Sentence:  Fractions from the column which were to be subjected to analytical ultracentrifugation were concentrated by negative pressure dialysis and dialyzed for 16 hr in the cold against at least 500 volumes of phosphate buffered saline , <WSD>pH</WSD> 7.2 , ionic strength 0.154 . 
Meaning of the word marked with <WSD> tags:  (from potential of Hydrogen) the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; provides a measure on a scale from 0 to 14 of the acidity or alkalinity of a solution (where 7 is neutral and greater than 7 is more basic and less than 7 is more acidic);