Under the condition of different pH (7~11) and different ethanol volume fraction (45% to 85%), the ultraviolet-visible absorption spectra of malachite green were studied in neutral and alkaline ethanol solution, the maximum absorption wavelength at 620 nm was found, and the matching degree of standard curve was better established. In low power trench-type ultrasound apparatus, the absorption of the malachite green solution was measured under ultrasound and non-ultrasound, respectively, the difference values of the ultraviolet absorption of the malachite green solution under low power trench-type ultrasound were measured results of the hydroxyl free radical oxidation degrading malachite green, therefore hydroxyl free radical from low power trench-type ultrasound was determined indirectly. Then the contents of hydroxyl free radical in four conditions were measured. The detection limit of the method of 8. 4×10~6 mmol·L-1 and the relative standard deviation of the method of 9. 4×10-5 ~3. 7×10-4 mmol·L-1 were determined, a higher testing precision and good reproducibility were confirmed. It can be applied for fast detection of neutral and alkaline ethanol solution system in the case of very low concentration of hydroxyl free radicals. Since malachite green is heat sensitive, so compared to measuring temperature, the method possessed better functions for thermal effects of ultrasound.%研究了不同pH(7～11)、不同乙醇体积分数(45％～85％)的孔雀石绿乙醇溶液的紫外-可见光吸收特性,通过最大吸收波长为620 nm处的吸光度与浓度关系工作标准曲线,在低强度超声场中,分别检测超声条件和非超声条件下孔雀石绿溶液吸光度变化,两者的差值就是超声场产生的羟自由基导致的孔雀石绿吸光度变化,从而间接测定了超声场产生的羟自由基浓度.确定了4个超声条件产生的羟自由基浓度,最小检测限达到8.4×10-6 mmol · L-1,相对标准偏差为9.4×10-5～3.7×10-4 mmol·L-1,显示出较高精确度和较好重复性,特别适于中性、碱性乙醇溶液体系中羟自由基极低浓度情况下的快速检测.由于孔雀石绿对热敏感,因此该法可以比测量温度,更好地反映超声场热效应的作用.
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