Chromatographic analysis of tocol-derived lipid antioxidants

Immobilization of two dendritic organic phases onto silica and their molecular shape recognition for polycyclic aromatic hydrocarbons, tocopherols and carotenoid isomers

BACKGROUND

Molecular shape selectivity, based on the size and shape parameters of the molecule, such as length and planarity, is a separation process that can be used for compounds with restricted shapes, such as isomers. The separation of geometric isomers is challenging because these compounds have similar physicochemical properties but differ slightly in molecular shape. The ability to separate and quantify these isomers is important in high performance liquid chromatography (HPLC), which is one of the most widely used techniques in separation science today, because the shape of the molecule has a strong influence on biological processes.

RESULTS

We prepared symmetrical discoidal dendrimeric organomolecule gelators (GSDM) and o-phenylenediamine-derived low-molecular-weight dendrimeric organomolecule gelators (G1) and bonded them to silica surfaces. The dendritic organic compound-grafted silica (SiO2@GSDM and SiO2@G1) was used as HPLC stationary phases for the separation of shape-restricted isomers of polycyclic aromatic hydrocarbons (PAHs), carotenoids and tocopherols. The two phases exhibit a very high molecular shape selectivity compared to the commercially available alkyl phases. There are differences in molecular shape selectivity between the two stationary phases. Changes in the chemical structure of dendritic organic compounds can alter the orientation of the molecules, as well as changes in the molecular recognition ability. It was found that SiO2@GSDM has high molecular linear selectivity for PAHs at different temperatures, even at 50 °C. The planar selectivity of SiO2@GSDM was better for triphenylene and o-terphenyl benzenes compared to SiO2@G1.

SIGNIFICANCE

This separation behavior may be attributed to the combined effect of weak interaction centers, which allowed the effective separation of bioactive and shape-restricted isomers through multiple interactions. Furthermore, SiO2@GSDM showed better separation of tocopherols and carotenoids, suggesting that the backbone and ordered structure of organic molecular gelators is an effective way to improve the shape selectivity of the molecules, whereas the molecular orientation of the functional groups influences the separation mechanism of the shape-restricted isomers.

Surface Modification of Silica with β-Alanine Derivatives for Unique Applications in Liquid Chromatography

Column purchasing cost is an important issue for an analyst to analyze complex sample matrices. Here, we report the development of an amino acid (β-alanine)-derived stationary phase (Sil-Ala-C12) with strategic and effective interaction sites (amide and urea as embedded polar groups with C12 alkyl chain) able to separate various kinds of analytes. Owing to the balanced hydrophobicity and hydrophilicity of the phase, it showed exceptional separation abilities in both reversed-phase high-performance liquid chromatography (RP-HPLC) as a hydrophobic phase and hydrophilic interaction chromatography (HILIC) as a hydrophilic phase. Remarkably, the baseline separation was achieved for the challenging β- and γ-isomers of tocopherol. Usually, three columns such as pentafluorophenyl or C30, C18, and sulfobetaine HILIC are required for the analysis of vitamin E, capsaicinoids, and vitamin C in chili peppers (Capsicum spp.), respectively. However, only Sil-Ala-C12 was able to separate these analytes. A single column can serve 3-4 purposes, which suggests that Sil-Ala-C12 had the potential to reduce column purchasing costs.

Free and Esterified Tocopherols, Tocotrienols and Other Extractable and Non-Extractable Tocochromanol-Related Molecules: Compendium of Knowledge, Future Perspectives and Recommendations for Chromatographic Techniques, Tools, and Approaches Used for Tocochromanol Determination

Free and esterified (bound) tocopherols, tocotrienols and other tocochromanol-related compounds, often referred to "tocols", are lipophilic antioxidants of great importance for health. For instance, α-tocopherol is the only tocochromanol with vitamin E activity, while tocotrienols have a positive impact on health and are proposed in the prevention and therapy of so-called modern diseases. Tocopherols, tocotrienols and plastochromanol-8 are the most well-known tocochromanols; in turn, knowledge about tocodienols, tocomonoenols, and other rare tocochromanol-related compounds is limited due to several challenges in analytical chemistry and/or low concentration in plant material. The presence of free, esterified, and non-extractable tocochromanols in plant material as well as their biological function, which may be of great scientific, agricultural and medicinal importance, is also poorly studied. Due to the lack of modern protocols as well as equipment and tools, for instance, techniques suitable for the efficient and simultaneous chromatographical separation of major and minor tocochromanols, the topic requires attention and new solutions, and/or standardization, and proper terminology. This review discusses the advantages and disadvantages of different chromatographic techniques, tools and approaches used for the separation and detection of different tocochromanols in plant material and foodstuffs. Sources of tocochromanols and procedures for obtaining different tocochromanol analytical standards are also described. Finally, future challenges are discussed and perspective green techniques for tocochromanol determination are proposed along with best practice recommendations. The present manuscript aims to present key aspects and protocols related to tocochromanol determination, correct identification, and the interpretation of obtained results.

Deep eutectic solvent-based liquid-phase microextraction coupled with reversed-phase high-performance liquid chromatography for determination of α-, β-, γ-, and δ-tocopherol in edible oils

For simultaneous analysis of four fat-soluble tocopherols (α-, β-, γ-, and δ-) in edible oils, an efficient and green method using deep eutectic solvent-based liquid-phase microextraction (DES-LPME) coupled with reversed-phase high-performance liquid chromatography (RP-HPLC) was developed. The DESs formed by different quaternary ammonium salts and ethanol were used as the extractants. Tetrabutylammonium chloride (TBAC)-ethanol DES at a molar ratio of 1:2 achieved the best extraction efficiency. Under the optimized conditions, the detection limits were in the range of 2.1-3.0 ng mL^-1. The intra-day and inter-day repeatability were in the ranges of 3.9-5.3% and 4.8-7.1%, respectively, and the recoveries for the real samples varied from 80.7% to 105.4%. The developed method was successfully employed for the determination of all four tocopherol homologues with an RP-HPLC system containing a COSMOSIL π-NAP column in five edible oils collected locally. Graphical abstract.

Study on the influence of palm oil on blood and liver biochemical parameters, beta-carotene and tocochromanols content as well as antioxidant activity in rats

In the ongoing discussion on the health properties of palm oil, a study of the effect a diet supplemented with palm oil on blood and liver biochemical parameters, beta-carotene and tocochromanols content as well as antioxidant activity was undertaken. Forty Wistar rats were randomly divided into five groups, fed with a diet supplemented with plant-based frying commercial fat, palm oil, 7.5% palm oil and 2.5% concentrate from palm oil and 10% of rapeseed oil, respectively. After 21 days, blood samples and livers were collected to determine beta-carotene and tocochromanols concentrations, antioxidant activity using DPPH* radical scavenging activity and TEAC methods, insulin, glucagon, serum triacyloglycerols and cholesterol levels, glucose in blood serum and glycogen in the livers. Research has shown valuable biological properties of palm oil in terms of plasma glucose, total cholesterol, low-density lipoprotein (LDL) cholesterol, and triacylglycerol concentrations which was related to the high content of beta-carotene and tocochromanols. PRACTICAL APPLICATION: Public concern over the health properties of palm oil has been growing. Therefore, this study supplements existing knowledge in this area based on experimental rat observations. In the presented research, plasma glucose was significantly reduced and no additional growth of total or LDL cholesterol, as well as triacylglycerol concentration, was observed after consuming a palm oil-based diet. Palm oil was a good source of beta-carotene and tocochromanols, which were preferentially distributed in rats' livers. Bioavailability of vitamin E-active compounds in palm oil supplemented rats' livers was relatively high as compared to the rapeseed oil group, therefore this observation complements literature in the field of tocotrienols and tocopherols. Studies have not confirmed the harmful effect of palm oil on rats, however in depth human studies appear to be a promising direction for further research.

Ultrafast determination of vitamin E using LC–ESI–MS/MS for preclinical development of new nutraceutical formulations

Aim: We proposed a rapid and high quality method to determine α-tocopherol (α-T) in different biopharmaceutical samples using liquid chromatography-diode array detector on-line ESI–MS/MS. Materials & methods: A working standard solution of α-T and internal standard, phenyl-5,7-dimethyl-d6-α-tocopherol, were used for optimization and validation of the method. Levels of α-T in nanoemulsions, serum and plasma samples were evaluated. Results & conclusion: Precision (1% for retention time, 5% for peak area and 3% for relative peak area), linearity range (among 0.625–20.0 μg ml-1), LOD and LOQ, accuracy and matrix effect were studied. The validated chromatographic method is presented as valuable analytical tool for the determination of α-tocopherol in loaded drug delivery systems and in biodistribution levels in blood samples.

Chromatographic Separation of Vitamin E Enantiomers

Vitamin E is recognized as an essential vitamin since its discovery in 1922. Most vegetable oils contain a mixture of tocopherols and tocotrienols in the vitamin E composition. Structurally, tocopherols and tocotrienols share a similar chromanol ring and a side chain at the C-2 position. Owing to the three chiral centers in tocopherols, they can appear as eight different stereoisomers. Plant sources of tocopherol are naturally occurring in the form of RRR while synthetic tocopherols are usually in the form of all-racemic mixture. Similarly, with only one chiral center, natural tocotrienols occur as the R-isoform. In this review, we aim to discuss a few chromatographic methods that had been used to separate the stereoisomers of tocopherols and tocotrienols. These methods include high performance liquid chromatography, gas chromatography and combination of both. The review will focus on method development including selection of chiral columns, detection method and choice of elution solvent in the context of separation efficiency, resolution and chiral purity. The applications for separation of enantiomers in vitamin E will also be discussed especially in terms of the distinctive biological potency among the stereoisoforms.

Separation of Vitamin E on a 100-Å Phenogel Column

The effect of π-electrons and hydroxyl group on the separations of vitamin E on a swelling-controlled polystyrene-divinylbenzene (Phenogel) column using toluene/isooctane as the mobile phase was investigated. The effect of the π-electrons was demonstrated in the baseline separation of α-tocopherol and α-tocotrienol on a 100-Å Phenogel column. In addition, baseline separation of α-, (β- + γ-)- and δ-tocopherol could be achieved on this column. The separation mechanism of these isomers are due to the difference in the interactions between the hydroxyl group on the chromanol ring of each tocopherol and the gel matrix caused by the steric hindrance of methyl group(s). It was concluded that solutes of the same molecular size but different in the polar groups could be separated on a high performance size-exclusion chromatography by controlling the swelling of the gel matrix via modification of the mobile phase.

GC-MS and LC-MS approaches for determination of tocopherols and tocotrienols in biological and food matrices

Tocopherols and tocotrienols, widely described as vitamin E derivatives, have been proven to take part in a number of important biological functions. Among them, antioxidant properties had been investigated and documented in the literature. Since tocochromanols have revealed their plausible beneficial impact on several pathological processes, such as cancerogenesis or cognitive impairment diseases, there is a growing interest in quantitative determination of these compounds in biological fluids, tissues and plant organs. However, due to vitamin E chemical features, such as lipophilic and non-polar characteristics, quantitative determination of the compounds seems to be problematic. In this paper we present current analytical approaches in tocopherols and tocotrienols determination in biological and food matrices with the use of chromatographic techniques, especially gas chromatography (GC) and high performance liquid chromatography (HPLC) coupled with mass spectrometry. Derivatization techniques applied for GC-MS analysis in the case of tocol derivatives, especially silylation and acylation, are described. Significant attention is paid to ionization process of tocopherols and tocotrienols.

A review of characterization of tocotrienols from plant oils and foods

Tocotrienols, members of the vitamin E family, are natural compounds found in a number of vegetable oils, wheat germ, barley and certain types of nuts and grains. Vegetable oils provide the best sources of these vitamin E forms, particularly palm oil and rice bran oil contain higher amounts of tocotrienols. Other sources of tocotrienols include grape fruit seed oil, oats, hazelnuts, maize, olive oil, buckthorn berry, rye, flax seed oil, poppy seed oil and sunflower oil. Tocotrienols are of four types, viz. alpha (α), beta (β), gamma (γ) and delta (δ). Unlike tocopherols, tocotrienols are unsaturated and possess an isoprenoid side chain. A number of researchers have developed methods for the extraction, analysis, identification and quantification of different types of vitamin E compounds. This article constitutes an in-depth review of the chemistry and extraction of the unsaturated vitamin E derivatives, tocotrienols, from various sources using different methods. This review article lists the different techniques that are used in the characterization and purification of tocotrienols such as soxhlet and solid-liquid extractions, saponification method, chromatography (thin layer, column chromatography, gas chromatography, supercritical fluid, high performance), capillary electrochromatography and mass spectrometry. Some of the methods described were able to identify one form or type while others could analyse all the analogues of tocotrienol molecules. Hence, this article will be helpful in understanding the various methods used in the characterization of this lesser known vitamin E variant.

Rapid determination of alpha tocopherol in olive oil adulterated with sunflower oil by reversed phase high-performance liquid chromatography

A new method is developed to determine the presence of sunflower oil in olive oil. α-tocopherol is selected as discriminating parameter for detecting sunflower oil adulterant in olive oil. Admixtures of olive oil and sunflower oil (5 %, 10 %, 15 % and 20 % sunflower oil in olive oil) are prepared. These admixtures are analysed by reversed phase high pressure liquid chromatography coupled with fluorescence detector. The sample preparation does not require saponification or addition of antioxidant. The chromatographic system consists of a C18 column with methanol: acetonitrile (50:50) mobile phase. Fluorescence detector excitation wavelength is set at 290 nm and emission wavelength is set at 330 nm. The α tocopherol concentration increases linearly in olive oil adulterated with sunflower oil. The method is simple, selective, sensitive and is precise (RSD = 2.65 %) for α tocopherol. The present method can precisely detect 5 % sunflower oil in olive oil.

Pressurized liquid extraction and dispersive liquid-liquid microextraction for determination of tocopherols and tocotrienols in plant foods by liquid chromatography with fluorescence and atmospheric pressure chemical ionization-mass spectrometry detection

Pressurized liquid extraction (PLE) and dispersive liquid-liquid microextraction (DLLME) were used to isolate and preconcentrate tocopherols and tocotrienols from plant foods. The Taguchi experimental method was used to optimize the six factors (three levels for each factor), affecting DLLME, namely: carbon tetrachloride volume, methanol volume, aqueous sample volume, pH of sample, sodium chloride concentration and time of the centrifugation step. The influencing parameters selected were 2 mL of methanol:isopropanol (1:1) (disperser solvent), 150 µL carbon tetrachloride (extraction solvent) and 10 mL aqueous solution. The organic phase was injected into reversed-phase liquid chromatography (LC) with an isocratic mobile phase composed of an 85:15 (v/v) methanol:water mixture and a pentafluorophenyl stationary phase. Detection was carried out using both fluorescence and atmospheric pressure chemical ionization mass spectrometry (APCI-MS) in negative ion mode. Quantification was carried out by the standard addition method. Detection limits were in the range 0.2-0.3 ng mL(-1) for the vitamers with base-line resolution. The recoveries obtained using the optimized DLLME were in the 90-108% range, with RSDs lower than 6.7%. The APCI-MS spectra, in combination with fluorescence spectra, permitted the correct identification of compounds in the vegetable and fruit samples. The method was validated according to international guidelines and using two certified reference materials.

A single extraction and HPLC procedure for simultaneous analysis of phytosterols, tocopherols and lutein in soybeans

A saponification/extraction procedure and high performance liquid chromatography (HPLC) analysis method were developed and validated for simultaneous analysis of phytosterols, tocopherols and lutein (a carotenoid) in soybeans. Separation was achieved on a phenyl column with a ternary, isocratic solvent system of acetonitrile, methanol and water (48:22.5:29.5, v/v/v). Evaporative light scattering detection (ELSD) was used to quantify β-sitosterol, stigmasterol, campesterol, and α-, δ- and γ-tocopherols, while lutein was quantified with visible light absorption at 450 nm. Peak identification was verified by retention times and spikes with external standards. Standard curves were constructed (R(2)>0.99) to allow for sample quantification. Recovery of the saponification and extraction was demonstrated via analysis of spiked samples. Also, the accuracy of results of four soybeans using the described saponification and HPLC analytical method was validated against existing methods. This method offers a more efficient alternative to individual methods for quantifying lutein, tocopherols and sterols in soybeans.

Microtox aquatic toxicity of petrodiesel and biodiesel blends: the role of biodiesel's autoxidation products

The acute Microtox toxicity of the water accommodated fraction (WAF) of six commercial soybean biodiesel/petrodiesel blends was investigated at different oil loads. We analyzed five fatty acid methyl esters (FAMEs), C10-C24 n-alkanes, four aromatics, methanol, and total organic carbon (TOC) content. At high oil loads, the WAFs' toxicity was significantly higher for blends containing biodiesel. At the lowest load, the WAFs' toxicity decreased almost linearly with decreasing biodiesel in the blend. At intermediate loads, the WAFs of all the blends appeared to have a similar toxicity. Analysis of WAFs confirmed the presence of autoxidation byproducts of FAMEs at high oil loads. Pure unsaturated FAMEs and n-alkanes were nontoxic when present in water at their reported solubility limits. However, 24-h equilibrated WAFs of pure FAMEs were highly toxic for C18:1 and C18:3, but not for C18:2. The authors concluded that at high oil loads, the acute toxicity of the WAFs was caused by FAMEs' autoxidation byproducts, whereas at low oil loads, the toxicity appeared to be caused primarily by the aromatic compounds present in petrodiesel. The addition of a synthetic antioxidant in biodiesel did not appear to affect the concentration of autoxidation byproducts in the WAF but resulted in a slight decrease in its toxicity. The major autoxidation byproducts identified in the WAF of commercial biodiesel were present neither in the WAFs of pure unsaturated FAMEs nor in the WAF of a different soybean biodiesel that was transesterified in our laboratory, which was nontoxic. We concluded that the process of transesterification of biodiesel might be a more critical factor in determining the aquatic toxicity of the fuel than the source of feedstock itself.

Preparation and certification of standard reference material 3278 tocopherols in edible oils

Standard Reference Material (SRM) 3278 Tocopherols in Edible Oils has been issued for use as a quality assurance tool in the measurement of tocopherols. Like other natural-matrix SRMs, this material can be used in method validation or in assignment of tocopherol values to in-house quality control materials. Because most edible oils contain one predominant tocopherol isoform, the SRM is a blend of sunflower, soy, canola, and safflower oils to provide roughly comparable chromatographic peak heights of the two main tocopherols, γ and α, with smaller amounts of δ and β. The four tocopherol isoforms were determined by three independent liquid chromatography methods with absorbance and fluorescence detection. Various chromatographic and detection modes are used for assignment of certified values because biases inherent to one method should not be present in the other, and the existence of bias can therefore be identified.

Chromatographic analyses of tocopherols and tocotrienols in palm oil

Analyses of tocols (tocopherols and tocotrienols) in palm oil have been extensively reported in the past. However, due to the scarcity of individual tocotrienol standards, calibrations have mostly been carried out using only α-tocopherol as standard. Moreover, even if the individual tocotrienols are being used, their reliability is often questioned, because tocotrienols are highly susceptible to oxidation and deterioration. This paper reports on the study of the deterioration rate of individual tocotrienol standards upon storage as well as different calibration methods for the tocols in palm oil.

Rapid baseline-separation of all eight tocopherols and tocotrienols by reversed-phase liquid-chromatography with a solid-core pentafluorophenyl column and their sensitive quantification in plasma and liver

Of the eight natural vitamin E congeners (α-, β-, γ-, and δ-tocopherol and α-, β-, γ-, and δ-tocotrienol), the non-α-tocopherol congeners have unique biological properties that may contribute to human health. Their study in vivo has been complicated by the lack of a simple analytical method that completely resolves and sensitively detects all eight natural tocopherols and tocotrienols in biological matrices. We thus developed and validated (according to the FDA guidelines for bioanalytical method validation) the first reversed-phase liquid chromatographic method for the baseline-separation and quantification of all eight tocopherols and tocotrienols. Analytes were extracted from human plasma or mouse liver and separated on a Phenomenex Kinetex PFP column (2.6 μm, 150 × 4.6 mm) by elution with methanol:water (85:15, vol/vol) at a flow rate of 0.8 mL/min. The developed RP-LC method used a solid-core pentafluorophenyl stationary phase and achieved baseline separation of all eight vitamin E congeners within 15 min at a backpressure of 23 MPa, which is suitable for most conventional HPLC systems. The method was fast, linear, accurate, and precise with detection limits of 27-156 pg and good recoveries (82-122%) for all analytes. In conclusion, we developed and validated the first RP-LC method for baseline resolution of all eight tocopherols and tocotrienols extracted from plasma and liver, which should be useful for the quantification of individual vitamin E congeners in large epidemiological studies and randomized controlled trials.

Optimization and validation of the reversed-phase high-performance liquid chromatography with fluorescence detection method for the separation of tocopherol and tocotrienol isomers in cereals, employing a novel sorbent material

The separation and determination of tocopherols (Ts) and tocotrienols (T3s) by reversed-phase high-performance liquid chromatography with fluorescence detection has been developed and validated after optimization of various chromatographic conditions and other experimental parameters. Analytes were separated on a PerfectSil Target ODS-3 (250 × 4.6 mm, 3 μm) column filled with a novel sorbent material of ultrapure silica gel. The separation of Ts and T3s was optimized in terms of mobile-phase composition and column temperature on the basis of the best compromise among efficiency, resolution, and analysis time. Using a gradient elution of mobile phase composed of isopropanol/water and 7 °C column temperature, a satisfactory resolution was achieved within 62 min. For the quantitative determination, α-T acetate (50 μg/mL) was used as the internal standard. Detection limits ranged from 0.27 μg/mL (γ-T) to 0.76 μg/mL (γ-T3). The validation of the method was examined performing intraday (n = 5) and interday (n = 3) assays and was found to be satisfactory, with high accuracy and precision results. Solid-phase extraction provided high relative extraction recoveries from cereal samples: 87.0% for γ-T3 and 115.5% for δ-T. The method was successfully applied to cereals, such as durum wheat, bread wheat, rice, barley, oat, rye, and corn.

Method for simultaneous analysis of eight vitamin E isomers in various foods by high performance liquid chromatography and fluorescence detection

The objective of this study was to optimize a method to investigate the occurrence and to quantify the full isomeric composition of vitamin E (α-, β-, γ- and δ-tocopherols and tocotrienols) in 6 vegetables (raw and cooked), 3 herbs/spices, raw and cooked eggs, vegetable oils (canola, olive and soybean), flaxseed and sorghum (flour and seeds) and soy (flour) by HPLC with fluorescence detection. Different conditions of extraction and analysis were tested. The optimized method consisted of direct extraction with solvent (hexane:ethyl acetate, 85:15, v/v). For analysis normal phase column was used with mobile phase consisting of hexane:isopropanol:acetic acid (98.9:0.6:0.5) with isocratic elution and fluorescence detection. Excellent separation of all isomers was obtained along with adequate quantification in the foods analyzed. Recovery rates of standards ranged from 91.3 to 99.4%. The linearity range for each isomer varied from 2.5 to 137.5 ng/mL (R² greater than 0.995 in all cases). Detection limits ranged from 21.0 to 48.0 ng/mL for tocopherols and from 56.0 to 67.0 ng/mL for tocotrienols, while quantification limits ranged from 105.0 to 240.0 ng/mL for tocopherols and from 280.0 to 335.0 ng/mL for tocotrienols. The optimized method was considered simple, fast and reliable, and also preserved vitamin E isomers when compared to validated methods involving saponification.

Comparative study of lipophilic and hydrophilic antioxidants from in vivo and in vitro grown Coriandrum sativum

Coriander is commonly used for medicinal purposes, food applications, cosmetics and perfumes. Herein, the production of antioxidants in vegetative parts (leaves and stems) of in vivo and in vitro grown samples was compared. In vitro samples were clone A- with notorious purple pigmentation in stems and leaves and clone B- green. Seeds were also studied as they are used to obtain in vivo and in vitro vegetative parts. Lipophilic (tocopherols, carotenoids and chlorophylls) and hydrophilic (sugars, ascorbic acid, phenolics, flavonols and anthocyanins) compounds were quantified. The antioxidant activity was evaluated by radical scavenging activity, reducing power and lipid peroxidation inhibition. The in vivo sample showed the highest antioxidant activity mainly due to its highest levels of hydrophilic compounds. Otherwise, in vitro samples, mainly clone A, gave the highest concentration in lipophilic compounds but a different profile when compared to the in vivo sample. Clones A and B revealed a lack of β-carotene, β- and δ-tocopherols, a decrease in α-tocopherol, and an increase in γ-tocopherol and clorophylls in comparison to the in vivo sample. In vitro culture might be useful to explore the plants potentialities for industrial applications, controlling environmental conditions to produce higher amounts of some bioactive products.

Analysis of vitamin E metabolites in biological specimen

Vitamin E is known as the most important lipid antioxidant and is widely used to prevent age-associated diseases. Despite increasing knowledge about human vitamin E metabolism, little is known to justify its widespread use. As meta-analyses revealed even harmful effects of high vitamin E doses, a profound understanding of vitamin E metabolism is mandatory. By recent advances in analytical methodology, new metabolites with distinct physicochemical and biological properties were discovered. This review covers current methods to analyze vitamin E metabolites in biological samples. Special emphasis is laid on analytical applications for the identification and quantification of metabolites with a modified hydroxychromanol ring or a truncated side chain.