Pre-processing methods

If the task is multivariate calibration, for example, the proper choice of a pre-processing method will essentially aflFect the quality of the resultant model. For more details about the use of these techniques together with PCA and PLS, readers are advised to consider the fundamental monograph by Erikson et al [8]. 

Prior to PCA the data are often pre-processed to convert them into a form most suitable for the application of PCA. Commonly used pre-processing methods for PCA arc scaling and mcaii-ccntcring of the data, which arc described in Section 4.3. 

Savolainen et al. investigated the role of Raman spectroscopy for monitoring amorphous content and compared the performance with that of NIR spectroscopy [41], Partial least squares (PLS) models in combination with several data pre-processing methods were employed. The prediction error for an independent test set was in the range of 2-3% for both NIR and Raman spectroscopy for amorphous and crystalline a-lactose monohydrate. The authors concluded that both techniques are useful for quantifying amorphous content however, the performance depends on process unit operation. Rantanen et al. performed a similar study of anhydrate/hydrate powder mixtures of nitrofurantoin, theophyllin, caffeine and carbamazepine [42], They found that both NIR and Raman performed well and that multivariate evaluation not always improves the evaluation in the case of Raman data. Santesson et al. demonstrated in situ Raman monitoring of crystallisation in acoustically levitated nanolitre drops [43]. Indomethazine and benzamide were used as model... 

For the total sets, two spectrum pre-processing methods MSC and SNV were used. Figure 4 illustrates the results of the cross validation when MSC and SNV were used as the spectrum... 

MSC and SNV were used as the pre-processing method. According the result in tablel, the optimal principal component number was chosen as 10. Then UVE algorithm was used to select the effective variables. The results are shown in figure 5. 

Fredriksson M, Petersson P, Jornten-Karlsson M, Axelsson BO, Bylund D. An objective comparison of pre-processing methods for enhancement of liquid chromatography-mass spectrometry data. J Chromatogr A 2007 1172 135—150. 

Particle size can only be a process parameter in cases where further use of the particles is compatible with size reduction or other pre-processing methods which open the plant cells and increase the surface of the solid. 

The research and process development by Innventia [70] in recent times has resulted in a sharp drop in the energy requirement for manufacturing nanocellulose in the last few years. With new pre-processing methods, they have lowered the energy consumption... 

Quality tests as integral parts of spectral pre-processing have been described in the previous sections. In the following we will therefore focus on pre-processing methods for classification analysis such as normalisation, spectral filtering (de-noising, derivatives) and feature selection. 

The EMSC is a model-based multivariate data pre-processing method and is based on linear statistical regression modelling.It can be extended to... 

Hansen PW. Pre-processing method minimizing the need for reference analyses. J Chemom 2001 15 123-131. 

FIGURE 5 Different spectral pre-processing methods and their influence in a commercial cookie. 

Tomasi G, van den Berg F, Andersson CA. Correlation optimized warping and dynamics time warping as pre-processing methods for chromatographic data. J Chemom 2004 18 1 11. 

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