Chemical Analysis of Zooplankton by Calibration-Free Laser-Induced Breakdown Spectroscopy

Ratios of light metals (Li, Na, K, Mg, and Ca) in zooplankton (Calanusspp.) were determined by laser-induced breakdown spectroscopy without reference samples under the assumption of local thermodynamic equilibrium. The temperature of plasma formed as a result of laser ablation of zooplankton was estimated from the CN rotation-vibration bands, and the electron density was estimated from the Stark broadening of Mg I 383.23 nm, Li I 610.37 nm, and Ca II 396.85 nm lines. These experimentally determined parameters were used for plasma modeling, taking into account the transport of radiation. This made possible a selection of analytical emission lines free from self-absorption. The results are compared with the results of elemental analysis by atomic emission and inductively coupled plasma mass spectrometry. The influence of the ionization equilibrium on the correctness of results is discussed. The described method is proposed to be used for direct semiquantitative determination of Li, Mg, and Ca ratios in zooplankton.