Just Published: Analytica Chimica Acta

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Analytica Chimica Acta
http://rss.sciencedirect.com/publication/science/5216

Selected papers from the latest issue:

Introducing nonlinear, multivariate ‘Predictor Surfaces’ for quantitative modeling of chemical systems with higher-order, coupled predictor variables

14 September 2012, 05:52:17

Publication year: 2012
Source:Analytica Chimica Acta, Volume 746
Rebecca B. Horton, Morgan McConico, Currie Landry, Tho Tran, Frank Vogt
Innovations in chemometrics are required for studies of chemical systems which are governed by nonlinear responses to chemical parameters and/or interdependencies (coupling) among these parameters. Conventional and linear multivariate models have limited use for quantitative and qualitative investigations of such systems because they are based on the assumption that the measured data are simple superpositions of several input parameters. ‘Predictor Surfaces’ were developed for studies of more chemically complex systems such as biological materials in order to ensure accurate quantitative analyses and proper chemical modeling for in-depth studies of such systems. Predictor Surfaces are based on approximating nonlinear multivariate model functions by multivariate Taylor expansions which inherently introduce the required coupled and higher-order predictor variables. As proof-of-principle for the Predictor Surfaces’ capabilities, an application from environmental analytical chemistry was chosen. Microalgae cells are known to sensitively adapt to changes in environmental parameters such as pollution and/or nutrient availability and thus have potential as novel in situ sensors for environmental monitoring. These adaptations of the microalgae cells are reflected in their chemical signatures which were then acquired by means of FT-IR spectroscopy. In this study, the concentrations of three nutrients, namely inorganic carbon and two nitrogen containing ions, were chosen. Biological considerations predict that changes in nutrient availability produce a nonlinear response in the cells’ biomass composition; it is also known that microalgae need certain nutrient mixes to thrive. The nonlinear Predictor Surfaces were demonstrated to be more accurate in predicting the values of these nutrients’ concentrations than principal component regression. For qualitative chemical studies of biological systems, the Predictor Surfaces themselves are a novel tool as they visualize nonlinearities and more importantly the coupling among predictor variables. Thus, they can serve as a novel tool for studies in bioanalytical chemistry, biology, and ecology.

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This Prediction Surface Y β ˆ ( x ) describes how the FT-IR spectrum of the microalgae species Dunaliella parva changes as a function of the carbon concentration x = c C in the culturing medium. The black spectrum was obtained from a D. parva sample grown under an unknown carbon concentration which is determined by that concentration for which the spectrum fits closest onto the Predictor Surface.

► Novel nonlinear chemometric calibration incorporates higher-order and coupled predictor terms. ► Predictor Surfaces visualize nonlinearities and coupling among chemical parameters. ► Microalgae cells act as in situ bioprobes for quantifying environmental parameters. ► Novel monitoring method for shifts in marine ecosystems and resulting ecological consequences.

Sample preparation methods for subsequent determination of metals and non-metals in crude oil—A review

14 September 2012, 05:52:17

Publication year: 2012
Source:Analytica Chimica Acta, Volume 746
Paola A. Mello, Juliana S.F. Pereira, Marcia F. Mesko, Juliano S. Barin, Erico M.M. Flores
In this review sample preparation strategies used for crude oil digestion in last ten years are discussed focusing on further metals and non-metals determination. One of the main challenges of proposed methods has been to overcome the difficulty to bring crude oil samples into solution, which should be compatible with analytical techniques used for element determination. On this aspect, this review summarizes the sample preparation methods for metals and non metals determination in crude oil including those based on wet digestion, combustion, emulsification, extraction, sample dilution with organic solvents, among others. Conventional methods related to wet digestion with concentrated acids or combustion are also covered, with special emphasis to closed systems. Trends in sample digestion, such as microwave-assisted digestion using diluted acids combined with high-efficiency decomposition systems are discussed. On the other hand, strategies based on sample dilution in organic solvents and procedures recommended for speciation analysis are reported as well as the use of direct analysis in view of the recent importance for crude oil field. A compilation concerning sample preparation for crude oil provided by official methods as well as certified reference materials available for accuracy evaluation is also presented and discussed.

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► Sample preparation strategies used for crude oil in last ten years are discussed. ► Methods related to wet digestion with concentrated acids or combustion are covered. ► Trends in sample preparation are discussed, as well as speciation analysis. ► Methods focusing on further metals and non-metals determination are discussed. ► Official methods are covered and certified reference materials are summarized.

Insights into information contained in multiplicative scatter correction parameters and the potential for estimating particle size from these parameters

14 September 2012, 05:52:17

Publication year: 2012
Source:Analytica Chimica Acta, Volume 746
Yi-Chieh Chen, Suresh N. Thennadil
This paper investigates the nature of information contained in scatter correction parameters. The study had two objectives. The first objective was to examine the nature and extent of information contained in scatter correction parameters. The second objective is to examine whether this information can be effectively extracted by proposing a method to obtain particularly the mean particle diameter from the scatter correction parameters. By using a combination of experimental data and simulated data generated using fundamental light propagation theory, a deeper and more fundamental insight of what information is removed by the multiplicative scatter correction (MSC) method is obtained. It was found that the MSC parameters are strongly influenced not only by particle size but also by particle concentration as well as refractive index of the medium. The possibility of extracting particle size information in addition to particle concentration was considered by proposing a two-step method which was tested using a 2-component and 4-component data set. This method can in principle, be used in conjunction with any scatter correction technique provided that the scatter correction parameters exhibit a systematic dependence with respect to particle size and concentration. It was found that the approach which uses the MSC parameters gave a better estimate of the particle diameter compared to using partial least squares (PLS) regression for the 2-component data. For the 4 component data it was found that PLS regression gave better results but further examination indicated this was due to chance correlations of the particle diameter with the two of the absorbing species in the mixture.

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► Indepth analysis of information contained in MSC parameters. ► MSC parameters vary systematically with particle size and concentration. ► A novel method to extract the mean particle diameter from the MSC parameters.

Electroanalytical and isothermal calorimetric study of As(III) complexation by the metal poisoning remediators, 2,3-dimercapto-1-propanesulfonate and meso-2,3-dimercaptosuccinic acid

14 September 2012, 05:52:17

Publication year: 2012
Source:Analytica Chimica Acta, Volume 746
Santiago Cavanillas, Elena Chekmeneva, Cristina Ariño, José Manuel Díaz-Cruz, Miquel Esteban
A recently developed methodology, which combines voltammetry, ITC, ESI-MS and several chemometric tools, has been applied for the first time to the study of As(III) complexes. The ligands considered, DMSA and DMPS, are commonly used to treat heavy metal poisoning. The study yields a reliable and consistent picture of the binding of As(III) by the chelating therapy agents DMSA and DMPS providing an unambiguous description of the stoichiometries of the complexes (ML2, with the occasional appearance of ML in the case of DMSA), both ligands have stability constants of the same order, with a log β 2 of 9.2 and 9.8, respectively. These values confirm the potential efficiency of both ligands in the treatment of As(III) poisoning.

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► A voltammetric approach is applied to the study of As(III) complexation by poisoning remediators. ► Voltammetry measurements are complemented with Isothermal Titration Calorimetry (ITC) and Electrospray Ionization Mass Spectrometry (ESI-MS). ► Voltammetric data are analyzed by Gaussian Peak Adjustment (GPA) method.

Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode

14 September 2012, 05:52:17

Publication year: 2012
Source:Analytica Chimica Acta, Volume 746
Pascal Salaün, Kristopher B. Gibbon-Walsh, Georgina M.S. Alves, Helena M.V.M. Soares, Constant M.G. van den Berg
The oxidation potentials of As⁰/As^III and Sb⁰/Sb^III on the gold electrode are very close to each other due to their similar chemistry. Arsenic concentration in seawater is low (10–20nM), Sb occurring at ∼0.1 time that of As. Methods are shown here for the electroanalytical speciation of inorganic arsenic and inorganic antimony in seawater using a solid gold microwire electrode. Anodic stripping voltammetry (ASV) and chronopotentiometry (ASC) are used at pH≤2 and pH 8, using a vibrating gold microwire electrode. Under vibrations, the diffusion layer size at a 5μm diameter wire is 0.7μm. The detection limits for the As^III and Sb^III are below 0.1nM using 2min and 10min deposition times respectively. As^III and Sb^III can be determined in acidic conditions (after addition of hydrazine) or at neutral pH. In the latter case, oxidation of As⁰ to As^III was found to proceed through a transient As^III species. Adsorption of this species on the gold electrode at potentials where Sb^III diffused away is used for selective deposition of As^III. Addition of EDTA removes the interfering effect of manganese when analysing As^III. Imposition of a desorption step for Sb^III analysis is required. Total inorganic arsenic (iAs=As^V +As^III) can be determined without interference from Sb nor mono-methyl arsenious acid (MMA) at 1.6<pH<2 using E dep =−1V. Total inorganic antimony (iSb=Sb^V +Sb^III) is determined at pH 1 using E dep =−1.8V without interference by As. The methods were tested in samples from the Irish Sea (Liverpool Bay). As^III was determined on-board ship immediately after sampling. As^III concentrations were found to range from 0.44 to 1.56nM and were higher near the coast. Sb^III was below the detection limit (<0.1nM Sb^III), iAs was comprised between 8 and 25nM while iSb varied from 0.5 to 1.7nM.

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► Inorganic speciation of arsenic and antimony in seawater at a gold electrode. ► Sensitive methods both in relatively low acidic and in neutral conditions of pH. ► New experimental approaches to decrease detection limits and avoid interferences. ► As^III remains adsorbed on the gold surface after stripping during a short time. ► On-board analysis of As(III) at sub nanomolar levels.