Sensitivity of the 4-hydroxy-TEMP spin trap to pH. Four-hydroxy-TEMP (50 mM) was prepared in buffers of varying pH: pH 6, (MES); pH 7, (Potassium phosphate); pH 8, (Tris-HCl); pH 9, (Glycine); pH 10 CAPS, pH 11, (water), with and without addition of 100 µM rose bengal and then exposed to light (1000 µE) for 5 min.