iZAR Model Rocket Workshop

2016/201

Zeolite/iron oxide composite as sorbent for magnetic solid-phase extraction of benzene, toluene, ethylbenzene and xylenes from water samples prior to gas chromatography-mass spectrometry

This study reports a new composite based on ZSM-5 zeolite decorated with iron oxide magnetic nanoparticles as a valuable sorbent for magnetic solid-phase extraction (MSPE). A proposal is made to determine benzene, toluene, ethylbenzene and xylenes (BTEX) as model analytes in water samples using gas chromatography-mass spectrometry. A two-step multivariate optimization strategy, using Plackett⬜Burman and circumscribed central composite designs, was employed to optimize experimental parameters affecting MSPE. The method was evaluated under optimized extraction conditions (i.e., amount of sorbent, 138 mg; extraction time, 11 min; sample pH, pH of water (i.e., 5.5⬜6.5); eluent solvent volume, 0.5 mL; and elution time, 5 min), obtaining a linear response from 1 to 100 μg L↙1 for benzene; from 10 to 100 μg L↙1 for toluene, ethylbenzene and o-xylene; and from 10 to 75 μg L↙1 for m,p-xylene. The repeatability of the proposed method was evaluated at a 40 μg L↙1 spiking level and coefficients of variation ranged between 8 and 11% (n = 5). Limits of detection were found to be 0.3 μg L↙1 for benzene and 3 μg L↙1 for the other analytes. These values satisfy the current normative of the Environmental Protection Agency and European Union for BTEX content in waters for human consumption. Finally, drinking water, wastewater and river water were selected as real water samples to assess the applicability of the method. Relative recoveries varied between 85% and 114% showing negligible matrix effects.The authors would like to thank the Spanish Ministry of Science and Innovation (project no. CTQ2011-23968), Generalitat Valenciana (Spain) (projects nos. GVA/2014/096 and PROMETEO/2013/038) for the financial support. E. Fernández also thanks Ministry of Education for her FPU grant (FPU13/03125)

Determination of siloxanes in water samples employing graphene oxide/Fe3O4 nanocomposite as sorbent for magnetic solid‐phase extraction prior to GC–MS

A new, fast, simple, and environmentally friendly analytical method has been developed to determine six siloxanes in water samples: octamethyltrisiloxane, octamethylcyclotetrasiloxane, decamethyltetrasiloxane, decamethylcyclopentasiloxane, dodecamethylpentasiloxane and dodecamethylcyclohexasiloxane. The analytical method consists of magnetic solid‐phase extraction employing graphene oxide/Fe3O4 as sorbent for the separation and preconcentration of siloxanes prior to GC–MS determination. The extraction procedure was optimized by means of a Plackett‐Burman design. Under the optimized extraction conditions (graphene oxide/Fe3O4, 20 mg; extraction time, 10 min; eluent volume, 0.5 mL ACN; elution time, 2.5 min; sample volume, 20 mL), the method rendered repeatability levels with a relative standard deviation between 9 and 20% (n = 6, 10 μg/L). Methodological limits of detection ranged from 0.003 to 0.1 μg/L. The linearity of the method was studied between the methodological limit of quantification and 100 μg/L, obtaining correlation coefficient values between 0.990 and 0.999. The applicability of the method was assessed by analyzing drinking, river and wastewater samples. Relative recovery values ranged between 70 and 120% (1 and 60 μg/L spiking level) showing that the matrix had a negligible effect on extraction. Finally, the greenness of this method was confirmed by the semiquantitative Eco‐Scale metrics.The authors would like to thank “Vicerrectorado de Investigación y Transferencia de Conocimiento” of the University of Alicante (UAUSTI16-04), the Ministry of Science and Innovation of Spain (project no. CTQ2011-23968), the Ministry of Economy, Industry and Competitiveness of Spain (project no. CTQ2016-79991-R, AEI/FEDER, UE) for the financial support. L. Costa thanks the Capes Foundation within the Ministry of Education in Brazil (Process 99999.012013/2013-07)

Determination of four bisphenols in water and urine samples by magnetic dispersive solid‐phase extraction using a modified zeolite/iron oxide composite prior to liquid chromatography diode array detection

A novel approach is presented to determine four bisphenols in water and urine samples, employing magnetic dispersive solid‐phase extraction combined with liquid chromatography and diode array detection. A modified zeolite‐based magnetic composite was used as an efficient sorbent, combining the advantages of magnetic materials with the remarkable properties of zeolites. A multivariate optimization design was employed to optimize some experimental factors affecting magnetic dispersive solid‐phase extraction. The method was evaluated under optimized conditions (i.e., amount of sorbent, 50 mg; sample pH, unadjusted; NaCl concentration, 1.25%; extraction and elution time, 2 min; eluent solvent, ethanol; eluent solvent volume, 400 µL), obtaining good linearity with correlation coefficients ranging between 0.995 and 0.999 (N = 5) (from 2 to 250 µg/L for bisphenol A, bisphenol AP, and bisphenol P and from 5 to 250 µg/L for bisphenol AF). Method repeatability was assessed obtaining coefficients of variation between 3 and 11% (n = 6). Finally, the method was applied to spiked real samples, obtaining for water samples relative recoveries between 83 and 105%, and for urine samples between 81 and 108% for bisphenol A, bisphenol AP, and bisphenol AF, and between 47 and 59% for bisphenol P.The authors would like to thank the Spanish Ministry of Economy and Competitiveness and European Union (FEDER funds) (project no. CTQ2016-79991-R) and Generalitat Valenciana (Spain) (project no. PROMETEO/2018/087) for the financial support. P. Baile also thanks Ministry of Education, Culture and Sports for her FPU grant (FPU14/04589)

Hyphenation of single-drop microextraction with laser-induced breakdown spectrometry for trace analysis in liquid samples: a viability study

In this work, an analytical methodology based on single drop microextraction (SDME) followed by Laser-Induced Breakdown Spectrometry (LIBS) has been tested for trace metal determination in liquid samples. By this method, analytes in the samples were extracted into a small volume of toluene as ammonium pyrrolidinedithiocarbamate (APDC) chelates. After that, the analyte-enriched toluene was dried on a solid substrate and, finally, the resulting solid residue was analyzed by LIBS. Analyte extraction by the SDME procedure was optimized for the first time by using a multivariate optimization approach. Under optimum SDME conditions, analytical figures of merit of the proposed SDME-LIBS methodology were compared to those of the direct LIBS analysis method (i.e., without the SDME procedure). An estuarine water certified reference material was analyzed for method trueness evaluation. The results obtained in this study indicate that SDME-LIBS methodology leads to a sensitivity increase of about 2.0–2.6 times the ones obtained by LIBS. Detection limits of SDME-LIBS decrease according to the obtained sensitivity improvement, reaching values in the range 21–301 μg kg−1 for the analytes tested. The measurement repeatability was similar in both SDME-LIBS (13–20% RSD) and LIBS (16–20% RSD) methodologies, mainly limited by the LIBS experimental setup used in this work for LIBS analysis of liquid samples. The SDME-LIBS analysis of the certified reference material led to recovery values in the range of 96% to 112%.The authors are grateful to the Spanish Government (projects CTQ2011-23968) and the Regional Government of Valencia (Spain) (ACOMP/2013/072) for the financial support. M.A.A. is grateful to the University of Alicante for his PhD fellowship. This work is part of the PhD degree of M.A.A

Tungsten coil atomic emission spectrometry combined with dispersive liquid–liquid microextraction: A synergistic association for chromium determination in water samples

A novel and environment friendly analytical method is reported for total chromium determination and chromium speciation in water samples, whereby tungsten coil atomic emission spectrometry (WCAES) is combined with in situ ionic liquid formation dispersive liquid–liquid microextraction (in situ IL-DLLME). A two stage multivariate optimization approach has been developed employing a Plackett–Burman design for screening and selection of the significant factor involved in the in situ IL-DLLME procedure, which was later optimized by means of a circumscribed central composite design. The optimum conditions were complexant concentration: 0.5% (or 0.1%); complexant type: DDTC; IL anion: View the MathML sourcePF6−; [Hmim][Cl] IL amount: 60 mg; ionic strength: 0% NaCl; pH: 5 (or 2); centrifugation time: 10 min; and centrifugation speed: 1000 rpm. Under the optimized experimental conditions the method was evaluated and proper linearity was obtained with a correlation coefficient of 0.991 (5 calibration standards). Limits of detection and quantification for both chromium species were 3 and 10 µg L−1, respectively. This is a 233-fold improvement when compared with chromium determination by WCAES without using preconcentration. The repeatability of the proposed method was evaluated at two different spiking levels (10 and 50 µg L−1) obtaining coefficients of variation of 11.4% and 3.6% (n=3), respectively. A certified reference material (SRM-1643e NIST) was analyzed in order to determine the accuracy of the method for total chromium determination and 112.3% and 2.5 µg L−1 were the recovery (trueness) and standard deviation values, respectively. Tap, bottled mineral and natural mineral water samples were analyzed at 60 µg L−1 spiking level of total Cr content at two Cr(VI)/Cr(III) ratios, and relative recovery values ranged between 88% and 112% showing that the matrix has a negligible effect. To our knowledge, this is the first time that combines in situ IL-DLLME and WCAES.The authors would like to thank the Spanish Ministry of Science and Innovation (Project no. CTQ2011-23968), Spanish Ministry of Education, Culture and Sport (Project no. PHB2010-0018-PC), Generalitat Valenciana (Spain) (Project no. ACOMP/2013/072), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior in Brazil (Grant CAPES-DGU n. 243/11). L. Vidal also thanks the Spanish Ministry of Education, Culture and Sport for her travel Grant (HBP-2010-0030) and S.G. Silva is grateful to the Grant 2011/13288-7, São Paulo Research Foundation (FAPESP)

Metal applications of liquid-phase microextraction

This review focuses on the combination of elemental detection techniques with liquid-phase microextraction (LPME), namely, single drop microextraction, hollow fiber based liquid-phase microextraction, dispersive liquid-liquid microextraction, and related techniques. General features of different microextraction procedures, historical overview and automation of LPME are described and compared, along with examples of new developments and applications presented to demonstrate its potential for trace and ultra-trace metal analysis. Furthermore, potential applications and an outlook on the combination of LPME and elemental detection techniques for inorganic analysis are presented.The authors would like to thank the Spanish Ministry of Economy and Competitiveness and European Union (FEDER funds) (project n. CTQ2016-79991-R) for the financial support. P. Baile also thanks Ministry of Education, Culture and Sports for her FPU grant (FPU14/04589)

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

A 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.The authors are grateful to the Spanish Government (project no. CTQ2011-23968) and Regional Government of Valencia (Spain) (project no. ACOMP/2013/072) for the financial support

Electrochemical Sensor for the Determination of Methylthiouracil in Meat Samples

Two analytical methods based on miniaturized electrochemical sensors, voltammetric and amperometric sensors, have been developed for the determination of 6-methyl-2-thiouracil (MTU) in meat consumption samples (beef liver and foie). A multivariate approach has been considered to optimize the experimental procedure including extraction and electrochemical detection. Under optimal conditions and at a typical working potential of 1.55 V (vs Ag pseudo-reference electrode), response is linear in the range 0 to 20 µg L−1 MTU concentration range. The empirical limit of detection is 0.13 µg L−1, lower than the maximum concentration established by legislation. The electrochemical methods have been used to analyze MTU-spiked meat samples, and recovery values varying between 85 and 95% with coefficients of variation <30%. The analytical methods developed with the miniaturized electrochemical sensors can successfully determine the concentration of MTU in real meat samples with high accuracy, being the results obtained similar to those provided by other methods such as UV-Vis spectrophotometry. Finally, the degree of sustainability of the electrochemical sensors-based developed method has been quantified by means of the Analytical Eco-Scale.This research was funded by Spanish Ministry of Science and Innovation grant number PID2021-126155OB-I00 and Regional Government of Valencia grant number CIPROM/2021/062, and Spanish Ministry of Science, Innovation and Universities (RED2018-102522-T)