Potentials And Limitation of the Skimmer System
Jan Hanss, Andreas Kalytta and Armin Reller Solid State Chemistry, University of Augsburg, Universitätsstraße 1, 86159 Augsburg, Germany
In earlier days the thermobalances were coupled to mass spectrometers covering a range up to 100 AMU. To day even 1024 AMU become usual. This has been achieved by changing the coupling from capillary systems to Skimmer or Super Sonic Systems. The Problem of the capillary systems is the limitation of the temperature in the transferline. While in the Skimmer System both the sample and the inlet of the mass spectrometer have nearly the same temperature. The condensation problem of the evolving gases in the transfer part is almost negligible.
But what about calibration of the MS system. Everybody using a capillary system finds a horizontal baseline for the masses, i.e. calibrating the mass spectrometer is unproblematic. With the Skimmer system one usually cannot perform a reliable calibration. The sensitivity of the MS decreases with temperature; and to realise an accurate calibration takes a lot of time. To our knowledge, nobody carries out quantitative analyses of the evolved gas using a Skimmer system.
An easy way for calibration is the PulsTA technique, developed by M. Maciejewski and technically realised by NETZSCH. But this method works only under special conditions in the Skimmer System.
Results:
Figure 1: Calibration of CO2 with 1 ml pulses of CO2 before and after the mass loss of the NaHCO3. Measurement in nitrogen (100 ml/min).
NaHCO3 in nitrogen NaHCO3 in helium sample mass 10,20 mg 7,08 mg theoretical evolved CO2 2,625 mg 1,855 mg calculated evolved CO2 5,739 mg 2,105 mg quotient calculated/theoretical 2,19 1,13
Possible ways out of this dilemma will be presented.
zurück