As the frequency is fixed, o> is a fixed value. We will consider only monocharged ions (z = 1) e, the elementary charge, is a constant and ro and zo are constant for a given trap qz will increase if V increases, and decrease if m increases. This is represented in Figure 2.21, where higher mass ions are represented by larger balls. If V is increased, all the ions will have a higher qz value. If this value is equal to 0.908, /3 is equal to one, and the ion... [Pg.108]

It should be noted that if an ion fragments during the analysis, it is possible that its m/z ratio is such that its qz value is higher than the resonant ejection value. If, later on, by increasing V, it reaches the stability limit (qz = 0.908) and is ejected, it will then be detected at a wrong m/z, as the data system expects it to be expelled by resonance. Its apparent m/z will be higher than the true one. These ghost peaks will occur more if the resonance frequency corresponds to a lower qz value. [Pg.110]

Principle of resonant ejection. Upper ions are stored in the 3D trap at a voltage Va of the fundamental RF. An additional RF is applied to the end caps corresponding to qz = 0.8. On increasing V (lower panel) ions are moved to higher qz values. In the figure, the smallest ion has reached qz = 0.8 and is ejected by resonance. This ejection occurs at a lower value of V than the one needed to eject by instability at qz = 0.908. [Pg.111]

Mass selective ejection of the ions in a radial direction occurs by applying an AC voltage between the two cut rods. As for the 3D ion trap, an AC frequency corresponding to qz = 0.88 is used. Ions of successively higher masses are brought to this qz value by increasing V. An ejection efficiency of about 50 % is achieved at 5 Th s scan rate [25]. [Pg.121]

The scattering intensity is, in principle, non-zero at any point along the CTRs, and the bulk Bragg peaks are located along each surface rod, notated by surface Bragg indices H and K, at Qz values dictated by the bulk crystal structure. The CTR structure is shown schematically in Figure 6B, where the thin vertical lines are the CTRs, and the spots on these rods correspond to bulk Bragg conditions. [Pg.166]

The second step is the optimization of CID parameters. Optimization is the same technique whether the activation mode is resonant or non-resonant. This step requires optimization of two parameters the collision energy and the qz value at which the precursor ions are trapped. The qz corresponds to the component of q according to the z axis of the ion trap (axis through the center of both endcap electrodes (see Chapter 4). This value of qz, often neglected by novice users, is important because it determines the value of the m/z ratio beyond which the daughter ions will be stored in the ion trap. It also conditions the energy that must be supplied to fragment the precursor ion. [Pg.99]

Eqs. (1-76) show that these values of the coefficients produce the Navier-Stokes approximations to pzz and qz [see Eq. (1-63)] the other components of p and q may be found from coefficient equations similar to Eq. (1-86) and (1-87) (or, by a rotation of coordinate axes). The first approximation to the distribution function (for this case of Maxwell molecules) is ... [Pg.36]

Finally we observe from Fig. 1 the magnitude of Gw qz) decreases for increasing at fixed w. Thus, the only way to fulfill the Bethe sum rule at arbitrarily large values of q will be to include basis functions of arbitrarily high angular momentum. This confirms a previously reached conclusion [12],... [Pg.187]

Obviously, in the case of PS these discrepancies are more and more reduced if the probed dimensions, characterized by 2ti/Q, are enlarged from microscopic to macroscopic scales. Using extremely high molecular masses the internal modes can also be studied by photon correlation spectroscopy [111,112], Corresponding measurements show that - at two orders of magnitude smaller Q-values than those tested with NSE - the line shape of the spectra is also well described by the dynamic structure factor of the Zimm model (see Table 1). The characteristic frequencies QZ(Q) also vary with Q3. Flowever, their absolute values are only 10-15% below the prediction. [Pg.81]

In comparing two distribution functions, a plot of the points whose coordinates are the quantiles qz (pc), qzz(pc) for different values of the cumulative probability pc is a QQ-plot. If zi and zz are identically distributed variables, then the plot of Z -quantiles versus Z2-quantiles will be a straight line with slope 1 and will point toward the origin. [Pg.229]

In this limit the two events become independent. This is what we expect from a system where no communication between the sites exists. In the example of Fig. 1.1, the conditional probability of finding site i is occupied given that site j is occupied differed from the unconditional probability, only because of the finite values of n and m. If one site is occupied, then there remain only (n - 1) ligands to be arranged at the (m - 1) sites. This is the only reason for the correlation between the sites. One site knows that another site is occupied only due to the fact that the number of arrangements has changed from Q) to QZ ) Clearly, in this example it does not matter which site is i and which site is j (i j). When -4 and m oo, this communication between the sites is lost, i.e., g. ... [Pg.5]

Fig. 54 shows some first systematic measurements by Bantle et al.207,209), who changed the delay time by factors of 1 2 4 8 the suggested optimum condition for a recording of the full correlation time corresponds to a value of 4, i.e. the TCF has decayed here to e 2 of the original value at channel 80220. Evidently, the qz dependence can in these four cases be represented by... [Pg.95]

Compositions CsMgj xNixCl3 show Ni2+ emission at about 5000 cm-1 [40]. The emission band shows vibrational structure yielding an S value of about 2.5. From this value Qo—QZ is found to be 0.7 A, which gives dr=0.24 A for the change in the Ni-Cl distance. This emission is due to a transition from one of the crystal-field components of the first excited state 3nt ground state (3d8, Oh notation). The lifetime of the excited state is 5.2 ms. The luminescence is quenched above 200 K. [Pg.18]

By expanding the circled region in Fig. 13, the ion-trap stability diagram (Fig. 14) plotted in terms of the parameters az and qz is obtained. These parameters are directly related to the RF (qz) and DC (az) voltages applied to the ion-trap electrodes. The areas of stability have boundaries where the (lu parameters (u — z or r) have values 0 and 1. fju is a complex function of au and qu and is directly related to the fundamental secular frequency of the ion (mu) and the main RF frequency (Q) by the equation... [Pg.77]

Figure 2.15 displays the iso-p lines for pu = 0 and pu = 1 respectively. One of the two diagrams refers to the z coordinate and the other to the r coordinate. Remember that au = az = -2ar and qu = qz = -2qr. The area inside these limit values for pu corresponds to a, q values for a stable trajectory. However, for an ion to be stable in the ion trap, it must have a stable trajectory along both z and r, which correspond to the overlap of the stability areas of the two diagrams. [Pg.103]

Typical stability diagram for a 3D ion trap. The value at = 1 along the qz axis is qz = 0.908. At the upper apex, = 0.149 998 and = 0.780 909. Drawn with data taken from March R.E and R.J. Hughes, Quadrupole Storage Mass Spectrometry, Chemical Analysis Vol. 102, Wiley Interscience, 1989. [Pg.105]

If we again consider the equation for qz, we can write an equation with these limit values giving the maximum observable mass OTmax ... [Pg.109]

As this value of qz is lower than 0.908 (the /l = I stability limit), this ion will have a stable trajectory in this trap operated at 5000 V amplitude of the fundamental RF. [Pg.109]

If, however, the applied frequency corresponds to a lower qz, the ions will be ejected at a lower V value. Thus, for the same maximum V value, the highest ejectable mass will be higher. This is another way to increase the mass range. For example, the Bruker Esquire instrument allows ions at fi = 2/11 to be ejected, corresponding to qz = 0.25, which allows the mass range to be extended up to 6000 Th. [Pg.110]

The dashed line represents the shift of the stability diagram resulting from the space charge effect. To reach the stability limit / = 1, qz, and thus V, has to have a higher value. This could lead to an error on the mass if proper caution is not taken. [Pg.119]

© 2019 chempedia.info