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

Abstract

Abstract. A design of and initial results from a Knudsen Effusion Mass Spectrometer (KEMS) are presented. The design was adapted from high temperature alloy studies with a view to using it to measure vapour pressures for low volatility organics. The system uses a temperature controlled cell with an effusive orifice. This produces a molecular beam which is sampled by a quadropole mass spectrometer with electron impact ionization calibrated to a known vapour pressure. We have determined P298 and ΔHsub of the first 5 unsaturated straight chain dicarboxylic acids: 2.15±1.19×10−2 Pa and 75±19 kJ mol−1 respectively for Oxalic acid, 5.15±0.76×10−4 Pa and 91±4 kJ mol−1 for Malonic acid, 9.19±2.26×10−5 Pa and 93±6 kJ mol−1 for Succinic acid, 4.21±1.66×10−4 Pa and 123±22 kJ mol−1 for Glutaric acid and 5.21±3.84×10−6 Pa and 125±40 kJ mol−1 for Adipic acid.