A reversed-phase ultra-high performance liquid chromatography method was established for the determination of 1-deoxynojirimycin (1-DNJ) in milk powder. The sample was extracted ultrasonically using a mixed solution of hydrochloric acid (0.01 mol/L) and methanol (1:1, V/V). After purification via low-temperature centrifugation, the extract was derivatized with 9-fluorenylmethoxycarbonyl chloride under alkaline conditions. Glycine was used to neutralize the derivatives, which was terminated by adding a 1% (V/V) acetic acid solution. The analyte was separated on a reversed-phase C₁₈ column and detected using a diode array detector at a wavelength of 266 nm. Qualitative analysis was performed based on the retention time, and quantitative analysis was conducted using the external standard method. The results showed that the calibration curve exhibited a good linear relationship in the concentration range of 1-50 μg/mL. The limit of quantification was 18.0 mg/kg, and the limit of detection was 6.0 mg/kg. The recoveries of 1-DNJ from spiked samples at concentration levels of 18.0-270.0 mg/kg were 105.4%-106.6%, 94.1%-97.4%, 96.7%-102.7%, and 100.5%-104.5% with relative standard deviations of 1.18%, 1.76%, 2.08%, and 1.57%, respectively. This method is characterized by high sensitivity, accuracy and repeatability, and is suitable for the determination of the content of 1-DNJ in milk powder.

A reversed-phase high performance liquid chromatographic (HPLC) method was established for the determination of erythrosine in fermented milk. After enzymatic hydrolysis, the sample was extracted with anhydrous ethanol, and purified by solid phase extraction using an HLB column under alkaline conditions. The separation was performed on a C₁₈ reverse-phase column by gradient elution using a mobile phase comprising 20 mmol/L ammonium acetate buffer solution (pH 6.5) and methanol. The detection wavelength was set at 520 nm, and quantification was performed by the external standard method. The results showed that the linear range for erythrosine was 0.05–20.00 μg/mL. The limit of quantitation (LOQ) and the limit of detection (LOD) of erythrosine in fermented milk samples were 0.2 and 0.1 mg/kg, respectively. The recoveries from fermented milk samples spiked at levels of 0.2–2.0 mg/kg were 96.5%–105.6%, and the relative standard deviations (RSD) were 1.87%–2.21%. The method is simple and accurate, has high recovery and good repeatability, and is suitable for the determination of erythrosine in fermented milk.