Preparation of Mixed Food Samples Using Microwave Acid Digestion with Novel iWave Contactless In-Situ Temperature Measuring Technology

With the continued globalization of trade, it has become increasingly important in recent years to ensure the safety of the food supply, as there have been numerous instances of metals contamination. This has led to increased demand for better analytical techniques and lower detection limits for elements of interest. Food samples require some form of sample preparation prior to final analysis and in most cases a complete digestion of solid samples is required. As spectroscopic instrumentation has improved resulting in lowered detection limits, CEM has made advances in microwave sample preparation technology to simplify the technique and ensure complete digestions. The latest of these innovations is iWave™.

iWave utilizes Light Emitting Technology™ (LET) that renders the vessel transparent. This allows for a temperature measurement of every sample in real time. For the last 25 years, the fiber optic probe has been considered the gold standard for temperature measurement in microwave acid digestion. Now, iWave has the accuracy of a fiber optic probe without the time consuming set up and considerable consumable cost.

In order to highlight the benefits of this new technology, several types of food samples were prepared in a single run using standard IR and MARS 6™ with iWave. These samples were then prepared for elemental analysis.

Instrumentation

The samples were digested using a CEM MARS 6, with iWave contactless in-situ temperature sensing, in 75-mL MARSXpress™ vessels, on the 40-position turntable.

Method Details

Four different retail products (American cheese slices, ground sausage, granola bars, and milk powder) were digested in the MARS 6 with standard IR and iWave. Samples of 0.5 g were digested with 10 mL of HNO₃, ramped to 210 °C for 20 min and held at that temperature for 15 min.

Figure 1: iWave's contactless temperature measurements track perfectly with the fiber optic probe.

Results

All of the digested samples were clear and particle free upon dilution. The samples digested using iWave resulted in a more complete digestion of all the samples in this mixed food study. Figure 2 highlights the increased precision of the power over time. This ability to fine adjust the power control allows MARS 6 with iWave to analyze a greater variety of sample types in a single run.

Figure 2: Using iWave, the power response is much tighter than the standard IR sensor, resulting in greater control of the reaction.

Conclusion

Based on this mixed food study, the benefits of using microwave acid digestion with iWave technology include:

• The ability to run more diverse types of mixed foods, such as high fat sausage and high carbohydrate granola, in the same batch.

• Additional control over the sample reaction, generating a better digestion that delivers the optimum analytical results.

• A new straightforward standard for temperature measurement in microwave acid digestion.

CEM Corporation
3133 Smith Farm Rd., Matthews, NC 28104
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Website: CEMAnalytical.com