Advanced review of the contributing factors for the Microwave Digestion of food matrices for trace elemental analysis

Microwaves are electromagnetic waves which move at the speed of light. Samples directly exposed to this phenomenon are heated faster than conventional conduction heating methods. This is exploited in acid assisted digestion where a food sample in a suitable acid matrix can be completely destroyed leaving a clear solution of measurable elements. In pressurised systems the temperature can be rapidly increased far above the conventional boiling point of the solvent and the closed microwave vessel environment is ideal for volatile elements.

There is a constant aspiration to achieve lower levels of detection and advances in instrument capabilities with specialised plasma based techniques for the identification and quantification of individual elements at ultra-trace levels have evolved. To realise this; sample preparation, digestion efficiency and sample introduction need to be optimised. Exogenous inputs such as preparation environment, reagent grade, the analyst and apparatus cleaning steps all have the potential to leave an elemental footprint on the sample and therefore contribute to the uncertainty of the analytical result. Knowledge of sample composition and subsequent interaction with microwaves and plasma are an important consideration for complete digestion without which the result is not accurate.