Sentence:  The precipitate was washed twice with an 80 % saturated solution of * * f , dissolved in a small quantity of 0.1 M neutral phosphate buffer , dialyzed against cold distilled water till free from ammonium ions , and lyophilized <WSD>using</WSD> liquid nitrogen . 
Meaning of the word marked with <WSD> tags:  put into service; make work or employ for a particular purpose or for its inherent or natural purpose