Study of spectral lines behaviour with a double pulse 1064-1064 nm laser-induced breakdown spectroscopy system at the direct analysis of algae on the filter

The nickel and zinc contamination of algae on a cellulose filter was studied with double pulse 1064-1064 nm laser-induced breakdown spectroscopy (LIBS). Samples of the green alga Desmodesmus subspicatus were contaminated with zinc and nickel. The surface concentrations on the filter calculated from the reference Inductively Coupled Plasma Mass Spectrometry analysis were 25 and 64 ng cm-2 for nickel and zinc respectively. The algae are resting on the filter after drying and a double adhesive tape was used to fix the sample on the microscopic glass. During optimization method a compromise of 23-30 mJ pulse energies were set for maintaining a detectable or highest signal intensity of the analyte and not destroying the filter. Best conditions for maximum analyte signal and minimum deviation between the spectral behaviour of the analyte and the compared line of Na I, K I, Mg I, Mg II, Mn I, Mn II, Ca I, Ca II, and C I was 700 ns gate delay and 0 s interpulse delay. The deviation was rather more influenced with the signal-to-noise ratio of the analyte line than the closeness of the upper-level energies of the compared lines. The filter without algae showed systematically lower electron number density and total emissivity by units of percents than the filter with algae.