The validity and reliability of a novel isotope ratio infrared spectrometer to quantify 13C enrichment of expired breath samples in exercise.

The traditional method to measure 13CO2 enrichment in breath involves isotope ratio mass spectrometry (IRMS), which has several limitations such as cost, extensive training, and large space requirements. Here, we present the validity and reliability data of an isotope ratio infrared spectrometer (IRIS)-based method developed to combat these limitations. Eight healthy male runners performed 105 min of continuous running on a motorized treadmill while ingesting various carbohydrate beverages enriched with 13C and expired breath samples were obtained every 15 min in triplicates. A total of 213 breath samples were analyzed using both methods, whereas 212 samples were repeated using IRIS to determine test-retest reliability. Bland-Altman analysis was performed to determine systematic and proportional bias, and intraclass correlation coefficient (ICC) and coefficient of variation (CV) to assess level of agreement and magnitude of error. The IRIS method demonstrated a small but significant systematic bias to overestimate δ13CO2 (0.18‰; P < 0.05) compared with IRMS, without any proportional bias or heteroscedasticity and a small CV (0.5%). There was a small systematic bias during the test-retest of the IRIS method (-0.07‰; P < 0.05), no proportional bias, an excellent ICC (1.00), and small CV (0.4%). The use of the Delta Ray IRIS to determine 13C enrichment in expired breath samples captured during exercise has excellent validity and reliability when compared with the gold standard IRMS.NEW & NOTEWORTHY The use of IRIS to determine 13C enrichment in expired breath samples captured during exercise to determine exogenous glucose oxidation during exercise has excellent validity and reliability when compared with the gold standard IRMS.

High-resolution isotopic monitoring of cave air CO2.

RATIONALE: CO2 is the main driver of many chemical processes in cave environments. Understanding CO2 fluxes in a given cave system through monitoring campaigns has become a standard procedure in a wide variety of fields such as paleoclimatology or show cave management. However, conventional methods lack the resolution of isotopic data to capture many transient processes occurring in caves. METHODS: A novel approach using isotope ratio infrared spectrometry (IRIS) to monitor cave air pCO2 , δ13 C and δ18 O values in situ was tested and compared with conventional monitoring methods (handheld pCO2 meter and discrete cave air samples for conventional isotope ratio mass spectrometry). This also involved the development of a field-deployable experimental setup to operate the equipment in rough cave environments. RESULTS: Comparison between data obtained by means of a Thermo Fisher Scientific Delta Ray IRIS instrument shows overall good agreement with conventional monitoring methods in terms of pCO2 and δ13 C values. In addition, IRIS allows the δ18 O values of cave air CO2 to be measured. CONCLUSIONS: IRIS allows identification and tracking of processes at various timescales ranging from transient visitor impact on the cave atmosphere to seasonal trends in cave ventilation. However, the need for an uninterrupted power supply (110/220 V AC) and the relatively large dimensions of the equipment (698 × 1092 × 704 mm, 80 kg) limit the number of caves where deployment of the instrument is feasible. Copyright © 2017 John Wiley & Sons, Ltd.

Note on the spring region of Gacka River (Croatia).

We present the first results of a study of the Gacka River spring area, an important Croatian drinking water resource. Stable isotope data (obtained at the Stable Isotope Laboratory SILab in Rijeka) are used in combination with hydrological and meteorological data. The delta18O values give information on the mean catchment altitudes of the three main springs of Gacka River (Majerovo vrelo, Tonkovica vrelo and Pecina). Hydrological, meteorological and stable isotope data indicate good mixing of infiltrated and ground waters. The precipitation d-excess shows a seasonally varying influence of continental and maritime air masses.