Cavity ring-down spectroscopy (CRDS) is a reliable and stable analysis technique, and has been widely applied to the measurement of trace level gas species (e.g., moisture, ammonia, and formaldehyde). Generally speaking, performance of commercially-available CRDS is satisfactory. However, how to upgrade the performance of commercially-available CRDS by manufacturer-provided function is vital for customer to improve analysis capability. In our experience, we found that the reading of commercially-available CRDS usually evaluated from the ring-down time (Tau) under fixed laser temperature setting, although temperature/wavelength drift is expected to occur during measurement. Temperature/wavelength drift is especially critical for stability of CRDS operated under low pressure, as spectrum of low pressure condition is typically sharper because of less collisional broadening effect. Herein, we show delicately the optimization of stability of commercially-available CRDS by continuous spectrum scan function through Labview-based program. As demonstrations, a CRDS for moisture and a CRDS for formaldehyde were tested. In our test, the CRDS analyzes the same concentration of sample gas under normal measuring mode and continuous spectrum scan mode in two different rounds, and results are compared. The stable moisture and formaldehyde gas were supplied by simplified trace-moisture generator (STMG) and magnetic suspension balance/permeation-tube humidity generator, respectively. Our results indicate that the temperature/wavelength drift indeed occur during long-term test, and this could be efficiently solved by continuous spectrum scan, so that the CRDS reading efficiently improved for more than two times (standard deviation 31 ppb vs. 77 ppb, under 5300 ppb formaldehyde) through continuous spectrum scan mode. We anticipate that the continuous spectrum scan mode could be a potentially optional function for commercially-available CRDS, especially for customers who need long-tern but not real-time analysis.
– I am interested in the development of standards of reactive gas mixtures (e.g., formaldehyde, moisture).
– I am interested in the development of trace level gas analyzers.
– I am interested in the development of method for laboratory evaluation of air quality sensors.
Magnetic suspension balance, Dynamic gas preparation method, Nonlinear microscopy, Confocal microscopy, Raman microspectroscopy