Mechanization of measurement of laser induced breakdown spectroscopy/ring-oven pre-concentration: determination of copper in cachaça

Abstract

The hyphenation of the micro-analytical sensing characteristics of LIBS with the ring-oven pre-concentration capability results in better detectability of this spectrophotometric technique, as has been recently demonstrated. However, the system described previously was heavily dependent on operator skills to fire laser shots onto the ring perimeter, a slow procedure that limits the number of laser pulses that can be integrated to achieve a better signal-to-noise ratio. This drawback is overcome in this present work by allying a mechanical spinning device with an internal standard (Li) to permit reproducible and operator free measurement of the ring contents by LIBS. The system was evaluated and employed to develop a new analytical method aiming to determine copper in cachaça®, a Brazilian spirit made of sugar cane juice. The internal reference was used to correct for most of the variables affecting the precision of the analytical signal due to sample matrix variation, ring making, and measurement by LIBS. Sample volumes of spirits as low as 60 μL can, after pre-concentration using the ring-oven (pre-concentration factor = 15), yield a detection limit of 0.3 mg L⁻¹ for copper and average absolute errors, when compared with the results obtained by the atomic absorption reference method, of 0.5 mg L⁻¹.