Artificial Intelligence Assisted Mid-Infrared Laser Spectroscopy In Situ Detection of Petroleum in Soils  
[PERSON]  
1 School of Basic and Biomedical Science, Universidad Simon Bolivar, Barranquilla 080002, Colombia; [EMAIL_ADDRESS]  
[PERSON]  
2 Grupo de Investigacion Quimica Supramolecular Aplicada, Programa de Quimica, Universidad del Atlantico, Barranquilla 080001, Colombia; [EMAIL_ADDRESS]  
[PERSON]  
3 Morrissey College of Arts and Sciences, Boston College, Chestnut Hill, MA 02467, USA; [EMAIL_ADDRESS]  
[PERSON]  
5 Harraquilla 080002, Colombia; [EMAIL_ADDRESS]  
[PERSON]  
1 School of Basic and Biomedical Science, Universidad Simon Bolivar, Barranquilla 080002, Colombia; [EMAIL_ADDRESS]  
Footnote 1: email: {leonardo.pacheco-pache  
methodologies to detect petroleum in soil [7; 8; 9; 10; 11; 12; 13; 14] and water bodies [15; 16; 17; 18] to assess damage and develop solutions for places contaminated by petroleum spills [19; 20; 21]. The particular soil type such as sand, silt, and clay and the amount of organic matter present determine the fate of petroleum hydrocarbons and the extent of damage to vegetation [22]. [PERSON] et al. [23] reported that \"pollution by petroleum hydrocarbons exerts adverse effects on plants indirectly, generating toxic minerals in the soil available for being absorbed, moreover, leads to a deterioration of the soil structure; loss of organic matter content; and loss of mineral nutrients from the soil, such as potassium, sodium, sulfate, phosphate, and nitrate\". Moreover, soils are exposed to leaching and erosion. The presence of these pollutants has resulted in the loss of soil fertility, low crop yields, and possible harmful consequences to humans and the entire ecosystem [24]. The current methods used for the detection of petroleum residues in these areas include spectroscopic and chromatographic techniques such as gas chromatography, mass spectrometry, and hyphenated separation/detection techniques. However, these techniques do not allow real-time measurements [25] and require long detection times, which is a critical factor for addressing the problems associated with pollution. In a search for alternatives, more efficient, rapid analysis techniques that can overcome this challenge, such as mid-infrared (MIR) laser spectroscopy using quantum cascade lasers (QCLs) have been found as a possible solution [26]. These devices are characterized by room-temperature operation, continuous-wave operation, high output power, high wall-plug efficiency [27], small footprints, long lifetimes, low energy consumption, and high long-term power stability [28]. Another characteristic of QCLs is the possibility of widely tuning their output frequencies [29]. The main objective of this study was to employ MIR laser spectroscopy using a QCL source to detect insoluble pollutants such as petroleum and its derivatives in soils by simulating contaminated areas. Matrices such as powdered mixtures and soils, in particular, are not easy to analyze by the use of back-reflection infrared spectroscopy in active mode [30; 31; 32; 33]. Diverse soil types with various particle sizes were tested in this study. These solid materials show high coefficients of absorption in the MIR region, thus preventing the ready detection of pollutants. This makes contactless in situ acquisition difficult using conventional thermal sources because the sample absorbs almost completely the MIR light, and the amount of back-reflected light is minimal. Therefore, measurements of diffuse reflectance using MIR generate weak signal intensities and, consequently, low signal to noise ratios (S/N). This is affected if the analysis is carried out in a remote sensing modality [34; 35]. A quadratic decrease in the signal with distance and angular dependence is experienced [33; 36; 37]. A QCL emits a markedly more significant number of photons per unit wavelength in comparison to a globar source. This increases the reflected light and the S/N.