Lipophilicity of Some Preservatives Estimated by RP-TLC Using Stationary Phases with Different Polarity

Reversible polarity-switch of thin-layer chromatography by photo-induction with multi-regulation in spatial dimension

Generally, thin-layer chromatography always undertakes the indispensable role in rapid screening and identification of specific compounds. Stationary phase is the core part of thin-layer chromatography with fixed property, which leading to the limitations of separation mode of only regulating the composition of mobile phase. This work was an attempt to fabricate the unique photosensitive thin-layer chromatography to make up the above major drawback. 4-[3-(Triethoxysilyl)propoxy]azobenzene (azo-PTES) was synthesized as photosensitive modifier to fabricate the photosensitive stationary phase, and the transformation of cis-trans structure of azo-PTES proceeds along with polarity difference under 365 nm and 473 nm irradiation. Based on this, the proposed photosensitive thin-layer chromatography shows the reversible switch of polarity of stationary phase by photoinduction, followed by the deserved reversible separation behavior. Furthermore, multi-regulation in spatial dimension was achieved based on the high freedom of spatial regulation of photoinduction, which brings about the integration of stationary phase with different polarity, just by photoinduction. The concept of photosensitive thin-layer chromatography provides new idea for improving separation efficiency and developing multi-dimensional thin-layer chromatography on the one plate.

Direct bioautography hyphenated to direct analysis in real time mass spectrometry: Chromatographic separation, bioassay and mass spectra, all in the same sample run

Mass spectra were recorded directly in situ the bioautogram, i.e., in the presence of microorganisms, bioassay medium and substrate reagent. The desorption-based direct analysis in real time mass spectrometry (DART-MS) was applied immediately after direct bioautography (DB). It turned out to be an advantageous combination, as it offered the possibility of a straightforward mass spectrometric detection of bioactive analytes within the bioautogram, and at the same time, it was discriminating microorganism cells and highly polar bioassay medium ingredients which could otherwise stress the MS system. DB-DART-MS was investigated for bioactive compounds in cosmetics using the Bacillus subtilis and Aliivibrio fischeri bioassays for detection of Gram-positive and Gram-negative antimicrobials, respectively, and the planar yeast estrogen screen for detection of estrogen-effective compounds. The influences of the three different bioassay matrices on the analyte response and DB-DART-MS performance on different layers were studied on the example of parabens in hand creams. It was shown that with increasing culture medium complexity, the ion suppression increased. As proof-of-principle, the mass spectrometric quantification at the nanogram level in situ the bioautogram was verified by comparison to HPTLC-DART-MS. The total paraben contents of hand creams 1 and 2 were 0.17-0.20% and 0.30-0.34%, respectively, depending on the method used (DB-DART-MS with two different bioassays or HPTLC-DART-MS as well as on RP_W or NP plate). In contrast to the current practice of applying the sample twice and subjecting one track to the bioassay and another to MS, the introduced hyphenation DB-DART-MS is straightforward and highly efficient.

Evaluation of the lipophilicity of selected sunscreens--a chemometric analysis of thin-layer chromatographic retention data

The lipophilicities of 22 selected sunscreens, preservatives, and vitamins used in topical skin products were measured by thin-layer chromatography. Lipophilicity was calculated in silico from the sunscreen molecular structures and compared to the experimental octanol/water partition coefficients found in the literature. The retention of the compounds was investigated on an RP-18 stationary phase with mobile phases consisting of water and one of six organic modifiers (dioxane, tetrahydrofuran, acetone, acetonitrile, methanol, and dimethylformamide) at different concentrations. The theoretical lipophilicities were calculated by several computational algorithms and the results of these calculations were compared using cluster analysis. The results showed that two out of the six investigated organic modifiers (dioxane and acetone) may be used to estimate the octanol/water partition coefficients of highly lipophilic compounds having lipophilicities that cannot be measured directly by the shake-flask method.

The Determination of Partition Coefficient of 6-Mercaptopurine Derivatives by Thin Layer Chromatography

Mercaptopurine and its derivatives are used in the treatment of leukemia. To estimate their lipophilicity, a simple and novel thin layer chromatography method was developed. The mobile phase was the mixture of acetonitrile and water. The acetonitrile content varied by 5% from 50% to 80%. The linear relationship between and for substances with known lipophilicity was found. The lipophilicity of purine derivatives was worked out from the calibration curve. The most lipohilic compound was methylazathioprine (0.64).

Comprehensive evaluation of lipophilicity of biogenic amines and related compounds using different chemically bonded phases and various descriptors

The retention behavior for a series of biogenic amines and related sympathomimetic drugs has been investigated in reversed-phase thin-layer chromatography using RP-2, RP-8, RP-18W, and Diol stationary phase and mixtures of phosphate buffer (pH = 7.10) and methanol in different proportions as mobile phases. Several methodologies like arithmetic mean of experimental retention values, extrapolation to zero methanol concentration procedure and principal component analysis were applied to retention data values (R(M)) in order to determine relevant parameters (mean of R(M) - mR(M), R(M0), and scores corresponding to the first principal component - PC1/R(M) respectively) encoding information on the lipophilic behavior of compounds. High similarities in lipophilicity behavior of investigated amines were highlighted by mR(M) and PC1/R(M) lipophilicity indices for all of the studied stationary phases. The experimental results were compared with some computed lipophilicity parameters expressed as distribution coefficients at working pH (logD), partition coefficients (logP(N), logP(I), and diff(logP(N-I))) concerning both neutral and fully protonated species and difference between both species, and also with various lipophilicity values (logP) generated by different commonly used software. Significant correlations were observed between the experimental lipophilicity indices mR(M) respectively PC1/R(M) and diff(logP(N-I) ) values in all cases.