Francisco Pena-Pereira

Ionic Liquids and Deep Eutectic Mixtures: Sustainable Solvents for Extraction Processes

In recent years, ionic liquids and deep eutectic mixtures have demonstrated great potential in extraction processes relevant to several scientific and technological activities. This review focuses on the applicability of these sustainable solvents in a variety of extraction techniques, including but not limited to liquid- and solid-phase (micro) extraction, microwave-assisted extraction, ultrasound-assisted extraction and pressurized liquid extraction. Selected applications of ionic liquids and deep eutectic mixtures on analytical method development, removal of environmental pollutants, selective isolation, and recovery of target compounds, purification of fuels, and azeotrope breaking are described and discussed.

Speciation of mercury by ionic liquid-based single-drop microextraction combined with high-performance liquid chromatography-photodiode array detection.

Room temperature ionic liquids can be considered as environmentally benign solvents with unique physicochemical properties. Ionic liquids can be used as extractant phases in SDME, being compatible with chromatographic systems. A single-drop microextraction method was developed for separation and preconcentration of mercury species (MeHg(+), EtHg(+), PhHg(+) and Hg(2+)), which relies on the formation of the corresponding dithizonates and microextraction of these neutral chelates onto a microdrop of an ionic liquid. Afterwards, the separation and determination were carried out by high-performance liquid chromatography with a photodiode array detector. Variables affecting the formation and extraction of mercury dithizonates were optimized. The optimum conditions found were: microextraction time, 20 min; stirring rate, 900 rpm; pH, 11; ionic liquid type, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C(6)MIM][PF(6)]); drop volume, 4 microL; and no sodium chloride addition. Limits of detection were between 1.0 and 22.8 microg L(-1) for the four species of mercury, while the repeatability of the method, expressed as relative standard deviation, was between 3.7 and 11.6% (n=8). The method was finally applied to the determination of mercury species in different water samples.

Liquid-phase microextraction approaches combined with atomic detection: a critical review.

Liquid-phase microextraction (LPME) displays unique characteristics such as excellent preconcentration capability, simplicity, low cost, sample cleanup and integration of steps. Even though LPME approaches have the potential to be combined with almost every analytical technique, their use in combination with atomic detection techniques has not been exploited until recently. A comprehensive review dealing with the applications of liquid-phase microextraction combined with atomic detection techniques is presented. Theoretical features, possible strategies for these combinations as well as the effect of key experimental parameters influencing method development are addressed. Finally, a critical comparison of the different LPME approaches in terms of enrichment factors achieved, extraction efficiency, precision, selectivity and simplicity of operation is provided.

Perspectives on the replacement of harmful organic solvents in analytical methodologies: a framework toward the implementation of a generation of eco-friendly alternatives

Volatile organic solvents derived from non-renewable fossil feedstocks are commonplace in analytical laboratories. In spite of their convenient performance in countless unit operations, their environmental, health and safety issues represent a major area of concern. The progressive replacement of organic solvents obtained from fossil resources by eco-friendly alternatives would involve remarkable advances within the framework of green analytical chemistry, while avoiding future uncertainties regarding forthcoming regulations. This perspective tackles the problem of organic solvent use in analytical methodologies, providing relevant information for solvent selection and identifying a range of solvents derived from natural and/or renewable resources, namely bio-based molecular solvents, ionic liquids composed wholly of biomaterials and natural deep eutectic mixtures that could potentially be exploited toward advanced, more benign, analytical methodologies. In addition, physicochemical properties are provided, and a number of challenging aspects to be considered in the implementation of eco-friendly alternatives are evaluated.

Griess micro-assay for the determination of nitrite by combining fibre optics-based cuvetteless UV–Vis micro-spectrophotometry with liquid-phase microextraction

A novel, simple and low cost method for the determination of nitrite using headspace single-drop microextraction and cuvetteless ultraviolet-visible micro-spectrophotometry is described. A Griess reagent-containing aqueous microdrop exposed to the headspace was used as extractant of the volatile nitrogen oxides generated from nitrite by direct acidification of the aqueous sample. Experimental parameters affecting the headspace single-drop microextraction performance such as composition and volume of the extractant phase, sample volume, concentration of acetic acid, ionic strength, sample agitation, temperature and microextraction time were systematically examined. Measurements were carried out at 540 nm under optimized conditions. A detection limit of 1.5 microg L(-1) and an enrichment factor of 193 were achieved. Intra-day repeatability and inter-day reproducibility, expressed as relative standard deviation, were 3.5% (n=7) and 10.6% (three consecutive days), respectively. The proposed method, characterized by its enhanced sensitivity and selectivity in comparison with the standardized colorimetric assay, was successfully applied to the analysis of several environmental water samples.

Headspace single-drop microextraction coupled to microvolume UV–vis spectrophotometry for iodine determination

Headspace single-drop microextraction has been combined with microvolume UV-vis spectrophotometry for iodine determination. Matrix separation and preconcentration of iodide following in situ volatile iodine generation and extraction into a microdrop of N,N-dimethylformamide is performed. An exhaustive characterization of the microextraction system and the experimental variables affecting iodine generation from iodide was carried out. The procedure employed consisted of exposing 2.5 microL of N,N-dimethylformamide to the headspace of a 10 mL acidic (H(2)SO(4) 2 molL(-1)) aqueous solution containing 1.7 molL(-1) Na(2)SO(4) for 7 min. Addition of 1 mL of H(2)O(2) 1 molL(-1) for in situ iodine generation was performed. The limit of detection was determined as 0.69 microgL(-1). The repeatability, expressed as relative standard deviation, was 4.7% (n=6). The calibration working range was from 5 to 200 microgL(-1) (r(2)=0.9991). The large preconcentration factor obtained, ca. 623 in only 7 min, compensate for the 10-fold loss in sensitivity caused by the decreased optical path, which results in improved detection limits as compared to spectrophotometric measurements carried out with conventional sample cells. The method was successfully applied to the determination of iodine in water, pharmaceutical and food samples.

Green chemistry in analytical atomic spectrometry: a review

As a result of the greater consciousness within the analytical community on the impact of chemicals on human health and environment, green issues are increasingly taken into account when choosing an established analytical method or developing a new one. Apart from typical analytical characteristics (e.g., sensitivity, limit of detection, repeatability, etc.), other features such as the amount of sample/reagents, operation time, use of energy-effective apparatus, waste production, etc. should be highlighted in order to meet the principles of Green Chemistry. Although conventional approaches for trace element analysis by atomic spectrometry usually involve well-established sample pre-treatments based on ‘wet chemistry’, and high consumption of gases, reagents, etc. is inherent to many techniques in this group, there are still many avenues where green issues can be implemented. For greening atomic spectrometry, green chemistry principles should be applied to every step of the analytical process, i.e., from sampling and sample pre-treatment to data processing. In this review, main pathways for greening atomic spectrometry such as downsizing of instrumentation, use of portable instruments, solid sampling, application of clean energies (ultrasound, microwaves, etc.) for sample pre-treatment, development of on-site, on-line and at-line approaches vs. typical off-line methods, application of modern extraction techniques (e.g., solid- and liquid-phase microextraction), green solvents and derivatization agents and use of chemometric tools for method optimization, signal processing, etc. are discussed in a critical way.

Ion pair-based dispersive liquid–liquid microextraction for gold determination at ppb level in solid samples after ultrasound-assisted extraction and in waters by electrothermal-atomic absorption spectrometry

A new methodology was developed for the determination of ultratrace levels of gold in water samples, soils and river sediments. Dispersive liquid-liquid microextraction was used to preconcentrate the ion pair formed between AuCl(4)(-) and [CH(3)(CH(2))(3)](4)N(+) in a microliter-range volume of chlorobenzene using acetone as disperser solvent. When solid samples were analyzed, the method consisted of a combination of ultrasound-assisted extraction and dispersive liquid-liquid microextraction with final detection by electrothermal-atomic absorption spectrometry. Since an HCl medium was required for the formation of the AuCl(4)(-) complex, HCl together with HNO(3) was used as extractants for ultrasound-assisted extraction. After optimization, the enrichment factor obtained was 220 for water samples. Moreover, the extraction efficiency was around 96%. The repeatability, expressed as relative standard deviation ranged from 3.6% to 9.7%. The instrumental detection limit was 8.4 ng L(-1), whereas the procedural detection limits were 42 ng L(-1) for water samples and 1.5 ng g(-1) for environmental solid samples.

A solvent selection guide based on chemometrics and multicriteria decision analysis

The selection of suitable solvents is a crucially important subject in a wide range of chemical processes. This study presents a solvent selection guide where 151 solvents were assessed, including a significant number of recently reported bio-based solvents. The assessment procedure involves grouping of solvents according to their physicochemical parameters and ranking within clusters according to their toxicological and hazard parameters. Grouping of solvents resulted in the formation of three clusters – nonpolar and volatile (35 solvents), nonpolar and sparingly volatile (35 solvents) and polar ones (81 solvents). The comparison of toxicological and hazard related data indicated that solvents from the third cluster should be preferentially chosen. Within each group, a solvent ranking was performed by means of the TOPSIS procedure based on 15 different criteria. Because of the lack of certain data (especially toxicological), different ranking confidence levels were introduced. The highest confidence rankings were performed only for some solvents but with all the considered criteria. Low confidence rankings were created for all solvents but were based on certain criteria only. The results of our solvent selection guide (SSG) are generally in agreement with the results of others but allow for finer ranking of solvents. The assessment procedure is easy to adapt to individual chemists’ needs and allows including new solvents to the ranking.

Determination of iodate in waters by cuvetteless UV–vis micro-spectrophotometry after liquid-phase microextraction

The combination of liquid-phase microextraction and microvolume UV-vis spectrophotometry has been applied to the determination of iodate in natural water samples. The method is based on the reduction of iodate into vapor iodine and extraction of this volatile onto a single drop of N,N-dimethylformamide. The following derivatization reaction was employed: Optimum conditions employed for iodate determination were as follows: 2.5 microL N,N-dimethylformamide exposed to the headspace of a 10 mL acidic (HCl 0.2 mol L(-1)) aqueous solution stirred at 1400 rpm for 7 min after addition of 1 mL of KI 10(-3)mol L(-1) for in situ iodine generation. The limit of detection was determined as 1.1 microg L(-1). The repeatability, expressed as relative standard deviation, was 4.2% (n=6). A large preconcentration factor (i.e. 396) was obtained in only 7 min.