Sentence:  Assay of C1 esterase involves <WSD>microformal</WSD> titration of the acid liberated from ATEe (a stock concentration of 1.6 M in 2-methoxy-ethanol) during 15-min incubation at 37C according to the method of Levy and Lepow (11). 
Meaning of the word marked with <WSD> tags:  Involving substances in which extremely small volumes are involved (such as antibiotics, antibodies or viruses).