However, we observed the presence of residual BTEX in the blank, above all toluene. This could be due to residual compounds in the online system or due to small quantities of BTEX in the nitrogen cylinder. These values were taken into account in the calibration curves results. Analytical blank for the 2-stage-desorb mode was realized with conditioned CarbopackTMB tubes spiked with 20 µL of methanol for liquid spiking, and with a nitrogen stream for gas spiking