Abstract

A comparison between microcrystalline tests performed on microscope slides and flat
capillary tubes with inner diameters ranging from 0.1 to 0.7 mm was carried out to explore the
appropriateness of tubes for rapid testing of suspected drugs of abuse in the laboratory as well
as in the field. Tests for mephedrone, cocaine and phencyclidine were chosen as examples to
investigate the handling of the capillary tubes, the influence on crystal habit, size and the effects
on the limit of detection. Image stacking software was used to increase the depth of field of
micrographs taken from developed microcrystals greatly enhancing the interpretability even
months after carrying out the microcrystalline test.
Additionally, the potential of seeding capillary tubes with a reagent was studied. Pretreatment
of tubes would allow microcrystalline tests to be carried out quicker and anywhere
without the necessity of taking along expensive and hazardous reagents. The sealing of capillary
tubes containing developed microcrystalline tests in order to preserve results for a long period
of time was successfully done by applying paraffin wax to the open ends.
Finally, it was concluded that capillary tubes are suitable vessels for performing
microcrystalline tests. The increased portability of the improved set-up allows tests to be safely
executed outside laboratories without impairing the quality of the result. Findings were applied
to six legal high samples purchased online between May and August 2011. The active
ingredients like MDAI as well as cutting agents like caffeine were successfully identified using
the microcrystalline test technique in capillary tubes.