Patent ID: 8623292

Claim:
An absorbent article capable of determining the ionic strength of urine comprising: a substantially liquid impermeable layer; a liquid permeable layer; an absorbent core positioned between the substantially liquid impermeable layer and the liquid permeable layer; and a lateral flow assay device integrated into the article and positioned such that the device is in fluid communication with the urine when provided by a wearer of the article, the device comprises: a buffering zone, the buffering zone including a polyelectrolyte disposed therein; an detection or indicator zone, the detection zone having a buffering component comprising a weak polymeric acid and weak polymeric base with a pKa ≦10 −3 , and a charged polymeric surfactant that is responsive to relative ion concentrations in a sample solution, and a charged pH indicator with a charge opposite to that of the charged polymeric surfactant non-diffusively immobilized therein; said charged polymeric surfactant is soluble in amounts of greater than or equal to about 1% by weight (≧1 wt. % solute) in water and aqueous solutions of low ionic concentration of ≦0.1 wt. % salts, but insoluble (<1 wt. % solute) in aqueous solution of high ionic concentrations of >0.1 wt. % salts.