scope:

This guideline describes a sampling procedure for metals and metalloids in PM₁₀ aerosol, microwaveassisted pressure digestion of the sample in an oxidising acid mixture and analysis using graphite furnace atomic absorption spectrometry (GF-AAS), inductively coupled plasma mass spectrometry (ICP-MS) or optical emission spectrometry (ICP-OES) with inductively coupled plasma.

The method can be used to determine Pb, Cd, Ni and As, bound to particles, within the framework of the European Council Directive 2008/50/EC on ambient air quality and cleaner air for Europe.

In addition, this method can be used to determine further elements, also bound to particles, in a variety of airborne dust fractions. Inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GF-AAS) have proven reliable and sensitive analytical methods for the determination of Pb, Cd, Ni and As that are bound to particles in the PM₁₀ aerosol, as well as for other heavy metals. Inductively coupled plasma optical emission spectrometry (ICP-OES) is mainly used for analysing alkali metals and alkaline earth metals, as well as Fe, Mn, Al and Zn. Table 2 gives an overview of suitable analytical techniques and the typical lower limits of their working ranges for the determination of elements in airborne dust (PM₁₀).

The homogeneity of the distribution of the dust on the filters shall be demonstrated in cases where partial samples of the dust-coated filters are digested and analysed. Experiments on element recovery from dusts with certified elemental contents have shown that the digestion method used in Section 4.3 (pursuant to DIN EN 14902) can produce lower results, in particular for elements bound as silicates. The efficiency of different digestion variants for the determination of a variety of elements was tested both on certified reference materials and on quartz fibre filters coated with dust in an interlaboratory comparison, in which members of the research group participated. Table 3 gives the recoveries of different elements in the certified reference material (SRM NIST 1648a "urban particulate matter") for each digestion variant that was tested. A conscious decision was made when selecting SRM NIST 1648a, that contains a substantial proportion of components bound as silicates, to choose a material that constitutes a difficult matrix compared to real samples, as this also allows recovery to be tested in an extreme case. The use of digestion variants without hydrofluoric acid and high temperatures produces clearly lower results for elements like sodium, potassium and aluminium, as well as chromium, which are partially bound as silicates. Lower results are obtained for antimony due to the production of the insoluble metantimonic acid in cases where nitric acid is used exclusively as the digestion acid.

Based on experience, the matrices for real PM₁₀ airborne dust samples in Central Europe are generally less critical than SRM NIST 1648a. Table 4 shows the relative element recoveries in the different digestion samples during determination of elements in PM₁₀ airborne dust at a measuring station in Baden- Württemberg. Detailed descriptions of the recovery experiments and the different digestion variants are provided in guideline VDI 2267 Part 3.

Table 3 makes clear that full digestion of all elements in the reference material SRM NIST 1648a is only achieved with the digestion variants 6 and 7 (with hydrofluoric acid and at high temperatures).

The relative element recoveries were determined through digestion of PM₁₀ airborne dust filters using the different digestion variants and the rough determination of the concentrations of elements bound to particles. The mean values of the element concentrations obtained with digestion variants 6 and 7 were used as the nominal values.