Cleaning of digestion vessels

Table of Contents

Pressure digestion vessels such as those used in modern microwave digestion systems for element determination in analytical chemistry are exposed to high temperatures and pressures. To ensure that the vessels have a long service life, regular cleaning is recommended. The concentration of the blank is usually the main cause of error in analytical chemistry. To minimize the risk of contamination or the introduction of blank values, all digestion vessels should be cleaned conscientiously. In the case of borosilicate glass, PE, PP or PTFE, the Environmental Protection Agency (EPA) recommends the following procedure:

  1. rinse with ultrapure water
  2. (1:1) HCl between 80-100°C, >2h
  3. (1:1) HNO3 between 80-100°C, >2h
  4. rinse with ultrapure water

Complete digestion and purification with water

A digestion is generally considered complete once a clear solution is present after digestion. Whether a digestion was fully successful, can only be determined using spectrometer measurement (ICP,AAS) and determining element concentration.  Conveniently, vessels made of TFM™-PTFE can be reused directly after being cleansed with double-distilled water (3 x 20mL). In the case of leaching tests, as described e.g. in DIN EN 16174 or EPA 3050, no complete digestion is carried out. The samples shall be filtered before analysis. If no residues can be detected in the vessel, cleaning with double-distilled water (3 x 20mL) is also sufficient here. Irrespective of this, it is generally recommended to carry out a blind digestion at regular intervals. For this purpose, only the acid is subjected to digestion without the sample under the same digestion conditions as in the presence of the sample.

Samples with different element concentrations

Especially in laboratories with high sample throughput and samples of different origin and matrix, it can happen that the concentrations of an element (ppm/ppb) vary in different digestions (e.g. digestion A determination of element X in the ppm range; digestion B determination of element X in the ppb range). In trace analysis, the purity of the vessels and reagents is the basic requirement for a good analysis. For this reason, the vessels should always be thoroughly cleansed in advance.