The isotopic composition provides information about the origin of the species. Additionally, the physical processes behind the isotopic fractionation can be studied through precise isotopic ratio determination. Complex human physiology is not an exception and isotopic fractionation provides signatures of diseases, medical conditions and changes in various body functions. Modern optical techniques, such as multipass tuneable diode laser absorption spectroscopy (TDLAS), allow for sensitive, compact, and real-time instruments deployable in hospital environment, even as a bed-side units.
Most abundant isotopologues of carbon dioxide (CO2) are the main (16O12C16O), 13C (16O13C16O), and 18O (16O12C18O) having natural abundance of 98 %, 1 %, and 0.3 %, respectively. Relative changes of the exhaled CO2 isotopic ratios, either artificially induced by isotopic labelling or naturally varied by disease-originated changes in body physiology, provide a non-invasive fingerprint to number of medical conditions. Isotope-selective breath analysis has been previously applied to gastric, pancreatic, liver, and colon disease diagnostics. Recently stable isotopes of exhaled CO2 have shown great potential in early detection of sepsis, diagnostics of pre-diabetes and type-2 diabetes. However, to fully exploit the novel diagnostics, both ratios 13C and 18O and continuous monitoring are a prerequisite. Currently there are no commercial instruments capable of fulfilling these needs.
Researchers from Environmental metrology group of MIKES Metrology have been developing atmospheric CO2 isotope analysers based on mid-IR multipass TDLAS for years. It was not until merger of VTT and MIKES at the beginning of 2015 that provided the necessary VTT internal collaboration and expertise in miniaturisation to develop a compact breath CO2 isotope analyser capable of determining 13C and 18O ratios in real-time.
The developed instrument is very compact (28 × 20 × 12 cm3), has embedded gas handling and electronics. The optical multipass cell has amongst the smallest sample volume – to – optical path ratios ever reported with below 45 µl effective sample volume. The instrument is capable of determining the isotopic ratios in real time with fast exchange times, thus allowing for continuous monitoring, and determining the isotopic ratios and isotope fractionation throughout the breath cycle.