Anna W. Sobanska

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.

Normal-phase TLC analysis of UV filters avobenzone and octocrylene in sunscreen preparations

TLC separation of the UV filters avobenzone (AVO) and octocrylene (OCR) on RP-18 and silica gel 60 as stationary phases, with numerous mobile phases, revealed that these compounds have similar retention properties under almost all the chromatographic conditions investigated. Analysis of avobenzone in the presence of octocrylene may be achieved on silica gel 60 with cyclohexane-diethyl ether 1:1 (v/v) as mobile phase, at the selective wavelength 380 nm, at which octocrylene does not absorb (Method A). Analysis of octocrylene in the presence of avobenzone by the same method was, however, impossible because of insufficient chromatographic separation of AVO and OCR and overlap of the absorption ranges of AVO and OCR (with OCR peaks being obscured by those of AVO). An alternative separation strategy was proposed that proved successful for OCR in the presence of AVO. This involved chromatography on silica gel 60 with cyclohexane-piperidine 15:1 (v/v) as mobile phase (Method B). When these chromatographic conditions were used, retention of avobenzone changed substantially and OCR peaks became clearly visible. Spectrodensitometric scanning for OCR was then performed at 300 nm. Both methods were validated, and gave calibration plots of good linearity.

Quantification of Sunscreen Ethylhexyl Triazone in Topical Skin-Care Products by Normal-Phase TLC/Densitometry

Ethylhexyl triazone (ET) was separated from other sunscreens such as avobenzone, octocrylene, octyl methoxycinnamate, and diethylamino hydroxybenzoyl hexyl benzoate and from parabens by normal-phase HPTLC on silica gel 60 as stationary phase. Two mobile phases were particularly effective: (A) cyclohexane-diethyl ether 1 : 1 (v/v) and (B) cyclohexane-diethyl ether-acetone 15 : 1 : 2 (v/v/v) since apart from ET analysis they facilitated separation and quantification of other sunscreens present in the formulations. Densitometric scanning was performed at 300 nm. Calibration curves for ET were nonlinear (second-degree polynomials), with R > 0.998. For both mobile phases limits of detection (LOD) were 0.03 and limits of quantification (LOQ) 0.1 μg spot−1. Both methods were validated.

Simultaneous Multiple-Development HPTLC Quantification of Water- and Oil-Soluble Sunscreens

Acomplex mixture of sunscreens of different lipophilicity was quantified for the first time by thin-layer chromatography (TLC) followed by densitometric scanning in absorption mode. Multiple-development normal-phase TLC was performed on silica gel 60 as stationary phase. Two mobile phases were used: A — cyclohexane-diethyl ether 5:1 (v/v) and B — ethyl acetate-ethanol-water 70:35:30 (v/v). After development with mobile phase A, two oil-soluble sunscreens, avobenzone (AVO) and octyl salicylate (OS), were analyzed at 360 and 300 nm, respectively. Subsequent development of the same plates with mobile phase B made it possible to quantify a water-soluble sunscreen — phenylbenzimidazol sulfonic acid (PBS) at 300 nm. Calibration curves were non-linear. Limits of detection (LOD) and quantification (LOQ) were LOD (OS) 0.02 µg spot−1, LOQ (OS) 0.06 µg spot−1, LOD (AVO) 0.03 µg spot−1, LOQ (AVO) 0.08 µg spot−1, LOD (PBS) 0.02 µg spot−1, and LOQ (PBS) 0.06 µg spot−1. The method was validated and applied to the analysis of a commercially available cosmetic product.

Simultaneous NP TLC Analysis of the Sunscreens Diethylamino Hydroxybenzoyl Hexyl Benzoate and Octyl Methoxycinnamate

A simple, rapid, and effective method for TLC separation of two EU-authorized UV filters octyl methoxycinnamate (OMC) and diethylamino hydroxybenzoyl hexyl benzoate (DHHB) on silica gel 60 is proposed. Separation conditions were optimized and cyclohexane-diethyl ether-acetone 15:1:2 (v/v) was used as mobile phase. Quantification of both filters on the same chromatographic plates was achieved by densitometric scanning in absorption-reflectance mode at 300 and 360 nm, respectively. The method enabled separation of other UV-absorbing ingredients commonly found in cosmetic sunscreen preparations, for example parabens or ethylhexyltriazone (ET). Good quality, linear calibration plots were generated over the range 200–2000 ng per spot both for OMC and DHHB. The method was validated.

Quantification of Sunscreen Benzophenone-4 in Hair Shampoos by Hydrophilic Interactions Thin-Layer Chromatography/Densitometry or Derivative UV Spectrophotometry

Benzophenone-4 (BZ4) was separated from surfactants, dyes, preservatives, and other components of hair shampoos by thin-layer chromatography on silica gel 60 stationary phase, with ethyl acetate-ethanol-water-pH 6 phosphate buffer (15 : 7 : 5 : 1 v/v/v/v) as mobile phase. Densitometry scanning of chromatograms was performed at 285 nm. The densitometric calibration curve for BZ4 was nonlinear (second-degree polynomial), with R > 0.999. The limits of detection and quantification were ca. 0.03 and ca. 0.1 μg spot−1, respectively. The results obtained by HPTLC-densitometry were compared to those obtained by zero and 2nd derivative UV spectrophotometry. In the case of spectrophotometric methods, calibration curves were linear with R > 0.9998. The chromatographic method was fully validated.

RP-18 chromatographic-based study of the blood—brain barrier permeability of selected sunscreens and preservatives

Chemical ultraviolet (UV) filters and preservatives used currently in sunscreen preparations are compounds of diverse structures, and the safety of their application depends on their inability to penetrate the skin and other barriers present in the human body. However, at least some of these chemicals meet the general requirements of the good blood—brain barrier (BBB) permeability described in the literature sources. The objective of this study was to examine the behavior of selected cosmetic raw materials (UV filters and preservatives) towards the BBB on the basis of the BBB permeability models developed in our earlier study, based on easily accessible RP-18 thin-layer chromatographic data and calculated molecular descriptors. The computed BBB permeability parameters B1 and B2 correlate with the chromatographic data (RF, RF/PSA) and calculated physicochemical descriptors usually associated with the BBB permeation (HA, Sa, DM, log D). The relationships between these values were developed by stepwise multiple regression analysis, validated, and found to explain 93–96% of the total variance. The models of the BBB permeation based on classification functions obtained previously from discriminant function analysis were used to assign the studied compounds to the groups of good (CNS+) or poor (CNS−) blood—brain barrier permeability, suggesting the inability of the majority of these compounds to cross the BBB. The universal character of BBB permeability models developed earlier was confirmed.

Quantification of sunscreen 2-phenylbenzimidazole-5-sulfonic acid in cosmetic products and water samples by HPTLC/densitometry with fluorescent detection

AbstractThe water-soluble sunscreen 2-phenylbenzimidazole-5-sulfonic acid (PBS) was quantified in a sun-care product and water samples by thin layer chromatography followed by densitometric scanning in fluorescence mode (cut-off filter 370 nm, wavelength of excitation — 300 nm). Normal phase TLC was performed on silica gel 60 as stationary phase. Mobile phase used was ethyl acetate-ethanol-water 70:35:30 (v/v/v). The limit of detection (LOD) was 0.0004 μg spot-1, and the limit of quantification (LOQ) was — 0.001 µg spot−1 without any sample pre-concentration.

Application of planar chromatographic descriptors to the prediction of physicochemical properties and biological activity of compounds

ABSTRACT A review of applications of thin layer chromatography (TLC) in drug discovery is given. TLC is presented as a tool to determine the solutes physicochemical properties (lipophilicity, dissociation constant, water solubility) and to predict the interactions of drugs with biomembranes, blood-brain barrier permeability, plasma protein binding, volume of distribution, gastric and skin absorption. Results of modeling based on thin layer chromatographic descriptors are correlated with those obtained by other in vitro techniques used to study drug bioavailability (caco-2 cells, Madin-Darby canine kidney cells, liposome partition). Modified stationary phases used to study receptor-drug interactions are also discussed. Some new trends and ideas in TLC chromatography and its applications in the drug discovery process are presented. GRAPHICAL ABSTRACT

SPE/TLC/Densitometric Quantification of Selected Synthetic Food Dyes in Liquid Foodstuffs and Pharmaceutical Preparations

Selected synthetic food dyes (tartrazine, Ponceau 4R, Brilliant Blue, orange yellow, and azorubine) were isolated from liquid preparations (mouthwashes and beverages) by Solid Phase Extraction on aminopropyl-bonded silica with diluted aqueous sodium hydroxide as an eluent. The extraction step was followed by thin layer chromatography on silica gel 60 with chloroform-isopropanol-25% aq. ammonia 1 : 3 : 1 (v/v/v) as mobile phase and the densitometric quantification of dyes was achieved using quadratic calibration plots (R2 > 0.997; LOQ = 0.04–0.09 μgspot−1). The overall recoveries for all studied dyes were at the average level of over 90% and the repeatability of the proposed procedure (CV ≤ 4.1%) was sufficient to recommend it for the routine quantification of the aforementioned dyes in liquid matrices.