High performance liquid chromatography system

The name, age, sex, symptoms, and signs of the study subjects were collected. After 4 mL venous blood was taken from the elbows of the study subjects, the level of 5‐HT was determined using the high‐performance liquid chromatography system (Gilson), the 5‐HT standard sample (Sigma), and the high‐performance liquid chromatography ultraviolet light method. In brief, for detection of 5‐HT, the equipment was connected to the UV diode array detector. We actualized the chromatographic separation of 5‐HT with C18 Column (4.6 × 250 mm, 5 μm) under isocratic elution. The mobile phase is 0.05 mol/L KH₂PO₄ (apparent pH = 5)/acetonitrile (90:10, V/V), and the wavelength of the UV detector was set at 280 nm. The stock solution containing 100 μg/mL serotonin hydrochloride was diluted subsequently into 6 calibrators with concentrations of 1000, 500, 250, 125, 62.5, and 31.25 ng/mL, respectively. Each solution is prepared in 3 mL volume, and all solutions were preserved at 4°C. Additionally, all subjects received the vestibular function tests, including the caloric test (less than 0.025 Hz), head‐shaking test (1‐2 Hz), and vestibular autorotation test (2‐6 Hz) to assess the horizontal semicircular canal functions at different frequency. The above operations were conducted by the attending physicians from Neurology Department.