Vapour Generation Atomic Absorption Spectrometry VGAAS

4 Vapour Generation Atomic Absorption Spectrometry (VGAAS) 

In the past, certain elements, e.g., antimony, arsenic, bismuth, germanium, lead, mercury, selenium, tellurium, and tin, were difficult to measure by direct AAS [39-45]. 

A novel technique of atomisation, known as vapour generation via generation of the metal hydride , has evolved. This technique has increased enormously the sensitivity and specificity for these elements [41-43,45]. In these methods, the hydride generator is linked to an atomic absorption spectrometer (flame graphite furnace) or inductively coupled plasma optical emission spectrometer (ICP-OES) or an inductively coupled plasma mass spectrometer (ICP-MS). Typical detection limits achievable by these techniques range from 3 pg/1 (arsenic) to 0.09 pg/1 (selenium). 

This technique makes use of the property that these elements exhibit formation of covalent, gaseous hydrides that are unstable at high temperatures. Antimony, arsenic, bismuth, selenium, tellurium, and tin (and to a lesser degree germanium and lead) are volatilised by the addition of a reducing agent such as sodium tetrahydroborate(III) to an acidified solution. Mercury is reduced by stannous chloride to the atomic form in a similar manner. 

Automating the sodium tetrahydroborate system based on continuous flow principles represents the most reliable approach in the design of commercial instrumentation. Pahlavanpour and co-workers [46] described a simple system for multi-element analysis using an ICP spectrometer based on the sodium tetrahydroborate approach. PS Analytical Limited developed a reliable and robust commercial analytical hydride generator system along similar lines using different pumping principles from those discussed by Pahlavanpour and co-workers [46]. 

---