How do you measure trace moisture in gases for semiconductor and specialty gas applications?

Trace moisture measurement (ppb-ppm) technologies: Chilled Mirror (measures dewpoint directly - accurate, requires clean sample), Cavity Ring-Down Spectroscopy (CRDS - ppb sensitivity, fast response), TDLAS (optical absorption - very specific, requires low-moisture measurement cells), and capacitance polymer sensors (good for process monitoring, less accurate at extreme trace levels). Applications: semiconductor UHP gases, specialty gases, and natural gas pipelines. Considerations: sample system is critical (all-metal, electropolished, purged construction to prevent moisture adsorption/desorption), very slow response at low levels due to surface effects, and calibration challenges (accurate moisture standards difficult at ppb levels). Background and blank correction essential.