Dispersive liquid–liquid microextraction combined with laser-induced breakdown spectrometry and inductively coupled plasma optical emission spectrometry to elemental analysis

Determination of Fe, Cu, and Pb in edible oils using choline chloride:ethylene glycol deep eutectic solvent-based dispersive liquid-liquid microextraction associated with microwave-induced plasma optical emission spectrometry

A new simple, fast and environmentally friendly deep eutectic solvent based dispersive liquid-liquid microextraction (DES-based DLLME) methodology assisted by vortex is presented for the separation and preconcentration of three elements (i.e., Fe, Cu and Pb) from edible oil samples (i.e., soybean, sunflower, rapeseed, sesame, and olive oil) prior to the determination by microwave-induced plasma optical emission spectrometry (MIP-OES). The deep eutectic solvent selected as extractant (i.e., choline chloride and ethylene glycol, 1:2) is synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR) and differential scanning calorimetry (DSC), and the extraction conditions are optimized by a two steps experimental design. Under the optimum extraction conditions (i.e., diluted sample weight: 8.6 g; DES volume: 100 μL; extraction time: 1 min; centrifugation time and speed: 3 min and 3000 rpm; and dispersion system: vortex) the analytical method presents excellent linearity (i.e., R2 values higher than 0.99) in the range 10-500 μg kg-1, repeatability (i.e., CV values lower than 9.2%), and limits of detection (LOD) values of 3, 2 and 0.7 μg kg-1 for Pb, Fe and Cu, respectively. None of the analytes displayed amounts over the upper limit permitted by law, and recovery values of all analytes evaluated in the different samples using external standard calibration were close to 100%, which excludes significant matrix effects. Finally, AGREEprep metric has been used to evaluate the method greenness (final score of 0.47) and it has been compared successfully with previous publications for the same type of analytes and matrices.

Application of organic gas steam-liquid extraction system for extraction and separation of uranium from water samples as a new efficient method

In this study, for the first time the organic gas steam-liquid extraction (OGS-LE) method is used as a simple, efficient and scalable to industrial application technique for the extraction and separation of uranium (VI) from aqueous samples. OGS-LE is done by a special handmade extraction cell. In this method, the organic solvent vapor produced in the evaporator unit is introduced into the aqueous sample by using nitrogen as a carrier gas. By inserting the vapor bubbles of the organic solvent into the aqueous sample, the organic solvent dissolves in water and the organic solvent concentration in water reaches supersaturation. During this process, equilibrium occurs between the dissolved organic solvent and the insoluble organic solvent, and it is collected on top of the aqueous phase. Uranium has been extracted with cyanex 272 and tetrabutylammonium bromide (TBAB) as extractant into n-heptane from the alkaline aqueous media by the OGS-LE method. Cyanex 272 and TBAB were used as the complexing ligand and the ion pairing reagent, respectively. The mechanism of extraction was proposed depending on the deprotonating of cyanex 272 and ionic interaction with the quaternary ammonium bases. Face Central Composite Design (FCCD) was used to evaluate the effect of various factors. Under the optimized conditions, uranium extraction could be completed in a single stage with the extraction efficiency of more than 90% from an aqueous solution containing alkali, alkaline Earth and transition metal ions. The precision, obtained by performing five replicates under the optimized conditions, was 90.12% ± 0.75% (percentage of extraction ± RSD).

Multipurpose made colorimetric materials for amines, pH change and metal ion detection

Sensors are routinely developed for specific applications, but multipurpose sensors are challenging, due to stability and poor functional design. We report organic materials that operate in solution and gas phase. They show a strong response behaviour to at least three types of environmental changes: pH, amine and metal ion binding/detection. We have confirmed and validated our findings using various analytical and computational methods. We found that the changes in polarity of the solvent and pH not only red shift the tail of the absorption spectra, but also extend the peak optical absorption of these structures by up to 100 nm, with consequential effects on the optical gap and colour changes of the materials. Acid–base response has been studied by spectrophotometric titrations with trifluoroacetic acid (TFA) and triethyl amine (TEA). The experiments show excellent reversibility with greater sensitivity to base than acid for all compounds. Analysis into metal sensing using Zn(ii) and Cu(ii) ions as analytes show that the materials can successfully bind the cations forming stable complexes. Moreover, a strong suppression of signal with copper gives an operative modality to detect the copper ion as low as 2.5 × 10⁻⁶ M. The formation of the metal complexes was also confirmed by growing crystals using a slow diffusion method; subsequent single crystal X-ray analysis reveals the ratio of ligand to metal to be 2 to 1. To test sensitivity towards various amine vapours, paper-based sensors have been fabricated. The sensors show a detection capability at 1 ppm of amine concentration. We have employed CIE L*a*b* colour space as the evaluation method, this provides numeric comparison of the samples from different series and allows comparison of small colour differences, which are generally undetectable by the human-eye. It shows that the CIE L*a*b* method can assess both sensitivity to a particular class of analytes and a specificity response to individual amines in this subclass offering an inexpensive and versatile methodology.

Multi-responsive colorimetric sensors based on the hydrazone motif, which are perfectly suited for chemo sensing applications have been developed.

Evaluation of Thin Film Microextraction for trace elemental analysis of liquid samples using LIBS detection

An analytical methodology based in the combination of Thin Film Microextraction with Laser-induced Breakdown Spectroscopy (TFME-LIBS) was investigated, for the first time, for detection of Cu, Cr, Ni and Pb in aqueous solutions. In this methodology, the analytes were extracted in a thin film of adsorbent material deposited on a solid support, which was introduced in the sample to analyse. After extraction, the analytes retained in the adsorbent were analysed by LIBS. In order to obtain adsorbent films useful for the microextraction step, two different experimental procedures for film generation, denoted as Drop Casting Deposition and Mould Deposition, were evaluated. In both cases, graphene oxide was used as adsorbent material. The mould deposition procedure was found to produce more homogeneous graphene oxide layers, leading to more uniform distribution of the adsorbed analytes on the graphene oxide surface. Experimental parameters affecting the TFME procedure, such as the adsorbent amount and extraction time, were studied. Under optimum microextraction conditions, the analytical figures of merit of the proposed TFME-LIBS method were evaluated, leading to limits of detection ranging from 41 μg kg^-1 and 52 μg kg^-1. Method trueness, evaluated from the analysis of a real sample of bottle water, led to recovery values about 70%, indicating the existence of strong matrix effects probably due to the presence of major cations in the bottle water. After 50% dilution of the sample with deionized water, recoveries values improved to 100%-108%.

Magnetic Fe3O4@Mg/Al-layered double hydroxide adsorbent for preconcentration of trace metals in water matrices

A magnetic Fe₃O₄@MgAl-layered double hydroxide (MLDH) nanocomposite was successfully synthesized and applied as an effective adsorbent for preconcentration of trace As(III), Cd(II), Cr(III), Co(II), Ni(II), and Pb(II) ions from complex matrices. The quantification of the analytes was achieved using the inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The nanocomposite was then characterized using BET, FTIR, SEM, and EDS. Due to its high adsorption surface area, compared to traditional metal oxide-based adsorbents, MLDH nanocomposite exhibited high extraction efficiency. Several experimental parameters controlling the preconcentration of the trace metals were optimized using response surface methodology based on central composite design. Under optimum conditions, the linearity ranged from 0.1 to 500 µg L⁻¹ and the correlation of coefficients (R²) were higher than 0.999. The limits of detection (LODs) and quantification (LOQs) were 0.11–0.22 µg L⁻¹ and 0.35–0.73 µg L⁻¹, respectively. The intra-day (n = 10) and inter-day precisions (n = 5 working days) expressed in the form of percent relative standard deviations (%RSDs) were below 5%. The proposed method was successfully applied for the analysis of the As(III), Cd(II), Cr(III), Co(II), Ni(II), and Pb(II) ions in different environmental water samples.

A simple and rapid technique for the determination of copper based on air-assisted liquid-liquid microextraction and image colorimetric analysis

In this study, a new, cheap, simple and rapid method for the determination of copper in water and food samples using air-assisted liquid-liquid microextraction and digital image decomposition into the primary colors Red (R), Green (G) and Blue (B) is introduced. In the proposed method, sodium diethyl-dithiocarbamate (Na-DDTC) and carbon tetrachloride (CCl4) were used as the chelating agent and extraction solvent, respectively. The digital images of the extraction phase were obtained using an Android mobile phone and analyzed using a free app (Color Grab). Then the value of the B channel was taken as the analytical signal. The effects of different parameters influencing the extraction efficiency were investigated and optimized. Under the optimal conditions, the limit of detection (LOD) and quantitation (LOQ) were 1.5 and 5 μg L-1, respectively. The repeatability of the proposed method, expressed as the relative standard deviation (RSD), was 4.53% for intra-day (n = 8, C = 100 μg L-1) and 5.66% for inter-day (n = 5) precision. The proposed method was applied for the determination of trace amounts of copper in rice, lettuce and water samples with satisfactory results validated by the Graphite Furnace Atomic Absorption Spectrometry technique.

Recent progress in chemosensors based on pyrazole derivatives

Colorimetric and fluorescent probes based on small organic molecules have become important tools in modern biology because they provide dynamic information concerning the localization and quantity of the molecules and ions of interest without the need for genetic engineering of the sample. In the past five years, these probes for ions and molecules have attracted great attention because of their biological, environmental and industrial significance combined with the simplicity and high sensitivity of absorption and fluorescence techniques. Moreover, pyrazole derivatives display a number of remarkable photophysical properties and wide synthetic versatility superior to those of other broadly used scaffolds. This review provides an overview of the recent (2016-2020) findings on chemosensors containing pyrazole derivatives (pyrazoles, pyrazolines and fused pyrazoles). The discussion focuses on the design and physicochemical properties of chemosensors in order to realize their full potential for practical applications in environmental and biological monitoring (sensing of metal ions, anions, explosives, and biomolecules). We also present our conclusions and outlook for the future.

Matte photographic paper as a low-cost material for metal ion retention and elemental measurements with laser-induced breakdown spectroscopy

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 0.50-7.50 mg L^-1 copper in solution, with detection and quantification limits estimated at 0.08 and 0.24 mg 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.

Additivity of optical emissions applied to neodymium and praseodymium quantification in metallic didymium and (Nd,Pr)-Fe-B alloy samples by low-resolution atomic emission spectrometry: An evaluation of the mathematical approach used to solve spectral interferences

In this work, the effectiveness of a mathematical approach to solve the spectral interferences involved in the optical emission of two chemical species (neodymium and praseodymium) when using monochromators with low-resolution in atomic spectrometry is evaluated. Although recent technological advances have promoted spectrometers equipped with high-resolution monochromators, which have a great instrumental capability in the separation of nearby lines and consequently avoid spectral interferences, many laboratories still have old spectrometers installed with insufficient resolution to overcome such interferences. In order to evaluate a mathematical approach based on Lambert-Beer's Law, the optical emissions of neodymium and praseodymium were monitored on a low-resolution (200 pm) flame atomic emission spectrometry (F-AES). These two elements were strategically chosen as an application model because they exhibit similar physicochemical properties, joint occurrence in nature and because they are increasingly used in the manufacture of super-magnets, a material increasingly required by the high technology industry. The effectiveness of the mathematical approach was evaluated in three different ways: (i) by recovery of the analytes in synthetic mixtures containing known quantities of the species; (ii) by spike and recovery trials on a representative blend of dissolved samples and (iii) by comparing the results obtained with another analytical method: Inductively coupled plasma optical emission spectrometry (ICP-OES) with a higher spectral resolution. The results indicate the effectiveness of this simple mathematical approach, allow the "survival" of instruments equipped with low-resolution monochromators and demonstrate the applicability of this approach to spectral correction. In addition, this work contributes an analytical method for the quantification of neodymium and praseodymium in metallic alloy samples involved in the production of super-magnets, aiding in the strict quality control of these materials.

Butan-1-ol as an extractant solvent in dispersive liquid-liquid microextraction in the spectrophotometric determination of aluminium

Determining aluminium ions at μg L^-1 scale currently requires either costly analytical techniques such as inductively coupled plasma, and/or graphite furnace atomic absorption spectrometry. Dispersive liquid-liquid microextraction (DLLME) is designed to promote separation and preconcentration, thus making it possible to determine the analyte of interest without significant matrix influence. This study was aimed at the development of a spectrophotometric method to determine Al³⁺ after microextraction of its complex with quercetin. Butan-1-ol was used as a novel extractant solvent in the DLLME process. The parameters influencing complexation and microextraction, such as the amount of quercetin and volume of extractant were evaluated by univariate analysis. In optimised conditions were estimated for the proposed method: linear range from 7.5 to 165.0 μg L^-1, LOD of 2.0 μg L^-1, and LOQ of 7.0 μg L^-1. The accuracy was checked by applying the proposed method to water (NIST SRM-1643e) and rice flour (NIST SRM-1568c) certified reference materials and spike-and-recovery trials with distinct samples (mineral water, green tea, thermal spring water, contact lens disinfecting solution, saline concentrate for hemodialysis and urine).

Melted Paraffin Wax as an Innovative Liquid and Solid Extractant for Elemental Analysis by Laser-Induced Breakdown Spectroscopy

This work proposes a new development in the use of melted paraffin wax as a new extractant in a procedure designed to aggregate the advantages of liquid phase extraction (extract homogeneity, fast, and efficient transfer, low cost and simplicity) to solid phase extraction. As proof of concept, copper(II) in aqueous samples was converted into a hydrophobic complex of copper(II) diethyldithiocarbamate and subsequently extracted into paraffin wax. Parameters which affect the complexation and extraction (pH, DDTC, and Triton X-100 concentration, vortex agitation time and complexation time) were optimized in a univariate way. The combination of the extraction proposed procedure with laser-induced breakdown spectroscopy allowed the precise copper determination (coefficient of variation = 3.1%, n = 10) and enhanced detectability because of the concentration factor of 18 times. A calibration curve was obtained with a linear range of 0.50-10.00 mg L^-1 (R² = 0.9990, n = 7), LOD = 0.12 mg L^-1, and LOQ = 0.38 mg L^-1 under optimized conditions. An extraction procedure efficiency of 94% was obtained. The accuracy of the method was confirmed through the analysis of a reference material of human blood serum, by the spike and recovery trials with seawater, tap water, mineral water, and alcoholic beverages and by comparing with those results obtained by graphite furnace atomic absorption spectrometry.