Mass spectrometry molecular formula, determining

Amongst products isolated from Heliotropium spathulatum (Boraginaceae) were 9 mg of a new alkaloid which gave a positive Ehrlich reaction with p-dimethylaminobenzaldehyde The molecular formula determined by mass spectrometry is CisH2sNOs. What is the structure of the alkaloid given the set of NMR results 54 Reference is useful in providing the solution to this problem. Conditions CDCI3, 9 mg per 0.3 ml, 25 °C, 400 MHz ( //), 100 MHz ( C). (a) HH COSY plot ... 

P.C. Jurs, B.R. Kowalski and T.L. Isenhour, Computerized learning machines applied to chemical problems. Molecular formula determination from low resolution mass spectrometry. Anal. Chem., 41 (1969)21-27. 

In recent years the application of electrospray ionization (ESI) mass spectrometry, quadrupole time-of-flight (QqTOF) mass spectrometry, and Fourier transform ion cyclotron resonance (FT-ICR) are used for further structural characterization of DOM (Kujawinski et al., 2002 Kim et al., 2003 Stenson et al., 2003 Koch et al., 2005 Tremblay et al., 2007 Reemtsma et al., 2008). MS/MS capabilities provide the screening for selected ions, and FT-ICR allows exact molecular formula determination for selected peaks. In addition, SEC can be coupled to ESI and FTICR-MS to study different DOM fractions. Homologous series of structures can be revealed, and many pairs of peaks differ by the exact masses of -H2, -O, or -CH2. Several thousand molecular formulas in the mass range of up to more than 600 Da can be identified and reproduced in element ratio plots (O/C versus H/C plots). Limitations of ESI used by SEC-MS are shown by These and Reemtsma (2003). 

The starting point for mass spectrometric characterizations is often the determination of the molecular weight. If the impurity arose after exposure to oxygen and a mass shift of 16 is observed between the drug substance and the impurity, it can be concluded that the impurity is oxidized drug substance. High mass accuracy mass spectrometry may also be used for molecular formula determination. 

In a modem, state-of-the-art mass spectrometry laboratory, the determination of the molecular formula of an unknown substance is done using exact masses. The spectroscopist must be careful, however, as the method cannot be used if the molecular ion peak is very weak or absent. 

The molecular ions of both CjHjqS and CgHj,0 appear at miz 102 in low-resolution mass spectrometry. Show how determination of the correct molecular formula can be made from the appearance and relative intensity of the M + 2 peak of each compound. 

Mass spectrometry can help determine the molecular mass and thus the molecular formula. 

Among the modem procedures utilized to estabUsh the chemical stmcture of a molecule, nuclear magnetic resonance (nmr) is the most widely used technique. Mass spectrometry is distinguished by its abiUty to determine molecular formulas on minute amounts, but provides no information on stereochemistry. The third most important technique is x-ray diffraction crystallography, used to estabUsh the relative and absolute configuration of any molecule that forms suitable crystals. Other physical techniques, although useful, provide less information on stmctural problems. 

A compound with the molecular formula C7///JNO3, determined by mass spectrometry, was isolated from the plant Petiveria alliacea (Phytolaccaceae). What is its structure given the set of NMR results 52 ... 

The male sex hormone testosterone contains C, H, and O and has a mass of 288.2089 amu as determined by high-resolution mass spectrometry. What is the likely molecular formula of testosterone ... 

To find the molecular formula of a compound, we need one more piece of information—its molar mass. Then all we have to do is to calculate how many empirical formula units are needed to account for the molar mass. One of the best ways of determining the molar mass of an organic compound is by mass spectrometry. We saw this technique applied to atoms in Section B. It can be applied to molecules, too and, although there are important changes of detail, the technique is essentially the same. 

A fourth technique used for the characterization of molecules is mass spectrometry. It is included in this chapter because the structural information it provides is similar to that obtained from the other techniques although the principle is entirely different. It is a destructive method in which the fragmentation pattern of sample molecules is used to determine empirical formulae and molecular weights, and to identify structural features. 

The molecular formula of a compound shows the actual number of each kind of atom present in a molecule of the compound. To work out the molecular formula of a compound, we need to know both the empirical formula and the relative molecular mass of the compound. The latter can be determined by mass spectrometry (see p. 73). 

The exact mass of a compound determined by high-resolution mass spectrometry is 212.0833. What is the molecular formula of the compound ... 

The chemical makeup of a substance is described by its percent composition—the percentage of the substance s mass due to each of its constituent elements. Elemental analysis is used to calculate a substance s empirical formula, which gives the smallest whole-number ratio of atoms of the elements in the compound. To determine the molecular formula, which may be a simple multiple of the empirical formula, it s also necessary to know the substance s molecular mass. Molecular masses are usually determined by mass spectrometry. 

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