HIGH-SPEED GAS-CHROMATOGRAPHIC ANALYSIS OF A SIMULATED PROCESS STREAM USING ON-COLUMN THERMAL-DESORPTION MODULATION FOR SAMPLE PRECONCENTRATION AND INTRODUCTION

On-column thermal desorption modulation is an effective sample input technique for narrow-bore gas chromatography. This technique accepts a continuously flowing sample stream and so is readily adapted to process stream monitoring. A thermal desorption modulator fabricated on the column but operated at a lower temperature than the column functions as a sample preconcentration and introduction device. The modulator portion of the column is kept at room temperature to increase its sample hold-up capacity. A portion of the sample stream to be monitored flows continuously into the modulator and through it in to the following column. The modulator has low thermal mass and is rapidly heated by passing an electrical current through a thin electrically conductive film applied to the outside of the column. Any sample retained within the modulator while at room temperature is released by a thermal pulse and carried on into the column as a concentration pulse analogous to a sharp injection. The narrow-bore column is highly efficient and generates chromatograms within a period as short as four seconds. During this time, the modulator refills and is ready to generate another pulse. Thus, a series of high-speed chromatograms monitoring the process stream is obtained. © 1990 Oxford University Press.