Arium pro ultrapure water purification system

Food-grade carrageenans were purchased from ShiShi Globe Agar Industries Co., Ltd. (Fujian, China). Hydrochloric acid (density approximately 1.19 g/mL, guaranteed reagent grade) was obtained from Nanjing Chemical Reagent Co., Ltd. (Nanjing, China). Chromatographically pure acetonitrile was purchased from Merck Co., Ltd. (Branchburg, NJ, USA). All solutions were prepared with ultrapure water (18.2 MΩ cm, an Arium® Pro ultrapure water purification system; Sartorius, Göttingen, Germany). We obtained positive samples of pork, beef, lamb, chicken, and duck containing 0.20 g/kg carrageenan labeled as A, B, C, D, and E, respectively. Samples were from the Supervision, Inspection and Testing Center for Quality of Meat Products (Nanjing, China). In addition, we acquired commercial food products including various kinds of livestock and poultry meat and meat products from a local supermarket in Nanjing, China. Other analytically pure reagents were obtained from Nanjing Chemical Reagent Co., Ltd. (Nanjing, China).

All amino acids except l-leucine and l-phenylalanine were purchased from TCI (Zwijndrecht, Belgium), l-leucine from Merck (Darmstadt, Germany), hydrogen peroxide solution from Scharlab (Sentmenat, Spain), and l-phenylalanine, 2-oxoacid standards, and formaldehyde solution from Sigma Aldrich (Steindorf, Germany), and used without further purification. High-density IDA-Agarose 6BCL nickel charged was from GE Healthcare Life Science. Water for analytical HPLC and for the preparation of buffers and other assay solutions was obtained from an Arium pro ultrapure water purification system (Sartorius-Stedim Biotech). All other solvents used were of analytical grade.