# A Matrix Effect Correction Method for Portable X-ray Fluorescence Data
## 3 Results and Discussion
### Evaluation of the Correction Results
#### 3.3.2 Similar Correction Effect  
As for the other elements, these two methods had similar correction effects. However, some of these elements were well corrected, including Al, Si, P, S, K, Ca, Ti, Mn, Fe, Cu, Zn, As, Rb, Sr, Zr, Pb, Mg, Ni, Y, Nb, Sb and Bi, and some were not, including Se, Ba, Tl and U. It can be seen that there was no significant difference between the SLR and MEC regression values of the former group of elements, all of which were close to their reference values (Figure 2), indicating that these two regression methods both had a good correction effect.  
However, it should also be noted that the MEC method did not play a significant role in eliminating the matrix effect for these elements, which may be because they were just slightly affected by the matrix effect. For example, although some trace elements had much lower contents and weaker characteristic X-ray fluorescence intensities than the major elements, as long as they were just slightly affected by the matrix effect, a good correction effect could also be obtained, such as the elements Rb, Sr, Zr, Ni, Y, Nb and Sb. As for the elements Al, Si, P, S, K, Ca, Ti, Mn, Fe, Cu, Zn, As, Pb and Mg, they could produce an extremely high intensity of characteristic X-ray fluorescence under X-ray irradiation due to their high contents in the certified reference samples, and therefore, other elements would have little impact on them. The statistical parameter results show that these two methods both had large \(R^{2}\) values close to one and small _MAE_, _MAPE_, _RMSE_ and _RMSPE_ values (Figures 3-5), which also indicate good correction effects.  
For the correction of Ba, Tl, Se and U, neither of these two methods worked, and their regression values were quite different from their reference values (Figure 2). The testing accuracy of these elements was low, and there was no linear relationship between their testing values and reference values (Figure 1), which may be the reason for the poor correction effect of the SLR method. As for the MEC method, the poor correction effect may be attributed to the fact that these elements are influenced not only by the selected major elements but also by other elements or factors. Nevertheless, compared with the SLR method, the new method had better statistical parameters for Ba and Tl (Figures 3-5). For example, the _MAE_, _MAPE_, _RMSE_ and _RMSPE_ values of Ba and Tl decreased significantly. As for Se and U, there was almost no difference between the parameters.  
Regardless of whether the element was affected by the matrix effect, the new method could attain a considerable correction effect, indicating that a lot of the matrix effect was stripped off. Compared with the SLR method, the regression values of the elements V, Cr, Ta and W obtained from the new method were closer to their reference values, especially for elements Co, Mo, Cd and Sn (Figure 2). As for the elements slightly or not affected by the matrix effect, these two regression methods had considerable and almost the same correction effects. Collectively, the SLR method tends to deal with the matrix effect at a macro level without exploring the relationship between elements, while the new method has a better correction result for the matrix effect with the aid of the major elements.