Thin-layer chromatography with eutectic mobile phases—preliminary results

Journal of Chromatography A 1621 (2020) 461044

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Short communication

Thin-layer chromatography with eutectic mobile phases—preliminary
results
Danuta Raj
Department of Pharmacognosy and Herbal Medicines, Wroclaw Medical University, Borowska 211a, 50-556, Wrocław, Poland

a r t i c l e

i n f o

Article history:
Received 10 October 2019
Revised 10 March 2020
Accepted 11 March 2020
Available online 14 March 2020
Keywords:
Chelidonium
Chromatography
Eutectic solvents
Isoquinoline alkaloids
NADES
TLC

a b s t r a c t
The presented paper is the first to show thin layer chromatography (TLC) analysis based on eutectic mobile phases (Deep Eutectic Solvents – DES). During the experiment 25 eutectic mixtures were investigated
for their chromatographic properties. Most of them belong to the natural deep eutectic solvents (NADES)
group. Also, new eutectic liquids based on phenolics and terpenes, not previously employed in analytical practice, were tested. The eutectic liquids were investigated as pure or diluted with solvents used
in chromatographic routine: methanol, water, acetone, chloroform or diethyl ether. The analyses were
carried out using classic and high performance silica gel plates. The working solution was a mixture of
five alkaloids found in genus Chelidonium, namely sanguinarine, coptisine, chelerythrine, chelidonine, and
berberine, with UV light detection of 366 nm. This report proves that eutectic TLC is possible and that the
eutectic interactions play a crucial role in the separation process. In most of the tested modifications at
least partial separation was achieved. The most successful mobile phase, which enabled separation of all
the tested alkaloids, was the equimolar mixture of menthol and phenol with a 35% addition of methanol.
The system was also effective in separating alkaloids in the real Chelidonium maius extract sample.
© 2020 The Author(s). Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license.
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1. Introduction
From the physicochemical point of view DES is a class of liquids composed of hydrogen bonds donors and acceptors, which
after mixing show strong melting point depression compared to
the pure components. The mixture is characterized by minor vapor pressure, overall high solvation capacity and – in many cases
– low toxicity and eco-friendliness [3]. In particular, the solubilization properties exhibited by DES drew the attention of phytochemists, as these solvents are able to efficiently extract a wide
range of compounds, including alkaloids, ginkgolides, ginsenosides,
flavonoids, xanthones, catechins and essential oils [4–6]. This led
to the question of the possibility of employing eutectic solvents
in chromatographic techniques. Successful assays were performed
in countercurrent separation [7,8]. One publication indicates that
NADES do not disrupt LC systems [9], however it does not consider
the attempt of eutectic separation. Several reports can be found regarding a DES used as a mobile phase modifier in HPLC analyses
[10–13]. In these cases eutectic mixtures were added to a mobile
phase in a maximum 4% concentration, far below the 50% concentration limit pointed to in the literature data as the moment of disE-mail address:

ruption of intramolecular bondings which create an eutectic matrix
[6]. To the Author’s best knowledge, at this time there is no report
about the chromatographic system involving stationary phase and
pure eutectic solvents.
In this work, I present the results of a preliminary investigation
of DES being employed as mobile phases in thin layer chromatography (TLC). The work intends to present that eutectic liquids allow chromatographic separation of mixtures of natural compounds,
with particular regard to alkaloids. For this purpose several eutectic solvents have been selected, which are recognized as eutectic
mixtures and classified as NADES. They were employed to separate a mixture of selected natural compounds, either as pure or
after dilution with methanol, water, acetone, chloroform or diethyl
ether.
2. Materials and methods
2.1. Preparation of mobile phases
The eutectic mobile phases were prepared according to one of
three procedures [2,6] (Table 1). Procedure 1 (P1) consisted of simply mixing the components with subsequent spontaneous liquefying, resulting in a homogenous and stable liquid. Procedure 2

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2

D. Raj / Journal of Chromatography A 1621 (2020) 461044
Table 1
The list of pure DES prepared within the experiment.
Components

Molar ratio

No

Obtaining procedure

Camphor + phenyl salicylate
camphor + chloral hydrate
phenol + chloral hydrate
phenol + menthol
phenol + thymol
choline chloride + lactic acid
choline chloride + malonic acid
choline chloride + raffinose
choline chloride + rhamnose
choline chloride + xylitol
choline chloride + malic acid + proline
citric acid + fructose
citric acid + xylitol
citric acid + raffinose
citric acid + L-α -alanine
citric acid + proline
citric acid + sorbitol
citric acid + glucose
malic acid + L-α -alanine
malic acid + xylitol
malic acid + sorbitol
malic acid + glucose
malic acid + fructose
malic acid + sucrose
proline + glucose

1:1
1:1
1:1

1:1
1:1
1:1
1:1
11:2
2:1
5:2
1:1:1
1:1
1:1
3:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1

D1
D2
D3
D4
D5
D6
D7

D8
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
D19
D20
D21
D22
D23
D24
D25

P1
P1
P1
P1
P1
P1
P1
P2
P2
P3
P3

P3
P3
P3
P3
P3
P3
P3
P3
P3
P3
P3
P3
P3
P3

(P2) consisted of mixing the components and subsequent heating
to 50 °C until a homogenous and stable liquid was formed. Procedure 3 (P3) consisted of mixing the components with the addition
of water, using the smallest amount of water necessary for dissolution of the components, and subsequent evaporation of water
using a rotary evaporator (R-210, Büchi, Germany) at 60 °C to the
stable mass.
The eutectic liquids were used as pure or diluted with the addition of 10, 20, 30 or 40% water, methanol, chloroform, diethyl
ether, or acetone (W, M, C, E or A, respectively), which was marked
in their names as a suffix containing an abbreviation of the solvent
and degree of dilution (e.g., D1 -W10 means that D1 DES contains
10% water). The dilutions were made using wt/wt ratio (Table 2).
Additional information on the methodology for obtaining the
working solution, a real Chelidonium extract sample and chromatographic parameters is included in Supplementary material.
3. Results and discussion
DES are characterized by a relatively high viscosity, which is
probably the reason why researchers have not yet attempted stationary phase-based chromatographic separations using DES. However, the literature data regarding DES point at two favorable

pieces of information: specific eutectic mixtures differ significantly
in viscosity, in a range of 20–10 0 0 times more than water [15] and
they can be diluted up to 50% without breaking the intramolecular interactions, which would allow further a further decrease in
viscosity and presumably could facilitate chromatography on a stationary phase. Moreover, dilution with water was mentioned as a
way of fine-tuning the polarity of DES [6], which would ease the
optimization of a mobile phase’s elution strength.
As the working solution, a mixture of alkaloids from genus Chelidonium were selected (sanguinarine, coptisine, chelerythrine, chelidonine, berberine – Fig. S1), given that the plant alkaloids possess
numerous pharmacological effects, including spasmolytic, antiinflammatory, antimicrobial, antiviral, cholagogue, and antiproliferative, and it is widely used in traditional phytotherapy [14]. Moreover, the selected alkaloids are visible in 366 nm UV light [14],
which enables detection without derivatization. The working mixture is also significantly complex, as the mentioned alkaloids were

only recently separated on silica gel plates with a single mobile
phase [16].
The mobile phases tested within the experiment have lowvolatility [6]. After development they did not evaporate from the
chromatographic plates, and during the preliminary stage of experiment the resulting impregnation of silica gel with mobile phase,
in many cases, blocked wetting it with spraying reagents. In some
cases, reactions between mobile phase components and a spraying reagent did not allow to form visualized bands (data not presented). Thus, UV 366 mn detection was applied.
3.1. Preparation of mobile phases
In order to select DES for the purpose of the experiment, literature data was reviewed for the information on eutectic mixtures
possible to be employed in the chromatographic process. During
the search the assumption was made that eutectic mixtures to be
included, must be liquid and stable in ambient temperature, should
contain nature-derived compounds or simple chemicals and shall
be simple in preparation. Part of the examples of creating eutectic
mixtures were defined as pharmaceutical incompatibilities (D1 –D5
[17]) and these were not previously employed in analytical practice, e.g. extraction. Other eutectic mixtures were found in the literature describing NADES (D6 –D25 [2,6,9,15]). For the NADES-based
eutectics, the main including criterion was relatively low viscosity
according to the data presented in the source papers. Furthermore,
DES with water being the essential component (e.g., choline chloride:fructose:water 5:2:5; [9]) were excluded, as the initial water
amount would interfere with the projected dilution steps. The classic eutectic mixture containing choline chloride:urea 1:2 [18] was
also excluded based on the preliminary experiments, as it proved

to solidify during the chromatographic process.
DES used within the experiment were created using the molar
ratio suggested in the literature data. In the absence of such information a default ratio 1:1 was applied based on the available
information [1,6]. The preparation procedures for the specific eutectic liquids were taken from the literature data [2,6,17]. Where
possible, spontaneous liquefaction was employed (P1) or liquefaction supported by heating (P2). In the remaining cases water addition and subsequent evaporation was necessary (P3) [2,6].


Table 2
DESs dilutions and their chromatographic properties.
Modification
Methanol
D1
D2
D3
D4
D5
D6
D7

D9
D10
D11
D12
DES

D13
D14
D15
D16
D17

D18
D19
D20
D21
D22
D23
D24
D25

D1 -M10
–
D2 -M10
2
D3 -M10
2
D4 -M10
3
D5 -M10
2
D6 -M10
0
D7 -M10
0
D8 -M10
0
D9 -M10
0
D10 -M10
0
D11 -M10

0
D12 -M10
n.s.
D13 -M10
n.s.
D14 -M10
n.s.
D15 -M10
n.s.
D16 -M10
n.s.
D17 -M10
n.s.
D18 -M10
n.s.
D19 -M10
n.s.
D20 -M10
n.s.
D21 -M10
n.s.
D22 -M10
n.s.
D23 -M10
n.s.
D24 -M10
n.s.
D25 -M10
n.s.

D1 -M20
–
D2 -M20
2
D3 -M20
2
D4 - M20
5
D5 -M20
3
D6 -M20
0
D7 -M20
0
D8 -M20
0
D9 -M20
0
D10 -M20
0
D11 -M20
0
D12 -M20
n.s.
D13 -M20
n.s.
D14 -M20
n.s.
D15 -M20
n.s.

D16 -M20
n.s.
D17 -M20
n.s.
D18 -M20
n.s.
D19 -M20
n.s.
D20 -M20
n.s.
D21 -M20
n.s.
D22 -M20
n.s.
D23 -M20
n.s.
D24 -M20
n.s.
D25 -M20
n.s.

D1 -M30
–
D2 -M30
2
D3 -M30
2
D4 -M30
5
D5 -M30

4
D6 -M30
0
D7 -M30
0
D8 -M30
0
D9 -M30
0
D10 -M30
0
D11 -M30
0
D12 -M30
n.s.
D13 -M30
n.s.
D14 -M30
n.s.
D15 -M30
n.s.
D16 -M30
n.s.
D17 -M30
n.s.
D18 -M30
n.s.
D19 -M30
n.s.
D20 -M30

n.s.
D21 -M30
n.s.
D22 -M30
n.s.
D23 -M30
n.s.
D24 -M30
n.s.
D25 -M30
n.s.

Water
D1 -M40
–
D2 -M40
2
D3 -M40
3
D4 -M40
5
D5 -M40
5
D6 -M40
0
D7 -M40
0
D8 -M40
0
D9 -M40

0
D10 -M40
0
D11 -M40
0
D12 -M40
n.s.
D13 -M40
n.s.
D14 -M40
n.s.
D15 -M40
n.s.
D16 -M40
n.s.
D17 -M40
n.s.
D18 -M40
n.s.
D19 -M40
n.s.
D20 -M40
n.s.
D21 -M40
n.s.
D22 -M40
n.s.
D23 -M40
n.s.
D24 -M40

n.s.
D25 -M40
n.s.

D1 -W10
–
D2 -W10
–
D3 -W10
–
D4 -W10
–
D5 -W10
–
D6 -W10
0
D7 -W10
0
D8 -W10
0
D9 -W10
0
D10 -W10
0
D11 -W10
0
D12 -W10
n.s.
D13 -W10
n.s.

D14 -W10
n.s.
D15 -W10
n.s.
D16 -W10
n.s.
D17 -W10
n.s.
D18 -W10
n.s.
D19 -W10
n.s.
D20 -W10
n.s.
D21 -W10
n.s.
D22 -W10
n.s.
D23 -W10
n.s.
D24 -W10
n.s.
D25 -W10
n.s.

D1 -W20
–
D2 -W20
–
D3 -W20

–
D4 -W20
–
D5 -W20
–
D6 -W20
0
D7 -W20
0
D8 -W20
0
D9 -W20
0
D10 -W20
0
D11 -W20
0
D12 -W20
3
D13 -W20
2
D14 -W20
1
D15 -W20
n.s
D16 -W20
0
D17 -W20
n.s
D18 -W20

n.s
D19 -W20
n.s
D20 -W20
n.s
D21 -W20
0
D22 -W20
n.s
D23 -W20
n.s
D24 -W20
3
D25 -W20
0

D1 -W30
–
D2 -W30
–
D3 -W30
–
D4 -W30
–
D5 -W30
–
D6 -W30
0
D7 -W30
0

D8 -W30
0
D9 -W30
0
D10 -W30
0
D11 -W30
0
D12 -W30
3
D13 -W30
2
D14 -W30
1
D15 -W30
2
D16 -W30
0
D17 -W30
3
D18 -W30
4
D19 -W30
2
D20 -W30
2
D21 -W30
0
D22 -W30
3

D23 -W30
4
D24 -W30
3
D25 -W30
0

Acetone
D1 -W40
–
D2 -W40
–
D3 -W40
–
D4 -W40
–
D5 -W40
–
D6 -W40
0
D7 -W40
0
D8 -W40
0
D9 -W40
0
D10 -W40
0
D11 -W40
0

D12 -W40
3
D13 -W40
2
D14 -W40
1
D15 -W40
2
D16 -W40
0
D17 -W40
3
D18 -W40
4
D19 -W40
2
D20 -W40
2
D21 -W40
0
D22 -W40
3
D23 -W40
4
D24 -W40
3
D25 -W40
0

D1 -A10

3
D2 -A10
1
D3 -A10
1
D4 -A10
3
D5 -A10
1

D1 -A20
3
D2 -A20
1
D3 -A20
1
D4 -A20
3
D5 -A20
2

D1 -A30
4
D2 -A30
1
D3 -A30
2
D4 -A30
4
D5 -A30

3

Chloroform
D1 -A40
4
D2 -A40
1
D3 -A40
2
D4 -A40
5
D5 -A40
4

D1 –C10
2
D2 –C10
1
D3 –C10
1
D4 –C10
2
D5 –C10
2

D1 –C20
2
D2 –C20
1
D3 –C20

1
D4 –C20
2
D5 –C20
2

D1 –C30
2
D2 –C30
1
D3 –C30
1
D4 –C30
2
D5 –C30
2

Diethyl ether
D1 –C40
2
D2 –C40
1
D3 –C40
1
D4 –C40
2
D5 –C40
2

D1 -E10

2
D2 -E10
1
D3 -E10
1
D4 -E10
2
D5 -E10
2

D1 -E20
2
D2 -E20
1
D3 -E20
1
D4 -E20
2
D5 -E20
2

D1 -E30
2
D2 -E30
1
D3 -E30
1
D4 -E30
2
D5 -E30

2

D1 -E40
2
D2 -E40
1
D3 -E40
1
D4 -E40
2
D5 -E40
2

D. Raj / Journal of Chromatography A 1621 (2020) 461044

D8

Pure
2
Pure
1
Pure
1
Pure
2
Pure
2
Pure
0
Pure

0
Pure
0
Pure
0
Pure
0
Pure
0
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.
Pure

n.s.
Pure
n.s.
Pure
n.s.
Pure
n.s.

Numbers refer to the number of bands possible to distinguish in the chromatogram: 0 – no separation; 5 – all the compounds were detectable; n.s. – the mobile phase not suitable for chromatographic purposes (timeout); - –
the mobile phase components were not miscible. For the sake of readability of the Table, the non-miscible D6 –D25 dilutions with acetone, chloroform, and diethyl ether were excluded.
3


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D. Raj / Journal of Chromatography A 1621 (2020) 461044

The experiments were projected to investigate the chromatographic properties of both pure DES and their dilutions. It was decided that 10%, 20%, 30% and 40% diluting solvent would be added
to the initial DES. The 50% dilution is indicated as a boundary for
the eutectic properties [2,6], and thus it was excluded. Apart from
water, which was the main dilution agent in the literature data
[6], methanol, chloroform, acetone and diethyl ether, the solvents
widely used in TLC routine, were included.
D1 –D5 did not mix with water in any proportion. Methanol was
expected to be a proper solvent as the solubility of all the chemicals included in D1 –D5 in the alcohol is at least good. Surprisingly,
D1 did not mix with methanol up to a concentration of 60%, while
further addition of methanol allowed the components to dissolve.
Apart from water (and regarding the case mentioned above) the
D1 –D5 were miscible with the tested solvents. In turn, the choline
chloride-based DES (D6 –D11 ) were fully miscible only with water

and methanol and to some extent with acetone (from 10 to 20%,
depending on the particular DES). Since the acetone dilutions were
not possible to obtain within the whole investigated range, they
were excluded from the experiment. The D12 –D25 were miscible
only with water and methanol, in every investigated ratio.
3.2. Chromatography with pure DES
TLC analyses performed with pure eutectic solvents were able
to carry out the separation of the investigated mixture depending
on the properties of the individual tested DES (Table 2). For the
pure DES the whole chromatographic process is relatively long and
lasts from 3 to more than 12 h. In the case of development lasting
longer than 12 h, it was assumed that the specific mobile phase
(either pure or diluted DES) is unsuitable for the TLC purposes. D1
- D5 had a development time between 180 and 240 min. They enabled forming bands, and the initial separation could be seen, with
up to two recognizable bands (Table 2, Fig. 1A - B). D1 , D4 and D5
as pure enabled low retention which indicates low polarity, while
D2 and D3 DES were moving the investigated compounds close to
the solvent front. D6 –D11 had development time of 120–210 min.
They were characterized by too high polarity for the tested standards, which resulted in moving the investigated compounds to
the solvent front (Fig. 1I). The pure D12 –D25 were unsuitable for
chromatographic purposes due to excessive time of development.
3.3. Chromatography with diluted DES
The addition of diluting solvents to DES influenced to varying
degrees the resolution and time of development. In order to ensure
comparability of the results, the chromatograms of the pure solvents were also presented (Fig. 1N-R). For the D1 –D5 dilutions had
an impact on the chromatogram development time, but interestingly, not all the diluting solvents decreased it. The 40% methanol
and acetone dilutions were the quickest, allowing 70–90 min development, while the diethyl ether proportionally slowed it down,
reaching 410 min for the 40% dilution. The addition of polar compounds, like acetone or methanol, significantly improved the resolution, whereas non-polar ones (chloroform, diethyl ether) did
not. Nevertheless, chloroform managed to shorten the development time, which may be an advantageous observation for future
eutectic-TLC use. For acetone and methanol, the ability to fine-tune

the elution strength was proved and resulted in good resolution of
the alkaloids. The most efficient were DES containing a terpenoid
and compound with phenolic ring (D1 , D4 , D5 ). The differences
could be better observed after dilution due to increased Rf in such
cases. The most efficient were D1 -A40, D4 -M30, D4 -M40, D4 -A40,
D5 -M40 and D5 -A40 (Fig. 1C–H). Comparison of 40% dilution with
acetone of D1 , D4 and D5 indicates their rank according to polarity
as follows: D1 < D5 < D4 . D4 and D5 differ only in the saturation

of the ring of the terpenoid compound (in menthol the ring is saturated while in thymol it is aromatic), and the unsaturation is associated with lower polarity. Moreover, the lowest polarity is noted
for D1 which contains phenyl salicylate that includes two aromatic
rings. The observation is contrary to the standard eluotropic series,
where a saturated ring indicates a much lower elution strength
than an aromatic one (e.g., cyclohexane vs. benzene). This is noteworthy, considering methanol dilutions, neither the pure DES nor
pure solvent were able to move efficiently the investigated compounds (Fig. 1A, N). It was only the mixture of both that managed
to move the alkaloids towards the solvent front (Fig. 1E). Thus, it
may be concluded that the diluted DES was more polar than either the pure eutectic or solvent individually. The nature of the
phenomenon has yet to be investigated.
The D6 –D11 were diluted with water or methanol, which in every case accelerated the chromatographic process. Regarding polarity of the solvents, the standards could not be withdrawn from
the solvent front. For D12 –D24 water dilution decreased the development time in a concentration-dependent manner (Table 2) – 40%
dilutions were developed between 240 and 360 min. The same DES
mixed with methanol, however, were much slower (800 min. and
more) and were disqualified as mobile phases. The degree of separation was differential. The best chromatographic properties, regarding both time and separation, were observed for D18 -W40 and
D23 -W40 modifications (Fig. 1K – L). Water had a negligible impact
on resolution.
Given that D4 -M30 and D4 -M40 gave promising results, it was
decided to lower the threshold of dilution, testing also D4 -M27.5,
D4 -M32.5, D4 -M35 and D4 -M37.5. The best results were achieved
with D4 -M35, which interestingly had a different pattern of the
standards compared to D4 -M30 and D4 -M40. Using the HPTLC

plate for the selected mobile phase further improved the results. D4 -M35 was subsequently tested with the real sample obtained from the Chelidonium maius herb and proved to be efficient
(Fig. 1T; Table S1-S2) and is considered to be applicable.
The influence of methanol and diethyl ether on a development
time was ambiguous. In silica gel-based TLC, due to the low viscosity, they generally enabled short-lasting analyzes. Thus, the mentioned solvents were supposed to decrease the development time.
Actually, their effect was incongruous. Diethyl ether slowed down
the process in every investigated case, but methanol either improved (D2 –D11 ) or worsened (D12 –D25 ) the parameter. The observed phenomenon could be linked with the viscosity changes of
the mobile phase, but the parameter was not tested during the investigation and the explanation needs additional experiments.
Water addition had little impact on the elution strength of the
tested DES. This is contrary to what was expected regarding the
information presented in the literature data [6], where water was
being used for modifications of DES polarity. The phenomenon may
result from additional interactions between water and stationary
phase’s functional groups that do not occur during extraction from
plant material.
It was a matter of interest whether other solvents apart from
water would dilute DES without disrupting the eutectic matrix.
At the initial stage of the experiment, it was taken under consideration that after dilution the separation may depend only on
chromatographic properties of the solvents, leaving DES as an inert part of the mobile phase. That would give the same separation pattern for all same-solvent dilutions (e.g., 40% acetone dilutions would be similar regardless of DES used). However, chromatograms obtained with different eutectics and the same solvent
were not alike but had similar features to the specific pure DES
(Fig. 1E, G). This means that the eutectic matrix was preserved after dilution with the tested solvents in the investigated range and
that the matrix had a substantial impact on the chromatographic
process. Additional support for that conclusion is an observation


D. Raj / Journal of Chromatography A 1621 (2020) 461044

5

Fig. 1. Chromatograms obtained with the selected mobile phases, using TLC Si60 plates, unless otherwise noted. All the pictures were taken at 366 nm. Mobile phases,
left to right: A–D4 ; B–D5 ; C–D1 -A40; D–D4 -M30; E–D4 -M40; F–D4 -A40; G–D5 -M40; H–D5 -A40; I–D7 ; J–D7 -W40; K–D18 -W40; L–D23 -W40; M–D4 -M35 on HPTLC plate. The

working solution developed in pure solvents: N – methanol; O – water; P – acetone; Q – chloroform; R – diethyl ether; S – the working solution developed in D4 -M60; T
– Chelidonium maius root extract developed with D4 -M35 mobile phase on HPTLC plate. Alkaloids marked in the chromatograms: Be – berberine, Ce – chelerythrine, Ci –
chelidonine, Co – coptisine, Sa – sanguinarine.

made at the preliminary stage of the experiment: a chromatogram
made using 60% dilution (Fig. 1S) was significantly different from
the one obtained within the eutectic range while similar to the
pure methanol one (Fig. 1N).
The issue observed during the experiment is problematic downregulation of specific DES elution strength. While DES polarity can
be easily up-regulated with the addition of polar solvents, the nonpolar ones do not change the elution. Lowering DES content along
with replacing it with less polar compounds in case of eutectic
mobile phases is not effective. Thus, the solution to the presented
problem may be using different DES with lower polarity as a starting point.

matographic mobile phases based on non-classical interactions to
be widely employed.
Author contribution
I am the only Author of the manuscript, therefore I am responsible for the: Conceptualization, Methodology, Validation, Investigation, Resources, Writing - Original Draft, Writing - Review &
Editing, Visualization, Supervision, Project administration
Declaration of Competing Interests
None.

4. Conclusions
CRediT authorship contribution statement
Eutectic TLC is possible and can result in good separation, even
for the complicated matrices that proved to be problematic for a
classic TLC. It is most probable that, in a short time, new DES types
with low viscosity will emerge, allowing for a new class of chro-

Danuta Raj: Conceptualization, Investigation, Methodology, Validation, Visualization, Writing - original draft, Writing - review &

editing.


6

D. Raj / Journal of Chromatography A 1621 (2020) 461044

Acknowledgments
´
I would like to thank Dr. Sylwia Zielinska
for advising and supplying with standards, and Natalia Maryniak for her technical support.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.chroma.2020.461044.
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