Rapid sequential heart-cut multidimensional gas chromatographic analysis

Abstract

A method is described which allows the sequential fast analysis of heart-cuts taken during the first column elution of an essential oil sample in a multidimensional gas chromatography experiment. In this investigation, a relatively short, narrow bore capillary column is used in the second dimension, with fast cryogenic modulation permitting rapid delivery of cryofocussed heart-cuts into the second column of the multidimensional arrangement. In this implementation, the total analysis time on the second column is of the order of 30 s, which is less than the duration of the sampled heart-cuts (1 min), with peak theoretical efficiencies of about 7000 m −1. Thus, the method should allow on-line heart-cutting of as many discrete heart-cuts as one may require from the first dimension chromatogram, and so two-dimensional separation can be achieved for almost the whole sample in one single analysis without the need for repeat injections or cycling of the oven temperature. The method is demonstrated by the transfer and rapid re-injection of 1 min heart-cuts taken from an initial separation stage of peppermint essential oil. The cryofocussing and fast analysis step is shown to increase signal response by up to 40-fold. Total peak capacity in the described system is measured to be of the order of 1800, with capacities of about 20–30 for each 30 s second dimension analysis. By increasing the frequency of sampling to remove excessive (unused) time to develop the 2 D separation, it should be possible to achieve peak capacities of 5000 or more baseline resolved peaks.