Skimmer coupling

Principles and Characteristics Simultaneous thermal analysis techniques, such as TG-DSC/DTA offer vital information on polymer structure based on heat flow behaviour and mass change [290], but little direct information on the composition of evolved gas products. A more complete thermal profile is provided when a thermal analyser is coupled to an identification tool. Henderson et al. [433] have recently described TG-DSC/DTA with evolved gas analysers (MS and FTIR). The skimmer coupling is the most advanced commercial way of combining a thermobalance or simultaneous TG-DSC/DTA instrument with a quadrupole mass spectrometer [338]. For descriptions of interface techniques in this coupled instrumentation, cfr. ref. [411]. Simultaneous TG-DSC-MS is capable of operation up to 2000°C [434]. 

Polymer Characterization by an Advanced Simultaneous Thermogravimetric—Mass Spectrometric Skimmer Coupling System... 

The Skimmer coupling system (2) is based on the NETZSCH thermobalance STA 409 with top loading sample arrangement for TG or simultaneous TG-DSC. 

The high mechanical precision, a prerequisite for the optimum performance of this type of coupling aiming in perfect gas flow conditions, could up to now only be achieved by using corrosion resistant stainless steel. Thus the Skimmer coupling can be applied up to 800°C in inert and oxidizing atmosphere. The fact that the coupling... 

Figure 1. Schematic drawing of the skimmer coupling system within the STA furnace.

Burning or pyrolytic procedures can be simulated by using the NETZSCH ST A 409/QMS with the Skimmer coupling. In addition to detecting weight loss and... 

Residual oxygen in the coupled TG-MS system would lower the decomposition range of the PP to the temperature of the melamine decomposition. This would exclude a separate evaluation of the melamine resin content (here 20.38%) in the blend. The vacuum-tight construction of the ST A 409 Skimmer coupling system allows the precise atmosphere control and, in this example, an accurate determination of the relative thermal stability of the blend components. 

The part that marries the plasma to the mass spectrometer in ICPMS is the interfacial region. This is where the 6000° C argon plasma couples to the mass spectrometer. The interface must transport ions from the atmospheric pressure of the plasma to the 10 bar pressures within the mass spectrometer. This is accomplished using an expansion chamber with an intermediate pressure. The expansion chamber consists of two cones, a sample cone upon which the plasma flame impinges and a skimmer cone. The region between these is continuously pumped. 

Figure 5. The inductively-coupled plasma source (inspired by Niu and Houk 1996). The original figure has been modified to show the electrical potentials, the vacuum cascade (top), and the distribution of ions and neutral (bottom) in an MC-ICP-MS similar to the VG Plasma 54. The zone with incipient voltage acceleration right behind the skimmer show maximum space-charge effect with the lighter ions being most efficiently driven off by the strong axial current of positive ions.

In addition, determination of a variety of sulfonamides has been carried out by coupling capillary LC with quadrupole MS through an ESP interface induced dissociation of the analytes by increasing the skimmer voltage could allow confirmation at the low-picomole range (110). LC-ESP-MS has been also found suitable for the determination of four coccidiostats in poultry products (111). 

The HELIOS mass separator vat the Mainz TRIGA reactor is one of the few facilities where a gas-jet transportation system has been coupled successfully to a mass separator. Details of the gas-jet system, the integrated skimmer-ion sources, the separator and its collector facilities have been published elsewhere [Maz 80, Maz 81]. Recently, HELIOS was applied for spectroscopic studies of neutron-rich isotopes of praseodymium [Bru 85] and neodymiurn [ Kar 85], Work is in progress in order to replace the existing ion sources by an inductively oupled jplasma ion source (ICP). In case of a successful coupling of the gas-jet with the ICP source it should be possible to ionize any element in the periodic table because temperatures of 6000 -10000 K are reached in the plasma. 

Figure 1 Schematic diagram of a typical commercial inductively coupled plasma mass spectrometry (ICP-MS) instrument (A) liquid sample, (B) peristaltic pump, (C) nebulizer, (D) spray chamber, (E) argon gas inlets, (F) load coil, (G) sampler cone, (H) skimmer cone, (I) ion lenses, (J) quadrupole, (K) electron multiplier detector, (L) computer.

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