Ultrasound-assisted gas-liquid systems

There are three major uses of US in analytical systems involving gas-liquid systems, which can exist as such or be created during sample preparation, namely nebulization, defoaming and degassing. 

Nebulization is a physical process widely used in analytical chemistry for introducing samples into atomic spectrometers [66], Ultrasonic nebulizers are the most effective devices for this operation. Rather than a step preceding sample preparation, nebulization is a sample preparation operation and so close to detection that the nebulizer is a component of flame and plasma spectrometers that influences their efficiency. This warrants separate discussion on ultrasonic nebulizers in Chapter 8. 

Non-analytical uses of US-assisted nebulization span the medicai and pharmaceutical fields, where aerosoling or aerolization is more frequentiy used than nebuiization [67,68], The use of uitrasound to assist the formation of micro-to-nano drops as the first step of spray-drying (atomization) aiso faiis in this group, aibeit in the industriai area. 

Defoaming is the operation by which foam is removed. Foam is the dispersion of a gas in a iiquid where the distances between individuai bubbies are very smaii. in a foam system, the voiume ratio of gas to iiquid is very high and the buik density approaches that of a gas. Foam can cause probiems in anaiyticai operations such as chromatographic separation and moiecuiar spectrometric detection. 

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