ABSTRACT
Matte photographic paper was explored as a low-cost material for metal-ion retention. The extraction was promoted by ultrasound, the mechanical waves of which forced adhesion to the photographic paper surface of an ion pair formed by DTAB (dodecyltrimethylammonium bromide) with the anionic coordination complex formed by metal ions and SPADNS (1,8-dihydroxy-2-(4-sulfophenylazo)naphthalene-3,6-disulfonic acid trisodium salt). As a proof of concept, the migration of copper ions present in aqueous solution to the solid phase and their direct measurement by laser-induced breakdown spectroscopy (LIBS) was evaluated. The main parameters that affected the extraction (paper type and sonication time) and analyte detection in the solid phase (delay, spot size and accumulated number of pulses) were optimised in a univariate way. The conditions influencing the complexation reaction and formation of the ion pair in aqueous solution (pH and copper, SPADNS and DTAB concentrations) were set according to a previous study. Under the optimised conditions, it was possible to use this extraction technology as an alternative in determining copper content in aqueous solutions by LIBS, overcoming the intrinsic difficulties of this instrumental technique in the analysis of liquid samples. The calibration curves were obtained in a linear range of 0.50-7.50â¯mgâ¯L-1 copper in solution, with detection and quantification limits estimated at 0.08 and 0.24â¯mgâ¯L-1, respectively. The precision of the method was less than 4.3% and the accuracy was checked by spike and recovery tests on liquid samples with different chemical compositions and by comparison of LIBS results with graphite furnace atomic absorption spectrometry data. The potential of the proposed method for extraction of Al3+, Ag+, Fe3+, Mn2+, Ni2+ and Zn2+ was also evaluated and adequate extraction efficiencies were obtained. The proposed method stands out due to its low cost and ease of execution.
