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Analytica Chimica Acta (v.572, #2)

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n3).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n3).

Contents (pp. iii-iv).

Headspace liquid-phase microextraction using ionic liquid as extractant for the preconcentration of dichlorodiphenyltrichloroethane and its metabolites at trace levels in water samples by Cun-Ling Ye; Qing-Xiang Zhou; Xin-Ming Wang (pp. 165-171).

A novel technique, high temperature headspace liquid-phase microextraction (HS-LPME) with room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) as extractant, was developed for the analysis of dichlorodiphenyltrichloroethane ( p, p′-DDT and o, p′-DDT) and its metabolites including 4,4′-dichlorodiphenyldichloroethylene ( p, p′-DDE) and 4,4′-dichlorodiphenyldichloroethane ( p, p′-DDD) in water samples by high performance liquid chromatography with ultraviolet detection. The parameters such as salt content, sample pH and temperature, stirring rate, extraction time, microdrop volume, and sample volume, were found to have significant influence on the HS-LPME. The conditions optimized for extraction of target compounds were as follows: 35% NaCl (w/v), neutral pH condition, 70°C, 800rpm, 30min, 10μL [C₄MIM][PF₆], and 25mL sample solutions. Under the optimized conditions, the linear range, detection limit (S/N=3), and precision (R.S.D., n=6) were 0.3–30μgL⁻¹, 0.07μgL⁻¹, and 8.0% for p, p′-DDD, 0.3–30μgL⁻¹, 0.08μgL⁻¹, and 7.1% for p, p′-DDT, 0.3–30μgL⁻¹, 0.08μgL⁻¹, and 7.2% for o, p′-DDT, and 0.2–30μgL⁻¹, 0.05μgL⁻¹, and 6.8% for p, p′-DDE, respectively. Water samples including tap water, well water, snow water, reservoir water, and wastewater were analyzed by the proposed procedure and the recoveries at 5μgL⁻¹ spiked level were in the range of 86.8–102.6%.

Keywords: Ionic liquid; Headspace liquid-phase microextraction; High-performance liquid chromatography; Organochlorine pesticides

Pressurized liquid extraction as a novel sample pre-treatment for trace element leaching from biological material by Jorge Moreda-Piñeiro; Elia Alonso-Rodríguez; Purificación López-Mahía; Soledad Muniategui-Lorenzo; Esther Fernández-Fernández; Darío Prada-Rodríguez; Antonio Moreda-Piñeiro; Adela Bermejo-Barrera; Pilar Bermejo-Barrera (pp. 172-179).

Pressurized liquid extraction (PLE), commonly used for organic compounds extraction, has been applied for trace element leaching from marine biological material in order to determine major and trace elements (Al, As, Cd, Co, Cu, Fe, Hg, Li, Mn, Pb, Se, Sr, V and Zn). The released elements by formic acid PLE have been evaluated by inductively coupled plasma-optical emission spectrometry (ICP-OES). Different variables, such as formic acid concentration, extraction temperature, static time, extraction steps, pressure, mean particle size and diatomaceous earth (DE) mass/sample mass ratio were simultaneously studied by applying an experimental design approach (Plackett–Burman design (PBD) and central composite design (CCD)). Results showed that the extraction temperature was statistically significant (confidence interval of 95%) for most of the elements (high metal releasing was achieved at high temperatures). In addition, formic acid concentration was also statistically significant (confidence interval of 95%) for metals such as Cd and Cu. Most of the metals can be extracted using the same PLE operating conditions (formic acid concentration of 1.0M, extraction temperature at 125°C, static time of 5min, one extraction step, extraction pressure at 500psi and DE mass/sample mass ratio of 2). Taking in mind PLE requirements at the optimised operating conditions (125°C), a time of 6min is needed to pre-heat the cell. Therefore, the PLE assisted multi-element leaching is completed after 12min. Analytical performances, such as limits of detection and quantification, repeatability of the over-all procedure and accuracy, by analysing GBW-08571, DORM-2, DOLT-3 and TORT-2 certified reference materials, were finally assessed.

Keywords: Pressurised liquid extraction; Trace elements; Mussels; Inductively coupled plasma-optical emission spectrometry

Improved methods for urinary atrazine mercapturate analysis—Assessment of an enzyme-linked immunosorbent assay (ELISA) and a novel liquid chromatography–mass spectrometry (LC–MS) method utilizing online solid phase extraction (SPE) by Marja E. Koivunen; Katja Dettmer; Roel Vermeulen; Berit Bakke; Shirley J. Gee; Bruce D. Hammock (pp. 180-189).

Elimination of interfering substances in urine by solid phase extraction (SPE) prior to analysis resulted in 10-fold improvement in the sensitivity of atrazine mercapturate (AM) enzyme-linked immunosorbent assay (ELISA) compared to previous reports. Of the two tested SPE systems, Oasis^® HLB and MCX, the mixed-mode MCX gave good recoveries (82%) of AM in spiked samples measured by ELISA, whereas the reverse-phase HLB phase was not compatible with the immunochemical method. At relatively high concentrations of urinary AM (>20ngmL⁻¹), sample dilution was effective enough for the elimination of interfering substances. The new liquid chromatography–mass spectrometry (LC–MS) method developed for AM utilizes online-SPE with Oasis^® HLB, column switching and a stable-isotope internal standard. The limit of quantification (0.05ngmL⁻¹) indicates improved sensitivity compared with most previously published LC–MS methods for AM. Validation of all three methods, LC–MS, ELISA+SPE and ELISA+dilution with spiked urine samples showed good correlation between the known and measured concentrations with R² values of 0.996, 0.957 and 0.961, respectively. When a set ( n=70 plus 12 blind duplicates) of urine samples from farmers exposed to atrazine was analyzed, there was a good agreement ( R²=0.917) between the log normalized data obtained by ELISA+SPE and LC–MS. High correlation among the data obtained by the two tested methods and the LC–MS method by the Center of Disease Control and Prevention (CDC), together with low variability among the blind duplicates, suggests that both methods reported here would be suitable for the analysis of urinary AM as a biomarker for human exposure of atrazine.

Keywords: Atrazine mercapturate; Enzyme-linked immunosorbent assay (ELISA); Solid phase extraction (SPE); Online solid phase extraction; Liquid chromatography–mass spectrometry (LC–MS); Human biomonitoring

Analysis of Strychnos alkaloids in traditional Chinese medicines with improved sensitivity by sweeping micellar electrokinetic chromatography by Chun Wang; Dandan Han; Zhi Wang; Xiaohuan Zang; Qiuhua Wu (pp. 190-196).

The application of an on-line sweeping preconcentration method in micellar electrokinetic chromatography (MEKC) for the determination of Strychnos alkaloids, namely strychnine and brucine, has been investigated in this work. After experimental optimizations, the best separation was achieved in 50mmoll⁻¹ H₃PO₄ (pH 2.0) containing 100mmoll⁻¹ SDS and acetonitrile in a ratio of 4:1 (v/v), with an applied voltage of −20kV at 20°C. The sample matrix consisted of 100mmoll⁻¹ H₃PO₄ (pH 2.0), and sample introduction was performed at 0.5psi for 270s, with photodiode array detection at 203nm. Compared with the conventional MEKC injection method, up to 100-fold improvement in concentration sensitivity was achieved in terms of peak height by using this sweeping injection technique. In the method, the compound berberine was used as the internal standard for the improvement of the experimental reproducibility. The calibration curve was linear over a range of 0.5–15μgml⁻¹ for both strychnine and brucine, with a correlation coefficient of 0.998 and 0.997, respectively. The detection limits (S/N=3:1) for strychnine and brucine were 0.05 and 0.07μgml⁻¹, respectively. The sweeping-MEKC method has been successfully applied to the analysis of strychnine and brucine in Strychnos nux-vomica L. and its Chinese medicinal preparations.

Keywords: Micellar electrokinetic chromatography; Sweeping; Strychnine; Brucine

A novel monolithic column for capillary electrochromatographic separation of oligopeptides by Chun-Chi Lin; Guan-Ren Wang; Chuen-Ying Liu (pp. 197-204).

A monolithic column was prepared usingl-phenylalanine as template and a covalent approach through the formation of Schiff base with o-phthalaldehyde (OPA). OPA, allylmercaptan,l-phenylalanine, and triethylamine were stirred at first, then methacrylic acid, 2-vinylpyridine, ethyleneglycol dimethacrylate, α,α-azobisisobutyronitrile, and 1-propanol were added to the reaction mixture. The resulting material was introduced into a capillary column. Following thermal polymerization, the template was then extracted with a mixture of HCl and methanol. The column was employed for the capillary electrochromatographic separation of oligopeptides. A capillary column of 75 (50)cm×75μm ID with a mobile phase of phosphate buffer (pH 7.0, 40mM)/methanol (5%, v/v), an applied voltage of +15kV, and detection at 214nm, could baseline separate angiotensin I, angiotensin II, [Sar¹, Thr⁸] angiotensin, oxytocin, vasopressin, tocinoic acid, β-casomorphin bovine, β-casomorphin human, and FMRF amide within 20min. The separation behavior of the templated polymer was also compared with that of the non-templated polymer. As a result, it can be concluded that the electrochromatographic separation of this set of peptides was mediated by a combination of electrophoretic migration and chromatographic retention involving hydrophobic, hydrogen bonding, electrostatic as well as the Schiff base formation with OPA in the cavity of the templated polymer.

Keywords: Monolithic column; Capillary electrochromatography; Oligopeptides

A novel monolithic column for capillary electrochromatographic separation of oligopeptides by Chun-Chi Lin; Guan-Ren Wang; Chuen-Ying Liu (pp. 197-204).

Keywords: Monolithic column; Capillary electrochromatography; Oligopeptides

Ultraviolet absorbance detection of colchicine and related alkaloids on a capillary electrophoresis microchip by Qin Lu; Christine L. Copper; Greg E. Collins (pp. 205-211).

The separation and UV absorbance detection of four toxic alkaloids, colchicine, thiocolchicine, colchicoside, and thiocolchicoside, on a microchip-based capillary electrophoresis device are reported. To increase the sensitivity of UV absorbance detection, optical cells with extended path lengths were integrated into the separation channel during the microfabrication process. The absorbance values realized on the microchip using these optical cells were proportional to the increase in average depths according to the Beer-Lambert Law, resulting in sensitivity enhancements by as much as five times. Linearity of response was observed from 5.0 to 500mgL⁻¹ of colchicine, with detection limits ranging from 2 to 6mgL⁻¹ depending upon the specific alkaloid and the dimension of the optical cell. The extraction of colchicine from spiked milk samples was performed and an average recovery rate of 83% with a relative standard deviation of 3.8% was determined using the optimized conditions on the microchip.

Keywords: Colchicine; Alkaloids; Ultraviolet absorbance; Microchip; Capillary electrophoresis

Ultraviolet absorbance detection of colchicine and related alkaloids on a capillary electrophoresis microchip by Qin Lu; Christine L. Copper; Greg E. Collins (pp. 205-211).

Keywords: Colchicine; Alkaloids; Ultraviolet absorbance; Microchip; Capillary electrophoresis

Characterization and application of a new ultraviolet derivatization reagent for amino acids analysis in capillary electrophoresis by Qishu Qu; Xiaoqing Tang; Chengyin Wang; Gongjun Yang; Xiaoya Hu; Xiao Lu; Yin Liu; Shouchun Li; Chao Yan (pp. 212-218).

A new ultraviolet (UV) labeling reagent, p-acetamidobenzenesulfonyl fluoride (PAABS-F), was designed and synthesized to label and determine the amino acids by capillary electrophoresis (CE) with diode-array detector (DAD). PAABS-F is very stable and easy to synthesize. It reacted with primary or secondary amino acids very quickly under facile conditions to give corresponding derivatives in high yield with excellent sensitivity and stability. No by-products were observed in amino acid derivatives when stored at room temperature under natural daylight for at least 7 days. Both amino acids standard solution and real samples reacted with this new UV labeling reagent smoothly to form high UV-absorption derivatives. The labeled 20 standard amino acids were efficiently separated by CE and the mass detection limits ( S/ N=3) were ranged from 59.3fmol forl-tryptophan to 1.70pmol forl-histidine.

Keywords: Abbreviations; PAABS-F; p; -acetamidobenzenesulfonyl fuoride; UV; ultraviolet; CE; capillary electrophoresis; HPLC; high performance liquid chromatography; GC; gas chromatography; OPA; o; -phthaldiadehyde; PITC; phenyl isothiocyanate; Dansyl-Cl; 1-dimethylaminonaphthalene-5-sulphonyl chloride; FDNB; 1-fluoro-2,4-dinitrobenzene; DAD; diode-array detector; PTC; phenylthiocarbamylUltraviolet; Derivatization; Amino acids; Capillary electrophoresis

Puff-by-puff resolved characterisation of cigarette mainstream smoke by single photon ionisation (SPI)-time-of-flight mass spectrometry (TOFMS): Comparison of the 2R4F research cigarette and pure Burley, Virginia, Oriental and Maryland tobacco cigarettes by Thomas Adam; Stefan Mitschke; Thorsten Streibel; Richard R. Baker; Ralf Zimmermann (pp. 219-229).

Soft single photon ionisation (SPI)-time-of-flight mass spectrometry (TOFMS) is applied for the characterisation and comparison of puff-by-puff resolved and total yields of cigarette mainstream smoke from single tobacco type cigarettes (Virginia, Oriental, Burley, and Maryland) and the 2R4F University of Kentucky research cigarette. Puff-by-puff characteristics of various smoke components within one cigarette type as well as between different cigarette types can differ tremendously. This is demonstrated by means of a few selected compounds. Puff yields vary between 15 and 106μm for acetaldehyde, 6 and 57μm for NO, and between 1 and 8μm for butadiene. Thereby, cigarettes containing 100% Oriental and Burley tobacco exhibit a very unique behaviour for the first and last puff. Different cultivation and processing methods as well as burning characteristics are most likely responsible for this. Since the 2R4F cigarette contains all four tobacco types it combines features of all of them. However, for some smoke constituents, smoking of the 2R4F reference cigarette results in exceptionally high yields which might not be attributable to the four pure tobacco types, but to other factors. In addition, comparison of the different cigarettes was also carried out by normalising the yields to puff resolved particulate matter. This procedure minimises effects caused by unequal smoke formation and represents another approach in evaluating the data.

Keywords: Single photon ionisation; Puff-by-puff; Cigarette smoke; Tobacco

Identification of C-21 steroidal glycosides from the roots of Cynanchum chekiangense by high-performance liquid chromatography/tandem mass spectrometry by Yuanpo Tai; Xiaoji Cao; Xiaoyu Li; Yuanjiang Pan (pp. 230-236).

High-performance liquid chromatography coupled with electrospray tandem mass spectrometry (HPLC/ESI–MS/MS) was used to identify C-21 steroidal glycosides with immunological activities in roots of Cynanchum chekiangense. In the MS/MS spectra, fragmentation reactions of the [M+Na]⁺ were recorded to provide structural information about the glycosyl and aglycone moieties. To further confirm the fragments structures, off-line Fourier transform ion cyclotron resonance tandem mass spectrometry (FT-ICR–MS/MS) was also performed. In the study, four known steroidal glycosides cynascyroside C, chekiangensosides A and B, glaucoside H, and four novel steroidal glycosides chekiangensosides C, D, E and chekiangensoside A isomer were identified based on mass spectral data, NMR spectral data and standards. This is the first report on identifying steroidal glycosides in roots of C. chekiangense by HPLC/ESI–MS/MS directly, which could save time and material consuming efforts in traditional phytochemistry analysis.

Keywords: Cynanchum chekiangense; Steroidal glycosides; High-performance liquid chromatography–electrospray tandem mass spectrometry; Fourier transform ion cyclotron resonance–tandem mass spectrometry

Stability-indicating high-performance thin-layer chromatographic determination of levonorgestrel and ethinyloestradiol in bulk drug and in low-dosage oral contraceptives by Ali Reza Fakhari; Afshin Rajabi Khorrami; Mojtaba Shamsipur (pp. 237-242).

A stability-indicating high-performance thin-layer chromatography (HPTLC) method was developed and validated for simultaneous determination of steroidal hormones levonorgestrel and ethinyloestradiol both in bulk drug and in low-dosage oral contraceptives. Optimization of conditions for the spectrodensitometric procedure was reached by eluting HPTLC silica gel plates in a 10cm×10cm horizontal chamber. The solvent system consisted of hexane–chloroform–methanol (1.0:3.0:0.25, v/v/v). This system was found to give compact, dense and typical peaks for both levonorgestrel ( R_f=0.65±0.03) and ethinyloestradiol ( R_f=0.43±0.02). Densitometric analysis of the drugs was carried out in the reflectance mode at 225nm by using a computer controlled densitometric scanner. The calibration curves of levonorgestrel and ethinyloestradiol were linear in the range of 200–800 and 40–160ng per spot, respectively. The method was validated for precision, robustness and recovery. As the proposed method can effectively separate the drugs from their degradation products, it can be employed as a stability-indicating method.

Keywords: Oral contraceptive; Levonorgestrel; Ethinyloestradiol; High-performance thin-layer chromatography determination

Cross-sensitive rare-earth metal sensors based on bidentate neutral organophosphorus compounds and chlorinated cobalt dicarbollide by A.V. Legin; D.O. Kirsanov; V.A. Babain; A.V. Borovoy; R.S. Herbst (pp. 243-247).

A variety of new chemical sensors (ion selective electrodes) for determination of rare-earth (RE) and trivalent metal cations such as yttrium(III), lanthanum(III), praseodymium(III), neodymium(III) and europium(III) that are commonly present in aqueous radiological samples, e.g. in high-level liquid waste (HLW) and solutions from reprocessing spent nuclear fuel, have been developed and studied. The sensors are based on bidentate neutral organophosphorus compounds, such as methylene bridged diphosphine dioxides and carbamoylmethylphosphine oxides, which are efficient extractants, especially when used in conjunction with chlorinated cobalt dicarbollide, for recovery and concentration of the RE and actinide elements from acidic HLW derived from the nuclear fuel cycle. The sensors exhibit remarkable sensitivity to RE cations and indicate promise for HLW analysis.

Keywords: Chemical sensors; Rare-earth cations; Organophosphorus compounds; Chlorinated cobalt dicarbollide

Application of SiO₂–poly(dimethylsiloxane) hybrid material in the fabrication of amperometric biosensor by Wei-Jen Ho; Chiun-Jye Yuan; Ohara Reiko (pp. 248-252).

Silica xerogel was widely used in the development of biosensors by coupling the desired biological components to various transducers. Unfortunately, the application of xerogels is limited due to their poor mechanical properties and poor structural maintenance of entrapped biomaterials. In this study, the availability of poly(dimethylsiloxane) (PDMS)-modified silica sol–gel (TEOS/PDMS Ormosil) glass in the immobilization of enzymes and its application in the fabrication of amperometric biosensor was investigated. We demonstrated that most of activity of encapsulated horseradish peroxidase can be preserved in PDMS-modified SiO₂ glass compared with conventional silica xerogel. The synthesized monoliths exhibited high transparency and crack-free. The enzyme electrode based on glucose oxidase encapsulated TEOS/PDMS Ormosil glass on Pd electrode was fabricated and characterized electrochemically. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The biosensor exhibited a series of good properties: high sensitivity (1.63μAmM⁻¹ analyte), short response time and high reproducibility. The results indicate that TEOS/PDMS Ormosil glass has great potential to the immobilization of biomaterials as well as the fabrication of biosensors.

Keywords: Sol–gel; Ormosil; Enzyme encapsulation; Amperometric biosensor

Application of SiO₂–poly(dimethylsiloxane) hybrid material in the fabrication of amperometric biosensor by Wei-Jen Ho; Chiun-Jye Yuan; Ohara Reiko (pp. 248-252).

Keywords: Sol–gel; Ormosil; Enzyme encapsulation; Amperometric biosensor

Voltammetric determination of boron by using Alizarin Red S by İbrahim Şahin; Nuri Nakiboğlu (pp. 253-258).

A novel voltammetric method for boron determination in ppb level is described. Boron complexes with Alizarin Red S (ARS) and the complex, as well as the free ligand, both adsorbs on a hanging mercury drop electrode. The method is based on the monitoring the anodic peak of the complex at −0.47V in ammonium acetate–phosphate buffer (pH 7). The maximum peak current was obtained by scanning the potential from −700mV versus Ag/AgCl to more positive potentials without accumulation in the presence of 1×10⁻⁶molL⁻¹ of ARS. The instrumental parameters were mainly differential pulse mode with a pulse duration of 0.02s and a scan rate of 5mVs⁻¹. The limit of detection based on signal to ratio of 3 was calculated as 15μgL⁻¹. The calibration plot for boron was linear in the range of 0–500μgL⁻¹. The interference of various ions was examined and serious interference was observed from antimony(III). The relative standard deviation was found to be 5.1% for the 100μgL⁻¹ boron level ( n=10). The method was applied to the determination of boron in water and seawater samples with high boron content. The results obtained from the developed method were compared with Azomethine-H-method and no statistically significant difference was found.

Keywords: Boron; Voltammetry; Alizarin Red S

Voltammetric determination of boron by using Alizarin Red S by İbrahim Şahin; Nuri Nakiboğlu (pp. 253-258).

Keywords: Boron; Voltammetry; Alizarin Red S

Examination of n=2 reaction mechanisms that reproduce pH-dependent reduction potentials by Eugene T. Smith (pp. 259-264).

Flavo- and quinoproteins often exhibit trends in reduction potentials that approximate −30mV per pH unit. At least five different reaction mechanisms can model the behavior described by the following Nernst equation:Eobserved=E0′+(0.059/2)log[H+]. The pH-reduction potential profile described by this equation can be reproduced by various models using different reaction mechanisms, and these mechanisms yield different reduction potentials and acid dissociation constants. In order to understand these discrepancies, this article discusses how the various methods reproduce this pH-dependent Nernst equation.

Keywords: Quinones; pH-dependent redox reactions; Flavoproteins; Bioelectrochemistry

Examination of n=2 reaction mechanisms that reproduce pH-dependent reduction potentials by Eugene T. Smith (pp. 259-264).

Keywords: Quinones; pH-dependent redox reactions; Flavoproteins; Bioelectrochemistry

Variable selection for discriminating herbal medicines with chromatographic fingerprints by Fan Gong; Bo-Tang Wang; Yi-Zeng Liang; Foo-Tim Chau; Ying-Sing Fung (pp. 265-271).

When discriminating herbal medicines with pattern recognition based on chromatographic fingerprints, typically, the majority of variables/data points contain no discrimination information. In this paper, chemometric approaches concerning forward selection and key set factor analysis using principal component analysis (PCA), unweighted and weighted methods based on the inner- and outer-variances, Fisher coefficient from the between- and within-class variations were investigated to extract representative variables. The number of variables retained was determined based on the cumulative variance percent of principal components, the ratio of observations to variables and the factor indicative function (IND). In order to assess the methods for variable selection and criteria levels to determine the number of variables retained, the original and reduced datasets were compared with Procrustes analysis and a weighted measure of similarity. Moreover, the tri-variate plots of the first three PCA scores were used to visually examine the reduced datasets in low dimensional space. Herbal samples were finally discriminated by use of Bayes discrimination analysis with the reduced subsets. The case study for 79 herbal samples showed that, the methods of forward selection associating the variables with the loadings closest to 0 and key set factor analysis were preferable to determine the representative variables. Procrustes analysis and the weighted measure were not indicative to extract representative variables. High matching between the original and reduced datasets did not suggest high prediction accuracy. Visually examining the PC1–PC2–PC3 scores projection plots with the reduced subsets, not all the herb samples could be separated due to the complexity of chromatographic fingerprints.

Keywords: Variable selection; Herbal medicine; Chromatographic fingerprint; Bayes discrimination analysis

Variable selection for discriminating herbal medicines with chromatographic fingerprints by Fan Gong; Bo-Tang Wang; Yi-Zeng Liang; Foo-Tim Chau; Ying-Sing Fung (pp. 265-271).

Keywords: Variable selection; Herbal medicine; Chromatographic fingerprint; Bayes discrimination analysis

Classification study of skin sensitizers based on support vector machine and linear discriminant analysis by Yueying Ren; Huanxiang Liu; Chunxia Xue; Xiaojun Yao; Mancang Liu; Botao Fan (pp. 272-282).

The support vector machine (SVM), recently developed from machine learning community, was used to develop a nonlinear binary classification model of skin sensitization for a diverse set of 131 organic compounds. Six descriptors were selected by stepwise forward discriminant analysis (LDA) from a diverse set of molecular descriptors calculated from molecular structures alone. These six descriptors could reflect the mechanic relevance to skin sensitization and were used as inputs of the SVM model. The nonlinear model developed from SVM algorithm outperformed LDA, which indicated that SVM model was more reliable in the recognition of skin sensitizers. The proposed method is very useful for the classification of skin sensitizers, and can also be extended in other QSAR investigation.

Keywords: Classification; Skin sensitization; Linear discriminant analysis; Support vector machine

Resonance Rayleigh scattering study on the interaction of gold nanoparticles with berberine hydrochloride and its analytical application by Shao Pu Liu; Zhuo Yang; Zhong Fang Liu; Jiang Tao Liu; Yan Shi (pp. 283-289).

The interaction of gold nanoparticles with berberine hydrochloride has been studied by using resonance Rayleigh scattering (RRS) spectra. In pH 3.8–5.5 aqueous solution, citrate acid ([H₂L²⁻]) self-assembled on the surface of positively charged gold nanoparticles (average diameter is about 12.0nm) to form a supermolecular complex with negative charges. By virtue of electrostatic attraction, hydrophobic force and charge transfer, the complex bound with berberine to form complex, which had bigger diameter (35nm) than gold nanoparticles. The formation of the binding production not only resulted in the red shift of absorption of gold nanoparticles from 518 to 672nm, but also led to the greatly enhancement of RRS intensity. At the same time, the intensities of second-order scattering (SOS) and frequency-doubling scattering (FDS) were also increased. Under definite condition, the increment of the RRS (Δ I) were proportional to the concentration of berberine. A sensitive and simple method for the determination of berberine based on the RRS technique has been developed. The detection limit (3 σ) for berberine was 0.40ngmL⁻¹ and the quantitative determination range was 1.33–240ngmL⁻¹. In this work, the optimum conditions of reaction, the effect of foreign substances and the analytical application had been investigated.

Keywords: Resonance Rayleigh scattering; Gold nanoparticle; Berberine hydrochloride

Sonoelectrochemical synthesis of spike-like gold–silver alloy nanoparticles from bulk substrates and the application on surface-enhanced Raman scattering by Yu-Chuan Liu; Kuang-Hsuan Yang; Shung-Jim Yang (pp. 290-294).

The synthesis of non-spherical spike-like gold–silver alloy nanoparticles on platinum substrates was first developed by sonoelectrochemical methods in this study. First, a silver substrate was roughened by a triangular-wave oxidation–reduction cycle (ORC) in an aqueous solution containing 0.1M HCl. Silver-containing complexes were found in the solution after the ORC treatment. Then a gold substrate was subsequently roughened by the similar ORC treatment in the same silver complexes-containing solution. After this procedure, Au- and Ag-containing complexes were left in the solution. Subsequently, the Au working electrode was immediately replaced by a Pt electrode. A cathodic overpotential was applied under controlled sonication and slight stirring to synthesize Au–Ag alloy nanoparticles on the Pt substrate. Encouragingly, the surface-enhanced Raman scattering (SERS) of Rhodamine 6G on the Au–Ag alloy nanoparticles-deposited Pt substrate exhibits a higher intensity by eight-fold of magnitude and a better resolution, as compared to that obtained on the Au nanoparticles-deposited Pt substrate.

Keywords: Gold–silver alloy nanoparticles; Sonoelectrochemical methods; Surface-enhanced Raman scattering; Oxidation–reduction cycle; Spike-like structure

Novel self-protective phosphorescence from crystalline nanoparticles assembled by 3-bromo- and 3-iodo-carbazoles based on halogen–halogen interaction in suspension solutions by Wen Juan Liang; Yu Wang; Feng Feng; Wei Jun Jin (pp. 295-302).

The crystalline nanoparticles can be assembled by 3-bromo- and 3-iodo-carbazole (3-BrC and 3-IC) based on the halogen–halogen interaction in suspension aqueous solutions. As the colloid-like suspension was dropped onto film the particles further aggregate as rod-like structures with size of 3μm in length and 1μm in width. The halogen–halogen interaction are well proved by single crystal X-ray data, and the data reveal that each bromine atom interacts with the neighboring two, and each iodine atom interacts with the neighboring five and I–I interaction is stronger than that of Br–Br. Both 3-BrC and 3-IC can emit novel self-protective room temperature phosphorescence (RTP) in the range of 480 to near 800nm at the excitation of 338nm, and 3-BrC shows additionally the delayed fluorescence emission from 350 to 480nm, both possessing the charge-transfer character caused by halogenations. RTP decay possesses the bi-exponential property and RTP lifetimes are 3.37, 31.16ms (with ethanol) and 1.52, 30.83ms (with THF) for 3-BrC or 3.53, 14.95ms (with ethanol) and 1.68ms, 13.74ms (with THF) for 3-IC, showing “ heavier atom �?, I, makes intersystem crossing rate k_ISC from both S₁ to T₁ and T₁ to S₀ faster. For the results, the detection limits of 3-BrC and 3-IC can reach 2.4×10⁻⁷ and 9.0×10⁻⁸molL⁻¹, respectively, with wider linear range and higher precision compared with other systems.

Keywords: 3-Bromocarbazole; 3-Iodocarbazole; Room temperature phosphorescence; Halogen–halogen interaction

The crystalline nanoparticles can be assembled by 3-bromo- and 3-iodo-carbazole (3-BrC and 3-IC) based on the halogen–halogen interaction in suspension aqueous solutions. As the colloid-like suspension was dropped onto film the particles further aggregate as rod-like structures with size of 3μm in length and 1μm in width. The halogen–halogen interaction are well proved by single crystal X-ray data, and the data reveal that each bromine atom interacts with the neighboring two, and each iodine atom interacts with the neighboring five and I–I interaction is stronger than that of Br–Br. Both 3-BrC and 3-IC can emit novel self-protective room temperature phosphorescence (RTP) in the range of 480 to near 800nm at the excitation of 338nm, and 3-BrC shows additionally the delayed fluorescence emission from 350 to 480nm, both possessing the charge-transfer character caused by halogenations. RTP decay possesses the bi-exponential property and RTP lifetimes are 3.37, 31.16ms (with ethanol) and 1.52, 30.83ms (with THF) for 3-BrC or 3.53, 14.95ms (with ethanol) and 1.68ms, 13.74ms (with THF) for 3-IC, showing “ heavier atom ”, I, makes intersystem crossing rate k_ISC from both S₁ to T₁ and T₁ to S₀ faster. For the results, the detection limits of 3-BrC and 3-IC can reach 2.4×10⁻⁷ and 9.0×10⁻⁸molL⁻¹, respectively, with wider linear range and higher precision compared with other systems.

Keywords: 3-Bromocarbazole; 3-Iodocarbazole; Room temperature phosphorescence; Halogen–halogen interaction

Palladium and the electrochemical quartz crystal microbalance: A new method for the in situ analysis of the precious metal in aqueous solutions by Nathan A. Carrington; D. Lynn Rodman; Zi-Ling Xue (pp. 303-308).

A new method for the quantitative determination of palladium(II) by the electrochemical quartz crystal microbalance (EQCM) technique has been developed. Using a bare carbon-coated quartz crystal, Pd(II) ions are directly deposited from aqueous solution as palladium metal onto the crystal surface, and the Pd(II) concentration is determined with a detection limit of 0.0156mM, or 1.66ppm. No complexing agent or preconcentration of palladium is required for the analysis. The palladium is stripped from the crystal through its electrochemical oxidation, regenerating the crystal for subsequent multi- cycle palladium analyses. A conventional gold-coated quartz crystal was incapable of carrying out the same measurements. The EQCM technique presented is simple, sensitive, and reproducible for the detection of this widely used precious metal.

Keywords: Electrochemical quartz crystal microbalance; Palladium; Carbon-coated quartz crystal; Electrochemistry

A comprehensive immunoassay for the detection of microcystins in waters based on polyclonal antibodies by Jian-Wu Sheng; Miao He; Han-Chang Shi; Yi Qian (pp. 309-315).

Microcystins (MCs) are a group of closely related toxic cyclic heptapeptides produced by common cyanobacteria (blue-green algae), and microcystin–leucine–arginine (MC-LR) is among the most frequent and most toxic microcystin congeners. In this study, a free amino group was introduced to MC-LR at its seventh amino acid residue with 2-mercaptoethylamine, and the product aminoethyl-MC-LR was coupled to bovine serum albumin (BSA) and horseradish peroxidise (HRP) by glutaraldehyde to be complete antigen (MC-LR-BSA) and labelled hapten (MC-LR-HRP), respectively. Polyclonal antibodies against MC-LR were generated by immunization with MC-LR-BSA. A direct competitive enzyme-linked immunosorbent assay (dc-ELISA) was established to detect the MCs in waters, which showed a good cross-reactivity with MC-LR, MC-RR, MC-YR, MC-LF, MC-LW and nodularin, and have a detection limit for MC-LR 0.12μgL⁻¹, the 50% inhibition concentration (IC₅₀) for MC-LR was 0.63±0.06μgL⁻¹ and the quantitative detection range was from 0.17 to 2.32μgL⁻¹, the analysis result of water samples showed good recovery and reliability. So the comprehensive and reliable dc-ELISA will well potentially suit for sensitive analysis for total MCs in drinking as well as resource water samples.

Keywords: Microcystins; Coupling ratio; Polyclonal antibody; Enzyme-linked immunosorbent assay (ELISA)

A comprehensive immunoassay for the detection of microcystins in waters based on polyclonal antibodies by Jian-Wu Sheng; Miao He; Han-Chang Shi; Yi Qian (pp. 309-315).

Keywords: Microcystins; Coupling ratio; Polyclonal antibody; Enzyme-linked immunosorbent assay (ELISA)

A novel flow-based strategy for implementing differential kinetic analysis by Paula R. Fortes; Silvia R.P. Meneses; Elias A.G. Zagatto (pp. 316-320).

Differential kinetic analysis can be implemented in a multi-pumping flow system, and this was demonstrated in relation to an improved spectrophotometric catalytic determination of iron and vanadium in Fe–V alloys. The method exploited the influence of Fe(II) and V(IV) on the rate of iodide oxidation by Cr(VI) under acidic conditions; therefore the Jones reductor was needed. The sample was inserted into an acidic KI stream that acted also as carrier stream, and a Cr(VI) solution was added by confluence. Successive measurements were performed during sample passage through the detector, each one related to a different yet reproducible condition for reaction development. Data treatment involved multivariate calibration by the PLS algorithm.The proposed system is very simple and rugged, allowing about 50 samples to be run per hour, meaning 48mg KI per determination. The first two latent variables carry ca. 94% of the analytical information, pointing out that the intrinsic dimensionality of the data set is two. Results are in agreement with inductively coupled argon plasma–optical emission spectrometry.

Keywords: Flow analysis; Differential kinetic analysis; Partial least squares; Catalytic methods; Multi-pumping flow system; Spectrophotometry

A novel flow-based strategy for implementing differential kinetic analysis by Paula R. Fortes; Silvia R.P. Meneses; Elias A.G. Zagatto (pp. 316-320).

Keywords: Flow analysis; Differential kinetic analysis; Partial least squares; Catalytic methods; Multi-pumping flow system; Spectrophotometry

Author index (pp. 321-323).

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Analytica Chimica Acta (v.572, #2)

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Analytica Chimica Acta (v.572, #2)