# Simultaneous Analysis of Heavy Metal Concentration in Soil Samples
## 3 Results
### Qualitative Description of FT-IR Spectra
\begin{table}
\begin{tabular}{c|c|c|c|c|c|c|c} \hline \hline
**Metals** & **Unit** & **Range** & \
\begin{tabular}{c} **Number** \\ **of** \\ **Variables** \\ \end{tabular} & **RMS** & **RMSCV** &
\begin{tabular}{c} **\%** \\ **RMS** \\ \end{tabular} & **RMSCV** \\ \hline Co & mg/kg & [1.00,27.00] & 8 & 3.7606 & 4.4483 & 14.46 & 17.11 \\ Cr & mg/kg & [4.10,223.00] & 9 & 26.4988 & 33.0388 & 12.11 & 15.09 \\ Mo & mg/kg & [1.00,14.00] & 3 & 2.1376 & 2.2116 & 16.44 & 17.01 \\ Sn & mg/kg & [1.00,12.00] & 7 & 1.9682 & 2.2370 & 17.89 & 20.34 \\ Zn & mg/kg & [1.00,1530.00] & 7 & 215.4163 & 254.7562 & 14.09 & 16.66 \\ Ba & mg/kg & [22.00,2120.00] & 6 & 330.3738 & 386.9383 & 15.75 & 18.44 \\ Hg & mg/kg & [0.01,3.68] & 12 & 0.3643 & 0.5201 & 9.93 & 14.17 \\ As & mg/kg & [4.00,620.00] & 4 & 71.8133 & 75.3721 & 11.66 & 12.24 \\ Cd & mg/kg & [1.00,2.70] & 9 & 1.0321 & 1.3691 & 15.40 & 20.43 \\ Cu & mg/kg & [22.00,2840.00] & 4 & 593.1701 & 631.7240 & 21.05 & 22.42 \\ Ni & mg/kg & [3.10,67.00] & 11 & 5.9458 & 7.9458 & 9.30 & 12.43 \\ Pb & mg/kg & [18.00,2840.00] & 3 & 363.9935 & 376.5499 & 12.90 & 13.34 \\ Se & mg/kg & [2.00,7.00] & 7 & 0.7632 & 0.8864 & 15.26 & 17.73 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The RMS and RMSCV values for the PLS model based on DRIFT data in the MIR. \begin{table}
\begin{tabular}{c|c|c|c|c|c|c|c} \hline \hline
**Metals** & **Unit** & **Range** & \
\begin{tabular}{c} **Number** \\ **of** \\ **Variables** \\ \end{tabular} & **RMS** & **RMSCV** &
\begin{tabular}{c} **\%** \\ **RMS** \\ \end{tabular} & **RMSCV** \\ \hline Co & mg/kg & [1.00,27.00] & 4 & 4.4228 & 4.7491 & 17.01 & 18.27 \\ Cr & mg/kg & [4.10,223.00] & 10 & 9.8576 & 31.5702 & 4.50 & 14.42 \\ Mo & mg/kg & [1.00,14.00] & 6 & 1.9733 & 2.1884 & 15.18 & 16.83 \\ Sn & mg/kg & [1.00,12.00] & 9 & 0.9858 & 2.2671 & 8.96 & 20.61 \\ Zn & mg/kg & [1.00,1530.00] & 9 & 97.0534 & 224.6956 & 6.35 & 14.70 \\ Ba & mg/kg & [22.00,2120.00] & 10 & 135.9009 & 363.9009 & 6.48 & 17.35 \\ Hg & mg/kg & [0.01,3.68] & 9 & 0.2096 & 0.4168 & 5.71 & 11.36 \\ As & mg/kg & [4.00,620.00] & 1 & 75.3621 & 76.3621 & 12.23 & 12.40 \\ Cd & mg/kg & [1.00,7.70] & 9 & 0.6850 & 1.2343 & 10.22 & 18.42 \\ Cu & mg/kg & [22.00,2840.00] & 1 & 562.4353 & 573.5291 & 19.96 & 20.35 \\ Ni & mg/kg & [3.10,67.00] & 8 & 4.3375 & 6.9293 & 6.79 & 10.84 \\ Pb & mg/kg & [18.00,2840.00] & 10 & 96.2981 & 348.2871 & 3.41 & 12.34 \\ Se & mg/kg & [2.00,7.00] & 8 & 0.4981 & 0.8552 & 9.96 & 17.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The RMS and RMSCV values for the PLS model based on ATR data in the NIR. Comparison of results obtained using different infrared regions, namely, far infrared ATR (1800-100 cm\({}^{-1}\)), and mid infrared DRIFT (4000-400 cm\({}^{-1}\)), which are presented in Figures 5 and 6 and in Tables 1 and 2, indicate slightly better results for the far IR range (lower values of %RMS and %RMSCV for every metal). This result confirmed that the crystal structure of inorganic compounds was affected in the presence of heavy metals, since heavy atom skeletal bending vibrations can be observed in the far IR range. However, differences between these two ranges were not large, which suggested that the common range of 1800-400 cm\({}^{-1}\) was crucial for both ranges. In this range, interactions between metal ions and organic functional groups (carbonylic, phenolic, alcoholic, and \(\pi\)-bonds) are observed. Individual metals form complexes with organic groups of different energy. The stronger new bond with metal is, the weaker organic group becomes, which results in a wider frequency shift of the peak for the 'pure' organic group. The PLS models constructed for mercury and nickel were characterized by a relatively good fit and prediction abilities (the lowest RMS and RMSCV among all constructed models).