How come my cresol purple solution (cf SOP 6b, Dickson) has no absorbance peak at 578 nm?

I'm  having problems with the method based on cresol purple to measure pH in sea water. I made a 10 mM solution of pure cresol purple in Milli Q water, as did Easley & Byrne 2012 and Liu et al...

20 July 2016 9,420 6 View