Use of Simple Vials and Racks

With SRC, a large stainless steel pressure reactor acts as both the microwave cavity and reaction vessel.  This reactor contains a TFM Teflon liner in which all samples are placed and subsequently subjected to the same temperature and pressure conditions.  Prior to the digestion run, the reactor is pre-pressurized  As the stainless steel reactor is in itself pressurized, the need for individual pressure vessels, as used in standard  closed vessel digestion, are no longer needed. Instead, samples are simply weighed into glass (disposable), quartz (reusable), or Teflon vials and loaded into a rack – just like loading an autosampler! In fact the sample vials, after digestion, could be placed directly in an instrument autosampler for analysis. The photograph shows an UltraWAVE sample rack loaded with 15mL glass vials, following digestion. Loose fitting TFM caps prevent condensation from falling into the vials but still allow pressure equalization with the chamber. Sample handling is minimized, which reduces the risk of contamination – a key advantage for ultratrace analysis by ICP-MS. The separate microwave run required to clean closed reaction vessels is eliminated, which greatly increases productivity. Simply throw away used glass vials, or clean used quartz vials in acid.

For most efficient and effective cleaning of quartz vials use Milestone’s TraceCLEAN. For high throughput labs the reduction in labor saving (no vessels to assemble/disassemble) and in consumables costs (vessels, caps, shields) compared to closed vessel digestion is significant.

High Temperature and Pressure Ensures Complete Digestion

After the reactor is sealed and prior to the microwave run, the SRC is pre-pressurized with nitrogen. This immediately raises the boiling point of the digestion reagents inside eliminating the potential for sample cross contamination via boiling and spitting, and also prevents the loss of volatiles. The SRC operates at very high temperature and pressure conditions – up to 200 bar and 300 deg. C, so complete digestion of even the most difficult samples types is assured. The very high pressure conditions means that much higher sample weights can be digested compared to closed vessel systems. Since all samples are, in effect, inside the same vessel, there is direct pressure and temperature control of every sample – giving the best possible control of digestion conditions. There is no need to use slower and less accurate indirect temperature (IR) or indirect pressure control.

Digest Different Samples - Simultaneously

With closed vessel digestion, a sample is chosen as a reference vessel: temperature and pressure in that sample is directly monitored and the program adjusts power to prevent an overpressure situation. This means that only samples of the same weight and type as the reference sample can be digested at the same time. With SRC there is no such limitation: since all samples are in the same vessel, any combination of sample types and acid chemistries can be digested in the same run – all under the same, optimal conditions. For example, consumer products, nutraceuticals, and polymer samples can be digested simultaneously, greatly increasing the productivity of labs with multiple sample types to digest. Unlike closed vessel digestion, there is no need to batch samples of the same matrix together for digestion. Also, reference materials can be digested at the same time as samples, even though the sample matrix is different, enabling for the first time, in-run quality control of the digestion process.

For more details on the labor savings made possible by SRC technology, download the Milestone technical note Productivity Benefits of Single Reaction Chamber Microwave Digestion – the UltraCLAVE Advantage

Maximum run capacity is 15 samples with the UltraWAVE and 40* samples with the UltraCLAVE ( *Optional rack that holds 77 X 12mL vials for microsampling applications such as clinical, in these cases, 77 samples can be digested simultaneously)

Digestion run time with the UltraWAVE is faster than closed vessel digestion due to its very rapid heating and cool down time, and slightly longer with UltraCLAVE due to the additional cooling time required by its large chamber.