F. Bosch-Reig

Sugar profiles of Spanish unifloral honeys

The levels of various sugars (fructose, glucose, sucrose, maltose, maltulose, kojibiose, isomaltose, raffinose, erlose and melezitose) as well as the glucose/fructose and glucose/water ratios were determined in different Spanish unifloral honey types (rosemary, orange blossom, lavender, sunflower, eucalyptus, heather, honeydew). Sugars were determined by gas chromatography of the trimethylsilyloxime derivatives. There were significant differences among the honey types in relation to sugar composition. Fructose, glucose, sucrose, maltose and the glucose/water ratio were selected by discriminant analysis as the better parameters for the correct classification of the honey samples into their parent types. These sugars appear to be very valuable as characterization parameters for honeydew honey, followed by sunflower, heather and eucalyptus honeys, with 100%, 92.9%, 83.3% and 75.0% correct classifications, respectively. For the remaining honey types the percentages of successful classifications ranged from 53.8% to 69.2%.

Evaluation and elimination of the blank bias error using the H-point standard addition method : application to spectrophotometric determinations using absorbent blank

Abstract The basis of the H-point standard addition method in the cases where the analyte determination requires the use of an absorbent reagent is considered. The method evaluates and eliminates the blank bias error present in such procedures by using the absorbance increment at two selected wavelengths as the analytical signal of the calibration graphs. Three different determinations were tested: the determination of proteins with the biuret method, thorium with thoron and of magnesium with Titan Yellow. These procedures are better described by the proposed method than by the traditional approach using absorbance values against reagent blank.

Generalized H-point standard additions method for analyte determinations in unknown samples

The generalized H-point standard additions method (GHPSAM) is proposed. The method locates the linear spectral behaviour for the unknown global interference, if it exists, in all the spectral regions measured. The linear spectral interval for the interference is located from second derivative data. After this, the method validates the linearity supposition and estimates the analyte concentration free from bias error. So, only the data measured from the method are enough to obtain the unbiased analyte concentration in the presence of unknown interferences. Mixtures of phenol and 4-chloro-2-nitrophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol have been tested in order to check the validity of the method. The method also has been applied to the determination of amphetamine in urine samples. It works well in a lot of spectral situations, except in the cases when the global interference and the analyte are linear in the same spectral region.

Study of the behaviour of the absorbent blanks in analytical procedures by using the H-Point standard additions method (HPSAM)

This paper studies the behaviour of reagent blank in different extractive-colorimetric procedures (determination of sympathomimetic amines with NQS reagent) by using the H-Point Standard Additions Method (HPSAM) in order to study and characterize the different possibilities that the blank can introduce in an analytical procedure. We define two kinds of blanks: the external blank (from reagent alone solutions data) and the internal blank (from extrapolation of reagent plus analyte solutions data). Comparison between both gives the information about the reproducibility of the behaviour of the reagent blank. A procedure to evaluate, and characterize, errors (if they exist) is described, and a guide for optimizing the measuring procedure is presented.

Analytical study of proteinaceous binding media in works of art by gas chromatography using alkyl chloroformates as derivatising agents

In this work, we present the results obtained in an analytical study of the different types of proteinaceous binding media most commonly used in paintings, using GC-FID as the technique of analysis and GC-MS as a confirmatory technique. The application of this methodology requires prior hydrolysis of the proteins in the binding media to obtain free amino acids and then volatile derivatives, in this case by reaction with chloroformates due to advantages of speed, safety and the aqueous medium in which the reaction occurs. The method proposed for the proteinaceous binding media study is to calculate the proportions of the different amino acids with respect to alanine. This method provided good characterisation of different binding media, such as pork gelatine, beef gelatine, albumin, egg white and casein. The proposed method is used for the identification of binding media (including mixtures of binders) present in real samples from paintings in the city of Valencia, Spain.

H-Point standard additions method for resolution of binary mixtures with simultaneous addition of both analytes

Abstract The basis of the H-point standard additions method, HPSAM, with simultaneous addition of both analytes is proposed for the resolution of binary mixtures. It is a modification of the previously described H-point standard additions method that permits the resolution of both species from a unique calibration set by making the simultaneous addition of the two analytes. The method uses as analytical signals the absorbances at pairs of wavelengths where each species shows the same absorbance. The required data to apply the method are the absorbance values at the previously selected wavelengths for the sample alone and spiked with both species at known concentrations. Linear relations between absorbance values and added concentration of analyte are found, and the intersection of the lines at the previously selected wavelengths permits to obtain the analyte concentration in the sample. Wavelength pairs can be selected to obtain the most precise results. The effect of the relation of the concentrations of the two species in the standard and in the sample has been studied. Some mixtures of phenol and o-cresol, species highly overlapped (absorption maxima: for phenol at 234.6 and 287.0 nm; for o-cresol at 236.6 and 288.4 nm) and with similar absorptivities have been tested. If the matrix effect is known to be absent, the method can be employed with absortivity coefficients of the pure compounds.

Development of the H-point standard additions method for the use of spectrofluorimetry and synchronous spectrofluorimetry

The basis of the H-point standard additions method (HPSAM) is developed for the use of fluorimetric and synchronous spectrofluorimetric measurements. The method permits the transformation of the indeterminate error resulting from the presence of an interference in the determination of an analyte into a systematic constant error that can be evaluated and permits the determination of the analyte free from bias error. Some examples are presented. Phenol fluorescence calibrations in water have a high interference from the Raman emission band of the solvent. The HPSAM permits the elimination of this interference, because the method can eliminate the blank bias error. Resolution of highly overlapped species, such as phenol-o–cresol mixtures, can be carried out with the method. In order to show this possibility, synchronous spectrofluorimetry was chosen to eliminate the blank signal.

Identification of Synthetic Resins Used in Works of Art by Fourier Transform Infrared Spectroscopy

Differentiation between the synthetic polymers used in former restorations of works of art and the original materials used by the artist is of great interest; such differentiation is needed to establish an adequate process of restoration for the work of art. A specific method of sample preparation based on a filtration and deposition-evaporation sequence is proposed, which permits the separation and preconcentration of the synthetic polymer that is being analyzed and avoids problems arising from the simultaneous interpretation of IR spectra obtained from complex mixtures of organic and inorganic compounds present in small artistic samples. In addition to the identification of characteristic IR absorption bands, quantitative diagnostic criteria based on two-dimensional diagrams of relative intensity of selected peaks have been developed. Standards of acrylic, alkyd, cellulose nitrate, epoxy, ketone, poly(vinyl acetate), polyurethane, silicone synthetic polymers and semi-synthetic wax used as binding media, adhesives, and coatings have been prepared by this proposed experimental procedure, and IR spectra have been obtained. Finally, several samples from paintings and artistic objects dating from the 16th to the 20th century have been analyzed, and synthetic and semi-synthetic organic materials have been successfully identified by comparison with the standards using the proposed method of analysis.

Development of the H-point standard additions method for coupled liquid chromatography and UV-visible spectrophotometry

Abstract This work establishes the fundamentals of the H-point standard additions method for liquid chromatography for the simultaneous analysis of binary mixtures with overlapped chromatographic peaks. The method was compared with the deconvolution method of peak suppression and the second derivative of elution profiles. Different mixtures of diuretics were satisfactorily resolved.

Electrochemical identification of metal ions in archaeological ceramic glazes by stripping voltammetry at graphite/polyester composite electrodes

The electrochemical response of metal ions in different samples of coloured ceramic tin-lead glazes attached to graphite/polyester composite electrodes is described. In addition to the ubiquous signals for lead, reductive dissolution processes are followed by anodic stripping peaks for Co, Cu, Sb, Mn, Sn and Fe, enabling the direct identification of such elements in microsamples proceeding from archaeological glazed tiles from Valencia (Spain) workshops (16th-18th century). Additional anodic and cathodic peaks corresponding to redox processes involving metal species in solution generated during stripping processes are also used. Peak potentials, Tafel plots and shape parameters are used for characterising the different species.