Multivariate determination of [sup.13]C[O.sub.2]/[sup.12]C[O.sub.2] ratios in exhaled mouse breath with mid-infrared hollow waveguide gas sensors

The [sup.12]C[O.sub.2]/[sup.13]C[O.sub.2] isotope ratio is a well-known marker in breath for a variety of biochemical processes and enables monitoring, e.g., of the glucose metabolism during sepsis. Using animal models--here, at a mouse intensive care unit--the simultaneous determination of [sup.12]C[O.sub.2] and [sup.13]C[O.sub.2] within small volumes of mouse breath was enabled by coupling a novel low-volume hollow waveguide gas cell to a compact Fourier transform infrared spectrometer combined with multivariate data evaluation based on partial least squares regression along with optimized data preprocessing routines. Keywords FT-IR spectroscopy * Mid-infrared gas sensor * Hollow waveguide * Mouse sepsis model * Glucose/insulin metabolism disorder * [sup.13]C[O.sub.2] enrichment TTR Multivariate data analysis