FA-SIFT

The technique used is the Flowing Afterglow Selected Ion Flow Tube (FA-SIFT), a short description of which is given elsewhere337,338 it allows the preparation of ions in a first flow tube, their separation from complex reaction mixtures with a quadrupole, the... 

The reaction chemistry of smaller IS negative ions is receiving continued attention. Recently, Bierbaum and co-workers have used the Boulder FA-SIFT to monitor the reactivity of various C and C H ions with atomic and molecular hydrogen [245]. The absence of any reaction with H2 is important given the predominance of hydrogen as an IS molecule, while for C7, CR, Cy and C,r, associa-... 

FA-SIFT flowing afterglow - selected ion-flow tube... 

Three main types of experimental techniques have been used high pressure mass spectrometry (HPMS), flowing afterglow (FA or FA-SIFT) studies, and pulsed ion cyclotron resonance (ICR) spectrometry. See Chapter 7 for further discussion and leading references. 

Milligan DB, Fairley DA, Freeman CG, et al. A flowing afterglow-selected ion flow tube (FA/SIFT) comparison of SIFT injector flanges and Hj +N revisited. Int J Mass Spectrom. 2000 202 351-61. 

Figure A3.5.5. Rate constants for the reaction of Ar with O2 as a fiinction of temperature. CRESU stands for the French translation of reaction kinetics at supersonic conditions, SIFT is selected ion flow tube, FA is flowing afterglow and HTFA is high temperature flowing afterglow.

The ion reaction chamber in the present work was at a relatively high pressure (10 torr), so that conditions were similar to those used with our previous pulsed-electron high-pressure sources.8,9 Reactors operating at lower pressures such as 1 torr or less should also be suitable. Thus, ES could probably be easily adapted for use with flow tubes such as FA and SIFT. 

To overcome this, instrumental techniques such as pulsed high-pressure mass spectrometry (PHPMS), the flowing afterglow (FA) and allied techniques like the selected-ion flow tube (SIFT), and ion cyclotron resonance (ICR) spectrometry and its modem variant, Fourier transform mass spectrometry (FTMS), have been developed. These extend either the reaction time (ICR) or the concentration of species (PHPMS, FA), so that bimolecular chemistry occurs. The difference in the effect of increasing the pressure versus increasing the time, in order to achieve bimolecular reactivity, results in some variation in the chemistry observed with the techniques, and these will be addressed in this review as needed. 

It is interesting to note that the earlier FA experiments only recognised the two major product channels in reaction (17) whereas the SIFT, which is especially valuable for the determination of product distributions, identified the minor 0+ product channel... 

An important development for ion/molecule reaction studies by FA is the extension of the method using so-called selected ion flow tube (SIFT) facilities (Adams and Smith, 1976). In the latter configuration ions are generated in an external ion source, extracted and separated by a quadruple mass filter, after which ionic species of a single mass-to-charge ratio are injected into the flow tube. This set-up permits the ion/molecule reactions of mass selected ions to be studied in the absence of ions of other masses (similar to studies of mass selected ions in FT-ICR after application of so-called ion ejection techniques see above) and neutral precursors, while a wide choice of neutral substrates is possible. 

The gas phase acid/base properties of molecules have been subject to equilibrium or bracketing measurements employing mass spectrometric techniques like ion cyclotron resonance (ICR) [4], Fourier transform ion cyclotron resonance (FT-ICR) [5,6], Flowing afterglow (FA) and Selected ion flow tube (SIFT) [7], and high pressure mass spectrometry (HPMS) [8]. Proton transfer between neutral molecules are then investigated by measurements of reactions... 

Apart from the proton transfer reactions discussed in Section II, phosphorus species undergo a range of other ion-molecule reactions in the gas phase. The types of instruments which have been used to study ion-molecule reactions of phosphorus species include ion cyclotron resonance (ICR) mass spectrometers and the related FT-ICR instruments, flowing afterglow (FA) instruments and their related selected-ion flow tubes (SIFT) and also more conventional instruments This section is divided into four topics (A) positive ion-molecule reactions (B) negative ion-molecule reactions (C) neutralization-reionization reactions and (D) phosphorus-carbon bond formation reactions. 

Chitin and Chitosan. Chitin through the courtesy of Kypro Co., sifting to remove fines and extraneous non-shell flakes, the remaining material was ground in a Thomas Wiley laboratory mill (Model 4, A. H. Thomas Co., Philadelphia, FA) to pass a 2.00 mm screen. Using a Ro Tap Testing Sieve Shaker (Model B, W. S. Tyler, Inc., Mentor, OH), three fractions of each material were collected <1.00-0.50 mm <0.50-0.25 mm and <0.25 mm. 

Smith, D SpanSl, P. (2015) SIFT-MS and FA-MS Methods for Ambient Gas Phase Analysis Developments and Applications in the UK. Analyst 140 2573-2591. 

The conventional type of drift-tube (DT) experiment, in which ions drift under the influence of a weak electric field, has been widely used in the measurement of ion mobilities, equilibrium constants, and IMR rate constants as a function of ion kinetic energy from 0.05 to about 5 eV [9]. The capabilities of this technique have been extended soon by incorporating an ion drift-tube section into the gas-flowing region of the basic FA device [10]. These FA and DT instruments (namely, flow-tube mass spectrometry) and their many derivative techniques such as the powerful selected ion flow tube (SIFT) method, variable temperature FA, and guided ion beam tandem mass spectrometry have been employed in many laboratories worldwide. 

The techniques for measuring rate constants and prodnct distribntion (branching ratios) for ion-molecule reactions are varied, but the majority of the data have been determined using the FA, drift-tube (DT), selected ion flow tube (SIFT), high-pressure mass spectrometric techniques, or ICR. These methods are detailed in Chap. 4. A number of surveys of all classes of ion-molecule reactions have appeared in the literature Ferguson [16], Sieck et al. [17], Albritton [18], Anicichet al. [19], Ikezoe et al. [20], some of which include termolecular reactions or are limited to selected methods. Anicich listed [21] an index to the hterature for gas phase bimolecular positive ion-molecule reactions as a comprehensive survey of ion-molecule reaction kinetics and product distribution of the reactions. Over 2300 references are cited. This index covers the hterature from 1936 to 2003. It was limited to selected reactions, listed by reactant ion, that were important for chemical modehng ionic processes in planetary atmospheres, cometary comas, and intersteUar clouds. 

An important adaptation of the FA technique comprises the implementation of ion separation methods, which allows for more advanced flow drift tubes and selected ion flow tubes (SIFT) [105, 106] (see below). More recently, flow drift tubes (see Sect. 4.6) and flowing atmospheric pressure afterglow (FAPA) devices [107] have been developed. 

The selected ion flow tube (SIFT) solved the key limitation of the FA technique, the tendency for several distinct primary ions to form when polyatomic gases are used in the discharge, by employing a mass filter to allow ions of only one specific miz into the flow tube. This breakthrough originated from work by Adams and Smith and led to a technique which is still in use today [12],... 

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