Mass increase spectrum

A tandem-in-space mass spectrometer consists of an ion source, a precursor ion activation device, and at least two nontrapping mass analyzers. The first mass analyzer is used to select precursor ions within a narrow m/z range. Isolated precursor ions are allowed to enter the ion activation device, for example, a gas-filled collision cell, where they dissociate. Created fragments continue on to the second mass analyzer for analysis. The second mass analyzer can either acquire a full mass fragment spectrum or be set to monitor a selected, narrow, m/z range. In principle the second mass analyzer could be followed by more ion activation devices and mass analyzers for MSn experiments. However, due to rapidly decreasing transmission and increasing experimental... 

Fig. 1. Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TOF) spectrum of a trypsin-digested one-dimensional gel band. Peaks are labeled with their monoisotopic masses. Note that these are not the masses of the peptides, but of the peptide (pseudo)molecular ions. In MALDI spectra, peptide molecular ions arise predominantly through the addition of a proton to the peptide, giving a mass increase of 1.007 Da. The molecular ions are usually denoted as MH+ or [M+H]+.

Smith et al. studied the binding of biotin and some biotin derivatives to avidin and strepavidin.38 In the initial experiment, they measured the ESI mass spectrum of avidin (Fig. 12A) observing four charge states (15 + to 18 +) corresponding to a molecular mass of 63,915 Da which correlates well with the expected mass of 63,870 Da. The spectrum obtained for a mixture of avidin-biotin (lower plot) shows that peaks are shifted to higher m/z values that correspond to a mass increase of 973 u. This indicated that four biotin molecules are indeed bound to avidin. The mass increase is accompanied by a reduction of one unit in the charge states, which now range from 14+ to 17 +. This study demonstrated that the ESI process transfers the solution complex to the gas phase. 

An in-depth study of mass spectra of over 29 000 different compounds containing only the elements C, H, N, O, F, Si, P, S, Cl, Br and I showed that, on average, the probability of the presence of a peak in a spectrum halves every 100 Th [20], Thus the probability of having in a mixture compounds with ions typical of the same m/z decreases as the mass increases. 

Positions of some bands in IR absorption spectrum of the pigment/Ag nanoparticles (Fig. 1) are shifted in comparison to their position in the IR spectrum of pure ultramarine. It means silver to participate in the reaction with ultramarine. Silver gets the bond with Si-0 and Al-O tetrahedra to form Si-O-Ag and Al-O-Ag bonds. Hence, the oscillator masses increase and the oscillation frequencies decrease. So, adding silver particles results in the vibration band shift to the long-wave range. Besides, the intensity of absorption decreases because of the bond energy redistribution, ultramarine... 

Rotational level spacings, and hence the frequencies of transitions between rotational levels, depend upon the values of the rotational constant, 5 , and the rotational quantum number J, according to equation (1.25). The largest known rotational constant, for the lightest molecnle (H2), is about 60 cm, so that rotational transitions in this and similar molecules will occur in the far-infrared region of the spectrum. As the molecular mass increases, rotational transition freqnencies decrease, and rotational spectroscopy for most molecnles occurs in the millimetre wave and microwave regions of the electromagnetic spectrnm. 

Figure 4 Using mass spectrometry to confirm identity and disuifide bond formation for a CXCL12 mutant. (A) The intact mass spectrum of foided and oxidized CXCL12 S-1 S4V with the charge state enveiope inset. (B) The denatured and reduced protein, compared to the oxidized, and refoided protein the mass increased in size by 4 Da with aii four cysteines being reduced and the charge state enveiope has shifted to a iower m/z.

Figure 8.S Avoiding H/D scrambling by adjustment of the declustering conditions in the electrospray ion source. The ETD mass spectra display the c -lon (left panel) and charge-reduced precursor Ion (right panel) obtained from ETD experiments on (a) unlabeled and (b-c) selectively labeled peptide PI. The Isotopic labeling of the model peptide Is shown by the schematic. The ETD spectrum in (b) was recorded at defined mild declustering ion source conditions for minimal collisional activation, while the ETD spectrum in (c) was recorded with excessive collisional activation. The centroids are indicated by a dotted red line. Extensive scrambling in (c) is evident by the mass increase (2.1 Da) due to the presence of deuterium in the c-ion (compare (b) with (c)). Note the deuterium content of the c -ion corresponds to complete (100%) H/D scrambling. Reproduced with permission from [47] 2009 American Chemical Society. (See insert for color representation of the figure.)...

As illustrated in Figure 8.8, the apparent mass resolution gradually decreases as the ion mass increases. The actual value of the upper mass limit where oligomers are resolved is dependent on several factors, including the number of components present in a polymer sample, the mass(es) of the repeat units(s), and the matrix/sample preparation method. For the latter, whenever possible, the formation of two or more cation adducts should be avoided. The addition of a preferred cation suppresses other cationization and can improve the quality of the spectrum by reducing peak overlap. 

Because it is necessary to reduce the molar amount of polymer loading as the molecular mass increases, this would suggest a practical hmit to the mass range for polymer analysis by MALDI. As molecular mass increases, the sensitivity of the instrument is challenged on two fronts (i) decreased sensitivity due to a loss in detector efficiency and (ii) decreased sensitivity from the requirement of lower (molar) sample loading. In the analysis of PS, this hmit appears to occur at -1.5 milHon Da. In order to obtain the MALDI mass spectrum of PS with a nominal mass of 1.5 miUion Da [29], 5 fmol of total polymer was loaded onto the probe. 

Background subtraction. This step is also referred to as baseline subtraction or baseline correction. Raw MALDI-MS signals exhibit a global variation in the baseline that varies from spectrum to spectrum, and must be corrected. The baselines vary slowly and smoothly as the mass increases. Hence, the aim here... 

I hus, at low molecular masses and <7 0 (see Equation 65), the scattering spectrum of polymer. solutions is a simple Lorentzian. As molecular mass increases, the intramolecular motion complicates the spectrum. S q,u ) turns out to be the sum of several Lorentzians. 

The short pulse of ions produced by laser desorption is ideally suited to mass analysis by time-of-flight (ToF), which makes it possible to record a complete mass spectrum for a single laser shot. Actually, MALDI has greatly contributed to the revival of ToF-MS. The detection efficiency decreases as the ion mass increases. Key instrumental parameters of MALDI-MS are mass resolution and mass accuracy. Mass resolution of MALDI-ToFMS has increased considerably by pulsed extraction techniques. Resolutions of 30,000 or better and mass accuracy at low ppm level are achieved, which allow separation of single oligomers. The sensitivity of ToF is in the sub-fmol range. Recently also the... 

The di-nuclear case has been considered numerically by Frolov (1999) in a study of the hydrogen molecular ion. In extremely acciuate calculations on the discrete states of this system, he investigated what happened when first one and then two nudear masses are increased without limit. He showed that when one mass increased without limit, any discrete spectrum persisted but when two masses were allowed to increase without limit, the Hamiltonian ceased to be well-defined and this failure led to what he called adiabatic divergence in attempts to compute discrete eigenstates. This sort of behavior would certainly be anticipated from the present discussion. 

Relativistic electrons radiate not only at the gyrofrequency, but also at the harmonics. The relativistic mass increase with energy causes the harmonic spacing to decrease with increasing energy until the synchrotron spectrum is essentially smeared into a continuum. The radiation from a relativistic electron is highly nonisotropic. The emitted radiation is concentrated within a narrow cone about the instantaneous direction of the velocity vector with an approximate half-cone-width given by... 

An example of enhanced ion production. The chemical equilibrium exists in a solution of an amine (RNH2). With little or no acid present, the equilibrium lies well to the left, and there are few preformed protonated amine molecules (ions, RNH3+) the FAB mass spectrum (a) is typical. With more or stronger acid, the equilibrium shifts to the right, producing more protonated amine molecules. Thus, addition of acid to a solution of an amine subjected to FAB usually causes a large increase in the number of protonated amine species recorded (spectrum b). 

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