Quadrupole Mass Filter Technology

Developed in the early 1980s, quadrupole-based systems represent approximately 85% of all ICP mass spectrometers used today. This design was the first to be commercialized, and as a result, today s quadrupole ICP-MS technology is considered a very mature, routine trace element technique. A quadrupole consists of four cylindrical or hyperbolic metallic rods of the same length and diameter. They are typically made of stainless steel or molybdenum and sometimes coated with a ceramic coating 

Practical Guide to ICP-MS A Tutorial for Beginners, Second Edition 

FIGU RE 7.1 The mass separation device is positioned between the ion optics and the detector. 

FIGURE 7.2 Photograph of a quadrupole system mounted in its housing (copyright 2003-2007, all rights reserved, PerkinElmer Inc.). 

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In mass spectrometers, ions are analysed according to the ml7. (mass-to-charge) value and not to the mass. While there are many possible combinations of technologies associated with a mass-spectrometry experiment, relatively few forms of mass analysis predominate. They include linear multipoles, such as the quadrupole mass filter, time-of-flight mass spectrometry, ion trapping forms of mass spectrometry, including the quadrupole ion trap and Fourier-transform ion-cyclotron resonance, and sector mass spectrometry. Hybrid instruments intend to combine the strengths of the component analysers. 

The GC detector is the last major instrument component to discuss. The GC detector appears in Fig. 4.7 as the box to which the column outlet is connected. Evolution in GC detector technology has been as great as any other component of the gas chromatograph during the past 40 years. Among all GC detectors, the photoionization (PID), electrolytic conductivity (EICD), electron-capture (ECD), and mass selective detector (MSD) (or quadrupole mass filter) have been the most important to TEQA. The fact that an environmental contaminant can be measured in some cases down to concentration levels of parts per trillion (ppt) is a direct tribute to the success of these very sensitive GC detectors and to advances in electronic amplifier design. GC detectors manufactured during the packed column era were found to be compatible with WCOTs. In some cases, makeup gas must be introduced, such as for the ECD. Before we discuss these GC detectors and their importance to TEQA, let us list the most common commercially available GC detectors and then classify these detectors from several points of view. 

Magnetron Cluster Source with a Quadrupole Mass Filter at the Toyota Technological Institute... 

Early quadrupole mass filters were very limited in mass range and resolution but their physical simplicity and the absence of a magnet made them attractive for upper atmosphere and space applications. Major development occurred in the 1960s inspired by this application. This same period also coincided with a rising demand for residual gas analysers because ultrahigh vacuum technology began to have routine... 

The incorporation of linear ion trap technology into PTR-MS was reported by Mielke and co-workers in 2008 [54], The quantity of ions that could be stored within the ion trap was 50 times larger than that in a 3D ion trap, which should confer a concomitant improvement in the limit of detection. Thus PTR-MS based on a linear ion trap as a mass analyser offers a detection sensitivity which has the potential to approach that achievable with systems based on quadrupole mass filters, although the best limit of detection so far achieved is near 100 pptv. Also, the linear ion trap preserves the easy use of MS/MS techniques exploited in 3D ion traps, which thus aids in compound identification. 

It should be noted that up until now, only single multipole-based cells have realized commercial success, but a recent development has placed an additional quadrupole prior to the collision/reaction cell multipole and the analyzer quadrupole. This first quadrupole acts as a simple mass filter to allow only the analyte masses to enter the cell, while rejecting all other masses. With all nonanalyte, plasma, and sample matrix ions excluded from the cell, sensitivity and interference removal efficiency is significantly improved compared to traditional collision/reaction cell technology coupled with a single quadrupole mass analyzer. 

Linear quadrupole instruments are widely spread. Recent developments in the technology now make it possible to work simultaneously with fullscan and selected ion monitoring (SIM) modes in a single run. In GC tandem MS, a first quadmpole acts as a mass selective filter and the second quadrupole is used as the collision cell with addition of a collision gas such as helium or argon. In a third quadrupole the full mode is performed to obtain the full mass spectrum of the product ions. 

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