Hplc grade acetonitrile acn

High-performance liquid chromatography (HPLC)-grade acetonitrile (ACN) and methanol (MeOH) were obtained from TEDIA (Ohio, USA). Nitric acid (GR, approximately 68%) and perchloric acid (GR, approximately 72%) were purchased from Nanjing Chemical Reagent Co., Ltd. (Nanjing, China). Ultrapure water was produced using a water purification machine from a Millipore purification system (Millipore, MA, USA). Analytical standard cotinine (purity > 98%) and isotopic internal standard cotinine-d3 (purity > 98%) were purchased from Cerilliant (Texas, USA). Sodium standard (Na, 1 mg/mL), potassium standard (K, 0.1 mg/mL), calcium standard (Ca, 1 mg/mL), magnesium standard (Mg, 0.1 mg), iron standard (Fe, 1 mg/mL), and zinc standard (Zn, 1 mg/mL) were purchased from the National Research Center for Standard Materials (Beijing, China). Lanthanum (III) oxide (purity ≥ 99.99%) was supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Cesium chloride (purity ≥ 99.99%) was obtained from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Standard compounds were stored following to the supplier’s recommendations. Stock solutions of individual compounds were prepared in water or MeOH, and the calibration solutions were diluted from individual stock solutions.