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Technical Details
Why the UltraClave?
The primary limitation of conventional microwave labstations is the vessel technology inside. Vessels must be constructed of materials that are microwave transparent, chemically resistant, and inert for trace-level analytical procedures. Some plastics fulfill these requirements. However, the limited mechanical strength and temperature resistance of these materials constrain their operational capabilities for certain chemical applications.
The UltraClave removes those limitations, by combining high-pressure vessel technology with the advantages of microwave heating. The problem of how to get microwaves into a metal chamber was not a trivial one, but in solving it, Milestone has opened a new realm of possibilities to chemists.
Operating Principle
| Note: for a graphical depiction of the UltraClave sequence of operations, click here. |
Microwave-transparent sample containers are loaded into the instrument, either open or covered. The cover of the UltraClave is lowered automatically by an electronic motor. Next, the closure mechanism is engaged, sealing the vessel(s) for high-pressure operation. The interior of the UltraClave's 4.2 liter, stainless steel pressure vessel is protected by a special Titanium Nitride coating for acid and chemical resistance.
Microwave heating and reaction parameters are entered into the control terminal. The built-in compressor introduces pressurized nitrogen gas into the UltraClave. This high-pressure nitrogen atmosphere greatly exceeds the pressure developed inside individual sample containers during traditional microwave heating. Nitrogen pressure compensation ensures that sample solutions remain inside the containers, with no losses nor cross-contamination.
Continuous, unpulsed microwave energy from the system magnetron is introduced into the UltraClave through a special microwave-transparent conduit in the bottom of the pressure vessel. Heat transfer to the samples is direct, via microwave absorption. The internal geometry of the vessel is optimized for direct microwave coupling with zero reflectance, ensuring maximum heating efficiency. Heat radiating from samples to the surrounding nitrogen is removed by a recirculating cooling system, and the stainless steel vessel remains at approximately room temperature throughout the entire heating cycle.
At the conclusion of a microwave heating program, energy transfer and sample heating cease instantaneously. Nitrogen pressure is gradually released by a computer-controlled valve. Once atmospheric pressure is reached, the closure can be disengaged and the cover lift operated, to open the UltraClave for removal of samples.
| Comparative Digestion Efficiencies (% sample decomposition) | |||
|---|---|---|---|
| Sample (weight) | UltraClave 270°C/100 bar |
Standard microwave digestion 200°C/30 bar |
High-pressure conventional "bomb" system 300°C/100bar |
| Pharmaceutical (0.600 g) |
100% colorless/clear | 88% light yellow | 99% colorless |
| Organic Dye (0.500 g) |
99.9% colorless/clear | 65% brown-yellow | 98% colorless |
| Plastic (0.400 g) |
99.8% colorless/clear | incomplete digestion; brown/cloudy | 97% light yellowish |
| Time | 15 minutes (digestion) 25 minutes (total cycle time) |
60 minutes | 120 minutes (digestion) 480 minutes (total cycle time) |
Return to: UltraClave overview or Digestion overview.
General: Go to the Milestone front page, or send us an inquiry.