Software-Based Method to Flag Water Samples Contaminated with Trace Organics Such as Methanol and Methane

The Picarro L2120-i is a high-performance stable isotope analyzer for liquid and vapor water samples. The L2120-i analyzer utilizes a time-based optical measurement technique called Cavity Ring-Down Spectroscopy (CRDS). With this technique, the analyzer simultaneously measures values for δ¹⁸O and δD from optical spectra of specific stable isotopologues of water (H₂¹⁶O, H₂¹⁸O, and HDO). A typical optical spectrum is shown in the figure to the left. CRDS quantifies the optical absorption by measuring the rate of decay (the ring-down) of laser light in a cavity containing a gaseous sample. Increased sample concentration leads to faster decay mechanisms (via molecular rotation & vibration) and a faster ring-down time. The laser is tuned across the spectrum.At each key spectral point a ring-down curve is collected. The full range of ring-downs are then processed into a spectral image. The laser wavelength is controlled using a patented wavelength monitor. This level of control results in incredibly stable spectra as well as highly quantitative concentration and isotope analyses.