Design and construction of a simple Knudsen Effusion Mass Spectrometer (KEMS) system for vapour pressure measurements of low volatility organics

摘要

A design of and initial results from a Knudsen Effusion Mass Spectrometer(KEMS) are presented. The design was adapted from high temperature alloystudies with a view to using it to measure vapour pressures for lowvolatility organics. The system uses a temperature controlled cell with aneffusive orifice. This produces a molecular beam which is sampled by aquadropole mass spectrometer with electron impact ionization calibrated to aknown vapour pressure. We have determined andΔ of the first 5 saturated straight chain dicarboxylicacids: 2.15±1.19×10 Pa and 75±19 KJ molrespectively for oxalic acid, 5.73±1.14×10 Pa and91±4 KJ mol for Malonic acid,1.13±0.47×10 Pa and 93±6 KJ mol forSuccinic acid, 4.21±1.66×10 Pa and123±22 KJ mol for Glutaric acid and6.09±3.85×10 Pa and 125±40 KJ mol forAdipic acid.