Retention time, in chromatography

Retention time, in chromatography, 6 374-375, 409-410 ( )-Reticuline, 2 90 Retina, 7 307-308 Retinal, 25 787. See also Vitamin A carotenes and, 25 790 Retinitis pigmentosa, 17 659 Retinoic acid, 25 787-789, 790. See also Vitamin A... 

The measurements of dipole moments and retention times in chromatography were found to be especially useful in assigning the configuration (cis-trans geometry) of cyclic four-, five-, and six-membered sulfoxides (236,237). These methods were also applied to the determination of configuration of steroidal sulfoxides (216,238). 

The principal advantage of sensors is therefore their fast response time in comparison to the retention time in chromatography, but the sensor response is partially a sum signal of the favourably enriched analyte and the cross-sensitive compounds, which makes a independent calibration necessary. Furthermore, it is essential for the sensor layer to allow a completely reversible inclusion process, while still maintaining high selectivities and high enrichment factors. 

In general, boiling point and AyapH cannot be predicted. The prediction of retention time in chromatography requires the use of predictable properties. The retention time can be calculated in silica using a model phase, but vaporization has not been quantitatively analyzed. In gas chromatography, vaporization may be related to analyte volatility. The retention on methylsilicone phases was quantitatively analyzed in silica as the molecular interaction energy values. In this model system, retention time may correspond with the molecular interaction as described for retention on the methylsilicone phase. The smallest MIPS was obtained for PAHs, and the values... 

Migration time in electrophoresis is analogous to retention time in chromatography. 

No matter how it is defined, measured, or calculated, the polarity of molecules correlates with macroscopic properties such as density, miscibility/solubility, boiling point, melting point, critical point, retention time in chromatography, dilation capacity, and viscosity. 

These techniques when coupled with detectors, the most popular being the UV-Vis detector for HPLC, may detect a separated compound, by matching the retention time to that of a known standard compound and pattern of UV-Vis scan. In addition to univariate identification, e.g., retention time in chromatography, and wavelength/frequency in spectrometry, the use of mass spectrometry is an excellent tool to define the chemical identification. 

Gas Chromatography (gc). A principal advantage of gas chromatography has been the faciUty with which it can be combined with mass spectrometry for amino acid identification and confirmation of purity. The gc-mass spectrometry combination offers the advantage of obtaining stmctural information rather than the identification by retention time in hplc. 

Guo, D, Mant, C. T., Taneja, A. K, Parker, J. M. R., and Hodges, R. S., Prediction of peptide retention times in reversed-phase high-performance liquid chromatography. I. Determination of retention coefficients of amino acid residues of model synthetic peptides, /. Chromatogr., 359, 499, 1986. 

Davis, J.M. (2004). Assessment by Monte Carlo simulation of thermodynamic correlation of retention times in dual-column temperature programmed comprehensive two-dimensional gas chromatography. J. Sep. Sci. 27, 417. 

Photochemistry of Model Compounds. Preliminary photochemical studies have been carried out on l,3-diphenoxy-2-propanol (3)8 as a model compound for bisphenol A-epichloro-hydrin condensates 1. The utilization of 3 as a model compound for thermal degradation of 1 has been reported. Irradiation (254 nm) of 3 in acetonitrile (N2 purge) provides two major volatile products, which have been identified as phenol and phenoxyacetone (4), by comparison of retention times (gas chromatography) with known samples. A possible mechanism for... 

Hanai, T., Tran, C., Hubert, J. (1981) An approach to the prediction of retention times in liquid chromatography../. High Resolution Chromatography Chromatography Communication (J. HRC CC) 4, 454—460. 

Urushigawa Y, Yonezawa Y. 1979. Chemico-biological interactions in biological purification systems VI. Relation between biodegradation rate constants of di-n-alkyl phthalate esters and their retention times in reverse phase partition chromatography. Chemosphere 5 317-320. 

PEPPERMINT PHENOLIC COMPOUNDS SEPARATED BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY (RT1 AND RT2 = RETENTION TIMES IN MIN MEASURED IN GRADIENTS 1 AND 2)... 

HPLC retention times Partition coefficients can also be derived from retention times in high-pressure liquid chromatography (HPLC) analyses This approach provides some experimental advantages that simplify the analytical procedures and allow the handling of mixtures... 

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. 

The elution order of phthalic esters is related to the carbon chain length. The longer the chain length, the shorter the retention time in normal-phase liquid chromatography, and the elution order is reversed in reversed-phase liquid... 

Various methods have been employed for the prediction of retention times in reversed-phase liquid chromatography. 

A quantitative analysis of the structure-retention relationship can be derived by using the relative solubility of solutes in water. One parameter is the partition coefficient, log P, of the analyte measured as the octanol-water partition distribution. In early work, reversed-phase liquid chromatography was used to measure log P values for drug design. Log P values were later used to predict the retention times in reversed-phase liquid chromatography.The calculation of the molecular properties can be performed with the aid of computational chemical calculations. In this chapter, examples of these quantitative structure-retention relationships are described. 

The prediction of retention times in a given eluent from log P has been proposed for aromatic hydrocarbons.19 The log A values of phenols21 and nitrogen-containing compounds22 were also related to their logP, and the calculated log P was used for the qualitative analysis of urinary aromatic acids, i.e. for the identification of metabolites in urine from the differences of log P in reversed-phase liquid chromatography.23,24... 

Figure 4.1 Correlation of predicted and observed retention times in reversed-phase chromatography. The predicted retention times for 58 peptides of 2 to 16 residues in length were obtained by summation of retention coefficients for each residue in the peptide. Retention coefficients were determined from the retention of model synthetic peptides with the structure Ac-Gly-XX-(Leu)3-(Lys)2-amide, where X was substituted by the 20 protein amino acids. (Reproduced from D. Guo, C.T. Mant, A.K. Taneja, and R.S. Hodges, J. Chromatogr., 359 519 [1986]. With permission from Elsevier Science.)...

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