V.D.4 Sensitivity
Because it is possible to use well established rotational spectroscopy theory to calculate absolute absorption as a function of concentration, it would be possible to establish the sensitivity of the sensor from these calculations and an engineering evaluation of the noise in the system. However, we chose to establish the sensitivity of the system by actual measurement of a dilute sample. Since very dilute samples are difficult to prepare and transport, we chose to look at the deuterium isotope CH2DCN so that we could take advantage of the isotopic dilution of deuterium.
Figure V.D.4-1
Figure V.D.4-1 shows an observation of this species at a pressure of 69 ppt, with 1 second/point integration. Analysis of the S/N and number of signal channels establish its sensitivity at 2 ppt.