Retention time thin layer chromatography

An aliquot may be removed at this stage and analyzed by either gas chromatography or thin-layer chromatography to ensure that the reaction is complete. Benzobarrelene has a retention time of ca. 5 minutes in a gas chromatographic analysis under the conditions stated in Note 6, but with a column temperature of 104°. The completion of the reaction is also indicated by a purple coloration of the precipitated sodium chloride. 

Reference substances can be used for confirmation of identity of the substance by, e.g. infrared spectrophotometry where the spectrum of the substance to be examined must be concordant with the spectrum of the GRS, or by thin layer chromatography where the migration and appearance of the spots of both the substance to be examined and the GRS are the same, or by liquid chromatography where the retention time of both the substance to be examined and the GRS are the same. 

Thin Layer Chromatography is a valuable analytical technique. It is cheap, fast and simple. Optimization of TLC is therefore of the highest importance and subject of many studies. A review of optimization methods is given by Nurok [1]. The aim of such optimizations is to find a mobile phase composition at which a good separation of all solutes is possible. However, not only the mobile phase has influence on the retention time, but also the temperature and the relative humidity. 

Derivative formation prior to chromatographic analysis has been used successfully. An unidentified component of urine was found which had a retention time very close to that of pregnanediol and which could not be separated from it by thin layer chromatography. The trimethylsilyl ether derivatives and the tri-fluoroacetate derivatives of the two compounds would not provide resolution only the acetate derivatives could be separated. 

Chromatographic Parameter-Relationships Correlations between Kov/ and various chromatographic parameters (CGP), such as HPLC retention time and thin-layer chromatography (TLC) capacity factors, allow the experimental estimation of Kow [19]. Usually, the CGP-A ow correlation is evaluated for a calibration set of compounds with accurately known K0w values. The Kow of a new compound can then be estimated by determining its CGP under the same experimental conditions as those used for the calibration set. 

Confirmation of the identity of the gas chromatographic components has been accomplished by thin layer chromatography, relative retention times on different gas chromatographic columns, "p" values, and most recently by mass spectrometry. Dicofol can be separated from its phenone by using a Florisil column (17) or TLC. Dehydrochlorination of dicofol to DBP can be used as a confirmatory test for the parent compound. Gajan and Lisk (23) used cathode ray polarography to analyze vegetables for dicofol residues. 

Retention is measiued as either the retention time (Rt) or retention factor (Rf). Rt is used in high-performance liquid chromatography (HPLC) and gas chromatography, whereas Rf is used in paper and thin-layer chromatography. Rf is calculated using the following formula ... 

NMR spectra, retention time in HPLC or thin layer chromatography (TLC), and can behave differently in chemical reactions with achiral reagents. The commercial glycopyrrolate product contains only the threo isomers iS,R) (lO)and (i2,S)-(ll)-... 

Thus, techniques used to give further evidence for the identity of a pesticide residue should be inteUigently chosen. If evidence from infrared or mass spectroscopy is not available, then adequate criteria of identification would be one or two GLC retention times, plus an Rp value from paper or thin-layer chromatography or an extraction p-value. Alternatively, one or two GLC retention times plus a GLC retention time of a derivative formed by chemical reaction would be a basis for confidence. 

Analytical thin-layer chromatography on silica gel indicated some separation with n-hexane or with n-pentane as eluents, but not with cyclohexane. Analytical HPLC performed with hexanes (S-gm Econosphere silica. Alltech/Appiied Science) gave a satisfactory separation (retention times 6.64 and 6.93 min for 50 and C70, respectively, at a flo.w rate of 0.5 mL/mln detector wavelength, 256 nm), indicating the content of C70 to be approximately 15% for the Los Angeles samples. Two other minor peaks, possibly other unidentified C species, were observed (retention times 5.86 and 8.31 min), but they constituted less than 1.5% of the total mass. 

The elution of a strong solvent shock of finite amplitude causes the effect known, in thin-layer chromatography, as demixion. The solvent front is eluted before the limit retention time of the strong solvent at infinite dilution and it is extremely sharp. The components eluted before the solvent front are eluted im-der isocratic conditions in the pure weak solvent. The sudden breakthrough of the strong solvent constitutes an extremely steep gradient of the strong solvent inside the column. It is accompanied with the very rapid elution of numerous components that are poorly or not resolved. Such a situation must be avoided in analytical applications. 

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