1 Introduction

Literally, the meaning of vitamins is vital amines that are low molecular weight organic compounds and essential for human health. Out of thirteen compounds recognized as vitamins, nine are water-soluble vitamins (or hydrophilic vitamins) which include thiamine (B1), riboflavin (B2), nicotinamide/nicotinic acid (B3), pantothenic acid (B5), pyridoxine (B6), folic acid (B9), cyanocobalamin (B12), and vitamin C (ascorbic acid). In combination, these are known as "Vitamin B-Complex." The remaining four are fat-soluble (or lipophilic) vitamins which include retinol (vitamin A), tocopherol (vitamin E), calciferol (vitamin D), and anti-hemorrhagic vitamins (vitamin K). These vitamins play specific and vital functions in metabolism. The deficiency or excess of vitamins can cause health problems. These vitamins do not provide energy (calories) directly, but they do help regulate energy-producing processes. Except for vitamins D and K, other vitamins have to be taken from food because they are not synthesized by the body. Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when an organism does not get enough of the vitamin from the food. A secondary deficiency may be due to an underlying disorder that prevents or limits the absorption or use of the vitamin, due to “lifestyle factors” such as smoking, excessive alcohol consumption, or the use of medications that interfere with the absorption or use of the vitamin. Well-known human vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy), and vitamin D (rickets). The sources as well as the functions, the physical properties of hydrophilic vitamins and lipophilic vitamins are summarized in Tables 1, 2, and 3 respectively.

Table 1 List of sources, name of vitamins, and their functions
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Table 2 Physical properties of water-soluble vitamins
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Table 3 Physical properties of fat-soluble vitamins
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1.1 Chromatography

Chromatography is a physical method of analysis in which a mobile phase passes over a stationary phase and the mixture of compounds can be separated into its components. Chromatography has been widely used in pharmaceuticals, biotechnology, natural products, plant analysis, bio-analysis, toxicology, etc.

Depending on the nature of stationary or mobile phases and the mechanism of distribution involved, chromatographic techniques can be classified as (1) high-performance liquid chromatography (HPLC), (2) gas chromatography (GC), (3) thin-layer chromatography (TLC), (4) gel permeation chromatography (GPC), (5) partition chromatography (PC), (6) countercurrent chromatography (CCC), (7) supercritical fluid chromatography (SCFC), (8) ion-exchange chromatography (IEC) etc.

TLC being a subdivision of liquid chromatography is carried out on a flat surface and hence, it is sometimes referred to as planar chromatographic separation technique. In TLC, the mobile phase (a liquid) migrates through the stationary phase (thin layer of porous sorbent on a flat inert surface) by capillary action.

High-performance thin-layer chromatography (HPTLC) is a sophisticated form of TLC with better and advanced separation efficiency and detection limits. The main difference between HPTLC and TLC is the particle and pore size of sorbents. HPTLC is a flexible, versatile, and economical process in which various stages are carried out independently. The important distinguishable properties of TLC and HPTLC are summarized in Table 4. Similarly, the distinguishable properties of HPTLC and HPLC are also summarized in Table 5.

Table 4 Distinguishable characteristics of TLC and HPTLC
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Table 5 Characteristic properties of HPTLC and HPLC
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2 Literature survey

In the year 2011, Ali et al. [1] published a book chapter on the role of TLC/HPTLC in biomedical applications. A year later, they reviewed the contemporary work on the application of TLC and HPTLC for the analysis and separation of vitamins and amines [2]. Since then, only a few review articles have been reported so far [3,4,5]. Literature survey also reveals that, compared to the use of TLC/HPTLC, more emphasis has been given to the application of HPLC in the analysis of vitamins as indicative by more than 70 papers reported during 2011‒2019 on the use of HPLC for the separation and determination of different types of vitamins. In the present communication, the works conducted during 2011‒2019 on the TLC/HPTLC of water-soluble and fat-soluble vitamins are presented in Table 6; it is clear that HPTLC has been more frequently used than normal-phase thin-layer chromatography (NP-TLC) and reversed-phase thin-layer chromatography (RP-TLC) for the separation of water-soluble and fat-soluble vitamins. Table 6 also reveals that more work has been reported on the separation and identification of vitamin C as compared to the other types of vitamins. Modified silica gel layers are also proved more efficient for the researchers in the separation and analysis of different types of vitamins as Sobanska reviewed admirably the applications of modified silica gel in TLC [6].

Table 6 Summary of the work done during 2011‒2019 on the use of TLC/HPTLC for the analysis of water- and fat-soluble vitamins
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Cimpoiu et al. [7] developed a TLC method in which two different stationary phases (silica gel and cellulose plates), coated side by side, act as gradient adsorbent and a mixture of methanol + benzene + formic acid (6:4:1, v/v) as the mobile phase used for the separation of water-soluble vitamins (B6,B3, B2, C, B1, B12, and B9). The experimental values of RF for different water-soluble vitamins were: B6 = 0.81, B3 = 0.69, B2 = 0.63, C = 0.41, B1 = 0.20, B12 = 0.12 and B9 = 0.05. The developed method is relatively simple and inexpensive enabling the combination of a large variety of stationary and mobile phases for the analysis of various mixtures. Moreover, the spots from a plate developed on the stationary phase can be transformed to the second plate, without the scraping of bands, extraction, and re-spotting. This TLC with stationary phase gradient method was found to be highly applicable for identifying the water-soluble vitamins in the alcoholic extracts of Hippophae rhamnoides and Ribes nigrum.

Dzema et al. [8] used silica gel modified with hyperbranched (hb) poly(ethyleneimine) (PEI) polymers as the stationary phase and distilled water as the mobile phase for the separation of water-soluble vitamins: thiamine hydrochloride (B1), sodium riboflavin-5-phosphate (B2), pyridoxine (B6), ascorbic acid (C), and cyanocobalamin (B12). The addition of polymers to the mobile phase did not result in changes in the efficiency and selectivity parameters of analytes because of the strong sorptive retention of the polymers on the silica surface (due to electrostatic and hydrogen bond interactions), which prevented the modifier from moving along the TLC plate. The influence of polymer structure (degree of substitution of PEI terminal amino groups with oligosaccharides and molecular weight of dendritic core [5 or 25 kDa]) as well as the content of PEI-OS (polyethylenimine oligosaccharides) in the stationary phase and a method of modification of the stationary phase on the efficiency of vitamin and amino acid determination and on the enantioselectivity factors of β-blockers separation were investigated. As for vitamin B6, an increase in retention and decrease in efficiency were observed for the case of using polymers, having less dense oligosaccharide shells as components of the stationary phase. The increase in the analytes affinity to the polymer-modified stationary phase points to the interaction between pyridoxine and the polymers.

3 Conclusion and future prospects

The literature survey reveals that both isocratic and mixed solvents are commonly used as mobile phases for the separation of different vitamins. None of the studies during 2011‒2019 showed the use of surfactants or ionic materials as impregnating agents or mobile phase modifiers. Both TLC and its refined version, HPTLC, are simple and inexpensive techniques for the analysis of biomolecules including vitamins, particularly in the poorly funded laboratories of developing countries. The advantages of HPTLC are semiautomation, greater resolution, and reduced consumption of mobile phase. Although TLC and HPTLC cannot reach the resolution and detection limit of HPLC, the former techniques provide sufficient resolving power for most of the sample types. There is a need of developing novel coating materials, modifiers, detecting reagents, and environment-friendly mobile phases for the efficient utilization of these simple and low-budget chromatographic techniques for the separation and determination of biomolecules including different types of vitamins. Figure 1 describes the relative magnitude (%) of published papers on different types of vitamins using HPTLC/TLC and Fig. 2 represents the relative magnitude (%) of the number of papers published on water-soluble vitamins (B-complex and vitamin C) during 2011‒2019.

Fig. 1
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Representation of the magnitude (%) publications of different types of vitamins during 2011‒2019

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Fig. 2
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Representation of the magnitude (%) of publications of water-soluble vitamins during 2011‒2019

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