Supported liquid membranes for the determination of vanillin in food samples with amperometric detection

Rapid Sample Screening Method for Authenticity Controlling of Vanilla Flavours Using Liquid Chromatography with Electrochemical Detection Using Aluminium-Doped Zirconia Nanoparticles-Modified Electrode

A rapid and sensitive technique for frauds determination in vanilla flavors was developed. The method comprises separation by liquid chromatography followed by an electrochemical detection using a homemade screen-printed carbon electrode modified with aluminium-doped zirconia nanoparticles (Al-ZrO₂-NPs/SPCE). The prepared nanomaterials (Al-ZrO₂-NPs) were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). This method allows for the determination of six phenolic compounds of vanilla flavors, namely, vanillin, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, vanillyl alcohol, vanillic acid and ethyl vanillin in a linear range between 0.5 and 25 µg g^-1, with relative standard deviation values from 2.89 to 4.76%. Meanwhile, the limits of detection and quantification were in the range of 0.10 to 0.14 µg g^-1 and 0.33 to 0.48 µg g^-1, respectively. In addition, the Al-ZrO₂-NPs/SPCE method displayed a good reproducibility, high sensitivity, and good selectivity towards the determination of the vanilla phenolic compounds, making it suitable for the determination of vanilla phenolic compounds in vanilla real extracts products.

Liquid Membranes for Efficient Recovery of Phenolic Compounds Such as Vanillin and Catechol

Investigations were carried out to obtain different lignin monomers such as vanillin and catechol as efficiently as possible, to prevent side reactions e.g., during lignin degradation. Therefore, extraction experiments were performed to determine the influence of parameters such as initial pH in the aqueous phase, organic phases containing alcohols or solvating extractants, and monomer concentrations. Cyanex 923 (Cy923) and tri-n-butyl-phosphat (TBP) diluted in kerosene were the organic phases chosen to evaluate the transport of vanillin because of their high efficiencies (>76.8%) and suitability in membrane technologies. The most efficient vanillin transport was accomplished with Cy923, as > 90% of vanillin was transferred after 5 h. However, the permeability coefficient at carrier concentration of > 0.48 mol/L was influenced not only by the diffusion but also by the organic mixture viscosity. Thus, this concentration was used in the membrane experiment containing a mixture of vanillin and catechol in the feed phase. Catechol was transported about 7% faster to the receiving phase than vanillin, presumably due to its chemical structure. Side reactions were avoided using the current liquid membrane set-up, allowing the further industrial application of an entire process, which, e.g., recovers vanillin from enzymatic lignin conversion by membrane technology.

[Fluorophothometric determination of aldehyde by utilizing condensation reaction with resorcinol]

A simple and sensitive fluorophotometric method for the determination of aldehyde was established by utilizing condensation reaction with resorcinol. In the determination of vanillin that is one of aldehydes, the calibration curve exhibited linearity over the vanillin concentration range of 3.0-7600 ng ml(-1) at an emission wavelength of 507 nm with an excitation of 410 nm and with the relative standard deviations (n=5) of 2.5%, 2.0% for 7.6 ng ml(-1), 760 ng ml(-1) of vanillin, respectively. This method was successfully applied in the assay of vanillin in cold medicine.

Automated, on-line membrane extraction

Over the last few years, membranes have been used to develop new approaches in analytical extraction, concentration and cleanup. An important advantage of membrane processes is that the sample and the extraction phase can be continuously brought into contact without physical mixing, and may be directly interfaced to an analytical instrument. This provides the basis for automated, real-time monitoring. Membrane extraction has been applied to a wide range of organic and inorganic analytes, and has been directly interfaced with chromatography, spectroscopy and mass spectrometry. Implementations of membrane extraction are diverse, encompassing different types of membranes, module designs and configurations. This review highlights some of these, and particularly the unique capabilities in automated, and on-line measurements.

Sample preparation techniques for the determination of trace residues and contaminants in foods

The determination of trace residues and contaminants in complex matrices, such as food, often requires extensive sample extraction and preparation prior to instrumental analysis. Sample preparation is often the bottleneck in analysis and there is a need to minimise the number of steps to reduce both time and sources of error. There is also a move towards more environmentally friendly techniques, which use less solvent and smaller sample sizes. Smaller sample size becomes important when dealing with real life problems, such as consumer complaints and alleged chemical contamination. Optimal sample preparation can reduce analysis time, sources of error, enhance sensitivity and enable unequivocal identification, confirmation and quantification. This review considers all aspects of sample preparation, covering general extraction techniques, such as Soxhlet and pressurised liquid extraction, microextraction techniques such as liquid phase microextraction (LPME) and more selective techniques, such as solid phase extraction (SPE), solid phase microextraction (SPME) and stir bar sorptive extraction (SBSE). The applicability of each technique in food analysis, particularly for the determination of trace organic contaminants in foods is discussed.

Electrochemically Modulated Liquid−Liquid Extraction of Ions

The development of ion extraction methods under electrochemical control via electrochemistry at the interface between two immiscible electrolyte solutions is discussed. A hydrodynamic flow injection system was used for the potentiostatic extraction of non-redox-active species from a flowing aqueous phase into a stationary organogel phase. The ions tetraethylammonium, 4-octylbenzenesulfonate (4-OBSA-), and p-toluenesulfonate (p-TSA-) were studied as model analytes. The extraction study comprised examination of the influence of extraction potentials, aqueous-phase flow rate, and target species concentration. The extraction process can be monitored in situ by means of the ion-transfer current, which has opposing signs for anions and cations. Hydrodynamic voltammograms were obtained from these experiments. The selective extraction of 4-OBSA-, from its mixture with p-TSA-, as well as coextraction of both anions is shown. The results demonstrate the utility of electrochemical modulation for the controlled extraction of ions from an aqueous phase into an organogel electrolyte phase. This offers potential benefits for various analytical processes including sample preparation and cleanup.

Recent applications of sample preparation techniques in food analysis

Even with the emergence of advanced techniques of separation and identification, it is rarely possible to analyse food without manipulation. The traditional techniques for sample preparation are time consuming and require large amount of reagents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. The more analytical techniques have become highly developed, the more has sample clean-up become important in order to fully take advantage of them. Due to the multiplicity of food matrices, it is not possible to use one sample preparation technique, so many methods have been proposed for meeting all the requirements. The newest variations of wet digestion, solvent and sorbent extraction and membrane separation are summarised and their most recent applications to food analysis are provided.

Advances in the voltammetric analysis of small biologically relevant compounds

The problems associated with attempting to apply voltammetric techniques to the analysis of biologically relevant organics within complex media are identified and, through reviewing the very recent literature (1999-mid-2001), possible solutions are described. The boundaries of the search were limited to research targeted at the resolution of specific problems, associated with quantitative determinations. Various strategies have emerged to counter problems of poor sensitivity and selectivity and these have been summarized and critically appraised. Where possible, the characteristics of each approach have been distilled into a table format to ease comparison. Emphasis has been placed on the collation of information that will improve the intrinsic electrode response and as such should be of value to those interested in pursuing electroanalytical methodologies regardless of context.

Membrane-based techniques for sample enrichment

Sample preparation techniques based on non-porous membrane extraction generally offer a high degree of selectivity and enrichment power, together with convenient possibilities for direct and automated connections to chromatographic and other analytical instruments. In this review principles and applications for techniques as supported liquid membrane extraction, microporous membrane liquid-liquid extraction, polymeric membrane extraction and membrane extraction with a sorbent interface are described and compared.