Chromatographic Properties Research Articles

Model of retention time and density of gradient peak capacity for improved LC-MS method optimization: Application to metabolomics

A general and deterministic model is derived from the fundamentals of liquid chromatography to calculate retention time, peak width, peak capacity, and density of peak capacity in gradient liquid chromatography. The calculation of these chromatographic properties accounts for 1) the presence of initial (separation of the earliest eluters) and final (column wash) isocratic steps before and after the linear gradient, respectively, 2) the pre- (flow through needle and preheater tubes) and post-column (outlet and emitter tubes before MS detection) dispersion, 3) the compression of the chromatographic band, and 4) the retention of the organic modifier onto the RPLC column. The multiple and variable method parameters may include the column dimensions, particle size, flow rate, temperature, initial and final isocratic hold times, gradient time, gradient steepness, column conditioning/sample load time, and the pre- and post-column tube dimensions. The model enables the users to perform robust multi-dimensional optimization of UHPLC-MS methods and offers the possibility to predict the expected MS feature density for increased method performance. Method optimization can be further improved by matching the observed MS feature density (number of metabolites detected as function of time) to the predicted density of peak capacity. It is directly applied to the optimization of high-throughput RPLC separation methods specifically designed for large-scale urinary metabolic phenotyping.

Feeding Brassica vegetables to rats leads to the formation of characteristic DNA adducts (from 1-methoxy-3-indolylmethyl glucosinolate) in many tissues

Juices of Brassica vegetables are mutagenic and form characteristic DNA adducts in bacteria and mammalian cells. In this study, we examined whether such adducts are also formed in vivo in animal models. Rats fed raw broccoli ad libitum in addition to normal laboratory chow for 5 weeks showed one major adduct spot and sometimes an additional minor adduct spot in liver, kidney, lung, blood and the gastrointestinal tract, as determined by 32P-postlabelling/thin-layer chromatography. Adducts with the same chromatographic properties were formed when herring sperm DNA (or dG-3’-phosphate) was incubated with 1-methoxy-3-indolylmethyl glucosinolate (phytochemical present in Brassica plants), in the presence of myrosinase (plant enzyme that hydrolyses glucosinolates to bioactive breakdown products). UPLC–MS/MS analysis corroborated this finding: 1-Methoxy-3-indolylmethyl-substituted purine nucleosides were detected in the hepatic DNA of broccoli-fed animals, but not in control animals. Feeding raw cauliflower led to the formation of the same adducts. When steamed rather than raw broccoli was used, the adduct levels were essentially unchanged in liver and jejunum, but elevated in large intestine. Due to inactivation of myrosinase by the steaming, higher levels of the glucosinolates may have reached the large bowl to be activated by glucosidases from intestinal bacteria. In conclusion, the consumption of common Brassica vegetables can lead to the formation of substantial levels of DNA adducts in animal models. The adducts can be attributed to a specific phytochemical, neoglucobrassicin (1-methoxy-3-indolylmethyl glucosinolate).

Chromatographic Properties of Hydrogenated HPHT Microdiamond

Chromatographic Properties of Hydrogenated HPHT Microdiamond

Immobilization of phosphonium-based ionic liquid stationary phases extends their operative range to routine applications in the flavor, fragrance and natural product fields

Phosphonium-based ionic liquids (ILs) have proven to be successful stationary phases (SPs) for gas chromatography (GC) in several fields of application because of their unique selectivity and good chromatographic properties. This study focuses on the use of two ILs as GC SPs that are based on the phosphonium derivatives trihexyl(tetradecyl)phosphonium chloride ([P66614+] [Cl−]), and trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)sulfonyl]imide ([P66614+][NTf2−]), which have previously been shown to be complementary in terms of chromatographic selectivity and retention. Their application in routine analysis has been limited by their lower maximum allowable operating temperatures (MAOT) (200 °C for the [P66614+][Cl−] IL and 180 °C for [P66614+][NTf2−]), which restricts their use to samples that consist of analytes with relatively high volatility. A previous study carried out in the Authors’ laboratory focused on extending the use of the [P66614+][Cl−] IL SP to the analysis of samples with analytes of medium-to-low volatility by optimizing column characteristics and operative conditions. This study addresses the immobilization of both the [P66614+][Cl−] and [P66614+][NTf2−] ILs to the inner wall of fused silica columns to increase their MAOT under soft and hard reaction conditions. The resulting MAOT depended on more or less drastic immobilization conditions, and reached 220 °C for soft immobilization (So-Im) and 240 °C for hard immobilization (Ha-Im) in the [P66614+][Cl−] IL columns, and 200 °C for So-Im and 220° for Ha-Im in columns coated with the [P66614+] [NTf2−] IL. The influence of immobilization on the separation power and performance of all the columns has been evaluated using i) the Grob test, ii) a model mixture of 41 compounds of different polarity, structure, and with different organic functional groups representative of the flavor and fragrance field, iii) a standard mixture of 37 fatty acid methyl esters, iv) the peppermint essential oil, v) two mixtures of sesquiterpenic alcohols (farnesols and santalols), and vi) a standard mixture of 16 pesticides. These test samples were also used to demonstrate the complementarity of the two phosphonium-based IL SPs in terms of selectivity and retention.

Correlation of the organic sorbents texture with chromatographic characteristics of monolithic HPLC columns based on 1-vinyl-2-pyrrolidone

Monolithic sorbents based on styrene/divinylbenzene/1-vinyl-2-pyrrolidone copolymer have been synthesized inside the glass tubes with the inner diameter of 2 mm. The effect of the porogenic solvent nature and divinylbenzene content on the textural and chromatographic properties of sorbents was studied. Polypropylene glycol with the molecular weight 2025 g/mol and triblock copolymer Pluronic 10R5 (poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol)) with the molecular weight 2000 g/mol were found to be the most suitable porogenic solvents. The fraction of divinylbenzene in the initial polymerization mixture was shown to affect the textural characteristics of sorbents (specific surface area, pore size and volume). The dependence of hydrodynamic permeability and columns loading capacity on divinylbenzene content in the initial reaction mixture was elucidated. Separation examples for the prepared columns are given.

Total Synthesis of (–)-Aristoquinoline via an Intramolecular Nitrilium Ion Cyclization

AbstractThe enantioselective total synthesis of the alkaloid aristoquinoline has been achieved in seven steps and 26% overall yield. A new preparation of the useful synthetic building block (–)-α-terpinyl amine was also developed in order to avoid stoichiometric mercury reagents or azide-containing intermediates. Key steps in the optimized synthetic route include an intramolecular nitrilium ion cyclization to form the characteristic azabicyclo[3.3.1]nonane ring system and a dia­stereoselective reduction of the resulting imine mixture to afford the natural product. An isomer of aristoquinoline containing an exocyclic alkene was also obtained and found to exhibit unusual chromatographic and spectroscopic properties.

Study of Chromatographic Properties of Catecholamines and their Acidic Metabolites Using Novel Molecularly Imprinted Polymers as Stationary Phases

Quantitative analysis of catecholamines and their acidic metabolites can provide vital information for diagnosis and treatment of various diseases (such as adrenal tumors). However, complicated purification protocols are usually required to isolate the analytes. Molecularly imprinted polymers (MIPs) have attracted considerable attention as a method of selectively separating desired compounds from their matrix. Therefore, we propose a synthetic procedure for new molecularly imprinted sorbents that possess selective binding sites for both catecholamines and their acidic metabolites. The new polymer utilizes non-covalent and semi-covalent imprinting methods. The binding properties of MIPs were evaluated using chromatographic experiments. The results suggest that the MIPs bind with catecholamines much more selectively than with their acidic metabolites. Therefore, increasing sorption selectivity of the acids would make it possible to perform simultaneous extraction of both compound groups.

Grafting copolymer brushes on polyhedral oligomeric silsesquioxanes silsesquioxane-decorated silica stationary phase for hydrophilic interaction liquid chromatography

A strategy is proposed to develop a stationary phase for hydrophilic interaction liquid chromatography (HILIC) using the synergistic effect of polyhedral oligomeric silsesquioxane (POSS) and copolymer brushes. Octahedral octa-aminopropylsisesquioxane (8NH2-POSS) was first bound to silica gel, followed by bromination to form a cubic initiator. Then, using acrylamide (AM) and dihydroxypropyl methacrylate (DPMA) as mixed monomers, surface initiated-atom transfer radical polymerization was conducted to prepare a stationary phase comprising cubic copolymer brushes with amide and diol groups. The characterization of the stationary phase confirmed the successful synthesis of Sil-NH2-POSS/Poly(AM-co-DPMA). The chromatographic properties were investigated using nucleosides, organic acids and β-agonists to find that our designed column has superior hydrophilic property, better separation performance compared with classical HILIC columns consisting of diol- or amino-modified silica. The systematic investigation of the retention mechanism and separation selectivity using various types of polar compounds revealed that Sil-NH2-POSS/Poly(AM-co-DPMA) follows a mixed-mode retention composed of HILIC and electrostatic interactions. Besides, it exhibits good column efficiency and stability. The role of 8NH2-POSS in the separation was evaluated by comparing the performance of Sil-NH2-POSS/Poly(AM-co-DPMA) and poly(AM-co-DPMA)-modified silica without 8NH2-POSS. In conclusion, our designed based on POSS and hydrophilic copolymer brushes can contribute to the development of HILIC separation materials with enhanced performance.

Enantioselective multiple heart cutting online two-dimensional liquid chromatography-mass spectrometry of all proteinogenic amino acids with second dimension chiral separations in one-minute time scales on a chiral tandem column

In this work, we present a unique, robust and fully automated analytical platform technology for the enantioselective amino acid analysis using a multiple heart cutting RPLC-enantio/stereoselective HPLC-ESI-QTOF-MS method. This 2D-LC method allows the full enantioselective separation of 20 proteinogenic AAs plus 5 isobaric analogues, namely allo-Threonine (aThr), homoserine (Hse), allo-isoleucine (aIle), tert-Leucine (Tle) and Norleucine (Nle), after pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC; AccQ). This N-terminal AA-derivatization method introduces on the one hand beneficial chromatographic properties for 1D RP-LC (stronger retention) and 2D chiral separation (better chiral recognition), and on the other hand favorable detection properties with its chromophoric, fluorophoric, and easily ionizable quinoline mass tag. The entire separation occurs within a total 2DLC run time of 45 min, which includes the 1D-RP run and the 68 s 2D chiral separations of 30 heart-cuts (from the 1D-RP-run) on a chiral quinine carbamate (core-shell QNAX/fully porous ZWIX) tandem column. This relatively short overall run time was only possible by utilizing the highly efficient “smart peak parking” algorithm for the heart cuts and the resulting optimized analysis order thereof. 1D retention time precisions of <0.21% RSD were a requirement for the time-based sampling mode and finally led to a robust, fully automated enantioselective amino acid analysis platform.This achiral-chiral 2DLC method was applied for the amino acid stereoconfiguration assignment of three peptides (aureobasidin A, a lipopeptide research sample, and octreotide) using an L-[u-13C15N] labelled internal AA standard mix spiked to each sample. The isotopically labelled L-AA standard allowed an easy and straightforward identification and configuration assignment, as well as the relative quantification of amino acids within the investigated peptides, allowing the direct determination of the number of respective amino acids and their chirality within a peptide.

Phytochemical investigation and differential effects of Cestrum elegans isolated compounds as antimicrobial and virucidal against hepatitis A virus

A new steroidal saponin, named as (25R)-6α-[(β-D-glucopyranosyl) oxy]-5α-spirostan-3β-yl β-D-glucopyranosyl (1''→3')-O-β-D-glucopyranosid (2) was isolated from the flowers of Cestrum elegans. In addition, a known steroidal saponin (1), a flavonoid compound (3) along with a triterpene saponin (4) were isolated for the first time in genus Cestrum and identified based on their chromatographic properties, chemical and spectral data (HR-ESI-MS, 1H, 13C NMR, 1H-1H COSY, HSQC, and HMBC). The four compounds are characterized by different effects against Gram positive, Gram negative bacteria, antifungal and antiviral activities. The maximum non-toxic concentration (MNTC) on vero cell line was 1.56 µg/mL for all compounds. While compound 1 and 3 showed the highest biological activities against hepatitis A virus possess 34.3% and 25% antiviral activity respectively..

Chromatographic Method for Evaluation of Polymeric GC Stationary Phases Ageing Using the Novel Non-Cross-Linked Poly(3-(Tributoxysilyl)Tricyclononene-7) as the Model Stationary Phase.

The chromatographic properties and thermal stability are investigated for the polymeric stationary phase based on the norbornene polymer. It was shown that without additional cross-linking, poly(3-(tributoxysilyl)tricyclononene-7) demonstrates properties similar to liquid chromatographic stationary phases. It was also found to be more thermally stable than previously studied trimethylsilyl- and trimethoxysilyl- derivatives. The long-term heating at 170 °C resulted in an increase of mass transfer rate between stationary and mobile phases which could be observed as a decrease of parameter C of Van Deemter equation. This effect is rather unusual, as the polymeric stationary phases tend in decrease of the layer volume and porosity while ageing. Additionally, the values of thermodynamic parameters of sorption are calculated for the polymeric stationary phase: enthalpy of sorption varied −28 to −37 kJ/mol, entropy change was −41 to −51 J/mol K. The compensation curves were plotted for the alkanes, arenes, and alcohols, and the parameters of compensation plot were calculated, demonstrating the different sorption mechanisms both for hydrocarbons and oxygen-containing compounds, and different classes of organic compounds.

Revisiting Chiral Recognition Mechanism on Chicken Alpha 1-Acid Glycoprotein: Location of Chiral Binding Sites and Insight into Chiral Binding Mechanism

Chiral stationary phases based on chicken alpha 1-acid glycoprotein (cAGP) have been used for enantioseparations of various compounds. However, the chiral binding sites and mechanism have not been clarified yet. Based on chromatographic properties of native and W26-modified cAGP columns and docking simulations of studied compounds into the generated model structure of cAGP, the chiral binding sites were located on cAGP and the chiral binding mechanism was discussed. On cAGP, there existed a binding cavity lined with H25, W26, Y47, R128, T129, D161 and E168, which contribute electrostatic or hydrogen bonding interactions. Benzoin and chlorpheniramine enantiomers interacted with cAGP at almost the same sites a little away from W26, while propranolol enantiomers docked, slightly shifting toward H25 and W26. Furthermore, in addition to hydrophobic interactions, ionic interactions between amino groups of chlorpheniramine enantiomers and a carboxyl group of D161 or E168 played an important role in the chiral recognition, while hydrophobic interactions and hydrogen bonding interactions worked for the chiral recognition of benzoin and propranolol enantiomers.

Separation of Chromatographic Co-Eluted Compounds by Clustering and by Functional Data Analysis.

Peak overlapping is a common problem in chromatography, mainly in the case of complex biological mixtures, i.e., metabolites. Due to the existence of the phenomenon of co-elution of different compounds with similar chromatographic properties, peak separation becomes challenging. In this paper, two computational methods of separating peaks, applied, for the first time, to large chromatographic datasets, are described, compared, and experimentally validated. The methods lead from raw observations to data that can form inputs for statistical analysis. First, in both methods, data are normalized by the mass of sample, the baseline is removed, retention time alignment is conducted, and detection of peaks is performed. Then, in the first method, clustering is used to separate overlapping peaks, whereas in the second method, functional principal component analysis (FPCA) is applied for the same purpose. Simulated data and experimental results are used as examples to present both methods and to compare them. Real data were obtained in a study of metabolomic changes in barley (Hordeum vulgare) leaves under drought stress. The results suggest that both methods are suitable for separation of overlapping peaks, but the additional advantage of the FPCA is the possibility to assess the variability of individual compounds present within the same peaks of different chromatograms.

A fieldable, high-throughput, cost-efficient high performance liquid chromatography-ultraviolet absorption detection (HPLC-UV) method for the quantitation of bispyridinium quaternary aldoxime cholinesterase reactivators in blood

AbstractMono- and bis-pyridinium quaternary aldoximes (K-oximes) have long been employed as cholinesterase reactivator components of antidotes against lethal cholinesterase-inhibiting organophosphorous chemicals. Their positive charge poses difficulties in their chromatographic analysis, resulting in the publication of different approaches for each K-oxime. A multiplexed method is presented for the rapid quantitation of 10 K-oximes in blood with its utility demonstrated in vivo. Liquid chromatography with absorbance detection was employed. Reversed-phase separation was achieved on a highly nonpolar stationary phase. Method validation was based on the respective guideline of the European Medicines Agency. Times to peak concentrations and 120-min areas under the time–concentration curves were determined in rats following intraperitoneal administration. Adequate retention and separation of K-oximes with acceptable peak shapes in short isocratic runs was achieved by adjusting ionic strength, organic content and the concentration of the ion-pairing agent of the mobile phase. Chromatographic properties were governed by optimizing the concentration of dissolved ions. Accurate adjustment of the organic content was indispensable for avoiding peak drifting and splitting. Dose-adjusted exposure to K-347 and K-868 was exceptionally low, while exposure to K-48 was the highest. The method is suitable for screening systemic exposure to various K-oximes and can be extended.

Pharmacognostic and physicochemical evaluation, HPLC analysis and antiproliferative properties of Kigelia africana (Lam.) Benth

Introduction/Objective of study: Kigelia africana (Bignoniaceae) is enriched with bioactive constituents and has thus found various uses in African folklore. This study aims to evaluate the pharmacognostic, physicochemical, chromatographic and antiproliferative properties of K. africana.Methodology: Standard methods were used to determine the qualitative microscopy, moisture content, ash and extractive value. Furthermore, HPLC analysis was conducted on the samples in order to detect and quantify some phenolic compounds (gallic acid, chlorogenic acid, rutin, ferulic acid, caffeic acid and quercetin). The Sorghum bicolor model was used for the antiproliferative assay. All experiment was carried out in triplicates.Results: Microscopy revealed amphistomata with the presence of non-glandular unicellular, uniseriate trichomes on K. africana leaf. Cellulose, tannins, calcium oxalate crystals on the leaf and stem bark, while the roots lacked calcium oxalate crystals. Ash contents were leaf (21.8 ± 0.1) %w/w, stem bark (4.8 ± 0.03)%w/w and root (3.9 ± 0.2)%w/w. Moisture content was (10.5 ± 0.5) %w/w and (9.5 ± 0.2) %w/w for the root and leaf parts, respectively. All values were within WHO limits for crude drugs. The stem bark and root parts contained more water-soluble constituents than alcohol soluble constituents. From the results of HPLC analysis the leaf, stem bark and root extracts gave 24 peaks, 16 peaks and 30 peaks, respectively, a few peaks matched with reference compounds- quercetin, caffeic acid, ferulic acid and rutin. Results of antiproliferative assay showed that methotrexate was significantly (p ˂ 0.05) more effective than the stem bark (from 2-64 mg/mL) with inhibitions ranging from 72.0 ± 1.4% - 90.0 ± 2.4% and root extracts (from 4 – 64 mg/mL) that had inhibitions ranging from 50.3 ± 1.5% - 97.7 ± 0.4% but comparable with leaf extract (from 16 mg/mL - 64 mg/mL) with inhibitions ranging from 68.4 ± 0.8% - 99.0 ± 0.1%.Conclusion: Further information which can be included in an official monograph of the plant for its proper identification and quality control has been provided by this study. Kigelia africana exhibited effective antiproliferative activities and the presence of phenolic compounds.

6-GINGEROL AND PHYSICOCHEMICAL PROPERTIES AS MONITORING PARAMETER FOR A NATURAL GROWTH PROMOTER NBIOTIC™ PREMIX DURING FEED PELLETIZATION STRESS

Background: Feed is an important input for poultry and swine production, representing 50–70% of the total production costs. Feed processing provides an opportunity to improve poultry and swine performance. Herbal gut function modulators are used in poultry and swine feeds to improve nutrient utilization and efficiencies of biomass production. Nbiotic™ Premix is a phytoformulation of AYURVET LIMITED, INDIA used in poultry and swine as a natural growth promoter (NGP) to effectively replace antibiotic growth promoters (AGP). Pelletization used to prevent wastage of feed, reduce bulk and improve digestibility and palatability. In present work we have assessed the stability of the Nbiotic™ Premix herbal formulation under different pelletization thermal stress conditions. Methods: Formulation was kept under controlled temperature (90oC) and moisture (2.0 % w/w) for different time intervals (0, 5, 10 minutes). Chromatographic techniques (HPLC and HPTLC) and physicochemical properties were used to monitor the formulations stability. Nbiotic™ Premix was stable at all the experimental investigation of pelletization thermal stress. Results: No significant change in the 6-gingerol content (250.0 ppm (± 2.0 % at RT 10.05 minutes) and difference between peak areas and the retention factor (RF) values for the control samples and various thermal stress conditioned samples were observed. A comprehensive study of HPLC and HPTLC measurements have been applied for assessing the stability of Nbiotic™ Premix. Developed methods (HPLC &amp; HPTLC) were found to be rapid, sensitive and reliable in determining its stability. As evident, Nbiotic™ Premix can undergo pelletization process without any degradation. In conclusion, present study will help towards developing appropriate stability monitoring parameters for herbal products which is a major challenge in the nutraceutical industry in current scenario.

Prospects of using hyperbranched stationary phase based on poly(styrene-divinylbenzene) in mixed-mode chromatography

Evaluation of the chromatographic properties of covalently bonded hyperbranched stationary phase based on poly(styrene-divinylbenzene) (PS-DVB) and containing zwitterionic fragments in the structure of functional layer was conducted in suppressed ion chromatography (IC), reversed phase high performance liquid chromatography (RP HPLC), and hydrophilic interaction liquid chromatography (HILIC) modes. Besides the possibility of resolving 20 inorganic anions and organic acids using KOH eluent in suppressed IC, prepared resin provided the separation of alkylbenzenes in RP HPLC, water-soluble vitamins, amino acids, and sugars in HILIC mode. Trends in the retention of hydrophobic and polar analytes on the prepared stationary phase indicated the dominating effect of analyte nature on the retention mechanism and proved satisfactory hydrophilization of PS-DVB surface with hyperbranched functional layer for retaining polar compounds. The obtained results revealed good prospects of using hydrophobic PS-DVB substrate for preparing stationary phases for mixed-mode chromatography.

Preparation and characterization of graphitic carbon-nitride nanosheets agglomerated poly (styrene-divinylbenzene) anion-exchange stationary phase for ion chromatography

In this paper, graphitic carbon-nitride (g-C3N4) nanosheets agglomerated poly (styrene–divinylbenzene) (PS-DVB) anion-exchange stationary phase was prepared and applied in ion chromatography. The mono-dispersity, diameters, porosity and surface characteristics of g-C3N4 nanosheets agglomerated PS-DVB microspheres were measured by scanning electron microscope and nitrogen adsorption–desorption measurements. The quaternized g-C3N4 nanosheets agglomerated PS-DVB anion-exchange stationary phase was characterized by Fourier Transform Infrared Spectroscopy, Elemental Analysis, Breakthrough Curve and Mechanical Intensity Test. The chromatographic properties of self-fabricated anion-exchange column packed with septuple quaternized g-C3N4 nanosheets agglomerated PS-DVB microspheres were investigated by separating six conventional anions and four monovalent organic acids. According to the results, g-C3N4 nanosheets were successfully agglomerated onto the surface of PS-DVB microspheres; g-C3N4 nanosheets agglomerated PS-DVB showed good reactivity due to the presence of terminal amino groups; baseline separation of six conventional anions and four monovalent organic acids were obtained on this column. Finally, the self-fabricated column was successfully applied to the determination of mercaptoacetic acid in water reducer.

Phytochemical and Antimicrobial Studies of Pachypodium Lamerei

Five compounds were reported for the first time in the tribe Malouetieae from the leaves and stems of Pachypodium lamerei viz., fatty acid methyl ester (stearic acid methyl ester 1), a mixture of two steroidal aglycones (β-sitosterol 2 and stigmasterol 3), a pentacyclic triterpene (ursolic acid 4) and a steroidal glucoside (β-sitosterol-3-O-β-D-glucopyranoside 5). The structure elucidation was based on comparison of their physical, chemical, chromatographic properties, spectral data with literature as well as direct comparison with authentic compounds. The petroleum ether fraction and the total ethanolic extract of (leaves and stems) exhibited minimum inhibitory concentrations (MICs) against Pseudomonas aeruginosa (1.06 and 2.52 μg/ml), respectively. These results are comparable to that obtained by amikacin (MIC, 2.38 μg/ml). Moreover, the petroleum ether fraction displayed the lowest MIC (16.45 μg/ml) against Candida albicans. This result is greatly promising since the standard drug (ketoconazole) exhibited MIC (185.87 μg/ml). This is the first time to estimate both antibacterial and antifungal activities of any of Pachypodium species.

Novel Adsorbents for Hydrophilic Chromatography Based on Silica Gel Covalently Modified with Poly(ethylene glycol)

Novel stationary phases based on aminopropyl silica gel covalently modified with poly(ethylene glycol) (PEG) with different matrix-to-polymer mass ratios are obtained. The chromatographic properties of the adsorbents are studied using the Tanaka test procedure for hydrophilic stationary phases (and by way of example of separating model mixtures of sugars, amino acids, and water-soluble vitamins). It is shown that varying the thickness of the layer of (PEG) not only affects the efficiency but also makes it possible to tailor the selectivity toward polar analytes in the hydrophilic interaction liquid chromatography mode.