High temperature diaphragm valve-based comprehensive two-dimensional gas chromatography

Abstract

A high-temperature diaphragm valve-based comprehensive two-dimensional gas chromatography (GC×GC) instrument is demonstrated which readily allows separations up to 325°C. Previously, diaphragm valve-based GC×GC was limited to 175°C if the valve was mounted in the oven, or limited to 265°C if the valve was faced mounted on the outside of the oven. A new diaphragm valve has been commercially developed, in which the temperature sensitive O-rings that previously limited the separation temperatures have been replaced with Kalrez O-rings, a perfluoroelastomer, allowing for significantly higher temperatures permitting a greater range of volatile and semi-volatile compounds to be readily separated. In the current investigation, a separation temperature up to 325°C is demonstrated with the valve mounted directly in the oven. Since the temperature limit for most commonly used GC columns is at or below 325°C, the scope of diaphragm valve-based GC×GC is now dramatically broadened to encompass a majority of all column stationary phase chemistries. A 44-component mixture of alkanes, alcohols, and polyaromatic hydrocarbons is used to study this new configuration whose boiling points range from 98°C (n-heptane) to 450°C (n-triacontane). For the test mixture using a modulation period PM of 1.0s, peak shapes on second dimension separations, 2D, are symmetric with average widths at base of 79.4ms, producing a 2D peak capacity of 2nc∼12. Based on the average peak width of 2.4s for the first dimension separation with a run time of 32.5min, the 1D peak capacity is 1nc∼800. Thus, the ideal two-dimensional peak capacity nc,2D is 9600. Little variation in within-analyte 2D peak width was observed with an average %RSD of less than 3.0%. Furthermore, retention time on 2D was very reproducible with an average %RSD less than 0.5%. Measured peak areas (sum of all 2D peaks for given analyte) had an average %RSD of 4.4%. The transfer fraction from 1D to 2D was experimentally determined to be ∼30%, while the detection sensitivity for valve-based GC×GC was ∼8 times higher than one dimensional GC due to zone compression. After a year of use with temperatures consistently up to 325°C, there has been no deterioration of the valve or its performance for GC×GC. Separations of vacuum pump oil and orange oil are also reported to demonstrate practical utility.