FLIIMP - a free, open source software for the processing, calibration and reporting of liquid water isotope measurements on cavity-ring down spectrometers

Precise and accurate measurements of the stable isotope composition of water with cavity ring down laser spectrometers require post-processing and calibration of raw analytical signals that involves a number of critical procedures to counteract instrumental drift, inter-sample memory effects, and the quantification of total uncertainty. Due to advent of off-the-shelf water isotope analyzers, there is an increased demand from a variety of new, often smaller labs to obtain guidance and assistance when performing such tasks.Here we present a new, lightweight, free software tool for the post-processing and calibration of water isotope data files from Picarro-brand cavity ring-down spectrometers. It is developed at the Facility for Advanced Isotopic Research and Monitoring of Weather, Climate and Biogeochemical Cycling (FARLAB) at the University of Bergen. FLIIMP1 (FARLAB liquid water isotope measurement processor) is written in MATLAB, but also exists as downloadable precompiled code and runs on Windows, MacOS and Linux. In its current version 2.1, FLIIMP facilitates sample processing by a graphical user interface that guides the user along the processing steps from corrections for memory effects, drift, and mixing ratio to calibration. FLIIMP provides detailed memory correction procedures, creates calibration reports and data files, and includes tools to monitor long-term measurement system behavior. Being an open-source software for the major operating systems, users can adapt FLIIMP to their laboratory environment, and the community can contribute to the software development. We hope that adoption of FLIIMP at other laboratories will lead to its further development into a mature set of calibration and correction routines for consistent, accurate, well-documented measurements of the stable isotope composition in liquid water samples.   1 Sodemann, H, Mørkved, PT, and Wahl, S. (2023) FLIIMP - a community software for the processing, calibration, and reporting of liquid water isotope measurements on cavity-ring down spectrometers. Methods X 11:2023 DOI:https://doi.org/10.1016/j.mex.2023.102297