**3. 2DLC for determination of five major proteins and seven additives in milk powders**

 Two-dimensional liquid chromatography has been used in many aspects. Herein, a 2DLC method was introduced for the simultaneous determination of five major proteins and seven additives in milk powders. Considering the macromolecular proteins, C4 column was placed in the first dimension (1D), and C18 column was placed in the second dimension (1D) for analysis of the seven additives. Finally, the five proteins in milk powders were separated completely on the 1D column, and the seven additives can be simultaneously analyzed on the 2D column. In the middle of 1D and 2D, a trapping column and a ten-port switching valve was served. This method was compared with the conventional one-dimensional liquid

chromatography (1DLC) in terms of sample preparation, limit of detection (LOD), and recovery.
