Prospects For Interlaboratory Reproducibility

As yet, no systematic study has been undertaken to determine the level of inter-laboratory reproducibility obtainable with Curie-point Py-MS. Preliminary data, however, suggest that the prospects for inter-laboratory reproducibility between instruments of the same basic design as shown in Figure 18 are promising. Figures 23 and 24 show spectra of Douglas fir wood and urban particulate (NBS, SRM 1648), respectively, obtained on different Py-MS instruments in two different laboratories. In spite of a similar basic design, the two instruments, a fully automated system built at the F.O.M. Institute for Atomic and Molecular Physics in Amsterdam (see Figure 20) around a Riber QM17 mass filter, and a Py-MS system at the Biomaterials Profiling Center, University of Utah, Salt Lake City, built by Extranuclear Labs. Inc. (Pittsburgh) around a Spectrel 275 quadrupole mass filter, were significantly different with regard to the dimensions of the expansion chamber, ion source and mass filter. Also there were notable differences in the operating conditions of the pyrolyser, ion source and quadrupole mass filter. Moreover, the Douglas fir samples were obtained from different batches. Hence, in many ways the spectra in Figures 23 and 24 present "worst case" examples of inter-instrumental and inter-laboratory reproducibility and the presence of some obvious differences in these spectra is therefore not surprising. Careful examination, however, reveals the most severe differences to be attributable to different ion transmission efficiencies in the low and high mass ranges of the spectra. Note especially the high transmissivity in the high mass range shown by the Extranuclear Labs, system, which employs a quadrupole rod system of larger dimensions than the F.O.M. system.

It should be pointed out that optimal correspondence between spectra obtained on different quadrupole systems can be achieved only by trial and error, since instrument settings such as "electron energy" and "ion energy" provide only a rough

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