Field-desorption mass spectrometry has been used to characterize polystyrene oligomers of molecular weight up to 15 000 Da. The technique shows good agreement with molecular weight data calculated using vapour-phase osmometry and gel-permeation chromatography but in addition provides much more detailed information in terms of oligomer distribution and the nature of end groups present in the oligomers.Field-desorption mass spectrometry (FDMS) has been used in the characterization of synthetic polymers',* and has been able to provide information on the repeat units involved, average molecular weights and oligomer distribution. The technique's ability to generate only molecular or quasi-molecular ions makes it a particularly appropriate method in the characterization of oligomeric/polymeric species.Earlier FDMS studies3 involving polystyrene oligomers have demonstrated the analysis of these at molecular weights up to 10 000 Da while a slightly later study4 demonstrated the use of the technique in the determination of oligomer distributions up to 5300 Da and its capabilities in the calculation of average molecular weight data. Costello et al.,' have also reported the utility of FDMS in the characterization of a range of polymeric materials and the subsequent calculation of average molecular weights. The availability of the present generation of double-focusing mass spectrometers combining high sensitivity field-desorption ion sources with high mass (> 10 000 Da) analysers and high sensitivity detectors has prompted our group to revisit some of the issues involved in the analysis of polystyrene oligomers. EXPERIMENTAL Chemicals.The polystyrene samples included in this study were gel-permeation chromatography (GPC) standards supplied by Polymer Laboratories Ltd, Church Stretton, UK. These materials are characterized by the manufacturers as indicated in Table 1. Author to whom correspondence should be addressed.Mass spectrometry. All mass spectra were recorded using a model ZAB2-SE reversed geometry mass spectrometer (VG Analytical Ltd, Wythenshawe, UK) equipped with the standard VG combined fi" desorption/fast-atom bombardment (FD/FAB) source. The samples were analysed using 10 pm activated carbon FD emitters supplied by Linden ChroMasSpec (Bremen, FRG) and the sample was applied to the emitter using the standard syringe technique. The standards were prepared as solutions in toluene. The emitter was typically programmed from 0-40 mA or until the signal intensity disappeared. All data were acquired at a resolution of 1000. Data were acquired into the VG Opus datasystem in multichannel analysis (MCA) mode. Gel-permeation chromatography (GPC). All four samples were characterized by GPC using a 30 cm X 7.5 mm ID polystyrene/divinylbenzene GPC column (500 A pore size) in series with a 10OOOA pore-size column. Stabilized tetrahydrofuran was used as the eluant at a flow rate of 1cm3/min. This was delivered using a Knauer high-performance liquid chromatography system and detection was achieved by a refractiveindex detector. R...

Procedures are described for the quantitative determination of the asbestos and a-quartz contents of bulk samples by use of X-ray powder diffractometry. The method gives satisfactory results for several different types of asbestos and for mixtures of two or more different types. Problems with sample grinding and preferred-orientation effects have been largely overcome. An effective procedure has been developed for grinding samples to a suitable particle size for accurate quantitative work. This procedure works equally well for all the types of asbestos studied and the sample is intimately mixed with the internal standard, nickel(I1) oxide, at the same time. A sample press has been designed that enables the same pressure to be applied to each sample when sample holders are filled for the diffractometer, giving the same degree of preferred orientation each time. Calibration lines have been calculated for chrysotile, amosite, crocidolite and anthophyllite, and results are given for mixtures containing two or more types of asbestos as well as other commonly occurring minerals.Similar techniques are used to grind samples containing quartz and to mix them with internal standard. Work on both synthetic and real samples is described and results are compared with those obtained by use of an infrared spectroscopic method.

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