Quadrupole mass

A triple quadrupole instrument (QqQ) is a combination of two mass quadrupole mass filters (tandem mass spectrometry) separated by a collision cell which is also a quadrupole operating in RE-only mode (Pig. 1.18). A common nomencla-... 

Quadrupole mass analyzers consist of four rods that produce a radio frequency quadrupole field. Only a single mass-to-charge ratio has a stable trajectory through the mass analyzer, but the electric potentials can be swept rapidly, either continuously or in discrete steps to measure a variety of masses. Quadrupole mass spectrometers are used in a wide variety of applications, but are not widely used in cosmochemistry. 

The rest of the mass spectrometer can be a conventional organic Instrument. High mass quadrupole mass filters or magnetic sector Instruments may be used. A mass range to 5000 D Is advis-... 

Mass analysers are essentially characterised by their resolution, their sensitivity and the maximum analysable mass. Quadrupole spectrometers are relatively simple in design and offer a mass resolution of unity. 

In this paper, we analyze these aspects in more detail combining data from flow reactor studies, infrared studies in a flow reactor cell and results obtained in a high-speed transient micrcu eactor coupled with a mass quadrupole detector (TAP - Temporal Analysis of Products - Reactor). Furthermore, we show and discuss how it is possible to limit and control these effects of deactivation by the addition of SO during Q-Cs alkane oxidation. 

The catalysts were characterized by X-ray diffraction (Philips PW 1710 diffractometer, (CuKa radiation) and FT-IR (Perkin Elmer 1750 instrument) analyses. N2 adsorp-tion/desorption isotherms were recorded at 77°K using a Catasorb apparatus. NH3-TPD (thermodesorption) tests were made in a flow system (0.3 g sample) after adsorption of ammonia (5% NH3 in He) at 1(X)°C up to complete saturation, flushing with He for 10 min and then heating up to 550°C at a rate of 10°C/min. The catalysts were pretreated in a pure He flow at 4(X)°C up to complete removal of adsorbed water. The NH3 concentration was followed with an on-line mass quadrupole detector. 

These results show for the first time that it is possible to generate and detect high-mass ions (> 1500 Da) after their parent compounds have been introduced into a mass spectrometer by SFC. Both of these examples, PDMS and silylated oligosaccharides, are mixtures of relatively volatile compounds. We have not succeeded in observing ions related to less volatile materials, like sucrose octaoleate, that require high SFC elution pressures (370 atm). Future SFC-MS work will examine the applicability of this technique to high mass species that are less volatile. The combination of this unique separations method and a high-mass quadrupole mass spectrometer will be a powerful analytical tool. 

Catalytic tests were carried out in a conventional plug-flow-type reactor witii on-line gas-chromatographic or mass quadrupole atuilysis, the latter system was used when the change in surface reactivity with time-on-stream was monitored. Further details on the apparatus for the catalytic tests have been previously reported [9]. Tests were made using 1 g of sati le with particle dimensions in the 0.1-0.2 mm range, 3% propane and a O2/C3 and NH3/C3 ratio of 2.0 and 1.0, respectively, a reaction temperature of 500"C, and a total flow rate of 8 L/h. 

B1.7.4 QUADRUPOLE MASS FILTERS, QUADRUPOLE ION TRAPS AND THEIR APPLICATIONS... 

Dawson P H 1976 Quadrupole Mass Spectrometry and its Applications (Amsterdam Elsevier)... 

Marsh R E and Hughes R J 1989 Quadrupole Storage Mass Spectrometry (New York Wiley-Intersolenoe)... 

Usypchuk L L, Flarrison A G and Wang J 1992 Reactive collisions in quadrupole cells. Part I. Reaction of [CFl3NFl2] with the isomeric butenes and pentenes Org. Mass Spectrom. 27 777-82... 

Asano K, Goeringer D and McLuckey S 1998 Dissociation kinetics in the quadrupole ion trap Proc. 46th Conf Am. Soc. Mass Spectrom. 

Brodbelt J, Liou C-C and Donovan T 1991 Selective adduct formation by dimethyl ether chemical ionization is a quadrupole ion trap mass spectrometer and a conventional ion source Ana/. Chem. 63 1205-9... 

Gronert S 1998 Estimation of effective ion temperatures in a quadrupole ion trap J. Am. Soc. Mass Spectrom. 9 845-8... 

Son M, Frankevich V, Nappi M, Santini R E, Amy J W and Cooks R G 1996 Broad-band Fourier transform quadrupole ion trap mass spectrometry Anal. Chem. 68 3341 -20... 

This is the standard referenoe volume for the theory and applioation of quadrupole mass speotrometry. 

Only if the total charge on the system (q) equals zero will the dipole moment be unchanged Similar arguments can be used to show that if both the charge and the dipole moment ar zero then the quadrupole moment is independent of the choice of origin. For convenience the origin is often taken to be the centre of mass of the charge distribution. 

Positive ions are obtained from a sample by placing it in contact with the filament, which can be done by directing a gas or vapor over the hot filament but usually the sample is placed directly onto a cold filament, which is then inserted into the instrument and heated. The positive ions are accelerated from the filament by a negative electrode and then passed into a mass analyzer, where their m/z values are measured (Figure 7.1). The use of a suppressor grid in the ion source assembly reduces background ion effects to a very low level. Many types of mass analyzer could be used, but since very high resolutions are normally not needed and the masses involved are quite low, the mass analyzer can be a simple quadrupole. 

The Q in Q/TOF stands for quadrupole (see Chapter 25, Quadrupole Ion Optics ). A Q/TOF instrument — normally used with an electrospray ion inlet — measures mass spectra directly to obtain molecular or quasi-molecular mass information, or it can be switched rapidly to MS/MS mode to examine structural features of ions. The analyzer layout is presented in Figure 20.2. 

The term Q/TOF is used to describe a type of hybrid mass spectrometer system in which a quadrupole analyzer (Q) is used in conjunction with a time-of-flight analyzer (TOP). The use of two analyzers together (hybridized) provides distinct advantages that cannot be achieved by either analyzer individually. In the Q/TOF, the quadrupole is used in one of two modes to select the ions to be examined, and the TOF analyzer measures the actual mass spectrum. Hexapole assemblies are also used to help collimate the ion beams. The hybrid orthogonal Q/TOF instrument is illustrated in Figure 23.1. 

Schematic diagram of an orthogonal Q/TOF instrument. In this example, an ion beam is produced by electrospray ionization. The solution can be an effluent from a liquid chromatography column or simply a solution of an analyte. The sampling cone and the skimmer help to separate analyte ions from solvent, The RF hexapoles cannot separate ions according to m/z values and are instead used to help confine the ions into a narrow beam. The quadrupole can be made to operate in two modes. In one (wide band-pass mode), all of the ion beam passes through. In the other (narrow band-pass mode), only ions selected according to m/z value are allowed through. In narrow band-pass mode, the gas pressure in the middle hexapole is increased so that ions selected in the quadrupole are caused to fragment following collisions with gas molecules. In both modes, the TOF analyzer is used to produce the final mass spectrum.

A hexapole assembly of rods (poles) is built similarly to the quadrupole, but now there are three sets of opposed rods evenly spaced around a central axis. The hexapole cannot act as a mass filter by applying a DC field and is used only in its all-RF mode. It is therefore a wide band-pass filter and is used to collimate an ion beam. (Like-charged particles repel each other, and an electrically charged beam will tend to spread apart because of mutual repulsion of ions unless steps are taken to reduce the effect.)... 

A single instrument — a hybrid of a quadrupole and a TOF analyzer — can measure a full mass spectrum of ions produced in an ion source. If these are molecular ions, their relative molecular mass is obtained. Alternatively, precursor ions can be selected for MS/MS to give a fragment-ion spectrum characteristic of the precursor ions chosen, which gives structural information about the original molecule. 

In the transverse direction of the quadrupoles, an ion will oscillate among the poles in a complex fashion, depending on its mass, the voltages (U, V), and the frequency (to) of the alternating RF potential. By suitable choices of U, V, and to, it can be arranged that only ions of one mass will oscillate stably about the central axis in this case, all other ions will oscillate... 

For a beam of ions injected into the quadrupole assembly from an ion source, depending on mass, some (M,) pass along the central axis, but others (Mj, Mj) are deflected to the rods. 

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