Search results for " composition"
showing 10 items of 1437 documents
Gas chromatographic–mass spectrometric investigation of the chemical composition of beebread
2009
Beebread consumption has a very long tradition; however, its composition and bioactive properties have not been studied thoroughly up to now. This study is expected to expand the knowledge of chemical composition of this bee product as a natural remedy and functional food ingredient. With the help of successive extraction with organic solvents of different polarity, more than 200 compounds were extracted from five samples of beebread and then identified by GC-MS method. The content of some phenol compounds (p-coumaric acid, kaempherol, isorhamnetin) with antioxidant properties has been determined quantitatively. Different content of free aminoacids have been detected in the analyzed samples…
Towards the optimization of complementary systems in reversed-phase liquid chromatography
2002
Previously reported optimization methodology, which seeks complementary mobile phases (CMP) in isocratic chromatography, has been extended to include more than one system simultaneously (i.e. more than one organic solvent and/or column). In the literature the benefits of complementarity are not usually fully exploited—few working conditions giving rise to interactions as different as possible are examined, without developing a fully linked optimization. The proposed approach is compared critically with use of a single mobile phase or CMP which consider one system only. The strategy greatly expands the capability of isocratic chromatography in the analysis of complex samples that cannot be r…
Free fatty acids and other volatile compounds for the characterisation of “Vastedda della valle del Belìce” cheese Acidos grasos libres y otros const…
2010
The analysis of the volatile constituents of “Vastedda della valle del Belice”, a typical Sicilian pasta filata cheese, was performed using solid phase microextraction and high-resolution gas chromatography/mass spectrometry. The research aimed to verify if the volatile fraction, determinant for cheese flavor, differs among producers and/or production seasons. The samples were provided by four producers from the area of the Protected Designation of Origin (PDO) production, during two different seasons of production. A total of 42 volatile components were identified: the main components were found to be butanoic, hexanoic, octanoic, and decanoic acid. Free fatty acids were quantified using t…
High-performance liquid chromatographic determination of Maillard compounds in store-brand and name-brand ultra-high-temperature-treated cows' milk.
2000
Furosine and furfural products of the Maillard reaction are used as specific indicators of the effect of heating treatments on milk quality. Their contents were measured in representative samples of store- and name-brand ultra-high-temperature-treated milks using RP-HPLC with UV detection. Furosine contents ranged from 40.32 to 50.67 and from 65.48 to 310.58 mg/100 g protein in name- and store-brand milks, respectively. Of the furfurals, only hydroxymethylfurfural was detected. The free hydroxymethylfurfural contents of store-brand milks ranged from 0.22 to 1.70 mg/100 g protein. Total hydroxymethylfurfural contents ranged from 0.29 to 0.41 and from 0.72 to 2.21 mg/100 g protein, for name- …
Robust interpretive optimisation in high-performance liquid chromatography considering uncertainties in peak position.
2005
In the context of interpretive chromatographic optimisation, robustness is usually calculated by introducing deliberated shifts in the nominal optimal conditions and evaluating their effects on the monitored objective function, mimicking thus the experimental procedures used in method validation. However, such strategy ignores a major source of error: the uncertainties associated to the modelling step, that may give rise to deceiving results when conditions that were expected to yield baseline separation are reproduced in the chromatograph. Two approaches, based on the peak purity concept, are here proposed to evaluate the robustness of the objective function under the perspective of measur…
Infrared biospectroscopy for a fast qualitative evaluation of sample preparation in metabolomics.
2014
Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to study the dynamic metabolomic responses of biological systems under different physiological or pathological conditions. To obtain an integrated snapshot of the system, metabolomic methods in biomedicine typically analyze biofluids (e.g. plasma) that require clean-up before being injected into LC-MS systems. However, high resolution LC-MS is costly in terms of resources required for sample and data analysis and care must be taken to prevent chemical (e.g. ion suppression) or statistical artifacts. Because of that, the effect of sample preparation on the metabolomic profile during metabolomic method d…
Determination of water-soluble vitamins in energy and sport drinks by micellar electrokinetic capillary chromatography
2016
Abstract A method for the determination of water-soluble vitamins in several energy and sport drinks by micellar electrokinetic chromatography (MEKC) has been developed in this work. The separation of vitamins was studied in terms of background electrolyte composition (borate content, pH, surfactant type and content) and in other MEKC parameters. A study of the possible compounds found in the vitamin-enriched drinks that could interfere in vitamin determination was also performed, and a modified procedure with enhanced resolution was developed. The proposed method was successfully applied to the analysis of water-soluble vitamins in a variety of energy and sport drinks and also in fruit nec…
On the Measurement of Dead Time in Micellar Liquid Chromatography
1996
Abstract Modelling of the retention of solutes in micellar liquid chromatography allows the optimization of the resolution of a mixture of solutes and the determination of physico-chemical retention parameters. Both tasks imply the calculation of capacity factors, which are severely affected by the value of dead time. However, the determination of the dead time is not easy when a micellar mobile phase is used owing to the wide and variable perturbations that appear at the heads of the chromatograms. Four different criteria of determination of a reference time in the chromatograms are proposed and compared. The criteria are applied to mobile phases containing a varying concentration of surfa…
Evaluation of several global resolution functions for liquid chromatography
1999
Abstract An interpretative approach, that makes use of the overlapped fraction of each chromatographic peak as elementary resolution criterion, was applied to the separation of mixtures of compounds. The elementary resolution measurements for all peaks in the chromatogram were reduced to a single numerical value using several functions: normalised by the mean resolution product, unnormalised product, geometrical mean of the unnormalised product, and worst elementary resolution value. The descriptive capability of these reduction functions was evaluated through the observation of global resolution diagrams and the change in the shape of the chromatograms in the selected factor space. michrom…
Botanical Origin Authentication of Polish Phacelia Honey Using the Combination of Volatile Fraction Profiling by HS-SPME and Lipophilic Fraction Prof…
2019
Eleven samples of Polish Phacelia tanacetifolia Benth., three Brassica napus and one Salix spp. honeys were characterized by melissopalynology and analysis of the compositions of their volatile fractions. Headspace solid-phase microextraction coupled with gas chromatography mass spectrometry (HS-SPME/GC–MS) using PDMS/CAR/DVB fiber was used for the isolation of low-molecular weight compounds which create a volatile fraction. To differentiate and indicate the most representative unifloral samples, chemometric techniques such as principal component analysis (PCA) and hierarchical-tree clustering (HTC) were applied to the dataset of the chromatographic fingerprints. Based on the obtained resul…