AAS measurements using the graphite furnace technique

Nitrogen is frequently used as shielding gas. As a rule, however, argon is used in the case of elements which form nitrides, e.g. barium, molybdenum, titanium and vanadium. In order to reduce condensation of the sample and evaporation of the matrix products at the cooler ends of the cuvette, the shielding gas is usually fed in at the ends and escapes from the sample insertion hole. The flow of gas is usually optimized by the equipment 

The sensitivity of this technique depends directly on the volume of the sample. Volumes of between 10 and 20 pi are very frequently used. The use of an automatic feed system is of considerable importance in this graphite tube AAS technique, having a crucial influence on the sample dosing on which precision and accuracy depend. Thus, not only the point in the graphite tube at which a sample is introduced is important, but also how the drop is applied to the tube wall. These factors can only be completely controlled by automation. A degree of reproducibility better than 1 % is achieved in this way. 

The majority of commercial appliances allow temperature and time selection for evaporation of the solvent, for the incineration phase and for the atomization phase. It is important for the sample to evaporate completely 

In the case of non-saline waters, the maximum heating rate is usually selected, as this generally reduces chemical interference. Sensitivity is also increased, particularly with such low-volatile elements as molybdenum, titanium and vanadium. It is of considerable importance to heat the cuvette to a higher temperature than the atomization temperature of the element to be determined. 

The signals produced can be evaluated with the aid of the peak-area method or the peak-height method. Suitable integrators are available for this purpose in modern equipment. 

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