Mixed 9.06 mg m-Cresol purple (Lot# MKBR3556V) with 10 ml RO water.
The first test on the spec showed a raw absorbance ratio (578nm/434nm) of ~2.
The pH of presevred experimental seawater samples ranges between 8.0-7.3 (pHT). A dye ratio should be closer to 1 will minimize influence of dye pH on sample.
Adding two drops (~100 ul) of 0.1N HCl dropped the ratio to 0.95. See the corresponding color change below.
The accuracy of the dye was valided by via spec pH and DIC measurements of Dickson CRM (batch 171).