Infrared spectroscopy and multivariate method to quantify methane in gas sample emitted by cows

The purpose of this work was to develop a new multivariate calibration method using partial least squares (PLS) regression to quantify methane (CH4) in samples of gases eructed by ruminants and exhaled together with the respiration of cows. Four Holstein cows were confined and received a diet of 18.7 kg of dry matter per day for 4 days. During this period, samples of the gas exhaled by these cows were collected. Gas sampling was performed using evacuated PVC canisters during a period of 24 h, and in this case, two gas samples were collected per animal as well as two samples of the background environment in which the animals were confined. In total, 40 samples were collected and submitted to analysis. Samples were analyzed by gas chromatography and then by infrared spectroscopy using a long optical path gas cell. The results of both analyses were used to develop the multivariate calibration model, PLS regression. The results show a high correlation between chromatography method and infrared analyses with values of determination coefficients greater than 0.96 and root mean square error (RMSE) values lower than 23.3 ppm.