L. Favretto

Stereospecific analysis of the triacylglycerol fraction and linear discriminant analysis in a climatic differentiation of umbrian extra-virgin olive oils

Abstract Stereospecific analysis of the triacylglycerol fraction is an important tool for the characterisation of extra-virgin olive oils. The composition in the sn-1, sn-2 and sn-3 positions of triacylglycerols of extra-virgin olive oils produced in years 1992–1994 in areas characterised by increasing environmental severity (groups 1 and 2, respectively) is considered. This analytical method is based on chromatographic techniques, coupled with enzymatic ones. Linear discriminant analysis (LDA) has been applied successively for the differentiation and classification of the two groups for each year according to the positional distribution of fatty acids (palmitic, palmitoleic, stearic, oleic and linoleic acids) in the glycerol backbone. Even though the data were not very numerous, LDA has allowed a partial or total separation of scores along the discriminant eigenvector according to the climatic groups.

Rapid determination of the molecular-weight distribution of ethylene glycol oligomers by thin-layer chromatography and their photometric evaluation☆

Abstract Thin-layer chromatography, coupled with the direct photometric measurement of the spots visualized with iodine vapour, offers a suitable means of estimating the molecular-weight distribution of oligomeric polyethylene glycol derivatives. The present work is restricted to the lower oligomers in order to permit a comparison with gas chromatographic data, but more interest is attached to the resolution of higher oligomers, for which gas-liquid chromatography is unsuitable.

Gas chromatographic separation and chemometric analysis of mandarin essential oils

Abstract Capillary gas chromatography with flame ionization detection was applied to the separation of components of mandarin essential oils. Fifty-nine genuine samples were considered over the period October 1982–January 1983. Essential oils were obtained from unripened green fruits and ripened red fruits, as well as from fruits at intermediate ripening. Thirty-four pure components were systematically identified, but only 13 were used as variables for the further characterization by a chemometric procedure. Principal component analysis was applied to the differentiation of samples with different maturation and obtained with different technologies.

Chemometric studies on minor and trace elements in cow's milk

Abstract In raw milk nine minor and trace elements (Cr, Mn, Fe, Ni, Cu, Zn, Mo, Cd and Pb) were determined in the dissolved ash by means of atomic absorption spectrometry and electrothermal atomization in a graphite furnace. The application of linear principal component analysis to the data matrix has permitted the reduction of the number of variables to four principal components accounting for 74% of the total variability. The two-dimensional plot of the scores (the milk samples) for the first principal components has pointed out a differentiation according to the two kinds of cows feeding. Successively, the technique of linear discriminant analysis has fully confirmed the separation between the two types of milk.

Principal components analysis for the estimation of interdependences among trace metals in cow milk

Seven trate metals (Cr, Mn, Fe, Ni, Cu, Cd, Pb) were determined in the dissolved ash of pasteurized milk by electrothermal atomic absorption spectrometry. The distribution of the concentration (c) of the metals in milk of χ = log10c for eaeh metal was investigated by means of the Lin-Mudholkar test for normality. Logarithmically transformed variables were first considered for further processing, as their distribution passed the normality test at a 0.05 significance level for a sample size of 48. The correlation matrix around the mean was used as a starting matrix for principal components analysis; the principal components were obtained from the FACTOR program of the SPSS package. Dimensions were reduced to four principal components, accounting for 78% of the total variance. Various orthogonal rotations indicated associations with Cd- Pb, Cr- Ni, and Mn- Cu. The correlation matrix was also estimated from the c matrix after row- normalization for each sample. The first eigenvalue estimated from this matrix accounted for 50% of the total variance, bur three eigenvalues were needed to reach 80% of explained variance. Cadmium and lead formed a cluster of variables, indicating a common origin. Features concerned with natural metal contents and contamination during transport and processing are diseussed.

Principal component analysis for the identification of pollution sources in mussel survey by trace metals

ZusammenfassungDie Analyse der Hauptkomponenten wurde auf die Korrelationsmatrix, die aus der 8 × 43-Datenmatrix hervorgeht, angewandt. Diese 8 Spurenmetalle sind Mn, Co, Ni, Cu, Zn, Cd, Hg, Pb, die im Fleisch der Miesmuscheln (Mytilus galloprovincialis Lamarck) gefunden worden sind. Die Miesmuscheln stammen aus zwei Gegenden des Golfes von Triest. Vier Hauptkomponenten erklären 76–78 % der totalen Varianz der beiden Stichproben. Die orthogonale-rotierte Faktorenmatrix zeigt, daß Co und Ni an die erste Hauptkomponente und Cd und Pb an die erste (Lage 2) oder an die zweite Hauptkomponente (Lage 1) gebunden sind. Die Herkunft der Spurenmetalle im Muschelfleisch aus dem Golf von Triest wird diskutiert.SummaryPrincipal component analysis has been applied to analyze the correlation matrix obtained from a 8 × 43 data matrix. The 8 trace metals are Mn, Co, Ni, Cu, Zn, Cd, Hg, Ph, which are contained in the soft part of mussels (Mytilus galloprovincialis Lamarck). Mussels were sampled from two sites in the Gulf of Trieste. In both samples, 76–78% of the total variance is explained by the four principal components. The orthogonally rotated factor matrix indicates that Co and Ni are bonded to the first principal component and Cd and Pb to the first (site 2) or second principal component (site 1). The origin of trace metals in the soft part of mussels from the Gulf of Trieste is discussed.

Terrigenous debris and mussel pollution — a differentiation based on trace element concentration by means of multivariate analysis

Abstract The total content of nine trace elements (Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb) of the soft edible part of mussels (Mytilus galloprovincialis Lamarck) sampled in two different sites was considered. The first sampling site was located at the extremity of a pier near the sewage of Trieste in a polluted area of the Muggia Bay (Gulf of Trieste in the Northern Adriatic Sea), whereas unpolluted mussels were simultaneously sampled in the second one, i.e. a hatchery just off the southern extremity of the bay. The sampling was extended over a year and occurred with a frequency of nearly ten days. Both mussel groups had an equal sample numerosity (n1=n2=43) and standard atomic absorption methods were used for all the trace elements. Linear discriminant analysis (LDA) was applied to this two-group sampling in order to test a possible differentiation between the polluted and unpolluted mussels. LDA gave in this two-group sampling a nearly complete separation of scores, whereas the bidimensional and tridimensional score plots, obtained by means of linear principal component analysis (LPCA), gave a certain degree of entanglement. The detrital origin of pollutants is also discussed.

Multivariate data analysis of sea waters and mussels in relation to pollution sources of trace elements

ZusammenfassungDer Gesamtgehalt von Cu, Zn, Pb in den oberen Schichten des Seewassers aus der Bucht von Muggia (Golf von Triest) wurde nach einer puls-inversvoltammetrischen Methode untersucht. Es wurden die Beziehungen dieser Spurenelemente zu den bekannten Verunreinigungsursachen diskutiert. Weiterhin wurde der Gehalt von Mn, Co, Ni, Cu, Zn, Cd, Hg, Pb im Fleisch von Miesmuscheln (Mytilus galloprovincialis Lamarck) untersucht. Die Mollusken stammen aus der Umgebung des Hafens von Triest, in der Nähe eines wichtigen Abwasserkanals. Die Korrelationsmatrix geht aus der 8 × 43-Datenmatrix nach einer logarithmischen Transformation der Konzentrationsvariablen hervor, dies basiert auf der Analyse der Hauptkomponenten. 8 Variable wurden auf 4 Hauptkomponenten, die 80% der totalen Varianz erklären, reduziert. Die orthogonal-rotierte Faktorenmatrix zeigt, daß Co, Ni, Cd und Pb an die erste Hauptkomponente, Cu und Zn an die zweite, Hg an die dritte und Mn an die vierte Hauptkomponente gebunden sind. Die Ergebnisse dieser Forschung werden mit denen vorhergehender mehrdimensionaler Analysen aus zwei Gegenden in der Bucht von Muggia verglichen. Die Herkunft der Spurenelemente im Muschelfleisch aus dem Golf von Triest werden diskutiert.SummaryThe total concentration of Cu, Zn and Pb in surface sea waters from the Bay of Muggia (Gulf of Trieste, Northern Adriatic Sea) was determined by anodic stripping voltammetry. The association of these trace elements in relation to the known sources of pollution was discussed. The content of eight trace elements (Mn, Co, Ni, Cu, Zn, Cd, Hg, Pb) in the soft part of mussels (Mytilus galloprovincialis Lamarck) is also considered. The wild molluscs were sampled in the harbour of Trieste, in the proximity of an important city sewer. Principal component analysis was used to analyse the correlation matrix obtained from an 8 × 43 data matrix after a logarithmic transformation of the concentration variables. Eight variables were reduced to four principal components, which explained 80% of the total variance. The orthogonally rotated factor matrix shows that Co, Ni, Cd, and Pb are associated with the first principal component, Cu and Zn to the second, Hg to the third and Mn to the fourth principal component. The results of this multi-variate data analysis are compared with those already obtained from two sampling sites in the Bay of Muggia and the origin of some trace metals in the soft part of mussels from the Gulf of Trieste is discussed.

Gas-liquid chromatographic fractionation of polyoxyethylene non-ionic surfactants : Polyoxyethylene mono-n-alkyl ethers

The gas-liquid chromatographic fractionation of the commercial biodegradable surfactants RO(CH2CH2O)nH (where R is an n-alkyl group and n is the number-average degree of polymerization) can be approached only for n ⩽ 4, as the truncation of the molecular-weight distribution occurs at higher n values. Although conversion into trimethylsily (TMS) derivatives improves the volatility of the oligomers, there is only a slight advantage in using this conversion procedure: TMS derivatives have the same elution temperature as untreated compounds above ca. 330°. The use of an internal standard as a reference compound for comparison of peak areas is a useful procedure, which has been tentatively applied to the reconstruction of the distribution of the surfactant with R = n-dodecyl and n = 7.1. The choice of the internal standard is discussed.

Chromatographic studies on the extraction of polyoxyethylene alkylphenyl ether non-ionic surfactants from water at trace levels

Abstract The extraction of polyoxyethylene non-ionic surfactants of the type RO(CH2CH2O)nH, (where R is a p-tert.-nonylphenyl group and n is the degree of polymerization) from water at trace levels with some organic phases has been studied by gas chromatography. Of the solvents tested, 1,2-dichloroethane appears to be suitable as a non-fractionating phase for extracting these polydisperse non-ionic surfactants. The evaluation of the distribution constants of monodisperse compounds (6 ⩽ n ⩽ 11) by a spectrophotometric procedure confirmed the gas chromatographic results.