Sources and Reaction Chambers

Figure 4. Ion source and reaction chamber for ion-molecule equilibria. Solution to be electrosprayed flows through elestrospray capillary ESC at 1 -2 pL/min. Spray and ions enter pressure reduction capillary PRC and emerge into forechamber FCH maintained at 10 torr by pump PL. Ions in gas jet, which exits PRC, drift towards interface plate IN under influence of drift field imposed between FCH and IN. Ions enter the reaction chamber RCH through an orifice in IN and can react with reagents in the reagent gas mixture RG. This flows into RCH and out of RCH to FCH where it is pumped away. Ions leaking out of RCH through orifice OR are detected with a mass spectrometer. To reduce the inflow of solvent vapors into the pressure reduction capillary PRC, a stream of dry air is directed through the pipe Al, at 60 L/min, and pure N2 is directed at SG into the annular space at the entrance of the pressure reduction capillary, PRC. From Klassen, J. S. Blades, A. T. Kebarle, P. J. Phys. Chem. 1995, 99, 1509, with permission.

Figure 5. Front end of triple a quadrupole mass spectrometer with an ion source and reaction chamber (see Figure 4) mounted in front of an evacuated space containing skimmer cone CB, AC only quadrupole lens Qo, and first quadrupole Qi. The second and third quadrupoles, Q2 and Q3, are not shown. CR denotes cryopumping surfaces. IQ is an interquad lens.

Figure 7. Ion source and reaction chamber for the study of ion-molecule reactions at different temperatures. Notation used is same as in Figure 4 except CB = copper block, EL = electrode attached to pressure reducing capillary, TC = thermocouple, TS = thermal shield, ISP = evacuated space reduces thermal conductivity from CB to flange. From Klassen, J. S. Blades, A. T. Kebarle, P. ). Am. Chem. Soc. 1996, with permission.

A very similar experimental setup was apphed by the group of Castleman [171, 172] in their gas-phase ion-equihbrium studies iuvolving gas-phase hydration of metal cations like Pb and BP. A thermocouple in the reaction chamber enabled continuous monitoring of the temperature. A gating grid between ion source and reaction chamber allowed more acciuate control of the eneigy of the ions entering the reaction cell. 

In the ICR technique [11,12], ions are constrained in cyclotron motion (see Fig. 1) by the application of magnetic and electric fields to electrodes which form the boundaries of a small low-pressure chamber serving as both ion source and reaction region. The ions motion is mass-dependent, and calibration of the electric field strength ensures that only ions of a particular mass are effectively trapped within the ion chamber. Transverse drift of ions, towards the chamber s end cap, is another aspect of the ion motion which can be controlled as required. ICR chambers of widely different geometry (see Fig. 2) have been used for studying a variety of ion properties. Characteristic operating conditions are a reaction... 

The pulsed technique employed by Henchman et uses an ordinary source in which a short electron pulse provides reactant ions. Another short pulse applied to a repeller plate accelerates these to a definite energy (about 1 eV). Before emerging from the exit slit of the chamber, the reactant ions may collide with un-ionized gas to give product ions. The forward velocity of both reactant and product ions is measured by applying a variably delayed gating pulse to a deflection electrode outside of the ionization chamber. A more recent version of the apparatus incorporates separate ion production and reaction chambers, as well as a stopping potential analyzer. ... 

Next to using a mass spectrometer to monitor and detect the product ions generated in ion-molecule reactions, these ions can also be studied using (laser) spectroscopy. One of the challenges in such studies is the low concentration of ions present in the source or reaction chamber. Informative reviews on the spectroscopy of molecular ions have been published [177-179],... 

Some of the problems encountered in the mass spectrometric study of ion-molecule reactions are illustrated in a review of the H2-He system (25). If the spectrometer ion source is used as a reaction chamber, a mixture of H2 and He are subjected to electron impact ionization, and both H2+ and He+ are potential reactant ions. The initial problem is iden-... 

The present description is based on previous publications from this laboratory56-59 and the interested reader will find additional details and references in that work. Two different ion-source reaction chambers are used. One of these sources which operates at room temperature is shown in Figure 4. The second source, a variable temperature source will also be described. The electrospray generator and the ion-source reaction chamber are shown in Figure 4, while the mounting of the ion source and the front end of the mass spectrometer are shown in Figure 5. 

The solution to be electrosprayed is passed through the electrospray capillary (ESC) by means of a motor driven syringe. Some of the spray containing the ions then enters the pressure reducing capillary (PRC) leading to the forechamber (FCH) of the ion source. The exit tip of the PRC directs the gas jet in a direction parallel to the bottom of the FCH, i.e. across the interface plate (IN). An orifice of 4 mm diameter in the interface plate connects the FCH to the reaction chamber (RCH). The ions in the jet exiting from the PRC are deflected out of the jet towards this orifice and into the RCH by means of an electric field applied across the FCH. A weak field is also applied across the RCH. At the bottom of the RCH a small orifice, 100 pm diameter, allowed some gas and ions to leak into the vacuum of the mass... 

In order to avoid such uncontrolled collisional activation, we chose to use apparatus which is closely related to the ion-source reaction chambers developed for thermal ion-molecule equilibria (see preceding Section A). In fact, sources like those shown in Figures 4 and 7 are well suited for providing thermalized ions however they provide somewhat low ion intensities, typically some 50,000 counts/s of a given major ion in a mass spectrum after mass analysis. However, such intensities are completely sufficient for CID threshold measurements and the source... 

The low-pressure source used in the apparatus (Figure 9) also has a forechamber, between CAP and IN, which now is called the low-pressure source (LPS) and a reaction chamber between IN and OR. However now the reaction chamber is supplied with pure N2 and acts as an ion thermalization (IT) chamber. The pressure reduction capillary CAP is now coaxial with the orifice in IN leading to IT, and it is this coaxial arrangement that leads to higher ion intensities. Both LPS and IT are maintained at 10 torr. The drift field between IN and the orifice OR is kept low, Elp < 6 volt/cm torr, a value that is consistent with essentially thermal ions. 

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. 

The important and stimulating contributions of Kebarle and co-workers 119 14 > provide most of the data on gas-phase solvation. Several kinds of high pressure mass spectrometers have been constructed, using a-particles 121>, proton- 123>, and electron beams 144> or thermionic sources 128> as primary high-pressure ion sources. Once the solute A has been produced in the reaction chamber in the presence of solvent vapor (in the torr region), it starts to react with the solvent molecules to yield clusters of different sizes. The equilibrium concentrations of the clusters are reached within a short time, depending on the kinetic data for the... 

Br-atom initiated oxidation of dimethyl sulfide (DMS) in a large-volume reaction chamber gave SO2, CHsSBr, and DMSOJ A rapid addition of Br atoms to DMS takes place, forming an adduct that mainly reforms reactants but also decomposes unimolecularly to form CHsSBr and CH3 radicals. DMSO is formed from the reaction of BrO radicals with DMS. The reaction CH3O2 + Br CH3O + BrO is postulated as the source of BrO radicals. 

The plasma energy recycle and conversion (PERC) process is an indirectly heated ex situ thermal recycling and conversion technology. According to the vendor, it treats hazardous waste, mixed radioactive waste, medical waste, municipal solid waste, radioactive waste, environmental restoration wastes, and incinerator ash in gaseous, hquid, slurry, or solid form. The technology uses an induction-coupled plasma (ICP) torch as its heat source coupled to a reaction chamber system to destroy hazardous materials. 

Akimoto, H H. Takagi, and F. Sakamaki, Photoenhancement of the Nitrous Acid Formation in the Surface Reaction of Nitrogen Dioxide and Water Vapor Extra Radical Source in Smog Chamber Experiments, lnt. J. Chem. Kinet., 19, 539-551 (1987). 

Torr. The essential items for plasma generation are (1) an energy source for the ionization (2) a vacuum system for maintaining the plasma state and (3) a reaction chamber. 

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