Sentence:  For protein identification , fractions from the column were concentrated by pervaporation against a stream of air at 5 ` C or by negative pressure dialysis in an apparatus which permitted simultaneous <WSD>concentration</WSD> of the protein and dialysis against isotonic saline . 
Meaning of the word marked with <WSD> tags:  strengthening the concentration (as of a solute in a mixture) by removing diluting material