Rapid, direct determination of strontium in natural waters by laser-induced breakdown spectroscopy

Abstract

We report a LIBS technique for Sr determination in different types of natural waters, which provides sufficient sensitivity for strontium quantification in marine studies, and for the safety control of drinking waters. The technique provides rapid measurements, not longer than 1 min per sample, without any preconcentration or dilution of waters. We demonstrated that the ionic line Sr II 407.77 nm was preferable for strontium quantification in natural waters compared to atomic line Sr I 460.73 nm, since the ratio between them equaled to ∼30. One of the obstacles is a variability of the total content of salts in waters from 0.01% to 5%. We found that the salinity had a strong influence on electron density (N_e); N_e increased dramatically in the case of low salinity (0 to 100 mg L⁻¹), and it did not change essentially for the salinity above 150 mg L⁻¹. At the same time, plasma temperature (∼1.1 × 10⁴ K) was independent of salinity. Since an increase of salinity suppressed the ionic signal of strontium, the addition of NaCl as an ionization buffer diminishes considerably the matrix effects on analytical results. LODs of Sr varied from 25 μg L⁻¹ for pure or fresh waters to 200 μg L⁻¹ for salty waters. We have shown that the suggested technique provided the accurate determination of strontium in samples of the Laptev Sea water and four types of mineral waters within the concentration range from 1 to 20 mg L⁻¹.