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How to switch to SiliCycle TLC Plates?

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SiliCycle is manufacturing a wide selection of TLC plates in various sizes (plate size, thickness) and chemistries (C18, NH2, CN, 10% Silver Nitrate). SiliCycle SiliaSiliaPlate represent an efficient economical alternative to other manufacturers TLC plates while demonstrating high separation power due to the narrow particle size distribution used for manufacturing.

However, switching from one manufacturer’s TLC plates to another can cause small changes in the analytes of interest retention factor (Rf) due to difference in the supporting silica granulometry or activity. Few simple tricks are commonly used in order to quickly and easily reoptimize the elution so that the original TLC pattern can be obtained.

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Elutropic Strength

The retention factor (Rf) can be tuned by changing the polarity of the solvent system used for sample elution. In binary or tertiary mixtures, the ratio of individual solvent is modified so that the desired elutropic strength can be obtained. Alternatively, solvent system constituted of a single solvent can be modified so that a second solvent is added to the new solvent mixture so that the resulting system polarity will differ.

In the simple case of two TLC plates from two different manufacturers but with identical type of chemistry (plain silica, C18, etc.), a good methodology consists of first changing slightly the polarity of the elution solvent, using a solvent strength table as shown below:

Relative Solvent Strength (εo)
Solventεo
Fluoroalkanes-0.25
n-Pentane0.00
Isooctane0.01
Petroleum ether0.01
n-Decane0.04
Cyclohexane0.04
Cyclopentane0.05
1-Pentene0.08
Carbon disulfide0.15
Carbon tetrachoride0.18
Xylene0.26
i-Propyl ether0.28
i-Propyl chloride0.29
Toluene0.29
n-Propyl chloride0.30
Benzene0.32
Ethyl Bromide0.35
Ethyl Sulfide0.38
Chloroform0.40
Methyl chloride0.42
Ethylene dichloride0.44
Methylethyl ketone0.51
1-Nitropropane0.53
Triethylamine0.54
Acetone0.56
Dioxane0.56
Tetrahydrofuran0.57
Ethyl acetate0.58
Methyl acetate0.60
Diethylamine0.63
Nitromethane0.64
Acetonitrile0.65
Pyridine0.71
Dimethyl sulfoxide0.75
i-Propanol0.82
Ethanol0.88
Methanol0.95
Ethyleneglycol 1.1

The resulting solvent system polarity (εo system) is calculated using the following equation:

εo system = C1εo1 + C2εo2 + …+ Cnεon

where εo1, εo2, & εon are the elutropic strength of individual solvent
and C1, C2 & Cn are the ratio of each solvent constituting the solvent mixture

All these optimization steps can be performed with systems specially designed for multisolvents TLC elution or at smaller scale using smaller TLC plates (2.5x7.5cm).

Silica Particle Granulometry (Particle Size and Size Distribution)

The particle size, size distribution and geometry affect directly the pattern and quality of a chromatographic separation (TLC, HPLC). Thus, special attention might have to be addressed when using new or different TLC plates.

As described by Van Deemter, the size of chromatographic particles has an effect on the kinetic of interaction, thus on the separation efficiency. For example, in high-performance liquid-chromatography (HPLC) the use of smaller chromatographic particle enables a net increase in separation efficiency. However, a decrease in particle size also causes a decrease in the solvent elution rate in TLC such that longer eluting time are required. A narrow particle size distribution will result in a more homogeneous coating that enables more efficient separation. Since small differences exist between manufacturer’s particle size distributions, TLC eluted spots might also differ in diameter or shape. Thus, SiliCycle only employs its SiliaFlash irregular silica gels characterized by a narrower particle size distribution compared to the industry standard for the manufacturing of its TLC plates.

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> SiliCycle SiliaFlash Irregular Silica Gels for Chromatography