[vietanhvietnam_123]

Hello everyone in the forum!

I really need help for my analysis. My blank samples usually turn light pink (few times it even turns purple) when adding pyridine/barbituric acid, so it affects badly to my results. Initially, i thought the reagents was not clean because of my uncareful manipulation . However, even though i tried to be more careful at every step, there were only few times my blank was good enough. I also researched on the documents and also on the internet but couldn't find satisfying solution.
Is there anyone who is familiar to this problem? Are there any interferences that can have significant influence on the color development? Please give me an advice

Thank you so much!

[Corribus]

I think it would be helpful to tell a little more about your procedure. I personally am not familiar with this analysis but that doesn't mean I couldn't help if I had a little more information about what you're doing.

[vietanhvietnam_123]

Thank you for spending your time on my problem. I need to develop the purple color for samples containing CN- before UV-VIS measurement. And here is my procedure:

Firstly, 5ml of sample is added to volumetric flask (25ml), which contains a certain volume of NaOH (dilution solution). Then 0.5 ml of Acetate buffer (pH = 5.5) and 1ml of Chloramine-T, respectively, are added. Mix and keep the flask stand still in 2 min. Finally, 2.5 ml Pyridine/Barbituric acid is added for color development. Add distilled water to the line and mix evenly. Wait for full color development in 8 mins then measure the sample within 20+-5 mins.