2. Molecular separators

These devices, designed in the 1960s, were instrumental in the development of GC-MS [17] . They are mounted between the column and the ionization chamber. Their purpose is to increase the concentration of solute relative to that of the carrier gas, and to reduce the total flow rate of gas entering the MS. Today, they are often no longer necessary, and are no longer included in common versions of commercial GC-MS instruments. Occasionally, they are required only for specific applications or experimental set-ups. Their ideal qualities are as follows:

• fully and quantitatively transmit the constituents to be analyzed. In particular, do not adsorb small quantities of products onto the walls, as this reduces the sensitivity of the analysis in progress, and may...