Availability Of Standard Reference Materials

A difficult problem in the compilation of a reference collection of pyrolysis mass spectra of complex biomaterials is the limited availability of suitable standard materials. Although complex biomaterials can be found among the large collection of Standard Reference Materials issued by the National Bureau of Standards (ref. 82), these materials have not been thoroughly characterised and defined with respect to their organic structure and composition. Moreover, although NBS Standard Materials of biological origin are usually available as a thoroughly homogenised, fi ne powder, the NBS does not guarantee (ref. 83) homogeneity of the material down to sample sizes below 100 micrograms such as are normally used in Py-MS. Of course, inhomogeneity problems may be detected by repeated Py-MS analyses and, if necessary, can be corrected by averaging the results of multiple determinations.

Table 1 lists NBS Standard Reference Materials which in the opinion of the authors may have potential value as complex biological reference samples in Py-MS, and spectra from some of which can be found in this book. Preliminary studies on four materials indicated in Table 1 failed to detect marked inhomogeneities at the 10 microgram level (ref. 84). Less sophisticated, but inexpensive and generally available reference materials for less demanding applications in Py-MS studies on biomaterials are, for instance, the polysaccharides amylose and cellulose, the proteins albumin and keratin and complex materials such as milk homogenate and soft wood powder (Douglas fir). Homogenised bovine milk is especially useful as different samples show relatively little variation in their pyrolysis mass spectra. Moreover, it is composed of a wide variety of biological compounds, needs little sample preparation (dilution with water) and produces a thin, uniform coating on the pyrolysis filament. Convenient sources of some high purity synthetic polymers are stationary phases for gas chromatography and ion exchange resins. However, considerable differences in pyrolysis patterns may be found between products from different manufacturers or even between different batches from a single commercial source.

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