Ion sampling

The TRAPI was developed by Matsuoka and co-workers " and has been used to determine the rate constants of about a dozen IM reactions at atmospheric pressure. As a first approximation, the TRAPI experiment might be described as an atmospheric pressure version of the PHPMS with initial ionization caused by a pulsed X-ray source. The X-rays cause relatively even ionization throughout the 6.4-cm ion source volume by penetrating through thin sections of the ion source walls formed by 25- im thick molybdenum foil. A 16-pm ion-sampling aperture is located at the center of one of these thin walls. The ions that pass through this aperture are measured by an associated mass spectrometer as a function of time after the X-ray pulse. 

If any of these factors are of significance, the rate constants deduced from such measurements would probably be lower than those operative in the more interior regions of the TRAPI ion source. To our knowledge, these questions concerning the possible impact of viscous-flow ion sampling on TRAPI measurements have not been resolved. 

Eisele, F. L Direct Tropospheric Ion Sampling and Mass Identification, Int. J. Mass Spectrom.. Ion Processes, 54, f f9—f26 (f983). 

E) G.N. Spokes B.E. Evans, "Ion Sampling from Chemical Plasmas , lOthSympCombstn (1965), pp 639-49... 

Mass analysis is a relatively simple technique, with the number of ions detected being directly proportional to the number of ions introduced into the mass spectrometer from the ion source. In atomic mass spectrometry the ion source produces atomic ions (rather than the molecular ions formed for qualitative organic analysis) which are proportional to the concentration of the element in the original sample. It was Gray who first recognized that the inductively coupled plasma would make an ideal ion source for atomic mass spectrometry and, in parallel with Fassel and Honk, and Douglas and French developed the ion sampling interface necessary to couple an atmospheric pressure plasma with a mass spectrometer under vacuum. 

Figure 1.2 shows the basic instrumentation for atomic mass spectrometry. The component where the ions are produced and sampled from is the ion source. Unlike optical spectroscopy, the ion sampling interface is in intimate contact with the ion source because the ions must be extracted into the vacuum conditions of the mass spectrometer. The ions are separated with respect to mass by the mass analyser, usually a quadrupole, and literally counted by means of an electron multiplier detector. The ion signal for each... 

Mach disc. See Ion sampling Magnetic sector. See Mass analyser Mass analyser ... 

Degradation of l-(4-Pyridyl)pyridinium Ion. Samples of l-(4-pyridyl)-pyr-idinium dichloride and dibromide dissolved in dilute hydrochloric acid were treated with concentrated sodium hydroxide solution until strongly basic. The... 

Fig. 25 Schematic of an inductively coupled plasma-MS interface during ion sampling. (Reproduced with permission from Elsevier.)...

A clinical sample (whole blood, serum, plasma, urine, gastric juice, bile fluid, sweat, etc.) differs from any other analytical sample because of the presence of heterogeneous organic (e.g., proteins) and organic or inorganic components (e.g., urea or sodium ion), sample changes in time (owing to, e.g., denaturation of proteins, escape of C02) and small sample size (even a few tens of microliters). 

Duffin, K. L., Wachs, T., and Henion, J. D. (1992). Atmospheric pressure ion-sampling system for liquid chromatography/mass spectrometry analyses on a benchtop mass spectrometer. Anal. Chem. 64 61-68. 

Instrumental developments facilitate the miniaturization opportunity. Advances in chromatography led to the use of capillary HPLC techniques (Liu et al., 1993 Kassel et al., 1994 Arnott et al., 1995) for the powerful separations of increasingly smaller samples. For mass spectrometry, developments with the LC/MS interface that resulted in increased ion transmission and ion sampling helped to... 

Preparation of Con A Derivatives. Ca -Zn -Con A was obtained from Miles-Yeda. Ca +-Mn -Con A was prepared as previously described (6). Atomic absorption analysis of these two Con A preparations showed essentially equal amounts of the transition metal ion and calcium ions. Sample solutions (0.6 ml) contained Con A at the appropriate concentration in pH 5.60, 0.1N potassium acetate buffer, y = 1.0 in potassium chloride. The final protein concentration was determined spectrophotometrically using = 12.4 at 280 nm ( 7,j)). 

Fig. 8.5. Schematic of an API interface for CEC—MS. 1, introduction of column effluent from CEC and spraying device 2, atmospheric pressure region 3, ion sampling aperture 4, atmospheric pressure to vacuum interface 5, skimmer 6, ion transfer optics (adapted from ref. [11]).

SWIFT excitation affords another method of resonance selection or ejection and has been applied in ICP-IT-MS by C. I. Frum to effect both ion isolation and collision-induced dissociation of ions sampled from an ICP [58]. An example of the isolation of 142Ce from a mixture containing all the lanthanide isotopes is shown in Fig. 9.14. In the absence of SWIFT excitation (Fig. 9.14a) space charge effects on both the lanthanides and Y+ are evident (space charge for Th+ is reduced by the prior ejection of lighter ions during the mass scan). Space charge effects are eliminated on application of SWIFT ion isolation. 

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