Graphite Furnace Atomic Absorption Spectrometry (GF-AAS)
Graphite Furnace Atomic Absorption Spectrometry is a technique that is very suitable for the analysis of metals at ultra-trace levels (ng/ml). A small amount of a solution to be analysed, is injected into a graphite furnace. The furnace is heated with a special temperature-program. First the solvent of the solution is evaporated, followed by ashing of the sample, which removes most of the sample-matrix. The last stage of the heating-program is the atomisation-phase, which creates a cloud of free atoms in the graphite furnace. The concentration of free atoms in the furnace is measured by absorption of element specific irradiation through the graphite furnace. This irradiation is produced by a hollow cathode lamp, which contains the element of interest in its cathode. The amount of absorption is a measure for the concentration of the element in the sample-solution.
Some ‘volatile’ elements like arsenic, antimony and mercury can be measured as their hydrides (As, Sb,...) or as ‘cold vapour’ (Hg). With this very specific technique, the volatile hydrides are heated in a quartz tube, which again produces free atoms, that are measured with atomic absorption.
Flame Atomic Absorption Spectrometry (Flame-AAS)
Atomic Absorption Spectrometry is an analytical technique for the determination of elements based upon the absorption of electromagnetic radiation by free atoms, in the visible and ultraviolet region (λ = 190-850 nm). The technique typically makes use of a flame to atomize the sample. To obtain a cloud of free atoms, a solution of the analyte is aspirated into a flame when using flame-AAS. Most of the free atoms remain in the electronic ground state. If irradiated with light of their own characteristic resonance wavelength, these atoms will absorb some of the radiation by excitation of the electrons, the absorbance being proportional to the population density of atoms in the flame, thereby permitting a quantitative analysis.
AAS is not an absolute technique, which means calibration with standard solutions is required for every new series of measurements.
Cold Vapor Atomic Absorption Spectrometry (Cold Vapor AAS)
Mercury analyses (bound en free) are very important to investigate lifetime and competition issues and the effects of different phosphors and precoats on all kind of lamps, including TL and CFL. Measurements with the FIMS (Flow Injection Mercury System) are based on the Cold Vapor AAS technique. Cold Vapor AAS is used for measuring low amounts of mercury. The sample solution, containing ionic mercury, is mixed with a strong reducing agent (tin(II)chloride) forming atomic mercury. An inert carrier gas (e.g. argon) transports the mercury to a quartz tube, placed in the light beam of a mercury lamp. The absorption is registered by a solid state detector. Cold Vapour AAS is not an absolute technique, which means calibration with standard solutions is required for every new series of measurements.
A major advantage of the technique is the inherent separation of the mercury from the matrix.