Solid-phase extraction (SPE) is an effective analytical tool commonly used for the fractionation, preconcentration and purification of a component of interest from complex biological and environmental samples. 1 Unfortunately, the classical procedure of the SPE protocol optimization for the isolation of a number of analytes from multicomponent samples, particularly using the breakthrough curves method, can be expensive. This is because a quantitative amount of pure standards must be used. Moreover, such a procedure is usually time consuming, due to a number of fractions across a wide range of binary mobile phases for each analytical standard that should be collected and quantified. Therefore, an alternative method for the rapid computation of appropriate binary mixture concentrations and volumes for the purification and elution steps of a solid-phase extraction protocol based on e.g. the solvation parameter model have been proposed and tested. 2,3 On the other hand, the SPE cartridge can be considered as a short chromatographic column, and the retention of analytes in a such system should be simply predicted using retention data from HPLC experiment, in which a similar type of stationary phase and a wide range of solvent composition were studied. Recently, it has been suggested that planar chromatography may be used as a convenient pilot technique for estimating the SPE and HPLC behaviors of pesticide groups, separated under RP conditions. 4,5 The main advantage of such an approach is that on the plate a number of samples can be analyzed simultaneously, and therefore appropriate retention data can be collected within a relatively short period of time compared to the SPE or HPLC techniques.One of the advantages of modern HPTLC plates over classical TLC systems is that the eluent developing distance can be reduced to less than 50 mm, even for separations involving a non-forced developing mode. This idea is based on an observation that the minimum values of the plate height (H) can be achieved if the solvent migration distance along the HPTLC plate ranges from 30 to 40 mm. 6 Therefore, it can be expected that within and close to this migration distance range more dense spots can be obtained. In practice, under such conditions efficient separation for many types of compounds was observed, whereas the total analysis time was dramatically reduced compared to chromatographic separation performed on 10 or 20 cm long TLC plates. [7][8][9][10][11][12] Previously, it had been demonstrated that micro thin-layer chromatography performed on the wettable with water RP18 plates and organic/water mobile phases, can be a useful technique for estimating the SPE behavior of estetrol, which was eluted from octadecylsilica packed cartridges. 11 The main goals of present paper are to show the high separation throughput and capability of micro-planar chromatography as a fast and robust retention data source, as well as to demonstrate that this technique can be useful for an accurate prediction of the SPE behavior over a wide range of k...
Temperature-controlled micro thin-layer chromatography (TLC) was applied for separation and quantification studies of testosterone and its derivatives including methyltestosterone, testosterone propionate, isobutyrate, phenylpropionate, isocaproate, enanthate and caprate. Chromatographic studies were performed on silica-, octadecylsilica- and aluminum-coated plates working inside a small thermostated horizontal chamber unit allowing one-dimensional and two-dimensional developing modes with an elution distance of 45 mm. Retention properties of steroids were investigated across a whole range of binary mixtures such as methanol/water, acetonitrile/water, methanol/dichloromethane and acetone/hexane (0-100% v/v). Moreover, the effect of temperature ranging from -20 to +60 degrees C under saturated and unsaturated chamber conditions was also investigated. Our results revealed that depending on the mobile phase polarity the separation system based on the low carbon load wettable with water RP18W plates may work as a normal-phase (NP) or reversed-phase (RP) chromatographic system. It has been also demonstrated that micro TLC equipment can be applied as a fast retention screening device as well as simple and robust quantitative tool for determination of testosterone residue containing testosterone derivatives in complex samples.
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