A matrix-matched reference material for validating petroleum Re-Os measurements

This study presents two matrix-matched reference materials developed for petroleum Re-Os measurements. We present the Re and Os mass fractions and 187Re/188Os and 187Os/188Os values (ratio of the number of atoms of the isotopes) for repeatedly measured aliquots (ca. 120–150 mg test portions) of the NIST Research Material 8505 (RM 8505) crude oil, and its asphaltene and maltene fractions, and ~ 90 g of homogeneous asphaltene powder isolated from this oil. Measurements were performed using the Carius tube-isotope dilution negative-thermal ionisation mass spectrometry methodology. The RM 8505 crude oil contains 1.98 ± 0.07 ng g−1 Re and 25.0 ± 1.1 pg g−1 Os, with Re-Os isotope amount ratios of 452 ± 6 for 187Re/188Os and 1.51 ± 0.01 for 187Os/188Os (n = 20, 95% conf.). The homogeneous asphaltene sample contains 16.52 ± 0.10 ng g−1 Re and 166.0 ± 0.9 pg g−1 total Os, and possesses isotope amount ratios of 574 ± 3 for 187Re/188Os and 1.64 ± 0.01 for 187Os/188Os (n = 24, 95% conf.). The intermediate precision of these data makes the RM 8505 whole oil and the (~ 90 g) homogenised asphaltene appropriate petroleum matrix-matched reference materials for Re-Os measurements. The asphaltene fraction of the oil is the main carrier of Re and Os of the RM 8505 whole oil, and caution is suggested in using asphaltene and maltene fractions of a single oil for Re-Os geochronology

Multivariable classification of pumpkin seed oils using absorption spectra

Classification models for edible oil samples which represent the most widespread brands of Austrian pumpkin seed oils were elaborated using several techniques of multivariate data analysis. Characterization of the samples was achieved by UV-VIS, Near IR and FT IR spectral methods and complemented by basic sensorial classification given by a panel of experts. Chemometrical treatment of measured data enabled to detect important spectral features, mostly suitable for categorization of investigated oils into two or three classes, defined according to their sensory quality. Thus classification was made into (a) two categories, containing good (fully satisfactory) or bad (not fully satisfactory) oils, (b) three categories, involving excellent, satisfactory and bad oil brands. The classifocation models, elaborated separately for each kind of spectra, enable to predict the category into which a hitherto unclassified oil sample belongs. It will perspectively facilitate determination of the chemical substances responsible for bad taste, improper odour and inconvenient colour of the respective oil brands, as well as selection of substances contributing to the excellent sensorial perception of the tested market products