I have been contacted by a student who is using a Shimadzu Prominence UFLC. I am not personally familiar with it. She is having the following problem

Injection of a series of linearity solution of differing concentration (Chlorhexidine digluconate in water 1 ugmL upto 100 ugml) twice over a period of few hours gave different responces. These always appear to decrease in peak area. These same solutions were found to be reproduciable when injected on a 1100 system.

thanks