Sentence:  The precipitate was washed twice with an 80 % saturated solution of * * f , dissolved in a small quantity of 0.1 M <WSD>neutral</WSD> phosphate buffer , dialyzed against cold distilled water till free from ammonium ions , and lyophilized using liquid nitrogen . 
Meaning of the word marked with <WSD> tags:  having only a limited ability to react chemically; chemically inactive