The use of simplex optimiztion in evaluating complex chromatograms of mixtures

The application of simplex optimization to the qualitative and quantitative evaluation of chromatograms of complex mixtures is outlined. The chromatogram is considered as a linear combination of pure component chromatograms (assuming no interactions are present); if suitable components are selected and the coefficients of the linear combination are properly evaluated, the experimental chromatogram can be reproduced numerically. The simplex method is then used to evaluate the solution with minimal error. The quantitation of polychlorobiphenyls from Aroclor mixtures in marine sediments and fish, and the identification of essential oils in a perfume base extract are outlined. Errors of ≤19% (25% in environmental samples) between the experimental and reconstructed chromatograms were achieved.     

Polymer Compatibility by Continuous Thermodynamics

Abstract

By applying a continuous distribution function instead of the mole fractions, mass fractions, etc. of individual components, continuous thermodynamics permits a drastic reduction of the computational expense for calculating phase equilibria in complex multi-component systems such as petroleum fractions, shale oils, polymer solutions, and polymer mixtures. In this paper, continuous thermodynamics is applied to compatibility in mixtures of two polymers. If, e.g., the cloud-point curve is known, the shadow curve, the spinodal, the critical mixing point, and other interesting quantities may easily be calculated. Some examples are given to illustrate the method.     

Quality control of automotive engine oils with mass-sensitive chemical sensors--QCMs and molecularly imprinted polymers

Molecularly imprinted polyurethanes were used as sensor materials for monitoring the degradation of automotive engine oils. Imprinting with characteristic oils permits the analysis of these complex mixtures without accurately knowing their composition. Mass-sensitive quartz crystal microbalances (QCMs) coated with such layers exhibit mass effects in addition to frequency shifts caused by viscosity, which can be compensated by an uncoated quartz or a non-imprint layer. Incorporation of degradation products into the imprinted coatings is a bulk phenomenon, which is proven by variation of the sensor layer height. Therefore, the resulting sensor effects are determined by the degradation products in the oil.     

Dependence on chain length of NMR relaxation times in mixtures of alkanes

Many naturally occurring fluids, such as crude oils, consist of a very large number of components. It is often of interest to determine the composition of the fluids in situ. Diffusion coefficients and nuclear magnetic resonance (NMR) relaxation times can be measured in situ and depend on the size of the molecules. It has been shown [D. E. Freed et al., Phys. Rev. Lett. 94, 067602 (2005)] that the diffusion coefficient of each component in a mixture of alkanes follows a scaling law in the chain length of that molecule and in the mean chain length of the mixture, and these relations were used to determine the chain length distribution of crude oils from NMR diffusion measurements. In this paper, the behavior of NMR relaxation times in mixtures of chain molecules is addressed. The author explains why one would expect scaling laws for the transverse and longitudinal relaxation times of mixtures of short chain molecules and mixtures of alkanes, in particular. It is shown how the power law dependence on the chain length can be calculated from the scaling laws for the translational diffusion coefficients. The author fits the literature data for NMR relaxation in binary mixtures of alkanes and finds that its dependence on chain length agrees with the theory. Lastly, it is shown how the scaling laws in the chain length and the mean chain length can be used to determine the chain length distribution in crude oils that are high in saturates. A good fit is obtained between the NMR-derived chain length distributions and the ones from gas chromatography.     

Quality control of automotive engine oils with mass-sensitive chemical sensors – QCMs and molecularly imprinted polymers

Molecularly imprinted polyurethanes were used as sensor materials for monitoring the degradation of automotive engine oils. Imprinting with characteristic oils permits the analysis of these complex mixtures without accurately knowing their composition. Mass-sensitive quartz crystal microbalances (QCMs) coated with such layers exhibit mass effects in addition to frequency shifts caused by viscosity, which can be compensated by an uncoated quartz or a non-imprint layer. Incorporation of degradation products into the imprinted coatings is a bulk phenomenon, which is proven by variation of the sensor layer height. Therefore, the resulting sensor effects are determined by the degradation products in the oil. Received: 5 August 1999 / Revised: 26 October 1999 / Accepted: 1 November 1999     

Combining chromatography and chemometrics for the characterization and authentication of fats and oils from triacylglycerol compositional data—A review

The characterization and authentication of fats and oils is a subject of great importance for market and health aspects. Identification and quantification of triacylglycerols in fats and oils can be excellent tools for detecting changes in their composition due to the mixtures of these products. Most of the triacylglycerol species present in either fats or oils could be analyzed and identified by chromatographic methods. However, the natural variability of these samples and the possible presence of adulterants require the application of chemometric pattern recognition methods to facilitate the interpretation of the obtained data. In view of the growing interest in this topic, this paper reviews the literature of the application of exploratory and unsupervised/supervised chemometric methods on chromatographic data, using triacylglycerol composition for the characterization and authentication of several foodstuffs such as olive oil, vegetable oils, animal fats, fish oils, milk and dairy products, cocoa and coffee.     

Populus nigra L. bud absolute: a case study for a strategy of analysis of natural complex substances

The new European regulations (e.g., REACH) require that Natural Complex Substances such as essential oils, absolutes, concretes, and resinoids are registered. This need implies that the chemical composition of these complex mixtures is characterized as exhaustively as possible in view of defining their toxicological risk. This study proposes an analysis strategy to be applied to the chemical characterization of poplar absolute as an example of Natural Complex Substances of vegetable origin. In the first part, the proposed strategy is described, and the advantages and the limitations related to the combination of conventional analytical techniques such as gas chromatography (GC) without and with sample derivatization and high-performance liquid chromatography (HPLC) are critically discussed. In the second part, the qualitative data obtained with GC and HPLC analysis of poplar bud absolute confirm the sample complexity which mainly consists of phenolic components. Fourteen compounds (i.e., phenolic acids, phenylpropanoids, and flavonoids) were then chosen as markers representative of the main classes of components characterizing poplar bud absolute. The marker quantitation carried out by GC-SIM-MS and HPLC-PDA analyses gives similar results confirming the reliability of both techniques. These results demonstrate that conventional analytical techniques can positively and effectively contribute to the study of the the composition of Natural Complex Substances, i.e., matrices for which highly effective separation is necessary, consisting mainly of isomers or homologous components. The combination of GC and HPLC techniques is ever more necessary for routine quality control when conventional instrumentations are used.

Direct measurement of lipid-soluble arsenic species in biological samples with HPLC-ICPMS

Lipid-soluble arsenicals (arsenolipids) occur in a wide range of biological samples where they may play a key role in the biosynthesis of organoarsenic compounds from inorganic arsenic. The study of these compounds has been hindered, however, by the lack of a suitable analytical technique able to separate and measure the various lipid species. As a source of arsenolipids, we used 10 crude fish oils from various regions of the world. Total arsenic analyses on the fish oils, performed with ICPMS following acid digestion with microwave-assisted heating, gave concentrations from 4.3 to 10.5 mg As kg(-1). All of the arsenic was soluble in non-polar solvents such as hexane. Analysis of the fish oils for arsenolipids was performed by normal phase HPLC-ICPMS with various mixtures of organic solvents as mobile phases. Inherent problems of instability associated with the introduction of organic solvents to the plasma were overcome by the use of reduced column flow, a chilled spray chamber, and the addition of oxygen directly to the plasma. All ten fish oils appeared to contain the same 4-6 major arsenolipids, but in varying amounts depending on the origin of the fish. Further chromatography with both normal phase and reversed-phase conditions on some of the oils indicated the presence of many more minor arsenolipids. Quantification was achieved by external calibration against triphenylarsine oxide or triphenylarsine sulfide, and the sum of species following HPLC of the oils matched well the total arsenic results (92-107%). The method was applied to samples of food supplements (fish oil capsules) and a packaged food product (cod liver) whereby arsenolipids were measured and found to be significant arsenic constituents. This study represents the first attempt to directly measure intact arsenolipids and, with appropriate sample preparation, may be suitable for quantitative measurement of these arsenicals in a range of biological samples, including foodstuffs.     

Phase Behavior of Ternary Systems of the Type H2O?Oil?Nonionic Amphiphile (Microemulsions)

Liquid multicomponent systems of the type H₂O-oil-amphiphile-electrolyte are of growing interest, both in industry and in research. In applications technology, there are two problems to solve: 1. To prepare stable homogeneous solutions of H₂O and nonpolar liquids with as little amphiphile as possible which can be diluted with H₂O in all proportions without phase separation; e.g., concentrated solutions of drugs, herbicides, or insecticides. 2. To prepare stable mixtures of an aqueous, an amphiphile, and an oil phase with as little amphiphile as possible which are employed in tertiary oil recovery and in the pharmaceutical industry. Furthermore, such systems may be used for performing chemical reactions in heterogeneous liquid mixtures with continuously variable properties. In research, such systems are of interest for both experimental and theoretical studies of critical phenomena, especially near so-called tricritical points. Last but not least, their properties may stimulate further research in the field of associated solutions. In this paper we summarize the results of our studies on the phase behavior of ternary systems with nonionic amphiphiles, in particular with respect to the evolution of liquid three-phase bodies. The results suggest that the tricritical points in such systems should be regarded as kinds of pivot points from which the phase behavior evolves. If this were an approach to reality, the phase behavior would be governed in more or less good approximation by universal scaling laws, irrespective of the particular microstructure of the solutions. Finally, we discuss the effect of electrolytes on the phase behavior both in a quaternary phase tetrahedron and a pseudoternary phase prism representation. Although in practice most systems consist of mixtures of oils, amphiphiles, and electrolytes, an understanding of the phase behavior of truly ternary and quaternary systems with chemically well-defined components permits at least qualitative predictions with respect to the phase behavior of the multicomponent mixtures encountered in practice.     

Liquid chromatography/electrospray ionisation mass spectrometric investigations of imidazoline corrosion inhibitors in crude oils

The so-called imidazolines (2-alkyl-1-[ethylalkylamide]-2-imidazolines and 2-alkyl-1-ethylamine-2-imidazolines) are a group of surface-active compounds, complex mixtures of which are used by various industries as surfactants and corrosion inhibitors. Although their industrial synthesis was reported over 100 years ago, few methods for the determination of individual imidazolines in mixtures, including industrial matrices such as crude oils, have been reported. Here we demonstrate that spiking of crude oils with synthetic imidazolines followed by solid-phase extraction and liquid chromatography/electrospray ionisation multistage mass spectrometry (LC/ESI - MS(n)) allows an estimation of low (<10) parts per million concentrations of individual imidazolines in crude oils. Whilst non-optimised at present, the method is a significant advance and may prove useful not only for improving an understanding of the mechanisms of industrial imidazoline synthesis and for monitoring downhole and topside oilfield operations, but also for the determination of the fate of imidazoline-based oilfield corrosion inhibitors and surfactants in the environment.     

The composition-explicit distillation curve technique: Relating chemical analysis and physical properties of complex fluids

The analysis of complex fluids such as crude oils, fuels, vegetable oils and mixed waste streams poses significant challenges arising primarily from the multiplicity of components, the different properties of the components (polarity, polarizability, etc.) and matrix properties. We have recently introduced an analytical strategy that simplifies many of these analyses, and provides the added potential of linking compositional information with physical property information. This aspect can be used to facilitate equation of state development for the complex fluids. In addition to chemical characterization, the approach provides the ability to calculate thermodynamic properties for such complex heterogeneous streams. The technique is based on the advanced distillation curve (ADC) metrology, which separates a complex fluid by distillation into fractions that are sampled, and for which thermodynamically consistent temperatures are measured at atmospheric pressure. The collected sample fractions can be analyzed by any method that is appropriate. The analytical methods we have applied include gas chromatography (with flame ionization, mass spectrometric and sulfur chemiluminescence detection), thin layer chromatography, FTIR, corrosivity analysis, neutron activation analysis and cold neutron prompt gamma activation analysis. By far, the most widely used analytical technique we have used with the ADC is gas chromatography. This has enabled us to study finished fuels (gasoline, diesel fuels, aviation fuels, rocket propellants), crude oils (including a crude oil made from swine manure) and waste oils streams (used automotive and transformer oils). In this special issue of the Journal of Chromatography, specifically dedicated to extraction technologies, we describe the essential features of the advanced distillation curve metrology as an analytical strategy for complex fluids.     

Antioxidant and anti-inflammatory activities of essential oils: a short review

Essential oils are complex mixtures isolated from aromatic plants which may possess antioxidant and anti-inflammatory activities of interest in thye food and cosmetic industries as well as in the human health field. In this work, a review was done on the most recent publications concerning their antioxidant and anti-inflammatory activities. At the same time a survey of the methods generally used for the evaluation of antioxidant activity and some of the mechanisms involved in the anti-inflammatory activities of essential oils are also reported.     

The Petroleum Industry Surfactants Synthesized from Fish Oils

Biodegradable surfactants for the petroleum industry have been synthesized by the sulfurization of fish oils. A qualitative composition analysis of surfactants was conducted by FTIR spectroscopy that showed the presence of sulfonic acid groups in the samples. Previously, several samples of the technical fish oils (fish processing waste) have been studied with regard to their use for the synthesis of biodegradable surfactants. It has been shown by gas–liquid chromatography, FTIR spectroscopy, high-performance liquid chromatography, and mass spectrometry method that samples under study contain a large amount of saturated and nonsaturated fatty acids with hydrocarbon radicals comprising from 16 to 22 carbon atoms. The results reveal that the concentration of oleic acid approaches to 15 wt%. Fish oils with a high content of free fatty acids were used as the basis for the synthesis of technical, environmentally friendly surfactants that can be applied in the petroleum industry.     

The simultaneous analysis of proteins, lipids, and diterpenoid resins found in cultural objects

We report a GC-MS method for the simultaneous analysis of proteins oil, and diterpenoid resins found in cultural objects. The method was initially designed for protein analysis of protenaceous paints and adhesives and involves acid hydrolysis as the first step. The amino acids in the protein hydrolysates, thus obtained, are treated with propan-l-ol/ hydrogen chloride and then pentafluoropropionic anhydride. The procedure was found also to yield the propyl esters of fatty acids derived from lipids and diterpenoid acids derived from natural resins, and thus allows the choice of a single method for the analysis of artists media which contain either oil s or proteins or mixtures of both proteins and oils or even resins. Thus natural mixtures such as egg yolk and also mixtures made by the artist such as animal glue/seed oil emulsions can be analysed. Coupled with FTIR analysis of paints and the staining of cross sections, to indicate layer structure the method can help to elucidate the paints and adhesives used by artists.     

Identification of components in fast pyrolysis oil and upgraded products by comprehensive two-dimensional gas chromatography and flame ionisation detection

Pyrolysis oil and upgraded products are promising energy carriers. Characterisation of the oils is hampered due to the presence of a large number of components (>400) belonging to a broad variety of chemical compound classes (i.e., acids, aldehydes, ketones). In this study, a comparison of the capabilities of 2D-GC-FID and GC-MS to determine the molecular composition of these oils is made. As such, it represents a chromatographic study for a real application in green catalytic technology. Split-injection of the oil samples, diluted in tetrahydrofuran (THF), was applied without any sample pre-treatment. GC-MS application resulted in coelution, while 2D-GC showed significantly higher chromatographic resolution. Model compound mixtures were used for compound identification in the 2D-GC analysis while GC-MS was used to confirm the molecular structures. The combination of both 2D-GC-FID and GC-MS proved to be a useful method, without the requirement of a 2D-GC/TOF instrument. The technique was applied successfully to identify and quantify the main components in pyrolysis oil and upgraded pyrolysis oil made by hydrodeoxygenation (HDO) technology. Compared to GC-MS, 2D-GC-FID provides a fast overview of the various chemical compound classes present in the oils.     

Rapid in situ determination of total oil concentration in water using ultraviolet fluorescence and light scattering coupled with artificial neural networks

Real-time measurement of total oil concentration in complex samples is required in wastewater discharge streams from ships and processing industries. A novel technology has been developed for the accurate quantification of a variety of single oils and their mixtures. Four major types of oils (lube oils 2190 and 9250, diesel fuel marine (DFM), and jet fuel (JP5)), each of which consisted of a dozen subtypes of oil samples, were examined to obtain both fluorescence and light scattering spectra as a function of concentration of single oils and mixtures. Tremendous variations in both fluorescence and scattering were observed among oil types, subtypes, and mixtures. The spectral response of an oil mixture was not the simple summation of respective single oils. To account for all these variations, a multivariate, nonlinear calibration method is applied to associate instrumental responses with oil concentrations using artificial neural networks (ANNs). The neural network architecture has been established by optimizing network parameters such as epochs, the number of neurons in the hidden layer, and learning rates in order to achieve the maximum accuracy of oil concentration measurements. It is demonstrated that the simultaneous, combined use of fluorescence and light scattering significantly improves the accuracy of measurement for oil samples. The newly developed technique permits the reliable, real-time determination of the total concentration of various oils and mixtures in water.     

Optimization of a technique for the estimation of the composition of edible oil blends

The fatty acid, sterol and tocopherol contents of edible oils were used to determine the formulation of blends of oils, which are themselves complex mixtures, by means of a weighted least-squares estimator with backwards elimination. A t-test was used to determine whether an oil should be eliminated from the blend. Initially, the minimum t-value was set at 2.7, which corresponds to a probability of ca. 0.01 if normal distribution is assumed. Some compounds are present in one oil but cannot be detected in others and are valuable in differentiating between various oils. Assumptions about levels for the undetected compounds and their corresponding weightings were made earlier in order to implement the weighted least-squares technique. A simplex optimization procedure was applied to avoid the use of assumed values. An optimum for the t-value as well as for the levels and the weightings of the undetected compounds was established. Analytical results for 378 pure oils were used to develop the models. The optimized technique is slightly better for assessing the composition of unknown blends than the original technique, when tested on 93 samples which were blends of known amounts of sunflower-seed oil, groundnut oil, cottonseed oil, maize oil, olive oil and palm oil.     

Analysis of gin essential oil mixtures by multidimensional and one-dimensional gas chromatography/mass spectrometry with spectral deconvolution

The composition of essential oils and their mixtures used to formulate gin is usually too complex to separate all sample components by standard capillary gas chromatography (GC). In particular, minor constituents that possess important organoleptic properties can be masked by co-elution with major sample components. A solution is provided that combines gas chromatography/mass spectrometry (GC/MS) with "interactive" spectral deconvolution software. Sequential two-dimensional (2D) GC/MS is used to produce a target compound library, with orthogonal GC-GC providing the separation power required to obtain peak retention times and the corresponding mass spectra needed for the deconvolution database. The combination of these two techniques, mass spectral deconvolution and automated sequential 2D-GC/MS, offers a very effective synergy for both identifying key constituents that determine the perception of flavor and aroma and the quality control needed to analyze mixtures of complex essential oils.     

Instability of hexane-acetonitrile mobile phases used for the chromatographic analysis of triacylglycerides

Comprehensive 2-D LC is an emerging separation technique that has seen a rapid increase in applications in the last decade. The technique has been applied for the separation of numerous complex mixtures including triacylglycerides (TAG). Determination of TAG in food products such as rice, palm, and canola oils have been previously described and the technique of choice utilizes a silver-modified silica column with hexane-ACN as the mobile phase. Repeated retention time inconsistencies were experienced in our studies when this mobile phase was applied to the separation of natural and synthetic mixtures containing TAG. The present report summarizes a study performed to determine the relative stability of ACN, propionitrile (PCN), and butyronitrile (BCN) at concentrations ranging from 0.43 to 2.8% in hexane and heptane. The data obtained suggest that unless evaporative loss of the mobile phase is prevented, TAG retention time irreproducibility can be significant when using mobile-phase mixtures prepared with ACN or PCN. BCN should be used as the solvent modifier in cases where evaporation cannot be prevented.     

PHYSICAL-CHEMICAL BEHAVIOR OF CONFECTIONERY FATS

Confectionery coatings employ hard butter fat systems made from both lauric and non-lauric source oils. These oils are routinely modified by a combination of treatments including hydrogenation, fractionation and interesterification to achieve desired physical properties. Such processing methods create heterogeneous triglyceride mixtures consisting of a variety of compositional and positional isomers. Published phase diagrams of “simple” binary triglyceride mixtures of closely related molecules are complex, and suggest that innumberable unique liquid and solid phases may co-exist at any given temperature ( and pressure ) in vastly more complex triglyceride mixtures such as confectionery hard butters. Thus we may view confectionery fat systems as multiphasic mixtures (liquid, solid and compositional) with a propensity to undergo liquid content fluctuations and crystal size/morphology changes in response to slight changes in temperature. A true equilibrium among all phases may indeed never be attained, and a potential for movement of certain components in response to temperature change is probably constant. Surface growth of long needle-like fat crystals, “fat bloom”, most likely results from this non-equilibrium condition and serves to reduce the system's free energy. The ever present, ever changing liquid phase(s) is viewed as the vehicle for free energy minimization via triglyceride migration and ongoing crystal growth.