Experimental evidence suggests that the magnetic field (MF) has a wide range of effects on various phenomena. For example, MF can alter the activity of drugs [1] and also affect growth rate and photosynthesis [2]. The use of an MF in the process of magnetic refrigeration in cooling power is one of its exciting applications in industry, obtained by entropy changes due to exposing magnetic materials in MF [3]. Therefore, studying the behavior of materials in MF can be a valuable source of information [4].

The use of an MF to study the aromaticity of compounds is a well-known approach. Applying an MF perpendicular to the molecular ring generates a current of moving electrons and affects the electron motion [5]. An electron current density is induced, and a proportional magnetic dipole moment is formed by applying an external and uniform MF (B) to the molecule [6]. The electron density values of a molecule help to understand its chemical properties [7]. Studies show that the MF influences the electron cloud density deviation and, thus, affects chemical bonds. Applying a strong MF to H2 molecules changes the spatial symmetry, ground state spin, and binding energy, and the extent of these changes depends on the intensity and orientation of the MF [[8], [9], [10]]. Therefore, MF is a powerful tool for restructuring molecular systems, allowing the creation of new properties within them. The cause of these changes is the influence of the MF on spin polarization and polarization [[11], [12], [13]].

Applying an MF to a ferromagnetic system causes an interaction between the magnetic dipole moment (μm) and applied MF (B) and adds an additional energy term in Hamiltonian, expressed as:Δε=−μm•B

This term, known as the Zeeman effect, causes the energy levels to shift according to their spin dipole moments (μm). When a very strong MF is applied to the molecular system, it induces a noticeable modulation of the conductance with the change in the phase of the electron due to the Aharonov-Bohm effect. In addition, studies have shown that MF can change the spin polarization and orbital symmetry of the ferromagnetic system [11].

Another intriguing aspect of the MF is its effect on radical pair reactions. The MF controls the interconversion of the singlet-triplet states by influencing the electrons' spin involved in radical formation reactions. An illustration of this is the effect of the MF on the transformation of ortho and para hydrogen. In ortho hydrogen, the total nuclear spin is one (triplet) because the spins of the opposing protons are parallel. In parahydrogen, the nuclear spins are antiparallel, giving a total spin of zero (singlet). The conversion rate of ortho and parahydrogen is very low and therefore they are two separate molecules. The MF can induce spin reorientation, leading to the conversion of ortho and para hydrogen into each other [14]. Consequently, the use of an MF can alter the quantum efficiency of fluorescence [15].

The MF can affect electrochemical reactions in three ways: by altering mass transfer, the deposit morphology, and electrode kinetic [16]. The placement of magnetic microparticles on the electrode surface and the change in the electron exchange reaction rate is an example of the MF effect on the kinetics of electron transfer. In this case, which is another example of a radical-radical reaction, the spins of the reactants become polarized and produce two effects: 1) when the MF is applied, the spins have only one possible state, so the system entropy decreases. Given the tendency of systems to increase entropy, the reactivity of radical-radical reactions can be increased by applying an MF. 2) with the spin polarization of the reactants in the MF, their energy increases compared to the absence of the MF. Therefore, the net enthalpy of the activation barrier decreases, and the reaction rate increases [17]. By affecting the spin polarity of the reactants in MF, it can be said that the MF causes a change in the enthalpy and entropy of the system and changes the rate of the electrochemical reactions.

MFs can also affect chemical reactions. The most crucial change in chemical reactions is the change in the energy of the electrons. Electrons have intrinsic momentum, and their conservation laws can specifically affect the direction of chemical reactions. When an MF is applied to a chemical reaction, the angular momentum of the electrons may not be conserved [18]. Therefore, applying an MF to chemical reactions can advance the reactions toward the formation of desired products [19]. Given the above examples, how does the MF find its way into chromatographic systems?

Numerous studies have reported the use of MF for material separation in purification, pharmaceuticals, biochemical activities, and analytical chemistry [[20], [21], [22]]. Based on the fascinating effects of MF on chromatographic systems, a new field known as Magnetic Chromatography (MC) has emerged. This chromatography effectively separates particles with different magnetic susceptibilities [21,23,24]. As well known, chromatographic techniques are based on different interactions of components with the stationary and mobile phases, which can be altered by MF [25]. The application of MF results in changes in chromatographic parameters, including peak shape, peak width (W), retention factor (Rf), and separation efficiency [1,26] depending on the intensity and direction of MF, as well as the structures of the stationary phase, mobile phase, solutes, and their interactions [1,25]. Thus, MF can be an additional element in chromatographic systems either beneficial or detrimental [4].

Thin layer chromatography (TLC) is a specific technique for the investigation of the effect of MF on materials. TLC is advantageous due to its simplicity, inexpensiveness, and ease of sample preparation compared to column chromatography. There are limited reports in the literature to study the effect of MF on conventional TLC, mainly by Malinowska et al. for the analysis of plant extracts [4], carboxylates [27], 1,2,4-triazole [28], derivatives of 2-(2,4-dihydroxyphenyl)-1,3,4-thiadiazoles [29], polyaromatic hydrocarbons [1,26,30] and, ternary and quaternary alkaloids [31].

Using TLC to investigate the effect of MFs on drugs, such as ketoconazole (KZ) and clotrimazole (CZ), is a fascinating approach. KZ and CZ are antifungal drugs, that are used to treat oral, esophageal, and vaginal candidiasis and exhibit a wide range of antimicrobial activity effects [32]. Various chromatography techniques, such as high-performance liquid chromatography (HPLC) [33], TLC-densitometry [34], and gas-liquid chromatography (GLC) [35], are used to separate these drugs. The effect of MFs on drug separation has not been examined in any of the research.

In this study, centrifugal acceleration thin-layer chromatography (CTLC) was used to investigate the effect of MF on drug separation. A chromatotron device performs CTLC, and separation is a result of the centrifugal and capillary forces. The mobile phase is introduced into the center of a rotating stationary phase by a pump at a constant flow rate and the components are separated as the concentric circular bands. CTLC provides higher resolution in less time than conventional TLC by the control of two critical factors including the flow rate of the mobile phase and the rotational speed of the support disc [36,37].

For the first time, the effects of internal and external MFs on the separation of clotrimazole (CZ) and ketoconazole (KZ), as the model drugs, using CTLC were investigated in this work. For this purpose, a low-cost chromatotron was initially designed at the laboratory scale. In the second step, several proportions of ferromagnetic-SiO2 nanoparticles (NPs) were mixed with the silica gel slurry to create an internal MF. Next, the neodymium magnets were placed under the CTLC plate at a specific direction and angle to generate an external MF in the system. The changes inRf, W, selectivity factor (α), resolution (Rs), ΔRf (RfCZ−RfKZ), and ring shape were examined under various MF states.