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Analytica Chimica Acta (v.694, #1-2)

Editorial Board (pp. iii).

Lectin typing of Campylobacter jejuni using a novel quartz crystal microbalance technique by Maria E. Yakovleva; Anthony P. Moran; Gulnara R. Safina; Torkel Wadström; Bengt Danielsson (pp. 1-5).

Seven Campylobacter jejuni strains were characterised by a lectin typing assay. The typing system was based on a quartz crystal microbalance technique (QCM) with four commercially available lectins (wheat germ agglutinin, Maackia amurensis lectin, Lens culinaris agglutinin, and Concanavalin A), which were chosen for their differing carbohydrate specificities. Initially, the gold surfaces of the quartz crystals were modified with 11-mercaptoundecanoic acid followed by lectin immobilisation using a conventional amine-coupling technique. Bacterial cells were applied for lectin typing without preliminary treatment, and resonant frequency and dissipation responses were recorded. The adhesion of microorganisms on lectin surfaces was confirmed by atomic force microscopy. Scanning was performed in the tapping mode and the presence of bacteria on lectin-coated surfaces was successfully demonstrated. A significant difference in the dissipation response was observed for different C. jejuni strains which made it possible to use this parameter for discriminating between bacterial strains. In summary, the QCM technique proved a powerful tool for the recognition and discrimination of C. jejuni strains. The approach may also prove applicable to strain discrimination of other bacterial species, particularly pathogens.

Keywords: Campylobacter jejuni; Lectin typing; Quartz crystal microbalance; Energy dissipation; Atomic force microscopy

Nanotechnology and chip level systems for pressure driven liquid chromatography and emerging analytical separation techniques: A review by N.V. Lavrik; L.T. Taylor; M.J. Sepaniak (pp. 6-20).

Pressure driven liquid chromatography (LC) is a powerful and versatile separation technique particularly suitable for differentiating species present in extremely small quantities. This paper briefly reviews main historical trends and focuses on more recently developed technological approaches in miniaturization and on-chip integration of LC columns. The review emphasizes enabling technologies as well as main technological challenges specific to pressure driven separations and highlights emerging concepts that could ultimately overcome fundamental limitations of conventional LC columns.

Keywords: Microfluidic; Pressure driven separation; HPLC; Pillar arrays; Liquid chromatography; Nanocolumns

Development of analytical procedure for the determination of methyltin, butyltin, phenyltin and octyltin compounds in landfill leachates by gas chromatography–inductively coupled plasma mass spectrometry by Mitja Vahčič; Radmila Milačič; Janez Ščančar (pp. 21-30).

Display Omitted► Methyl-, butyl-, phenyl- and octyl-tins in landfill leachates was determined. ► Simultaneous determination based on GC-ICP-MS. ► Procedure enables routine monitoring of organotins in landfill leachates.Landfilling is the most common disposal of municipal waste. During the decomposition of different waste materials, several toxic compounds are leached. Although organotin compounds (OTC) represent an important group of pollutants in landfill leachates, there are only few analytical procedures reported for their analysis. These procedures are complex or recommend the use of enriched stable isotopes that are available only for butyltins. In the present work analytical procedure for simultaneous routine speciation analysis of methyl-, butyl-, phenyl- and octyl-tins in landfill leachates by GC–ICP-MS was developed. For this purpose the applicability of methanol as co-extraction reagent and Tris–citrate buffer for adjustment of pH for derivatization of OTC in landfill leachates was carefully investigated. The use of NaBEt₄ and NaBPr₄ as derivatization reagents for liquid–liquid extraction into hexane was critically evaluated. 15m GC column was used for rapid separation of OTC. The developed analytical procedure was sensitive (LODs for OTC investigated in general better than 2ngSnL⁻¹) with good repeatability of measurement (RSDs mostly better than 3%) and was successfully applied in the analysis of OTC in landfill leachates using standard addition calibration method. Due to its simplicity and reliability it is appropriate to be used in routine laboratories for monitoring of OTC in landfill leachates.

Keywords: Methyltin, butyltin, phenyltin, octyltin compounds; Landfill leachates; Analytical procedure; Gas chromatography–inductively coupled plasma mass spectrometry

Estimation of the age of a weathered mixture of volatile organic compounds by Brianne M. Zorzetti; Jeremy M. Shaver; James J. Harynuk (pp. 31-37).

The ability to predict the amount of time that a light petroleum mixture has been weathered could have many applications, such as aiding forensic investigators in determining the cause and intent of a fire. In our study, an evaporation chamber that permits control of airflow and temperature was constructed and used to weather a model nine-component hydrocarbon mixture. The composition of the mixture was monitored over time by gas chromatography and a variety of chemometric models were explored, including partial least squares (PLS), nonlinear PLS (PolyPLS) and locally weighted regression (LWR or loess). A hierarchical application of multivariate techniques was able to predict the time for which a sample had been exposed to evaporative weathering. A classification model based on partial least squares discriminant analysis (PLS-DA) could predict whether a sample was relatively fresh (< 12h exposure time) or highly weathered (>20h exposure time). Subsequent regression models for these individual classes were evaluated for accuracy using the root mean square error of prediction (RMSEP). Prior to regression model calculation, y-gradient generalized least squares weighting (GLSW) was used to preprocess the data by removing variance from the X-block, which was orthogonal to the Y-block. LWR was found to be the most successful regression method, whereby fresh samples could be predicted to within 40min of exposure and highly weathered samples predicted to within 5.6h. These results suggest that our hierarchical chemometric approach may also allow us to estimate the age of more complicated light petroleum mixtures, such as gasoline.

Keywords: Gas chromatography; y; -Gradient generalized least squares weighting; Weathering; Partial least squares discriminant analysis; Locally weighted regression

Flatbed scanners as a source of imaging. Brightness assessment and additives determination in a nickel electroplating bath by M. Vidal; J.M. Amigo; R. Bro; M. Ostra; C. Ubide; J. Zuriarrain (pp. 38-45).

Desktop flatbed scanners are very well-known devices that can provide digitized information of flat surfaces. They are practically present in most laboratories as a part of the computer support. Several quality levels can be found in the market, but all of them can be considered as tools with a high performance and low cost. The present paper shows how the information obtained with a scanner, from a flat surface, can be used with fine results for exploratory and quantitative purposes through image analysis. It provides cheap analytical measurements for assessment of quality parameters of coated metallic surfaces and monitoring of electrochemical coating bath lives. The samples used were steel sheets nickel-plated in an electrodeposition bath. The quality of the final deposit depends on the bath conditions and, especially, on the concentration of the additives in the bath. Some additives become degraded with the bath life and so is the quality of the plate finish. Analysis of the scanner images can be used to follow the evolution of the metal deposit and the concentration of additives in the bath. Principal component analysis (PCA) is applied to find significant differences in the coating of sheets, to find directions of maximum variability and to identify odd samples. The results found are favorably compared with those obtained by means of specular reflectance (SR), which is here used as a reference technique. Also the concentration of additives SPB and SA-1 along a nickel bath life can be followed using image data handled with algorithms such as partial least squares (PLS) regression and support vector regression (SVR). The quantitative results obtained with these and other algorithms are compared. All this opens new qualitative and quantitative possibilities to flatbed scanners.

Keywords: Image analysis; Flatbed scanner; Principal component analysis; Partial least squares regression; Support vector regression; Nickel electrodeposition; Coating quality

Detection of antibiotic residues in bovine milk by a voltammetric electronic tongue system by Zhenbo Wei; Jun Wang (pp. 46-56).

A voltammetric electronic tongue (VE-tongue) was developed to detect antibiotic residues in bovine milk. Six antibiotics (Chloramphenicol, Erythromycin, Kanamycin sulfate, Neomycin sulfate, Streptomycin sulfate and Tetracycline HCl) spiked at four different concentration levels (0.5, 1, 1.5 and 2 maximum residue limits (MRLs)) were classified based on VE-tongue by two pattern recognition methods: principal component analysis (PCA) and discriminant function analysis (DFA). The VE-tongue was composed of five working electrodes (gold, silver, platinum, palladium, and titanium) positioned in a standard three-electrode configuration. The Multi-frequency large amplitude pulse voltammetry (MLAPV) which consisted of four segments (1Hz, 10Hz, 100Hz and 1000Hz) was applied as potential waveform. The six antibiotics at the MRLs could not be separated from bovine milk completely by PCA, but all the samples were demarcated clearly by DFA. Three regression models: Principal Component Regression Analysis (PCR), Partial Least Squares Regression (PLSR), and Least Squares-Support Vector Machines (LS-SVM) were used for concentrations of antibiotics prediction. All the regression models performed well, and PCR had the most stable results.

Keywords: Electronic tongue; Antibiotics; Principal component analysis; Discriminant function analysis; Partial Least Squares Regression

A simple contactless impedance probe for determination of ethanol in gasoline by F. Opekar; R. Čabala; T. Kadlecová (pp. 57-60).

A contactless impedance probe with either a planar or a tubular detection cell has been developed and tested for rapid determination of the ethanol content in gasoline. The probe cell is connected as a capacitor determining the frequency of an electronic astable multivibrator. The multivibrator frequency depends on the permittivity of the test gasoline in the detection cell which is strongly influenced by the ethanol content as one of the major polar additives. The ethanol concentrations obtained with the impedance probe agree, within the reliability interval, with those obtained by GC–MS measurements and fall into the limits recommended by the appropriate European Standard. The gasoline samples are analyzed without any pretreatment.

Keywords: Contactless impedance detection; Planar cell; Tubular cell; Ethanol; Gasoline; GC–MS

Study on urinary metabolic profile of phenylketonuria by micellar electrokinetic capillary chromatography with dual electrochemical detection—Potential clinical application in fast diagnosis of phenylketonuria by Dongli Zhang; Wenli Li; Junbo Zhang; Wanrong Tang; Chenxu Qian; Minghao Feng; Qingcui Chu; Jiannong Ye (pp. 61-66).

The urinary metabolic marker compounds, namely phenylpyruvic acid (PPA), 2-hydroxyphenylacetic acid (oOPAA), 4-hydroxyphenylacetic acid (pOPAA), phenyllactic acid (PLA) and phenylacetic acid (PAA) of phenylketonuric individuals were detected by a novel method of micellar electrokinetic capillary chromatography with capacitively coupled contactless conductivity detection and amperometric detection (MECC-C⁴D/AD). Electrophoretic runs were performed in a 35mmolL⁻¹ SDS/60mmolL⁻¹ H₃BO₃–Na₂B₄O₇ running buffer (pH 8.2) at a separation voltage of 16kV, and five marker compounds and the major coexisting compound uric acid (UA) could be well separated within 23min. Highly linear response was obtained for five marker compounds over three orders of magnitude with detection limits ranging from 6.6×10⁻⁶ to 6.4×10⁻⁸gmL⁻¹ (S/N=3). The proposed method has been used to detect the marker compounds simultaneously in urine samples with the advantages of obtaining more information about target analytes and avoiding redundant measurements and high assay cost. Urinary patterns in phenylketonuric babies were distinct and easily distinguished from those of healthy newborns. The proposed MECC-C⁴D/AD method could find clinical application in early noninvasive diagnosis of phenylketonuria (PKU), as significant differences could be found in the urinary content of five marker compounds among the phenylketonuric babies without or with dietotherapy and the healthy babies.

Keywords: Phenylketonuria (PKU); Micellar electrokinetic capillary chromatography with dual electrochemical detection (MECC-C; ⁴; D/AD); Urine; Marker compound; Phenylpyruvic acid

Determination of indoor air quality of a phytosanitary plant by Daniel Sanjuán-Herráez; Yelko Rodríguez-Carrasco; Luis Juan-Peiró; Agustín Pastor; Miguel de la Guardia (pp. 67-74).

A new methodology has been developed to determine volatile organic compounds (VOCs) and pesticides in ambient air using membrane based devices as passive samplers. Pesticides were determined by gas chromatography with mass spectrometry detection (GC–MS) after their microwave-assisted extraction (MAE) from the passive sampler and the required clean-up. On the other hand, VOCs were also caught with the same samplers and directly determined by head space (HS) coupled to GC–MS. The use of samplers filled with florisil and activated carbon allows us to catch with a simple device both, VOCs and pesticides, with a high vapor pressure. Results obtained in the deployment of samplers in different sites of a phytosanitary plant evidenced the presence of high quantities of chlorpyriphos at thousand ngm³ and also metalaxyl, oxyfluorphen and lindane at ngm³ together with carbon disulfide, 2,2,4-trimethylpentane, ethylbenzene and xylene.

Keywords: Phytosanitary plant; Passive samplers; Air quality; Pesticides; Volatile organic compounds

Membrane assisted passive sampler for triazine compounds in water bodies—Characterization of environmental conditions and field performance by Hlengilizwe Nyoni; Luke Chimuka; Branislav Vrana; Ewa Cukrowska (pp. 75-82).

In this work, a simple, inexpensive and very selective membrane assisted passive sampler (MAPS) that does not use organic solvents, based on a thin walled silicone hollow fibre membrane for extraction of ionizable organic compounds in water bodies is reported. The potential for passive sampling of basic compounds is demonstrated. By changing the acceptor solution from acidic to basic conditions, the MAPS can be successfully used to extract acidic organic compound. The influence of environmental factors such as temperature, sample matrix and hydrodynamics on enrichment factors and sampling rates have been investigated in order to calibrate the passive sampler for measurement of TWA concentration of triazines. The selectivity, extraction efficiency and enrichment factor of the developed sampler has been compared to the Chemcatcher passive sampler.It was found that the chemical uptake of basic triazine compounds into the passive sampler remained linear and integrative throughout the 7 days exposure periods. For atrazine, propazine, prometryne and terbutryne a large 3 days time lag was experienced. A plot of natural logarithms of the amount taken up by the sampler against exposure time gave linear relationship for these compounds. The sampling rates for individual triazine compounds increased with change of hydrodynamic conditions from static to turbulent. The presence of 20mgL⁻¹ humic substances in solution was found to have no significant effect on the concentration of compounds trapped in the acceptor solution. Once these compounds are trapped in the acceptor solution they do not diffuse back during the deployment period. A strong dependence of the sampling rates on the type of protective cover used was noted. Stainless steel protective cover was found to be the better than the iron mesh as it did not rust during deployment. The detection limits on HPLC with UV detection ranged from 0.50 to 4.50μgL⁻¹ for MAPS, 0.40 to 3.50μgL⁻¹ for Chemcatcher passive sampler and 0.35 to 4.50μgL⁻¹ for SPE with 7 days exposure of passive samplers. Preliminary field trial of the potential of the MAPS to monitor ionizable triazine compounds in Hartebeespoort dam found west of Johannesburg, South Africa was compared to Chemcatcher and SPE technique with C₁₈ sorbents for grab samples. No quantifiable amounts of triazine compounds were found in any of the deployed passive samplers in the preliminary field applications. Triazine compounds were also not detected in grab samples after SPE. However, data from laboratory studies support the feasibility of MAPS to measure the freely dissolved fraction of ionizable organic chemicals in water. The MAPS also exhibited slightly better selectivity towards matrix components found in natural water compared to SPE technique or Chemcatcher with C₁₈ disk as trapping media.

Keywords: Water monitoring; Passive sampling; MAPS; Environmental factors; Triazines; HPLC/UV

Supported liquid membrane-protected molecularly imprinted fibre for solid-phase microextraction of thiabendazole by Francisco Barahona; Esther Turiel; Antonio Martín-Esteban (pp. 83-89).

In this work, molecularly imprinted polymer fibres (MIP-fibre) have been prepared and evaluated for solid-phase microextraction (SPME), using thiabendazole (TBZ) as template. Inherent limitations of molecular imprinted polymers, such as target recognition in aqueous media, have been solved with the use of organic supported liquid membrane (SLM) protecting the MI-SPME process.MIP-fibres were located inside a polypropylene hollow capillary and protected by an organic solvent immobilized as a thin SLM in the pores of the capillary wall. The extraction procedure involved two simultaneous processes: liquid phase microextraction using polypropylene hollow fibres (HF-LPME) of the analytes from the sample to an organic acceptor solution through a SLM; and SPME of the analytes from the organic acceptor solution to a MIP-fibre inside the polypropylene capillary.The developed methodology was optimized and applied to the extraction of TBZ form spiked orange juices. Calibration curves showed good linearity in the concentration range under study (0.01–5.00mgL⁻¹) and a regression coefficient better than 0.995 was obtained. The detection limit was 4μgL⁻¹, low enough to permit the satisfactory analysis of TBZ in real samples, according to European regulation. Relative standard deviations ranged below 10%, indicating good repeatability.By this manner, the advantages of inherent selectivity of MIP SPME fibres and the enrichment and sample cleanup capability of the HF-LPME have been successfully combined into a single device.

Keywords: Molecularly imprinted polymers; Solid-phase microextraction; Hollow fibre liquid-phase microextraction

Flow injection determination of free fatty acids in vegetable oils using capacitively coupled contactless conductivity detection by Ahmad Makahleh; Bahruddin Saad (pp. 90-94).

A single line flow injection analysis (FIA) method that incorporated a preconcentrator column packed with C₁₈ particles and capacitively coupled contactless conductivity detector (C⁴D) was developed for the determination of free fatty acid (FFA) in vegetable oils. The carrier stream was methanol/1.5mM sodium acetate (pH 8) 80:20 (v/v) at a flow rate of 1.0mLmin⁻¹. Calibration curve was well correlated ( r²=0.9995) within the range of 1–200mgL⁻¹ FFA (expressed as palmitic acid). Sampling rate of 40–60h⁻¹ was achieved. Good agreement was found between the standard non-aqueous titrimetry method and the proposed method when applied to the determination of FFA in palm (crude, olein, and refined, bleached and deodorised) and other vegetable (soybean, rice bran, walnut, corn and olive) oils. The proposed method offers distinct advantages over the official method, especially in terms of simplicity, high sampling rate, economy of solvents and sample, offering considerable promise as a low cost automated system that needs minimum human intervention over long periods of time.

Keywords: Flow injection analysis (FIA); Capacitively coupled contactless conductivity detector (C; ⁴; D); Free fatty acids; Vegetable oil

Liquid–liquid microextraction without phase separation in a multicommuted flow system for diltiazem determination in pharmaceuticals by Mariana A. Sanchez; Fábio R.P. Rocha (pp. 95-99).

Liquid–liquid microextraction without phase segmentation was implemented in a multicommuted flow system for determination of the anti-hypertensive diltiazem. The procedure was based on ion pair formation between the drug and the dye bromothymol blue at pH 3.5. The detection was performed without phase separation in a glass tube coupled to a fiber-optics spectrophotometer. The total volume of chloroform was reduced to 50μL in comparison with 10mL consumed in batch. A linear response was observed between 9 and 120μmolL⁻¹, with a detection limit of 0.9μmolL⁻¹ (99.7% confidence level). The coefficient of variation ( n=10), sampling rate and extraction efficiency were estimated as 0.6%, 78 determinations per hour and 61%, respectively. About 30μg of bromothymol blue was consumed and the waste volume was 380μL per determination. The results for pharmaceutical samples agreed with those obtained by the reference procedure at the 95% confidence level.

Keywords: Flow analysis; Liquid–liquid microextraction; Multicommutation; Spectrophotometry; Diltiazem

Three aromatic amino acids in gastric juice as potential biomarkers for gastric malignancies by Kai Deng; Sanren Lin; Liya Zhou; Qiuming Geng; Yuan Li; Ming Xu; Renhua Na (pp. 100-107).

.Display Omitted► Offering three potential gastric juice biomarkers in screening gastric cancer.For screening early-stage gastric malignancies, the existing serum biomarkers have limited sensitivity and specificity. Gastric juice biomarkers are scarce and require further investigation. We divided this study on searching potential biomarkers into four parts: (1) detection of differential fluorescence spectrum and peaks in the gastric juice from patients using fluorescence spectroscopy and HPLC, (2) identification and validation of differential peaks using LC/MS and NMR, (3) quantification of potential biomarkers, and (4) establishment of diagnostic detection. The fluorescence intensity (FI), tyrosine, phenylalanine, tryptophan and total protein content were significantly higher in the gastric juice of patients with gastric malignancies (all P<0.01). With all P<0.001, the areas under the receiver operating characteristic curves of the biomarkers were tyrosine, 0.838; phenylalanine, 0.856; and tryptophan, 0.816. At a specificity of 79.4%, the sensitivity for gastric malignancy detection with phenylalanine was 87.9% only. Aromatic amino acids in gastric juices could be used as potential diagnostic biomarkers to screen gastric malignancies. It is a less-invasive and economical method compared to gastric biopsy.

Keywords: Aromatic amino acid; Gastric juice biomarker; Gastric malignancy; High performance liquid chromatography; Mass spectrometry; Nuclear magnetic resonance

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry of polychlorinated biphenyls by Taiki Matsui; Tomohiro Uchimura; Totaro Imasaka (pp. 108-114).

A sample mixture of polychlorinated biphenyls (PCBs) was measured by gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) using four types of laser sources. When a fourth harmonic emission (266nm) of a picosecond Nd:YAG laser (1064nm) was utilized, highly chlorinated PCBs larger than hepta-CBs were not observed. A fifth harmonic emission (213nm) of the picosecond Nd:YAG laser allowed the measurement of PCBs from di-CBs to octa-CBs, and the limit of detection (LOD) was several pg for each component of PCBs. The LOD for the total amount of PCBs, which was calculated using the protocol provided by the Ministry of the Environment, Japan, was 1000pg. The signal intensity of the congeners with chlorine atoms at the ortho positions (non-coplanar PCBs) was enhanced by using the fifth harmonic emission. When the fourth harmonic emission remaining after fifth harmonic generation was simultaneously used, the LOD for total PCBs was improved to 667pg. The PCB sample was also measured using a third harmonic emission (267nm) of a femtosecond Ti:sapphire laser (800nm), providing an LOD of 677pg. Thus, the two-color beam (266/213nm) of a picosecond Nd:YAG laser had a comparable, or even slightly superior, performance to the more expensive femtosecond Ti:sapphire laser.

Keywords: Polychlorinated biphenyls; Gas chromatography; Multiphoton ionization; Time-of-flight mass spectrometry

Colorimetric assay for mercury (II) based on mercury-specific deoxyribonucleic acid-functionalized gold nanoparticles by Jikui Wu; Lanying Li; Dan Zhu; Pingang He; Yuzhi Fang; Guifang Cheng (pp. 115-119).

A colorimetric nanoprobe—mercury-specific DNA-functionalized gold nanoparticles (Au–MSD) was developed for sensing Hg²⁺. The new mercury-sensing concept relies on measuring changes in the inhibition of “non-crosslinking” aggregation of Au–MSD-induced by the folding of mercury-specific DNA strand through the thymine–Hg²⁺–thymine (T–Hg²⁺–T) coordination. In the absence of Hg²⁺, a high concentration of MgCl₂ (50mM) results in a rapid aggregation of Au–MSD because of the removal of charge repulsion. When Hg²⁺ is present, the particles remain stable due to the folding of MSD functionalized on the particle surface. The assay enables the colorimetric detection of Hg²⁺ in the concentration range of 0.1–10μM Hg²⁺ ions with a detection limit of 60nM, and allows for the selective discrimination of Hg²⁺ ions from the other competitive metal ions. Toward the goal for practical applications, the sensor was further evaluated by monitoring Hg²⁺ in fish tissue samples.

Keywords: Colorimetric detection; Mercury; DNA; Nanoparticles; Sensors

A novel glycoconjugated N-acetylamino aldehyde hydrazone azo dye as chromogenic probe for cyanide detection in water by Jalal Isaad; Ahmida El Achari (pp. 120-127).

A new selective chemodosimeter probe of cyanide anions in aqueous media was developed by the introduction of a simple glyco-conjugated o-(carboxamido) aldehyde hydrazone into an azo dye as chemodosimeter that recognizes cyanide anions among other competing anions such as acetate, dihydrogen phosphate, fluoride through reversible covalent bonding. The sensing properties of the new materials were investigated in pure water and have demonstrated a very high selectivity toward the cyanide anions. The detection limit of the new chromogenic probe was measured to be 1.29μM which is much lower than most recently reported chromogenic probes for cyanide determination.

Keywords: Cyanide sensing; Internal charge transfer; o; -(carboxamido) hydrazone; Carbohydrate; Water

A surface fit approach with a disposable optical tongue for alkaline ion analysis by M.M. Erenas; O. Piñeiro; M.C. Pegalajar; M.P. Cuellar; I. de Orbe-Payá; L.F. Capitán-Vallvey (pp. 128-135).

A disposable optical tongue for the alkaline ions Na(I) and K(I) is described. The two-sensor layout prepared on a transparent support consists of non-specific polymeric membranes working by ionophore–chromoionophore chemistry. The non-specific behavior of the membranes was controlled by means of the crown ether-type ionophore present. The imaging of the tongue, after reaction for 3min with the unknown solution, by means of a conventional flatbed scanner working by transmission mode, makes it possible to calculate the H (hue) value of the hue, saturation, value (HSV) color space used as a robust and precise analytical parameter. The modelling of the response of the two-sensor tongue as a sigmoidal surface is used to characterize the behavior of the tongue and as a basis to infer the concentration values. To compute the concentration of two analytes from the two hue values obtained using the optical tongue, a surface fit approach was used. The tongue works over a wide dynamic range (1.0×10⁻⁴–0.1M both in Na(I) and K(I)). The sensing membranes show good intramembrane (1.4% RSD) and intermembrane precision (0.71% RSD) and lifetime (around 45 days in darkness). The procedure was used to analyze Na(I) and K(I) in different types of natural waters (tap and mineral), validating the results against a reference procedure.

Keywords: Disposable optical tongue; HSV color space; Sodium and potassium determination; Water analysis; Answer surface modelling

The sensitive, anion-selective detection of arsenate with poly(allylamine hydrochloride) by single particle plasmon-based spectroscopy by Surin Hong; Soomin Park; Suseung Lee; Young In Yang; Hyeon Don Song; Jongheop Yi (pp. 136-141).

The use of single gold nanoparticle plasmon-based spectroscopy for the sensitive, anion-selective detection of arsenate is described. The method is based on the selective formation of electrostatic complexes between arsenate and poly(allylamine hydrochloride) (PAH) and changes in the single particle plasmon in Rayleigh scattering profiles. PAH, when modified with gold nanoparticles, binds arsenate via its amine-functionalities. The scattering properties of the resulting selectively formed complexes are altered, leading to significant changes in the surface plasmon resonance wavelength. The limit of detection of the method was determined to be 10nM, which is ca. 13 times more sensitive than U.S. EPA regulation levels. The response is essentially linear in the concentration range of 50–300nM. The method also shows good selectivity for arsenate in the presence of other environmentally relevant anions, including H₂PO₄⁻, SO₄²⁻, NO₃⁻, and Cl⁻.

Keywords: Analytical method; Arsenate; Gold nanoparticle; Rayleigh scattering; Single particle plasmon

Remarkable enantioselectivity of molecularly imprinted TiO₂ nano-thin films by Naoki Mizutani; Do-Hyeon Yang; Roman Selyanchyn; Sergiy Korposh; Seung-Woo Lee; Toyoki Kunitake (pp. 142-150).

TiO₂ nano-thin films with imprinted ( R)- and ( S)-enantiomers of propranolol, 1,1′-bi-naphthol, and 2-(4-isobutylphenyl)-propionic acid were fabricated on quartz plates by spin-coating their solutions with Ti(O-ⁿBu)₄ in a toluene-ethanol mixture (1:1, v/v). After template removal, the imprinted films showed better binding for original templates than to the corresponding enantiomers. The assessment of template incorporation, template removal, and re-binding was conducted through UV–vis measurements. Significant enhancement of enantioselectivity was achieved by optimization of the film thickness and by heat-treatment of the imprinted films. After subtraction of non-specific binding, the optimized films provided chiral recognition with the enantioselectivity of almost 100% for ( R)-propranolol and 95% for ( S)-propranolol.

Keywords: Molecular imprinting; Surface sol–gel process; TiO; ₂; gel films; Enantiomer; Chiral discrimination

Size-selective separations of biological macromolecules on mesocylinder silica arrays by Sherif El-Safty; M.A. Shenashen (pp. 151-161).

Display Omitted► Our aim is to control the separation of biological macromolecules, such as insulin (INS), α-amylase (AMY), β-lactoglobulin (β-LG), and myosin (MYO). ► Thus, we fabricated hexagonal silica nanotube arrays inside anodic alumina membrane (AAM) as promising size-exclusion filters. ► The mesocylinder filters shows evidence of controlled filtration and molecular transport processes of biomolecules.In order to control the design functionality of mesocylinder filters for molecular sieving of proteins, we fabricated tight mesocylinder silica nanotube (NT) arrays as promising filter candidates for size-exclusion separation of high-concentration macromolecules, such as insulin (INS), α-amylase (AMY), β-lactoglobulin (β-LG), and myosin (MYO) proteins. In this study, hexagonal mesocylinder structures were fabricated successfully inside anodic alumina membrane (AAM) nanochannels using a variety of cationic and nonionic surfactants as templates. The systematic design of the nanofilters was based on densely patterned polar silane coupling agents (“linkers”) onto the AAM nanochannels, leading to the fabrication of mesocylinder silica arrays with vertical alignment and open surfaces of top-bottom ends inside AAM. Further surface coating of silica NTs hybrid AAM with hydrophobic agents facilitated the production of extremely robust constructed sequences of membranes without the formation of air gaps among NT arrays. The fabricated membranes with impermeable coated layers, robust surfaces, and uniformly multidirectional cylinder pores in nanoscale sizes rapidly separate large quantities of proteins within seconds. Meanwhile, comprehensive factors that affect the performance of the molecular transport, diffusivity, and filtration rate through nanofilter membranes were discussed. The mesocylinder filters of macromolecules show promise for the efficient separation and molecular transport of large molecular weight and size as well as concentrations of proteins.

Keywords: Biological macromolecules; Arrays; Mesocylinder; Filter membranes; Size-selective separation; Permeation flux

Competitive immunoassay of phenobarbital by microchip electrophoresis with laser induced fluorescence detection by Yong Huang; Shulin Zhao; Ming Shi; Jinwen Liu; Hong Liang (pp. 162-166).

A microchip electrophoresis method with laser induced fluorescence detection was developed for the immunoassay of phenobarbital. The detection was based on the competitive immunoreaction between analyte phenobarbital and fluorescein isothiocyanate (FITC) labeled phenobarbital with a limited amount of antibody. The assay was developed by varying the borate concentration, buffer pH, separation voltage, and incubation time. A running buffer system containing 35mM borate and 15mM sodium dodecyl sulfate (pH 9.5), and 2800V separation voltage provided analysis conditions for a high-resolution, sensitive, and repeatable assay of phenobarbital. Free FITC-labeled phenobarbital and immunocomplex were separated within 30s. The calibration curve for phenobarbital had a detection limit of 3.4nM and a range of 8.6–860.0nM. The assay could be used to determine the phenobarbital plasma concentration in clinical plasma sample.

Keywords: Microchip electrophoresis; Competitive immunoassay; Laser induced fluorescence detection; Phenobarbital; Human plasma

Extremely highly efficient on-line concentration and separation of gold nanoparticles using the reversed electrode polarity stacking mode and surfactant-modified capillary electrophoresis by Fu-Ken Liu (pp. 167-173).

Display Omitted► The extremely highly efficient on-line concentration and separation of gold nanoparticles using the reversed electrode polarity stacking mode and surfactant-modified capillary electrophoresis. ► Sample: (A) using reversed electrode polarity stacking mode and (B) using convention operation. ► Trace (B) is magnified 20 times.In this study, gold nanoparticles (Au NPs) were separated using the reversed electrode polarity stacking mode (REPSM) of a capillary electrophoresis (CE) system for on-line enhancement prior to performing surfactant-modified CE separation. Under optimized conditions [running electrolyte buffer, sodium dodecyl sulfate (70mM) and 3-cyclohexylamino-1-propanesulfonic acid (10mM) at pH 10.0; applied voltage, 20kV; operating temperature, 25°C; REPSM strategy for sample on-line concentration; REPSM applied prior to initializing separation], two parameters were varied to further enhance the concentration and separation of the Au NPs: (i) the rate of polarity switching (from −20 to +20kV) between the REPSM and surfactant-modified CE separation modes and (ii) the length of the capillary column. At a polarity switching rate of 1333kVmin⁻¹ and a column length of ca. 83.5cm, the resolution of the separation of a mixture of 5.3- and 40.1-nm Au NPs was greater than 19; in addition, the numbers of theoretical plates for the 5.3- and 40.1-nm-diameter Au NPs were greater than 15,000 and up to 1.15×10⁷, respectively—the latter being extremely high. Thus, this CE-based method for separating Au NPs provided high performance in terms of separation resolution and the number of theoretical plates, both of which were improved by greater than fivefold relative to those published previously. Notably, the sensitivity enhancement factors for the 5.3- and 40.1-nm-diameter Au NPs were improved (by ca. 20- and 500-fold, respectively) relative to those obtained using conventional surfactant-modified CE separation.

Keywords: Gold nanoparticles; On-line concentration; Separation; Reversed electrode polarity stacking mode; Surfactant-modified CE separation

Comment on the uncertainties in isotope patterns of molecules by Juris Meija; Zoltán Mester (pp. 174-176).

Here we outline several misconceptions and caveats in the uncertainty evaluation of isotope patterns of molecules, most notably the failure of the traditional first-order error propagation models in certain situations. We also demonstrate that many of the questions regarding the uncertainty evaluation of molecular isotope patterns have direct analytical solutions that do not require elaborate computational approaches.

Keywords: Isotope patterns; Error propagation; Second-order; Natural variations; Mass spectrometry

Response to “Comments on the uncertainties in isotope patterns of molecules” by J. Meija and Z. Mester (doi:10.1016/j.aca.2010.09.029) by J.I. Garcia Alonso; P. Rodríguez-González (pp. 177-180).

This manuscript presents a response to a recently published article in Analytica Chimica Acta by J. Meija and Z. Mester (doi:10.1016/j.aca.2010.09.029) in which the authors comment on some aspects of our previous work entitled “Determination of the uncertainties in the theoretical mass isotopomer distribution of molecules” Anal. Chim. Acta 664 (2010) 68–76. We present here new arguments to support our previous findings and to clarify some aspects regarding to the calculation of the uncertainty of isotope patterns. The uncertainty calculations proposed by Meija and Mester for carbon-only clusters have been compared with our previously developed first-order model based on the spreadsheet approach described by Kragten (J. Kragten, Analyst 119 (1994) 2161). The results obtained in this comparison demonstrate that the Kragten procedure can be applied safely for the calculation of the uncertainties in the mass isotopomer distribution of molecules when the u average value is calculated. In addition the procedure provides good results even when the first-order error propagation law failed for some particular cases (C₉₃ and C₁₈₆ clusters).

Keywords: Mass isotopomer distributions; Error propagation; Natural variations; Mass spectrometry

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Analytica Chimica Acta (v.694, #1-2)