Microwave Digestion Equipment

The Berghof microwave digestion system has many unique features that give it the edge for microwave digestion of samples. These include:

  • A special cylindrical oven rather than a rectangular shape.
  • Use of special TFM- PTFE vessels that outlast all other vessels.
  • Patented fast sample temperature for fast feedback on power control.
  • Contactless pressure control on each vessel.
  • Proper venting on each vessel to a fume cupboard.
  • Highest power flux per vessel available.
  • The safest system to use for Hydrofluoric acid digests.
  • No capping station necessary for vessel de-capping.

Correct oven shape: The top loading design of the Xpert model, allows the oven to be designed to closely match the rotor. This is desirable to ensure very even microwave loading or flux through the entire sample vessel rotor. Compared to other systems with rectangular ovens, this provides a significant advantage ensuring even sample vessel heat up and efficient conversion of microwave energy to vessel heat up. The Xpert vessels have the highest even microwave energy loading of any microwave at > 100 watts/vessel. Apart from the even power flux, another advantage of the top loading oven, is that it is not necessary to lift a full carousel of samples that may weigh up to 20kgs. Instead the Xpert allows individual sample vessels to be loaded into the carousel in situ.

Special TFM PTFE Vessels: The combination of acid, heat and pressure can be very demanding on sourcing a suitable material for digestion vessel construction. A variety of materials have been used including PFA, PEEK, PTFE and Quartz. All have to date had a limited life such that the vessel is classified as a consumable rather than a spare part. Berghof as a fluoro polymer manufacturer, have developed a unique material that is durable to digestion conditions for lifetimes in excess of 6 years. The material TFM-PTFE is specially formed in a hydrostatic bath such that there is no axial weakness in the material.

The higher density TFM vessel has better properties wrt. temperature, pressure and acid resistance. Importantly while conventional PTFE has an affinity to accumulate small levels of mercury in the structure, the higher density, hydrostatic TFM-PTFE shows no accumulation in the vessel with time making it ideal for mercury digests for low level analysis by ICP-MS. Ultra fast sample digest temperature measurement: The speedwave4 uses a patented temperature feedback design where instead of just recording the surface temperature of the vessel during digestion, the selective wavelength sensor gets the immediate temperature of the vessel contents rather than the lagging surface temperature. This is critical for fast ramp, exothermic reactions where fast control of the magnetron power loop is necessary. Contactless pressure measurement: Unknown sample carbon content, that forms CO2, can be one of the hidden factors that contributes to significant pressure creation during digestion. This makes it important to measure the pressure development in every vessel. The Xpert uses a polarized laser source to measure the vessel cap pressure. This does not require the connection of any wires or tubes to the vessel, a contactless measurement. The individual pressure reading is used with the temperature measurement to ensure correct control of the microwave digestion equipment. Proper venting of each vessel: Processing of the resulting pressure build up, during digestion, is important. The Berghof system allows the capture of ALL the digestion vapaour within each vessel.

The captive digestion provides correct recoveries when compared to CRMs such as Hg in tomato leaves. Each vessel is also connected to a special manifold so that in the event of a rupture disc failure, then the acidic vapour from that vessel is vented to a fume cupboard. From an OH&S consideration this is preferable.

With the digest of mercury in organic loaded samples, this pressure control is the most suitable as the alternative vessel cap release means loss of sample and low recoveries. The dangers of microwave digestion with Hydrofluoric Acid: The completely captive venting system for each vessel, means that the Speedwave4 is able to conform with OH&S guidelines and offer a safe and effective means of performing hydrofluoric acid microwave digestions. In the case of vessel rupture or overpressure, the HF vapour is vented to the fume cupboard without release to the microwave oven or laboratory atmosphere. No capping station required: the use of high density TFM has another benefit in that the fine machining of the vessel threads allows sufficient hand pressure to be applied to seal and unseal the vessels. This makes for faster overall microwave digestion and lower capital costs.

All of these advanced features mean the Speedwave4 microwave digestion instrument can digest more difficult samples at higher pressures and temperatures (100bar and 300 deg C) in a safer manner. A useful accessory for microwave digestion, is the BRB939 Acid Purification System. This allows AR grade acids to be purified to Ultrapure grade at a fraction of the cost of ultra pure acids.