To collect 37 batches of Scrophulariae Radix decoction pieces from the market as the research object, and to establish a quality grade standard of Scrophulariae Radix decoction pieces based on the correlation between quantitative appearance characteristics and intrinsic quality.

According to the traditional quality evaluation method, 37 batches of Scrophulariae Radix decoction pieces were divided into two grades—A and B. Their appearance characteristics were quantified while their moisture, ash, leaching and intrinsic quality indexes were detected, respectively. Finally, the independent sample t test analysis, orthogonal partial least squares discriminant analysis (OPLS-DA) and Pearson correlation analysis were carried out to reveal the correlation between appearance characteristics and intrinsic quality.

On the basis of meeting the quality control standard of Scrophulariae Radix recorded in the 2020 edition of the Pharmacopoeia of the People's Republic of China（referred to as Chinese Pharmacopoeia, ChP）, it was found that water-soluble extractives and alcohol-soluble extractives were the key indexes for the grades classification of Scrophulariae Radix decoction pieces. In summary, the lower the chromatic value and the greater the density（ρ）of Scrophulariae Radix decoction pieces, the higher the water-soluble extractives and the lower the alcohol-soluble extractives. The grading quality standard of “selected goods” and “gradeless and uniformly priced goods” of Scrophulariae Radix decoction pieces were preliminarily drawn up: the chromatic value（E^*ab）of “selected goods” of Scrophulariae Radix decoction pieces should be less than or equal to 5.5, the ρ of Scrophulariae Radix decoction pieces should be greater than or equal to 1.4 g·cm^-3, and the content of water-soluble extractives should be greater than or equal to 77%, the value of E^*ab of “gradeless and uniformly priced goods” of Scrophulariae Radix decoction pieces should be between 5.5 and 14, the value of ρ should be between 0.8 and 1.4 g·cm^-3, and the content of water-soluble extractives should be greater than or equal to 60%.

The appearance characteristics of Scrophulariae Radix decoction pieces are related with the internal quality, which is consistent with the traditional quality evaluation method, and it is convenient to scientifically judge the internal quality of Scrophulariae Radix decoction pieces from its appearance characteristics.