Sentence:  For protein identification , fractions from the column were concentrated by <WSD>pervaporation</WSD> against a stream of air at 5 ` C or by negative pressure dialysis in an apparatus which permitted simultaneous concentration of the protein and dialysis against isotonic saline . 
Meaning of the word marked with <WSD> tags:  the concentration of a colloidal solution whose colloid will not pass through a semipermeable membrane; solution is placed in a bag of the membrane and the solvent is evaporated off