Microwave Digestion of Powder Samples Using a Reconstitution Step

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Microwave digestion of powdered materials, such as infant formula and dairy powders, have proven to be a difficult task. Powders are inherently non-homogenous and digesting a sample large enough to provide a homogeneous representative sample often leads to excessive venting and incomplete digestion. Reconstituting the powdered samples in water greatly improves their homogeneity and yields more consistent and complete digestions. This application note will describe the procedure of reconstitution and digestion of four food powder samples using the MARS 6 microwave digestion system.


An estimated 1 million infants in the United States are fed formula from birth and, by the time they are three months old, about 2.7 million rely on formula for at least part of their nutrition. Accurate nutritional labeling of food products is a legal requirement in most countries to help consumers make informed healthy choices. This means all label claims need to be supported by accurate scientific measurements. For vulnerable groups such as babies and people requiring clinical nutrition products, infant formula nutrient analyses need to be very specific and able to accurately quantify even very low concentrations of heavy metals such as Pb, As, and Cd. In order to detect the low levels of heavy metal impurities obtaining a large representative sample is critical. This application note will focus on the preparation of powdered samples including infant formula, cheese powder, milk powder, and powdered butter. Samples will be reconstituted in warm water and an aliquot of each powder slurry will be prepared in the MARS 6 digestion system using the 75 mL MARSXpress vessel.