Volatile organometallic species

GC is widely used to separate volatile organometallic species. The favored approach involves derivatization (e.g., ethylation or hydride formation), preconcentration, chromatographic separation followed by element-specific detection using AAS, AES, or AES. For species such as methylmercury and methylarsenic compounds, derivatization is normally necessary prior to GC in order to form volatile species. The most common approach has been to convert both inorganic and organometal species via hydridization with sodium borohydride, or alkylation, e.g., using sodium tetraethylborate, to form volatile hydrides or alkylated species, respectively. Not all species of an element are amenable to derivatization. For example, the application of hydridization... 

The sample preparation procedure applied for organometallic speciation depends on the matrix in which the respective species is present, and the state in which the species exists. Volatile organometallics that have been sampled by cryofocusing or adsorption methods can more or less... 

In the ideal case, all the three objectives can be combined. Common examples are the derivatization of polar or ionic analytes for GC. In the case of organic analytes, molecules with active H atoms have to be derivatized in order to prevent the formation of hydrogen bonds between analyte molecules, which reduces their volatility or may even lead to thermal decomposition before volatilization. In the case of ionic organometallic analytes, derivatization may involve, for example, hydridization or alkylation, so that the ionic species can be transformed into neutral and thus volatile ones. 

Chemical methods are generally based on the reaction of surface hydroxyl groups with a selectively reacting compound to form a covalently bonded surface species of well known composition. As reactive compounds, diborane,4,5 boron trichloride,6,7 diazomethane,8 organosilanes,3,6,9,10,11,12,13,14 and organometallic compounds15 have been employed. a0H is then derived from the amount of the chemisorbed species as well as the amount of volatile reaction products. 

---