Chapter 22: Q2TY (page 566)
A compound with a molecular ion at m/z 117 has a peak at m/z 118 with a relative intensity of 9.3%. Is there an odd or even number of N atoms? How many carbons are in the formula?
Odd 8C, It cannot be 9C because C9N would be at m/z .122.
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30: (a)The mean free pathis the average distance a molecule travels before colliding with another molecule. The mean free path, l, is given by l 5 kT/(12sP), where kis Boltzmann’s constant, Tis temperature (K), Pis pressure (Pa), and s is the collision cross section. For a molecule with a diameter d, the collision cross section is pd2. The collision cross section is the area swept out by the molecule within which it will strike any other molecule it encounters. The magnetic sector mass spectrometer is maintained at a pressure of |1025 Pa so that ions do not collide with (and deflect) one another as they travel through the mass
analyzer. What is the mean free path of a molecule with a diameter of 1 nm at 300 K in the mass analyzer?
(b)The vacuum in an orbital mass separator is 1028 Pa. Find the mean free path in the orbital for the same conditions as (a).
The molecular ion region in the mass spectrum of a large molecule, such as a protein, consists of a cluster of peaks differing by 1 Da. This pattern occurs because a molecule with many atoms has a high probability of containing one or several atoms of and . In fact, the probability of finding a molecule with only and may be so small that the nominal molecular ion is not observed. The electrospray mass spectrum of the rat protein interleukin-8 consists of a series of clusters of peaks arising from intact molecular ions with different charge. One cluster has peaks at m/z 1 961.12, 1 961.35, 1 961.63, 1 961.88, 1 962.12 (tallest peak), 1 962.36, 1 962.60, 1 962.87, 1 963.10, 1 963.34, 1 963.59, 1 963.85, and 1 964.09. These peaks correspond to isotopic ions differing by 1 Da. From the observed peak separation, fi nd the charge of the ions in this cluster. From m/z of the tallest peak, estimate the molecular mass of the protein.
Explain what is meant by spectral, chemical, ionization, and isobaric interference.
Phytoplankton at the ocean surface maintain the fluidity of their cell membranes by altering their lipid (fat) composition when the temperature changes. When the ocean temperature is high, plankton synthesize relatively more 37:2 than
After they die, plankton sink to the ocean fl oor and end up buried insediment. The deeper we sample a sediment, the further back into time we delve. By measuring the relative quantities of cell-membrane compounds at different depths in the sediment, we can infer the temperature of the ocean long ago. The molecular ion regions of the chemical ionization mass spectra of 37:2 and 37:3 are listed in the table. Predict the expected intensities of M, M11, and M12 for each of the four species listed. Include contributions from C, H, O, and N, as appropriate. Compare your predictions with the observed values. Discrepant intensities in these data are typical unless care is taken to obtain high-quality data.
Find the number of rings 1 double bonds in molecules with the following compositions and draw one plausible structure for each: (a) (b)(c) fragment in a mass spectrum with the composition .
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