Turner, J. Z. Soper, A. K. J. Phys. Chem. 1994, 98, 8168  [c.39]

Electrospray is one method for effecting this differential solvent removal. The solution is passed along a short length of stainless steel capillary tube, to the end of which is applied a high positive or negative electric potential, typically 3-5 kV (Figure 8.1). When the solution reaches the end of the tube, the powerful electric field causes it to be almost instantaneously vaporized (nebulized) into a jet or spray of very small droplets of solution in solvent vapor. Spraying efficiency can be increased by flowing a gas past the end of the charged capillary tube. Before entering the mass spectrometer proper, this mist of droplets flows through an evaporation chamber that can be heated slightly to prevent condensation. As the droplets move through this region, solvent evaporates rapidly from the surfaces and the droplets get smaller and smaller. In addition to producing the spray, this method of rapid vaporization leaves no time for equilibrium to be attained, and a substantial proportion of the droplets have an excessive positive or negative electrical charge on their surfaces. Thus as the droplets get smaller, the electrical surface charge density increases until the natural repulsion between like charges causes the release of ions and neutral molecules. The end of the capillary tube is aimed at a small hole (target) at the opposite end of this evaporation region. After vaporizing from the surface of a droplet, solvent molecules of low molecular mass quickly and conveniently diffuse away from the line-of-sight trajectory to the inlet target. A Z-spray ion source operates slightly differently (see Chapter 10).  [c.56]

Z-Spray Combined Inlet/Ion Source  [c.65]

The Z-spray inlet/ionization source sends the ions on a different trajectory that resembles a flattened Z-shape (Figure 10.1b), hence the name Z-spray. The shape of the trajectory is controlled by the presence of a final skimmer set off to one side of the spray instead of being in-line. This configuration facilitates the transport of neutral species to the vacuum pumps, thus greatly reducing the buildup of deposits and blockages.  [c.65]

Z-Spray Combined Inlet/Ion Source  [c.67]

A Z-spray. source gets around this problem. Accordingly, a first skimmer orifice is moved from a line-of-sight position to one at right angles to the initial spray direction (Figure 10.4). Now, as the ions form in the background gas, they follow the gas flow toward the vacuum region of the mass spectrometer. Some vapor solvent is also drawn down into the skimmer orifice. More solvent diffuses from the gas stream, which then bends again through a second skimmer (the extraction cone). Mostly ions and background gas molecules (plus some residual solvent molecules) pass through the second skimmer and on to the mass analyzer. There is a drying gas flowing around the entrance to the skimmer to remove more solvent from any residual droplets (Figure 10.4).  [c.68]

With the Z-spray design, there is almost no buildup of products on the skimmer orifice, so instrumental sensitivity and performance remain constant over long periods of time. In addition, this arrangement is inherently a better ion collector than the line-of-sight mode and gives a useful gain in instrument sensitivity. The open arrangement resulting from the design gives better access to the inlet tube, facilitating its manipulation, which is particularly important in the placing of nanotubes. Finally, collisionally activated decomposition (CAD) of ions can still be effected by increasing the ion extraction voltage (cone voltage see Chapter 8).  [c.68]

Z-Spray Combined Inlet/Ion Source  [c.69]

The Z-spray inlet causes ions and neutrals to follow different paths after they have been formed from the electrically charged spray produced from a narrow inlet tube. The ions can be drawn into a mass analyzer after most of the solvent has evaporated away. The inlet derives its name from the Z-shaped trajectory taken by the ions, which ensures that there is little buildup of products on the narrow skimmer entrance into the mass spectrometer analyzer region. Consequently, in contrast to a conventional electrospray source, the skimmer does not need to be cleaned frequently and the sensitivity and performance of the instrument remain constant for long periods of time.  [c.69]

A liquid chromatograph (LC) is combined with a TOF instrument through a Z-SPRAY ion source. Two hexapoles are used to focus the ion beam before it is examined by a TOF analyzer, as described in Figure 20.3.  [c.154]

A solution containing the analyte of interest is sprayed from the end of a capillary by application of a high electric potential. The resulting charged droplets are stripped of solvent, and ions formed from analyte molecules travel into the mass spectrometer (Z-spray). The hexapoles do not separate ions according to m/z value but contain them into a beam. Finally, the slow-moving ions are focused and accelerated through a potential of about 40 V before passing in front of a deflector plate (electrode). A large electric potential of several kilovolts is applied to this electrode in pulses so that, at each pulse, a section of the ion beam is deflected and accelerated into the TOF analyzer. After reflection by the reflectron, the ions are detected at a microchannel plate multipoint collector.  [c.155]

Chapter 10 Z-Spray Combined Inlet/Ion Source  [c.391]

Z-spray is a novel kind of electrospray that functions as a combined inlet and ion source. Chapter 8 ( Electrospray Ionization ) should be consulted for comparison.  [c.391]

The Z-spray source utilizes exactly these same principles, except that the trajectory taken by the ions before entering the analyzer region is not a straight line but is approximately Z-shaped. This trajectory deflects many neutral molecules so that they diffuse away toward the vacuum pumps.  [c.391]

The Z-trajectory ensures excellent separation of ions from neutral molecules at atmospheric pressure. In line-of-sight or conventional electrospray sources, the skimmer is soon blocked by ions and molecules sticking around the edges of the orifice. In Z-spray sources, the final skimmer, being set off to one side, is not subjected to this buildup of material.  [c.391]

Z-spray sources require much less frequent maintenance than do conventional electrospray sources.  [c.391]

The Z-spray inlet/ion source is a particularly efficient adaptation of the normal in-line electrospray source and gets its name from the approximate shape of the trajectory taken by the ions between their formation and their entrance into the analyzer region of the mass spectrometer. A Z-spray source requires much less maintenance downtime for cleaning.  [c.392]

Z-spray. Z refers to the approximate shape of the trajectory of particles formed by electrospray ionization  [c.447]

In a selective-inversion experiment, it is the relaxation of the z magnetizations that is being studied. For a system without scalar coupling, this is straightforward a simple pulse will convert the z magnetizations directly into observable signals. For a coupled spur system, this relation between the z magnetizations and the observable transitions is much more complex [22].  [c.2110]

Solution issuing from the end of the inlet tube, held at an electrical potential of 3 kV, forms a spray of droplets at atmospheric pressure. Solvent evaporates from these droplets. Under the influence of the general gas flow toward the vacuum pumps, ions and neutral molecules move in an arc through the first skimmer orifice, as shown. After this opening, a split between ions and neutral molecules is effected. Most remaining solvent and other neutrals flow on toward the first-stage vacuum pump. But an electric-field gradient causes the ions to flow in an arc toward a second skimmer, often called the extraction cone, and on to the mass analyzer. A few neutrals diffuse through this second skimmer, as well, because of the differences in pressures on either side of it. Note the overall flattened Z-shape of the ion trajectory.  [c.69]

For use in ICP/MS, the charged droplets produced by the electrospray nebulizer pose a problem. The droplets do not coalesce because they carry the same sign of charge viz., they are either all positively or all negatively charged, depending on the sign of the applied electric potential. This same charge leads to the droplets repelling each other and spreading the aerosol spray many droplets will be attracted to the opposite electrode or to ground potential, causing them to migrate to the walls of the nebulizer or desolvation chamber. Beyond the loss of material, the charged species also provide an electrically conducting path in an otherwise nonconducting gaseous medium. As described in Chapter 6, Coronas, Plasmas, and Arcs, this situation is a recipe for an electrical discharge. Such discharges can interfere with the sensitive detection electronics of the instrument to produce a spike in the measurement of m/z values. It is essential to remove the charges from the droplets before they can be used in ICP/MS, which can be done by adding air or water vapor to the argon carrier gas. Removal of charge from the droplets is achieved by their reaction with oxygen or water (Figure 19.20). Although this scheme reduces the problem of electrical discharges, it does not remove the problem entirely.  [c.151]

If the molecule under consideration were being placed on an empty lattice, the second segment could go into any one of the z sites adjacent to the first. However, ni of the sites are already filled, so there is a chance that one of the z sites in the coordination sphere of the first segment is already occupied. To deal with this possibility, we assume that the fraction of vacant sites on the lattice as a whole also applies in the immediate vicinity of the segment positioned above. This fraction is (N - ni)/N, so the number of possible locations for segment 2 of the (i + l)th molecule is z(N - ni)/N.  [c.514]

In the derivation of Eq. (8.40) it is assumed that each polymer segment is surrounded by z sites which are occupied at random by either solvent molecules or polymer segments. Actually, this is true of only z - 2 of the sites in the coordination sphere—z - 1 for chain ends—since two of the sites are occupied by polymer segments which are covalently bound to other polymer segments. Criticize or defend the following proposition concerning this effect The kinds of physical interactions that we identify as London or dipole-dipole attractions can also operate between segments which are covalently bonded together, so the W22 contribution continues to be valid. A slight error in counting is made—to allow for simplification of the resulting function—but this is a tolerable approximation in concentrated solutions. In dilute solutions the approximation introduces more error, but the model is in trouble in such solutions anyhow, so another approximation makes little difference.  [c.575]

O. Glemser, H. Saver, and P. Konig, Z. Inorg. Chem. 257, 241 (1948).  [c.292]

As an adaptation of electrospray, Z-spray is a cleaner and more efficient method of generating and separating analyte ions from solvent and buffer agents. In conventional electrospray sources, droplets issue from the end of a narrow inlet tube as a cone-shaped spray. The low-molecular-mass solvent molecules tend to diffuse away toward the edges of the cone, while the high-mokculai-mass analyte ions continue along the axis of the cone until they enter the mass spectrometer analyzer through a small orifice (the skimmer). The narrow solution inlet, the cone axis, and the position of the orifice lie along one straight line-of-sight trajectory, as seen in Figure 10.1a. Ions produced in a conventional electrospray source travel along an approximately linear trajectory from formation to entering the analyzer. However, the ions that pass through the skimmer are accompanied by small quantities of neutral materials, and some of these neutral materials strike the edges of the skimmer and are deposited there, where they accumulate and gradually block the skimmer hole.  [c.65]

This chapter provides brief descriptions of analyzer layouts for three hybrid instruments. More extensive treatments of sector/TOF (AutoSpec-TOF), liquid chromatography/TOF (LCT or LC/TOF with Z-spray), and quadrupole/TOF (Q/TOF), are provided in Chapters 23, 22, and 21, respectively.  [c.153]

A solution containing the analyte of interest is sprayed from the end of a capillary by application of a high electric potential. The resulting charged droplets are stripped of solvent, and ions formed from analyte molecules are directed electrically into the mass spectrometer (Z-spray). The ion beam passes into a quadrupole analyzer, which can be operated in a narrow band-pass mode so as to transmit ions of defined m/z values or in its wide band-pass mode, in which all ions are transmitted regardless of m/z value. There is a further focusing hexapole, after which the ion beam is focused and accelerated by an electric lens before being passed into the TOF analyzer in front of a deflector electrode. A high electric potential is applied to this electrode in pulses so that, at each pulse, a section of the ion beam is deflected and accelerated into the TOF analyzer. After reflection by the reflectron, the ions are detected at a microchannel plate multipoint collector. The reflectron is used mainly to increase the time intervals at which successive m/z values are detected at the collector and to improve focusing. The quadrupole is operated in the narrow band-pass mode for MS/MS and in its wide band-pass mode for obtaining a full spectrum by the TOF analyzer.  [c.155]

The physical situation of interest m a scattering problem is pictured in figure A3.11.3. We assume that the initial particle velocity v is comcident with the z axis and that the particle starts at z = -co, witli x = b = impact parameter, andy = 0. In this case, L = pvh. Subsequently, the particle moves in the v, z plane in a trajectory that might be as pictured in figure A3.11.4 (liere shown for a hard sphere potential). There is a point of closest approach, i.e., r = (iimer turning point for r motions) where  [c.994]

Asher S A, Chi Z, Holtz J S W, Lednev I K, Karnoup A S and Sparrow M C 1998 UV resonance Raman studies of protein structure and dynamics XWf/r int. Conf on Raman Spectroscopy ed A M Heyns (New York Wley) pp 11-14  [c.1227]

The key feature of effective medium theory is the replacement of the complex )nment around each atom by a simplified model known as jellium. The jellium )nment corresponds to a homogeneous electron gas with a positive background, atom is considered to be surrounded by a sphere with a radius such that the rnic charge within each sphere due to the background jellium is equal and opposite charge on the atom. In the embedded-atom method the background electron density laced by a sum of electron densities from the neighbouring atoms. The many-body s known as an embedding function this gives the energy of each atom as a function electron density, ft. In the embedded-atom method the electron density p equals im of the electron densities 4>ij from neighbouring atoms (Equation (4.118)). In the and Baskes model a Coulomb potential was used for the pairwise potential but an effective charge Z(r) that decreases gradually with internuclear distance. The Iding function was represented with a cubic spHne equation that has a single mini-and goes to zero at vanishing density. The densities were obtained from quantum inical calculations.  [c.262]

Solutions can be examined by inductively coupled plasma mass spectrometry (ICP/MS) by either evaporating the solvent first and then volatilizing the solid residue or by nebulizing the solution and desolvating the resulting spray of fine droplets. After vaporization, residual sample (solute) constituents are swept into the center of an argon plasma flame, where they are fragmented into ions of their constituent elements. The m/z values of ions give important information for identification of the elemental composition of the sample, and measurement of ion abundances is used to provide accurate isotope ratios.  [c.397]

M. S. Malachowski, S. P. Levine, G. Herrin, R. C. Spear, M. Yost, and Z. Yi,/. Air Waste Management Assoc. 44(5), 673—682 (May 1994).  [c.295]

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Mass Spectrometry Basics (2003) -- [ c.69 , c.154 ]