A. Gustavo González

Universidad de Sevilla, Hispalis, Andalusia, Spain

Are you A. Gustavo González?

Claim your profile

Publications (61)128.57 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Fifty wines from the Denomination of origin (DO) of Condado de Huelva were analysed for mineral content by measuring 12 elements (Al, Ba, Ca, Cu, Fe, K, Mg, Mn, Na, P, Sr and Zn) using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Samples were previously digested by heating with H2O2/HNO3 mixture. The results obtained showed that metal data set were non-normally distributed and accordingly, non-parametric statistics were applied. The average levels (medians) of these elements found in the samples are as follows, in mg/L: 2.54 (Al); 0.06 (Ba); 82.58 (Ca); 0.21 (Cu); 3.53 (Fe); 865.34 (K); 68.87 (Mg); 0.71 (Mn); 32.77 (Na); 71.61 (P); 0.48 (Sr); 0.56 (Zn). The interrelation of metal couples was studied through the Spearman non-parametric sample correlation, being Fe/Al, P/Mg, and Zn/Ba the most important correlations established. As a result of this study, we can suggest that the contribution to the safety intake limits (per week) of the studied elements through the wine consumption is not significant. Actually, they range between 0.1% in Fe and 11.9% in Mg, for normal drinkers.
    Food Chemistry. 11/2012; 135(1):309–313.
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new method for determining dissolved cylindrospermopsin (CYN) in waters using solid-phase extraction (SPE) with graphitized carbon cartridges and quantification by liquid chromatography coupled with tandem mass spectrometry is described and discussed. The method has been suitably validated: the linear range covered is from 0.900 to 125 µg CYN/L. Limits of detection and quantification were 0.5 and 0.9 µg CYN/L, respectively, and allow CYN determination at concentrations below the guideline proposed of 1 µg CYN/L in natural waters. The method exhibits mean recoveries from 83 to 95%, and intermediate precision (relative standard deviation (%)) values from 5 to 12%, ensuring adequacy against the Association of Official Analytical Chemists guidelines. The method is robust against the following three influential factors considered in the cleanup stage: the batch of the graphitized carbon cartridges, the flow rate of the water sample through the cartridge, and the final redissolved water volume after SPE treatment. The method has been successfully applied to detection and quantification of CYN in water samples from aquaria of a toxicological in vivo laboratory experiment. Environ. Toxicol. Chem. 2012; 31: 2233-2238. © 2012 SETAC.
    Environmental Toxicology and Chemistry 07/2012; 31(10):2233-8. · 2.62 Impact Factor
  • A Gustavo González, M Angeles Herrador, Agustín G Asuero
    [Show abstract] [Hide abstract]
    ABSTRACT: Assessment of accuracy of analytical methods is a fundamental stage in method validation. The use of validation standards enables the assessment of both trueness and precision of analytical methods at the same time. Procedures of intra-laboratory testing of method accuracy using validation standards are outlined and discussed.
    Talanta 10/2010; 82(5):1995-8. · 3.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new HPLC–DAD method has been developed to identify and quantify free microcystins (MC) in biological samples from fish (intestine and liver). The toxins were extracted from 500 mg sample with a mixture of methanol–water (85 : 15, v/v) and the extracts obtained were purified employing immunoaffinity columns (IAC). The purification step was optimised by a full factorial 3 design. MC were separated using conventional C18 column and an acetonitrile-acidified water (pH 3) gradient. Detection and quantification limits resulted equal for the two toxins assayed (MC-RR and MC-LR) and were 0.15 and 0.5 µg g, respectively. The accuracy for each MC in liver samples were 96% (range 80–113%) for MC-RR and 101% (range 93–118%) for MC-LR. The results were slightly lower for intestine samples, with recoveries ranging between 85% (75–93%) for MC-RR and 88% (80–97%) for MC-LR. The proposed method was applied for the determination of free MC in fish intoxicated with these toxins, in order to determine its utility to evaluate the potential risks for human health if MC-contaminated fish are consumed. The results showed the transference of MC-LR from cyanobacterial cells to fish tissues.
    International Journal of Environmental Analytical Chemistry - INT J ENVIRON ANAL CHEM. 01/2010; 90(13):1000-1013.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to evaluate whether the enzyme-linked immunosorbent assay (ELISA) anti-Adda technique could be used to monitor free microcystins (MCs) in biological samples from fish naturally exposed to toxic cyanobacteria by using receiver operating characteristic (ROC) curve software to establish an optimal cut-off value for MCs. The cut-off value determined by ROC curve analysis in tench (Tinca tinca) exposed to MCs under laboratory conditions by ROC curve analysis was 5.90-μg MCs/kg tissue dry weight (d.w.) with a sensitivity of 93.3%. This value was applied in fish samples from natural ponds (Extremadura, Spain) in order to asses its potential MCs bioaccumulation by classifying samples as either true positive (TP), false positive (FP), true negative (TN), or false negative (FN). In this work, it has been demonstrated that toxic cyanobacteria, mainly Microcystis aeruginosa, Aphanizomenon issatchenkoi, and Anabaena spiroides, were present in two of these ponds, Barruecos de Abajo (BDown) and Barruecos de Arriba (BUp). The MCs levels were detected in waters from both ponds with an anti-MC-LR ELISA immunoassay and were of similar values (between 3.8-6.5-μg MC-LR equivalent/L in BDown pond and 4.8-6.0-μg MC-LR equivalent/L in BUp). The MCs cut-off values were applied in livers from fish collected from these two ponds using the ELISA anti-Adda technique. A total of 83% of samples from BDown pond and only 42% from BUp were TP with values of free MCs higher than 8.8-μg MCs/kg tissue (d.w.).
    Environmental Toxicology 08/2009; 26(1):45-56. · 2.71 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A comparative study of sample treatment for removing the organic matter (mainly alcohol) to analyse red wine samples for metal content (Al, Ba, Ca, Cu, Fe, K, Mg, Mn, Na, Sr and Zn) from ICP-OES has been carried out. Thus, three procedures have been assayed before metal analysis: Dry ashing (DA), wet ashing (WA) and the removal of alcohol by evaporation (AR). The obtained results showed that the three methods lead to unbiased recoveries close to 100%. However, the uncertainty of AR method was about twice of the remainder ones. From practical considerations, the DA procedure was considered more suitable for determining metal elements in wine samples by ICP-OES.
    Microchemical Journal 01/2008; 88(1):56-61. · 2.88 Impact Factor
  • Toxicology Letters - TOXICOL LETT. 01/2008; 180.
  • A Gustavo González
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, the critical aspects of supervised learning pattern recognition techniques are examined in order to apply the suitable methodology avoiding its abuse and misuse that could provide pitfalls and misleading results.
    Journal of Chromatography A 08/2007; 1158(1-2):215-25. · 4.61 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The metal content of 54 commercialized wines (30 samples from Tacoronte-Acentejo DO (class T) and 24 Valle de la Orotava DO (class O) wines) was performed by ICP-OES (Al, Ba, Cu, Fe, Mn, Sr, Zn, Ca, K, Na and Mg) and GF-AAS (Ni and Pb). Wine samples were processed by dry ashing followed by solution with 5% nitric acid. Metals were considered as suitable descriptors to differentiate between T and O classes. Supervised learning pattern recognition procedures were applied. Linear discriminant analysis (LDA) led to good results up to about 90% of correct classification. In order to improve the results, another kind of algorithms able to model non-linear separation between classes was considered: Probabilistic Neural Networks. Accordingly, excellent results were obtained, leading to sensitivities and specificities higher than 95% for the two classes.
    Talanta 05/2007; 72(1):263-8. · 3.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The characterization of “fino” wines from the Montilla-Moriles denomination of origin (DO) according to their mineral content was carried out by measuring twelve elements (Zn, P, Mn, Fe, Mg, Cu, Ca, Al, Sr, Ba, Na, K) using Inductively coupled plasma atomic emission spectrometry (ICP-AES) in fifty samples. The results obtained showed that mineral data sets were non-normally distributed and accordingly, non-parametric statistics (median, interquartile range) were applied. The interrelation of element couples was studied through the Spearman non-parametric sample correlation.
    Journal of Food Composition and Analysis. 01/2007;
  • A. Gustavo González, M. Ángeles Herrador
    [Show abstract] [Hide abstract]
    ABSTRACT: The objective of analytical method validation is to ensure that every future measurement in routine analysis will be close enough to the unknown true value for the content of the analyte in the sample. Classical approaches to validation only check performance against reference values, but this does not reflect the needs of consumers. A holistic approach to validation also takes into account the expected proportion of acceptable results lying inside predefined acceptability intervals.In this article, we give a detailed step-by-step guide to analytical method validation, considering the most relevant procedures for checking the quality parameters of analytical methods. Using a holistic approach, we also explain the estimation of measurement uncertainty and accuracy profiles, which we discuss in terms of accreditation requirements and predefined acceptability limits.
    TrAC Trends in Analytical Chemistry. 01/2007;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The metal content (Ca, Mg, Sr, Ba, K, Na, P, Fe, Al, Mn, Cu and Zn) of several ‘fino’ wines belonging to two Andalusian Denomination of Origin (DO) was determined by ICP-OES. Metal concentrations were selected as chemical descriptors for discrimination, because they play a primary role in the discrimination due to its correlation with soil nature, geographical origin and grape variety. The two studied Andalusian DO were the Jerez-Xérès-Sherry & Manzanilla-Sanlúcar de Barrameda (class D) and the Condado de Huelva (class C). Linear Discriminant Analysis (LDA) and procedures based on Artificial Neural Networks (ANN) leads to a perfect separation of classes, especially when applying Multi Layer Perceptrons ANN trained by back-propagation.
    Microchemical Journal. 01/2007;
  • A. Gustavo González, M. Ángeles Herrador
    [Show abstract] [Hide abstract]
    ABSTRACT: The accuracy of mass measurements when using electronic balances is considered within the frame of analytical assays in terms of the uncertainty budget according to the internal quality control routine, the calibration process, the balance specifications, and the weighing scenarios. Buoyancy corrections for both conventional and true mass are fully discussed. The procedure is illustrated with a worked example.
    Accreditation and Quality Assurance 12/2006; 12(1):21-29. · 1.13 Impact Factor
  • A Gustavo González, M Angeles Herrador
    [Show abstract] [Hide abstract]
    ABSTRACT: Accuracy profiles of chemical assays are introduced and derived from the uncertainty of the analytical result. The calculation of accuracy profiles is based on the estimation of the measurement uncertainty of the analytical assay from validation data. For the sake of illustration, a case study dealing with the spectrofluorimetric determination of quinine in tonic water is explained in detail.
    Talanta 12/2006; 70(4):896-901. · 3.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The use of the correlation coefficient for testing the linearity of calibration curves is performed according to the ANOVA checking of the lack-of-fit. The procedure is illustrated from a case study.
    Accreditation and Quality Assurance 05/2006; 11(5):256-258. · 1.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The volatile congener analysis of 52 commercialized whiskeys (24 samples of single malt Scotch whiskey, 18 samples of bourbon whiskey, and 10 samples of Irish whiskey) was carried out by gas chromatography/mass spectrometry after liquid-liquid extraction with dichloromethane. Pattern recognition procedures were applied for discrimination of different whiskey categories. Multivariate data analysis includes linear discriminant analysis (LDA), k nearest neighbors (KNN), soft independent modeling of class analogy (SIMCA), procrustes discriminant analysis (PDA), and artificial neural networks techniques involving multilayer perceptrons (MLP) and probabilistic neural networks (PNN). Classification rules were validated by considering the number of false positives (FPs) and false negatives (FNs) of each class associated to the prediction set. Artificial neural networks led to the best results because of their intrinsic nonlinear features. Both techniques, MLP and PNN, gave zero FPs and zero FNs for all of the categories. KNN is a nonparametric method that also provides zero FPs and FNs for every class but only when selecting K = 3 neighbors. PDA produced good results also (zero FPs and FNs always) but only by selecting nine principal components for class modeling. LDA shows a lesser classification performance, because of the building of linear frontiers between classes that does not apply in many real situations. LDA led to one FP for bourbons and one FN for scotches. The worse results were obtained with SIMCA, which gave a higher number of FPs (five for both scotches and bourbons) and FNs (six for scotchs and two for bourbons). The possible cause of these findings is the strong influence of class inhomogeneities on the SIMCA performance. It is remarkable that in any case, all of the methodologies lead to zero FPs and FNs for the Irish whiskeys.
    Journal of Agricultural and Food Chemistry 04/2006; 54(6):1982-9. · 2.91 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A method for the determination of 2-furaldehyde (F) and 5-hydroxymethyl-2-furaldehyde (HMF) in alcoholic beverages by high performance liquid chromatography (HPLC) is described. A C-18 column and an acetonitrile–water mobile phase with isocratic elution were used. UV detection at 280 nm was carried out. The method was validated according to the EURACHEM guidelines. The procedure offers a high specificity and detection limits of the order of 0.005 μg mL− 1. Recoveries of 94–103% were obtained from spiked samples at different levels with both analytes. Intermediate precision calculated for a period of 2 months was + 0.8% for HMF and + 0.4% for F. The method was applied to the analysis of alcoholic beverages like bourbon, rum, brandy, liquors and aperitif wines.
    Microchemical Journal 01/2006; · 2.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A spectrophotometric method for determining sucrose is proposed. Sucrose is hydrolyzed by invertase into glucose and fructose. Then, glucose is oxidized in presence of glucose oxidase and the produced hydrogen peroxide reacts with phenol-4-sulfonic acid sodium salt and 4-aminoantipyrine in presence of peroxidase, yielding a pink dye with an absorption maximum at 505 nm. This method was validated following the EURACHEM and VAM project guidelines for method validation. Trueness, precision, robustness, sensitivity and linearity were considered. The method was applied to the determination of sucrose in green and roasted coffee beans. A comparison with the HPLC method with pulsed amperometric detection was carried out.
    Talanta 11/2005; 67(4):760-6. · 3.50 Impact Factor
  • A. Gustavo González, M. Ángeles Herrador, Agustín G. Asuero
    [Show abstract] [Hide abstract]
    ABSTRACT: The uncertainty evaluation of mass measurements when using “in-house” calibrated analytical balances is revisited according to the Guide to the expression of Uncertainty Measurement (GUM). The calibration of analytical balances is discussed according to the guidelines of several bodies such as ASTM, UKAS and DKD/PTB. The remainder components of uncertainty can be estimated from the balance data sheet specifications.
    Accreditation and Quality Assurance 06/2005; 10(7):386-391. · 1.13 Impact Factor
  • A Gustavo González, M Angeles Herrador, Agustín G Asuero
    [Show abstract] [Hide abstract]
    ABSTRACT: The estimation of the measurement uncertainty of analytical assays based on the LGC/VAM protocol from validation data is fully revisited and discussed in the light of the study of precision, trueness and robustness.
    Talanta 03/2005; 65(4):1022-30. · 3.50 Impact Factor