Table 2.

Performance of the ATR-FTIR quantification models of Indigo Naturalis.

Ingredient (wt%)	Indigo		Indirubin		Calcium
	Calibration	Validation	Calibration	Validation	Calibration	Validation
Mean ± Std	2.29 ± 0.55	2.24 ± 0.43	0.17 ± 0.04	0.17 ± 0.03	27.86 ± 3.05	28.62 ± 2.80
Max	3.47	2.82	0.26	0.23	38.47	34.85
Min	1.18	1.46	0.09	0.12	23.65	24.37
Latent variables	6	6	10	10	9	9
R2	0.940	0.977	0.974	0.983	0.946	0.971
MRE	5.6%	2.4%	2.9%	2.2%	2.3%	1.8%