New methods for determining the volumetric flow rate in the column and the retention time of the unretained substance in gas chromatography

New methods for calculating the mean volumetric flow rate of the carrier gas and the retention time of the unretained substance in the column under conditions of gas chromatography were proposed. The methods are based on preliminary isothermal calibrations of the flow rate and holdup time for a packed column. A theoretical substantiation of the methods was given. Procedures of plotting calibration dependences for determining the indicated quantities at a desired temperature were described. The calculation results were compared to experimental data obtained by traditional methods. It was demonstrated that the use of calculation methods substantially simplifies the determination of the specific retention volume over a wide temperature range.     

The adsorption of organic compounds on a modified carbon adsorbent Carbopack B

The thermodynamic characteristics of adsorption of several organic compounds on the carbon adsorbent Carbopack B before and after its modification by a monomolecular layer of cholesteryl-n-pentyl oxybenzoate were determined by gas chromatography. The initial adsorbent was close in its properties to graphitized carbon black. Modification weakened adsorbate-adsorbent attraction and increased the mobility of adsorbed molecules, to a greater extent for nonpolar adsorbents and to a lesser extent for compounds capable of specifically interacting with modifier molecules.     

Analysis of Mixtures Containing Unknown Components by Gas Chromatography: Determination of Molecular Mass

New methods are proposed for the gas-chromatographic determination of the molecular masses of unknown components in complex mixtures within one cycle of analysis. The methods are based on the use of complex chromatographic data in the form of linear retention indices of compounds for a column with a nonpolar stationary phase and sensitivity indices of a thermal conductivity detector and a flame ionization detector.     

Averaging the pressure and flow rate of the carrier gas in a gas chromatographic column

Summary A systematic derivation of corresponding equations shows that averaging the pressure and the flow rate of the mobile phase in a gas chromatographic column over the column length and over the time that an unretained component resides in the column, requires the use of three different compressibility correction factors,j ₂ ¹ ,j ₃ ² , andj ₄ ³ . When multiplied by the adjusted retention volume,V _R-V_M, the Martin and James mobile phase compressibility correction factorj ₃ ² , only, produces the value of specific retention volume,V _g ^T , which is connected unambiguously with the thermodynamic phase distribution coefficient,K, of the sorbate.     

Subcritical water extraction of biologically active substances from milk thistle seed (<Emphasis Type="Italic">Silybum murianum</Emphasis> L.)

A method of subcritical water extraction (SCWE) of biologically active substances from milk thistle seed (Silybum marianum L.) that makes it possible to obtain aqueous extracts without using organic solvents is suggested. The contents of hepatoprotective biologically active substances (taxifolin, silychristin, silydianin, and silybin) in milk thistle seed extracts obtained by SCWE and by standardized liquid extraction procedures are compared.     

Adsorption of volatile organic compounds on Carbopack Y adsorbent modified by β-cyclodextrins

The thermodynamic study on the adsorption of vapor-phase organic compounds on surface of the Carbopack Y carbon-based sorbent modified by monolayer of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin or heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin was performed. The dependence of the thermodynamics of absorption on the structure of the adsorbate and modifier molecules was studied.