I made what I calculated to be an 11 mM stock solution of L-Trp (0.035 gr L-Trp dissolved in 15 ml of 100 mM KH2P04 pH 6.5.
I checked the abs of this, (10 ul of what I thought was an 11 mM stock solution added to 990 ul of my buffer in a 1 cm cuvette) and the abs at 278 nm was 1.2, using Ext. Coeff. of 5,579 M-1cm-1, I calculate the solution I made as being 22 mM. This is a fairly significant difference, and thinking something was wrong the first I did this I made a fresh stock solution of Trp and got the same results.
Does anyone have any idea what is going on? Am I using the correct Ex. Coeff?