Quantitative structure-retention chromatography data

A computer-assisted system for predicting retention of aromatic compounds has been investigated in reversed-phase liquid chromatography. The basic retention descriptions have been derived from the studies on quantitative structure-retention relationships. The system was constructed on a 16-bit microcomputer and then evaluated by comparing the retention data between measured and predicted values. The excellent agreement between both values were observed on an octadecyl-silioa stationsu y phase with acetonitrile and methanol aqueous mobile phase systems. This system has been modified to give us the information for optimal separation conditions in reversed-phase separation mode. The approach could also work well for any other reveraed— phase stationsury phases such as octyl, phenyl and ethyl silicas. 

Many attempts have been made to detemiine by other means different to the classical shake-flask method, which include countercurrent chromatography [3], and Reversed-Ph e Liquid Chromatography (RPLC) with C8, Cl8, 1-octanol coated Cl8 and phenyl stationary plmses [4], The establishment of a correlation between retention data in RPLC and log P assumes that die extent of chromatographic retention reflects the hydrophobicity of a solute. This approach is known as quantitative structure-retention relationships (QSRR) [5]. Chromatographic techniques offer a number of advantages over the static method. A great amount of relatively precise and reproducible data can be readily obtained, and the determinations are rapid and easy to be automated. Only a very small amount of sample is required, a wide dynamic range may exist and the impurities present in the sample can be simultaneously separated. 

Gough and Baker studied a number of conventional and modified stationary phases in order to find the best one for quantitative gas chromatography of heroin and structurally related compounds. Silanized 0V-210 was found to be the most suitable for the separation of heroin, codeine, acetylcodeine, morphine and 6-0-monoacetylmorphine. It gave the best reproducibility of retention times and less losses of the compounds by adsorption. For quantitative analysis 2.8 m by 4 mm I.D. glass columns and Diatomite CLQ, 80-100 mesh, as solid support were used at a column temperature of 225°C. Despite the fact that some of the compounds, particularly morphine, suffered adsorption losses during gas chromatography, these losses were reproducible, and satisfactory quantitative data could be obtained, as shown in Table 14.19. 

The simplest model phase in reversed-phase liquid chromatography (see Section 6.5) was not satisfactory for the quantitative analysis of the retention behavior of benzoic acid derivatives in silica. Therefore, several model phases were constructed and the energy values of their optimized structures were calculated using the MM2 program. The chromatographic retention data from ref. are listed in Table 6.8. 

Gas chromatography (GG-FID and GC-MS) can be used for both qualitative and quantitative analyses. Complete identification can be effected if GC retention data and mass spectral data are together taken into consideration. GC-FID identification is based on the comparison of retention times of analytes and authentic standards determined under identical GC conditions or by their co-chromatography. Unfortunately, standards of cuticular wax constituents are rarely commercially available. Some standards may be produced in the laboratory from pure components or natural extracts. For example, the carbon number in the analyses of wax esters can be assigned by comparison of their retention times with that of a synthetic wax ester of known structure (Evershed, 1992a). Beeswax is well-characterized so it can be used as a standard mixture. In beeswax wax esters, the predominant fatty acid moiety is hexadecanoic acid and the chain lengths of the alcohol moieties range from C26 to C36. 

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