A novel strategy for preparing calibration standards for laser-induced breakdown spectroscopy using beeswax as a substrate: A case study with cosmetic and lubricant oil samples

Abstract

A new calibration strategy based on the use of beeswax as a substrate for producing a synthetic multi-elemental calibration standard is proposed for laser-induced breakdown spectroscopy (LIBS). This approach was demonstrated by determining the Fe, Mg, Si, Ti, and Zn in lubricant and cosmetic samples. Besides an external standard calibration, we also proposed calibration strategies with and without the adjustment of mineral oil present in the calibration standards and three other different internal standard calibrations: C I 505.50 nm emission line and C2 516.4 and 545.7 nm emission bands. Concerning the lubricant oil samples, the best results were obtained by using the C2 emission band at 516.4 nm, which was used as an internal standard for determining Si and Zn. The C I emission line at 505.50 nm was the most adequate for Mg quantification, while for Fe quantification, the C2 emission band at 516.4 and 545.7 nm yielded similar results. Regarding the samples of cosmetic products, Si and Ti were quantified adequately by using the C2 emission band at 516.4 nm as an internal standard, while for Mg quantification, better results were achieved by using the C I emission line at 505.50 nm. Finally, for Fe quantification in face foundation and liquid lipstick samples, better results were obtained by employing the C I emission line at 505.50 nm and the C2 emission band at 516.4 nm, respectively. For all elements mentioned above, there was an agreement of between 90 and 110% comparing LIBS with inductively coupled plasma optical emission spectroscopy (ICP OES) and/or inductively coupled plasma mass spectrometry (ICP-MS). All the calibrations curves (using external and internal standards) showed a coefficient of determination (R2) higher than 0.95 and detection limits, in μg g−1, between 4 and 18 for Fe, 4 and 6 for Mg, 8 and 24 for Si, 4 and 14 for Ti, and 4 and 8 for Zn.