Atmospheric pressure chemical ionization (APCI) is used for less polar molecules where ESI fails to deliver reasonable quantities of ions. In contrast to ESI, it produces mainly singly-charged ions even for larger molecules.
APCI is only limited in the case of thermally unstable compounds, since evaporation of the solvent is done by heating the sample in the nebulizer needle. APCI is often used for metabolomics as well as for drug or pesticide screening.
The new Bruker APCI II source is of course compatible to Bruker's unique DirectProbe option DIP. The direct injection probe is a novel smart solid sample introduction technique allowing a rapid analysis of solids. Sample preparation is as simple as dipping a disposable glass capillary into the solid sample.