Microwave digestion for microbes
An.Huang
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Abstract
Before conducting inductively coupled plasma mass spectrometry (ICP-MS), all samples containing organic compounds need to be digested in order to eliminate all organic parts. Microwave digestion is a commonly used method for organism digestion. This protocol describes how to conduct microwave digestion on microbes.
Steps
Preparation of digestion vessels
Pick out digestion vessels from preservation boxes containing nitric acid (4%). Rinse and wash the vessels thoroughly. Also wash coordinated number of caps and plugs.
Put all vessels inside the oven and dried at 60°C for at least 1h 0m 0s.
Take all vessels out from the oven when they are completely dried and put all vessels into the fume hood.
Microwave digestion
Label all vessels according to the samples.
Add samples into digestion vessels.
Add 5mL nitric acid (70%) and 2mL hydrogen peroxide into the digestion vessels.
Plug the vessels and screw the caps tightly.
Here we skipped a step of pre-digestion, which is to heat these capped vessels at 80℃ overnight. Since our samples only contain microbes like bacteria, it is not a necessity to conduct this step. This part is designed for larger organisms like cellulose, which is hard to digest.
Put all vessels into microwave digester according to the manual of the digestion system.
Set the digest programme according to the vessel number. Please read the digestion system manual for more instruction.
When the digestion programme has finished, wait for around half an hour to let vessels cool down.
Volume consistency
Open the caps and unplug the vessels when the vessels have not completely cooled to room temperature. Pour the remaining liquid inside the vessel into a 50 mL centrifuge tube.
Use a dropper to add 3mL ddH2O into one vessel by the inside wall. Shake the vessel generally and pour the water into the same 50mL centrifuge tube in Step#11. Repeat this step for 6 to 8 times.
Add ddH2O until the liquid volume inside the 50 mL centrifuge tube reeds 50mL.
The digested samples in 50 mL tubes need to be stored at 4°C for further analysis.
Digestion vessel storage
Wash all digestion vessels using ddH2O for three times.
Submerge all vessels into nitric acid (4%) inside the preservation box.
