Analytica Chimica Acta (v.765, #C)

Display Omitted► Overview of olive oil analysis by 1H, 13C, and 31P NMR spectroscopy. ► Sample preparation. ► Experimental conditions and processing for metabonomic analysis. ► Multivariate statistical methods for NMR data analysis. ► Quality assessment and authentication of extra virgin olive oil.Nuclear Magnetic Resonance (NMR) Spectroscopy has been extensively used for the analysis of olive oil and it has been established as a valuable tool for its quality assessment and authenticity. To date, a large number of research and review articles have been published with regards to the analysis of olive oil reflecting the potential of the NMR technique in these studies. In this critical review, we cover recent results in the field and discuss deficiencies and precautions of the three NMR techniques (1H, 13C, 31P) used for the analysis of olive oil. The two methodological approaches of metabonomics, metabolic profiling and metabolic fingerprinting, and the statistical methods applied for the classification of olive oils will be discussed in critical way. Some useful information about sample preparation, the required instrumentation for an effective analysis, the experimental conditions and data processing for obtaining high quality spectra will be presented as well. Finally, a constructive criticism will be exercised on the present methodologies used for the quality control and authentication of olive oil.
Keywords: Olive oil; NMR spectroscopy; Quality; Authenticity; Statistical analysis;

Display Omitted► MCR is nowadays a well-established and widespread methodology for mixture analysis. ► The analytical issues requiring advanced applications of MCR are reviewed. ► Attention is paid to the literature published the years 2008–2012.Multivariate curve resolution (MCR) is a widespread methodology for the analysis of process data in many different application fields. This article intends to propose a critical review of the recently published works. Particular attention will be paid to situations requiring advanced and tailored applications of multivariate curve resolution, dealing with improvements in preprocessing methods, multi-set data arrangements, tailored constraints, issues related to non-ideal noise structure and deviation to linearity. These analytical issues are tackling the limits of applicability of MCR methods and, therefore, they can be considered as the most challenging ones.
Keywords: Chemometrics; Multivariate; Curve resolution; Mixture; MCR-ALS;

Display Omitted► NIR chemical imaging and chemometrics were used for studying thin films based drug delivery systems. ► Thin films were polymers mixtures of HPMC, PVP and PEG-400 loaded with the drug paracetamol. ► MCR-ALS provided initial biased results on quantification of polymers and additional calibration step was required. ► Three different strategies were tested to suppress the bias on the quantification by MCR-ALS. ► Parcetamol distribution in the thin films has direct correlation with the PVP and PEG, but inverse correlation with HPMC.Thin films loaded with the drug paracetamol were produced from polymer blends formed by hydroxypropylmethylcellulose (HPMC), polyvinylpyrrolidone (PVP) and polyethyleneglycol (PEG), at various mass ratios of polymers and drug defined by a d-optimal experimental design. NIR hyperspectral images were obtained from each thin film formulation and the pixel-to-pixel quantification of the constituents were carried out by partial least square (PLS) and multivariate curve resolution–alternating least square (MCR-ALS) with three different calibration/validation strategies. These strategies differ in the way to construct the calibration and validation matrices and they had to be carried out to suppress the bias on the quantification of the constituents in the polymer blend. The errors of prediction in the models from MCR-ALS were influenced by the calibration/validation strategy employed, but they were similar to the ones from PLS model. Concentration distribution maps were built after pixel-to-pixel predictions and their characteristics were analyzed.
Keywords: NIR hyperspectral imaging; Polymer thin films; Paracetamol; PLS; MCR-ALS;

Effects of supervised Self Organising Maps parameters on classification performance by Davide Ballabio; Mahdi Vasighi; Peter Filzmoser (45-53).
Display Omitted► We evaluated effects of SOMs parameters on classification and computational time. ► The study was conducted on eighteen real datasets. ► Significant parameters and their interactions on classification were highlighted. ► Optimal architectures to reduce the computational time of SOMs was proposed.Self Organising Maps (SOMs) are one of the most powerful learning strategies among neural networks algorithms. SOMs have several adaptable parameters and the selection of appropriate network architectures is required in order to make accurate predictions. The major disadvantage of SOMs is probably due to the network optimisation, since this procedure can be often time-expensive.Effects of network size, training epochs and learning rate on the classification performance of SOMs are known, whereas the effect of other parameters (type of SOMs, weights initialisation, training algorithm, topology and boundary conditions) are not so obvious.This study was addressed to analyse the effect of SOMs parameters on the network classification performance, as well as on their computational times, taking into consideration a significant number of real datasets, in order to achieve a comprehensive statistical comparison. Parameters were contemporaneously evaluated by means of an approach based on the design of experiments, which enabled the investigation of their interaction effects.Results highlighted the most important parameters which influence the classification performance and enabled the identification of the optimal settings, as well as the optimal architectures to reduce the computational time of SOMs.
Keywords: Self Organising Maps; Kohonen maps; Classification; Training algorithm; SOMs parameters;

Display Omitted► A gold nanoparticles modified glassy carbon electrode (AuNPs/GCE) was constructed. ► The electrochemical mechanism of BHA, BHT and TBHQ at the AuNPs/GCE was studied. ► The oxidation products of BHA and TBHQ were found to be the same. ► First-derivative method was used to resolve the overlapped voltammograms. ► Synthetic antioxidants in food samples were analyzed.Electrochemical behavior of three antioxidants: butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and butylated hydroquinone (TBHQ), was investigated at a glassy carbon electrode modified with gold nanoparticles (AuNPs/GCE). This electrode was characterized by scanning electron microscopy (SEM). The experimental results indicated that the modified electrode was strongly electroactive during the redox reactions of BHA, BHT and TBHQ, and this was confirmed by the observed increased redox peak currents and shifted potentials; in addition, the oxidation products of BHA and TBHQ were found to be the same. The experimental conditions were optimized and the oxidation peaks of BHA and BHT were clearly separated. Based on this, an electrochemical method was researched and developed for the simultaneous determination of BHA, BHT and TBHQ in mixtures with the use of first derivative voltammetry; the linear concentration ranges were 0.10–1.50 μg mL−1, 0.20–2.20 μg mL−1 and 0.20–2.80 μg mL−1, and detection limits were 0.039, 0.080 and 0.079 μg mL−1, for BHA, BHT and TBHQ, respectively. The proposed method was successfully applied for the analysis of the three analytes in edible oil samples.
Keywords: Gold nanoparticles modified glassy carbon electrode; Electrochemical behavior; Cyclic voltammetry; Food antioxidant analysis;

Novel electrochemical biosensor based on functional composite nanofibers for sensitive detection of p53 tumor suppressor gene by Xiaoying Wang; Xiaobing Wang; Xiaoning Wang; Fentian Chen; Kehui Zhu; Qian Xu; Meng Tang (63-69).
Display Omitted► A novel electrochemical p53 biosensor based on functional composite nanofibers (MWNTs–PA6–PPy) was developed. ► The MWNTs–PA6–PPy electrode with large specific surface area and good biocompatibility can be used to enhance stability, speed and sensitivity. ► The biosensor can detect 50 fM wild type p53 sequence. ► The strategy could be extended to develop various sensors for the detection of many kinds of analytes.A novel electrochemical biosensor based on functional composite nanofibers for sensitive hybridization detection of p53 tumor suppressor using methylene blue (MB) as an electrochemical indicator is developed. The carboxylated multi-walled carbon nanotubes (MWNTs) doped nylon 6 (PA6) composite nanofibers (MWNTs–PA6) was prepared using electrospinning, which served as the nanosized backbone for pyrrole (Py) electropolymerization. The functional composite nanofibers (MWNTs–PA6–PPy) used as supporting scaffolds for ssDNA immobilization can dramatically increase the amount of DNA attachment and the hybridization sensitivity. The biosensor displayed good sensitivity and specificity. The target wild type p53 sequence (wtp53) can be detected as low as 50 fM and the discrimination is up to 57.5% between the wtp53 and the mutant type p53 sequence (mtp53). It holds promise for the early diagnosis of cancer development and monitoring of patient therapy.
Keywords: Functional composite nanofibers; Electrospinning; Methylene blue; Wild type p53 sequence; Mutant type p53 sequence;

Sensitive voltammetric determination of paracetamol by poly (4-vinylpyridine)/multiwalled carbon nanotubes modified glassy carbon electrode by Hanieh Ghadimi; Ramin M.A.Tehrani; Abdussalam Salhin Mohamed Ali; Norita Mohamed; Sulaiman Ab Ghani (70-76).
Display Omitted► A P4VP/MWCNT modified glassy carbon electrode was fabricated and characterized. ► The electrode was useful for determination of paracetamol. ► At optimum conditions, ascorbic acid and uric acid did not interfere in the electrode activity. ► The electrode exhibited good sensitivity, reproducibility and stability. ► The electrode was used for the determination of paracetamol in formulation tablets and urine samples.A novel glassy carbon electrode (GCE) modified with a composite film of poly (4-vinylpyridine) (P4VP) and multiwalled carbon nanotubes (P4VP/MWCNT GCE) was used for the voltammetric determination of paracetamol (PCT). This novel electrode displayed a combined effect of P4VP and MWCNT on the electro-oxidation of PCT in a solution of phosphate buffer at pH 7. Hence, conducting properties of P4VP along with the remarkable physical properties of MWCNTs might have combined effects in enhancing the kinetics of PCT oxidation. The P4VP/MWCNT GCE has also demonstrated excellent electrochemical activity toward PCT oxidation compared to that with bare GCE and MWCNT GCE. The anodic peak currents of PCT on the P4VP/MWCNT GCE were about 300 fold higher than that of the non-modified electrodes. By applying differential pulse voltammetry technique under optimized experimental conditions, a good linear ratio of oxidation peak currents and concentrations of PCT over the range of 0.02–450 μM with a limit of detection of 1.69 nM were achieved. This novel electrode was stable for more than 60 days and reproducible responses were obtained at 99% of the initial current of PCT without any influence of physiologically common interferences such as ascorbic acid and uric acid. The application of this electrode to determine PCT in tablets and urine samples was proposed.
Keywords: Paracetamol; Multiwalled carbon nanotubes; Poly (4-vinylpyridine); Voltammetric determination;

Isotope pattern deconvolution-tandem mass spectrometry for the determination and confirmation of diclofenac in wastewaters by Ángel Castillo; Emma Gracia-Lor; Antoni Francesc Roig-Navarro; Juan Vicente Sancho; Pablo Rodríguez-González; J. Ignacio García Alonso (77-85).
Display Omitted► Isotope dilution with isotope pattern deconvolution (IPD) has been applied to LC–MS/MS. ► The procedure allows the determination of organic compounds without calibration graph. ► Diclofenac determination in wastewater showed the need of this methodology in LC–MS/MS. ► Confirmation was accomplished with routine transitions used in multiresidue analysis. ► IPD permits the minimal labeling of the analyte which minimizes isotopic effect.Isotope dilution mass spectrometry (IDMS) based on isotope pattern deconvolution (IPD) has been applied here to MS/MS (QqQ) in order to carry out the quantification and confirmation of organic compounds in complex matrix water samples without the use of a methodological IDMS calibration graph. In this alternative approach, the isotope composition of the spiked sample is measured after fragmentation by SRM and deconvoluted into its constituting components (molar fractions of natural abundance and labeled compound) by multiple linear regression (IPD). The procedure has been evaluated for the determination of the pharmaceutical diclofenac in effluent and influent urban wastewaters and fortified surface waters by UHPLC (ESI) MS/MS using diclofenac-d4 as labeled compound. Calculations were performed acquiring a part and the whole fragment cluster ion, achieving in all cases recoveries within 90–110% and coefficients of variation below 5% for all water samples tested. In addition, potential false negatives arising from the presence of diclofenac-d2 impurities in the labeled compound were avoided when the proposed approach was used instead of the most usual IDMS calibration procedure. The number of SRM transitions measured was minimized to three to make possible the application of this alternative technique in routine multi-residue analysis.
Keywords: Isotope pattern deconvolution; Tandem mass spectrometry; Isotope dilution mass; Spectrometry; Diclofenac;