Isolation of Single Crystals from Liquid Drops

Extract

Microscopists often recrystallize or precipitate compounds for purposes of identification. Almost as often, a few crystals form that are irresistibly beautiful and demand isolating for single-crystal x-ray diffraction, spindle stage, polarized IR absorption, or remounting in a crystal-rolling medium like Aroclor® 1260.

The isolation of one such crystal among hundreds from the center of a drop is not as difficult as it sounds. It is done at 50-100X under a stereomicroscope using a fine, usually a tungsten, needle. The needle may (rarely) need to be surface-treated by rubbing with a water-insoluble wax (then tissue-wiped “clean”) to prevent creeping of the solution up the needle and causing solution (and crystal) movement.

The needle is used to clear a path for the desired crystal by pushing the edge crust and other intervening crystals to one side. Complete clearance is not necessary. The desired crystal is then pushed with the needle along the slide to the edge and then well outside of the drop. A few smaller crystals and much solution may accompany it.