A Spectrochemical Snapshot of Heavy Elements in Nile River Sediments: Line Intensity Calculation

Abstract

ABSTRACT Nile River sediments were spectrochemically studied for the characterization of heavy elements. Ten sediment samples were milled and successfully pressed for obtaining homogeneously compact pellets. Their surface elemental analysis was obtained using ns-LIBS at two values of laser pulse energy: 25 mJ and 50 mJ. Despite the noticeable matrix effect, a snapshot visualizing the existing elements and their relative content detected in the investigated sediments is provided. The LIBS spectral data revealed the presence of some heavy elements such as Al, Ti, Fe, Mn, Ba, Co, Cr, Sr, and Cu in addition to other typical elements including Mg, Si, Ca, C, and Na. Their origin is easily linked to the illegal practices of the factories and companies discharging harmful wastes into the Nile, in addition to the probable agricultural sources. The LIBS results were supported and complemented by the XRD technique. Considering the inconsistent LIBS line intensity signal, a mathematical-based approach for spectral line intensity calculation is proposed. Assuring the existence of a local thermodynamic equilibrium condition (LTE), the plasma excitation temperature was determined for all samples using the Boltzmann plot (BP) applied to the spectral lines of MgI, FeI, CaI, and TiI, which cover different spectral regions. The BP linear fitting parameters and their averages are derived and exploited in calculating the spectral line intensity. The suggested method is claimed to theoretically adjust and balance any source of signal fluctuations arising from experimental conditions and/or instruments.