Mahalanobis distance to detect the gypsum samples

With all the soil samples we calculate the Principal Components scores and after the mahalanobis distance of every sample sores to the mean, and we draw a cut-off of 3, which normally is used to select as outliers the samples which are over it.

We can take those samples apart an see the spectra, to check their characteristics and in this case the spectra show that almost all are the gypsum samples, which we could not see clearly when plotted with the rest of the samples due to the overlapping.

We can select the rest of the samples and calculate a mew PC analysis and continue studying the characteristics of the samples.