F. Weeke

Sampling techniques in capillary gas chromatography

Abstract Four different sampling methods for capillary gas chromatography, including split and splitless sampling, have been investigated with respect to precise and accurate qualitative and quantitative analysis. A new method of direct sampling for capillary columns is presented and compared with the known techniques with respect to resolution, reproducibility of retention, decomposition of sensitive sample components and discrimination of high-boiling components in quantitative analysis. Multi-dimensional arrangements using capillary columns for the “main” separation as the most flexible and efficient sampling devices are discussed. If by selective sampling in such set-ups only a partial analysis of those components is achieved, which are of real interest in a particular analytical problem, analysis time can be saved and the performance of the separation can be improved.

Multidimensional gas chromatography (MDC) in capillary columns using double oven instruments and a newly designed coupling piece for monitoring detection after pre-separation

SummaryEluate transfer between coupled columns by flow switching, backflushing of the pre-column, and other procedures of multidimensional chromatography (MDC) are invaluable techniques to save analysis time to improve resolution, to gain more and better chromatographic information and to prevent contamination of main (high resolution) column and detectors such as ECD and TID. It is of advantage to maintain the coupled columns at different temperatures. Double oven instruments should therefore be used with advantage in multidimensional gas chromatography (MDGC). Flow switching can be done in between and after the system of coupled columns. Also, reactors can be coupled to high resolution columns with advantage [5].

New developments and experiences with glass capillary column production and sampling techniques

SummaryAn introductory discussion is given on the manufacture of glass capillary columns, including details of the methods of column testing and of the properties of the inner surfaces of glass capillaries. As a result a simple method for the testing of various kinds of support surfaces is presented which allows stepwise control of the column making procedure. A new kind of pretreatment of soft glass surfaces with HCl and HF at 450°C is described which allows the production of non-polar columns with much improved tailing behaviour for strongly polar solutes. Concerning capillary column sampling a new technique of “direct” sampling without previous vaporisation of the sample outside the column is presented together with a double column system for “selective” sampling of complex mixtures.

On-line hydrogenation of unsaturated and saturated sample components in capillary reactors coupled to either inlet or outlet of capillary columns

A special coupling piece for the connection of fused silica or softglass capillary hydrogenation reactors with capillary separation columns using a double oven GC instrument is described. The temperatures of reactor and column can be independently adjusted thereby. This system for on-line hydrogenation also includes two injectors to be used either before the reactor or before the column and a device for trapping the hydrogenated material inside the column. Platinum and palladium catalysts of various activities were investigated, aromatic hydrocarbons and compounds containing polar functional groups can be hydrogenated easily.

Radiation chemistry of ethers. Part VI. Photolysis at 254 nm of the diethyl ether–oxygen charge transfer complex

Oxygen-saturated diethyl ether exhibits a charge transfer absorption band (λmax. 215 nm) with considerable absorption at 254 nm. Photolysis was carried out with a low pressure mercury arc. Photolysis of products was avoided by keeping conversion low, and chain reactions were minimized by working at –30°. The major products(quantum yields) were: H2O2(0·24), 1-ethoxyethyl hydroperoxide (0·04), ethyl acetate (0·26), acetaldehyde (0·18), ethanol (0·18), ethyl formate (0·04), methanol (0·035), formaldehyde (0·005), and ethyl vinyl ether (0·013). A satisfactory material balance was obtained. The products formed are consistent with a primary photoprocess involving transfer of an electron to the O2 to give O2–. Further, deprotonation of the ether radical cation in the presence of O2 leads to the 1-ethoxyethylperoxyl radical. With the exception of 1-ethoxyethyl hydroperoxide all major products are believed to arise from disproportionation reactions of these two radicals.

Interactive processing of chromatograms with display terminals

SummaryThe use of display terminals for the interactive processing of gas chromatographic data in the Mülheim Computer System is described and discussed.The stepwise and flexible evaluation of chromatograms as they are especially met in research and development laboratories is facilitated considerably.1.The correlation of analogue and digital presentations of chromatographic results can easily be performed by the operator at the display screen via peak numbers or retention parameters.2.Chromatograms can be investigated in more detail by fast plotting of any desired section of the total chromatogram in any desired scales of coordinates.3.The fit of software constructed baselines to the chromatograms can be studied, baseline and solvent peak subtraction methods can be performed easily.