Determination of Natural Madder Dyes Using UV‐Vis and Near‐Infrared Spectroscopy for Rapid Industrial Quality Control

Natural madder dye, together with turmeric and indigo, is one of the most widely used plant‐derived colorants in sustainable textile production. However, significant variability in raw materials and processing routes often leads to unstable dyeing performance and limits industrial standardization. Rapid and reliable quantitative determination of active dye components prior to industrial application is therefore essential. In this study, 112 commercial madder dye samples collected from 16 manufacturers across China were analyzed. A UV‐Vis spectrophotometric method was first established at 450 nm for the determination of total madder pigments (including alizarin and hydroxylated alizarin), showing good linearity ( R 2 = 0.9996), repeatability (RSD = 2.27%), precision (RSD = 0.25%), and acceptable recovery. These reference values were subsequently used to develop a near‐infrared (NIR) quantitative prediction model. The optimal NIR spectral range was 7000–5400 cm −1 , and the best model was obtained using Savitzky–Golay (SG) smoothing combined with multiplicative scatter correction (MSC) and partial least squares (PLS) regression. The optimized NIR model showed excellent performance, with a calibration R 2 of 0.9608 and validation R 2 of 0.9850, while both calibration and validation RPD values exceeded 5. The proposed NIR method provides a rapid, nondestructive, and cost‐effective tool for industrial quality control of madder dyes and offers promising potential for at‐line monitoring, although further calibration transfer and periodic model updating will be required for long‐term large‐scale deployment. Wei Jiang and Huixian Zhou contributed equally to this work and are listed as co‐first authors. Brian K. Via and Chengfeng Zhou are co‐corresponding authors.