2.1 Reagents
HE used as analytes in this study were cyclotrimethylenetrinitramine (RDX), and 2,4,6-trinitrotoluene (TNT). TNT was purchased from ChemService (West Chester, PA, USA), and RDX was synthesized in the lab. Seven types of natural soils were used: first natural (Soil-1) and second natural soil (Soil-2) were obtained from suburban sites located near the municipality of Mayaguez, PR, USA (coordinates: 18°13’25.7”N 67°07’51.2”W); third natural soil (Soil-3) and fourth natural soil (Soil-4) from (coordinates: 18°9’36”N 67°6’40”W); fifth natural soil (Soil-5), sixth natural soil (Soil-6), and seventh natural soil (Soil-7) were obtained from suburban sites located near the municipality of Ponce, PR, USA (coordinates: 18°00’39.9”N 66°36’50.6”W).