Gustavo González

Determination of total arsenic, inorganic and organic arsenic species in wine

Forty-five wine samples from the south of Spain of different alcoholic strength were analysed for total arsenic and its inorganic [As(III), As(V)] and organic (monomethylarsonic acid [MMAA], dimethylarsinic acid [DMAA]) species. The As levels of the wine samples ranged from 2.1 to 14.6 µg l-1. The possible effect of the alcoholic fermentation process on the levels of the total arsenic and arsenical species was studied. The average total arsenic levels for the different samples were very similar, without significant differences between all types of wines. In table wines and sherry, the percentages of total inorganic arsenic were 18.6 and 15.6%, with DMAA or MMAA being the predominant species, respectively. In most samples, DMAA was the most abundant species, but the total inorganic aresenic fraction was considerable, representing 25.4% of the total concentration of the element. The estimated daily intakes of total arsenic and total inorganic arsenic for average Spanish consumers were 0.78 and 0.15 µg/person day-1, respectively. The results suggest that the consumption of these types of wines makes no significant contribution to the total and inorganic arsenic intake for normal drinkers. However, wine consumption contributes a higher arsenic intake than through consumption of beers and sherry brandies.

Fitting Straight Lines with Replicated Observations by Linear Regression. III. Weighting Data

The purpose of this article is to stress the importance of weighting in fitting straight lines with replicated observations. Nevertheless, single response data are also taken into account. Although the concept of weighting is treated on chemometric texts, a detailed procedure is not given. For this reason the present review covers the information concerning this topic. Ignoring non-constant variance (heterocedasticity) often leads to improper estimation and inference in a statistical model which quantifies a given relationship. There are two main solutions to remedy this problem: transform the data or perform a weighted least-squares regression analysis. Weighting with replication in homocedastic and heterodedastic condition, including transformation depending weights, and normalization of the weights are considered. Weighting of observations, however, presents a more difficult problem that has commonly been recognized. The review covers briefly topics as random errors and noise, modelling the variance as a function of the independent variable and variation of precision with concentration. By transforming variable it is possible to introduce non-linear terms to the mathematical framework of linear regression, in order to improve fit as to satisfy the necessary assumptions such as homocedasticity. However, transformation data, the analysis of variance and summary data analysis will be the subject of a future report. A number of applications concerning the uses of weighting in analytical chemistry and weighted linear regression are given in tabular form. The analytical, pharmaceutical, biochemical and clinical literature has been thoroughly revised.

Development and optimization of a method for the determination of Cylindrospermopsin from strains of Aphanizomenon cultures: Intra-laboratory assessment of its accuracy by using validation standards

The occurrence of cyanobacterial blooms in aquatic environments is increasing in many regions of the world due to progressive eutrophication of water bodies. Because of the production of toxins such as Cylindrospermopsin (CYN), contamination of water with cyanobacteria is a serious health problem around the world. Therefore it is necessary to develop and validate analytical methods that allow us to quantify CYN in real samples in order to alert the public of this toxin. In this work, an analytical method has been developed an optimized for the determination of CYN from Aphanizomenon ovalisporum cultures. The analytical procedure is based on solvent extraction followed by a purification step with graphitized cartridges and CYN quantification by LC-MS/MS. The extraction and purification steps were optimized using a two-level full factorial design with replications. A suitable and practical procedure for assessing the trueness and precision of the proposed method has been applied by using validation standards. The method has been suitably validated: the regression equation was calculated from standards prepared in extracts from lyophilized M. aeruginosa PCC7820 (r(2)≥0.9999) and the linear range covered is from 5 to 500 μg CYN/L, equivalent to 0.18-18.00 μg CYN/g dry weight lyophilized cells. Limits of detection and quantification were 0.04 and 0.15 μg CYN/g, respectively, the recovery range (%) oscillated between 83 and 94% and intermediate precision (RSD %) values from 5.6 to 11.0%. Moreover, the present method showed to be robust for the three factors considered: the batch of the graphitized carbon cartridges, the flow rate of the sample through the cartridge, and the final re-dissolved water volume after SPE treatment, which permits its validation. The validated method has been applied to different lyophilized cultures of A. ovalisporum (LEGE X-001) to evaluate CYN content. This procedure can be used for determining CYN in lyophilized natural blooms samples in environmental studies.

Presence and distribution of arsenical species in beers

The total content of arsenic and of its inorganic (As(III) and As(V)) and organic (monomethylarsonic acid, MMAA, and dimethylarsinic acid, DMAA) species were determined in a set of 21 alcoholic and alcohol-free beer samples using the technique of Hydride Generation Atomic Absorption Spectrometry. For total arsenic analysis, beer samples were dried and then microwave digested with nitric acid in polytetrafluoroethylene containers. For the speciation analysis, beers were previously subjected to ion exchange chromatography to elute the mentioned inorganic and organic arsenical species. Both microwave digestion and chromatographic separation methods were validated from certified reference materials and prepared standard solutions, respectively. The results obtained are presented in terms of the distribution and occurrence of arsenical species in the samples. The As levels of the beer samples were in the range of 1.5-12.4 micrograms/l. The influence of the production process for the alcohol-free beers in the speciation of arsenic is discussed. In alcoholic beers MMAA was the most abundant species, and for non-alcoholic beers inorganic As(III) was similar to the organic species. An estimated intake of total As of 0.47 microgram/person/day and 11.4 micrograms/person/day was obtained for average consumers and for heavy drinkers, respectively.

Asymmetric derivatives of carbohydrazide and thiocarbohydrazide as analytical reagents.

The synthesis and analytical properties of two asymmetric derivatives of carbohydrazide and thiocarbohydrazide with pyridine and phenol have been studied. The compounds tested are 1-(2-pyridylmethylideneamino)-3-(salicylideneamino)urea and 1-(2-pyridylmethylideneamino)-3-(salicylideneamino) thiourea. The analytical utility of these reagents is outlined. A spectrophotometric method for determining the formation constants of the complexes is described.

Ab initio CI calculations on the molecular structure of Sn2H4 isomers

Abstract An ab initio CI study on three Sn2H4 formulae isomers is reported. Geometry optimizations at RHF and two reference second-orderMoller-Plesset with respect to trans-bent structure by about 10 kcal mol−1. Stannilstannilene SnH3SnH appears to be slightly stabilized with respect to trans-bent distannene. A vibrational analysis shows that planar distannene is not a true minimum on the potential hypersurface. Geometrical structure and correlation effects are discussed. Dissociation energy of distannene into two stannene molecules is calculated to be 28.37 kcal mol−1.

Titration errors in acid-base titrations

Abstract An attempt to offer a unified treatment of titration error in acid-base titrations is given in this paper. Special attention has been paid to the relationships between the titration error and the maximum sharpness index for various kinds of acid-base titrations.

A theoretical approach to the molecular structure of vinylstannane and some structural isomers

Abstract A theoretical study of the electronic and molecular structure of vinylstannne SnH 3 CHCh 2 and structure isomers CH 2 SnHCH 3 and SnH 2 CHCH 3 has been caried out. Ab initio Hartree-Fock calculations were performed using an effective core potential to describe the core electrons of tin. Vinylstannane has a propene-like structure with a SnC bond similar to that of methylstannane. As in propene, the eclipsed rotamer is more stable than the bisected one. The molecular structures of CH 2 SnHCH 3 and SnH 2 CHCH 3 are planar according to the ΔE ST - E ( σ + π ) model. The structures of allylic-type species SnH 2 CHCH 2 and CH 2 SnHCH 2 (cations, radicals and anions) have also been considered.

On the evaluation of autoprotolysis constants of amphiprotic solvents from electrochemical measurements

Abstract A modified procedure for the evaluation of autoprotolysis constants from electrochemical techniques which takes into account deviations from the Nernstian slope is given. The method has been applied to the literature data given for several practical systems in order to illustrate it. The error propagation is obtained along with the normal calculation of the parameters.

Acid-base equilibria of biacetylmonoxime 2-picolyl-imine

Abstract The spectral characteristics of biacetylmonoxime 2-picolyl-imine (BMPA) are reported in this paper. The acid-base behavior of BMPA is spectrophotometrically studied.