Effect of sample pressure on membrane inlet mass spectrometry

✍ Scribed by István Futó; Hans Degn

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 677 KB
• Volume: 294
• Category: Article
• ISSN: 0003-2670
• DOI: 10.1016/0003-2670(94)80192-4

✦ Synopsis

The effect of sample pressures up to 6 bar on the signal of a membrane inlet mass spectrometer was studied with supported and unsupported membranes of silicone rubber. In both cases we found undesirable pressure effects. With a supported membrane increasing sample pressure causes a reduction of the signal. This is because lateral diffusion of analyte in the interstitial space between the membrane and the membrane support contributes to the transport of analyte to the mass spectrometer, and the space available for this diffusion is increasingly compressed by increasing sample pressure. With an unsupported membrane increasing sample pressure causes an increasing signal, which is caused by the fact that an unsupported membrane bulges increasingly with increasing sample pressure. The consequently increased area and decreased thickness of the membrane results in increased flux of analyte. Bulging depends strongly on the diameter of the unsuppported membrane area and on the thickness of the membrane. With a 0.185 mm thick membrane spanning a circular hole of 1 mm diameter the bulging is minimal and there is no significant aberration due to sample pressure up to 2 bar. With a larger diameter, a larger pressure or a thinner membrane, significant aberrations occur including change of relative selectivity to polar and unpolar analytes and hysteresis when the pressure is changed up and down. These effects are due to non-linear elastic deformation of the membrane. The effects described should be taken into account in the design of membrane probes for systems where pressure changes may occur.