20 years of fatty acid analysis by capillary electrophoresis

Fatty acids analysis by capillary electrophoresis: Fundamentals, advantages and applications

This review covers the know-how of the Grupo de Química Analítica e Quimiometria regarding the analysis of fatty acids by capillary electrophoresis acquired over its 20 years of existence. Therefore, the fundamentals, advantages, and applications of this technique for analyzing different fatty acids in samples such as food, oils, cosmetics, and biological matrices are presented and discussed. Capillary electrophoresis is, thus, shown as an interesting and valuable separation technique for the target analysis of these analytes as an alternative to the gas chromatography coupled to flame ionization detection, as it offers advantages over the latter such as low analysis times, low sample and reagent consumption, the use of a nondedicated column, and simpler sample preparation. In addition, the methods shown in this literature review can be useful for quality control, adulteration, and health-related research by regulatory agencies.

Separation of unsaturated C18 fatty acids using perfluorinated-micellar electrokinetic chromatography: I. Optimization and separation process

Ammonium perfluorooctanoate (APFOA) was used as a surfactant for the separation of free unsaturated C18 fatty acids by micellar electrokinetic chromatography. A simple background electrolyte of 50 mM APFOA water/methanol (90:10, v/v) at pH = 10 enabled the repeatable separation of oleic acid, elaidic acid, linoleic acid, and alpha-linolenic acid in less than 20 min. Separation conditions were optimized regarding various parameters (organic solvent, counterion, APFOA concentration, and pH). Because the repulsive interactions between fluorocarbon chains and hydrogenated chains are known to lead to segregation and phase separation, the choice of perfluorinated micelles to separate such perhydrogenated long-chain acids could appear astonishing. Therefore, the critical micelle concentration, the charge density, and the mobility of the micelles have been determined, resulting in a first description of the separation process.

A capillary electrophoresis method for free fatty acids screening and acidity determination in biodiesel

The advent of policies that incentivize or require alternative diesel fuels has increased the demand for the development of fast analytical methods aiming for the quality control of these fuels. This study approached an alternative method for the determination of biodiesel acidity employing capillary zone electrophoresis based on free fatty acids screening and quantification. Sample preparation comprised vortex-assisted liquid-liquid extraction of free fatty acids and was a crucial step for analysis. It was studied through a 3² full factorial design considering sample mass and the stirring time. Then, solvent suitability was evaluated univariately. The free fatty acid screening was carried out employing a capillary zone electrophoresis method able to separate C16:0, C18:0, C18:1 n-9, C18:2 n-6, and C18:3 n-3, major fatty acids in a variety of vegetable oils used for biodiesel synthesis. In addition to the straightforward sample preparation protocol, the running time of the developed method was only 12 min. Moreover, ultraviolet absorption indirect detection of analytes was approached to avoid analytes derivatization, considering the lack of chromophore groups in saturated fatty acids. Statistical tests did not evidence any significant differences in the biodiesel acidity determination expressed in percentage of free fatty acids when comparing the proposed capillary zone electrophoresis method and the traditional potentiometric titration approach within the 95% confidence interval, which demonstrates the suitability of this alternative method for the biodiesel quality control in routine.

Capillary electromigration methods for fatty acids determination in vegetable and marine oils: A review

Fatty acids determination is of paramount importance for quality control and suitable labeling of edible oils, required by regulatory agencies in several countries, and fast methods for this determination are worldly desired. This review article aimed to explore the available analytical methods for vegetable and marine oils analyses employing CE, which can be a straightforward and faster alternative than GC methods for fatty acid determination, considering some purposes. CE usually offers the possibility of a rapid analysis with a simple preparation of the sample, without requiring specific columns, which are inherent advantages of the technique. Instrumental conditions and the key points about fatty acids determination employing the technique are highlighted, and the main challenges and perspectives are also approached. Potential use of CE for edible oil analyses has been demonstrated for research and routine, which can be of interest for industries, regulatory agencies, and edible oil researchers. Therefore, we have explored the analytical approaches described in the last decades, intending to spread the interest of CE methods for fatty acid monitoring, label accuracy assessment, and food authenticity evaluation of edible oils.

Application of Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection (CE-C4D): 2017-2020

Capacitively coupled contactless conductivity detection (C⁴D) has emerged as influential to detect analytes that do not have chromogenic or fluorogenic functional group. Since our last review several new capillary electrophoresis (CE) methods coupled with (CE-C⁴D) have been communicated. The aim of this review is to give an update of the almost all the new applications of CE-C⁴D in the field of pharmaceutical, food and biomedical analysis covering the period from 2017 to April 2020. The utilization of CE with C⁴D in the areas of pharmaceutical, food and biomedical analysis is presented. Finally, concluding remarks and outlooks are discussed.

"Lipidomics": Mass spectrometric and chemometric analyses of lipids

Lipids are ubiquitous in the human organism and play essential roles as components of cell membranes and hormones, for energy storage or as mediators of cell signaling pathways. As crucial mediators of the human metabolism, lipids are also involved in metabolic diseases, cardiovascular and renal diseases, cancer and/or hepatological and neurological disorders. With rapidly growing evidence supporting the impact of lipids on both the genesis and progression of these diseases as well as patient wellbeing, the characterization of the human lipidome has gained high interest and importance in life sciences and clinical diagnostics within the last 15 years. This is mostly due to technically advanced molecular identification and quantification methods, mainly based on mass spectrometry. Mass spectrometry has become one of the most powerful tools for the identification of lipids. New lipidic mediators or biomarkers of diseases can be analysed by state-of-the art mass spectrometry techniques supported by sophisticated bioinformatics and biostatistics. The lipidomic approach has developed dramatically in the realm of life sciences and clinical diagnostics due to the available mass spectrometric methods and in particular due to the adaptation of biostatistical methods in recent years. Therefore, the current knowledge of lipid extraction methods, mass-spectrometric approaches, biostatistical data analysis, including workflows for the interpretation of lipidomic high-throughput data, are reviewed in this manuscript.

Test Paper for Colorimetric Inspection of Fatty Acids and Edible Oils

Fatty acids (FAs) are of interest to the areas of food science and medicine because they are important dietary sources of fuel for animals and play important roles in many biological processes. The health effects of FAs are different due to the diversity of olefinic bonds in the alkyl chains including number, position and configuration. However, the discrimination of FAs is difficult from a chemical sensing perspective due to the lack of diversity in terms of functional groups. Until now, only a few chemosensors have been developed for selective sensing of FAs based on their overall shape, however they are still limited in discrimination of FAs with subtle structural differences, moreover, they cannot be used for rapid and in situ inspections. Herein, for the first time, we designed a test paper for in situ colorimetric inspection for FAs based on the combination of the highly selective binding of Ag⁺ to olefinic bonds and Ag⁺ mediated color variation of 3,3′,5,5′,-tetramethylbenzidine. As a result, the sensor exhibited high sensitivity and good selectivity for five FAs with subtle structural differences. Furthermore, our method described herein was successfully applied to monitor the structural variations of FAs and quality changes in mixture edible hot pot oils with heat treatment in time course. Hence, the test paper presented herein holds great potential in the inspection of fats and edible oils in food industries.

Tributyl phosphate assisted hollow-fiber liquid-phase microextraction of short-chain fatty acids in microbial degradation fluid using capillary electrophoresis-contactless coupled conductivity detection

A tributyl phosphate assisted hollow-fiber liquid-phase microextraction coupled with capillary electrophoresis-contactless coupled conductivity detection (HF-LPME/CE-C⁴D) method has been developed for trace analysis of common short-chain fatty acids (SCFAs) without derivatization. Under the optimum conditions, ten SCFAs including a pair of isomers were well separated from their homologous FAs and the main coexisting inorganic anions within 40 min. Tributyl phosphate assisted HF-LPME produced excellent purification and enrichment for the model sample with high-salt matrix, microbial degradation fluid, and the limits of detection could reach 0.072-0.67 ng/mL (S/N = 3). Owing to its high sensitivity, good linearity, and acceptable recovery, this proposed method provided a sensitive and environment-friendly alternative for trace analysis of SCFAs in complicated samples.

Gas chromatography determination of fatty acids in the human erythrocyte membranes - A review

Blood fatty acid measurements can reflect exogenously consumed fatty acids allowing to resolve some metabolic disorders (e.g. diabetes, anorexia) or mental disorders (e.g. depression, anxiety, schizophrenia). For this purpose, fatty acids can be determined in the whole blood or various blood fractions such as the plasma, serum or erythrocytes. Measurement of fatty acids in the whole blood by dried blood spot technique is becoming increasingly popular and is often used mainly for the screening of newborns due to the use of the small sample volume. The most popular is determination of fatty acids in plasma or serum samples. While the profile of plasma fatty acids fluctuates based on daily dietary intake, the red blood cell membrane composition of fatty acids reflects the 2-3 month dietary intake. Such results can be more reflective in contrast to the plasma/serum and therefore the present review will summarize available information on gas chromatography determination of fatty acids in human red blood cell membranes. Selection of extraction and derivatization reagents as well as presentation of chromatographic conditions will be discussed here.

Supercritical fluid chromatography for lipid analysis in foodstuffs

The task of lipid analysis has always challenged separation scientists, and new techniques in chromatography were often developed for the separation of lipids; however, no single technique or methodology is yet capable of affording a comprehensive screening of all lipid species and classes. This review acquaints the role of supercritical fluid chromatography within the field of lipid analysis, from the early developed capillary separations based on pure CO₂ , to the most recent techniques employing packed columns under subcritical conditions, including the niche multidimensional techniques using supercritical fluids in at least one of the separation dimensions. A short history of supercritical fluid chromatography will be introduced first, from its early popularity in the late 1980s, to the sudden fall and oblivion until the last decade, experiencing a regain of interest within the chromatographic community. Afterwards, the subject of lipid nomenclature and classification will be briefly dealt with, before discussing the main applications of supercritical fluid chromatography for food analysis, according to the specific class of lipids.

High-Throughput Quantitative Lipidomics Analysis of Nonesterified Fatty Acids in Human Plasma

We present a high-throughput, nontargeted lipidomics approach using liquid chromatography coupled to high-resolution mass spectrometry for quantitative analysis of nonesterified fatty acids. We applied this method to screen a wide range of fatty acids from medium-chain to very long-chain (8 to 24 carbon atoms) in human plasma samples. The method enables us to chromatographically separate branched-chain species from their straight-chain isomers as well as separate biologically important ω-3 and ω-6 polyunsaturated fatty acids. We used 51 fatty acid species to demonstrate the quantitative capability of this method with quantification limits in the nanomolar range; however, this method is not limited only to these fatty acid species. High-throughput sample preparation was developed and carried out on a robotic platform that allows extraction of 96 samples simultaneously within 3 h. This high-throughput platform was used to assess the influence of different types of human plasma collection and preparation on the nonesterified fatty acid profile of healthy donors. Use of the anticoagulants EDTA and heparin has been compared with simple clotting, and only limited changes have been detected in most nonesterified fatty acid concentrations.