Digestion is a widely used sample preparation method and a primary dissolution method for several industries. Digesters typically feature a standard hotplate design or microwave technology, which heats a sample, breaking it down into its constituents. Standard hotplate/block digesters use conventional acids like hydrochloric and nitric acids, usually in open flasks or other glass containers. Closed flask methods are also used, capitalizing on higher pressures to reduce digestion time. Closed systems are typically used in biological and organic chemical labs, while open systems are generally used for environmental applications.

Microwave digesters work the same way as block digesters, but use microwave energy to heat the samples. The first commercial digestion units were introduced in the mid-1980s. However, microwave systems did not move into the mainstream until the late 1990s due to significant improvements in vessel designs and sensor capabilities. Microwave digestion’s appeal lies in its control over the digestion process, its improved reproducibility, faster temperature ramp-ups, enhanced worker safety and procedural ease.

Many regulatory protocols specify microwave digestion as a sample preparation method. The EPA has adopted microwave digestion for sample preparation prior to flame or graphite furnace atomic absorption, inductively coupled plasma (ICP) and ICP-MS for a number of priority pollutant metals.

Microwave digesters offer benefits for many applications, but do not completely replace hotplate or block digestion systems due to limitations. Along with higher initial cost, microwave digesters are limited in the range of acids that can be used. Microwave systems reach optimum temperatures faster, but do not generate enough heat for some applications. In addition, the sample load for microwave systems is significantly lower than block digesters.

There have not been many technological achievements in hotplate and block digesters for years. Vendors have adopted the same general specifications and configurations, but offer improvements in design to address issues such as overflow and spillage. Microwave digestion systems have improved significantly during the last decade, particularly the vessel design. Microwave vessels have become more robust to withstand increased pressures and have increased capacity and high-throughput capabilities. Microwave systems have improved their temperature control and have become easier to use with preprogrammed methods and automated chemical handling features.

Overall growth in the digester market is lackluster, but there are a few segments that offer solid growth opportunities, including the pharmaceutical and biotech industries and the Asia Pacific region for environmental applications.

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