Arsenic can find its way into food through a variety of paths. In the recent past, various organic arsenicals were used as herbicides and antimicrobial agents in growth fields as well as applied directly on fruits and fruit trees. Prior to 2003, arsenic was commonly used as a wood preservative. Sawing and/or sanding of this wood would yield arsenic contaminated sawdust. In some areas, arsenic is naturally found in rock formations and can enter soil and water which is used in the growth of food products. Foods can also be contaminated during manufacturing, processing, packaging and transport processes.
There are a few specific analytical challenges that an analyst must consider in the determination of arsenic in foods by GFAAS. Toxic elements, such as arsenic, which may be present in foods are biologically important at very low concentrations. The U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry (ATSDR) defines a minimal risk level for chronic inorganic arsenic exposure to be 0.0003 mg As/kg/day. For a 45 lb. child drinking a liter of fruit juice a day, the minimal risk level for that juice would then be about 6 μg/L. Therefore, the analytical technique employed for this application must have the capability to accurately measure arsenic in sample digestates at the sub-ppb concentration level.
A complete method has been developed for the determination of arsenic (As) in baby foods and baby fruit juices by Graphite Furnace Atomic Absorption Spectroscopy (GFAAS). This method includes sample preparation steps using microwave assisted closed vessel digestion. Foods come in a wide variety of complex sample types and matrices, but their fundamental major components are water and various carbohydrates. In this work, the samples were totally digested in a microwave oven so that the samples’ various carbohydrate matrices were completely destroyed prior to instrumental analysis. Microwave digestion has several analytical advantages for this type of analysis. Because the sample is placed in a sealed Teflon® polymer (PTFE) digestion vessel, contamination is minimized and there is no loss of volatile elements during the digestion procedure. In a sealed vessel, higher temperatures of digestion are reached thereby quickly yielding complete matrix decomposition. With the microwave system used here, each sample’s digestion process is thoroughly documented as to time, pressure and temperature. This gives an analytically repeatable and transferable digestion process.