Chiral analysis in food science

The challenge to develop enantioselective analytical methods to quantify chiral compounds in food and environmental matrices is an actual and imperative issue. It is well known that enantiomers may differ in their biological activities, but the stereochemistry and the discrimination of enantiomers are frequently ignored in analytical workflows. However, the knowledge about their proportion is crucial to guarantee food and environmental safety. In this sense, chiral analysis is a valuable tool to evaluate food quality and genuineness, to determine the geographical origin of a certain sample aiming to find out fraud or adulteration, to investigate toxicity and bioaccumulation of environmental contaminants (e.g., pharmaceuticals and pesticides). This chapter highlights the importance of chiral analysis in food matrices and its relationship with the environmental contamination. The last advances in chiral analysis by liquid chromatography (LC), gas chromatography (GC), and supercritical fluid chromatography (SFC) coupled to mass spectrometry (MS) are presented, with a special remark in the type of chiral column used for chromatography and the proposed workflow in the method development. Some of the most recent applications in chiral analysis of food and beverages, environmental monitoring of surface water, wastewater, soils, biodegradation studies, and contamination of foodstuff are presented and critically discussed.Graphical AbstractKeywordsChiral chromatographyChiral stationary phaseEnantiomersPesticidesPharmaceuticals

New psychoactive substances represent serious social and health problem as tens of new compounds are detected in Europe annually. They often show structural proximity or even isomerism, which complicates their analysis. Two methods based on ultra high performance supercritical fluid chromatography and ultra high performance liquid chromatography with mass spectrometric detection were validated and compared. A simple dilute-filter-and-shoot protocol utilizing propan-2-ol or methanol for supercritical fluid or liquid chromatography, respectively, was proposed to detect and quantify 15 cathinones and phenethylamines in human urine. Both methods offered fast separation (<3min) and short total analysis time. Precision was well <15% with a few exceptions in liquid chromatography. Limits of detection in urine ranged from 0.01 to 2.3ng/mL, except for cathinone (5ng/mL) in supercritical fluid chromatography. Nevertheless, this technique distinguished all analytes including four pairs of isomers, while liquid chromatography was unable to resolve fluoromethcathinone regioisomers. Concerning matrix effects and recoveries, supercritical fluid chromatography produced more uniform results for different compounds and at different concentration levels. This work demonstrates the performance and reliability of supercritical fluid chromatography and corroborates its applicability as an alternative tool for analysis of new psychoactive substances in biological matrixes.

Chiral separations in food analysis

Metabolomics has demonstrated a great potential in numerous biomedical research fields in the last years, such as the study of the underlying pathology of diseases, discovery of diagnostic biomarkers or drug development. Nowadays, the main challenge in metabolomics is to obtain comprehensive and unbiased metabolomic profiles due to the huge complexity, heterogeneity and dynamism of metabolome. For this purpose, mass spectrometry represents a very interesting analytical platform, since complexity of metabolome may be overcome through the use of different orthogonal separation techniques, including liquid chromatography, gas chromatography and capillary electrophoresis. Alternatively, direct mass spectrometry analysis, either by direct infusion or flow injection, has been postulated as an alternative in metabolomics, complementing hyphenated approaches. These techniques exhibit several advantages such as the ability for high-throughput screening, fast analysis and wide metabolomic coverage, since there is not exclusion of compounds due to the separation device. The present work explores the potential of metabolomic platforms based on direct infusion mass spectrometry for metabolic fingerprinting of serum samples. The most important issues to be considered in this type of approaches were reviewed, including sample handling, comprehensive analysis, data processing, as well as further identification of metabolites and global characterization of metabolomic fingerprints.

In recent years, discovering new drug candidates has become a top priority in research. Natural products have proven to be a promising source for such discoveries as many researchers have successfully isolated bioactive compounds with various activities that show potential as drug candidates. Among these compounds, phenolic compounds have been frequently isolated due to their many biological activities, including their role as antioxidants, making them candidates for treating diseases related to oxidative stress. The isolation method is essential, and researchers have sought to find effective procedures that maximize the purity and yield of bioactive compounds. This review aims to provide information on the isolation or separation methods for phenolic compounds with antioxidant activities using column chromatography, medium-pressure liquid chromatography, high-performance liquid chromatography, counter-current chromatography, hydrophilic interaction chromatography, supercritical fluid chromatography, molecularly imprinted technologies, and high-performance thin layer chromatography. For isolation or purification, the molecularly imprinted technologies represent a more accessible and more efficient procedure because they can be applied directly to the extract to reduce the complicated isolation process. However, it still requires further development and refinement.

Purification of high-throughput organic synthesis libraries by counter-current chromatography

Curcumin is a natural plant pigment that has been widely used in food production, drug development, and textile engineering. Gaining a deep understanding of the biological activities of curcumin and obtaining high-purity curcumin are of vital importance for basic research and applications of curcumin. In this review, we summarize recent advances in curcumin, mainly focusing on the methods of extracting and purifying curcumin from turmeric as well as applications based on biological activity. We systematically describe the advantages and disadvantages of traditional and modern extraction technologies. The usual purification methods include conventional methods (such as macroporous resin column chromatography and silica gel column chromatography, etc.) and auxiliary modern technologies (such as high-speed countercurrent chromatography and supercritical fluid chromatography). In terms of biological activity, the phenolic hydroxy group and methoxy group of curcumin are closely related to its antioxidant activity, endowing it with strong antibacterial, anti-inflammatory, and antitumor properties. Moreover, the development direction based on its multiple biological activities is also discussed.

Metconazole is one of the widely-used chiral triazole fungicides in controlling wheat leaf rust, powdery mildew, Fusarium head blight with high efficacy, and so forth. In the current work, the effects of chiral stationary phases, alcoholic modifiers, and column temperature on the chiral separation of metconazole were discussed in detail. Amylose tris(3,5-dimethylphenylcarbamate)-coated chiral stationary phase exhibited much stronger chiral recognition ability toward metconazole stereoisomers in the CO2 /ethanol mixture as compared to the others. Then, a two-step semi-preparative separation of metconazole was performed through supercritical fluid chromatography and high-performance liquid chromatography, and the enantiomeric excess values of four stereoisomers were achieved over 98%. Moreover, the enantioselective cytotoxicity of cis-metconazole against HepG2 cells has been investigated, and the order of the cell proliferation toxicity against HepG2 cells was (1R, 5S)-metconazole>(1S, 5R)-metconazole>the mixture. Briefly, this study would provide valuable information in the preparative separation of optically pure metconazole products through chromatographic techniques and their environmental risk assessment.

Plate height theory for compressible mobile phase fluids and its application to gas, liquid and supercritical fluid chromatography

Application of supercritical fluid chromatography to the analysis of liquid-crystal mixtures

High-resolution separation systems are essential for the analysis of complex mixtures in a wide variety of application areas. To increase resolution, multidimensional chromatographic techniques have been one key solution. Supercritical fluid chromatography provides a unique opportunity in these multidimensional separations based on its potential for high solvent compatibility, rapid duty cycles, and orthogonality to other separation modes. This review focuses on two-dimensional chromatography methods from the past decade that use supercritical fluid chromatography because of these advantages. Valving schemes and modulation strategies used to interface supercritical fluid chromatography with other liquid chromatography and gas chromatography techniques are described. Particular applications of multidimensional separations using supercritical fluid chromatography for the analysis of oils and chiral separations of pharmaceutical compounds are highlighted. Limitations of and a potential trajectory for supercritical fluid chromatography in this field are also discussed.

Separation of minor coumarins from Peucedanum praeruptorum using HSCCC and preparative HPLC guided by HPLC/MS

Supercritical fluid chromatography (SFC) serves as a high resolution chromatographic technique for the analysis of high molecular mass solutes that are beyond the volatility range of gas chromatography (GC). Multidimensional SFC is a relatively new technique which is growing at a rapid pace. SFC also serves as a high resolution chromatographic technique for the analysis of high molecular mass solutes that are beyond the volatility range of GC. SFC instrumentation has some similarities to both LC and GC. A syringe or reciprocating pump delivers the SFC mobile phase as a liquid to the injection valve. SFC is often applied to the analysis of high molecular mass samples such as fossil fuels, but such samples generally become more complex with increasing molecular mass because the number of possible isomers increases. In SFC, more than one of the operating parameters can be varied simultaneously; for example, the temperature may be continuously increased during a density/pressure program.

Green Separation Techniques for -Omics Platforms: Supercritical Fluid Chromatography

Crude oil at the wellhead is a hot, high pressure fluid that contains gases, oil, water vapor and solid impurities. This mixture is processed in a gas oil separator where it is brought to atmospheric pressure and separated into gases, water, solid and stabilized oil. Characterization of a stabilized crude oil is carried out using a number of analytical methods for both its physical and chemical properties. These methods include use of a densitometer for density measurement and a hydrometer for specific gravity and American Petroleum Institute (API) gravity. The densitometer provides more precise and reproducible measurement of density as well as better control of the temperature of the sample. Pour point is determined using a cooling and pouring method, water content determination by distillation, ash content by a high temperature burning method, while salt content of a crude is determined by an electrometric method. The metal contents are determined using inductively coupled plasma atomic emission spectrometry (ICPAES) and atomic absorption spectrometry (AAS). The ICPAES is faster as compared to AAS and provides simultaneous determination of a wide range of metals. The elemental analysis is carried out by oxidative combustion of the sample in which carbon, hydrogen and sulfur are measured in oxide form, while nitrogen is measured in the form of molecular nitrogen. Sulfur is also determined using atomic emission spectrometry (AES) and chemiluminescent detectors which are very sensitive as compared to the oxidative combustion method. In addition, chemiluminescent detectors also provide nitrogen determination. Molecular weight is determined using thermoelectric measurement of vapor pressure; however the values obtained are influenced by the temperature of the measurement and the type of solvent used for dissolving the sample. Gel permeation chromatography (GPC) is used for average molecular weight determination of crude oil. Physical distillation is used for producing light and middle distillates and residue fractions based on the desired boiling range or volume percent range of a crude oil as well as determination of the boiling range distribution. Gas chromatography (GC) is utilized for determination of boiling range distribution by simulated distillation, volatile compound determination and identification of crude oil spill. The faster analysis time, better reproducibility and equivalent results are some of the advantages of simulated distillation over physical distillation in the determination of the boiling range distribution of a crude oil. Gas chromatography/mass spectrometry (GC/MS) separates and identifies volatiles and low boiling components of a crude oil while mass spectrometry (MS) is utilized for assessing the molecular weights of the compounds. High‐performance liquid chromatography (HPLC) is used for separation and quantification of hydrocarbon group types such as saturates, aromatics and polars. Aromatics are further separated into monoaromatics, diaromatics, triaromatics and polyaromatics. Liquid chromatography (LC) is used to fractionate the whole crude oil into desired fractions such as acids, bases and neutral nitrogen compounds. Petroleum resins are separated from whole crude oil by a liquid chromatographic method using ion‐exchange resins. Liquid chromatography/mass spectrometry (LC/MS) provides separation and positive identification of high boiling compounds of a crude oil. Supercritical fluid chromatography (SFC) is used for separation and identification of hydrocarbon group types. Compared to HPLC, SFC provides better separation of high boiling components. Infrared (IR) spectroscopy is used for determination of type of functional group and hydrogen bonding, thermal analysis for evaluating the thermal stability of the crude oils and classification of hydrocarbons while titrimetry is used for determining acid number, base number and water content.