Clara Pérez-Ràfols

Glutathione modified screen-printed carbon nanofiber electrode for the voltammetric determination of metal ions in natural samples.

This work reports the development of a glutathione modified electrode via electrografting on a screen-printed carbon nanofiber substrate (GSH-SPCNFE). GSH-SPCNFE was compared to a classical screen-printed carbon electrode modified with glutathione (GSH-SPCE) for the simultaneous voltammetric determination of Cd(II) and Pb(II). Their electrochemical characterization and analytical performance suggest that SPCNFE could be a much better support for GSH immobilization. The applicability of GSH-SPCNFE for the determination of low concentration levels of Pb(II) and Cd(II) ions in environmental samples was successfully tested in a certified wastewater reference material by means of stripping voltammetry with a very high reproducibility and good trueness.

New approaches to antimony film screen-printed electrodes using carbon-based nanomaterials substrates.

Three different commercial carbon nanomaterial-modified screen-printed electrodes based on graphene, carbon nanotubes and carbon nanofibers were pioneeringly tested as electrode platforms for the plating with Sb film. They were microscopically and analytically compared to each other and to the most conventional unmodified carbon screen-printed electrode (SPCE). The obtained detection and quantification limits suggest that the in-situ antimony film electrode prepared from carbon nanofibers modified screen-printed electrode (SbSPCE-CNF) produces a better analytical performance as compared to the classical SPCE modified with antimony for Pb(II) and Cd(II) determination, approving its appropriateness for measuring low μg L(-1) levels of the considered metals. In-situ SbSPCE-CNF was successfully used for the simultaneous determination of Pb(II) and Cd(II) ions, by means of differential pulse anodic stripping voltammetry, in a certified reference estuarine water sample with a very high reproducibility and good trueness.

Penicillamine-modified sensor for the voltammetric determination of Cd(II) and Pb(II) ions in natural samples

A new penicillamine-GCE was developed based on the immobilization of d-penicillamine on aryl diazonium salt monolayers anchored to the glassy carbon electrode (GCE) surface and it was applied for the first time to the simultaneous determination of Cd(II) and Pb(II) ions by stripping voltammetric techniques. The detection and quantification limits at levels of µg L(-1) suggest that the penicillamine-GCE could be fully suitable for the determination of the considered ions in natural samples.

Liquid chromatographic fingerprints and profiles of polyphenolic compounds applied to the chemometric characterization and classification of beers

In this paper, liquid chromatography with UV-vis detection was used to generate compositional fingerprints of beers to be exploited for characterization and classification purposes. Chromatographic profiles recorded at 280 nm contained features mainly associated with polyphenolic components such as phenolic acids and flavonoids. Beers of different styles and brewed in various countries were analyzed by the proposed method and the data generated were treated chemometrically to assess characterization and classification models. Three different types of data sets based on chromatograms, peak areas and concentrations were explored by principal component analysis (PCA) to evaluate their performances to discriminate among ale and lager beers. The use of raw chromatographic profiles required a comprehensive pretreatment to improve the data quality. When dealing with peak areas, single and complex integrated peaks of known and/or unknown compounds were used as the source of analytical information. In these two approaches (chromatographic fingerprints and peak areas), calibration was not necessary so the sample analysis was simplified. In the case of concentrations, selected phenolic acids and flavonoids were considered as the data to discriminate among beer types. Differences in the polyphenolic composition were relevant and some components resulted in efficient markers of beer classes. Further studies based on partial least squares discriminant analysis (PLS-DA), soft independent modelling of class analogy (SIMCA) and other methods were used to discriminate beers according to brewing styles. Classifications were highly satisfactory in terms of selectivity and sensitivity as, in general, beers of test sets were correctly assigned to their actual classes.

Determination of Pd(II) using an antimony film coated on a screen-printed electrode by adsorptive stripping voltammetry

The use of an antimony film coated on a screen-printed carbon electrode (ex-situ SbSPCE) is proposed for the determination of Pd(II) at ppb levels in natural samples by adsorptive stripping voltammetry using dimethylglyoxime as chelating agent. Ex-situ SbSPCE produces a better analytical performance as compared to a commercially sputtered bismuth screen-printed electrode (BispSPE). The detection and quantification limits were 2.7 and 9.0µgL-1 respectively with a good linear behaviour in the wide examined concentration range (from 1µgL-1 up to 100.0µgL-1, R2=0.998). The proposed ex-situ SbSPCE showed an excellent repeatability with a relative standard deviation of 0.5% for ten successive measurements and a very good reproducibility (1.6% for three different ex-situ SbSPCE units within series of ten repetitive assays). Moreover, the ex-situ SbSPCE was successfully applied for the determination of low concentration levels of Pd(II) in spiked tap water with a very high reproducibility (0.2%) and providing equivalent results to those achieved by ICP-MS measurements.

Ag Nanoparticles Drop-Casting Modification of Screen-Printed Electrodes for the Simultaneous Voltammetric Determination of Cu(II) and Pb(II)

A new silver nanoparticle modified screen-printed electrode was developed and applied to the simultaneous determination of Pb(II) and Cu(II). Two different types of silver nanoparticles with different shapes and sizes, Ag nanoseeds and Ag nanoprisms, were microscopically characterized and three different carbon substrates, graphite, graphene and carbon nanofibers, were tested. The best analytical performance was achieved for the combination of Ag nanoseeds with a carbon nanofiber modified screen-printed electrode. The resulting sensor allowed the simultaneous determination of Pb(II) and Cu(II) at trace levels and its applicability to natural samples was successfully tested with a groundwater certified reference material, presenting high reproducibility and trueness.

Selenocystine modified screen-printed electrode as an alternative sensor for the voltammetric determination of metal ions

A novel selenium based screen-printed electrode was developed based on the immobilization of selenocystine on aryl diazonium salt monolayers anchored to a carbon-nanofiber screen-printed electrode support (SeCyst-SPCNFE). SeCyst-SPCNFE was analytically compared to a screen-printed carbon nanofiber electrode modified with L-Cystine (Cyst-SPCNFE) for the determination of Pb(II) and Cd(II) by stripping voltammetric techniques. Their analytical performance suggests that SeCyst-SPCNFE could be a much better alternative for metal ion determination at trace levels than Cyst-SPCNFE. The proposed electrode was successfully applied for the simultaneous voltammetric determination of trace Pb(II) and Cd(II) in a wastewater reference material with a very high reproducibility (3.2%) and good trueness (2.6%).

Experimental design for the determination of polyphenols by liquid chromatography: application to the chemometric characterization and classification of beers

This paper describes the development and application of a simple, rapid and inexpensive chromatographic method to determine polyphenols in beers. The separation was optimized by experimental design considering both resolution and analysis time as the objectives. Figures of merit were established under the selected experimental conditions. In general, repeatabilities of peak areas were better than 2%, detection limits were in the order of magnitude of 0.01 mg L−1 and quantitative recovery percentages were about 100 ± 5. Differences in the polyphenolic composition among beer types were encountered to be relevant. This finding was exploited to perform the characterization of commercial beers using chemometric methods such as principal component analysis. The results indicated that coumaric and ferulic acids were more abundant in lager while syringic and gentisic acids were typical of some ale varieties. Concentrations of polyphenols in the samples were used to build classification models to discriminate among lager and ale classes. Models proved to be highly efficient in terms of sensitivity and specificity. It was found that all the samples were correctly assigned to their actual classes.

A new multivariate standard addition strategy for stripping voltammetric electronic tongues: Application to the determination of Tl(I) and In(III) in samples with complex matrices

A new multivariate standard addition strategy applicable to stripping methods was proposed as an extention of the classical univariate standard addition method for the resolution of complex samples involving overlapped peaks and complex matrices. The proposed strategy consists in alternate additions of the considered analytes and the further extrapolation to a simulated blank solution measured by skipping the preconcentration step (deposition time = 0). This calibration approach was successfully tested in tonic water samples spiked with Tl(I) and In(III) using a sensor array based on a SeCyst-SPCNFE and an ex-situ-BiSPCE, providing good concordance between replicates and much better accuracy than the usual multivariate external calibration method.