Alkali metal adducts

Electronic Effects in Metallocenes and Certain Related Systems, 10, 79 Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons, 2, 115 Fast Exchange Reactions of Group I, II, and III Organometallic Compounds, 8,167 Fluorocarbon Derivatives of Metals, 1, 143 Heterocyclic Organoboranes, 2, 257... 

Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons E. de Boer... 

Alkali metal adducts often are observed, and even in negative ion mode (M + Na — 2H) are often abundant for monocharged ions. If they can be avoided, not only does the signal increase because it is not divided any more over several species but also better MS/MS spectra can be obtained. To eliminate these adducts, glassware should not be used during sample work-up. Then, addition of acid or, better still, ammonium acetate allows their interference to be reduced further. However, often alkali metal salts are added at low concentrations to suppress the protonated species. This is easier to achieve, but fragmentation of these adducts yields less sequence information than protonation. 

Electronic structure of alkali metal adducts of aromatic hydrocarbons... 

Optimum conditions for preparing alkali-metal adducts are, therefore, hard to predict critical variables are solvent, T, time, alkali metal, and the structure of the conjugated hydrocarbon. 

Anthocyanins in the presence of acidic matrixes such as MAA are predominately in the aromatic oxonium ion form 23) and are detected as [M] ions by MALDI-TOF mass spectral analysis 23,24). However, anthocyanins 23), in the same manner as polyflavan-3-ols 21,22,25), may also associate with naturally abundant sodium [M + Na] and potassium [M + K] forming alkali metal adducts. To suppress the formation of alkali metal adducts, we deionized the anthocyanin-polyfIavan-3-ol/matrix solution prior to deposition on the target. This approach resulted in the detection of andiocyanin-polyflavan-3 ols in die oxonium ion form [M]. ... 

G. Alkali Metal Adducts with Unsaturated Hydrocarbons.82... 

Practical Considerations CareM control of instrument parameters and sample purity is essential for the success of ESI-MS analysis of oligonucleotides. The following approaches have been used successfiiUy to purify oligonucleotide samples and suppress the alkali metal adduction ... 

Although so far only rarely investigated, cholesteryl esters possess characteristics similar to DAGs or TAGs, namely that they are exclusively detectable as alkali metal adducts [34, 69], and never as proton adducts. Even spectra of purified cholesteryl esters always contain a significant peak of free cholesterol (m/z 369.3), and this peak is normally more marked than that of the intact cholesteryl ester [70]. Although not yet carefully investigated, this unpHes a mechanism similar to TAG that is, a Umited stability of the adducts of cholesteryl esters. 

Wang, H.-Y., Yim, W.-L., Kluner, T, Metzger, J.O. (2009) ESIMS Studies and Calculations on Alkali-metal Adduct Ions of Ruthenium Olefin Mefathesis Catalysts and Their Catalytic Activity in Metathesis Reactions. Chem. Eur. J. 15 10948-10959. 

Singly charged ions encompass radical ions, protonated/deprotonated molecules, products of alkali ion additions, or complex ions with other charge carriers. In the case of singly charged radical ions, the molecular weight of an analyte molecule approximately equals to the m/z value of that ion (one electron affects the measurement by only 0.00055 u). In the case of protonated or deprotonated molecules, the m/z values are expressed as m -I- 1 or m - 1, respectively. Alkali metal adducts are also commonly observed in MS for example, m -l- 23 (sodium adducts) or m -i- 39 (potassium adducts). The alkali ions are mostly contaminants, which are very difficult to remove from sample vials, solvents, or sample plates. However, some analytes such as carbohydrates can only be ionized by association with alkali ions [5,6]. 

Owing to its compatibility with solution samples, ESI is preferred over other ionization methods in many MS fields. Applications of metal ion adducts have been reported for ESI [55-57]. For example, ESI can be used to produce alkali-metal adducts of antibiotics that do not form abundant [M+H]+ ions. Informative adducts between alkali-metal ions and peptides have been observed under a variety of conditions of electrospray ionization mass spectrometry (ESI-MS). It should be noted, however, that the presence of salt ion adducts cause the signal suppression and interference with the interpretation of the mass spectra, particularly in analytical MS of proteins and other biological molecules. 

Kamel A, Munson B. Collision induced dissoeiation studies of alkali metal adducts of tetracyclines and antiviral agents by electrospray ionization, hydrogen/deuterium exchange and multiple stage mass spectrometry. Eur J Mass Spectrom. 2008 14 281-97. 

---