# A Laser-Based Method for the Detection of Honey Adulteration
## 3 Results
### Dimensionality Reduction and Classification of LIBS Spectra for Adulteration Detection
**(c)** LDA canonical variable plot employing only the spectral lines of Ca (II), Na (I), and K (I) (see Figure 2). **(d)** Confusion matrix showing the prediction of the test samples using the LDA algorithm employing only the spectral lines of Ca (II), Na (I), and K (I). Afterwards, the data from the second approach (see Samples section, Section 2.1) were used as input for the algorithms. Thus, LDA was used to classify the LIBS spectra into three classes, namely the honey, the adulterated honey, and the glucose syrup classes. LDA is used here both for dimensionality reduction and as a classifier. The LDA output is graphically presented in Figure 4a. As can be seen the glucose samples are clearly separated from all the other samples. The honey samples and the adulterated honey samples are also clearly separated, although they are not very distant, indicating their similarities, as well as the fact that some overlapping could potentially occur between them, for instance when trying to predict new samples that are previously unseen by the algorithm. The classification accuracy is (95.6 \(\pm\) 0.8)% and resulted from a 10-fold cross-validation performed using the training data. The external validation accuracy was determined to be 90.5%. The corresponding confusion matrix is presented in Figure 4b. As can be seen, 60 spectra arising from the adulterated honey samples were misclassified as honey samples. These spectra correspond to samples that contain 10% and 20% (\(w/w\)) of glucose syrup. It is, thus, evident that some misclassifications may occur at low percentages of adulteration. Moreover, only three spectra from the adulterated samples were misclassified as glucose syrup. However, these spectra correspond to adulterated honey samples containing 90% (\(w/w\)) of glycose syrup. In fact, in this case, the LIBS spectra tend to be very similar to the spectra of glucose syrup, lacking the spectral lines of the inorganic elements (see Figure 1d) observed in the honey samples. Last, but not least, eight spectra of honeys were misclassified as adulterated honey samples. Figure 4: (a) LDA canonical variable plot employing the LIBS spectra. (b) Confusion matrix showing the prediction of the test samples using the LDA algorithm employing the LIBS spectra. (c) LDA canonical variable plot employing only the spectral lines of Ca (II), Na (I), and K (I) (see Figure 2). (d) Confusion matrix showing the prediction of the test samples using the LDA algorithm employing only the spectral lines of Ca (II), Na (I), and K (I). Next, the spectral lines of Ca, Na, and K, shown in Figure 1d, were used to assess the distinguishability of the adulterated honey samples from the honey samples. The results obtained using the LDA algorithm are presented in Figure 4c. As can be seen while the glucose syrup samples are separated from the other samples, some honey samples are overlapping with the adulterated honey samples. Again, they were the honey samples that were used for the preparation of the adulterated honey samples. The honey samples that were not used to prepare any adulterated samples are totally distinguished from the rest of the samples. The obtained classification accuracy was (90.2 \(\pm\) 1.8)% and resulted from a 10-fold cross-validation of the training data. The external validation accuracy was found to be 90.5%. The corresponding confusion matrix is shown in Figure 4d. A total of 64 spectra of adulterated honey samples were misclassified as honey, and five of them as glucose syrup. Additionally, only six spectra of honey samples were misclassified as adulterated honey samples. Despite the lower accuracies obtained compared to using the entire LIBS spectra, these results are remarkably interesting as they indicate that honey can be discriminated from adulterated mixtures with quite high accuracies by using the spectral lines of only three inorganic elements (i.e., Ca (II), Na (I), and K (I)), thus suggesting that these spectral lines can be used for the efficient detection of honey adulteration via LIBS.