Reducing systems, methanol-potassium hydroxide

In buffered solution, the DPPH radical can show variations in its stability. Al-Dabbas et al. (2007) found that in methanol solution containing acetate buffer (pH 5.0), the absorbance of the DPPH radical was not reduced in a wide range of concentrations examined (0.01-0.2 mmol L ), while in phosphate buffer (pH 7.0), a reduction of the DPPH radical absorbance was observed at concentrations above 0.05 mmol L. In other studies, Ozcelik et al. (2003) evaluated the variation in stability of the DPPH radical after 120 min. The absorbance of DPPH radical in potassium biphthalate buffer (pH 4.0) decreased by 25% in methanol solution and by -45% in acetone solution. DPPH radical in sodium bicarbonate buffer (pH 7) was stable in an acetone system (less than 10% reduction), but an -30% decrease occurred in the absorbance in a methanol system. DPPH radical in potassium carbonate-potassium borate-potassium hydroxide buffer (pH 10) was stable in a methanol system (less than 10% reduction), but a decrease of -70% occurred in the absorbance in an acetone system. Thus, the stability of DPPH in pH buffer solution mainly depends on the types of buffer and solvent used. 

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