Quadrupole mass analyze

In a quadrupole mass analyzer, four parallel rods are arranged equidistantly from a central (imaginary) axis. 

In both electron post-ionization techniques mass analysis is performed by means of a quadrupole mass analyzer (Sect. 3.1.2.2), and pulse counting by means of a dynode multiplier. In contrast with a magnetic sector field, a quadrupole enables swift switching between mass settings, thus enabling continuous data acquisition for many elements even at high sputter rates within thin layers. 

Different types of mass analyzers have been used for anthocyanin analysis single or triple quadrupole mass analyzers, TOP mass analyzer,ion trap mass analyzers,and the combination of analyzers cited above. " ... 

The quadrupole mass analyzer utilized by Q-ICPMS is comprised of quadrupole rods with combined DC and RF potentials that can be set to allow analyte ions with a specific... 

Figure 9.4 Soaematic diagram of a thexmospray interface ionization source connected to a quadrupole mass analyzer and Insert indicating the mechanism of vapor production by the heated thermospray.

Figure 3.9 Conceptual view of tandem mass spectrometry with a tandem-inspace triple quadrupole mass analyzer." The first mass analyzer (Ql) selects the precursor ion of interest by allowing only it to pass, while discriminating against all others. The precursor ion is then fragmented, usually by energetic collisions, in the second quadrupole (q2) that is operated in transmissive mode allowing all fragment ions to be collimated and passed into the third quadrupole (Q3). Q3 performs mass analysis on the product ions that compose the tandem mass spectra and are rationalized to a structure.

Multiple mass analyzers exist that can perform tandem mass spectrometry. Some use a tandem-in-space configuration, such as the triple quadrupole mass analyzers illustrated (Fig.3.9). Others use a tandem-in-time configuration and include instruments such as ion-traps (ITMS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS or FTMS). A triple quadrupole mass spectrometer can only perform the tandem process once for an isolated precursor ion (e.g., MS/MS), but trapping or tandem-in-time instruments can perform repetitive tandem mass spectrometry (MS ), thus adding n 1 degrees of structural characterization and elucidation. When an ion-trap is combined with HPLC and photodiode array detection, the net result is a profiling tool that is a powerful tool for both metabolite profiling and metabolite identification. 

One reason for lower sensitivity is the lack of flexibility to optimize the positions of the sprayers on the MUX interface another may be the lower electrospray desolvation efficiency on the MUX. The longer total cycle time on a MUX interface with a quadrupole MS in comparison to a single sprayer interface adds another concern. Assuming typical chromatographic peak widths appeared on average at 15 sec, 17 data points could be easily detected across the peak for each transition with a total cycle time of 0.88 sec on a conventional single sprayer set-up. With the MUX, only 12 data points could be detected across the same peak even with a total cycle time of 1.24 sec because of the introduction of additional interspray time on top of dwell time. Hence, when MUX is used with a quadrupole mass analyzer, it is important to consider dwell time and chromatographic peak width... 

Mass resolution describes the capability of an MS to distinguish ions with different m/z values. It is defined by the M/AM equation in which M is the m/z ratio of a mass peak and AM is the full width of a peak at half its maximum height. The mass resolution of an instrument often correlates with its accuracy. Mass range indicates the m/z range at which the mass analyzer best functions. For example, quadrupole mass analyzers exhibit a mass range of up to 4000 m/z, while the mass ranges of TOF extend up to 100,000. The operating principles of common MS instruments are discussed below. 

Q-switches, in YAG lasers, 14 698 Q-switching technique, 14 618, 673-678 Quadrature techniques in sampling, 26 1010-1011 Quadrupole mass analyzers, 24 109 Quadrupole moment, 1 620-621 selected molecules, 1 621t3 Quadrupoles, 15 661-662 Qualimet... 

P.H. Dawson, Quadrupole mass analyzers performance, design and some recent applications, Mass Spectrom. Rev., 5 (1986) 1-37. 

In the past decade, as systems have become simpler to operate, mass spectrometry (MS) has become increasingly popular as a detector for GC. Of all detectors for GC, mass spectrometry, often termed mass selective detector (MSD) in bench-top systems, offers the most versatile combination of sensitivity and selectivity. The fundamentals of MS are discussed elsewhere in this text. Quadrupole (and ion trap, which is a variant of quadrupole) mass analyzers, with electron impact ionization are by far (over 95%) the most commonly used with GC. They offer the benefits of simplicity, small size, rapid scanning of the entire mass range and sensitivity that make an ideal detector for GC. 

Typical quadrupoles transmit ions with mass-to-charge ratios ranging from 1-300 or greater with a mass-dependent resolution of twice the mass. More sophisticated instmments can achieve m/z of 4000 with comparable resolution. The suitability of a quadrupole mass analyzer depends in large part on the duty cycle... 

Fig. 2. Schematic diagram of a high resolution He time-of-flight spectrometer. N-nozzle beam source, SI, 2-skimmers, Al-5 - apertures, T - sample, G - gas doser, CMA - Auger Spectrometer, IG - ion gun, L - LEED, C -magnetically suspended pseudorandom chopper, QMA-detector, quadrupole mass analyzer with channeltron.

A linear quadrupole mass analyzer consists of four hyperbolically or cyclindrically shaped rod electrodes extending in the z-direction and mounted in a square configuration (xy-plane, Figs. 4.31, 4.32). The pairs of opposite rods are each held at the same potential which is composed of a DC and an AC component. 

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).

Ion trajectory simulations allow for the visualization of the ion motions while travelling through a quadrupole mass analyzer (Fig. 4.36). Furthermore, the optimum number of oscillations to achieve a certain level of performance can be determined. It turns out that best performance is obtained when ions of about 10 eV kinetic energy undergo a hundred oscillations. [110]... 

High-Resolution with Quadrupole Mass Analyzers... 

Thermospray (TSP) [29-31] unites three modes of operation. In pure TSP, a solution of the analyte and a volatile buffer, usually 0.1 M ammonium acetate, is evaporated from a heated capillary at a flow rate of 1-2 ml min into a heated chamber, hence the term thermospray. As the solvent evaporates, the analyte is forming adducts with ions from the buffer salt. While most of the neutrals are removed by a vacuum pump, the ions are extracted orthogonally from their main axis of motion by use of an electrostatic potential. The ions are transferred into a quadrupole mass analyzer through a pinhole of about 25 pm in diameter (Fig. 11.2). The quadrupole was employed according to its tolerance to poor vac-... 

Fig. 11.2. Schematic of a thermospray interface. A cartridge heater B copper block brazed to stainless steel capillary C capillary D copper tube E ion lenses E quadrupole mass analyzer G line to rotary vane pump H ion exit aperture J source heater. Reproduced from Ref. [30] by permission. American Chemical Society, 1983.

The quadrupole mass analyzer [1] consists of four parallel metal rods arranged as in Figure 1. 

Fig. 1.8 Di fferential pumping design with heated capilla. This configuration requires a dual stage pumping system before the ions are introduced into the quadrupole mass analyzer which needs to be operated at high vacuum. The role of the lenses is to focus ions. In some systems the lenses are replaced by hexapoles or octapoles.

Fig. 1.10 (A) Positive mode electrospray spectrum of human gamma interferon on a quadrupole mass analyzer. (B) Deconvoluted spectrum of human gamma interferon. The molecular mass was measured at 16908 2 Da.

The use of MALDI for the analysis of small molecules was recently reported. Particularly attractive is the coupling of a MALDI source with a triple quadrupole mass analyzer for quantitative analysis in the selected reaction monitoring (SRM) mode due to very high analysis speed. 

A quadrupole mass analyzer is made of four hyperbolic or circular rods placed in parallel with identical diagonal distances from each other. The rods are electrically connected in diagonal. In addition to an alternating radiofrequency (RE) potential (V), a positive direct current (DC) potential (U) is applied on one pair of rods while a negative potential is applied to the other pair (Fig. 1.17). The ion trajectory is affected in x and y directions by the total electric field composed by a quadrupolar alternating field and a constant field. Because there is only a two-dimensional quadrupole field the ions, accelerated after ionization, maintain their velocity along the z axis. 

The motion of ions in the quadrupole [x, y) is quite complex and can be described by the Matthieu equations. The solution of the Matthieu equations generate two terms, a and q, which are proportional to the RF and DC potentials, respectively. For a detailed description of Matthieu equations, please see reference [53], The trajectories of ions are stable when the ions never reach the rods of the quadrupole. To reach the detector an ion must have a stable trajectory in the x and y directions. With a quadrupole mass analyzer a mass spectrum is obtained by increasing the magnitude of U (DC) and V (RF) at a constant ratio. In a quadrupole mass analyzer when the DC voltage of a quadrupole is set to zero and... 

Fig. 1.17 The quadrupole mass analyzer is formed by four circular or hyperbolic rods placed in parallel. O Quadrupolar potential.

---