Single quadrupole filter

Aside from the single mass filter, the most common configuration for quadrupole mass spectrometers is the triple-quadrupole instrument. This is the simplest tandem mass spectrometer using quadrupole mass filters. Typically, the... 

Some of them comprise a single-liquid extraction and direa instrumental determination without a clean-up step [85-87]. This assumption relies on the ability of the mass analyzer to filter out by mass any coeluting impurities. However, many authors assert that further sample preparation prior to LC-MS analysis would benefit analysis [88-90] because ionization suppression can occur by matrix effects. A number of instrument types have been used single quadrupole, triple quadrupole, and linear ion trap [15,88-90]. 

Finally in this section, it is noted that single quadrupole mass filters (as opposed to triple quadrupole instruments) are generally used in trace quantitative analyses only for GC-EI(CI)-MS methods for thermally stable analytes (e.g. pesticides in various matrices) in SIM mode. (It is interesting that GC/MS instruments still appear to account for a large fraction of mass spectrometer units sold worldwide.) The same linear quadrupole devices can also be operated as 2D ion trap mass spectrometers, discussed in Sections 6.4.5 and 6.4.6. 

A mass spectrometer containing a single quadrupole mass filter cannot be used to perform this type of experiment. However spectrometers consisting of three quadrupoles in series (triple quadrupole mass spectrometers) are available for this purpose. The first quadrupole is used to select the parent ion, fragmentation takes place in the second quadrupole and daughter ions are selected by the third quadrupole. 

Restrictions on the use of ICP-MS in magnesium metabolic studies arise primarily from the limits on precision. Single-collector instruments, irrespective of whether they are equipped with a quadrupole filter, with or without an additional... 

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. 

Ions of different m/z values pass sequentially in time through the quadrupole mass filter to reach an in-line, single-point ion collector. 

Like sector analyzers, quadrupole analyzers are well suited for continuous ion sources such as ESI, but are not well-suited for pulsed ionization methods. Quadmpole mass spectrometers are generally substantially cheaper and smaller than sector instruments and Qq-TOFs. They are very often used in combination with GC and LC, and single or triple quadmpole mass filters are very common benchtop instruments for routine measurements. 

Fig. 11.16. Representation of three tandem mass spectrometry (MS/MS) scan modes illustrated for a triple quadrupole instrument configuration. The top panel shows the attributes of the popular and prevalent product ion CID experiment. The first mass filter is held at a constant m/z value transmitting only ions of a single mlz value into the collision region. Conversion of a portion of translational energy into internal energy in the collision event results in excitation of the mass-selected ions, followed by unimolecular dissociation. The spectrum of product ions is recorded by scanning the second mass filter (commonly referred to as Q3 ). The center panel illustrates the precursor ion CID experiment. Ions of all mlz values are transmitted sequentially into the collision region as the first analyzer (Ql) is scanned. Only dissociation processes that generate product ions of a specific mlz ratio are transmitted by Q3 to the detector. The lower panel shows the constant neutral loss CID experiment. Both mass analyzers are scanned simultaneously, at the same rate, and at a constant mlz offset. The mlz offset is selected on the basis of known neutral elimination products (e.g., H20, NH3, CH3COOH, etc.) that may be particularly diagnostic of one or more compound classes that may be present in a sample mixture. The utility of the two compound class-specific scans (precursor ion and neutral loss) is illustrated in Fig. 11.17.

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