The Picarro G2201-i is a high-precision isotopic analyzer that leverages patented Cavity Ring-Down Spectroscopy (CRDS) technology to simultaneously measure carbon isotope ratios (δ¹³C) of carbon dioxide (CO₂) and methane (CH₄). This instrument is crucial for researchers studying greenhouse gas dynamics, providing detailed isotopic signatures that help differentiate sources and sinks of these important atmospheric gases. It includes a small sample introduction module for analyzing discrete gas samples. This analyzer offers exceptional precision at a significantly lower operating cost compared to traditional Isotope Ratio Mass Spectrometry (IRMS) systems, requiring less calibration and maintenance. The G2201-i can operate in three distinct modes: CO₂-only, CH₄-only, or a combined CO₂/CH₄ mode. In the combined mode, measurements are interleaved every few seconds for a high sampling rate. Precision in combined mode is typically <0.16‰ for δ¹³C-CO₂ and <1.15‰ for δ¹³C-CH₄, with improved precision in single-molecule modes (<0.12‰ for δ¹³C-CO₂ and <0.8‰ for δ¹³C-CH₄). The CRDS technology provides an effective measurement path length of up to 20 kilometers within a compact, temperature- and pressure-controlled cavity, ensuring high linearity, precision, and accuracy over a wide dynamic range with minimal calibration. The Picarro G2201-i is widely applied in atmospheric science, agriculture and soil science, emission monitoring, ecology, food and beverage analysis, and petrochemical research. Its ability to track carbon movement from source to sink makes it invaluable for understanding global carbon cycles, assessing anthropogenic impacts, and monitoring natural emissions. The instrument is suitable for both laboratory applications and field-based monitoring, offering immediate results that can inform real-time research decisions. Key accessories and features include the Small Sample Introduction Module 2 (SSIM 2, A0314), which enables the analysis of discrete gas samples as small as 20 mL. Other available peripherals include a 16-Port Distribution Manifold (A0311) for sequential sampling from multiple sources and Closed System Measurement Packages (A0701/A0702) for recirculation experiments. The G2201-i is designed for ease of use, capable of operating for months without significant user interaction, and precisely measures CO₂, H₂O, and CH₄ concentrations, often eliminating the need for gas drying.