Lactic acid

L. chuanxiong was purchased from a local Chinese medicine herb market (Chengdu, China), dried at 60 °C until it reached the stable weight, crushed and pressed through a 40-mesh sieve, then kept at −20 °C prior to the experimental analysis.
A ferulic acid standard was obtained from Chengdu Must Biological Technology Co., Ltd (Chengdu, China). Choline chloride, ethylene glycol, 1,2-propanediol, glycerol, glucose, sucrose, maltose, malic acid, citric acid, lactic acid, oxalic acid, ethanol, methanol and other chemicals were purchased from Chengdu Kelong chemical reagent factory (Sichuan, China). Deionized water (electrical resistivity ≈ 18.2 MΩ cm) used in the experiments was purified by a water-purifying system of Sichuan Water Technology Development Co., Ltd.

Cadmium acetate (Cd(CH₃COO)₂·2H₂O, AR), sodium sulfide (Na₂S, AR), and thioacetamide (CH₃CSNH₂, AR) were obtained from Aladdin Co. Ltd (Shanghai, China). Thiourea (NH₂CSNH₂, AR) and thiosemicarbazide (NH₂CSNHNH₂, AR) were purchased from Adamas Reagent, Ltd (Shanghai, China). Triethylenetetramine (C₆H₁₈N₄, AR) was provided by Xiya Reagent Co. Ltd (Shangdong, China). Anhydrous ethanol (C₂H₅OH, AR), rhodamine B (C₂₈H₃₁ClN₂O₃, AR) and lactic acid (C₃H₆O₃, AR) were purchased from Kelong Chemical Reagent Co. Ltd (Chengdu, China). All chemicals were used directly without further purification. Ultra-pure water was used for all experiments. All the data were measured in triplicate.