text: spectrophotometry of leaf extract? i have completed a spectrophotometry practical and calculated concentrations of leaf pigments as the following values: chlorophyl a    16.41 micrograms cm-3 chlorophyl b     11.7  micrograms cm-3 protochlorophyllide   4.4  micrograms cm-3  apparently the ratio of chlorophyll a to chlorophyll b should be 3:1  but my results are giving me a ratio of 1.4:1 can anyone tell me if the wavelengths at which the solution was measured could have affected the results?  we were told to measure at wavelengths of 663nm  645nm   and 626nm as these are the red wavelengths at which maximum absorption occurs for chlorophyll a, chlorophyll b and protochlorophyllide respectively.  however i also have information that states maximum absorption of blue wavelengths as being 420nm for chlorophyll a and 435nm for chlorophyll b.  is this of relevance to my answer????  i have lots of reasons as to how inaccuracies with how the equipment was used could have affected my results chlorophyl being green absorbs both red and blue light. there will be a peak in absorbance in both red and blue regions. i think your measuring wavelengths are too close together and you will need some way to compensate for the overlap of the absorbances of the 3 compounds.