Some Problems in the Estimation of Chlorophyll-a and Phaeopigments from Pre- and Post-acidification Spectrophotometrie Measurements
✍ Scribed by Dr. Jan R. Moed; Dr. Gustaaf M. Hallegraeff
- Publisher
- John Wiley and Sons
- Year
- 1978
- Tongue
- English
- Weight
- 919 KB
- Volume
- 63
- Category
- Article
- ISSN
- 1434-2944
No coin nor oath required. For personal study only.
✦ Synopsis
The rate of conversion of chlorophyll-a to phaeophytin-a in dilute acid organic solvents is markedly pH-dependent. Tho widely used spectrophotometric measurement before and after acidification to discriminate between chlorophyll-a and phaeopigments is applicnhle only between pH 2.6-2.8. At higher pH the reaction proceeds slowly and occasionally may be incomplete. At lower pH complicating reactions may occur, such as breakdown of certain carotenoid pigments causing (time-dependent) increase of background absorption, and formation of di-cations of phaeophytin with spectral characteristics different from the usually obtained mono-cations of phaeophytin. Consequently, i t is stressed to control carefully the acid concentration, the water content of the solvent, and the amount of MgC03 used in the filtration procedure. I n general, for the purpose of spectrophotometric acidification experiments, acidification by dilute hydrochloric acid added to organic solvents containing 10-200/0 water, and omission of MgCO, would be preferable.
On the basis of observed complications in t h e red p a r t of t h e absorption spectrum of the pigment extract, i t is recommended to use the above stated pH-range.