a) What methods of sample introduction can be employed in CI-MS?
In CI, the analyte is introduced into the ion source the same way as described for EI, i.e., via direct insertion probe (DIP), direct exposure probe (DEP), gas chromatograph (GC), or reservoir inlet.
b) Would you expect tetrabutylphosphonium tetrafluoroborate and sodium oleate to be candidates for PICI?
No, because ionic analytes are not suitable for CI. They will decompose prior to analysis when attempting to evaporate them into the ion source. Desorption methods are recommended instead. (For a short compilation of analytes suitable for CI techniques see Table 7.5).
c) What is DCI? In what respect does is differ from other CI techniques?
CI in conjunction with a direct exposure probe (DEP) is known as desorption chemical ionization (DCI). In DCI, the analyte is applied from solution or suspension to the outside of a thin resistively heated wire loop or coil. Then, the analyte is directly exposed to the reagent gas plasma while being rapidly heated at rates of several hundred degrees per second to temperatures up to about 1500 °C. The rapid heating of the sample plays an important role in promoting molecular species rather than pyrolysis products.