F. García Montelongo

Separation of phenolic compounds by high-performance liquid chromatography with absorbance and fluorimetric detection

Phenolic compounds including phenolic aldehydes, acids and flavonoids are separated by high-performance liquid chromatography (HPLC) with analysis time shorter than described in the literature. The use of a fluorescence detector in series with absorbance detector allowed increasing selectivity and sensitivity for the determination of catechin, vanillic acid, syringic acid, epicatechin and trans-resveratrol in wine samples. An optimised sample preparation method using liquid-liquid extraction with diethyl ether at pH 2.0 was used. The optimised method was applied to analyse wine samples with good results.

Optimisation of sample preparation for the determination of trans-resveratrol and other polyphenolic compounds in wines by high performance liquid chromatography

Abstract Different methods for sample preparation as a preliminary stage for the simultaneous determination of trans -resveratrol and other polyphenolic compounds are compared with the aim to establish the best conditions for the determination of these compounds in wine samples by high performance liquid chromatography (HPLC). Sample preparation using liquid–liquid extraction and solid-phase extraction were compared. Liquid–liquid extraction using as organic solvent diethyl ether at pH 2.0 shows the best results. The dried extract was solved in methanol/water 1:1 (v/v) that improve drastically the separation efficiency. The developed method was applied to the analysis of wines from the Canary Islands.

Optimization of the separation of phenolic compounds by micellar electrokinetic capillary chromatography

A group of phenolic compounds including phenolic aldehydes, acids and flavonoids are separated by micellar electrokinetic chromatography (MECC). The influence of buffer (concentration and pH), concentration of sodium dodecylsulphate (SDS) and applied voltage were studied. To increase the selectivity of the separation and the resolution of the solutes organic solvents are added to the separation buffer, the best results were obtained when methanol was used at lower percentages. An optimized buffer (150 mM boric acid (pH 8.5)-50 mM SDS-5% methanol) provides the optimum separation with regard to resolution and migration time. This method was applied to the determination of these compounds in wine samples with good results.

Influence of alcoholic modifiers on the selectivity of the separation of a group of polycyclic aromatic hydrocarbons by micellar liquid chromatography

Abstract The role of micelles and alcohols as the modifiers of the aqueous mobile phase in reversed-phase liquid chromatography in controlling retention and selectivity of polyaromatic hydrocarbons (PAHs) is studied. Elution strength increases with an increase in the alcohol or micelle concentration, and enhancement of separation selectivity with elution strength was observed. Increasing micelle concentration has an opposite effect, when compared to increasing alcohol modifier concentration, on the separation selectivity, showing that for this group of PAHs the separation selectivity is better with mobile phases of medium concentration of micelles and moderately high alcohol percentages. The selectivity enhancement can be explained in terms of the competing equilibria in micellar liquid chromatography.

Levels of Metals in Canned Meat Products: Intermetallic Correlations

The analytical control of heavy metals in food is particularly important, since these pollutants are notably cumulative in nature and, therefore, can be toxic to humans. Their determination in foods of animal origin is of interest. In this study analyses of seven heavy metals in semipreserved ham and shoulder pork, preserved lunch pork and pork liver paste were performed to determine the possible influence of the container itself on the levels of metals in such products. Not only were the toxic elements cadmium and lead studied, but also copper, zinc, iron, nickel and manganese which, although not essentially toxic, could, in high concentration, cause public health hazards or a decrease in the organoleptic quality of the canned product, with resultant economic effect.

Comparative study of the zero-crossing, ratio spectra derivative and partial least-squares methods applied to the simultaneous determination of atrazine and its degradation product desethylatrazin-2-hydroxy in ground waters.

The application of the ratio spectra derivative and partial least-squares methods to the simultaneous determination of atrazine and its degradation product desethylatrazin-2-hydroxy is presented. When the different methods are applied to the determination of these products in ground waters, PLS method gives the best results due to the presence of interfering substances with overlapping spectra.

Correlations between lead, cadmium, copper, zinc, and iron concentrations in frozen tuna fish.

The presence of metallic pollutants in marine ecosystems has promoted wide research plans in order to evaluate pollution levels in marine organisms. However, little is known concerning environmental and physiological processes that regulate the concentration of trace metals in marine organisms. Even though the toxicity of lead and cadmium is well established, copper, zinc and iron are considered as essential elements for mammals. Little is known about heavy metals, other than mercury, concentrations in fresh and frozen tuna fish. Fifty samples obtained at the entrance of a canning factory in Santa Cruz de Tenerife (Canary Islands), were analyzed by atomic absorption spectrophotometry. Results were treated by applying the Statistical Package for the Social Sciences compiled and linked in the software of a Digital VAX/VMS 11/780 computer.

Solute-micelle association constants of some polynuclear aromatic hydrocarbons by micellar liquid chromatography with alcohol additives to mobile phase

SummaryThe interaction between some polynuclear aromatic hydrocarbons of environmental concern, and sodium dodecylsulphate and hexadecyltrimethylammonium bromide in the presence of methanol, 2-propanol and n-butanol has been evaluated by high-performance liquid chromatography using micellar mobile phases. Solute-micelle association constants have been determined for the compounds investigated. The results show that the addition of the alcohol to the mobile phase decreases the association constant values, methanol <2-propanol

Analytical applications of 3-(2′-thiazolylazo)-2,6-diaminopyridine: Spectrophotometric determination of palladium

Abstract 3-(2′-Thiazolylazo)-2,6-diaminopyridine reacts with palladium(II) in strongly perchloric acid media, to produce a blue 1:1 complex (λ max = 665 nm, ϵ = 1.37 × 10 4 liters · mol −1 · cm −1 ), which allows the spectrophotometric determination of 0.6 to 4.5 ppm of palladium. The method is applied to the determination of palladium in small samples of hydrogenation catalysts.

Simultaneous 2nd order derivative spectrophotometric determination of sorbic and benzoic acids in soft drinks

Abstract A method is developed for the simultaneous 2nd order spectrophotometric determination of 1 to 7 μg.mL−1 of each of benzoic and sorbic acids in non vegetal soft drinks, using a blank prepared from the same soft drink to be analyzed in order to avoid the interferece from other additives and colouring matter present.