Dispersive liquid–liquid microextraction for metals enrichment: A useful strategy for improving sensitivity of laser-induced breakdown spectroscopy in liquid samples analysis

Abstract

HighlightsAn analytical methodology based on DLLME-LIBS combination is presented. This method is aimed to improve sensitivity of LIBS in liquids analysis. DLLME-LIBS resulted more efficient than SDME-LIBS for enhancing LIBS sensitivity. t r a c tA rapid and efficient Dispersive Liquid-Liquid Microextraction (DLLME) followed by Laser-Induced Breakdown Spectroscopy detection (LIBS) was evaluated for simultaneous determination of Cr, Cu, Mn, Ni and Zn in water samples. Metals in the samples were extracted with tetrachloromethane as pyrrolidinedithiocarbamate (APDC) complexes, using vortex agitation to achieve dispersion of the extractant solvent. Several DLLME experimental factors affecting extraction efficiency were optimized with a multivariate approach. Under optimum DLLME conditions, DLLME-LIBS method was found to be of about 4.0-5.5 times more sensitive than LIBS, achieving limits of detection of about 3.7-5.6 times lower. To assess accuracy of the proposed DLLME-LIBS procedure, a certified reference material of estuarine water was analyzed.

Development and validation of a laser-induced breakdown spectroscopic method for ultra-trace determination of Cu, Mn, Cd and Pb metals in aqueous droplets after drying

“…To the best of our knowledge, especially for Cd and Pb, this is the only study that sub-ppm detection limits are obtained from the direct analysis of liquids. When the literature results that incorporate enrichment strategies followed by the use of aluminum substrate [34][35][36] are compared, the present results are still at least an order of magnitude lower. Enhancement factors of 9 and 21 for Cu, and 7 and 45 for Mn were observed with respect to DLLE and SDME approaches.…”

“…3(e), surface explosion with debris around the edges of the crater and contamination of the craters from the subsequent laser pulses are clearly observed. Instead of making several samplings with tightly focussed laser beam at different locations of a single droplet, as is shown in the literature by Aguirre et al in their several work [34][35][36], sampling the whole droplet area in a single laser shot may eliminates shot to shot variation of the signal due to inhomogeneous deposition of the analyte. In addition, sample losses between the samplings may also be prevented.…”

“…Recently, hyphenation of LIBS detection with Talanta 149 (2016) [53][54][55][56][57][58][59][60][61] common analytical sample enrichment methodologies like liquid phase micro-extraction (LPME), dispersive liquid-liquid microextraction (DLLME) and single drop micro-extraction (SDME) [34][35][36][37] are used to improve sensitivity and detection capability of the LIBS technique in liquids analysis. The precipitation of the analyte followed by membrane separation approach [38] also provided dramatic enhancements in detection limits of some elements.…”

“…Aluminum, in the form of thin foil and as a metallic alloy, was used as a sample loading substrate for droplet analysis, after liquid-liquid extraction procedures with extracting solvents of; 10% Triton X-114 [34]; ammoniumpyrolidinedithiocarbamate (APDC)-toluene [35,36], and 8-hydroxyquinoline (8-HQ)-1-undecanol [37] were used. For these cases, LIBS analyses were performed on droplets dried on the aluminum substrate either at room temperature or on a hot plate.…”

“…Aguirre et.al [34] reported that, with direct analysis of suspended droplets at the tip of a microsyringe, manganese emission lines were undetectable at concentrations lower than 0.2%, however, dry microdroplet analysis of manganese, extracted in 10 % Triton matrix, on aluminum metal substrate resulted with enhancement in Mn signals. Recently, the same group has also applied single drop microextraction (SDME) [35] and dispersive liquid-liquid extraction (DLLME) [36] methodologies for preconcentration, using toluene and tetrachloromethane as extraction solvents of Cr, Mn, Ni, Cu and Zn analytes in the form of (APDC) complexes. Microliters volume of analyte enriched solvents were converted into solid by drying on the heated aluminum foil surface prior to LIBS detection.…”