Mass data

The electrospray source can be coupled directly to a liquid chromatographic (LC) column so that, as components of a mixture emerge from the column, they are passed through the source to give accurate mass data. As an example, a mixture of the peptides shown in Figure 40.8(a) was separated by LC and accurately mass-analyzed by ES. 

Once the peaks have been collected and stored, the computer can be asked to work on the data to produce a mass spectrum and print it out, or it can be asked to carry out other operations such as library searching, producing a mass chromatogram, and making an accurate mass measurement on each peak. Many other examples of the use of computers to process mass data are presented in other chapters of this book. 

Additional ionization occurs by collision between the ions and other neutral species (ion/molecule collision see Chapter 1). Unless special steps are taken (see Chapters 8 and 11 ), the ions formed do not fragment, so little or no structural information is obtained. However, the lack of fragmentation does mean that good relative molecular mass data can be obtained. The assembly of ions formed by ion... 

Once the mass spectral information has been acquired, various software programs can be employed to print out a complete or partial spectrum, a raw or normalized spectrum, a total ion current (TIC) chromatogram, a mass chromatogram, accurate mass data, and metastable or MS/MS spectra. 

A. Cornu and R. Massot, Compilation of Mass Data, Code No. 19AD2, 1966. 

It follows, that the peak width of a solute could give an indication of its molecular weight and, although the data may not be precise, approximate values could be extremely valuable when dealing with very large molecular weight substances such as polypeptides and proteins. In particular, the technique would be very useful for those substances that are extremely difficult, or impossible, to vaporize in the ion source of a mass spectrometer to provide mass data. 

Care must be taken in the interpretation of accurate mass data. In this case, the experimentally determined values of 280.0628 and 280.0633 Da have a mass... 

Data systems, more broadly known as Laboratory Information Management Systems, are in almost universal use in laboratories, allowing the collection of mass data required by parallel and high-throughput analytical... 

Polymer/additive analysis greatly benefits from high-resolution mass data, which often leads to unambiguous identification of (known) additives. However, the investment and operating costs of this instrument do not easily justify its (exclusive) use for the purpose of routine polymer/additive analysis. Analysis of organic polymer additives by means of mass spectrometry is aided by the utilisation of precursor ion and second-generation product ion (MS3) scanning experiments [169], A four-sector... 

The empirical formula of a compound is determined from reacting mass data. 

In this chapter, you learned how to balance simple chemical equations by inspection. Then you examined the mass/mole/particle relationships. A mole has 6.022 x 1023 particles (Avogadro s number) and the mass of a substance expressed in grams. We can interpret the coefficients in the balanced chemical equation as a mole relationship as well as a particle one. Using these relationships, we can determine how much reactant is needed and how much product can be formed—the stoichiometry of the reaction. The limiting reactant is the one that is consumed completely it determines the amount of product formed. The percent yield gives an indication of the efficiency of the reaction. Mass data allows us to determine the percentage of each element in a compound and the empirical and molecular formulas. 

Average atomic mass data in brackets indicate atomic mass of most stable isotope of the element. 

Isotopic patterns provide a prime source of such additional information. Combining the information from accurate mass data and experimental peak intensities with calculated isotopic patterns allows to significantly reduce the number of potential elemental compositions of a particular ion. [31] Otherwise, even at an extremely high mass accuracy of 1 ppm the elemental composition of peptides, for example, can only be uniquely identified up to about 800 u, i.e., an error of less than 0.8 mmu is required even if only C, H, N, O and S are allowed. [27,32,33]... 

Is accurate mass data available for some of the peaks ... 

We observed that in the absence of ultrasound (C), but the presence of initiator (reaction number 1 and 2), the rate (or yield (Y) per unit time) and molar mass data (M ) conformed approximately, as expected, to that for conventional polymerisation - i. e. quadrupling the initiator concentration led a doubling of the yield (Eq. 5.4) and a halving of the molar mass (Eq. 5.5). 

The significant intrinsic limitation of SEC is the dependence of retention volumes of polymer species on their molecular sizes in solution and thus only indirectly on their molar masses. As known (Sections 16.2.2 and 16.3.2), the size of macromolecnles dissolved in certain solvent depends not only on their molar masses but also on their chemical structure and physical architecture. Consequently, the Vr values of polymer species directly reflect their molar masses only for linear homopolymers and this holds only in absence of side effects within SEC column (Sections 16.4.1 and 16.4.2). In other words, macromolecnles of different molar masses, compositions and architectures may co-elute and in that case the molar mass values directly calculated from the SEC chromatograms would be wrong. This is schematically depicted in Figure 16.10. The problem of simultaneous effects of two or more molecular characteristics on the retention volumes of complex polymer systems is further amplifled by the detection problems (Section 16.9.1) the detector response may not reflect the actual sample concentration. This is the reason why the molar masses of complex polymers directly determined by SEC are only semi-quantitative, reflecting the tendencies rather than the absolute values. To obtain the quantitative molar mass data of complex polymer systems, the coupled (Section 16.5) and two (or multi-) dimensional (Section 16.7) polymer HPLC techniques must be engaged. 

The purpose of the MS techniques is to detect charged molecular ions and fragments separated according to their molecular masses. Most flavonoid glycosides are polar, nonvolatile, and often thermally labile. Conventional MS ionization methods like electron impact (El) and chemical ionization (Cl) have not been suitable for MS analyses of these compounds because they require the flavonoid to be in the gas phase for ionization. To increase volatility, derivatization of the flavonoids may be performed. However, derivatization often leads to difficulties with respect to interpretation of the fragmentation patterns. Analysis of flavonoid glycosides without derivatization became possible with the introduction of desorption ionization techniques. Field desorption, which was the first technique employed for the direct analysis of polar flavonoid glycosides, has provided molecular mass data and little structural information. The technique has, however, been described as notorious for the transient... 

Residual oil impact estimates by modeling provided a severe test of GRID s capacity since the CMB impact estimates were small (less than one-quarter yg/m ) and the physical basis of the model inherently limits it s ability to predict point source plume transport. Since Initial comparisons (Figure 5) showed GRID estimated impacts to be overpredicted at all sites relative to CMB estimates, further improvements to the data base were suggested. Overall, annual model verification results for all sources were relatively poor with the dispersion model predictions consistently underestimating both the CMB-derlved estimates and the measured TSP mass data. 

Figure 2. Profiles of fine (< 2.5 f m) and coarse (2.5 /j/n < D < 75 ixm) soil particles and gravimetric mass data from the WFP network from October, 1979...

---