# Simultaneous Analysis of Heavy Metal Concentration in Soil Samples
## 3 Results  
### Qualitative Description of FT-IR Spectra  
Soil is very complex, it contains both inorganic components, such as silicates, carbonates, sulfates, nitrates, as well as phosphates, and organic compounds such as humic and fulvic acids. In Figure 2, an exemplary structure for the organic matter of soil is presented. Bands related to various functional groups, such as phenolic, carbonyl, carboxylic, anhydrides, and nitrogen-containing groups, are expected in the infrared spectrum of a soil sample. Spectra measured in the mid-infrared region represent fundamental vibration modes and enable one to identify different bonds and functional groups present in the sample. Spectra for all soils were found to be generally similar with differences resulting from the content of clay, quartz, organic compounds, and both fulvic and humic acids in the soils. Two exemplary Mid-IR spectra are presented in Figure 3.  
Bands due to the organic and inorganic compounds overlap; thus, their assignment to functional groups is difficult. However, some of them can be assigned to individual bonds and functional groups during a qualitative analysis of the spectra [4; 30; 31]. A broad band observed in the region from 3700 to 3000 cm\({}^{-1}\) is related to the stretching of the associated H-bonded hydroxyl group in the OH group of alcohols and the Si-OH group. The peaks at 3697 and 3624 cm\({}^{-1}\) are associated with vibrations of the Si-O-H bond. The peaks at approximately 2934 cm\({}^{-1}\) are attributed to vibrations of aliphatic CH\({}_{2}\) and the CH\({}_{3}\) group. Vibrations of amides and aromatic C=C bonds are observed in the region of 1700 to \(\sim\)1500 cm\({}^{-1}\). The peak observed at 1988 cm\({}^{-1}\) is connected to vibrations of cumulative C=C bonds or aromatic C-H. The peaks at approximately 1870 and 1794 cm\({}^{-1}\) can relate to anhydrides or the free COOH group. The peak with a maximum at 1610 cm\({}^{-1}\) is related to vibrations of aromatic C or conjugation of C=C with the C=O bond. The peak at 1159 cm\({}^{-1}\) can be ascribed to the stretching vibrations of the C-O bond in anhydrides, or Si-O-C and Si-O-Si in siloxanes. The peaks at approximately 1390 cm\({}^{-1}\) and 917 cm\({}^{-1}\) represent in plane and out of plane bending of the OH group. In the region 1400 to 950 cm\({}^{-1}\), vibrations due to various bonds containing oxygen are observed, especially alcohols, phenols, ethers, acetates, and carbohydrates. Bands assigned to the vibration of silicates SiO\({}_{4}\)\({}^{2-}\) are expected in the range 1100-900 cm\({}^{-1}\), carbonates CO\({}_{3}\)\({}^{2-}\) approximately 1450-1410 and 880-800 cm\({}^{-1}\), sulphates SO\({}_{4}\)\({}^{2-}\) in the range 1130-1080 cm\({}^{-1}\), nitrates NO\({}_{3}\)\({}^{-}\) in the range 1410-1340 and 860-800 cm\({}^{-1}\), and phosphates PO\({}_{4}\)\({}^{3-}\) in the range 1100-900 cm\({}^{-1}\)[30]. NIR and FIR spectra contain less information concerning the structure and functional groups. Bands observed in the near IR are mainly assigned to overtones and combinations of fundamental vibrational modes of groups containing C-H, O-H and N-H bonds. In the far infrared region, vibrations with large amplitude, such as torsional modes, ring puckering, crystal lattice vibrations and heavy  
Figure 3: Exemplary soil spectra measured using the diffuse reflectance (DRIFT) technique in the mid infrared (MIR) region. Figure 2: The hypothetical model structure for (**a**) humic acid and (**b**) fulvic acid. atom skeletal bending modes, and molecular rotation are mainly observed. Information for the intermolecular forces is gained from the far IR spectra. Exemplary NIR and FIR spectra are presented in Figure 4. In Figure 4a, ranges characteristic for overtone bands characteristic of excited vibrational states and combined bands that are the sum of other fundamental vibrations are marked. The detailed interpretation of each band is impossible in such a complex sample.