TM02-02 Revision of the Procedure Used to Calculate Concentrations of Chlorophyll a and b in Phytoplankton and Periphyton by High-Performance Liquid Chromatography

Name - Chl a, phytoplankton 
Lab Code - 586
Parameter Code - 70953 
Method Code - A 

Name - Chl b, phytoplankton
Lab  Code - 587
Parameter Code - 70954
Method Code - A

Name - Chl a, periphyton 
Lab Code - 588
Parameter Code - 70957 
Method Code - A 

Name - Chl b, periphyton 
Lab Code - 589 
Parameter Code - 70958 
Method Code - A 

The NWQL has analyzed samples by this method since 1978. Standard solutions for this method are prepared by dissolving purified chlorophyll a or b in a 90-percent acetone/water solution, measuring the spectrophotometric absorbance at specified wavelengths, and applying an extinction coefficient to calculate the concentration of chlorophyll in these standard solutions. The solvent used to prepare chlorophyll standards was changed to methanol in April 1988 because the acetone solution caused chromatographic problems. However, the extinction coefficient for chlorophyll in 90-percent acetone is different from the coefficient for chlorophyll in methanol. The difference in extinction coefficients was determined during a recent literature review.