Optimization of Fluorescence Derivative Method for Determination of Sulfur Dioxide Residues in Sulfur-fumigated Dangshen and Its Decoction Pieces by Response Surface Analysis

The samples of dangshen were fumigated with sulfur for 0,30,60,90 min,and processed into four sizes,sections,flakes,stir-frying with rice and honey,to determine the SO₂ residue of dangshen and its decoction pieces in different sulphur time. By single-factor experiments and response surface optimization experiments,the optimal derivation conditions were determined as follows:pH of the buffer solution was 6.6,the dosage of buffer solution was 1.5 mL,and the amount of o-phthalaldehyde was 2.1 mL.The concentration of ammonium acetate was 2.5 mmol/L,the dosage of ammonium acetate was 2.0 mL,the reaction temperature was 50 ℃,the reaction time was 5 min,and the static reaction time was 40 min,and the average fluorescence intensity measured under these conditions was 955865.21.The results of the fluorescence derivatization method showed that the concentration of sodium sulfite was between 0.01 and 0.2 μg/mL,and the fluorescence intensity had a good linear relationship. The detection limit was 1.89×10^-3μg/mL. The precision,stability,and repeatability RSD were 0.76%,4.13%,and 1.59%,the average recovery was 98.61%,and the RSD was 4.89%. The results of specific surveys were better. It could be used as a method for the determination of SO₂ residue in dangshen,and the measured results were 24.87% higher than those measured by acid-base titration on average. The measurement results showed that the SO₂ residues of the dangshen original medicinal in fumigated with sulfur for 0 and 30 min did not exceed the standards of Chinese Pharmacopoeia,and sulfur fumigation of the original medicinal material SO₂ residues for 60 and 90 min exceeded the standards. After processing of sulfur dangshen,the residual amount of SO₂ in the decoction pieces was significantly lower than that of the original medicinal materials,and the SO₂ residue in the decoction pieces of honey was the lowest.