I’m having a problem with my sandwich ELISA. I have a sample that I do the measure every three months since 2012. Until the early of this year, this sample have 4 ug/mL of protein. To July until now, my ELISA tests give results of 14 ug/mL of protein. All the other samples keep going the same results, only this sample is “wrong”. This sample, obviously, don’t increase the amount of protein. The kit that I use is the same (same bath), the washing buffers are the same (not same bath), and the reader is the same. That is confusing because only this sample gives this result. The standard curve is always good. The negative controls are good. I don’t know if this is important, but this sample has the smaller quantity of protein of all my samples. My other samples has between 30 to 50 ug/mL of protein.
Has someone a idea for what is going on?
Sorry about my english!