Application of TDLS technology measuring moisture across a variety of background gases without recalibration - Expert Paper
Achieving accurate and repeatable low-level moisture analysis in the specialty gas industry while minimizing analysis instrument maintenance is a challenge many laboratory analysis equipment suppliers have tried to meet over years with a number of different technologies. It is now clear that Tunable Diode Laser Spectroscopy (TDLS) has emerged as the clear technology leader, however, this general technique is not standing still. Instruments utilizing various versions of this technique are now available on the market.
The latest generation of laboratory moisture analyzers, based on a technique known as Advanced-TDLS, are able to operate for a period of years in non-ideal environments without the need for re-calibration. They can yield moisture measurements with ppb sensitivity in a wide variety of single and multi-component gas mixtures. In common with all TDLS techniques, high performance measurements are enabled by virtue of the ultra narrow diode laser bandwidth, which in turn enables selection of a single fine-structure water absorption line. The Advanced-TDLS technique further utilizes additional information buried within the shape of the water IR absorption line which, after correction for absolute pressure, is subtly dependent on the chemical composition of the (host) gas or gas matrix under investigation.