Mass scan

The mass scan mode is used to survey the entire mass spectrum within a certain volume of the specimen. 

A mass scan is acquired in cases when a survey of all impurities present in a volume of material is needed. Rather than measuring the secondary ion count rates of preselected elements as a fimction of sputtering time the count rates of all secondary ions are measured as a fimction of mass. Because a mass scan is continuously acquired over a mass range, no depth profiling or lateral information is available while operating in this mode. Figure 4 shows a mass scan acquired from a zirconia... 

Figure 4 Mass scan acquired from a zirconia crystai.

An unknown analytical response in lettuce was detected61 and thought to contain P and S. The initial GC/MS Cl CH4 data were dominated by ions at m/z 121, 197 and 291 (equation 40). The GC/MS Cl NH3 data, however, indicated that perhaps the molecule had a higher molecular weight of 306 (MH+ equal to m/z 307, cf. equation 40). Comparison with the Cl CH4 and Cl NH3 spectra of demeton-S- (199) and demeton-O-sulfones showed, however, that the retention time and mass spectra of the former only matched the unknown (except the omission of the ion at m/z 307). On another stationary phase (OV-101) limited mass scanning of the ion at m/z 121 revealed a second unknown (200) eluting at 4.2 min (the major unknown, i.e. demeton-S-sulfone at 3.0 min). The molecular weight of 200 was believed to be 306. Because of the presence of ions at m/z 121,... 

So how does the IRMS get its stability Collector slits are several times the width of the ion beams. This gives a flat-topped peak shape (Fig 6) which makes the ion current intensive to drift. The main source of drift is temperature variation which both affects the electronic components used for mass selection and caused expansion and contraction of mechanical parts. Simultaneous measurement of ion beams using a double or triple collector is more precise than sequential measurement by mass scanning with a single detector. Finally, frequent comparison of sample gas under identical conditions also contributes to stability. Ion beam stability is more important than resolution for isotopic measurements. 

Selected Mass Scan Law KER from Peak Width Analyzer and FFR Properties... 

The combustion efficiency of benzene was monitored with an on-line real time mass spectrometer Ametek model Dycor 1000) tracking the parent mass peak for benzene. (Mass scans showed that as the parent peak was removed no peak above m/e = 40 appeared so the benzene was not just being cracked into a smaller unsaturated hydrocarbon but was being consumed.)... 

The analytes are determined by acquiring a full mass scan and obtaining the extracted ion current profiles (EICP) for the primary mass-to-charge ratio and at least two secondary masses of each analyte. Ions recommended for this purpose are listed in the EMSL methods. 

The existence of a metastable ion and its relationship to m1 and m2 thus confirm that the ion m2 was in fact formed directly from mx. There are in theory many possible solutions to the equation, but the actual solution is normally obtained by inspection of the spectrum using major peaks, usually of similar intensity, as possible values for mx and m2. For spectrometers which have an exponential mass scan this is a simple operation since the distances between m and m2, and m2 and m1 will be identical. 

Li, A. C., Gohdes, M. A., and Shou, W. Z. (2007). N-in-one strategy for metabolite identification using a liquid chromatography/hybrid triple quadrupole linear ion trap instrument using multiple dependent product ion scans triggered with full mass scan. Rapid Commun. Mass Spectrom. 21 1421-1430. 

Williams, J., Poschl, U., Crutzen, P.J. et al. (2001) An atmospheric chemistry interpretation of mass scans obtained from a proton transfer mass spectrometer flown over the tropical rainforest of Surinam. Journal of Atmospheric Chemistry, 38 (2), 133-66. 

In lipid analyses with LC-MS, mass scanning methods have included MS full-scan acquisition with accurate mass, acquiring precursor and fragment exact mass data simultaneously with MSe scan, precursor ion scan and MRM. The most popular fragmentation method in MS/MS experiments has been collision-induced dissociation, but also higher energy collision dissociation has been utilized. 

In contrast to QqQ systems, IT mass spectrometers perform sequential ion trapping, isolation of precursor ions and subsequent mass scanning in a single small assembly (ion trap) making this system robust and valuable. 

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