SEM–EDS analysis and discrimination of forensic soil

Identification of Heavy Metals in Crystals of Sand and Silt Fractions of Soils by Scanning Electron Microscopy (SEM EDS/WD-EPMA)

“…The analysis of isolated crystals is the only way to accurately identify the mineral source of structural forms of heavy metals in soil fractions (Batista et al, 2017). The scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) has been used in several areas of soil science, such as discrimination of forensic soil (Cengiz et al, 2004), environmental chemistry (Teršič, 2011;Umar and Adamu, 2015), and soil genesis (Simas et al, 2007). The following studies show the association of heavy metals with soil minerals using SEM-EDS: i) Co, Cr, Ni, and V in magnesium silicates and Fe oxides from two serpentine quarries in Galicia (Arenas-Lago et al, 2016); ii) Pb-sulfides and Pb-molybdates in Meza River sediments, Spain (Miller and Gosar, 2009); and iii) several Pb-bearing minerals, such as, galena, anglesite, cerussite, mimetite, and pyromorphite in soils of an abandoned mine, South Wales (Umar and Adamu, 2015).…”

Elemental Analysis and Forensic Comparison of Soils by Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS)

“…A correct classification rate of 100 % was obtained for LA-ICP-MS, and tight, clearly distinct groupings were observed in the LDA canonical plot (see Figure 23). The following discrimination element menu was used: 27 Al, 137 Ba, 42 Ca, 7 Li, 25 Mg, 88 Sr, 47,49 Ti, 238 U, 51 V, and 91 Zr. The different shades denote the different sub-plots.…”

“…Isotopes to monitor were chosen for high relative abundance (except for the matrix elements) and minimal interferences. The following isotopes were monitored: 27 Al, 75 As, 137 Ba, 42 Ca, 111 Cd, 59 Co, 63 Cu, 57 Fe, 202 Hg, 7 Li, 25 Mg, 55 Mn, , 60 Ni, 31 66 Zn, and 91 Zr, as these elements were listed in the NIST SRM 2704 certificate. A summary of the figures of merit for these isotopes is given in Table 6.…”

“…Laser ablation: CETAC LSX500, 266nm, He carrier gas 0.9L/min, spot size 200µm, energy 9.2 J/cm 2 , tubing length 1.4m, ablation cell ~17mL 75 As, 111 Cd, 59 Co, 63 Cu, 57 Fe, 202 Hg, 60 Ni, 31 P, 123 Sb, 82 Se, 29 Si, 120 Sn, 232 Th, 205 Tl, 238 U, 66 Zn, 91 Zr…”

“…The soil particles must be fixed in order for the specimen to withstand repeated laser pulses. Some researchers have mounted powders on tape or adhesive SEM stubs [91][92][93][94][95] for elemental analysis by SEM, SEM/EDX, LIBS, and LA-ICP-MS. Cengiz et al [91] compared stub-mounted soil with pellets by SEM/EDX. Particles were coarsely sieved (< 5 mm), resulting in heterogeneous pellets, which far out-performed the stub-mounted soil in terms of precision.…”