Separation of steroids using temperature-dependent inclusion chromatography

A Review on Cyclodextrins/Estrogens Inclusion Complexes

This review focuses on the methods of preparation and biological, physiochemical, and theoretical analysis of the inclusion complexes formed between estrogens and cyclodextrins (CDs). Because estrogens have a low polarity, they can interact with some cyclodextrins' hydrophobic cavities to create inclusion complexes, if their geometric properties are compatible. For the last forty years, estrogen-CD complexes have been widely applied in several fields for various objectives. For example, CDs have been used as estrogen solubilizers and absorption boosters in pharmaceutical formulations, as well as in chromatographic and electrophoretic procedures for their separation and quantification. Other applications include the removal of the endocrine disruptors from environmental materials, the preparation of the samples for mass spectrometric analysis, or solid-phase extractions based on complex formation with CDs. The aim of this review is to gather the most important outcomes from the works related to this topic, presenting the results of synthesis, in silico, in vitro, and in vivo analysis.

Unexpected Encapsulation of Selected Polycyclic Aromatic Hydrocarbons by β-Cyclodextrin Studied Using UV-Vis Spectrophotometry, Micro-Planar Chromatography and Temperature Dependent Inclusion Chromatography

This research communication significantly extends our previous studies focusing on the temperature effects related to the unexpected chromatographic behavior of 1-acenaphthenol in the presence of native β-cyclodextrin (β-CD) additive, working under thin-layer chromatographic (TLC) conditions. We have applied complementary and orthogonal techniques including (i) temperature-controlled ultraviolet-visible (UV-VIS) spectroscopy, (ii) thermostated microplanar high-performance chromatography (micro-HPTLC) and (iii) temperature-dependent inclusion chromatography based on high-performance liquid chromatography (HPLC) to investigate the retention behavior of related host molecules. Particularly, various symmetric and asymmetric molecules were tested, such as: naphthalene and its derivatives including acenaphthylene, acenaphthene and selected dimethynaphthalenes: 1,8-DMN, 1,5-DMN, 2,3-DMN and 2,6-DMN. Reported raw experimental data, particularly performed in liquid phase and detected by UV-Vis spectrophotometry, may suggest that solubility changes of the supramolecular complexes studied and differences in total analysis time between TLC and HPLC separation can trigger strong retention of target components in planar chromatographic systems. This was also supported by principal component analysis (PCA) of the multi-source data obtained. It is hoped that the reported analyses enable the adjustment of phenomenological models describing liquid chromatography retention and the solubility behavior of low-molecular mass guest molecules, controlled by supramolecular interactions with selected macrocycles. It should be noted that the reported phenomenon, specifically supramolecular complexes precipitation, may have a number of practical applications. This can be used to improve the efficiency and selectivity of planar and/or microfluidic systems. On the other hand, precipitation via host-guest interactions may be applied for highly selective water purification technological processes that will be designed for the removal of given organic micropollutants.

Analysis of Selected Endocrine Disrupters Fraction Including Bisphenols Extracted from Daily Products, Food Packaging and Treated Wastewater Using Optimized Solid-Phase Extraction and Temperature-Dependent Inclusion Chromatography

The aim of this research is to demonstrate the concept and ability for the fast and preliminary screening of complex food and environmental samples for the presence of endocrine disrupters fractions, consisting of low-molecular mass micropollutants, particularly various bisphenols (A, B, C, E, F, S, Z, AF, AP, BP and FL). The developed analytical protocol for this research requires two main steps: (i) optimized solid phase extraction (SPE) for selective isolation, purification and pre-concentration of target fraction, and (ii) selective temperature-dependent inclusion chromatography for samples analysis via a HPLC-UV-VisDAD system using isocratic elution and internal standard quantification approach. The chromatographic experiment revealed that both β-CD and its hydroxypropyl derivative strongly interact with selected bisphenols. This is in contrast to the steroids and PAHs molecules investigated previously, where a strong interaction with β-cyclodextrin was observed. Integrated areas derived from acquired chromatographic profiles for each individual sample were used as the simple classification variable enabling samples comparison. We demonstrated that the proposed analytical protocol allows for fast estimation of EDC fractions in various daily use products, food and environmental samples. The materials of interest were selected due to the presence in surface water ecosystems of their residues, and finally, in raw wastewater including rice bags, plastic bags, cloths, sanitary towels, fish baits and various plastic foils from food products. Treated sewage water released directly to the environment from a municipal treatment plant (Jamno, Koszalin) was also investigated. It has been demonstrated that a whole range of low-molecular mass compounds, which may be detected using UV-Vis detector, can easily be emitted from various in daily use products. The presence of micropollutants in treated wastewater, water ecosystems and plastic waste utilization via technological wastewater treatment processes must be addressed, especially in terms of microplastic-based pollutants acting as endocrine disrupters. It is hoped that the proposed simple analytical protocol will be useful for fast sample classification or selection prior to advanced targeted analysis involving the more accurate quantification of specific analytes using e.g., mass spectrometry detectors.

Unexpected differences between planar and column liquid chromatographic retention of 1-acenaphthenol enantiomers controlled by supramolecular interactions involving β-cyclodextrin at subambient temperatures

We report the results of experimental work focusing on host-guest supramolecular complex creation between macrocyclic compound (β-cyclodextrin) and 1-acenaphthenol enantiomers (racemic mixture) in liquid phase composed of 35% acetonitrile in water (v/v) at different temperatures ranging from 0 to 90 °C. Experimental setup involved several analytical protocols based on classical non-forced flow planar chromatography (RP-18 TLC plates), micro-TLC (RP-18 W HPTLC plates), column chromatography (HPLC with C-18 and C-30 stationary phases), as well as UV-Vis spectrophotometry and optical microscopy. It has been found that under various planar chromatographic conditions (stationary plates type, chamber shape and volume, development mode, and saturation) non-typical retention properties (extremely high retention) of 1-acenaphthenol at subambient temperatures can be observed. To our knowledge, reported experimental results are in opposition to currently described retention models based on column chromatographic investigation of host-guest complexes (where in case of strong interaction of given analyte with macrocyclic mobile phases additive, which itself is non strongly retarded by stationary phase-close to the retention of dead volume marker, the retention of target compounds is shortened at low temperatures). To explain this TLC phenomenon that may have in our opinion a number of practical applications, especially for selective high throughput separation involving microchromatographic and/or microfluidic devices as well fractionation and extraction protocols (using, e.g., bar extraction systems), several experiments were conducted focusing on (i) acenaphthenol chromatography under different instrumental conditions, (ii) cyclodextrin retention measured as analyte or mobile phase additive, (iii) plate development time under different mobile phases and temperature settings, (iv) various column chromatographic conditions including C-30 and two C-18 stationary phases, (v) UV-Vis spectrophotometry, and (vi) microscopy inspection of precipitated CD-acenaphthenol crystals. Analysis of collected data has revealed that the most probable reasons for TLC retention behavior of 1-acenaphthenol under β-cyclodextrin additive conditions can be associated with (i) solubility changes of created host-guest complex, (ii) kinetics of solid complex precipitation, and (iii) differences in analysis time between planar and column chromatography. Because precipitation phenomenon may have a massive impact on analytes quantification involving macrocycles as the mobile phase additives, our previously reported data concerning a number of low-molecular compounds (mainly steroids and non steroidal endocrine disrupting chemicals) using HPLC methodology based on binary mobile phases without and with β-cyclodextrin and its hydroxypropyl derivative were re-examined and results discussed. Considering these data and the whole data set reported presently, the enhanced model of chromatographic retention driven by host-guest interaction was proposed.

Determination of endocrine disrupting compounds using temperature-dependent inclusion chromatography: I. Optimization of separation protocol

In the present work we optimised the separation of battery of key UV non-transparent low-molecular-mass compounds having possible endocrine disrupting compounds (EDCs) activity or which may be used as the endocrine effect biomarkers. Simple optimization strategy was based on strong temperature effect that is driven by electrostatic interactions between macrocyclic mobile phase additives like cyclodextrins and eluted components of interest under C18 stationary phase and acetonitrile/water mobile phase conditions. Particularly, the effect of temperature involving native beta-cyclodextrin and its hydroxypropyl derivative to improve separation of number of natural (d-equilenin, equilin, estetrol, estriol, estrone, 17beta-estradiol, 17alpha-hydroxyprogesterone, 20alpha-hydroxyprogesterone, cortisol, cortisone, progesterone, testosterone, tetrahydrocortisol and tetrahydrocortisone) and artificial steroids (ethynylestradiol, norgestrel isomers, medroxyprogesterone, mestranol, methyltestosterone, norethindrone, 17alpha-estradiol) as well as non-steroidal compounds (diethylstilbesterol, bisphenol A, 4-tert-butylphenol, dimethyl phthalate, dibutyl phthalate and dioctyl phthalate) was investigated. It has been found that successful isocratic separation of 27 chemicals can be achieved using acetonitrile/water eluents modified with beta-cyclodextrin or hydroxypropyl-beta-cyclodextrin at concentration of 10 mM and temperature of 47 degrees C. Separation protocol is simple, reliable, direct and non-radioactive and may be easily adapted for rapid separation and quantification of wide range of given steroids and related EDCs in environmental samples, particularly those that are characterised by unstable biological matrix and components of interest load.

Interaction of native alpha-cyclodextrin, beta-cyclodextrin and gamma-cyclodextrin and their hydroxypropyl derivatives with selected organic low molecular mass compounds at elevated and subambient temperature under RP-HPLC conditions

The main focus of this study was to explore the capability of native alpha-cyclodextrin, beta-cyclodextrin and gamma-cyclodextrin and their hydroxypropyl derivatives for host-guest interaction with 7,8-dimethoxyflavone, selected steroids (estetrol, estriol, estradiol, estrone, testosterone, cortisone, hydrocortisone, progesterone and 17alpha-hydroxyprogesterone) and polycyclic aromatic hydrocarbons (toluene, naphthalene, 1,8-dimethylnaphthalene, 1-acenaphthenol, acenaphthylene and acenaphthene) under reversed-phase liquid-chromatography conditions. The study revealed that native cyclodextrins interact more efficiently with the analytes investigated than do their hydroxypropyl counterparts. In the low-temperature region, enormously high ratios were observed for polycyclic aromatic hydrocarbons, particularly 1,8-dimethylnaphthalene, acenaphthene and acenaphthylene chromatographed on a beta-cyclodextrin-modified mobile phase. In such a case, the retention times of the polycyclic aromatic hydrocarbons were strongly reduced (e.g. from 127 to 1.2 min for 1,8-dimethylnaphthalene) and were close to the hold-up time of the high-performance liquid chromatography (HPLC) system (0.7 min). Moreover, chiral separation of 1-acenaphthenol optical isomers was observed and the elution order of the enantiomers was determined. Within the steroids group, strong interaction was observed for estradiol and testosterone. The results of cluster analysis indicate that beta-cyclodextrin as well as gamma-cyclodextrin and its hydroxypropyl derivative can be most effective mobile-phase additives under reversed-phase HPLC conditions for 3D-shape-recognition-driven separation, performed at subambient and elevated temperatures, respectively.

Determination of association constants of inclusion complexes of steroid hormones and cyclodextrins from their electrophoretic mobility

CE estimation of the association constants of several steroid hormones with beta-CD and gamma-CD and their hydroxypropyl derivative is presented. Estriol, 17beta-estradiol, ethynylestradiol, estrone, progesterone, mestranol and norethindrone are among the target analytes. The calculation of the cyclodextrin:analyte association constants were performed from the electrophoretic mobility values of steroids at different concentration of CDs in the run buffer. The reliability of the final data was ensured by employing three different linearisation plots (double reciprocal fit, Y-reciprocal fit and X-reciprocal fit). The highest inclusion affinity of target analytes was observed towards gamma-CD and its hydroxypropyl derivative, which is demonstrated by high association constant values and corresponding good linearity of the plots. The affinity of steroids towards a particular CD type based on physical and structural characteristics is explored.

Determination of estradiol and its degradation products by liquid chromatography

A novel HPLC method for simultaneous determination of estradiol and its seven degradation products in topical gel was developed. Zorbax SB-CN (150 mm x 4.6 mm, 5 microm) analytical column and mobile phase composed of acetonitrile, phosphoric acid 0.085%, and tetrahydrofurane (27:63:10, v/v/v) at flow-rate 1.0 ml min(-1) were used for the chromatographic separation using UV detection at 225 nm. The active substance estradiol was separated from all its known degradation products successfully. Two degradation products estrone and Delta(9(11))-estrone were not separated sufficiently, their peaks were evaluated as a sum of two components. The method was validated according to ICH guideline recommendations and thereafter it was successfully applied for stability tests of topical cream Estrogel HBF in the quality control laboratory. Limits of detection for degradation products ranged from 1.03 x 10(-5) to 1.14 x 10(-4) mg ml(-1), limits of quantitation for degradation products were in the range 3.43 x 10(-5) to 3.81 x 10(-4) mg ml(-1). The developed method is selective, precise, accurate and sensitive enough for determination of estradiol and its known degradation products.

Isocratic separation of ginsenosides by high-performance liquid chromatography on a diol column at subambient temperatures

An improved high-performance liquid chromatographic method for separation of a number of ginsenosides has been developed. The influence of temperature (from 0 to 25 degrees C) on the retention and separation of the ginsenosides was studied by applying a binary mobile phase (acetonitrile/water, 82:18 v/v) and a diol column (LiChrospher 100 Diol). The column temperature is one of the more important parameters for the retention and separation of the components investigated. Selected thermodynamic parameters, including changes of enthalpy (deltaH degrees) and entropy (deltaS degrees), were estimated from linear van't Hoff plots, and possible retention mechanisms were discussed. Moreover, the best separation conditions were selected based on optimization criteria including maximum retention time (t(R max)), minimum resolution (R(s min)), and relative resolution product (r). Temperature regions close to 14 degrees C offered the highest selectivity and almost equal distribution of the ginsenosides peaks across the chromatogram. Under such isocratic conditions, excellent separation of chromatographic standards and selected ginseng samples was achieved in less than 16 min.

Effect of the Net Surface Charge Density of Heptakis-6-bromo-6-deoxy-.BETA.-cyclodextrin Bonded Silica Gels on the Retention Behaviors of Neutral Cresol Isomers in HPLC

The effect of the surface charge density of heptakis-6-bromo-6-deoxy-beta-cyclodextrin (beta-CD-BR) bonded silica gels, which was used as the stationary phase of a packed capillary column for HPLC, was investigated concerning the retention behaviors of neutral cresol isomers. On the whole, the retention factors of the cresol isomers increased with an increase in the pH values of the mobile phase, although they were slightly smaller at pH 6.1 than at pH 4.7. An investigation on the retention variation using a van't Hoff plot revealed that the increase in the retention factor (k) at a higher pH region could be mainly attributed to the increase in DeltaS, while a partial decrease in k around pH 5 - 6 was caused by a decrease in the -DeltaH/T value. On the other hand, a measurement of the electroosmotic flow velocity under various pH of the mobile phase solutions revealed that the retention variations of the neutral cresol isomers were strongly correlated with the surface charge on the packing materials. The positive charge of secondary ammonium functional groups to bind beta-CD-BR inhibit the insertion of the cresol isomers into the cavity of beta-CD-BR while reducing the retention factor, whereas the negative charge of silanol group enhanced it through a local change in the mobile phase composition.

Evaluation of Methanol-Water and Acetonitrile-Water Binary Mixtures as Eluents for Temperature-dependent Inclusion Chromatography

In the present study the solubility of beta-cyclodextrin and 2-hydroxypropyl-beta-cyclodextrin at sub-zero and elevated temperatures (-10 and +30 degrees C) for a given composition of methanol/water and acetonitrile/water binary mixtures (Xs = 0.16) was studied. Moreover, the freezing temperature profiles of acetonitrile-based chromatographic mobile phases were measured, and the obtained results were compared with data available in the literature. Furthermore, the effect of the macrocycles concentration on the liquid-phase freezing points was determined. The low solubility of native beta-cyclodextrin in a methanol/water mixture at sub-zero temperature as well as the non-linear behavior of acetonitrile/water mixtures that were observed concerning the freezing point profile are discussed from a practical point of view.

Determination of steroids in human plasma using temperature-dependent inclusion chromatography for metabolomic investigations

Clinical and metabolomic investigations of complex human fluids require cost-effective methodologies that can rapidly assess the steroid hormone milieu of individual samples. The efficiency of quantification of many steroids is limited using immunoassays as these methods can only measure a single component of biological samples and are dependent upon the specificity of the antiserum used in the protocol. In this study, we optimised the solid-phase extraction protocol for the extraction of a range of steroids of varied polarity from estetrol to progesterone from human plasma. The final SPE procedure for efficient extraction of steroids was a washing mixture of 5 ml of 30% methanol and an elution solvent of 2 ml of 100% methanol using 0.5 g C-18 cartridges. This protocol resulted in a high recovery rate, ranging from 85.2 to 99.9% for both the internal standard (7,8-dimethoxyflavone) and steroids of interest. We also improved the separation methodology of our previous work using temperature dependent inclusion chromatography with a mobile phase composition of 35% acetonitrile and 12 mM of beta-cyclodextrin at 29 degrees C. Under these conditions most of the fluid components including estetrol were detected in the first 10 min with progesterone appearing at 43 min. This method is simplistic, inexpensive and reproducible with the capabilities of accurate quantification of steroids. Therefore it could have numerous clinical and metabolomic applications.

Gradient elution of organic acids on a β-cyclodextrin column in the polar organic mode and its application to drug discovery

A high performance liquid chromatographic method was developed that separated organic acids using the polar organic mode. The separation was obtained using a beta-cyclodextrin stationary phase with a mobile phase that was composed of acetonitrile/methanol/triethylamine (TEA)/acetic acid. The compounds were eluted under gradient conditions and the elution order depended on the number, type and position of the hydrogen bonding functional groups present in the molecule. Adjusting the acid to base ratio resulted in the biggest change in selectivity. In addition, increasing the methanol concentration decreased the retention times of the analytes, which had little effect on the selectivity. Using a certain set of conditions one could separate a large number of organic acids, which allowed these acids to be detected by UV and mass spectrometry. These conditions were used to evaluate the purity of potential pharmaceutical drug candidates that showed activity towards a kinase target vascular endothieal growth factor (Vegf). Each compound contained a carboxylic acid group that was critical to the activity. The method was able to give purity estimates of these samples, which were difficult to determine by other HPLC methods.

Recent Advances in the Analysis of Steroid Hormones and Related Drugs

The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis.

Simple chamber for temperature-controlled planar chromatography

This article describes a construction of a simple developing device designed for temperature control of thin-layer chromatographic plates. The plates can be developed by the ascending technique under temperature gradient or non-gradient conditions. Saturated or unsaturated chamber conditions can be easily selected. The effects that give rise to pseudo-non-linear Van't Hoff plots, e.g. a temperature irregularity inside the chamber or heat evolving during solvent adsorption near the migrating front of the mobile phase are minimized. The preliminary temperature-retention studies show that the device is suitable for temperatures ranging from -20 to 60 degrees C. Using a binary mobile phase mixture (methanol-water, 70:30, v/v) the velocity of the mobile phase front on the HPTLC RP-18W plates at different temperatures was investigated. Under these conditions the retention profiles of four natural estrogens (estetrol, estriol, 17beta-estradiol and estrone) were examined. The application of the described device for temperature-retention studies is also discussed.

Chromatographic behaviour of selected steroids and their inclusion complexes with beta-cyclodextrin on octadecylsilica stationary phases with different carbon loads

Retention and separation studies of selected estrogens, progestogens and their inclusion complexes with beta-cyclodextrin were conducted using two C18 HPLC columns with different carbon loads. The difference in carbon load between investigated octadecylsilica packing materials was about 50%. The mobile phases were composed of a 30% v/v acetonitrile-water mixture without and with addition of beta-cyclodextrin at a concentration of 12 mM. The experimental data revealed that retention of the steroids was significantly reduced on the column with the lower carbon load. Moreover, it was found that this column offers better separation power and shorter analysis time at the temperatures studied. However, the calculated values of the retention factor ratios (k0(mMCD))/k(12mMCD)) of the steroids were similar for both columns investigated. This observation suggests that the stationary phase structure appears to have little effect on the formation of host-guest complexes if the complexation process is localised to the chromatographic mobile phase. From a practical point of view, when the mobile phase is modified with beta-cyclodextrin, the separation of the steroids is strongly influenced by temperature. The best chromatographic conditions were determined for the separation of multicomponent samples on the column with lower carbon load. A possible retention mechanism for components of interest in the presence of macrocyclic additives is discussed.