Determination of vanillin and related flavor compounds in natural vanilla extracts and vanilla-flavored foods by thin layer chromatography and automated multiple development

Summary Thin layer chromatography on silica gel high performance layers and automated multiple development was used to separate the polar aromatic flavor compounds vanillin, ethyl vanillin, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxybenzyl alcohol, vanillic acid, coumarin, piperonal, anisic acid, and anisaldehyde commonly found in extracts of natural and artificial vanilla flavors. The ratio of 4-hydroxybenzoic acid, 4-hydroxybenzaldehyde and vanillic acid to vanillin in natural vanilla extracts was used to confirm the authenticity of extracts purchased in the United States of America and the United Kingdom. Natural vanilla extracts purchased in Mexico and Puerto Rico were identified as counterfeit products based on changes in the above ratio and the presence of synthetic flavor compounds such as ethyl vanillin and coumarin. It is also demonstrated that the proposed method is suitable for the determination of natural and synthetic vanilla flavors in solvent extracts from food, beverage and confectionery products. The main advantage of thin layer chromatography for the analysis of vanilla extracts and food stuffs flavored with vanilla is its high sample throughput since sample preparation requirements are minimal and multiple samples can be separated simultaneously.     

Factors affecting the rates of addition of free radicals to alkenes-determination of absolute rate coefficients using the persistent aminoxyl method

The rate of coupling of alkyl radicals with the persistent aminoxyl radical 1,1,3,3-tetramethylisoindolin-N-oxyl (1) has been used as a kinetic probe to determine absolute rate coefficients for the addition of alkyl radicals to methyl acrylate. The results are discussed in terms of the role of the structure and functionalization of the attacking radical on the rates of addition, particularly as they affect steric, polar, and enthalpic factors. The aminoxyl method is assessed against other methods for determining free radical addition rate coefficients.     

Matrix-induced peak enhancement of pesticides in gas chromatogrtaphy: Is there a solution?

In this study, it is shown that calibration solution prepared in control matrix extrix extract can be used to compensate for matrix-induced chromatographic response enhancement observed for certain pesticedes. This phenomenon is characterized by enhanced chromatographic response for certain pesticides in the presence of matrix du to reduced analyte loss during injection. Unacceptably high recoveries are seen for affected pesticides when maatrix-free solutions are used for reference and calibration. The effects of matrix concentration on overall enhancement and linear response were determined. When used as reference standards for the determination of recovery, matrix-standard solutions were found to provide acceptable recoveries for pesticides subject to matrix-induced chromatographic response enhancement along with other pesticides. General guidelines are presented for using matrix-standard calibration solutions in pesticide residue analysis.     

Influence of solvent effects on retention in reversed-phase liquid chromatography and solid-phase extraction using a cyanopropylsiloxane-bonded,silica-based sorbent

Summary The solvation parameter model is used to characterize the retention properties of a cyanopropylsiloxane-bonded, silica-based sorbent with methanol, acetonitrile, tetrahydrofuran, and isopropanol in water as mobile phases. The system constants over the composition range 1 to 50% (v/v) organic solvent indicate that retention occurs because of the relative ease of cavity formation in the solvated stationary phase compared to the same process in the predominantly aqueous mobile phase as well as from more favorable stationary phase interactions with solutes containing - and n-electrons. The capacity of the solute for dipole-type interactions is not important whereas all hydrogen-bond-type interactions result in reduced retention. Graphing the system constants as a function of mobile phase composition provides a simple mechanism for interpreting the change in capacity of the chromatographic system for retention in terms of changes in the relative weighting of fundamental intermolecular interactions. A comparison is also made with the retention properties of an octadecylsiloxane-bonded, silica-based sorbent with 30% (v/v) methanol in water as the mobile phase and the extraction characteristics of a porous polymer sorbent with 1% (v/v) methanol, acetonitrile, tetrahydrofuran, and isopropanol in water as the sample processing solvent. Changes in sorbent selectivity due to selective uptake of the processing solvent are much smaller for the cyanopropylsiloxane-bonded sorbent than the results found for a porous polymer sorbent.     

Evaluation of the Linear-Elution-Strength Model for the Prediction of Retention and Selectivity in Isothermal Gas Chromatography

Linear-elution strength theory and temperature-programmed gas chromatography is evaluated as a rapid method for predicting isothermal retention factors and column selectivity. Retention times for a wide range of compounds are determined at the program rates of 3 and 12 °C/min for the temperature range 60 to 160 °C on three open-tubular columns (DB-1701, DB-210 and EC-Wax) and used to predict isothermal retention factors for each column over the temperature range 60 to 140 °C. The temperature-program predicted isothermal retention factors are compared with experimental values using linear regression and the solvation parameter model. It is shown that isothermal retention factors predicted by the linear-elution-strength model only approximately represents the experimental data. The model fails to predict the slight curvature that exists in most plots of the experimental retention factor (log k) as a function of temperature. In addition, regression of the temperature-program predicted isothermal retention factors against the experimental values indicates that the slopes and intercepts deviate significantly from their target values of one and zero, respectively, in a manner which is temperature dependent. The temperature-program predicted isothermal retention factors result in system constants for the solvation parameter model that are different to those obtained from the experimental retention factors. These results are interpreted as indicating that linear-elution-strength theory predicts retention factors that fail to accurately model stationary phase interactions over a wide temperature range. It is concluded that temperature-program methods using linear-elution-strength theory are unsuitable for constructing system maps for isothermal separations.     

Pauli-Dirac matrix generators of Clifford Algebras

This article presents a Pauli-Dirac matrix approach to Clifford Algebras. It is shown that the algebra C₂ is generated by two Pauli matrices i₂ and i₃; C₃ is generated by the three Pauli matrices ₁, ₂, ₃; C₄ is generated by four Dirac matrices ₀, ₁, ₂, ₃ and C₅ is generated by five Dirac matrices i₀, i₁, i₂, i₃, i₅. The higher dimensional anticommuting matrices which generate arbitrarily high order Clifford algebras are given in closed form. The results obtained with this Clifford algebra approach are compared with the vector product method which was described in a recent article [Found. Phys. 10, 531–553 (1980) by Poole, Farach and Aharonov] and with the Dirac, Rashevskii and Ramakrishnan methods of matrix generation.Supported by the National Science Foundation under Grant ISP-80-11451.     

Solvent-assisted supercritical fluid extraction for the isolation of semivolatile flavor compounds from the cinnamons of commerce and their separation by series-coupled column gas chromatography

Solvent-assisted supercritical fluid extraction is superior to Soxhlet extraction, solvent extraction at reflux, and simultaneous setam distillation solvent extraction for the isolation of semivolatile compounds from the cinnamons of commerce. Optimized extraction conditions are described using carbon dioxide at 300 atm and 70°C to extract 0.5 g of powdered cinnamon mixed with 4.5 g of anhydrous sodium sulfate to which 1.0 ml of acetonitrile was added at the start of the sequential 30 min static and 30 min dynamic extraction. The semivolatile compounds were collected by solvent trapping in ethyl acetate and analyzed directly by series coupled-column gas chromatography after filtration and partial solvent evaporation. Twenty-one compounds identified by mass spectrometry were quantified in twenty-four samples of cinnamon and cassia purchased in Sri Lanka, Korea, United Kingdom, and the United States of America. True cinnamon is easily distinguished from cassia by the presence of eugenol, absence of δ-cadinene, much lower amounts of coumarin, and larger amounts of benzyl benzoate. Principal component analysis using the relative composition of the twelve major semivolatile compounds provides a clear distinction between true cinnamon and cassia as well as useful interspecies differences which can be used for further classification.     

On the relationship between the chemical bond energy and the electron energy levels of strongly ionic compounds

The analysis of experimental data suggests that the energy levels of ions in a crystal shift rigidly by an amount equal to the Madelung energy (electrostatic bond energy) maintaining the same separation as in the free ion. This leads to the conclusion that the electrostatic bonding energies of ions in a crystal is taken up partly by the orbital electrons and partly by the nuclear charge.