Silica Gel RP-18 Research Articles

Examination of the hydrophobicity of ACE inhibitors and their active metabolites by salting-out thin-layer chromatography

The behavior of five ACE inhibitors and their active degradation products in salting-out thin-layer chromatography (SO TLC) has been examined on silica gel, cellulose, and polyacrylonitrile (PAN) with aqueous ammonium sulfate solutions of different concentration as mobile phases. It was found that increasing the concentration of the salt in the mobile phase led to increased R M values for all the substances. Linear relationships were established between salt concentration and R M values and regression data of the plots obtained were used to determine the lipophilicity R M 0 and C 0 . Lipophilicity determined in this way was correlated with calculated log P values. For comparison of these results with chromatographic behavior in conventional RP TLC, the examined substances were subjected to thin-layer chromatography on RP-18 silica gel with methanol-water mobile phases.

TLC analysis of non-steroidal anti-inflammatory drugs and videodensitometric determination of fenbufen in tablets

The chromatographic separation of fenbufen, ibuprofen, ketoprofen, diclofenac sodium, mefenamic acid, and tiaprofenic acid has been investigated. Normal-phase chromatography on silica gel by the ascending and horizontal techniques, and reversed-phase chromatography on octadecyl-bonded silica gel (RP-18) in horizontal chambers, were performed with suitable mobile phases. The substances were identified by UV illumination at λ = 254 nm and by use of dyeing reagents. Reversed phase chromatography with phosphate buffer, pH 5.73–10% CTMA-Br in methanol, 3.5 + 6.5 ( v/v ), as mobile phase enabled better separation of the six drugs than normal-phase mode. A simple videodensitometric TLC method on silica gel RP-18 was developed and validated for quantitative determination of fenbufen in tablets. The limits of detection and quantification were determined by videodensitometry at λ = 254 nm. A calibration plot was constructed in the range 2.0–12.0 μg/5-μL spot and was linear with a good correlation coefficient (0.992...

Planar chromatography of some 1-arylpiperazines behaving as dopaminergic ligands

The chromatographic behavior of fourteen 1-arylpiperazine derivatives has been studied by thin-layer chromatography on both silica gel and RP-18 silica gel. Unmodified silica gel was used as polar stationary phase in combination with monocomponent and binary non-polar mobile phases. Binary mobile phases comprising mixtures of methanol, acetone, or dioxane (as organic modifiers) and water were used with RP-18 silica for studies of the chromatographic behavior of the compounds under reversed-phase conditions. An approximately linear relationship was obtained between R M values and the amount of organic modifier in the mobile phases employed. The effect of mobile phase composition on the retention of the substances is discussed, as is the selectivity of the chromatographic systems used. Separation mechanisms are proposed on the basis of the results obtained.

Bile acid composition in snake bile juice and toxicity of snake bile acids to rats

We determined the bile acid profiles in bile juice of snake gallbladders by HPLC on a silica gel RP-18 reversed-phase column. Cholic acid and chenodeoxycholic acid were predominant components in three of four snake species. To elucidate the toxic effect of snake bile acids on rats, a synthetic bile acid mixture was prepared mimicking the bile acid composition of a snake Naja naja atra bile juice. Twenty-four male Wistar rats were divided into four groups and treated orally at 3-day intervals with saline (control group) and different doses (1–3× doses) of the bile acid mixture. After treatment, the following parameters increased: the relative ratios of liver and kidney mass to body mass, the concentrations of red blood cell, hemoglobin and hematocrit in the blood, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, plasma urea nitrogen and creatinine in the plasma, and the levels of urine urea nitrogen and creatinine in the urine. Body mass of rats and the levels of Na +, K +, Ca ++ in the urine of rats were significantly decreased, especially for groups treated with 2× and 3× doses of the bile acid mixture. Examination of liver and kidney pathology also showed cell enlargement and lesion in cell integrity in treated groups, especially for groups treated with 2× and 3× bile acid mixture, indicating that short-term toxicity of snake N. naja atra bile acids was significant in rats.

Reversed-phase thin-layer chromatography of some foodstuff dyes

The chromatographic behavior of nine frequently used water-soluble food dyes has been studied by TLC on RP-18 silica gel. Reversed-phase chromatographic separations were performed with mobile phases containing ammonium sulfate and water with ethanol or acetone as organic modifiers. The effect of mobile phase composition on retention, and the selectivity of the chromatographic systems, are discussed, and on the basis of the results obtained separation mechanisms are proposed. It was established that ammonium sulfate as a component of the mobile phase significantly increased the reversed-phase behavior of the chromatographic systems used.

High-performance liquid chromatographic determination for aristolochic acid in medicinal plants and slimming products

A HPLC procedure with a silica gel RP-18 reversed-phase column for the determination of aristolochic acids I, II in medicinal plants and slimming products was developed. The mobile system 0.3% ammonium carbonate solution–acetonitrile (75:25, v/v) with pH 7.5 was the optimal buffer to clearly separate aristolochic acids I, II within 20 min. The recovery of aristolochic acids I, II in medicinal plants and slimming products was better than 90% by extracting with methanol and purifying through a PHP-LH-20 column. The major component was aristolochic acid I in Aristolochia fangchi and the level ranged from 437 to 668 ppm. Aristolochic acid II was the major component for Aristolochia contorta and its range was <1–115 ppm. Twelve out of 16 samples of slimming pills and powders contained aristolochic acids I and/or II. The major component in most slimming products was aristolochic acid II and the level ranged from <1 to 148 ppm. It may indicate that slimming products were not mainly made of A. fangchi.

Separation of Pyrimidine Bases on a HPLC Stationary RP-18 Phase Coated with Calix[4]resorcinarene

Lipophilic calix[4]resorcinarenes, derived from lauryl aldehyde and resorcinol, are strongly adsorbed on the modified silica gel RP-18 for HPLC chromatography, while their solutions are passed through the column. The calix[4]resorcinarene-coated RP-18 phases were found to be useful beds for HPLC separation of uracil, thymine and cytosine.

Separation of inorganic anions by ion chromatography on dye-coated silica gel RP-18

RP-18 was coated with methylene blue, methyl green and crystal violet to obtain anion-exchange columns with adsorbed quaternary ammonium groups. The retention behaviour of fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulphate anions was investigated on these columns using an aqueous solution of p-hydroxybenzoic acid as the mobile phase. Using crystal violet for coating, a permanently coated ion-exchange column was obtained, which allowed efficient separations of the seven anions without adding any organic modifier or dyestuff to the mobile phase.