Degas procedure

Gravimetric measurements require corrections to account for buoyancy effects while volumetric measurements must be corrected for the sample volume. It is often not realised that these corrections are equivalent. Helium is used to determine both corrections since it is assumed not to be adsorbed. The degas procedure for gravimetric instruments involves continuous monitoring of mass in relation to time, which allows outgas rate to be specified and the equilibrium state and any sample mass losses... 

Details of the accelerator, the procedure for irradiation, and the methods used to prepare and degas solutions, are described elsewhere... 

This procedure guarantees a reproducible preparation of your mobile phase and avoids problems associated with volume contraction. Always prepare a sufficient amount of mobile phase (approx. 1 1) and degas it. Degassing is possible with helium or the built-in degasser (see Tip No. 5). If you use buffers, you should filter them through a membrane. The eluent container should be well covered in order to avoid dirt contamination. 

Noisy or drifting baselines and pressure fluctuations are signs of insufficient degassing. You should degas your mobile phase or improve your degassing procedure. 

Polymer substrates were also metallized by evaporation. Prior to metal deposition, the specimens were cleaned in a 2 % aqueous detergent, rinsed and dried. A resistively-heated conical tungsten basket containing 99.99+ % purity copper foil served as the metal source. Typically 100-200 nm of metal was deposited in an Edwards E306A coating system. The chamber was evacuated to 2 x 10 4 Pa and held for at least 1 h prior to metal deposition in order to properly degas the substrates. Complete details of the evaporation procedure have been given previously... 

With two-part resin systems, the standard procedure was to weigh and mix resin components in a heated pressure pot, degas by the application of vacuum and transfer under pressure into a mold. A variant of this system is to use two-part meter mix equipment. 

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