Elemental scientists use microwave digestion as an acidic digestion method to dissolve metals for the purpose of attaining measurements related to atomic emissions or to achieve atomic absorption. Thus, microwave digestion is defined as a technique used to dissolve metals in acid by raising both the temperature and pressure through the application of radiation. Microwave ovens designed for laboratory use are the tools commonly used to carry out the process. Advantages inherent to the process revolve around reducing the time it takes to achieve digestion, which is a matter of minutes through the deployment of microwave digestion, as opposed to hours utilizing other workable methods like hot plate digestion. Crucial to conducting the process safely and accurately, however, is ensuring that both the microwave oven and the sample are prepared correctly.
Preparing the microwave oven to process the microwave digestion sample both safely and efficiently is important to the process. Safety concerns revolve around knowing how to operate the microwave oven correctly. Instructions to do so will vary among different models used in laboratories. Therefore, students and scientists will need to review the oven’s instruction manual before attempting to operate it. As well, laboratories usually publish specific policies for operating such equipment onsite, and users will need to familiarize themselves with those policies and adhere to them.
On the other hand, readying the sample is fairly uniform regardless of the preparer. While some samples are prepared a bit differently than others, all samples will have a few preparation rules that need to be followed. Carrying out the process involves putting an acidic solution inside a vessel that can handle acidic solutions and radiation, then dropping the sample inside the vessel before sealing it. Preparation of the sample requires it to be clean and dry before subjecting it to acid, while the vessel adheres to the same standards. Additional moisture or particles can cause the microwave oven to get too hot inside and melt the vessel containing the solution, creating a hazardous situation.
Predigestion is also an important step that must be taken when preparing unknown samples for microwave digestion. This is also a required step if the sample is suspected of containing reactive substances. Typically, the process involves preparation of the sample beforehand and then letting the vessel stand on the counter for a period of at least 15 minutes to discern a reaction before submitting the sample to microwave digestion. As well, regardless of the sample, it is important to note that once digestion is complete all labs will have posted a recommended cool down period before removal from the microwave oven. All users will need to adhere to the policy posted to mitigate the risk of a hazardous accident.