Studies on Analytical Methods for pH Value of Aqueous Solution of Flue-cured Tobacco

Because there was no standard method for tobacco pH value determination,pH value measurements might be varied for same tobacco sample as different analytical methods were used.It embarrassed the evaluation of tobacco quality in terms of pH value.In order to determine the suitable conditions for analyzing the pH value of tobacco, the effects of pH value of distilled water, storage state (closed or open),ab temperature and test time on pH value of aqueous solution of tobacco were studied through two-day track analysis.The results showed that the pH value measurements were scarcely affected by the pH value of distilled water and storage state,but significantly influenced by lab temperature,especially by higher lab temperature.At 25℃, the pH value of tobacco decreased by 5.2% within the first hour from starting the test. The decline was slowing down during the second day, when the pH values linearly correlated with the test times,the square of the coefficient of correlation (R 2) was 0.9961. At 12℃,the pH value of tobacco generally decreased very slowly, however, there was a slight rise during the first ten minutes. In addition, the pH values of two grades of redried lamina, B2F and C3F, grown in some major flue-cured tobacco planting areas of China were determined under proper conditions, namely extraction with common distilled water, open storage, testing during the second day and 25℃ of lab temperature.