GB1318400A - Mass spectrometry - Google Patents

Abstract

1318400 Mass spectrometers ASSOCIATED ELECTRICAL INDUSTRIES Ltd 26 Aug 1971 [28 Aug 1970] 41519/70 Heading H1D A mass spectrometry method comprises time division multiplexing a plurality of ion beams, e.g. from sources 1, 2, on a collinear array, to form a single beam to be analysed in a mass spectrometer (12) (Fig. 1, not shown), the mass spectrometer output at any time representing the passage of ions of a given mass to change ratio, to provide data on the plurality of beams. The output of the mass spectrometer may be sampled and digitized preferably by a digital computer further programmed to account for the multiplexing. Preferably the mass spectrometer is a scanning type and analyses a range of mass to charge ratios, in which case the multiplexing is preferably at a rate to sample individual peaks several times. The time divisions may be unequal to vary the relative sensitivities of the ion collections of the respective beams, the single beam focussing may be changed to vary the resolution, and the spectrometer may be single or double focusing, with magnetic sector and B and E sector respectively, time of flight, cycloidal focusing, or quadrupole type. Mass marking may be performed by including one or more reference substances separately or with the examined substance, e.g. hoptacosa fluorotributylamine and perfluorokerosene. The multiplexing may be by a plurality of pairs of plates (e.g. 20, 22) at different interlaced voltages and/or a hexapole ion beam deflecting arrangement, the multiplexing deflecting system being at the point of beam intersection. Ions striking detector (14) may be amplified by an electron multiplier. Data processing unit (16) may demultiplex the signal to form individual analyses, synchronizing link (18) being utilized, but not being necessary if unit (16) is sensitive to the beam switching or if detector (14) is so sensitive and informs unit (16), or may be programmed digital computer sampling at least once during each time division (cf. Fig. 2). Deflector fringe field correcting plates 36, 38 may be adjacent cylindrical beam deflector 30, the latter being earthed on beam 2 passage and multiplexing being via changeover switch 26 which is preferably a semi-conductor type. Reference is made to Specifications 1,161,432, 1,233,812 and 1,318,200.