Quadrupole mass analyzer technology

Fig. 4. 32. Schematic (a) and photograph (b) of a linear quadrupole mass analyzer. By courtesy of JEOL, Tokyo (a) and Waters Corp., MS Technologies, Manchester, UK. (b).

Instrumental Aspects. The early developments of static SIMS (largely driven by polymer surface analysis requirements in terms of practical application) were carried out with noble gas ion sources and quadrupole mass analyzers (QMS). The latter had the benefits of compactness, ready availability, and relatively straightforward adaptability to SIMS use in UHV systems. Although all the essential features of polymer surface analysis were introduced using this technology, the QMS has major limitations for static SIMS. Firstly, it is a serial device, so that only one mass at a time can be detected. Secondly, it has a limited mass range (<1000 Da) and the transmission (ie, sensitivity) decreases with mass (by at least m ). Thirdly, it is only possible to achieve a uniform mass resolution... 

Although ICP-MS was commercialized in 1983, the first 10 years of its development utilized a traditional quadrupole mass analyzer to separate the ions of interest. These worked exceptionally well for most applications, but proved to have limitations when determining difficult elements or dealing with more complex sample matrices. This led to the development of alternative mass separation devices that allowed ICP-MS to be used for applications that were previously beyond the capabilities of quadrupole-based technology. Before we discuss these different mass spectrometers in greater detail, let us take a look at the proximity of the mass analyzer in relation to the ion optics and detector. Figure 7.1 shows this in greater detail. 

There is no question that collision/reaction cells have given a new lease on life to quadrupole mass analyzers used in ICP-MS. They have enhanced its performance and flexibility, and most definitely opened up the technique to more demanding applications that were previously beyond its capabilities. However, it must be emphasized that when assessing this technology, it is critical that you fully understand the... 

Before we go on to discuss these in greater detail and how these parameters affect the data, it is important to remind ourselves how a scanning device like a quadrupole mass analyzer works. Although we wiU focus on quadrupole technology, the fundamental principles of measurement protocol wiU be very similar for all types of mass spectrometers that use a sequential approach for multielement peak quantitation. 

FIGURE 12.2 Detection and measurement protocol using a quadrupole mass analyzer. (From Integrated MCA Technology in the ELAN I CP-Mass Spectrometer, Application Note TSMS-25, PerkinElmer Instruments, 1993.)... 

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. 

The Guardian Explosives Detection Security Portal (Fig. 6) is manufactured and marketed by Syagen Technology, Inc., of Tustin, CA [48], This portal was the result of two research and development efforts that included collaboration between Syagen and Sandia National Laboratories, funded by TSL, and a project at Sandia, funded by DOE [33,49], The detector utilized in the portal is a quadrupole ion trap, time-of-flight (QitTof ) mass analyzer [50,51], The mass analyzer identifies explosives by time-of-flight and mass-to-charge (m/z) ratio, which increases the accuracy of the identification of the explosive. The foundation of the sample collection method in this portal is an air shower [52],... 

The technology of GC-MS can be downsized for field usage and is now commercially available. Inficon (USA) manufactures a field-portable GC-MS, Hapsite. Vapor is withdrawn for 30 s into the Tenax preconcentration system, thermally desorbed into the apolar capillary colmnn with elevated temperature control, and the separated components are finally analyzed by the electron ionization quadrupole mass spectrometer. GB, GD, GA, and HD are detected and identified within 12 min with postulated LOD values of 0.2, 0.5, 8, and 0.3 pg/m (Sekiguchi et al, 2006). Gaseous and weakly volatile (boiling temperature >250°C) CWAs cannot be detected. 

By examining this brief history of the development of instrumentation and methods, it should be clear what parameters define the instrument of choice for analysis of pharmaceutically important molecules. Such an instrument is one capable of performing LC-MS, typically using a reverse-phase HPLC separation and one of the API techniques. MS-MS capability is desirable—using an ion trap, a triple quadrupole, or other tandem mass analyzer instrument. Accurate mass measurement capability is also desirable. These attributes make up a prioritized list of capabilities for the ideal full-purpose instrument to be used in a pharmaceutical research environment. As one progresses through this list, the expense of the instrument increases, the sophistication of the instrument increases, and the intellectual and technological commitment required to do these experiments increases. 

Figure 6.10 Hybrid quadrupole trme-of-flight (QqTOF) mass analyzer. (Schematic diagram provided courtesy of Agilent Technologies.)...

The sample inlet is constituted of a heated fused silica capillary, which is maintained at approximately 200 "C and is encased in a flexible tube. The ion source, in the case of electronic ionization, is composed of electrically heated metallic filaments. Mass analyzers, separating the analytes, include time-of-flight (TOF), linear quadmpole (Q), linear quadrupole ion trap (LIT), quadmpole ion trap (QIT), Fourier transform ion cyclotron resonance (FT-ICR), etc. These detectors differ in their capacity to treat ion beams in a continuous or pulsed (TOF). Quadmpole mass analyzers stabilize and destabilize the ion paths with an oscillating electrical field. A triple quad is more recent technology and consists of three quadmpole stages. Quadmpole ion traps will sequentially eject ions that have been trapped in a ring electrode between two endcap electrodes. 

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