Flame Atomiser:

The role of atomiser is to produce the vapours of analyte that get excited through the thermal energy of the flame and then emit features radiation which is measured. The flame atomiser assembly consists of two elements. The prior one is a nebuliser while the sample within the form of a solution is drawn in and converted into a fine mist or an aerosol. That is then passed onto the second component that is the burner along along with air or oxygen and a fuel gas. Wtihin the flame a number of processes occur in which convert the analyte within excited species. Now let us learn about the nebulisers used in flame photometers. You will learn about the burners within the next subsection.

Nebuliser is a device used for sample introduction within the flame. The procedure is known as nebulisation and consists of thermal vapourisation and dissociation of aerosol particles at high temperatures producing small particle size along with high residence time. The numbers of nebulisation methods are available. A few are given below.

• Pneumatic nebulisation
• Ultrasonic nebulisation
• Electrothermal vapourisation
• Hydride generation (used for certain elements only)

Therefore, we would discuss about the pneumatic nebulisation only. It is the most generally employed nebulisation method in flame photometers.

Pneumatic nebuliser is the most generally used nebuliser for introducing aqueous/ liquid samples. Within this the sample solution is fed or aspirated within the nebuliser that converts liquid within a fine mist, or aerosol that is then fed within the flame. A general type of pneumatic nebuliser is known as concentric pneumatic nebuliser, as display in Figure. The concentric pneumatic nebuliser consists of a fine capillary surrounded through concentric tube along with a small orifice near one end of the capillary. A capillary is dipped within a solution of the analyte although the outer tube is linked to a high pressure gas supply. The analyte is sucked within the capillary through the high pressure gas stream flowing around the tip of the capillary by using the Bernoulli effect. The procedure is known as aspiration. The high velocity gas breaks up the liquid within several sized fine droplets. The other kinds of the pneumatic nebulisers also work on the similar principle

Figure: Concentric type pneumatic nebulizer