I am performing UV/Vis spectroscopy using for pesticide effects on chlorophyll a and b. Chlorophyll a is having a tendency to bring about negative values. The absorptions are performed on three separate solutions from three different extractions of chlorophyll a and chlorophyll b is giving positive results.
I did not fully understand your question or problem, but if you increase the amount of sample in the solvent, your negative values can be positive and you can calculate more accurately.
What is your extraction process? is it the same for chl a and chl b, or is there a different solvent for the two? Did you prepare a blank for each chlorophyll extraction?
Did you re-use a quartz cuvette, or did you use disposable cuvettes? If you used a quartz cuvette, was it clean when you zeroed the instrument? If there was residual pigment, you might have cleaned it with the blank solution, then any further samples would have appeared more dilute than the blank.
Matthew Wheal For chlorophyll a I am using methanolic KOH and for chlorophyll b I am using petroleum ether. Between each absorption I am washing with water then with the solvent of the chlorophyll.
Water washes between petroleum ether samples might create some "interesting" miscibility issues.
Methanolic KOH doesn't sound like an issue there, but did you adequately clean the cuvette to ensure a clean start to the analysis?
I think you might need to wash with the solvent three times before zeroing. If it still goes negative, wash with solvent again.
- Badges
- Science topic
- Similar topics
- Philosophy
- Philosophy Of Science
- Reasoning