We are spiking our charcoal thermal desorption tubes with a standard of methyl methacrylate. However, we are seeing many other peaks in addition to the methyl methacrylate peak that elute later. These peaks are not present in the background tube, and their intensity is random (meaning their intensity is not proportional to the amount of MMA on the tube). Does anyone have a hypothesis as to what sort of chemistry might be happening in the tube?