A simple, fast, precise and eco-friendly method, based on ion chromatography （IC） with a suppressed conductivity detector, was proposed for the determination of benzoic acid （BA） in milk in this paper. The chromatographic separation was accomplished by using an anion exchange column eluted with 3.2 mmol/L aqueous Na2C03 and 1.0 mmol/L aqueous NaHCO3 at a flow-rate of 0.7 mL/min. The method validation experiment provided excellent results with respect to linearity （correlation coefficient up to 0.9997）, limit of detection （0.1 ug/L）, recovery values （ranging from 88.0% to 93.0%） and relative standard deviation （RSD） （below 2.2%, n = 7）.
In this work, a new sample pretreatment method prior to HPLC separations was developed for the determination of auxins in plant samples, Owing to its large surface area and high adsorption capacity, multi-walled carbon nanotube （MWCNT） was chosen as the adsorbent for the extraction of auxins from plant samples. In this study, two important auxins were selected as model analytes, namely indole-3- butyric acid （IBA） and 1-naphthylacetic acid （NAA）. They could be extracted and concentrated due to their π-π stacking interactions with MWCNT. Then HPLC-UV was introduced to detect IBA and NAA after sample pretreatment. Factors that may affect the enrichment efficiency were investigated and optimized. Comparative studies showed that MWCNT was superior to CI 8 for the extraction of the two analytes. Validation experiments showed that the optimized method had good linearity （0.9998 and 0.9960）, high recovery （81.4%-85.4%）, and low detection limits （0.0030 mg/L and 0.0012 mg/L）. The results indicated that the novel method had advantages of convenience, good sensitivity, high efficiency, and it was feasible for the determination of auxins in plant samples.
