Triple quadrupole analyser

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

A triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and selectivity in the quantitative determination of sulfonylurea herbicides. Ion trap mass spectrometers may also be used, but reduced sensitivity may be observed, in addition to more severe matrix suppression due to the increased need for sample concentration or to the space charge effect. Also, we have observed that two parent to daughter transitions cannot be obtained for some of the sulfonylurea compounds when ion traps are used in the MS/MS mode. Most electrospray LC/MS and LC/MS/MS analyses of sulfonylureas have been done in the positive ion mode with acidic HPLC mobile phases. The formation of (M - - H)+ ions in solution and in the gas phase under these conditions is favorable, and fragmentation or formation of undesirable adducts can easily be minimized. Owing to the acid-base nature of these molecules, negative ionization can also be used, with the formation of (M - H) ions at mobile phase pH values of approximately 5-7, but the sensitivity is often reduced as compared with the positive ion mode. 

Different mass analysers can be combined with the electrospray ionization source to effect analysis. These include magnetic sector analysers, quadrupole filter (Q), quadrupole ion trap (QIT), time of flight (TOF), and more recently the Fourrier transform ion cyclotron resonance (FTICR) mass analysers. Tandem mass spectrometry can also be effected by combining one or more mass analysers in tandem, as in a triple quadrupole or a QTOF. The first analyzer is usually used as a mass filter to select parent ions that can be fragmented and analyzed by subsequent analysers. 

Mass spectrometric analysis was performed with a hybrid triple quadrupole/ linear ion trap Applied Biosystem MSD Sciex 4000QTRAP (Applied Biosystems, Foster City, USA) instrument equipped with a Turbospray ESI interface. For target quantitative analyses, data acquisition was performed in SRM, recording the transitions between the precursor ion and the two most abundant fragment ions. The developed instrumental method display excellent LODs in SRM mode between 0.5 and 1.2 pg (Table 2). 

In addition to the diversity of ionisation techniques available, mass spectrometers offer a selection of mass analyser configurations. Of note are single (MS) and triple quadrupole (MS—MS) instruments, ion trap analysers (MS)n, time-of-flight (ToF) analysers, sector field analysers, and Fourier transform-ion cyclotron resonance (FTICR) instruments. 

In this instrument, the final stage of the triple quadrupole is replaced by an orthogonal time-of-flight (ToF) mass analyser, as shown in Figure 3.10. The configuration is typical of the latest generation of ToF instruments in which a number of reflectrons, in this case two, are used to increase the flight path of the ions and thus increase the resolution that may be achieved. 

Figure 2.4 Comparison of (a) sensitivity, (b) variability, (c) selectivity, and (d) pricing between various chemical and immunological analyses for the presence of PPCPs in the environment. FID = flame ionization detector and EC = electrochemical detection. Note that GC-MS-MS can have mass detectors such as triple quadrupole and ion trap with ionization from El = electron ionization or Cl = chemical ionization, whereas LC-MS-MS with ionization from ESI = electrospray ionization, APCI = atmospheric pressure chemical ionization, or APPI = atmospheric pressure photoionization. (Adapted from Ingerslev and HaUing-Sprensen, 2003.)...

Swiderek, K. M. Davis, M. T. Lee,T. D. 1998. The identification of peptide modifications derived from gel-separated proteins using electrospray triple quadrupole and ion trap analyses. Electrophoresis, 19,989-997. 

Fig. 5 Statistical evaluation of LC-MS-based methods for tropane alkaloids referred in this chapter. (a) Relative frequency of ionization methods. +APCI positive atmospheric pressure chemical ionization, +ESI positive electrospray ionization, FAB fast atom bombardment, +TSP positive thermospray, (b) Relative frequency of scan modes used. MS full scan MS, MS/MS tandem mass spectrometry (product ion scan), MRM multiple reaction monitoring, SIM selected ion monitoring, (c) Relative frequency of mass analysers used. EBQtQ2 double focusing sector field mass spectrometer, IT ion trap, QqQ triple quadrupole, SQ single quadrupole. Considered publications were found by PubMed data-based search and references cited in these articles...

Triple-quadrupole and more recently hybrid instruments, for instance the quadrupole TOF instrument or the ion trap-FT ion cyclotron resonance mass spectrometer, allow one to obtain a mass spectrum resulting from the decomposition of an ion selected in the first analyser. The time-dependent decomposition of a selected ion can also be observed in ion cyclotron resonance and ion trap instruments. They allow fragments over several generations (MS") to be observed. 

Operations similar to the 3D traps can be performed, as for example to expel ions of all masses except one and observe the fragmentation, with or without ion excitation at the secular frequency. Then the fragments are analysed. This can be repeated several times for MS" experiments. All the other operations of a 3D trap can be applied, but it also has similar limitations, for example MS/MS is limited to fragmentation scans. Thus precursor ion scan or neutral loss scan that are available with triple quadrupole instruments cannot be used on ion traps (Figure 2.11). 

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. 

Low-energy CID spectra are measured using triple quadrupole, ion trap, ICR or hybrid instruments. For tandem mass spectrometers in space, the collision chamber is most often a quadrupole in the RF mode only, which allows one to focus the ions that are angularly dispersed by the collision. The pressure difference between the collision cell and the rest of the analyser is obtained through differential pumping. 

All mass spectrometric analyses were carried out on a triple quadrupole mass spectrometer (TSQ-700) from Finnigan-MAT (San Jose, CA) equipp with an electrospray ion source (ESI) operating at atmospheric pressure. Mass spectra were recorded in the positive ion mode. The electrospray needle was operated at a differential of 3-4 kV, the conversion dynode was set to -15 V. The drying gas was nitrogen and the temperature was set to about 200 °C. A sheath flow of 2-methoxyethanol was delivered with 2 pJ/min and the nitrogen sheath gas was set at 50 psi. Samples were directly introduced into the source with a flow rate of 2 p.l/min. Scans were continuously taken every three seconds. 

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