Theory of bulk and flow electrolysis and approach to parameter optimisation for chromatographic electrochemical detection

The performance and characteristics of an amperometric-coulometric detector for liquid chromatography were investigated as a function of the main chromatographic parameters. Hydroquinone was chosen as reference compound. Starting from the theory of bulk and flow electrolysis, the effect of eluent flow rate on the detector response was investigated and the agreement between experimental and calculated data was verified. The study was preceded by an investigation of the detector behaviour in different chromatographic operating conditions: void volume evaluation, effect of mobile phase composition on baseline behaviour, current/potential curve for analyte and mobile phase, analyte stability, linearity, repeatability of the detector response and electrochemical exclusion from interferences were examined

Determination of stability constants of metal-azo dyes complexes by ion-exchange and spectrophotometry

The stability constants of the complexes of Al, Cu, Fe, Ni with two sulphonated azo-ligands, namely Calcichrome and SPADNS, were determined with three different procedures. One procedure is based on ion exchange and involves the retention of the negatively charged complexes onto an anion exchange resin and the determination of free and complexed metal. The other two techniques are based on the different UV-visible absorbances of free ligand and complex: the first one provides a value for the conditional stability constants, which in turn allows the calculation of the apparent and thermodynamic constants; the second procedure is a graphic method of extrapolation and directly provides the value of the apparent stability constants

Speciation of copper and manganese in milk by solid-phase extraction/inductively coupled plasma-atomic emission spectrometry

A speciation method was developed to study distribution of copper and manganese species in cow milk. The method is based upon solid-phase extraction of selective fractions of the analytes, followed by elution and determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES), using it as a flow-injection detector. Fractions detected were cationic, anionic, neutral and casein-bound. A different behaviour is observed for the two metals

Determination of metals in highly saline matrices by solid-phase extraction and slurry-sampling inductively coupled plasma-atomic emission spectrometry

Matrix removal and preconcentration of metals from liquid samples were obtained with a solid-phase extraction/slurry-sampling procedure applied to inductively coupled plasma-atomic emission spectrometry (ICP-AES) detection. A polymeric, adsorbing resin (Amberlite XAD-2), dispersed in the sample, was used for total sorption of analytes previously complexed with a dithiocarbamate ligand. After filtration, the resin was recovered and re-dispersed by means of a non-ionic surfactant; metals retained were determined with the slurry-sampling technique. All parameters were optimised to yield a solution-like signal from the final dispersion. (C) 1998 Elsevier Science B.V. All rights reserved

Determination of metals in wine with atomic spectroscopy (flame-AAS, GF-AAS and ICP-AES); a review

Metals in wine occur at the mg l(-1) level or less and, though not directly related to the taste of the final product, their content should be determined because excess is undesirable, and in some cases prohibited, due to potential toxicity. Lead content in wine, for example, is restricted in several states by legislation to guarantee consumer health protection. Of several methods for metal determination, techniques of atomic spectroscopy are the most sensitive and rapid. Most of the elements present in wine can be determined with these techniques, at concentrations ranging from the mg l(-1) to the mug l(-1) level. Here, inductively coupled plasma-atomic emission spectrometry (ICP-AES), flame atomic absorption spectrometry (flame-AAS) and graphite furnace-atomic absorption spectrometry (GF-AAS) are compared for their characteristics as employed in metal determination in wine

Comparison of prediction power between theoretical and neural-network models in ion-interaction chromatography

The separation by ion-interaction chromatography (IIC) of metal complexes having single and double charges has been studied in order to compare the prediction power of oft (neural-network) and hard modelling (IIC equation). The two approaches have been used to model the retention behaviour as a function of the composition of the mobile phase, With ion-interaction mobile phases, the parameters involved included the concentrations of ion-interaction reagent, organic modifier and ionic strength. From a set of 69 experimental design points (the different mobile phase compositions at which capacity factors are measured), one test set of ten design points and ten training sets, containing from 59 to 11 design points, have been extracted. Chromatographic and chemometric considerations for the selection of the data sets and minimum number of observations required have been discussed. The study showed that the IIC equation predicted more accurately when few experimental data were available, while a similar prediction power was obtained with both models when the number of data was more than 17. Nevertheless the neural-network accounted for a greater versatility without the need to develop an equation. (C) 1998 Elsevier Science B.V