Picarro 2120i
The Picarro analyzer uses time-dependent optical absorption spectroscopy of the target gases to determine concentration. It is based on wavelength-scanned cavity ring-down spectroscopy (WS-CRDS), a technology in which light recirculates many times through the sample, creating a very long effective optical path in which the light interacts with the sample, allowing for excellent detection sensitivity in a compact instrument.
Although not a mass spectrometer, infrared spectroscopy allows for the precise determination of light isotopes since almost all small molecules in the gas phase (e.g., CO2, H2O, H2S, NH3) have a unique near-infrared absorption spectrum. At subatmospheric pressure, it consists of a series of sharp, narrow, and well-resolved lines, each at a characteristic wavelength. Because these lines are well-spaced and their wavelength is well-known, the concentration of any species can be determined by measuring the strength of this absorption, i.e., the height of a specific absorption peak. In conventional infrared spectrometers, trace gases provide too little absorption to measure, which typically limits sensitivity to parts per million at best. With CRDS (Cavity Ring-Down Spectroscopy), this sensitivity limitation is avoided by using an effective optical path of many kilometers.
In the instrument, a liquid water sample is converted to a vapor phase in a high-temperature flash process. The vapor is then sent into the laser cavity for analysis. It allows gases to be monitored in seconds or less at the parts per billion level, and some gases at the parts per billion level.
Instrumental Facilities
The Picarro L2120i Isotopic Analyzer consists of a spectrometer, a sample chamber, and an integrated computer. A single unit controls the operation of the system and converts spectroscopic measurements into gas concentration data.
Applications
The analyzer is ideal for applications as diverse as climate studies, paleoclimate reconstructions, isotopes in precipitation, groundwater and surface water tracers, aquifer dynamics, bird migration mapping, analytical hydrology testing, and metabolic activity.
Sample requirements
- Maximum reliability of the autoinjector/vaporizer/analyzer assembly is ensured by removing particles, suspended solids, or other material from it. This can be achieved by passing the water samples through a particle filter (2-10 microns) before filling the sample paths.
- Samples containing dissolved ionic solids (salts) can be injected into the vaporizer as normal.
- Care must be taken when analyzing water samples containing organic compounds. Certain compounds (usually those of lower molecular weight) interfere with the spectroscopic measurement and affect the measured isotopic ratios. Many organic compounds can be removed by pretreatment of the sample, however, some types of pretreatment cause isotopic fractionation, so control experiments should be performed with the specific method chosen.