Continuous trapping instrument

The research group of Hostettmann significantly contributed to the current widespread use of LC-MS in the analysis, characterization, and dereplication of plant phenols including flavonoids. Initially, thermospray and continuous-flow FAB were applied. ESI and APCl were implemented in the mid 1990s [39]. The group evaluated both Q-TOF and multistage MS" with an ion-trap instrument for the dereplication of flavonoids in erode plant extracts [12], and pioneered the application of on-line LC-NMR in this field [39]. 

All resins must be swollen with an appropriate solvent before use, with the exception of PEGA resins which are supplied as a slurry in methanol or water. Underivatized polystyrene resins do not swell particularly well in dimethyl-formamide (DI ), hence the resin must be first swollen in dichloromethane (DCM). In contrast, PEG-PS resins can be packed dry into the reaction vessel and be swollen directly with DMF. In continuous-flow instruments, pumping the solvent up the reaction column is an effective way to remove air bubbles trapped in the resin bed. 

One of the attractive features of SFE with CO2 as the extracting fluid is the ability to directly couple the extraction method with subsequent analytical methods (both chromatographic and spectroscopic). Various modes of on-line analyses have been reported, and include continuous monitoring of the total SFE effluent by MS [6,7], SFE-GC [8-11], SFE-HPLC [12,13], SFE-SFC [14,15] and SFE-TLC [16]. However, interfacing of SFE with other techniques is not without problems. The required purity of the CO2 for extraction depends entirely on the analytical technique used. In the off-line mode SFE takes place as a separate and isolated process to chromatography extracted solutes are trapped or collected, often in a suitable solvent for later injection on to chromatographic instrumentation. Off-line SFE is inherently simpler to perform, since only the extraction parameters need to be understood, and several analyses can be performed on a single extract. Off-line SFE still dominates over on-line determinations of additives-an... 

The compatibility is excellent with continuous ion sources such as ESI, dynamic SIMS, CF-FAB, ICP, El, Cl, etc. Sector instalments are not well-suited for pulsed ionization methods, although there are examples where MALDI sources have been utilized [225-229]. Sector instruments are usually larger and more expensive than other mass analyzers, such as TOFs, quadrupole filters, and traps. 

Quadmpole ion traps were originally coupled to continuous ion sources but also work well with pulsed ion sources. The cylindrical QIT is a compact device with a diameter and length of 5 cm and the linear QIT is the size of a quadmpole mass filter, that is, 20 cm long. As stand-alone instruments they are nowadays of benchtop size and, together with quadmpole mass filters, are considered to be standard low-cost devices, which are commonly coupled to LC systems. 

There are four main modes of operation of LC-NMR instruments, in terms of how the compound/fraction of interest is dealt with post chromatographic separation. These methods are continuous-flow, stop-flow, peak parking and peak trapping. There are several different variations within each of these modes (e.g. peak-slicing). Each one of these modes will be described in turn and advantages and disadvantages will be discussed. See Fig. 19.20. 

In the ion trap technology, ions are captured in three-dimensional electric fields. The continuous beam of ions fills the trap up to the limit of their space charge. When additional electric fields are applied, ions are ejected sequentially and detected. Accumulation of ions in the trap results in high sensitivity for these instruments. The trap can be operated in MS and MS/MS modes. In the latter, the ions of interest are maintained in the trap, whereas the other ions are excluded. Sequential fragmentation steps can be performed to generate MSn spectra, highly valuable for structural characterization studies. 

Chemists should help develop better methodology for isolating compounds from the environment, particularly the soil environment. We need more breakthroughs along the line of the trapping resin developed by Tang and Young. Chemists should continually develop improved separation and spectral analyses systems. The instruments now available are extremely powerful but, because of cost, are available to only a few laboratories. 

Quadrupole mass spectrometers were used in both the early ICP-MS instrument development research and the first commercial instruments. To date, quadrupole-based ICP-MS instruments continue to be predominant. During the last several years, ICP ion sources have been coupled with mass spectrometers of several different designs, including double-sector, single-sector, time-of-flight, ion trap, and Fourier transform ion cyclotron resonance. 

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