HELGES – Microwave Digestion

Microwave Digestion System: The microwave MLS Start can be used to digest samples to be analyzed by ICP-MS or ICP-OES. Special Teflon containers allow samples and acids to be heated at elevated pressures, and therefore temperatures above the atmospheric boiling point can be reached to facilitate chemical reactions during sample dissolution. A wide variety of samples can be digested using the microwave, e.g., plants, sediments, soils, rocks, water, human/animal tissue. The systems also allows controlled evaporation of large volumes of acid (HF, HCl, …) in connection with an acid-fume neutralizer.
Alkali-Fusion: A high-temperature oven (muffle furnace, up to 3500 °C) is used to dissolve samples in an alkali melt (e.g. Li₂B₄O₇ or NaOH). This digestion procedure is chosen if the element of interest would form volatile or insoluble species when strong acids are used for the dissolution (e.g. SiF₆ when dissolving silicates with HF or CaSO₄ when dissolving organic material with H₂SO₄×H₂O₂). In our laboratory, mainly NaOH fusion is used to dissolve silicates for stable Si isotope analysis. For this, the sample is weight in Ag crucibles, NaOH is added and the sample is digested at 750 °C degree. The silicates can afterwards readably be dissolved in weak HCl.