Patent ID: 7233865

Claim:
A method for determining the molecular weight of a sample solute comprising the steps of: providing a plus shaped microchannel network on a microfluidic chip, having at least four microchannels intersecting at a cross point; flowing a sample stream comprising a sample solute of unknown diffusivity from a first microchannel through said cross point into a second microchannel adjacent said first microchannel; flowing a blank stream from a third microchannel through said cross point to a fourth microchannel adjacent said third channel, such that said sample stream and said blank stream contact each other at said cross point; creating a sample curve by measuring the concentration of said sample solute that diffused from said sample stream to said blank stream at said cross point while altering the flowrate of one of said blank stream or said sample stream; determining a diffusion coefficient of said sample solute of unknown diffusivity by extrapolating data from similar curves of at least two solutes having known diffusion coefficients created under similar conditions as those generated by said sample solute; and determining the molecular weight of said sample solute based on the determined diffusion coefficient.