Standardization of IR spectra with wavelet transform

Analytical chemists always face a problem in comparison of the performance between analytical instruments. There is no simple rule to justify which one is better because of the variations between the instrumental responses. In order to correct this, a standardization approach is generally adopted. However, a calibration model as developed on an instrument cannot be employed for the other instrument in the real situation. Walczak et al. [28] suggested a new standardization method for comparing the performance between two near-infrared (NIR) spectrometers in the wavelet domain. In their proposed method, the NIR spectra from two different spectrometers were transformed to the wavelet domain at resolution level (J — 1). Suppose and correspond to the NIR spectra from Instruments 1 and 2, respectively, in the wavelet domain. A univariate linear model is applied to determine the transfer parameters t between and 

Once t is deduced from the standardization process, any sample spectrum from Instrument 2 in the wavelet domain can be transferred to the corresponding spectrum as acquired in Instrument 1. by  

the standardized NIR spectrum can be obtained via inverse WT on for subsequent data analysis. The results [28] show that the proposed standardization method in the wavelet domain is superior to the traditional standardization methods. 

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