We discuss miniaturization in mass spectrometry in terms of the mass analyzer, the mass spectrometer, and the total analytical system. Mass analyzer miniaturization has focused on ion traps. Decreases in mass analyzer size facilitate reduction of the sizes of the other components of a miniature mass spectrometer, especially the radio frequency electronics and vacuum system. Appropriate sample introduction systems are needed for performance optimization. The criteria by which a miniature mass spectrometer is judged include adequate performance in the traditional areas of resolution, detection limits, and specificity; ruggedness; reliability; and fully autonomous operation. Our discussion of the total analytical system emphasizes the removal of the bottleneck of sample preparation and suggests a solution to the combination of sampling, preconcentration, and ionization: ambient ionization methods. We also describe current miniature mass spectrometers.

Miniature mass spectrometers

Increased efforts are being made to develop miniature mass spectrometers, including those which are hand-portable, and to retain the performance characteristics of traditional laboratory instruments as much as possible in the miniature instruments. This review of miniature mass analyzers emphasizes analytical performance and compares the relative merits of each type of miniature mass analyzer. Miniature instruments discussed include sector, Wien filter, time-of-flight, linear quadrupole, quadrupole ion trap and Fourier transform ion cyclotron resonance mass spectrometers, as well as combinations of and variations on these major types. Special considerations that apply to small mass analyzers are noted and suggestions are made regarding the possible future development of this field. Copyright 2000 John Wiley & Sons, Ltd.

Miniature mass analyzers

A small mass spectrometer array is described in which each element is a cylindrical ion trap (CIT). The array contains four CITs, each having an inner radius of 2.5 mm, arranged in parallel and operated using a single electronics system under common conditions for trapping and mass analysis. By using an array of identically sized traps, higher ion capacity can be achieved than with a single miniature CIT, but the advantage of lower power and voltage requirements associated with the smaller ion trap is maintained. Overall signal intensity of the array of four traps is compared with that of a two-element CIT array to demonstrate the increased ion capacity of larger arrays. Resolution for m-dichlorobenzene is shown to be ∼180 (full width at half-maximum), with no significant loss in resolution as a result of using multiple CITs. The detection of 5 × 10-9 Torr partial pressure of krypton in argon with a signal-to-noise ratio of ∼30 for the most abundant isotope is shown, demonstrating the applicability of the...

A parallel miniature cylindrical ion trap array

The conventional quadrupole mass spectrometer (QMS) arrangement uses circular metallic rods as the mass filter excited electrically at voltages up to 1 kV depending upon the application. If the size and voltages can be reduced then the range of applications for QMS instruments would increase. The application of microelectromechanical systems (MEMS) technology allows the fabrication of submillimeter versions of such structures. In this article the development of a miniature QMS is reported in which the conventional rod arrangement has been replaced with a microengineered version. The structure is made in silicon with metallized specially drawn glass fibers of length 20–30 mm and diameter 0.5 mm to act as the quadrupole rods. This is about one order of magnitude smaller than most conventional QMS filters, with the potential for further reduction in size. The MEMS mass filter was mounted onto a commercial ion source, which was in turn attached to a vacuum flange and supplied by an electronic drive circuit at...

https://www.liverpool.ac.uk/media/livacuk/massspectrometry/pdfs/Silicon,based,quadrupole,mass,spectrometry,using,microelectromechanical,systems.pdf

Silicon based quadrupole mass spectrometry using microelectromechanical systems

https://link.springer.com/content/pdf/10.1016/S1044-0305(01)00248-3.pdf

Trade-offs in miniature quadrupole designs.

Monitoring of gas composition for processes in the mTorr range is not possible with a conventional residual gas analyzer (RGA) unless a pressure reduction pumping system is used. A miniature sensor, having dimensions compatible with the mean-free path of gas molecules can operate directly at mTorr pressures while being less expensive and more compact than a conventional apparatus. This article describes a quadrupole RGA which is scaled down by a factor of 7 to operate at pressures up to 10 mTorr. This sensor requires different construction methods and drive electronics than a traditional RGA. A unique ion source with high output has been developed. The small sensor has resolution characteristics very similar to standard size models but sensitivity is reduced in proportion to the ratio of cross-sectional area for each quadrupole r0. Response is linear to the mTorr range and a correction method for gas scattering, based on pressure measured by a total pressure gauge included in the ion source design, extend...

F. C. Currier

Papers

Miniature quadrupole residual gas analyzer for process monitoring at milliTorr pressures