Quadrupole analysers

The mass analyser most commonly used with ESI is the quadrupole analyser. The quadrupole is essentially a mass Alter. At a given set of parameters only ions with a specific m z value pass through the quadrupole and reach the detector. By scanning over an m z range, whole spectra can be obtained. 

The quadrupole analyser consists of four parallel rod-like metal electrodes. A direct current (DC) and an alternating current (AC) field are applied to these electrodes (Eig. 4.15). At a given field, ions of one defined m z ratio can pass 

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Mass spectrometers which have the capability of analysing samples by a FAB or FIB/LSIMS-source tend to be fitted with either one alternative or the other such mass spectrometers have either a magnetic sector or a quadrupole analyser (or hybrid or tandem combinations). 

QQQ, QqQ Triple quadrupole analyser SDE Simultaneous distillation extraction... 

The analyser will always be preceded by some form of collection optics, and followed by an ion detector (usually a channel electron multiplier which converts ions into electron showers). There are three types of analyser for use in SIMS spectrometers, the magnetic sector instrument, the quadrupole analyser and time-of -flight (TOF) systems. 

Mass spectra of reference vegetable and fossil waxes were also acquired by DI EI-MS with a Shimadzu QP 2010 mass spectrometer equipped with a quadrupole analyser (Figures 4.7 4.9). The mass spectrum of camauba is dominated by a base peak at m/z 57. At low mass range the pattern observed is that already discussed for other waxes with peaks spaced every 28 mass units corresponding to the fragmentation of long linear carbon chains. Two other areas of interest may be mentioned one between m/z 250 and 450... 

GC/MS separation of mixtures of the compounds are usually performed on capillary columns with low and mid polarity and a length in the range of 30 50 m, with a total separation time of20 40 min, and temperature ramping from 40 to 300 °C. Total ion current (TIC) profiles are often obtained using ion trap or quadrupole analysers. Quantification is performed by selected-ion monitoring (SIM) detection using calibration curves. 

The quadrupole analyser is an ideal detector for chromatography as it is capable of fast scanning and uses low voltages which make it tolerant of relatively high operating pressures, such as those encountered in LC-MS. 

The ions are propelled from the ion source into the quadrupole analyser (Figure 3.20) by a low accelerating voltage of only a few volts. They enter the space... 

An instrument that stores ions and then ejects those of selected masses is called an ion trap. Like quadrupole analysers such instruments employ electric fields to effect separation and are based on a similar technology. Such systems can be considered as alternatives to tandem MS. 

A cheaper and more sensitive mass spectrometer than a magnetic sector instrument is based on the quadrupole analyser (Fig. 9.2), which uses two electric fields applied at right angles to each other, rather than a magnetic field, to separate ions according to their m/z ratios. One of the fields used is DC and the other oscillates at radiofrequeney. 

Figure 5.7 Experimental arrangement a) of 90° reflecting ion optics of Varian ICP-MS b) cone with channels for collision gas c) 3 MHz quadrupole analyser with S-shaped pre-quadrupole. (Reproduced by permission of Varian, Inc)...

W. PAUL and H.S. STEINWEDEL describe the quadrupole analyser and the ion trap or quistor in a patent [31], W. PAUL, H.P. REINHARD and U. Von ZAHN, of Bonn University, describe the quadrupole spectrometer in Zeitschrift fur Physik in 1958. PAUL and DEHMELT receive the Nobel Prize in 1989 [32],... 

In the example shown in Figure 1.23 using the peaks at m/z 939.2 and 1372.5 (j = 6), we obtain z = 6(1372.5 - 1.0073)/(1372.5 - 939.2) = 19 and we can number all the peaks measured according to the number of charges. M can be calculated from their mass. The average value obtained from all of the measured peaks is 17 827.9 Da with a mean error of 2.0 Da. This technique allowed the determination of the molecular masses of proteins above 130 kDa with a detection limit of about 1 pmol using a quadrupole analyser. 

The quadrupole analyser is a device which uses the stability of the trajectories in oscillating electric fields to separate ions according to their m/z ratios. The 2D or 3D ion traps are based on the same principle. 

Quadrupole analysers [2,3] are made up of four rods of circular or, ideally, hyperbolic section (Figures 2.4 and 2.5). The rods must be perfectly parallel. 

Paul and Steinwedel, the former being the inventor of the quadrupole analyser, described an ion trap [9,10] in 1960. It was modified to a useful mass spectrometer by Stafford et al. [11] at the Finnigan Company. It is made up of a circular electrode, with two ellipsoid caps on the top and the bottom (Figure 2.12). 

The equations of the movement inside the trap are similar to those encountered for the quadrupole analyser (Section 2.1.2) ... 

Scheme of a hybrid mass spectrometer including a quadrupole analyser, a quadrupolar collision cell and an orthogonal acceleration time-of-flight analyser. 

As shown in Figure 2.68, the most common of these instruments include a quadrupole analyser Q1 and a quadrupolar collision cell q2, followed by an oa-TOF. They thus have the QqTOF configuration. This instrument can be described as a triple quadrupole where the last quadrupole is replaced by an oa-TOF, or as the addition of a quadrupole analyser and a collision cell to a TOF analyser. In some commercial instruments, the q2 quadrupole is replaced by an hexapole, but the principle remains the same. 

Quadrupole analyser a mass filter that produces a quadrupolar field with a DC component and an AC component such that only ions with a given m/z pass through. 

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