Analytical Sciences

Robust Curve Fitting Method for Optical Spectra by Least Median Squares (LMedS) Estimator with Particle Swarm Optimization (PSO)

Hideyuki SHINZAWA,*^,** Jian-Hui JIANG,** Makio IWAHASHI,*** and Yukihiro OZAKI*

*Department of Chemistry, School of Science and Technology, and Research Center for Near-Infrared Spectroscopy, Kwansei-Gakuin University, Hyogo 669-1337, Japan
**State Key Laboratory for Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, P. R. China
***School of Science, Kitasato University, Sagamihara, Kanagawa 228-8555, Japan

A curve fitting technique for optical spectra based on a robust estimator, least median squares (LMedS), is introduced in this study. For the effective calculation of LMedS, particle swarm optimization (PSO) is also introduced. Unlike a standard curve fitting method using least squares (LS) estimator, the method based on LMedS estimator is less influenced by outliers in experimental data. Two kinds of data sets, simulated data with outliers and temperature-dependent near-infrared (NIR) spectra of oleic acid (OA) are applied for the demonstration of the proposed method. The results clearly reveal that, compared with the LS estimator, the proposed method can effectively reduce undesirable effects of low SN ratio and can yield more accurate fitting results.

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