Standardized Sample Preparation for VOC Analysis

Sample preparation was performed according to our standard operating procedure, previously described by Rouvroye et al. [29 (link)]. In short, a calibrated scale (Mettler Toledo, AT 261 Delta Range, Columbus, OH, USA) was used to weigh approximately 500 mg of fecal and frozen urine sample. Subsequently, the sample was transferred to a glass vial (20 mL, Frickenhausen, Germany), which was restored in a −20 °C freezer [22 (link)]. The fecal and urine samples were sent to the BioMedical Sensors Lab, School of Engineering, University of Warwick (Coventry, UK) on dry ice (−80 °C) for VOC analyses.