A new approach to the problem of kaolinite interference in the determination of chrysotile asbestos by means of x-ray diffraction

In the determination of chrysotile asbestos by means of powder x-ray diffraction, a mathematical approach is used to overcome the problem of kaolinite interference. The overlapped peaks are deconvoluted by using least-squares and simplex optimization procedures.     

Use of experimental design for optimisation of the cold plasma ICP-MS determination of lithium,aluminum and iron in soft drinks and alcoholic beverages

A sensitive method for the simultaneous determination of (7)Li, (27)Al and (56)Fe by cold plasma ICP-MS was developed and validated. Experimental design was used to investigate the effects of torch position, torch power, lens 2 voltage, and coolant flow. Regression models and desirability functions were applied to find the experimental conditions providing the highest global sensitivity in a multi-elemental analysis. Validation was performed in terms of limits of detection (LOD), limits of quantitation (LOQ), linearity and precision. LODs were 1.4 and 159 ng L(-1) for (7)Li and (56)Fe, respectively; the highest LOD found being that for (27)Al (425 ng L(-1)). Linear ranges of 5 orders of magnitude for Li and 3 orders for Fe were statistically verified for each compound. Precision was evaluated by testing two concentration levels, and good results in terms of both intra-day repeatability and intermediate precision were obtained. RSD values lower than 4.8% at the lowest concentration level were calculated for intra-day repeatability. Commercially available soft drinks and alcoholic beverages contained in different packaging materials (TetraPack, polyethylene terephthalate (PET), commercial cans and glass) were analysed, and all the analytes were detected and quantitated.     

Analysis of food proteins and peptides by chromatography and mass spectrometry

The research topics and the analytical strategies dealing with food proteins and peptides are summarized. Methods for the separation and purification of macromolecules of food concern by both high-performance liquid chromatography (HPLC) on conventional packings and perfusion HPLC are examined. Special attention is paid to novel methodologies such those based on multi-dimensional systems that comprise liquid-phase based protein separation, protein digestion and mass spectrometry (MS) analysis of food peptide and proteins. Recent applications of chromatography and MS-based techniques for the analysis of proteins and peptides in food are discussed.     

Quantitative determination and separation of analogues of aminoglycoside antibiotics by high-performance liquid chromatography

Commercial bulk products and pharmaceutical drug formulations of aminoglycoside antibiotics obtained by fermentation (kanamycin, gentamicin, sisomicin and tobramycin) or by synthesis (amikacin) were analysed with high-performance liquid chromatography on a C8 reversed-phase column. The method is based on a pre-column derivatization of the aminoglycosides with a 2,4,6-trinitrobenzenesulphonic acid reagent and UV detection (350 nm). The quantitative determination was carried out vs. an external standard; both peak heights and areas were used. A gentamicin mixture was separated into five or four components, depending on the column used. Amikacin was separated from its possible regioisomers and kanamycin A was easily separated from its minor components B and C.     

Improved silica xerogel film processing for MALDI-TOF–MS quantitative analysis of peptides and small molecules

In this work, sol–gel derived silica films were prepared for direct desorption/ionization of organic compounds in MALDI-TOF–MS analysis with the aim of improving method precision and of reducing interfering signals at low m/z values. Two commonly used MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA), were incorporated into the sol–gel network in order to absorb laser energy and to induce analyte desorption/ionization with low or absent background signals in the mass spectra. To achieve a reproducible xerogel film formation, experimental parameters for its deposition were optimized. The gel matrices were characterized by Fourier Transform Infrared (FT-IR) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) analysis. The results proved the embedding of the matrix molecules in a disperse form into the homogeneous sol–gel material. The sol–gel matrix was then tested for the qualitative and quantitative analysis of two reference peptides, such as Bradykinin and P₁₄R. In addition, spectral quality and method performance were assessed for quantitation of melamine, a low-molecular weight compound of food safety concern. In all cases, high quality spectra and excellent mass accuracy (between 3.5 and 13 ppm) were observed. Furthermore, the experimental results evidenced a significant improvement of the measurement repeatability on spot and between spots (relative standard deviation <10%), with respect to the traditional dried-droplet sample deposition method. Good sensitivity and linearity in the concentration range explored were obtained for peptides and melamine, demonstrating the suitability of the sol–gel-based matrix to be used for quantitative analysis.     

Differentiation of the volatile profile of microbiologically contaminated canned tomatoes by dynamic headspace extraction followed by gas chromatography-mass spectrometry analysis

The aromatic profile of microbiologically contaminated canned tomatoes was analyzed by the dynamic headspace extraction technique coupled with gas chromatography-mass spectrometry. Canned tomatoes contaminated with Escherichia coli, Saccharomyces cerevisiae and Aspergillus carbonarius were analyzed after 2 and 7 days. About 100 volatiles were detected, among which alcohols, aldehydes and ketones were the most abundant compounds. Gas chromatographic peak areas were used for statistical purposes. First, principal component analysis was carried out in order to visualize data trends and clusters. Then, linear discriminant analysis was performed in order to detect the set of volatile compounds ables to differentiate groups of analyzed samples. Five volatile compounds, i.e. ethanol, β-myrcene, o-methyl styrene, 6-methyl-5-hepten-2-ol and 1-octanol, were found to be able to better discriminate between uncontaminated and contaminated samples. Prediction ability of the calculated model was estimated to be 100% by the “leave-one-out” cross-validation. An electronic nose device was then used to analyze the same contaminated and not contaminated canned tomato samples. Preliminary results were compared with those obtained by dynamic headspace gas chromatography-mass spectrometry, showing a good agreement.     

Mass spectrometry and hydrogen/deuterium exchange measurements of alcohol-induced structural changes in cellular retinol-binding protein type I

To bind and release its ligand, cellular retinol-binding protein type I (CRBP) needs to undergo conformational and dynamic changes to connect the inner, solvent-shielded cavity, where retinol is found to bind, and the outside medium. Retinol dissociation in vitro is favoured by water/alcohol mixtures whose moderately low dielectric constants mimic a property characteristic of the membrane microenvironment where this process occurs in vivo. Apo- and holo-CRBP, in either water/methanol or water/trifluoroethanol (TFE) mixtures, were analyzed at equilibrium by electrospray ionization with orthogonal quadrupole time-of-flight mass spectrometry (ESI-Q-TOFMS) to identify the alcohol-induced species. The questions were asked whether the presence of alcohols affects protein dynamics, as reflected by hydrogen/deuterium (H/D) exchange monitored by continuous-labelling experiments, and to which extent retinol dissociation influences the process. With increasing methanol, at pH near neutrality, apo-CRBP exhibits a progressively more compact conformation, resulting in reduced H/D exchange with respect to the native protein in water. Retinol dissociation from the holo-protein did not promote hydrogen replacement. Similarly, in the presence of the low TFE concentration sufficient to cause retinol dissociation, the hydrogen exchange of the resulting apo-protein was not exalted. However, in contrast with the alkanol, higher TFE concentrations induced a transition of apo-CRBP to a new alpha-helix conformation capable of exchanging all available hydrogen atoms.     

Development and validation of a solid phase micro-extraction-gas chromatography-mass spectrometry method for the determination of furan in baby-food

An efficient and simple method for the determination of furan in baby-food (vegetables and fruits) by solid phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS) was developed and validated. Experimental design was used to investigate the effects of temperature and time of extraction. The calculated regression model was used to find the experimental conditions providing the optimal SPME extraction yield. Validation was carried out in terms of limit of detection (LOD), limit of quantitation (LOQ), linearity, precision and trueness. LOD and LOQ values in the low ngkg(-1) were achieved, whereas linearity was established over two order of magnitude. Good precision was obtained both in terms of intra-day repeatability and between-day precision on two concentration levels (RSD% lower than 3.6%). Recovery values of 91.5+/-6.2% and of 96.1+/-1.3% (n=3) were calculated at 75 ngkg(-1) and 75 microgkg(-1) level. Finally, the applicability of the method to the determination of furan in a number of commercial and home-made baby-food samples was demonstrated.     

Liquid chromatography-electrospray mass spectrometry of beta-carotene and xanthophylls. Validation of the analytical method.

The investigation of beta-carotene and the xanthophylls beta-cryptoxanthin, lutein, zeaxanthin, canthaxanthin and astaxanthin using reversed-phase liquid chromatography-electrospray mass spectrometry interfaced with TurboIonspray (LC-TurboISP-MS) is described. Two narrow-bore C18 columns connected in series and an isocratic solvent system containing acetonitrile-methanol (0.1 M ammonium acetate)-dichloromethane at a flow-rate of 300 microl/min (without splitting) were used. Operating in the positive-ion mode over m/z 500-650, the effects on the formation of the molecular ion species or adduct ions and the MS detector response were investigated for carotenoids, varying the orifice plate voltage, the ring voltage and the ISP voltage. Both conventional ISP and TurboISP were performed; using the TurboISP-MS system, ionization efficiency increased with respect to ISP-MS, particularly at the highest temperature (500 degrees C). Good results were particularly obtained for beta-carotene, which was detectable at the low ng level, without the use of solution-phase oxidants. Using LC columns and acquiring in single-ion monitoring mode, detection limits were estimated to be in the 0.1-1 ng range; dynamic range was established between one- and two-orders of magnitude. Better sensitivity under positive-ion than negative-ion conditions was demonstrated.