Highly polar steroids, separation

Highly polar steroids, separation of, 974 High-performance liquid chromatography (HPLC),... 

Of the various techniques, reversed-phase systems are most frequently used. Their use in biochemical analysis is almost exclusive. It should be mentioned that for the successful determination of the highly polar steroids fully end-capped Cig columns must be used. Although reversed-phase systems are far more widely used in pharmaceutical steroid analysis, the use of normal-phase systems enables very difficult separation problems to be solved. 

The recovery of phytosterols or their concentration is the third step in their isolation. Methyl esters of fatty acids are distilled to raise the phytosterol content up to 50% by weight. Molecular distillation can be used for phytosterols. Phytosterol concentrates are used as raw materials for steroid drug preparation via microbial fermentation, in which the pure form of phytosterols are not necessary. The final recovery of phytosterols can be achieved by crystallization (physical), solvent extraction (chemical), or crystallization with additives via adduct formation and separation (physicochemical). Organic solvents or solvent mixtures composed of low- and high-polarity solvents and water are used for crystallization of phytosterols... 

Steroidal saponins are usually highly polar compounds occurring as complex mixtures, and their separation into individual components is a formidable task. The traditional purification and separation process for... 

Ion pair formation with anionic ion pair reagents. The separation of monoquaternary amino steroids (pancuronium bromide, vercuronium bromide) or bis-quaternary amino steroids (pipecuroni-um bromide) from their related steroids (intermediates, byproducts, and decomposition products) is difficult because of the highly polar nature of these steroids. 

The column used was 25 cm long, 4.6 mm in diameter, and packed with silica gel particle (diameter 5 pm) giving an maximum efficiency at the optimum velocity of 25,000 theoretical plates. The mobile phase consisted of 76% v/v n-hexane and 24% v/v 2-propyl alcohol at a flow-rate of 1.0 ml/min. The steroid hormones are mostly weakly polar and thus, on silica gel, will be separated primarily on a basis of polarity. The silica, however, was heavily deactivated by a relatively high concentration of the moderator 2-propyl alcohol and thus the interacting surface would be covered with isopropanol molecules. Whether the interaction is by sorption or displacement is difficult to predict. It is likely that the early peaks interacted by sorption and the late peaks by possibly by displacement. 

The most commonly described USP procedure for quantification is the scrap and elution approach. Low analyte recoveries can occur but can be minimized by using polar organic solvents such as methanol, ethanol, or acetone. Generally, analytes with high-Rf values can be desorbed with high recoveries by using the mobile phase. One example of this procedure is the USP assay procedure of the steroid methyl prednisolone acetate in cream formulation. This steroid is separated from its excipients by TLC, extracted from the sorbent, derivatized, and measured spectrophotometrically. 

Selection of the most suitable organic solvent should consider the polarity of analytes and their association with the surfactant. Solute log Fo/w values can be used, in most cases, as a guide to make this decision.Thus, with SDS as surfactant, a low concentration of propanol ( 1% v/v) is useful to separate compounds with log Po/w < 1 as amino acids. A greater concentration of this solvent ( 5% to 1%) is needed for compounds in the range 1 < log Po/w < 2 as diuretics and sulfonamides. Pentanol ( 2% to 6%) is more convenient for low polar compounds with log Po/w > 3 as steroids. For basic compounds, such as phenethylamines with 0electrostatic interaction between the positively charged solutes and the anionic surfactant adsorbed on the stationary phase. In this case, a high concentration of propanol ( 15%), or preferably, a moderate concentration of butanol (<10%) should be used. 

CE is an analytical separation technique capable of high-resolution separation of a diverse range of chemical compounds and is therefore well suited for metabolomics.17,64 It is particularly suitable for the separation of polar and charged compounds and compounds with widely different structures, functional groups, physiochemical properties, and concentrations, for example, organic acids, amino acids, nucleic acids, steroids, carbohydrates, and flavonoids in various matrices. CE is complementary to GC and HPLC, and in many cases, samples that cannot be... 

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