Quadrupole MS detector

The quadrupole MS detector is used in the same way as it is with GC, with the same sensitivity and ability to identify compounds. In use, most or all the solvent is removed before the sample enters the MS (see Chapter 14). 

The quadrupole MS detector was the first, and is still the most common, detector used for LC/MS, but a number of other mass spectrometers have been adapted to this application. Both three-dimensional spherical (ITD) and linear (LIT) ion trap detectors offer tremendous potential for general, inexpensive LC/MS systems. They both offer the ability to be used as either a mass spectral detector or as a MS/MS detector. The 3D ITD (Fig. 15.5) allows ions to be trapped in the ion trap where they can be fragmented by heavy gas collision and the fragments released by scanning the dc/RF frequency of the trap. 

Eurther analysis of the migration extract is preferably carried out using GC-MS and LC-MS. Eor GC-MS it is impossible to detect components with a molecular mass above 1000 Da due to volatility and the mass range of quadrupole MS detectors. With LC-MS the mass range can be chosen and thus the highest mass can be set at 1000 Da. Multi-methods exist with which almost all elements in the periodic system can be analysed in extracts at low levels. Combination of induced coupled plasma (ICP) and atomic absorption (AAS) coupled to MS is the preferred method. Quantification of each element is also possible with this method. 

Molecular Beams—Kinetics and Mechanism. —An outstanding example in this field is by Wachs and Madix who employed a modulated molecular beam source to study the reaction of HCOOH on Ni(llO). Products were examined individually as was the phase-lag in their appearance in their quadrupole MS detector. They could measure reaction rates for coverages of 10 to 1 monolayer and reaction times from 10 to 10 s over a temperature range of 400—800 K. The processes investigated were adsorption desorption of HCOOH, and HCOOH -> CO2, CO, H2, and H2O. Their findings on selectivity and rates for all possible reactions can be found in their paper. 

Using IC-MS with a single quadrupole MS detector and method programming of the cone voltage, sensitivity can be optimized for each of the haloacetic... 

Figure 9.1 Comparison of stationary phases for the UHPLC separation of fourteen illicit and licit drugs, (a) Column 1.9 [xm Thermo Fisher Scientific Hypersil GOLD aQ (100 X 2.1 mm) (b) Column 1.9 [xm Thermo Fisher Hypersil GOLD (100 x 2.1 mm) (c) Thermo Fisher Scientific Hypersil GOLD PFP (100 x 2.1 mm). Mobile phase A = Water, 0.1% formic acid, B = Acetonitrile, 0.1% formic acid. How rate = 1 mL/min. Instrument Thermo Fisher Scientific Accela UHPLC system coupled to Thermo Fisher Scientific MSQ Plus single quadrupole MS detector.

Figure 13.5. Diagram of quadrupole MS used as detector for gas chromatography.

PDA detectors can be operated at rapid data acquisition rates (up to 40 Hz) and are the most common used. Quadrupole MS systems are capable of supplying sufficient spectra for peak. For reliable component assignment, of course, TOF-MS systems possessing higher scan speed can be used. 

Mass Spectrometry. The use of a quadrupole mass spectrometer as a GC detector for nonmethane hydrocarbon analysis has come of age in recent years. Development of capillary columns with low carrier gas flows has greatly facilitated the interfacing of the GC and mass spectrometer (MS). The entire capillary column effluent can be dumped directly into the MS ion source to maximize system sensitivity. GC-MS detection limits are compound-specific but in most cases are similar to those of the flame ionization detector. Quantitation with a mass spectrometer as detector requires individual species calibration curves. However, the NMOC response pattern as represented by a GC-MS total ion chromatogram is usually very similar to the equivalent FID chromatogram. Consequently, the MS detector can... 

Vinyl chloride - Mass fragmentography followed by GC-MS, recon. in m/e 62 and 64 peaks, (quadrupole MS with multiple ion detector) [158]... 

Traditional detectors (i.e., FID electron capture detector, BCD nitrogen-phosphorous detector, NPD) supply only retention data. However, in many cases this is not enough for proper identification of analytes. Application of GC coupled with an MS detector gives much more information (i.e., the mass spectmm of each compound). GC-MS is a well known and frequently used technique that combines the highly effective separation of GC with the high sensitivity and selectivity of MS. Moreover, improvements in analytical instruments based on different types of mass analyzers (ion trap, quadrupole, and TOF) and the development of hybrid Q-TOF has enhanced the analytical capabilities of modem hardware. Different kinds of mass spectrometers are presented in Table 14.2 [119]. 

Gas chromatography equipped with a flame ionization detector (FID) and quadrupole MS have been employed for measuring carbon disulfide concentrations in the breath of workers following exposure to carbon disulfide (Campbell et al. 1985 Wells and Koves 1974). The MS technique is rapid and requires no sample preparation (Campbell et al. 1985). A detection limit of 1.6 ppb (5 pg/m3) of... 

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