Environmental Analysis Q and A
Flame atomic absorption and flame emission spectroscopy
Flame atomic emission and flame atomic absorption are allowed by most atomic absorption and commercial spectrometers. Usually, an inverse relationship exists between excitation energy and wavelength (Lajunen, 1992). According to Maxwell-Boltzmann law, energized atoms’ quantity in a flame decreases exponentially as the energy increases while temperature decreases. The method’s sensitivity in the atomic absorption spectrometry or AA is directly proportional to ground states’ atoms quantity (Clugston & Flemming, 2000). Atomic emission AES’ sensitivity on the other hand increases as the energized state’s atoms quantity rises. Another vital factor that should be considered is the energized atoms’ life span.
It is apparent that he excited atoms ration to ground state’s atoms is more favorable in the flame AES in the range of short wavelength of a spectrum unlike the spectrum of a long wavelength (Nimis & NATO, 2002). The sensitivity of Flame AAS is higher than that of flame AES once excitation potential goes beyond 3.5 eV. The spectrometry of flame AES is more sensitive in alkali metals than that of flame AAS.
ICP and AA
Atomic Absorption Spectrometry (AA) differs from Inductively Coupled Plasma Emission Spectrometry (ICP) in that AA depends on the atomic absorption but ICP is purely a spectroscopic technique for ionic/atomic emission. Another difference is about the means of producing ionic/atomic species. While AA uses a heating system made of graphite or a burning flame, ICP utilizes plasma. ICP and AA also differ in the way they detect frontiers. There are improved detection restrictions in furnace AA in most cases where the element can be atomized. In addition, the detection limits of the elements in group I such as potassium and sodium are enhanced in AA than in ICP. ICP on the other hand has improved detection limits for the refractory elements when compared to those of AA (Clugston & Flemming, 2000).
Why FAAS cannot measure mercury, selenium and Arsenic
Flame Atomic Absorption Spectroscopy (FAAS) may be a generally simple, widely acceptable and convenient method. However, it has high specificity level and determining elements like arsenic, selenium and mercury using it is impossible because it is not sufficiently hot. There is a tendency for graphite furnace to have higher sensitivity when compared to FAAS. A smaller sample solution volume is used with low precision levels. It is also prone to the matrix effects. A major shortcoming that FAAS has is its slowness when compared to XRF and ICP because only one element can be determined using it at a time (Nimis & NATO, 2002).
Clugston, M., & Flemming, R. (2000). Advanced chemistry. Oxford: Univ. Press.
Lajunen, L. H. (1992). Spectrochemical analysis by atomic absorption and emission. Cambridge: Royal Soc. of Chemistry.
Nimis, P. L., & NATO Advanced Research Workshop on Lichen Monitoring. (2002). Monitoring with lichens: Monitoring lichens. Dordrecht [u.a.: Kluwer Academic.