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Microwave digestion with top-loading concept for very simple handling and a high sample throughput
Berghof speedwave® four
Dr. Dieter Gutwerk
In many analytical laboratories today microwave digestion is a standard method of preparing samples for determining elements.
For microwave digestion the sample material is typically heated to 200 – 260°C in closed microwave-transparent pressure vessels with an acid mixture and thereby fully degraded and dissolved. The advantage of microwave digestion compared to conventionally heated stainless steel pressure digestion vessels lies in the accelerated heating-up phase and the possibility of simultaneous digestion of multiple samples. However, the economic efficiency of the overall system is determined less by the number of samples per run than by the handling costs and the working hours required for it. This finding was consistently taken into account in developing the Berghof speedwave® four microwave digestion system. The speedwave® four distinguishes itself by simple handling and low operating costs.
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| Fig.1: speedwave® four microwave digestion system |
Easy handling
A pressure-rated, PFA-coated circular oven chamber ensures a homogeneous microwave distribution thanks to the highly symmetrical arrangement. This enables all samples to heated evenly and facilitates a reproducible digestion quality.
The top-loading concept simplifies its handling decisively. The entire, heavy rotor no longer needs to be lifted and placed in the oven. The rotor remains in the oven and the vessels are simply inserted individually and removed again after digestion. The freestanding vessels in the rotor cool down with any additional cooling system within around 15 minutes. Thereafter the microwave digestion system can be loaded again with vessels immediately and restarted. Alternatively, the heated vessels can be removed immediately after digestion and the system reloaded. The sample throughput rate is significantly raised because the cooling down phase is omitted.
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| Fig.2: Handling simplified by top-loading concept |
speedwave® — optical sensor technology
The fast heating process in the microwave field is accompanied by a rapid increase in pressure and possibly by spontaneously induced exothermal reactions. To facilitate optimal and reliable process management the temperature development of all samples must be recorded continuously and the microwave output regulated accordingly. For reasons of safety it is expedient to make parallel records of the pressure development and to also include these in the output control.
Technologies developed and patented especially for measuring the temperature and pressure are used for the Berghof speedwave® four microwave digestion system.
The speedwave® DIRC thermometer for measuring without contact measures the temperature of every single sample directly. There is no time delay while the vessel walls or sensors are heating up. The reliability of the process control system and hence of the entire digestion system is raised effectively.
The optional, contact-free optical pressure check, speedwave® four OPC also makes it possible to record all internal vessel pressures. The use of hands-off sensor technology simplifies day-to-day work and lowers operating costs:
- It is no longer necessary to take measurements in a reference vessel. There is no need for sensor connections.
- Dip pipes no longer need to be mounted, sealed and cleaned.
- There are no more broken sensors and dip pipes and there are no costs incurred or time taken to renew them.
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| Fig.3: Optical sensor technology |
Digestion vessels
Pressure vessels made from solid TFM™-PTFE are used as digestion vessels. The vessel and lid are pressure-resistant and produced entirely from TFM™-PTFE. A pressure jacket and/or lid made from a different plastic material which is partly microwave-transparent and not resistant to acid (e.g. PEEK) is not necessary. The service life of these solid TFM™-PTFE pressure vessels is above average. Some of the pressure vessels from this product series have been in service for over 7 years. All of the vessels consist of only a few individual parts and are correspondingly fast and easy to lock or open. They are handled manually without any special tools.
Simple – fast - effective
Using standard vessels for routine samples (e.g. environment, food, pharmaceuticals) 12 – 24 samples can be digested per run. Typical heating cycles last 20 – 30 minutes.
During this time the next samples can already be prepared. This means that immediately after the heating program ends the user can exchange the vessels with the samples and start a new device cycle.
In our experience with a 12-fold rotary disk there is no problem for a single employee to process up to 192 samples in a 6-hour working day. (Fig. 5) Using a 24-fold rotary disk it is possible to even double the throughput.
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| Fig.4: Few individual parts – easy vessel handling |
Conclusion:
In the form of the speedwave® four microwave digestion system from Berghof a new device and vessel concept for microwave digestion is available that greatly simplifies how the system is handled and perceptibly reduced operating costs.
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| Fig.5: Assessment of the sample throughput per device and employee |
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