Patent ID: 8679052

Claim:
A method for accurately determining the diffusible or free concentration of an agent in a medium in which the properties of the probe may change, comprising: a) providing a probe, for which the window volume V w and inner radius α are known but the value of λ may change, comprising a section of relatively highly permeable membrane relative to any materials to which the membrane is attached for support and positioned between an inlet to a source of dialysate and an outlet to a receptacle, and through which membrane the diffusible agent is to be transferred; b) putting said probe in contact with said medium; c) perfusing a known quantity of a dialysate, for which the diffusion coefficient D of the diffusible agent is known, into the relatively highly permeable section of the probe at a specified flow rate Q; d) allowing said known quantity of dialysate to remain stationary for a specified resting time t R ; e) flushing out said known quantity of dialysate with a single pulse to collect a sample of dialysate of a known volume V S into said receptacle at the same flow rate used in step (c), above; f) determining the concentration of said diffusible agent in said dialysate; g) calculating the apparent recovery F R App ; h) repeating steps (c) through (g) with the same flow rate and sample volume but at least one different resting time; i) determining the value of λ, f D , F RQ and γ 1 for the probe using a chosen sample volume and flow rate from F R App vs. exposure time, subject to the constraint that the diffusion coefficient of the diffusible agent in the dialysate equals its known value; j) calculating the free concentration in the donor as C D,f =f D C D .