Quadrupole mass spectrometers performance characteristics

A second type of MS instrument capable of performing a product ion scanning experiment is the ion trap mass spectrometer. The difference between this instrument and the triple quadrupole mass spectrometer is the ion trap is capable of performing numerous sequential product ion experiments on the same compound. For example, a potential metabolite is dissociated into several characteristic fragment ions in the first stage of MS/MS. Then, one of these fragment ions can be further dissociated into smaller ions. This is a second stage of MS/MS known as MS. This process can continue until the site of meta-... 

The most widely used tandem mass analyzer for bioanalysis is the triple-quadrupole mass spectrometer (TQMS). In the TQMS format, a characteristic fragmentation transition is monitored for an analyte with more than one mass filter in combination, hence the term MS/MS. A diagram of a TQMS is presented in Figure 11.2. A TQMS consists of two mass selecting quadrupoles, Qi and Q3, and flanked by a center quadrupole (Q2) that acts as a collision cell. Since Q2 is operated in the RF-only mode, mass selection is not performed in this region. The Q2 rods are important, however, since they refocus ions... 

The analytical performance of four modes of LC-MS, multiple MS (MS"), and tandem MS operation (APCI and ESI with positive and negative ionizations) has been compared for two mass spectrometers, a triple-quadrupole and an ion-trap instrument.With 15 flavonoids as test compounds, the use of APCI in the negative-ion mode gave the best response, with the signal intensities and the mass-spectral characteristics not differing significantly between the two instruments. Under optimum conditions, full-scan limits of detection of... 

Besides the triple quadrupol instruments, other types of mass spectrometers might be used as well. Examples for these types of instruments are ion traps, time of flight mass spectrometers and also single quadrupol mass analyzers. Due to the characteristic and specific advantages and disadvantages of different instrument types, the overall assay performance (e.g. sensitivity, dynamic range and selectivity) may vary quite a bit from one instrument type to the other. 

A. PremstaUer, K.-H. Ongania, C.G. Huber, Factors determining the performance of triple quadrupole, quadrupole ion trap and sector field mass spectrometers in ESI-MS-MS of oligonucleotides. 1. Comparison of performance characteristics. Rapid Commun. Mass Spectrom., 15 (2001) 1045. 

Another requirement for a mass spectrometer is to use the most appropriate mass analyser. Several mass analysers with varying performance characteristics are available. However, the most commonly used in the SIMS experiment are magnetic-sector [21-23], quadrupole [24-26] and, recently, time-of-flight (TOF) [27-30] analysers. 

Tandem mass spectrometry is applicable to all types of biomolecules but typically requires specialized mass spectrometry instrumentation for implementation. The most common tandem mass spectrometer is a triple quadrupole instrument, wherein the first and third quadrupoles are used as mass analysers and the middle quadrupole is used as a collision chamber. MS/MS can be performed with double focusing sector instruments and in some cases with specialized TOF mass analysers. Quadrupole ion traps and FTICR mass spectrometers are ideally suited for MS/MS experiments, and due to the operational characteristics of these mass analysers... 

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