Stability of Elements at ppb Concentration Levels

Adsorption

Adsorption is divided into the following physical or chemical types:

• Physical adsorption is an attraction between the solid surface and adsorbing species consisting of van der waals interactions.
• Chemical adsorption or chemisorption is a chemical interaction which is strong enough to break or form chemical bonds.
• Types of losses such as ion-exchange, reduction, precipitation, and diffusion into a permeable solid are often also treated as adsorption.

In this guide, adsorption is taken to mean loss through the combined effects of all interactions with the walls of vessels or with filter paper.

The pH of the solution is an important consideration. Most trace analysts prefer to prepare or adjust solutions to a pH of < 2, as shown in Table 7.1 below.

Attempts have been made to prevent adsorption by complex formation, as shown in Table 7.2, but the use of relatively high levels of reagents increases the risk of contamination. Furthermore, it tends to influence the stability and chemistry of other analytes of interest.

Table 7.2: Prevention of Adsorption by Complex Formation¹

Attempts to remove adsorbed ions typically require extreme conditions and are only partially successful, as seen in Table 7.3.

Table 7.3: Desorption of Adsorbed Inorganic Ions¹

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