Progress and prospects in on-line-process gas and liquid chromatography

The present status of both process gas (PGC) and liquid (PLC) chromatographs is examined with regard to the main criteria that any process analyser should fulfil: reliability, credibility, fast response and low maintenance. Despite considerable improvements in the construction of these instruments, owing to the materials used, progress in technology and microelectronics and the advent of microprocessors, their reliability is still a matter of great concern.The deferred standard concept may offer a solution for these problems. Progress is also made by the introduction of fused-silica capillary columns in PGC, which allow a better resolution and a greater speed of analysis. However, this technology requires a redesign of PGCs.Further, particularly for PLC, a new approach based on the concept of instability instead of stability of the main parameters is proposed. This approach leads to a simpler, more reliable and less expensive PLC. The consequence is some radical changes in the design and functions of both the analytical and control units of the chromatograph. The analytical unit is plugged into the chemical reactor and is not temperature controlled. The control unit, incorporating a microcomputer and dedicated software, is able to characterize the peaks despite their fluctuating retention times, to readjust the time functions of the analytical sequence and to validate the detector response in the case of fluctuations of temperature or mobile phase flow-rate. This approach is useful for the implementation of temperature programming and, according to the validation function of the deferred standard, to allow the use of selective but unstable detectors in PGC.Simpler in hardware, PGCs and PLCs could become “intelligent apparatus” capable of new qualitative and quantitative tasks at a more competitive cost.