I'm having problems with the method based on cresol purple to measure pH in sea water. I made a 10 mM solution of pure cresol purple in Milli Q water, as did Easley & Byrne 2012 and Liu et al 2011. I adjusted the pH to 7.9, as specified in Dickson and did an absorbance spectra, using 50 ul of CP solution in 3 ml milli Q water. I got a nice peak at 434 nm but nothing at 578, so I obviously cannot have a ratio A578/ A 434 of 1.6 as asked in the SOP, What did I do wrong?
Thanks in advance, Elise
I think there is difference in your m-cresol purple. Please follow the procedure given in the following link
http://cdiac.ornl.gov/ftp/cdiac74/sop07.pdf
Let me know the result you get after you try this document. Also share some more details about exact absorbances at all three wavelengths with and without dye.
Hope this will help you.
thank you both for your help, I will read the pdf . I'll let you know about the results.
Dear Sir. Concerning your issue about the method based on cresol purple to measure pH in sea water and the absorbance spectra. You can try the method described by Clayton and Byrne (1993), who used m-cresol purple as an indicator dye. The following below link may help you in your analysis:
http://www.mri-jma.go.jp/Publish/Technical/DATA/VOL_57/tec_rep_mri_57.pdf
Thanks
Dear sir, Thank you very much for this suggestion. I found the paper and will read it with great interest. Elise
I am way to late answering to this question, but I will give my opinion if someone else find this post.
The problem is that you were using miliQ water and it is way too acidic for the measurement. The 578 nm peak of the more basic specie (H2I) of the mCP would not show because of this. My recomendation for other people with this problem would be to try to conduct your experiments usign seawater.
Regards,
Pablo
- Badges
- Science topic
- Similar topics
- Biological Science
- Biochemistry
- Biochemical Techniques
- Analytical Chemistry
- pH