Mass limitations

TOF mass spectrometers are very robust and usable with a wide variety of ion sources and inlet systems. Having only simple electrostatic and no magnetic fields, their construction, maintenance, and calibration are usually straightforward. There is no upper theoretical mass limitation all ions can be made to proceed from source to detector. In practice, there is a mass limitation in that it becomes increasingly difficult to discriminate between times of arrival at the detector as the m/z value becomes large. This effect, coupled with the spread in arrival times for any one m/z value, means that discrimination between unit masses becomes difficult at about m/z 3000. At m/z 50,000, overlap of 50 mass units is more typical i.e., mass accuracy is no better than about 50-100 mass... 

The APCl ionization regime is much more harsh that ESI and this precludes its use for the study of large biomolecules, with the mass limit for APCl being generally considered as below 2000 Da. Having said this, as will be shown later, the technique may still be used for the analysis of many thermally labile compounds without their decomposition, and small peptides have been studied. 

D.L. Olson, T. L. Peck, A. G. Webb, R. L. Magin, J. V. Sweedler 1995, (High resolution microcoil H-NMR for mass limited nanoliter-volume samples), Science 270, 1967... 

Ionisation method Principal ions detected (+/—) Mass spectrometer" Sample classes Approximate mass limit (Da)... 

Quantitative analysis of multicomponent additive packages in polymers is difficult subject matter, as evidenced by results of round-robins [110,118,119]. Sample inhomogeneity is often greater than the error in analysis. In procedures entailing extraction/chromatography, the main uncertainty lies in the extraction stage. Chromatographic methods have become a ubiquitous part of quantitative chemical analysis. Dissolution procedures (without precipitation) lead to the most reliable quantitative results, provided that total dissolution can be achieved follow-up SEC-GC is molecular mass-limited by the requirements of GC. Of the various solid-state procedures (Table 10.27), only TG, SHS, and eventually Py, lead to easily obtainable accurate quantitation. 

IS(TD) Internal standardisation (calibration) mLOD Mass limit of detection... 

In principle these should be predictable from theory, but in practice there are many grey areas such as the effects of rotation, convective mixing, mass loss, the mechanism of stellar explosions, nuclear reaction rates such as 12C(a, y)160, the evolution of close binaries and the corresponding mass limits between which various things happen for differing initial chemical compositions. Figure 5.14 shows a version of what may happen in single stars with different initial masses and two metallicities, Z Z and Z Z /20. 

Species are given with their proto-solar abundance by mass fraction, after Lodders (2003). The last column gives the yield calculated by Nomoto et al. for core-collapse supemovae within a Salpeter IMF between mass limits of 0.07 and 50 Mq. 

The question of upper mass limits to stars which explode as SN II and leave neutron-star remnants is discussed by Maeder (1992,1993) and by Brown, Bruenn and Wheeler (1992) it is highly controversial. (Note that Koppen and Arimoto (1991) when referring to the Scalo IMF use the version with b T) = 1, as I have done, whereas Maeder (1993) uses the version with b (T) = 0.48, corresponding to yields that are 3 times higher )... 

Assuming the star formation rate for the Galaxy given in Table 7.9 and that all stars between 10 and 100 M explode as Type II supemovae, estimate the corresponding supernova rates for the IMFs in Table 7.8. How much difference does it make if the upper mass limit for SN is 50 M (The observed rate for SN II in galaxies like our own is of the order of 2 to 3 per century.)... 

Fig. 8.36. Abundance ratio [Mg/Fe] as a function of [Fe/H] and time (for the case rmix = 0.1 Gyr), for three different assumptions about rmjX. Yields are taken from Thielemann, Nomoto and Hashimoto (1996) up to 40 A/ the long-dashed line shows an extension to an upper mass limit of 70 A/ (with rmjX = 0.1 Gyr) SN la yields are from Model W7 (Nomoto, Thielemann Yokoi 1984). After Thomas, Greggio and Bender (1998).

Properly speaking, me should be the reduced mass for the specific nuclear mass of the system. The values given in Table C.l for me and R,Xj pertain to the infinite-mass limit, which suffices for practical purposes (and can be easily corrected, if necessary). 

Mass Limit The m/z value above or below which ions cannot be detected in a mass spectrometer. 

R. P. Rodgers, E. N. Blumer, C. L. Hendrickson, and A. G. Marshall. Stable Isotope Incorporation Triples the Upper Mass Limit for Determination of Elemental Composition by Accurate Mass Measurement. J. Am. Soc. Mass Spectrom., 11(2000) 835-840. 

Smaller diameter probes reduce sample volumes from 500 to 600 pi typical with a 5 mm probe down to 120-160 pi with a 3 mm tube. By reducing the sample volume, the relative concentration of the sample can be correspondingly increased for non-solubility limited samples. This dramatically reduces data acquisition times when more abundant samples are available or sample quantity requirements when dealing with scarce samples. At present, the smallest commercially available NMR tubes have a diameter of 1.0 mm and allow the acquisition of heteronuclear shift correlation experiments on samples as small as 1 pg of material, for example in the case of the small drug molecule, ibu-profen [5]. In addition to conventional tube-based NMR probes, there are also a number of other types of small volume NMR probes and flow probes commercially available [6]. Here again, the primary application of these probes is the reduction of sample requirements to facilitate the structural characterization of mass limited samples. Overall, many probe options are available to optimize the NMR hardware configuration for the type and amount of sample, its solubility, the nucleus to be detected as well as the type and number of experiments to be run. 

Bisnovatyi-Kogan, G. S. (1968). The mass limit of hot superdense stable configurations. As-troflzika, 4 221-238. 

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