Improving productivity and costs in elemental analysis

You’ve decided to invest in a microwave digestion system for your trace element require­ments. So, how do you go about selecting the optimum technology for your samples? What types of mineral acids will be best suited for your ele­ments of interest, and what temperature and pressure will be required for the digestion process of your sample matri­ces? It’s only when you have a good un­derstanding of these issues that you can begin to look more closely at the pros and cons of the various commercially available microwave technologies.

Rotor-Based Technology

Let’s take a closer look at some of the recog­nised limitations of traditional rotor-based systems. The main drawback is that they require batching of similar matrices and chemistries because control of the power is based on the reaction of one vessel at a time. Regardless of how temperature is being measured, it’s still measuring the power level based on one sample at a time. By batching similar samples, under-digestion of some samples can be minimised due to the pressure and tem­perature required by others. In fact, the vessels in rotor-based systems are typi­cally made from Teflon, which limits the temperature and pressure. The multiple components of vessels require additional handling before and after digestion, which could impact productivity. Depending on detection limit requirements, the vessel liners may also require extra cleaning between runs.

SRC Technology Principles of Operation

As far as SRC technology is concerned, it differs from the rotor-based system, mainly because the samples are put into vials with loose-fitting caps, which sit in a rack that is lowered into a larger vessel containing a base load of acidified water. This base­load absorbs the microwave energy and transfers it to the vial, which allows every vial to react independently within the base load and ensures that all samples achieve maximum temperature with pressures contained up to 200 bar. No batching of samples is necessary and any combination of sample type and acid chemistry can be run simultaneously in the same chamber. The ultraWAVE unit, featuring the SRC technology, is shown on the left side of Figure 1, while an actual pho­tograph of sample vials being lowered into the chamber is shown on the right. As previously mentioned, loose-fitting caps are used to seal the vials. This is possible because they are pre-pressurised with 40 bar of nitrogen before the start of the microwave program, which acts as a gas cap and keeps all the vials inde­pendently closed. As the pressure builds, equilibrium is achieved inside and outside the vial. As a result, a variety of vial types including disposable glass, quartz, and Tef­lon, or any combination of these materials, can be used.

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Typical Applications

SRC microwave technology has found a place in a wide variety of market seg­ments, including contract, production and research laboratories in the phar­maceutical, food, agriculture, fossil fuel, petrochemical, polymer, metallurgical, geological, environmental, and consumer products industries. Widely differing sample types can be digested together without cross contamination, and that complete recovery of a volatile analyte such as Hg is achieved.

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High Productivity

Compared to any other conventional microwave digestion systems, the ultraWAVE is significantly easier to use, thus dramatically improving the laboratory workflow. Up to 26 samples are processed in 45 minutes start to finish. Ease to say that the ultraWAVE sample throughput is far better than any other microwave systems. The use of disposable glass vials eliminates the cleaning step, further enhancing the ultraWAVE productivity.

Low Operation Cost

Opening and closing the vessels, assembly and disassembly of the rotors are not required in the ultraWAVE anymore. The handling of the system is dramatically reduced, and tedious and time-consuming procedures are eliminated. The technology used in all conventional microwave lead to create stressful conditions in the TFM vessels, substantially reducing their lifetime. The design of SRC technology in the ultraWAVE strongly contributes to the reduction of the running costs by using inexpensive and handy vials suitable for any metals and trace metals determination.