Many samples have moisture contamination which will cause the presence of water vapor in the detector's sample chamber and the appearance of water vapor absorbance bands in spectra. A desiccant for water vapor reduction can be put into a large stainless steel cup as shown in Fig. 7 which is placed in the sample holder underneath the sample cup. Fig. 8 shows a large cup with polymer pellets which is placed above the desiccant cup. As mentioned in Section III. A., magnesium perchlorate is a very effective desiccant. Water vapor can be eliminated with the combination of purging the detector with dry helium, allowing adequate time for the desiccant to work, and minimizing the amount of sample in the cup. Use only enough material to cover the bottom of a small cup if water vapor is a problem. When not in use, desiccant should never be left in cups open to the room's atmosphere because moisture from the room will collect in the desiccant and form a corrosive liquid.

Fig. 7. Background: Large stainless steel cup loaded with desiccant resting on a cup fixture. Foreground: Desiccant cup has been placed underneath a slotted brass spacer insert in the sample holder. Sample cups are placed on the spacer. See Fig. 8.