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Study Notes: Positioning the Burner

The population of analyte atoms in the flame can be maximised by selection of correct flame type, flame stoichiometry (lean, rich etc.) and solution chemistry. Prior to analytical measurement however, it is necessary to ensure that light at the characteristic wavelength passes directly through the flame (analyte atom population).

Flame position is adjusted for each element to yield a maximum absorbance as free analyte atoms are not distributed evenly within the flame and distribution varies between analytes. Simple controls are used to position the flame correctly with respect to horizontal and vertical orientations.

Such adjustment ensures that the maximum population zone coincides with the optical path.

Adjustment in a yawing plane may also be effected by rotating the flame around a central axis passing down through the centre of the flame. This has the effect of causing the optical path to pass obliquely through the flame with a consequent reduction in absorbance and may be used to extend upwards the working concentration range that can be measured.

Of course, any adjustment to the flame itself such as fuel-oxidant ratio, changing total gas flow can raise or lower the flame itself and when flame conditions are changed it is important to adjust the burner position again to obtain maximum absorbance.

You must also ensure the maximum number of atoms in the flame to achieve the maximum analytical signal. The best position varies with flame conditions such as type of flame, flame stoichiometry and solution chemistry (eg use of releasing agents).Skip flash movie

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