No abstract

After a successful off-line feasibility study, the automation of comprehensively coupled liquid chromatography and gas chromatography (LC x GC) has been studied. Important aspects to consider when developing automated LG x GC include the relative speeds of the two dimensions, the compatibility of the LC eluent (type and flow rate) with the GC dimension, and the column loadabilities. Because the GC separation is relatively slow, the LC instrument has to be operated in the stop-flow mode. Two interfaces for transferring large numbers of subsequent LC fractions to the GC were constructed: one based on a six-port switching valve, and one which uses a dual side-port syringe. Both interfaces were found to perform fully acceptably. The actual transfer of the LC fraction to the GC was realised using a standard split injector to vaporise the compounds and LC eluent. Gas phase splitting was applied to match LC mass load and GC column loadability. The standard deviations of the peak areas obtained in this way were better than 7% (n = 6). The reliability of the system was demonstrated by the problem-free analysis of large series of oil and fat samples, with the focus on both intact triglycerides and their fatty acid methyl esters (FAMEs). Finally, the hyphenation of the automated LC x GC system to a sensitive and rapid-scanning time-of-flight mass spectrometer was realised. By using LC x GC-ToF MS, the information density of the chromatograms could be improved even further, which allowed easy identification of individual compounds as well as compound groups.

In this study the possibility of operating a wide‐bore column with an inner diameter of 530 μm at vacuum conditions was investigated as a route towards fast gas chromatography. High analysis speeds can be obtained as a result of the sub‐ambient pressure conditions present in the column, and the consequently high diffusion coefficient of the solute in the mobile phase. The advantage of using a wide‐bore column is the high sample capacity. To enable vacuum operation through coupling a wide‐bore column to a mass spectrometer, three types of restricting the column flow were investigated. The first method uses a narrow bore pre‐column (60 cm length×100 μm i.d.), the second method relies on the use of a tapered on column supercritical fluid chromatography restrictor (SFC‐restriction), whereas the third method makes use of a micro‐injection valve. It was concluded that the best performance was obtained using the narrow‐bore column restriction and the SFC‐type restriction. Analysis examples in the seconds‐ and minutes‐range are shown, with peak‐widths ranging from 0.1 to 2 seconds at half height. It was concluded that with a film‐thickness above 1.5 μm, the advantage of the increase in analysis‐speed due to low pressures is nullified due to retention time increase on a thick film column. © 2001 John Wiley & Sons, Inc. J Micro Sep 12: 613–622, 2000

One possible way to speed up a gas chromatographic analysis is the application of fast temperature programming by using resistive heating techniques. With this heating technique programming rates up to 20° per second can be reached. A relative standard deviation of retention times better than 0.2% is obtained. Using fast temperature programming the analysis‐times of a mineral oil sample, an industrial oligomer sample, and toxic compounds in diesel fuel have been reduced 5 to 20 times, compared to a standard temperature programmed analysis. In most cases resistive heating cannot be applied to reduce the analysis time of a complex sample. The use of fast temperature programming is preferable to the use of short columns and columns operated at above‐optimum carrier gas velocities.

Abstract:In the present work two new approaches to fast gas chromatography Ž . GC analysis are evaluated and compared to narrow-bore and conventional-bore columns. The first method uses packed capillary columns. These columns, 0.32 mm in diameter, are packed with spherical octadecylsilica particles with a diameter of 15 m. A second type of column studied is the multicapillary column. In this column, an excellent sample capacity and a high speed of analysis are combined. The performance of all column types is considered. Given are Hru curves and two practical applications are described. Finally, micropacked capillary columns, multicapillary columns, and narrow-bore columns are compared to conventional standard-bore columns. This comparison includes the main parameters of interest such as sample capacity, detection limit, analysis time, pressure drop, and maximum obtainable plate number. Packed columns and multicapillary columns are very suitable for fast separations of relatively simple samples. ᮊ