Single Reaction Chamber Microwave Digestion of Highly Organic Matrices

Sample matrices with high organic content have created a significant challenge for sample preparation methods. Several techniques that have been used to obtain high quality multi-element ICP-OES/ICP-MS data for trace metals analysis, including microwave digestion or a combination of high temperature ashing with digestion, do not provide a solution for all samples. Samples with high organic content, such as polymers, plastics, solvents, petroleum products, and some nutraceutical supplements present additional challenges for the conventional microwave digestion approach, with temperatures and pressures generated during the acid digestion step that are often out of range for traditional vessels. Additionally, a second limitation involves the inability to process multiple sample types or different acid combinations simultaneously.

Table I: Mixed organic samples for digestion

Results and Data

Single reaction chamber (SRC) technology has recently been described as a technique with the capability of digesting several different sample types simultaneously, including difficult catalysts and highly organic samples. Milestone's UltraWAVE microwave digestion system was used to digest a number of highly organic polymer matrices in disposable glass vials simultaneously, which has been shown to generate pressures exceeding those of conventional closed vessels. The program selected used a 15 min ramp to 160 °C, and then 15 min to 260 °C, followed by a 15 min hold time at 260 °C. Following digestion, the samples were concentrated to a volume of 1 mL, then diluted to 10 mL with deionized water and analyzed on an Agilent 7700 ICP-MS in Helium mode.

Table II: ICP-MS analysis of mixed organic matrices following single-reaction chamber digestion

Conclusion

The UltraWAVE is able to digest a number of difficult organic samples simultaneously, enabling independent sample types to be processed in a single operation. Both the design and capability allow difficult organic samples to be processed without time spent on method development work on a per sample basis.

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