Sentence:  Fractions from the column which were to be subjected to <WSD>analytical</WSD> ultracentrifugation were concentrated by negative pressure dialysis and dialyzed for 16 hr in the cold against at least 500 volumes of phosphate buffered saline , pH 7.2 , ionic strength 0.154 . 
Meaning of the word marked with <WSD> tags:  using or skilled in using analysis (i.e., separating a whole--intellectual or substantial--into its elemental parts or basic principles)