V. Peris Martinez

Fourier transform infrared spectroscopy and the analytical study of sculptures and wall decoration

Abstract An analytical examination of sculpture and wall painting, including several wooden polychromed carvings from Valencian churches (15th–17th centuries) using FT-IR spectroscopy is described. The organic and inorganic compounds used in the works of art and the different artistic techniques used in each historical intervention carried out in the sculptures are identified. The analytical information obtained with this technique on organic and inorganic compounds is extremely useful in the preliminary studies necessary for diagnosis and to decide on the conservation process.

Limit dilution method: determination of correction factors for resolving matrix effects in X-ray fluorescence analysis

Abstract A dilution method, the “Limit Dilution Method” (infinite dilution), offers one way to correct for interelement effects in X-ray fluorescence measurements. An algorithm is proposed for the graphical calculation of the relevant correction factors. Linearly calibrated curves for intensity vs dilution factor are used to make an analysis of two clays by the fusion technique, using lithium tetraborate as the diluent.

Spectrophotometric determination of fluoride in fluoride-bearing minerals after decomposition by fusion with sodium hydroxide

The decomposition of highly insoluble minerals (fluorspar and cryolite) by fusion with molten alkali-metal hydroxides is studied. The introduction of additives such as aluminium compounds or sodium peroxide to obtain total liberation of fluoride from calcium fluoride samples, is tested. The fusion is done in a silver crucible with a Bunsen burner. The cooled melt is easily soluble, giving solutions suitable for spectrophotometric fluoride determination by the Zr(IV)-fluoride-Erichrome Cyanine R method.

Polarographic determination of proguanil and chlorhexidine.

The method is based on the cathodic wave obtained for chlorhexidine and proguanil in buffered aqueous dimethylformamide media. Concentrations up to 8 x 10(-5) and 6 x 10(-4)M, respectively, can be determined. The difference in behaviour at various pH values or in the presence of surface-active agents, is useful for characterization of both biguanides.

INTER-LABORATORY NOTE X-ray fluorescence analysis of iron(III), potassium and sulfur oxides in cements with a hyperbolic addition–dilution model and using a single multicomponent standard

A mathematical addition–dilution model for matrix correction was applied to the determination of iron(III), potassium and sulfur oxides in an industrial cement by XRF. The samples were prepared in the form of pellets. A cement of known composition was used as a single multi-element standard and the compactant and diluent was mannitol. The intensities were measured with an energy dispersive X-ray spectrometer. The graphical representation of intensityversus addition–dilution factor fits a hyperbolic function and, therefore, the proposed mathematical model can be applied. The results obtained by the proposed method show complete statistical agreement when compared with the content of the standard studied, which demonstrates that the method is suitable for this type of industrial sample with a complex matrix.

Analysis of toxic elements in plastic components for toys. Multi-elemental determination by x-ray fluorescence

Abstract An x-ray fluorescence method is proposed for the multi-elemental determination of toxic elements in plastic articles for children, viz., Sb(III), Ba, Cd, Cr(III), Hg, Pb and As(III). Mineralization is achieved by using molten sodium hydroxide to decompose the organic matrix, with sodium nitrate as auxiliary oxidant. Stable solutions containing the chemical species for analysis are obtained. The species are separated from the solution by (co)precipitation, in a medium of NH+4-NH3 buffer (pH 8.5) with sodium diethyldithiocarbamate, sodium rhodizonate and Fe3+, which acts as a carrier. The precipitates deposited on filter-paper are placed in the x-ray spectrometer in fine layer morphology. The method was applied to several plastics of different characteristics, all components of childrens toys. The suggested method is statistically comparable to the method that includes a reference destruction of organic matter for each element studied and subsequent determination by atomic absorption spectrometry.

Determination of phosphorus in samples of vegetable origin: Mineralization with molten alkali and spectrophotometric determination

For determination of phosphorus in samples of vegetable origin (leaves and wheat flour) decomposition by means of molten alkali is proposed. Two procedures have been studied, one with dry reagents including an auxiliary oxidant, and the other with initially moist alkali with no extra oxidant. The fusion product is easily soluble and produces a solution suitable for elemental analysis. The phosphorus is determined by the molybdenum blue method. The suggested mineralization is rapid, accurate and precise.

Atomic-absorption spectrometric determination of calcium, magnesium and potassium in leaf samples after decomposition with molten sodium hydroxide

The decomposition of standard leaf samples of varied origin and nature by fusion with sodium hydroxide in an open system has been studied. The use of sodium nitrate as an auxiliary agent facilitated the mineralization of most of the samples. The solutions obtained were analysed for calcium, magnesium and potassium by flame atomic-absorption spectrometry. The method is fast and quite precise, with absolute standard deviations of 0.04-0.13, 0.002-0.03 and 0.04-0.12% for calcium, magnesium and potassium contents of O.8-5.0, 0.13-0.48 and 0.36-2.2% respectively. The limits of detection (mug/ml) in the determination step were 0.10 for calcium, 0.011 for magnesium, and 0.09 for potassium.

Correction parameters in X-ray fluorescence analysis applying the limit dilution method (LDM). I: Correction of the diluent effect and optimization of the selection of standards

Some corrective parameters: H, M, Y and Y/H are defined from the mathematical development justifying the Limit Dilution method (LDM) in XRF analysis. These corrective parameters, for a given diluent and dilution, are characteristic of the analyte in each sample. The influence of these parameters on important phenomena such as the diluent effect is evaluated by a theroretical model. Using parameters Y, an algorithm is proposed which corrects the diluent effect and establishes linear functions of fluorescence intensity vs. analyte concentration

Determination of fluoride in rocks, soils, and fluoride-bearing minerals by separation using direct distillation in sulfuric acid medium and spectrophotometric analysis

Abstract An analytical method for fluoride determination in geological samples is proposed. It is based on a previous fluoride separation by distillation with a Teflon reactor. The variables that influence distillation quantitation (temperature, time, and acid concentration) are optimized. The influence of some species on fluoride recovery during distillation are studied, and conditions to avoid this influence are suggested. Fluoride determination is carried out by means of a spectrophotometric method [La(III)-F−-Alizarin complexone system] (N. T. Crosby, A. L. Dennis, and J. G. Stevens, Analyst (London), 1968, 93, 643–652). The method is applied to the analysis of soils, rocks, and fluoride-bearing mineral samples. The precision of the procedure is significant, and relative error values of 0.40–3.45% are obtained. The accuracy of the method is statistically satisfactory.