Tubes were placed into reaction vial and vacuumed to 100 millitorr before
adding 20 μl of fresh redrying solution (consisting
of methanol: water: ethylamine at a ratio of 2:2:1
v/v) and was then mixed thoroughly. Samples were
vacuumed to 70 millitorr before adding fresh 20 μl
of derivation reagent (consisting of methanol: water:
triethylamine: PITC at a ratio of 7:1:1:1), mixed and
tubes returned to reaction vial and valve closed.