Sentence:  Fahey and Morrison used a single , continuous gradient at constant <WSD>pH</WSD> for the fractionation of anti - A and anti - B agglutinins from preisolated | g-globulin samples . 
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);