Microwave digestion
Microwave digestion is a fast, enclosed-vessel sample preparation technique to be used mainly in analytical chemistry to break down solid or complex samples particularly having strong acids into a clear solution for elemental or composition analysis.
It uses microwave energy to heat samples mixed with strong acids (like nitric acid, hydrochloric acid, or hydrogen peroxide) inside sealed, pressure-resistant vessels. The microwaves heat the acids uniformly, speeding up digestion.
The sample is placed in a digestion vessel with one or more acids. Microwave energy rapidly heats the mixture, raising temperature and pressure inside the sealed vessel so the acid attacks/dissolves the sample much faster and more completely than open-vessel heating. Closed-vessel (pressurized) systems are most common for trace-metal work; open systems exist for lower-temperature extractions.
Temperatures are raised well above the normal boiling points of the acids because of pressurization in closed vessels; many protocols reach ~160–250 °C and pressures that can be quite high (dependent on vessel design). Exact temperature/time/acid volumes depend on matrix and validated method.
Microwave digestion System
Microwave digestion System
- Use vessels and gaskets rated for the temperature and pressure you’ll reach; follow manufacturer maintenance and calibration guidance.
- HF needs special training, PPE, and emergency procedures (calcium gluconate gel availability, appropriate neutralization).
- Always run blanks, reagent controls, and CRMs; monitor temperature/pressure logs and never exceed vessel specifications.
The Process
How it works (simple steps)
- Certain Sample (soil, food, plant, pharmaceutical, metal, etc.) is readied.
- Acids are added in a Teflon or any vessel that can impart entire heat without becoming part of the reaction.
- Microwave Digestion Vessel is sealed and placed in a microwave digester with best specifications.
- Controlled microwave heating raises temperature and pressure.
- Sample fully dissolves into a clear solution.
Advantages
Advantages
- Much faster than conventional digestion
- Closed system → minimal contamination and loss of volatile elements
- Higher temperature & pressure → complete digestion
- Uses less acid and gives reproducible results
Applications
- Environmental analysis (soil, water, sludge)
- Food and agricultural samples
- Pharmaceuticals
- Metals and alloys
- Biological samples
Difference from conventional digestion
| Microwave digestion | Conventional digestion |
| Closed system | Open system |
| Faster than conventional (minutes) | Slower than newer ones (hours) |
| Less external contamination risk | Higher contamination risk |
| Complete control | Less control |