Two-dimensional separations and behaviour of Rauwolfia,Corynanthe and Pseudocinchona alkaloids on unmodified silica gel

Summary Very efficient procedures for separation by TLC in mild conditions of fifteen alkaloids of the Rauwolfia, Corynanthe, Pseudocinchona group are described. Questions relating to the appaent selectivity of separation systems and separation factors in polar or very polar neutral or acidic mobile phases are discussed. Proportions in solvents mixtures are v/v except where otherwise indicated. Abbreviations: TLC=thin-layer chromatography, RCP=Rauwolfia, Corynanthe and Pseudocinchona; other abbreviations: see formulaes and Fig. 1.     

Selectivity of liquid-adsorption chromatography on hydroxylated silica gel with nonpolar and polar eluents

Summary The effect of nonpolar (hexane, decane, benzene) and polar (water, isopropanol, water+isopropanol) eluents on separation of aromatic hydrocarbons and their derivatives in liquid-adsorption chromatography on hydroxylated silica gel columns has been studied. The work has revealed that the traditional application areas of hydroxylated silica gel in liquid chromatography may be extended. In particular it has been shown that, first, polar compounds may be separated on hydroxylated silica gel with nonpolar eluents at high temperatures (100–150°C) and that polar and nonpolar compounds may be separated using pure water as eluent. The effect of adsorbed moisture on retention behaviour of silica gel with nonpolar eluents has also been investigated.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Separation of common monovalent and divalent cations by ion chromatography on calcined silica gel cation-exchange stationary phases, with tyramine-oxalic acid-containing crown ether mobile phases and indirect photometric detection

Summary Pure silica gels (Pia Seed 5S-60-SIL) calcined at 200, 400, 600, 800 and 1000°C for 5 h have been used as cation-exchange stationary phases in ion chromatography with indirect photometric detection for common monovalent and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺ and Ca²⁺); 0.75mm tyramine (4-(2-aminoethyl)phenol)-0.25mm oxalic acid, pH 5.0, containing crown ethers (18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) or 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)) was used as mobile phase. With increasing calcination temperature, the amounts of the crown ethers adsorbed on the calcined silica gel column increased and, consequently, the effect of the crown ethers as retention modifiers for these cations increased. Excellent simultaneous separation and highly sensitive detection of these cations at 275 nm were achieved in 17 min by use of a 150 mm×4.6 mm i.d. column packed with silica gel calcined at 1000°C and use of 0.75mm tyramine-0.25mm oxalic acid, pH 5.0, containing either 0.5mm 18-crown-6 or 5.0mm 15-crown-5 as mobile phase.     

Modeling of retention of adrenoreceptor agonists and antagonists on polar stationary phases in hydrophilic interaction chromatography: a review

Retention prediction models for reversed-phase liquid chromatography (RPLC) have been extensively studied owing to the fact that RPLC remains the most widely used chromatographic technique especially in the field of pharmaceutical and biomedical analyses. However, RPLC is not always the method of choice for the analysis of some compounds that have high polarity. Hydrophilic interaction chromatography (HILIC) has been gaining interest in the last few years as an alternative option to RPLC for the analysis of polar and hydrophilic analytes. HILIC is a variant of normal-phase liquid chromatography, but utilizes water in a water-miscible organic solvent as the eluent in conjunction with a hydrophilic stationary phase. The present review aims to summarize recent contributions on the development of retention prediction models for a group of basic analytes, namely, the adrenoreceptor agonists and antagonists, on different polar stationary phases. The use of multiple linear regression and artificial neural networks in model building is highlighted.     

Effects of starvation for 4-20 days on the amino acid content of Biomphalaria glabrata as determined by cellulose HPTLC-densitometry with confirmation of identity using silica gel and RP-18 W plates with two mobile phases causing inversion of the separation mechanism

The effects of starvation at 4, 7, 10, 14, and 20 days on the amino acid content of Biomphalaria glabrata was determined by high performance thin layer chromatography (HPTLC)-densitometry. Cultures of control and starved snails were prepared for each duration of time. Samples were extracted using ethanol-water (70:30), and supernatant was collected after multiple centrifugations. Samples and standards were applied as bands using a CAMAG Linomat 4 onto cellulose HPTLC plates and developed in a 2-butanol-pyridine-acetic acid-water (39:34:10:26) mobile phase before spraying with ninhydrin detection reagent and scanning with a CAMAG 3 scanner to quantify ornithine (Orn), glycine (Gly), alanine (Ala), valine (Val), and leucine (Leu). Amino acid identification was confirmed by HPTLC on silica gel plates and RP-18?W plates using two different mobile phases causing inversion of the separation mechanism. Starvation led to an overall decrease in amino acid content in comparison to the control snails, however, the amount of amino acids in the starved snails had no correlation with the duration of starvation.     

Determination of very low levels of dissolved mercury(II) and methylmercury in river waters by continuous flow with on-line UV decomposition and cold-vapor atomic fluorescence spectrometry after pre-concentration on a silica gel-2-mercaptobenzimidazol sorbent

A new, simple and sensitive method for the simultaneous determination of mercury(II) and methylmercury chloride at sub-ng l⁻¹ levels in river waters is described. Inorganic and organic mercury were preconcentrated from fresh water samples simultaneously on a laboratory-made column containing 2-mercaptobenzimidazol loaded on silica gel and then quantitatively eluted with 0.05 M KCN solution and 2.0 M HCl to desorp inorganic and methylmercury species, respectively. After irradiation with an intensive UV source, MeHg⁺ was decomposed and mercury vapours were generated from inorganic and organic mercury using an acidic SnCl₂ solution in a continuous flow system and were subsequently determined with a cold vapour atomic fluorescence (CV-AFS) spectrometer. Detection limits (3σ) were 0.07 and 0.05 ng l⁻¹ (as Hg) for mercury(II) chloride and methylmercury chloride, respectively. Relative standard deviations of method (%R.S.D.) were 8.8 and 10 for inorganic and organomercuric species in the river water, respectively. The analysis of real samples, taken from different rivers, showed that inorganic mercury levels ranged from 4.0±0.6 to 12±1 ng l⁻¹ (as Hg and 95% confidence limit) and methylmercury levels at 0.2±0.02 ng l⁻¹(as Hg).