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Analytica Chimica Acta (v.598, #1)

Editorial Board (pp. co1).

Contents (pp. v-vi).

A novel efficient way to estimate the chemical rank of high-way data arrays by A-Lin Xia; Hai-Long Wu; Yan Zhang; Shao-Hua Zhu; Qing-Juan Han; Ru-Qin Yu (pp. 1-11).

A novel method, a subspace projection of pseudo high-way data array (SPPH), was developed for estimating the chemical rank of high-way data arrays. The proposed method determines the chemical rank through performing singular value decomposition (SVD) on the slice matrices of original high-way data array to produce a pseudo high-way data array and employing the idea of the difference of the original truncated data set and the pseudo one. Compared with traditional methods, it uses the information from eigenvectors combined with the projection residual to estimate the rank of the three-way data arrays instead of using the eigenvalue. In order to demonstrate the excellent performance of the new method, simulated and real three-way data arrays were carried out by the proposed method. The results showed that the proposed method could accurately and quickly determine the chemical rank to fit the trilinear model. Moreover, the newly proposed method was compared with the other four factor-determining methods, i.e. factor indicator function (IND), ADD-ONE-UP, core consistency diagnostic (CORCONDIA) and two-mode subspace comparison (TMSC) approaches. It was found that the proposed method can deal with more complex situations with existence of severe collinearity and trace concentration than many other methods can and performs well in practical applications.

Keywords: Subspace projection of pseudo high-way data array; Chemical rank; Three-way data array; High pressure liquid chromatography–diode array detector; Excitation–emission fluorescence data

Quantitative structure–retention relationships for organic pollutants in biopartitioning micellar chromatography by Binbin Xia; Weiping Ma; Xiaoyun Zhang; Botao Fan (pp. 12-18).

Quantitative structure–retention relationship (QSRR) models have been successfully developed for the prediction of the retention factor (log k) in the biopartitioning micellar chromatography (BMC) of 66 organic pollutants. Heuristic method (HM) and radial basis function neural networks (RBFNN) were utilized to construct the linear and non-linear QSRR models, respectively. The optimal QSRR model was developed based on a 6-17-1 radial basis function neural network architecture using molecular descriptors calculated from molecular structure alone. The RBFNN model gave a correlation coefficient ( R²) of 0.8464 and root-mean-square error (RMSE) of 0.1925 for the test set. This paper provided a useful model for the predicting the log k of other organic compounds when experiment data are unknown.

Keywords: Quantitative structure–retention relationship; Heuristic method; Radial basis function neural networks; Biopartitioning micellar chromatography

Removing uncertain variables based on ensemble partial least squares by Da Chen; Wensheng Cai; Xueguang Shao (pp. 19-26).

A strategy, named as removing uncertain variables based on ensemble partial least squares (RUV-EPLS), was proposed. In this strategy, the uncertainty in PLS regression coefficients is evaluated by the criterion of stability, and the variables whose regression coefficients carry a relatively large uncertainty are eliminated. Then, a new EPLS model with the remaining variables is constructed. To reasonably control the quality of the PLS member models in the RUV-EPLS, an objective criterion based on the F-test is used, which makes the RUV-EPLS convenient to perform in practice. To validate the effectiveness and universality of the strategy, it was applied to two different sets of near-infrared (NIR) spectra. It is of great interest to be found that the RUV-EPLS is not so sensitive to the outliers as many other calibration methods, and the selected variables are indeed known to be informative for corresponding compounds, which results in a reliable and high-quality calibration model. The study reveals that the RUV-EPLS method is of value to improve stability and predictive ability of multivariate calibration involving complex matrices that may contain a small number of outliers.

Keywords: Removing uncertain variables; Ensemble partial least squares; Prediction stability of calibration; F; -criterion

Application of probabilistic neural networks in qualitative analysis of near infrared spectra: Determination of producing area and variety of loquats by Xiaping Fu; Yibin Ying; Ying Zhou; Huirong Xu (pp. 27-33).

Near infrared (NIR) spectra of a sample can be treated as a signature, allowing samples to be grouped on basis of their spectral similarities. Near infrared spectroscopy (NIRS) combined with probabilistic neural networks (PNN) have been used to discriminate producing area and variety of loquats. Two varieties of loquats (‘ Dahongpao’ and ‘ Jiajiaozhong’) picked from two producing areas of ‘ Tangxi’ and ‘ Cunan’ in Zhejiang province were analyzed in this study. Principal component analysis (PCA) was applied before PNN modeling and the results indicated that the dimension of the vast spectral data can be effectively reduced. For each model, half samples were used to train the network and the remaining half were used to test the network. The results of the PCA–PNN models for discriminating the variety of samples from the same producing area or for discriminating the producing area of the same variety samples were much better than those of the PCA–PNN models for discriminating variety or producing area of all loquat samples. The results of this study show that NIRS combined with PCA–PNN is a feasible way for qualitative analysis of discriminating fruit producing areas and varieties.

Keywords: Near infrared spectroscopy; Probabilistic neural networks; Principal component analysis; Qualitative analysis

Urinary nucleosides based potential biomarker selection by support vector machine for bladder cancer recognition by Yong Mao; Xiaoping Zhao; Shufang Wang; Yiyu Cheng (pp. 34-40).

Urinary nucleosides are potential biomarkers for many kinds of cancers. But up to now, it has been little focused in bladder cancer recognition. The aim of present study is try to validate the potential of urinary nucleoside as biomarker for bladder cancer diagnosis by finding out some urinary nucleosides with good discriminative performance for bladder cancer recognition in urinary nucleoside profile.20 urinary samples for cancer and the same number for control are collected and treated by capillary electrophoresis–mass spectrometry experiments to achieve urinary nucleoside profile, in which 44 peaks were integrated and the ratios of the relative peak area to the concentration of urinary creatinine were used as features to describe all samples. Support vector machine based recursive feature elimination (SVM-RFE) and a new feature selection method called support vector machine based partial exhaustive search algorithm (SVM-PESA) were used for biomarker identification and seeking optimal feature subsets for bladder cancer recognition.Based on the urinary nucleoside profile, 22 optimal feature subsets consist of 3–4 features were found with 95% 5-fold cross validation accuracy, 100% sensitivity and 90% specificity by SVM-PESA, whose performance were much better than that of optimal feature subset selected by SVM-RFE. By analyzing the statistical histogram of features’ appearance frequency in several best feature subsets, urinary nucleosides with m/ z 317, 290 and 304 were thought as potential biomarkers for bladder cancer recognition.These results indicated urinary nucleosides may be useful as tumor biomarkers for bladder cancer, and the new method for biomarker selection is effective.

Keywords: Abbreviations; SVM-RFE; support vector machine based recursive feature elimination; SVM-PESA; support vector machine based partial exhaustive search algorithm; CV; cross validationBladder cancer recognition; Urinary nucleosides; Biomarker selection; Support vector machine; Partial exhaustive search algorithm; Capillary electrophoresis–mass spectrometry

Retention prediction of adrenoreceptor agonists and antagonists on a diol column in hydrophilic interaction chromatography by Noel S. Quiming; Nerissa L. Denola; Ikuo Ueta; Yoshihiro Saito; Satoshi Tatematsu; Kiyokatsu Jinno (pp. 41-50).

Retention prediction models using multiple linear regression (MLR) and artificial neural networks (ANN) were developed for adrenoreceptor agonists and antagonists chromatographed on a diol column under hydrophilic interaction chromatographic (HILIC) mode at three pH conditions (3.0, 4.0 and 5.0). Using stepwise MLR, the retention behavior of the analytes was satisfactorily described by a five-predictor model; the predictors being the percentage of acetonitrile in the mobile phase (% ACN), the logarithm of partition coefficient (log D), the number of hydrogen bond donor (HBD), the number of hydrogen bond acceptor (HBA), and the total absolute atomic charge of the molecule (TAAC). Among the five descriptors, % ACN had the strongest effect on the retention as indicated by its relatively higher standardized coefficient compared to the other four predictors. The inclusion of the four predictors which are related to the properties of the compounds (log D, HBD, HBA and TAAC), suggested hydrophilic interaction, hydrogen bonding and ionic interaction as possible mechanisms of retention of the analytes on the studied system. The models derived from MLR also showed adequate fit as proven by the high correlation ( R² as high as 0.9667) between observed and predicted log k values for the training set and good predictive power on the test set ( R² greater than 0.97). ANN analyses of the data were also conducted using the five predictors derived from MLR as inputs and log k as output. The trained ANNs showed better predictive abilities as compared to MLR models as indicated by relative higher R² and lower root mean square error of predictions (RMSEP) for both training and test sets. The derived models can be used as references for method development and optimization of chromatographic conditions for the separation of adrenoreceptor agonists and antagonists.

Keywords: Adrenoreceptors agonists/antagonists; Quantitative structure–retention relationships; Hydrophilic interaction chromatography; Mulitiple linear regression; Artificial neural network

Determination of gadolinium(III) ions in soil and sediment samples by a novel gadolinium membrane sensor based on 6-methyl-4-{[1-(2-thienyl)methylidene]amino}3-thioxo-3,4-dihydro-1,2,4-triazin-5-(2H)-one by Hassan Ali Zamani; Ghadir Rajabzadeh; Mohammad Reza Ganjali; Parviz Norouzi (pp. 51-57).

Highly selective and sensitive poly(vinyl chloride) (PVC) membrane electrodes based on 6-methyl-4-{[1-(2-thienyl)methylidene]amino}3-thioxo-3,4-dihydro-1,2,4-triazin-5-(2H)-one (MATDTO) as new carriers for gadolinium ion-selective electrode was reported. The membrane solutions containing PVC, o-nitrophenyl octyl ether (NPOE) as plasticizer, sodium tetraphenyl borate (NaTPB) as lipophilic ionic additive, and MATDTO, displays a calibration response for Gd³⁺ ions over a wide concentration range of 1.0×10⁻⁶–1.0×10⁻¹M with Nernstian slopes of 19.8±0.2mV per decade and a detection limit as 5.8×10⁻⁷M. The sensor has a relatively fast response time of <10s and can be used in the pH range 3.2–8.7 for at least 2 months without any significant divergence in potentials. The selectivity coefficients for mono-, di-, and trivalent cations indicate good selectivity for Gd(III) ions over a large number of interfering cations. The membrane sensor was used as an indicator electrode in the potentiometric titration of Gd(III) ions with EDTA. The proposed electrode was also applied to the determination of concentration of Gd(III) ions in soil and sediment samples and validation with CRMs.

Keywords: Gadolinium; 6-Methyl-4-{[1-(2-thienyl)methylidene]amino}3-thioxo-3,4-dihydro-1,2,4-triazin-5-(2H)-one; PVC membrane; Potentiometry

Derivatized humic acids modified gold electrode: Electrochemical characterization and analytical applications by Antonella Profumo; Francesca Zavarise; Daniele Merli; Ilenia Tredici; Giancarla Alberti; Stefano Protti; Maurizio Fagnoni (pp. 58-64).

The preparation and application of a humic acids modified gold electrode (HA-CME) have been described. Derivatization of HAs as β-thioesters caused their partial fragmentation and, thus, a consequent separation by size exclusion chromatography (SEC) was necessary.The CME prepared with functionalized HAs having an average MW of 52000 demonstrated to be effective for trace As(III) determination (LOQ=0.3μgL⁻¹). This CME has been characterized both by electrochemical techniques and atomic force microscopy (AFM). The HA-CME provided reliable measurements in natural waters at different salinity with no need of desalting the sample. Total inorganic arsenic could be determined after reduction of As(V) with SO₂. Under these conditions, organic arsenic species were not mineralized and did not interfere.

Keywords: CME; Humic acids; As determination; Electrochemical sensors

Utilising gallium for enhanced electrochemical copper analysis at the bismuth film electrode by Chad Prior; Claire E. Lenehan; G. Stewart Walker (pp. 65-73).

A sensitive anodic stripping voltammetric procedure at the bismuth film electrode (BFE) for trace analysis of copper (II) in the presence of gallium is presented. The new protocol circumvents the problems of overlapping stripping signals between copper and bismuth that previously hampered the analysis of copper at the BFE. The results illustrate that the addition of gallium not only improves the reproducibility of the bismuth stripping signal but also facilitates much improved resolution between the stripping signals of bismuth and copper. Investigations into the effect of gallium on the stripping response of copper and bismuth were studied showing a 4:1 gallium:copper mole ratio produces optimum signals from bismuth and copper indicating a possible stoichiometric relationship. Optimisation of other key variables including electrolyte composition, accumulation parameters and appropriate waveform settings were studied and optimised. The optimised procedures show a range of linear calibration plots ( R²>0.994) ranging from 2 to 500μgL⁻¹ and the relative standard deviation for a solution containing 100μgL⁻¹ copper was 3.7% ( n=10). Utilising an accumulation time of 300s the limit of detection was 1.4μgL⁻¹(S/N=3). This technique was successfully applied to the analysis of copper in tap water representing the first successful copper determination in real samples using the BFE.

Keywords: Bismuth electrode; Copper; Anodic stripping voltammetry; Gallium

Cell-sorption of paramagnetic metal ions on a cell-immobilized micro-column in the presence of an external magnetic field by Ai-Mei Zou; Ming-Li Chen; Xu-Wei Chen; Jian-Hua Wang (pp. 74-81).

The cell-sorption of paramagnetic ions of Mn²⁺ and Cr³⁺ onto a Chlorella vulgaris (C. vulgaris) cell-immobilized micro-column was significantly improved in the presence of an external magnetic field generated in a finite solenoid, by placing the micro-column in the center of the solenoid in a sequential injection system. Magnetic field creates an opposite drift velocity on the hydrated paramagnetic ions against the flow of the sample zone, retards the moving velocity of the metal ions and provides extra contacting time with the cells on the micro-column and offers more chances for the paramagnetic ions to interact with the various functional groups or binding sites on the cell surface, which significantly facilitates cell-sorption of the paramagnetic ions. The sorption efficiencies of Mn²⁺ and Cr³⁺ at the 20μgL⁻¹ level were improved from 45 to 80% and 60 to 90%, respectively, in a magnetic field of 240mT.The system was applied for the separation/preconcentration of ultra-trace level of manganese. The presence of an external magnetic field significantly alleviated the interfering effects from coexisting metal ions. Within a liner range of 0.025–0.5μgL⁻¹ and a sampling volume of 500μL, an enrichment factor of 21.2, a limit of detection of 0.008μgL⁻¹, along with a sampling frequency of 20h⁻¹ was attained, achieving a precision of 2.1% R.S.D. (0.2μgL⁻¹). Manganese contents in a certified reference material of riverine water and a snow water were analyzed.

Keywords: Cell-sorption; Chlorella vulgaris; Separation and preconcentration; Paramagnetic ions; Magnetic field

In situ derivatization and hollow fiber membrane microextraction for gas chromatographic determination of haloacetic acids in water by Pakorn Varanusupakul; Narongchai Vora-adisak; Bancha Pulpoka (pp. 82-86).

An alternative method for gas chromatographic determination of haloacetic acids (HAAs) in water using direct derivatization followed by hollow fiber membrane liquid-phase microextraction (HF-LPME) has been developed. The method has improved the sample preparation step according to the conventional US EPA Method 552.2 by combining the derivatization and the extraction into one step prior to determination by gas chromatography electron captured detector (GC-ECD). The HAAs were derivatized with acidic methanol into their methyl esters and simultaneously extracted with supported liquid hollow fiber membrane in headspace mode. The derivatization was attempted directly in water sample without sample evaporation. The HF-LPME was performed using 1-octanol as the extracting solvent at 55°C for 60min with 20% Na₂SO₄. The linear calibration curves were observed for the concentrations ranging from 1 to 300μgL⁻¹ with the correlation coefficients ( R²) being greater than 0.99. The method detection limits of most analytes were below 1μgL⁻¹ except DCAA and MCAA that were 2 and 18μgL⁻¹, respectively. The recoveries from spiked concentration ranged from 97 to 109% with %R.S.D. less than 12%. The method was applied for determination of HAAs in drinking water and tap water samples. The method offers an easy one step high sample throughput sample preparation for gas chromatographic determination of haloacetic acids as well as other contaminants in water.

Keywords: Haloacetic acids; Liquid-phase microextraction; Hollow fiber membrane; In situ derivatization; Water; Disinfection by-products

Quantification of human pharmaceuticals in water samples by high performance liquid chromatography–tandem mass spectrometry by Carolina Nebot; Stuart W. Gibb; Kenneth G. Boyd (pp. 87-94).

An improved analytical method for determination of human pharmaceuticals in natural and wastewaters with ngL⁻¹ sensitivity is presented. The method is applicable to pharmaceuticals from a wide range of therapeutic classes including antibiotics, analgesics, anti-inflammatories and anti-cancer compounds. Pharmaceuticals were extracted from waters using solid-phase extraction, and after concentration, analysed by high performance liquid chromatography with tandem mass spectrometric detection (HPLC–MS/MS). Identification of each compound was secured using retention time and by the selected reaction monitoring of two transitions, one of which was additionally used for quantification. Limits of detection ranged from 0.03 to 0.96ngL⁻¹ and were up to two orders of magnitude lower than those of previously published methods. The method was validated using spiked samples prepared from tap, river and sea water as well as wastewater effluents, collected from the North of Scotland. Analysis of wastewater effluents revealed the presence of mefenamic acid, ibuprofen, erythromycin, diclofenac and trimethoprim. None of the selected pharmaceuticals were detected in river, tap or sea water samples.

Keywords: Pharmaceuticals; High performance liquid chromatography–tandem mass spectrometry; Solid-phase extraction; Natural waters

Development of a new sample pre-treatment procedure based on pressurized liquid extraction for the determination of metals in edible seaweed by Jorge Moreda-Piñeiro; Elia Alonso-Rodríguez; Purificación López-Mahía; Soledad Muniategui-Lorenzo; Darío Prada-Rodríguez; Antonio Moreda-Piñeiro; Pilar Bermejo-Barrera (pp. 95-102).

A new, simple, fast and automated method based on acetic acid-pressurized liquid extraction (PLE) has been developed for the simultaneous extraction of major and trace elements (As, Ca, Cd, Co, Cr, K, Mg, Mn, Na, Pb, Sr and Zn) from edible seaweeds. The target elements have been simultaneously determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The influence of several extraction parameters (e.g. acetic acid concentration, extraction temperature, extraction time, pressure, number of cycles, particle size and diatomaceous earth (DE) mass/sample mass ratio) on the efficiency of metal leaching has been evaluated. The results showed that metal extraction efficiency depends on the mass ratio of the dispersing agent mass and the sample. The optimized procedure consisted of the following conditions: acetic acid (0.75M) as an extracting solution, 5min of extraction time, one extraction cycle at room temperature at a pressure of 10.3MPa and addition of a dispersing agent (at a ratio of 5:1 over the sample mass). The leaching procedure was completed after 7min (5min extraction time plus 1min purge time plus 1min end relief time). Limits of detection and quantification and repeatability of the over all procedure have been assessed. Method validation was performed analysing two seaweed reference materials (NIES-03 Chlorella Kessleri and NIES-09 Sargasso). The developed extraction method has been applied to red (Dulse and Nori), green (Sea Lettuce) and brown (Kombu, Wakame and Sea Spaghetti) edible seaweeds.

Keywords: Acetic acid-pressurized liquid extraction; Multi-element determination; Edible seaweeds; Inductively coupled plasma-optical emission spectrometry

Determination of Δ⁹-tetrahydrocannabinol in indoor air as an indicator of marijuana cigarette smoking using adsorbent sampling and in-injector thermal desorption gas chromatography–mass spectrometry by Su-Lien Chou; Yong-Chien Ling; Mo-Hsiung Yang; Chung-Yen Pai (pp. 103-109).

The marijuana leaves are usually mixed with tobaccos and smoked at amusement places in Taiwan. Recently, for investigation-legal purposes, the police asked if we can identify the marijuana smoke in a KTV stateroom (a private room at the entertainment spot for singing, smoking, alcohol drinking, etc.) without marijuana residues. A personal air-sampler pump fitted with the GC liner-tube packed with Tenax-TA adsorbent was used for air sampling. The GC-adsorbent tube was placed in the GC injector port and desorbed directly, followed by GC–MS analysis for the determination of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) in indoor air. The average desorption efficiency and limit of detection for Δ⁹-THC were 89% and 0.1μgm⁻³, respectively, approximately needing 1.09mg of marijuana leaves smoked in an unventilated closed room (3.0m×2.4m×2.7m) to reach this level. The mean Δ⁹-THC contained in the 15 marijuana plants seized from diverse locations was measured to be 0.32%. The Δ⁹-THC in room air can be successfully identified from mock marijuana cigarettes, mixtures of marijuana and tobacco, and an actual case. The characteristic Δ⁹-THC peak in chromatogram can serve as the indicator of marijuana. Positive result suggests marijuana smoking at the specific scene in the recent past, facilitating the formulation of further investigation.

Keywords: Δ; ⁹; -Tetrahydrocannabinol; Marijuana cigarette smoking; Indoor air; Gas chromatography–mass spectrometry

Characterization and identification of isomeric flavonoid O-diglycosides from genus Citrus in negative electrospray ionization by ion trap mass spectrometry and time-of-flight mass spectrometry by Peiying Shi; Qing He; Yue Song; Haibin Qu; Yiyu Cheng (pp. 110-118).

Flavonoid O-diglycosides are important bioactive compounds from genus Citrus. They often occur as isomers, which makes the structural elucidation difficult. In the present study, the fragmentation behavior of six flavonoid O-diglycosides from genus Citrus was investigated using ion trap mass spectrometry in negative electrospray ionization (ESI) with loop injection. For the flavonoid O-rutinosides, [ M−H−308]⁻ ion was typically observed in the MS² spectrum, suggesting the loss of a rutinose. The fragmentation patterns of flavonoid O-neohesperidosides were more complicated in comparison with their rutinoside analogues. A major difference was found in the [ M−H−120]⁻ ion in the MS² spectrum, which was a common feature of all the flavonoid O-neohesperidosides. The previous literature for naringin located the loss of 120Da to the glycan part, whereas the present study for naringin had shown that the [ M−H−120]⁻ ion was produced by a retro-Diels-Alder reaction in ring C, and this fragmentation pattern was confirmed by the accurate mass measurement using an orthogonal time-of-flight mass spectrometer. Combined with high performance liquid chromatography (HPLC) and diode array detection (DAD), the established approach to the structural identification of flavonoid O-diglycosides by ion trap mass spectrometry was applied to the analysis of extracts of two Chinese medicines derived from genus Citrus, namely Fructus aurantii and F. aurantii immaturus. According to the HPLC retention behavior, the diagnostic UV spectra and the molecular structural information provided by multistage mass spectrometry (MSⁿ) spectra, 13 flavonoid O-glycosides in F. aurantii and 12 flavonoid O-glycosides in F. a. immaturus were identified rapidly.

Keywords: Flavonoid; O; -diglycosides; Ion trap; Time-of-flight; Mass spectrometry

Fourier transform infrared spectroscopy as a suitable technique in the study of the materials used in waterproofing of archaeological amphorae by J. Font; N. Salvadó; S. Butí; J. Enrich (pp. 119-127).

The resinous materials from the interior surfaces of two Roman and one Iberian amphora were studied with Fourier transform infrared (FTIR) spectroscopy. The results were then compared with those obtained by synchrotron radiation-FTIR, scanning electron microscopy (SEM), and gas chromatography–mass spectrometry (GC–MS).The FTIR spectra obtained by the technique of KBr micropellets, prepared directly with the materials scraped from the amphora without any further sample preparation, provided enough information to establish their diterpenoic nature, and even to differentiate between the two main materials employed for waterproofing purposes, pitch and wood tar. Methyl dehydroabietic acid (DHAM) is the main chemical marker that allows a distinction to be made between these two materials.Pitch and wood tar were prepared in the laboratory heating pine resin and resinous pine wood, respectively. These resinous waterproofing materials were compared with the coatings extracted from the amphorae.The samples whose direct FTIR spectra showed a signal at ∼1740cm⁻¹, attributed to a carbonyl group of methyl ester, presented as well a peak of DHAM in the GC–MS chromatogram of the neutral fraction of their extract. Samples without this signal in their spectra did not present DHAM in their chromatogram.This work studies, for the first time, waterproofing of an amphora attributed to the Iberian culture.

Keywords: Pitch; Diterpenoid resin; Roman and Iberian amphorae; Colophony; Fourier transform infrared spectroscopy; Gas chromatography–mass spectrometry

Preliminary study on application of mid infrared spectroscopy for the evaluation of the virgin olive oil “freshness” by Nicoletta Sinelli; Maria Stella Cosio; Carmen Gigliotti; Ernestina Casiraghi (pp. 128-134).

The freshness of virgin olive oils (VOO) from typical cultivars of Garda regions was evaluated by attenuated total reflectance (ATR) and Fourier transform infrared (FTIR) spectroscopy, in combination with multivariate analysis. The olive oil freshness decreased during storage mainly because of oxidation processes. In this research, 91 virgin olive oils were packaged in glass bottles and stored either in the light or in the dark at room temperature for different periods. The oils were analysed, before and after storage, using both chemical methods and spectroscopic technique.Classification strategies investigated were partial least square discriminant analysis (PLS-DA), linear discriminant analysis (LDA), and soft independent modelling of class analogy (SIMCA).The results show that ATR-MIR spectroscopy is an interesting technique compared with traditional chemical index in classifying olive oil samples stored in different conditions. In fact, the FTIR PCA results allowed a better discrimination among fresh and oxidized oils, than samples separation obtained by PCA applied to chemical data. Moreover, the results obtained by the different classification techniques (PLS-DA, LDA, SIMCA) evidenced the ability of FTIR spectra to evaluate the olive oil freshness. FTIR spectroscopy results are in agreement with classical methods. The spectroscopic technique could be applied for the prediction of VOOs freshness giving information related to chemical modifications. The great advantages of this technique, compared to chemical analysis, are related to rapidity, non-destructive characteristics and low cost per sample. In conclusion, ATR-MIR represents a reliable, cheap and fast classification tool able to assess the freshness of virgin olive oils.

Keywords: Virgin olive oil; Freshness; Oxidation; Storage; Fourier transform infrared (FTIR) spectroscopy; Attenuated total reflection mid infrared (ATR-MIR) spectroscopy

Investigation of photobleaching and saturation of single molecules by fluorophore recrossing events by Sean M. Burrows; Randall D. Reif; Dimitri Pappas (pp. 135-142).

A method for investigation of photobleaching and saturation of single molecules by fluorophore recrossing events in a laser beam is described. The diffraction-limited probe volumes encountered in single-molecule detection (SMD) produce high excitation irradiance, which can decrease available signal. The single molecules of several dyes were detected and the data was used to extract interpeak times above a defined threshold value. The interpeak times revealed the number of fluorophore recrossing events. The number of molecules detected that were within 2ms of each other represented a molecular recrossing for this work. Calcein, fluorescein and R-phycoerythrin were analyzed and the saturation irradiance and photobleaching effects were determined as a function of irradiance. This approach is simple and it serves as a method of optimizing experimental conditions for single-molecule detection.

Keywords: Single-molecule detection; Photobleaching; Photon saturation

α-Glucosidase based bismuth film electrode for inhibitor detection by Suna Timur; Ülkü Anik (pp. 143-146).

A biosensing system based on α-glucosidase (AG) activity was developed by using bismuth film modified glassy carbon electrode (BiFE). AG enzyme was immobilized on the BiFE by means of gelatin membrane and the activity was measured by the following of liberated 4-nitrophenol from the 4-nitrophenyl-α-d-glucopyranoside (PNPGP) which is the synthetic substrate of the enzyme at the working potential of −950mV. The proposed system was used as an AG based biosensing system. Experimental data showed that the response current of 4-nitrophenol obtained at the BiFE was linear in concentration range between 0.033 and 0.33mM of PNPGP. Before examining the analytical characteristics, pH optimization of the AG-biosensor was also performed. Furthermore, the proposed method was applied to analyze two different AG inhibitors (Amaryl and Acorbose) which are important in Noninsulin-dependent diabetes mellitus (NIDDM).

Keywords: α-Glucosidase; Biosensor; Bismuth film electrode

A dual detector capillary waveguide biosensor for detection and quantification of hybridized target by Harbans S. Dhadwal; Bhaskar Mukherjee; Paul Kemp; Josephine Aller; Yuan Liu; JoAnn Radway (pp. 147-154).

We describe a novel technique for improving the sensitivity of analytical instruments based on the measurement of fluorescent intensity. Independent measurement of the Rayleigh scattered intensity component by means of a second photodetector leads to normalized data, which are independent of various experimental parameters. Incorporation of this technique into a fully automated capillary waveguide biosensor improved the instrument sensitivity by a factor of three. The technique enables quantification, as well as detection, of the hybridized target molecules.

Keywords: Deoxyribonucleic acid; Hybridization; Biosensor; Capillary; Fluorescence; Evanescent Wave

The development of a multi-nitroimidazole residue analysis assay by optical biosensor via a proof of concept project to develop and assess a prototype test kit by Lisa Connolly; Colin S. Thompson; Simon A. Haughey; Imelda M. Traynor; Sheryl Tittlemeier; Christopher T. Elliott (pp. 155-161).

An assay based on optical biosensor technology has been developed to detect a broad range of nitroimidazole drug residues and their metabolites (dimetridazole (DMZ), metronidazole (MNZ), ronidazole (RNZ), hydroxymetronidazole (HO-MNZ) and hydroxydimetridazole (HO-DMZ)) in chicken muscle. The detection limit for the procedure was determined as 0.5ppb for DMZ and detection capabilities (CC βs) ranged from <1ppb for DMZ, MNZ and RNZ to <2ppb for HO-MNZ and HO-DMZ. Intra-assay variation ( n=6) was calculated as 11.6% at a concentration of 1ppb DMZ and 4.7% at a concentration of 2ppb DMZ. Inter-assay variation ( n=3) was determined to be 14.2% at a concentration of 1ppb DMZ and 3.5% at a concentration of 2ppb DMZ.A prototype kit based on this assay was produced and a multinational study was undertaken to independently evaluate its performance. The resulting data showed that the kit can be implemented with little difficulty in laboratories of varying expertise and is sensitive enough to meet the standards required by international law. Feedback from this study led to the incorporation of some minor improvements to the kit. The commercial partner in the project, XenoSense Ltd., was consulted with regards to producing a commercial test kit based on the prototype assay. As feedback from the collaborative study had been positive with respect to speed, ease of use and performance of the kit, the decision to commercialise the kit was taken. In conclusion, the prototype nitroimidazole kit was shown to offer numerous advantages over existing analytical techniques.

Keywords: Abbreviations; ACR; assay cross-reactivity; CR; cross-reactivity; CV; coefficient variant; DMZ; dimetridazole; DSC; di-succinimidyl carbonate; EDC; N; -ethyl-; N; ′-(3-dimethylaminopropyl) carbodiimide hydrochloride; HO-DMZ; hydroxydimetridazole; HO-MNZ; hydroxymetronidazole; MNZ; metronidazole; MRPL; minimum required performance limit; NHS; N; -hydrosuccinimide; RNZ; ronidazole; SD; standard deviation; SPR; surface plasmon resonanceNitroimidazole; Residue; Metabolites; Poultry; Biosensor

Use of diffusive gradients in thin films and tangential flow ultrafiltration for fractionation of Al(III) and Cu(II) in organic-rich river waters by Paulo S. Tonello; André H. Rosa; Cassio H. Abreu Jr.; Amauri A. Menegário (pp. 162-168).

Diffusive gradients in thin films (DGT) and tangential-flow ultrafiltration (TF-UF) were combined for fractionation of Al and Cu in river water containing high content of dissolved organic carbon. A procedure based on ultrafiltration data is proposed to determine diffusion coefficients of the analytes in water samples and model solutions containing both free metal (M) and complex (metal – humic substance). Aiming to evaluate the accuracy of the proposed approach, the DGT results were compared with those from a protocol for determination of labile Al and Cu based on solid phase extraction (SPE). Good agreement between data from DGT and SPE were attained for model solutions. For analysis of real organic-rich water samples, differences between DGT and SPE measurements were consistent with the time-scales of the techniques. The concentration of labile Al determined by DGT were lower than the total dissolved concentrations (determined by inductively coupled plasma mass spectrometry) and exceeded the ultrafiltered concentration, indicating that inorganic Al species (species small enough to pass through 1kDa membrane) were minor species as compared with Al organic complexes. For both Al and Cu, there were species not measured by DGT as they are not sufficiently labile.

Keywords: Diffusive gradients; Tangential-flow ultrafiltration; Copper; Aluminum; Humic substances

Analysis of post-Byzantine icons from the Church of the Assumption in Cephalonia, Ionian Islands, Greece: A multi-method approach by Eleni Kouloumpi; Peter Vandenabeele; Graham Lawson; Vassilios Pavlidis; Luc Moens (pp. 169-179).

A multi-method approach has been developed for the characterisation of the proteinaceous binding media, drying oils and pigments present in samples from the panel paintings of the Church of the Assumption in Cephalonia (Ionian Islands, Greece). The analytical protocol involved the use of scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), Raman spectroscopy and gas chromatography. The identification of the pigments was achieved by SEM/EDX and Raman spectroscopy. The latter technique was also used for the detection of the binding media, while their characterisation was achieved by gas chromatographic analysis of ethyl chloroformate derivatives. The aim of this multi-method protocol was to obtain as much information as possible from the panel paintings of the Church of the Assumption, through non-destructive methods, before proceeding to gas chromatography. Little scientific information is available for the understanding of the construction technique and the materials used by the post-Byzantine artists and whatever is available comes mainly from artists’ manuals. One of the aims of this paper is to provide a scientific background to the technology of the Ionian post-Byzantine icons.

Keywords: Post-Byzantine icons; Art analysis; Energy dispersive X-ray analysis; Gas chromatography; Raman spectroscopy; Binding media

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Analytica Chimica Acta (v.598, #1)

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Analytica Chimica Acta (v.598, #1)