María P. Hernández-Artiga

Differentiation and classification of beers with flame atomic spectrometry and molecular absorption spectrometry and sample preparation assisted by microwaves

Abstract The characterization of beer samples has a lot of interest because their composition can affect the taste and stability of beer and consumer health. Flame atomic absorption spectrometry was used to determine Fe, Mn, Zn, Cu, Mg, Ca and Al. Sodium and K were determined by flame atomic emission spectrometry. A sample preparation method was developed, based on treatment with HNO 3 and H 2 O 2 in a microwave oven. This has many advantages over the methods found in the literature. The combination of the results of atomic spectrometry and the spectrum obtained by molecular absorption spectrometry provides information on the inorganic and organic components of the samples. The application of chemometric techniques to chemical composition data could be extremely useful for food quality control. The metal concentrations, the molecular absorption spectrum, the pH and conductivity of each sample were subject to analysis of variance and linear discriminant analysis. Twenty-five different beer samples were used to differentiate and classify different types of beers.

Determination of wear metals in marine lubricating oils by microwave digestion and atomic absorption spectrometry

Abstract The difficulties associated with the development of a microwave-assisted acid digestion of lubricating oils in determination of wear metals are presented. The interest of this sample treatment lies in its basis for determining the total metal contents with enough sensitivity by flame atomic absorption spectrometry (FAAS). It allows earlier diagnosis of the engine state than is obtained by the widely applied simple dilution procedure. Another advantage is the avoidance of contamination and loss of the metals to be determined. The procedure employs nitric acid and hydrogen peroxide in a four-stage programme. Fe, Cu, Cr and Pb are determined by FAAS as representative of engine wear. The limits of detection are 0.1 μg/g for Fe and Cr and 0.05 μg/g for Cu and Pb. A comparison with other procedures is presented for spiked samples. Different types of used lubricating oils supplied by an oil company were analysed to prove the suitability of the procedure proposed.

Voltammetric determination of 2-nitrophenol at a bentonite-modified carbon paste electrode

A bentonite-modified carbon paste electrode has been applied to the determination of 2-nitrophenol by differential pulse voltammmetry. The electrochemical reduction of 2-nitrophenol at −0.8 V is carried out in an artificial sea water-formic acid/sodium formate medium at pH 4. The peak height was found to be dependent on the pH over the range 2–11; the presence of a secondary process was observed in the pH range 8–11. The peak potential showed a dependence on pH, with two linear regions with different slopes. A linear relationship between peak intensity and concentration was obtained in the range 0.07–10 mgl−1, with a detection limit of 0.03 mg 1−1 and a coefficient of variation of 1.3% at 5 mg 1−1. The effects of organic and inorganic species on the 2-nitrophenol determination were studied with a view to testing the resolution of the voltammetric technique. The proposed method has been applied to sea water samples with good results.

Selective methods for polyphenols and sulphur dioxide determination in wines.

A critical review to the methods recommended by international bodies and widely used in the winery industry and research studies was performed. A Laccase biosensor was applied to the selective determination of polyphenols in wines. The biosensor response was characterised and it responds mainly to o-diphenols which are the principal polyphenols responsible for the stability and sensory qualities of wines. The spectrophotometric method to determine free and total sulphur dioxide recommended for beers was applied directly to wines. A sampling of 14 red and white wines was performed and they were analysed for biosensor polyphenol index (IBP) and sulphur dioxide concentration (SO2). The antioxidant capacity by the ABTS(+) spectrophotometric method was also determined. A correlation study was performed to elucidate the influence of the polyphenols and SO2 on the wines stability. High correlations were found between IBP and antioxidant capacity and low correlation between SO2 and antioxidant capacity. To evaluate the benefits of wine drinking a new parameter (IBP/SO2) is proposed.

Analytical Study of Hygiene Hazards Involved in Naval Industry Welding Processes

Abstract The metal contents of welding fumes produced at the shipyard Astilleros Espanoles in Puerto Real, Spain, were investigated to assess the hygiene hazards in order to improve health conditions at the factory. Personal and environmental samples were collected on a cellulose or polyvinylchloride filter with the aid of a sampler in compliance with National Institute for Occupational Safety and Health standard methods. Quantitative metal determinations were carried out by flame atomic absorption spectroscopy. A microscopic examination was also achieved to assess shape and size of metal particles. The results obtained for metals and particles were compared with established threshold limit values, and conclusions were drawn according to the type of welding procedure, sampling place, and use of fume extractor.

Spectrophotometric phosphate determination in urine by ligand exchange extraction

A new spectrophotometric method for the determination of phosphate in urine is proposed, based on the ligand exchange extraction produced by phosphate solution at pH 7.5 when it is shaken with a solution of Fe(III) indole-2-carboxylate iniso-amyl alcohol. The organic layer decoloration is measured at 400 nm and the phosphate indirectly determined. The sensitivity of the method is 1.07 × 103 1 mol−1 cm−1, the linear working range 1–15 × 10−5 mol/l of phosphate and the relative standard deviation 5%. It does not require previous treatment of the sample and it is free from interferences by other normal or pathological constituents of the urine samples. The results agreed closely with those obtained by using a Sigma Diagnostics procedure for inorganic phosphorus, based on the Fiske-SubbaRow method. The method does not require special instrumentation and is not expensive.

91 – The Evaluation of Beer Aging

Beer contains certain components, which act as protective agents in relation to consumers’ health, such as antioxidants, which decrease over time. The shelf life of package beer is determined to a large extent by the appearance of haze or deterioration of the flavor. A comprehensive understanding of the mechanisms involved in beer instability has yet to be achieved. The raw materials are considered the main source of haze precursors, although the brewing process also has effects. Flavor stability depends on the oxygen content of the packaged beer, which gives rise to active oxygen species. The process of beer aging in the package is discussed with the aim of evaluating the various methods found in the literature for the detection of beer aging. These methods have been classified according to the methodology used, as follows: methodologies to measure one compound or groups of similar compounds, methodologies to detect the time elapsed for appearance of OH• radicals, simulations adding exogenous free radicals to beer, and other methods related to the general properties of sensory analysis and sensors. Correlations between sensory analysis and chemical analysis are emphasized. Attention is given to controversial opinions of authors in relation to compounds with antioxidant properties which retard beer aging. The complexity of the mechanisms and the amount of compounds involved in beer aging is pointed out. The methods that follow the evolution of general properties are considered more closely related to beer aging than those following a single compound. A secondary aim is to shed light on a more holistic understanding of beer aging, the mechanisms of which are at present only poorly understood.

Classification and Prediction Techniques Applied to Metal Concentrations Produced by Welding Fumes in a Shipyard

Statistical multivariate techniques were applied to the metal content obtained from welder personal sampling at a shipyard. The data used were the concentration of Fe, Mn, Cu, Cr, Ni, Cd, Zn and the particle total content determined by AAS and by gravimetry. Predictive models for Fe and Mn concentrations have been obtained in function of the particle total content with the ridge linear regression. The sample classification techniques commonly used in contamination studies as principal component analysis (PCA) did not allow us to obtain differentiated groups. Linear discriminant analysis (LDA) was used as an alternative technique; it indicated that the extractor systems employed are not effective and they must be improved. Factor analysis (FA) was used as a tool to classify variables. The result is in accordance with the common origin of Fe, Mn and Cu.