We have some standardized methods for plant, soil and water samples. For other material, we develop a method to achieve complete digestion. We generally try to digest the maximum sample weight in the smallest extraction volume to achieve a concentrated digest solution.
Typical method parameters:
Small sample size:
- powdered samples facilitate digestion
- maximum 250 mg for organic samples (e.g. plants, animal tissue)
- maximum 500 mg for inorganic samples (e.g. soils)
Extraction volume: minimum 5 ml, typically 10 ml
Acid solution: typically nitric acid, hydrochloric acid, aqua regia or acid+water
Temperature: typically 180 ºC - 200 ºC depending upon sample type
Duration: ramp to temperature, holding and cool down can take 30-60 minutes depending upon selected program
Sample capacity per batch: minimum 6 and maximum 40 including blanks
Pre-digestion: highly reactive samples require pre-digestion for anywhere from 15 minutes to overnight
Filtration: in some cases filtration is required after digestion (usually soil samples)
- Because we do not use hydrofluoric acid in our lab, silicates may not be completely dissolved.
- Because nitric acid is reactive with organic material, the nature of the sample must be known prior to digestion.
- This instrument cannot digest samples containing the following: explosives, propellants, pyrophoric chemicals, hypergolic mixtures (nitric acid and phenol, triethylamine, or acetone, etc.), animal fats, aviation fuels, acetylides, glycols, perchlorates, ethers, lacquers, alkanes, ketones and alcohols.
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