History - Matsuda design
Professor Hisashi Matsuda of Osaka University designed mass spectrometers with the goal of limiting aberrations to the total ion beam and maximizing sensitivity. Matsuda’s designs are based on cylindrical-geometry double-focussing mass spectrometers. The key element that he introduced was the use of quadrupole lenses to improve the phase-space matching between ion optical elements, notably between the ESA and magnet in SHRIMP II type designs. This accomplished high sensitivity in the mass spectrometer designs by allowing flexibility to maximize transmission in the Z (vertical) plane.
A mass spectrometer is generally defined by its mass resolving power and its sensitivity. The resolving power can be defined by the equation
R = C/(Xs + Δ + d)
Where s and d are the source and collector slit widths respectively, and C, X, and Δ the mass dispersion, the image magnification, and the total amount of image aberrations respectively.
Matsuda uses four main figures of merit for his designs. These are:
C/X, the ratio of mass dispersion to image magnification,
PF, the performance factor that includes elements of C/X, DLT, magnet deflection angle, and others,
AF, the aberration factor that is essentially the mass resolution of a minimal source and collector slit sizes, and,
DLT, the total distance along the path length.
To obtain both high mass resolving power and sensitivity, the goal is to reduce image aberrations (hence high AF) maximize the value of C/X, but while keeping the instrument within engineering limits (appropriate PF, DLT).
Table 4 of Matsuda (1990) has calculated the figures of merit for several mass spectrometers. The mass spectrometers are expressed in terms of the ion optical elements with H = magnet, C = ESA, O = octupole, and Q = quadrupole. Hence the SHRIMP I design is CQH.
Mass Spec C/X PF AF/1000 DLT H - 60° single focus 1.00 2.18 0.1 4.51 CH - Hintenberger 1.23 0.74 1.7 8.12 HC - Reverse Hintenberger 0.80 1.19 16.3 8.12 CQH Osaka 1.76 10.6 135.8 6.84 QQHQC Osaka 4.53 20.0 54.8 6.11 QQQOHQC -3 20.29 100.0 315 6.31 QQHQCQ - SHRIMP RG 9.04 302
The single focus 60° magnet cannot produce high mass resolution because of the lack of an energy focusing component. The double focusing mass spectrometer of Hintenberger substantially improves the mass resolving power but the performance is poorer than the single focusing instrument. A notable feature of the reverse Hintenberger design is the much better AF parameter signaling very low aberrations. The Osaka CQH design (also SHRIMP I) is distinguished by a major jump in the PF and AF parameters. The Osaka QQHQC design has a much higher C/X parameter and PF, but the AF is significantly poorer than the CQH design. The QQQOHQC design presented in Matsuda (1990) yields the highest C/X, PF, and AF of any of the designs. A simpler version of this design for SHRIMP RG maintains high C/X and the aberration factor is nearly as high as the QQQOHQC design.
MATSUDA, H. 1974. Double focusing mass spectrometers of second order.
Int. J. Mass Spectrom. Ion Phys. 14, 219-233.
MATSUDA, H. 1990. Double-focussing mass spectrometers of third order. Nuclear Instruments and Methods in Physics Research A 298, 199-204.