Picarro CRDS is a rugged, compact, and field-deployable system that measures concentration and isotope ratios. The four primary analytical measurements of the instrument are the concentration of 12CO2, 12CH4, 13C-CO2, and 13C-CH4 with a resolution in parts per billion. Picarro Analyzers use time-based, optical absorption spectroscopy of target gases to determine concentration. They are based on wavelength-scanned cavity ring-down spectroscopy WS−CRDS, a technology in which light re-circulates many times through the sample, creating a long effective path length for the light to interact with the sample, enabling detection sensitivity in a compact and rugged instrument. The samples used in these instruments could be gas, liquid or solid. The Picarro measures δ13C in CO2 and CH4 at the same time in atmospheric concentration or connected to a CO2 generation module for carbonates/DIC analysis.