Hello Sanghee Park

The color reaction occurring at zero concentration could be because of the reagents used in the assay. I would suggest you use a reagent blank and then subtract the result of reagent blank from the test results. In colorimetry some assays do require reagent blank to be scanned as blank.

Secondly, the colorimetric tubes also play an important role. Keep the same tube to scan blank. Excessive use of the tubes could cause scratches and should not be used. Clean the tubes inside out. Avoid fingerprints on the outside of the tube especially the bottom half of the tube in order to avoid errors. The orientation of the tube in the chamber of the colorimeter must be the same each time.

Regards.

Hi...you can be by adding the inhibiting agent with the reaction mixture ... or we can use the blank solution

Hi there,

Simply use the control sample without substrate to set the zero of the spec.

Hi Sanghee Park , Here is what I understand. You have your colorimetric reagent, which shows a response even with zero analyte concentration. This really tells few things. First, your colorimetric reagent can be environment sensitive. Can you use highest grade solvents without any chemical stabilizers on them? Also, you can try to degass the solvents before using them.

Also, even if you have some positive response at the beginning even with zero analyte concertation, if you are using a graphical method, this wouldn't be a big issue. You can normalize your data and use relative response in the y axis. This will leave you an intercept in to the equation. But still will nor be a problem in developing a linearity.