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We found that use of a LMW sample from Polysciences Inc. which contained ≈ 1% ammonium chloride stopped electro-osmotic flow, even after dialysis. As PAAm is known not to adhere to channels [19], and ≈ 1% ammonium chloride solutions in water:methanol solvent demonstrated normal flow behavior, the mechanism preventing flow in the sample which included salt is not known. One possibility is the presence of a contaminant copolymer similar to poly-N-hydroxyethylacrylamide [20], which adheres to side-walls and significantly reduces the electro-osmotic mobility. 

