily detect the Raman scattering signals of water at 424nm where the maximum absorption of 5-Cl-PADAB reagent is located. In a solution of 5-Cl-PADAB, the Raman scattering signals of water are decreased owing to the IFE of 5-Cl-PADAB. If Co(II), which could form the binary complex of Co(II)/5-Cl-PADAB and consumes the 5-Cl-PADAB reagent, is present in such a case for a given amount of 5-Cl-PADAB solution, recovered Raman scattering signals could be observed and measured with a spectrofluorometer. It was found that the intensity of the enhanced Raman scattering signals is proportional to the Co(II) concentration over the range from 2.0×10⁻⁷molL⁻¹ to 1.0×10⁻⁵molL⁻¹, and the detection limit could reach 1.2×10⁻⁷molL⁻¹. With that, Co(II) in samples could be detected with R.S.D. values lower than 2.6% and recoveries over the range of 97.2–104.7%.

Keywords: Inner filter effect (IFE); Raman scattering; 4-[(5-Chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB); Co(II)

A quantitative method for determination of Co(II) based on the inner filter effect of reagents on the Raman scattering signals of water by Hui Ying Wang; Cheng Zhi Huang (pp. 142-148).

Keywords: Inner filter effect (IFE); Raman scattering; 4-[(5-Chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB); Co(II)

Aluminum-27 NMR studies of alcoholic (2-hydroxyethyl)trimethylammonium aluminate solutions by Abdolraouf Samadi-Maybodi; Nasser Goudarzi (pp. 149-157).

²⁷Al NMR spectroscopy is a power tool for investigation of the aluminate species existing in both aqueous and non-aqueous solutions. Aluminum-27 nuclear magnetic resonance (NMR) spectroscopy also can be used to determine thermodynamic properties of complexes in the solution. In this report,²⁷Al NMR spectroscopy was used to characterize species present in alkaline alcoholic aluminate solutions. (2-Hydroxyethyl)trimethylammonium (2-EHTMA) hydroxide was used as base. In solution of CH₃OH and H₂O in a mole ratio of 64:1 it was possible to detect five signals by aluminum-27 NMR, indicating formation of [Al(OH)4−_n(CH₃OH)_n]( n⁻¹⁾⁺ ( n=0,1, 2, 3 and 4) species. Aluminum-27 NMR spectroscopy has also used for investigation of the species present in the ethanolic 2-HETMA aluminate solutions. The equilibrium constants for the formation of aluminate complexes were also determined for both methanolic and ethanolic aluminate solutions. Aluminum-27 NMR spectra of propanolic and butanolic 2-HETMA aluminate solutions were also studied.

Keywords: Aluminum-27 NMR; Aluminum complexes; Alcoholic 2-HETMA aluminate solution; (2-Hydroxyethyl)trimethylammonium hydroxide

Aluminum-27 NMR studies of alcoholic (2-hydroxyethyl)trimethylammonium aluminate solutions by Abdolraouf Samadi-Maybodi; Nasser Goudarzi (pp. 149-157).

Keywords: Aluminum-27 NMR; Aluminum complexes; Alcoholic 2-HETMA aluminate solution; (2-Hydroxyethyl)trimethylammonium hydroxide

Systematic error arising from ‘Sequential’ Standard Addition Calibrations: Quantification and correction by Richard J.C. Brown; Matthew R. Roberts; Martin J.T. Milton (pp. 158-163).

Calibrations involving the sequential addition of aliquots of a standard solution to a solution of unknown analyte content may exhibit a systematic error. We show that this systematic error is related to the ratio of the mass fractions in the standard and unknown solutions. This relationship is consistent with experimental results from the determination of lead in aqueous solution by anodic stripping voltammetry using ‘Sequential’ Standard Addition Calibration (S-SAC). The magnitude of this systematic error has been described mathematically and a correction calculated. These mathematical relationships form the basis for a proposal for best practice in the use of S-SAC.

Keywords: Calibration; Standard addition; Systematic error; Anodic stripping voltammetry

Systematic error arising from ‘Sequential’ Standard Addition Calibrations: Quantification and correction by Richard J.C. Brown; Matthew R. Roberts; Martin J.T. Milton (pp. 158-163).

Keywords: Calibration; Standard addition; Systematic error; Anodic stripping voltammetry

Sections

Personal tools

Analytica Chimica Acta (v.587, #1)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.587, #1)