Vortex-assisted liquid–liquid–liquid microextraction (VALLLME) technique: A new microextraction approach for direct liquid chromatography and capillary electrophoresis analysis

Physical field-assisted deep eutectic solvent processing: A green and water-saving extraction and separation technology

Extraction of organic and bioactive compounds from plant materials with the traditional organic solvents aided by water or oil bath heating is not sustainable, because it consumes a lot of energy, time, water/oil, solvents, and results in lower yield. This review discusses deep eutectic solvent (DES) as a green solvent, physical field technology (PFT) as a water-saving and green technology, and how the coupling of PFT (ultrasound [US], microwave [MW], infrared [IR]) to DES will improve the yield and quality of protein, polysaccharides, polyphenols, pectin, and terpenoids extracted from plant materials. Ultrasonication increases DES extraction efficiency via cavitation dislodgement and pores creation. IR coupling to DES enhances the extraction yield of polyphenols and the antioxidant and antiradical activity. MW improves DES extraction yield, reduces energy consumption, operational cost, and compound degradation, and is inferred to be the greenest technology.

Application of microextraction techniques for indirect spectrophotometric determination of fluorides in river waters

The present study is dedicated to development of improved method for determination of trace amounts of fluorides in natural waters which is based on the interaction of fluorides with ion associate (IA) of Al(III), salicylic aldehyde acylhydrazones (benzhydrazone (SABH) and 4-picolinhydrazone (SAPH)) and polymethine dye Astra Phloxine FF (AP). Comparison of analytical forms [Al(SABH)₂]⋅AP and [Al(SAPH)₂]⋅AP showed that the analytical system Al(III)-SAPH-AP is more effective, namely, a higher level of preconcentration of the analytical form is ensured by and extraction equilibrium is achieved faster. Based on the study, we propose a new, fast, simple, reliable, sensitive, and accurate method of the indirect UV-Vis-spectrophotometric determination of fluorides grounded on the interaction of fluorides with IA of Al(III), SAPH and AP with the utilization of vortex-assisted liquid-liquid microextraction (VALLME). The method is based on the discoloration of the microextract of IA of Al(III), SAPH and AP (Al-SAPH-AP) in presence of fluoride ions due to the formation of fluoride complexes of aluminum with higher stability. The effect of various factors has been studied. The optimal conditions of the UV-Vis-spectrophotometric determination of fluorides were defined as: pH 7.0-10.0, 1.0⋅10^-6 mol⋅L^-1 Al(III); 4.0⋅10^-5 mol⋅L^-1 SAPH; 1.0⋅10^-6 mol⋅L^-1 AP; λ = 560 nm. VALLME have been carried out in 250 μL of CCl₄ at 20:1 vol ratios of aqueous and organic phases, with vortexing at 3000 rpm for 15 s followed by centrifugation at 2000 rpm for 2 min. The determination of fluorides is feasible in the presence of various interferences. The calibration curve shows the linear dependence in the range of 0.3-114 μg⋅L^-1 of the fluorides concentration (R² = 0.993) with the limit of detection of 0.086 μg⋅L^-1 and the limit of determination of 0.284 μg⋅L^-1. The accuracy of the proposed protocol of fluorides determination was verified towards a reference method on the samples of natural rivers waters (RSD 2.6-3.1%, recovery 98.3-101.4%).

Liquid phase microextraction techniques combined with chromatography analysis: a review

Sample pretreatment is the first and the most important step of an analytical procedure. In routine analysis, liquid–liquid microextraction (LLE) is the most widely used sample pre-treatment technique, whose goal is to isolate the target analytes, provide enrichment, with cleanup to lower the chemical noise, and enhance the signal. The use of extensive volumes of hazardous organic solvents and production of large amounts of waste make LLE procedures unsuitable for modern, highly automated laboratories, expensive, and environmentally unfriendly. In the past two decades, liquid-phase microextraction (LPME) was introduced to overcome these drawbacks. Thanks to the need of only a few microliters of extraction solvent, LPME techniques have been widely adopted by the scientific community. The aim of this review is to report on the state-of-the-art LPME techniques used in gas and liquid chromatography. Attention was paid to the classification of the LPME operating modes, to the historical contextualization of LPME applications, and to the advantages of microextraction in methods respecting the value of green analytical chemistry. Technical aspects such as description of methodology selected in method development for routine use, specific variants of LPME developed for complex matrices, derivatization, and enrichment techniques are also discussed.

Vortex-assisted liquid-liquid microextraction of strontium from water samples using 4',4″(5″)-di-(tert-butylcyclohexano)-18-crown-6 and tetraphenylborate

A vortex-assisted liquid-liquid microextraction method was developed for the chromatographic determination of strontium in aqueous samples. In the method, strontium was complexed with 4',4″(5″)-di-(tert-butylcyclohexano)-18-crown-6 in the presence of tetraphenylborate as the counter anion, which increased the hydrophobicity of the ion-association complex, resulting in its improved extraction into 1-octanol. Strontium from the organic phase was stripped with nitric acid back to aqueous solution and determined by ion chromatography. The optimum microextraction conditions were as follows: 2.0 mL aqueous samples with 3 mM tetraphenylborate; 150 μL of 1-octanol as the extractant phase with 10 mM DtBuCH18C6; vortex extraction time for 10 s; centrifugation at 6000 rpm for 4 min; stripping by 0.1 M nitric acid. Under the optimum conditions, the detection limit for strontium was 0.005 mg/L. The calibration curves showed good linearity over the range between 0.01 and 2.5 mg/L. Intra- and interday precisions of the present method were satisfactory with relative standard deviations of 1.7 and 2.1%, respectively.

A green ultrasonic-assisted liquid-liquid microextraction based on deep eutectic solvent for the HPLC-UV determination of ferulic, caffeic and cinnamic acid from olive, almond, sesame and cinnamon oil

A simple, inexpensive and sensitive ultrasonic-assisted liquid-liquid microextraction method based on deep eutectic solvent (UALLME-DES) was used for the extraction of three phenolic acids (ferulic, caffeic and cinnamic) from vegetable oils. In a typical experiment, deep eutectic solvent as green extraction solvent was added to n-hexane (as a typical oil medium) containing target analytes. Subsequently, the extraction was accelerated by sonication. After the extraction, phase separation (DES rich phase/n-hexane phase) was performed by centrifugation. DES rich phase (lower phase) was withdrawn by a micro-syringe and submitted to isocratic reverse-phase HPLC with UV detection. Under optimum conditions obtained by response surface methodology (RSM) and desirability function (DF), the method has good linear calibration ranges (between 1.30 and 1000 µg L(-1)), coefficients of determination (r(2)>0.9949) and low limits of detection (between 0.39 and 0.63 µg L(-1)). This procedure was successfully applied to the determination of target analytes in olive, almond, sesame and cinnamon oil samples. The relative mean recoveries ranged from 94.7% to 104.6%.