Automated Dispersive Liquid–Liquid Microextraction–Gas Chromatography–Mass Spectrometry

Dispersive liquid-liquid microextraction as a novel enrichment approach for compound-specific carbon isotope analysis of chlorinated phenols

Compound-specific isotope analysis (CSIA) via gas chromatography-isotope ratio mass spectrometry (GC-IRMS) is a potent tool to elucidate the fate of (semi-)volatile organic contaminants in technical and environmental systems. Yet, due to the comparatively low sensitivity of IRMS, an enrichment step prior to analysis often is inevitable. A promising approach for fast as well as economic analyte extraction and preconcentration prior to CSIA is dispersive liquid-liquid microextraction (DLLME) - a well-established technique in concentration analysis of contaminants from aqueous samples. Here, we present and evaluate the first DLLME method for GC-IRMS exemplified by the analysis of chlorinated phenols (4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol) as model compounds. The analytes were simultaneously acetylated with acetic anhydride and extracted from the aqueous phase using a binary solvent mixture of acetone and tetrachloroethylene. With this method, reproducible δ13C values were achieved with errors ≤ 0.6‰ (n = 3) for aqueous concentrations down to 100 μg L-1. With preconcentration factors between 130 and 220, the method outperformed conventional liquid-liquid extraction in terms of sample preparation time and resource consumption with comparable reproducibility. Furthermore, we have demonstrated the suitability of the method (i) for the extraction of the analytes from a spiked river water sample and (ii) to quantify kinetic carbon isotope effect for 2,4,6-trichlorophenol during reduction with zero-valent zinc in a laboratory batch experiment. The presented work shows for the first time the potential of DLLME for analyte enrichment prior to CSIA and paves the way for further developments, such as the extraction of other compounds or scaling up to larger sample volumes.

Updating the status quo on the extraction of bioactive compounds in agro-products using a two-pot multivariate design. A comprehensive review

Extraction is regarded as the most crucial stage in analyzing bioactive compounds. Nonetheless, due to the intricacy of the matrix, numerous aspects must be optimized during the extraction of bioactive components. Although one variable at a time (OVAT) is mainly used, this is time-consuming and laborious. As a result, using an experimental design in the optimization process is beneficial with few experiments and low costs. This article critically reviewed two-pot multivariate techniques employed in extracting bioactive compounds in food in the last decade. First, a comparison of the parametric screening methods (factorial design, Taguchi, and Plackett-Burman design) was delved into, and its advantages and limitations in helping to select the critical extraction parameters were discussed. This was followed by a discussion of the response surface methodologies (central composite (CCD), Doehlert (DD), orthogonal array (OAD), mixture, D-optimal, and Box-Behnken designs (BBD), etc.), which are used to optimize the most critical variables in the extraction of bioactive compounds in food, providing a sequential comprehension of the linear and complex interactions and multiple responses and robustness tests. Next, the benefits, drawbacks, and possibilities of various response surface methodologies (RSM) and some of their usages were discussed, with food chemistry, analysis, and processing from the literature. Finally, extraction of food bioactive compounds using RSM was compared to artificial neural network modeling with their drawbacks discussed. We recommended that future experiments could compare these designs (BBD vs. CCD vs. DD, etc.) in the extraction of food-bioactive compounds. Besides, more research should be done comparing response surface methodologies and artificial neural networks regarding their practicality and limitations in extracting food-bioactive compounds.

Solvent terminated natural deep eutectic solvent microextraction for concentration of curcuminoids in Curcumae Longae Rhizoma and turmeric tea

A novel solvent terminated microextraction method based on a natural deep eutectic solvent (L-menthol and lactic acid at a molar ratio of 1:2) coupled with HPLC was proposed, which was utilized for the separation and enrichment of bisdemethoxycurcumin, demethoxycurcumin and curcumin in Curcumae Longae Rhizoma and turmeric tea. The effects of independent parameters on extraction efficiency were optimized by single-factor analysis. Subsequently, four predominated parameters affecting extraction procedure, including extractant volume, salt concentration, demulsifier consumption and demulsification time, were further evaluated by central composite design. Under the optimized conditions, the linear ranges of calibration curves were 0.005-0.5 μg/mL for bisdemethoxycurcumin, 0.004-0.4 μg/mL for demethoxycurcumin and 0.0045-0.45 μg/mL for curcumin, respectively. In addition, the developed method provided low detection limits (0.1-0.4 ng/mL) and high enrichment factors (279-350). Its intra-day and inter-day precision were carried out by relative standard deviation ranged from 2.2% to 9.2%. Finally, the applicability of this method was assessed by the analysis of Curcumae Longae Rhizoma and turmeric tea samples. The results showed that these samples were detected successfully and the spiked recoveries over the range of 85.3%-108.9% with relative standard deviations 1.6%-8.9% were attained, indicating its high relative recoveries with good precision in real sample analysis. This article is protected by copyright. All rights reserved.

Triazine covalent organic polymer coated stir bar sorptive extraction coupled with high performance liquid chromatography for the analysis of trace phthalate esters in mineral water and liquor samples

Cyanuric chloride and 4,4'-diamino-p-terphenyl were adopted as monomers to synthesize poly (4,4'-diamino-p-terphenyl-triazine) (PDT) covalent organic polymer. PDT coated stir bar was prepared and evaluated for the extraction of five phthalate esters (PAEs) with relatively lower logP values (2.7-4.9), including diethyl phthalate, diallyl phthalate, dipropyl phthalate, benzylbutyl phthalate and dibutyl phthalate. It exhibited higher extraction recovery (> 65%) and faster extraction kinetics (50 min vs 240 min) for target PAEs over commercial polydimethylsiloxane coated stir bar. Based on the superior performance, PDT coated stir bar sorptive extraction was combined with high-performance liquid chromatography-diode array detection for trace analysis of five PAEs plasticizers. The limits of detection for target PAEs were 0.04-0.27 μg/L, with the enrichment factors of 54-80-fold. The potential of the method was demonstrated by detecting five target PAEs in Chinese liquor and mineral water samples. No target analytes were detected in Chinese liquor sample, and recoveries of 85.4-109% were obtained for target analytes in spiked liquor samples; trace diethyl phthalate (1.19-2.98 μg/L) and dibutyl phthalate (0.77-0.91 μg/L) were detected in two mineral water samples, with recoveries of 85.4-117% and 87.4-117% respectively in spiked mineral water samples.

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.

Facile magnetization of covalent organic framework for solid-phase extraction of 15 phthalate esters in beverage samples

Phthalate esters (PAEs), a category of widely used plasticizers, are tend to migrate from plastic packaging to drinks. In this paper, we develop a simple and rapid coprecipitation method for synthesis of a magnetic covalent organic framework (COF) adsorbent. The fabricated COF-(TpBD)/Fe₃O₄ was applied to magnetic solid phase extraction (MSPE) of 15 phthalate esters (PAEs) for subsequent GC-MS/MS determination in beverage samples. The as-synthesized magnetic adsorbent exhibited great potential in PAEs analysis with a limit of detection of 15 PAEs ranged from 0.005 to 2.748 μg L^-1 (S/N = 3). The intra-day and inter-day relative standard deviations (RSD) value of the PAEs were less than 8.8% and 9.9%, respectively. The adsorbent can be reused after washing with methanol. The developed method was successfully applied for the determination of trace PAEs in eight beverages with recoveries ranging from 79.3% to 121.8% and RSDs were less than 11.9%. This work provides a simple magnetization process, which facilitates the application of COFs for enrichment and separation of PAEs in beverages with different matrices.

Automated dispersive liquid-liquid microextraction based on the solidification of the organic phase

In this work, the dispersive liquid-liquid microextraction technique based on the solidification of the organic phase (DLLME-SFO) has been automated for the first time. DLLME-SFO is automated by hyphenating a sequential injection analysis (SIA) system with a custom-made robotic phase separator. Automated in-syringe DLLME is followed by phase separation in a 3D printed device integrating a Peltier cell set, mounted on a multi-axis robotic arm. The combined action of the flow system and the robotic arm is controlled by a single software package, enabling the solidification/melting and collection of the organic phase for further analyte quantification. As proof-of-concept, automated DLLME-SFO was applied to the extraction of parabens followed by separation using liquid chromatography, obtaining LODs between 0.3 and 1.3 µg L^-1 (4 mL of sample extracted in 1 mL of 1-dodecanol: MeOH, 15:85, v-v). The method showed a high reproducibility, obtaining intraday RSDs between 4.6% and 5.8% (n = 6), and interday RSDs between 5.6% and 8.6% (n = 6). The developed method was evaluated for the determination of parabens in water, urine, saliva, and personal care products.

Ionic liquid ultrasound-assisted dispersive liquid-liquid microextraction based on solidification of the aqueous phase for preconcentration of heavy metals ions prior to determination by LC-UV

Ionic liquid ultrasound-assisted dispersive liquid-liquid microextraction based on solidification of the aqueous phase was used for preconcentration of Ni²⁺, Co²⁺, Cd²⁺, Cu²⁺, Pb²⁺ in natural water samples prior to liquid chromatography with UV detection. In the proposed method, the ammonium pyrrolidinedithiocarbamate was used as a complexing agent and the phosphonium ionic liquid trihexyl(tetradecyl)phosphonium bis[(2,4,4-trimethyl)pentyl]phosphinate (Cyphos IL 104) was used as an extractant. Ultrasound energy was used to disperse the extractant in the aqueous phase. After microextraction, the ionic liquid and aqueous phases were separated by centrifugation. Then the aqueous phase was frozen and the lighter than water ionic liquid phase containing metal ions complexes with pyrrolidinedithiocarbamate was separated and dissolved in a small volume of methanol prior to injection into the liquid chromatograph. Several parameters including the volume of extractant, the pH of the sample, the concentration of complexing agent, the time of ultrasound energy treatment, the time and speed of centrifugation and the effect of ionic strength were optimized. Under the optimized conditions (10 µL of Cyphos IL 104, pH = 5, 0.3% w/v ammonium pyrrolidinedithiocarbamate, 60 s of ultrasound use, 5 min/5000 rpm (2516×g) of centrifugation, 2.0 mg of NaCl), preconcentration factors were 211, 210, 209, 207 and 211 for Ni²⁺, Co²⁺, Cd²⁺, Cu²⁺ and Pb²⁺ respectively. Linearity was observed in the ranges 0.2-75.0 µg L^-1 for Pb²⁺, Cd²⁺, Co²⁺ and 0.5-100.0 µg L^-1 for Cu²⁺, Ni²⁺. The limits of detection were 0.03 µg L^-1 for Ni²⁺, 0.03 µg L^-1 for Co²⁺, 0.03 µg L^-1 for Cd²⁺, 0.02 µg L^-1 for Cu²⁺, 0.02 µg L^-1 for Pb²⁺, respectively. The accuracy of this method was evaluated by preconcentration and determination of Ni²⁺, Co²⁺, Cd²⁺, Cu²⁺, Pb²⁺ in certified reference materials (TMRAIN-04 and NIST 1643e) with the recovery values in the range of 97-102%. The presented method has been successfully applied for the determination of analytes in natural water samples (river and lake waters).

Solvent-terminated dispersive liquid-liquid microextraction: a tutorial

Solvent-terminated dispersive liquid-liquid microextraction (ST-DLLME) is a special mode of DLLME in which a demulsifying solvent is injected into the cloudy mixture of sample/extractant to break the emulsion and induce phase separation. The demulsification process starts by flocculation of the dispersed microdroplets by Ostwald ripening or coalescence to form larger droplets. Then, the extractant either floats or sinks depending on its density as compared with that for the aqueous sample. The demulsifier should have high surface activity and low surface tension in order to be capable of inducing phase separation. The extraction efficiency in ST-DLLME is controlled by the same experimental variables of normal DLLME (n-DLLME) such as the type and volume of the extractant as well as the disperser. Other parameters such as pH and the temperature of the sample, the stirring rate, the time of extraction and the addition of salt are also important to consider. Along with these factors, the demulsifier type and volume and the demulsification time have to be optimized. By using solvents to terminate the dispersion step in DLLME, the centrifugation process is not necessary. This in turn improves precision, increases throughput, decreases the risk of contamination through human intervention and minimizes the overall analysis time. ST-DLLME has been successfully applied for determination of both inorganic and organic analytes including pesticides and pharmaceuticals in water and biological fluids. Demulsification via solvent injection rather than centrifugation saves energy and makes ST-DLLME easier to automate. These characteristics in addition to the low solvent consumption, the reduced organic waste and the possibility of using water in demulsification bestow green features on ST-DLLME. This tutorial discusses the principle, the practical aspects and the different applications of ST-DLLME.

Time-Profile Measurement of an Emulsion Using Multiphoton Ionization Time-of-Flight Mass Spectrometry in Combination with a Microscope

Multiphoton ionization time-of-flight mass spectrometry was applied to the measurement of an oil-in-water emulsion that contained toluene as a dispersed phase. Before the measurement, the sample was sufficiently creamed, and then stirred for a short period of time for dispersion. As a result, several intense spikes appeared on the time profile constructed from the peak area for toluene. In the present study, an optical microscope was used to observe the capillary column for sample introduction, and small toluene droplets along with their aggregates were found in the images of the emulsion flowing through the capillary. The aggregates produced intense spikes comprised of multiple plots, which could be easily marked by applying a moving median filter. In the present study, droplets with minimum diameters as small as 2.9 μm, which corresponds to 13 fL, could be calculated as detectable spikes.

Rapid and sensitive determination of multiple endocrine-disrupting chemicals by ultrasound-assisted in situ derivatization dispersive liquid-liquid microextraction coupled with ultra-high-performance liquid chromatography/tandem mass spectrometry

RATIONALE

Endocrine-disrupting chemicals (EDCs) in environment samples and food stuffs are an increasing serious public health issue due to their potency to interfere and deregulate several aspects of the endocrine system. Because of their extremely low abundance, it remains a challenging task to develop a sensitive detection method.

METHODS

4'-Carbonyl chloride rosamine (CCR) was used as a derivatization reagent for EDCs for the first time. A new ultrasound-assisted in situ derivatization/dispersive liquid-liquid microextraction (UA-DLLME with in situ derivatization) method for multiple EDCs including five estrogens, two alkylphenols, eight bisphenols, seven parabens and triclosan coupled with ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) has been developed and validated.

RESULTS

The ionization efficiency of EDCs was greatly enhanced through the introduction of a permanent charged moiety of CCR into the derivatives during electrospray ionization (ESI)-MS analysis. The main variables potentially affecting the UA-DLLME with in situ derivatization process are optimized. The recoveries and matrix effects of 23 EDCs for the spiking samples were in the range of 83.0-116.0% and 85.8-114.6%, respectively. Good method reproducibility was achieved.

CONCLUSIONS

The limits of detection (LODs) for 23 EDCs were 0.05-0.40 ng/L and 0.03-0.25 ng/g (dry weight, d.w.) for environment samples and food stuffs, respectively. The proposed method has been demonstrated to be suitable for simultaneous determination of multiple EDCs in real samples with high sensitivity, speediness, and good sample clean-up ability. Copyright © 2017 John Wiley & Sons, Ltd.

Innovative separation and preconcentration technique of coagulating homogenous dispersive micro solid phase extraction exploiting graphene oxide nanosheets

A uniquely novel, fast, and facile technique is introduced for the first time in which a scant amount of graphene oxide (GO), without modification, has been utilized in dispersive mode of solid phase extraction (SPE) for an efficient yet simple separation. The proposed method of coagulating homogenous dispersive micro solid phase extraction (CHD-µSPE) is based on coagulation of homogeneous GO solution with the aid of polyetheneimine (PEI). CHD-µSPE use full adsorption capacity of GO because in this method was used GO solution obtained from synthesis process without drying step and stacking nanosheets. In optimized condition, 30 µL GO solution (7 mg mL(-1)), obtained in synthesis process, was injected into 1.5 mL the sample solution followed by immediate injection of 53 µL PEI solution (1 mg mL(-1)). After inserting PEI, GO sheets aggregate and can be readily separated by centrifugation. PEI not only cause aggregation of GO, but also form three-dimensional network of GO with easy handling in following separation steps. Lead, cadmium, and chromium were selected as model analytes and the effecting parameters including the amount of GO, concentration of PEI, sample pH, extraction time, and type of desorption solvent were investigated and optimized. The results indicate that the proposed CHD-µSPE method can be successfully applied GO in dispersive mode of SPE without effecting on good capability adsorption of GO. The novel method was applied in determination of lead, cadmium, and chromium in water, human saliva, and urine samples by electrothermal atomic absorption spectrometry. The detection limits are as low as 0.035, 0.005, and 0.012 µg L(-1) for Pb, Cd, and Cr respectively. The intra-day precisions (RSDs) were lower than 3.8%. CHD-µSPE method showed a good linear ranges of 0.24-15.6, 0.015-0.95 and 0.039-2.33 µg L(-1) for Pb, Cd and Cr respectively. Method performance was investigated by determination of mentioned metal ions in river water, human urine and saliva sample with good recoveries in range of 94.2-103.0%. The accuracy of the method was underpinned by correct analysis of a standard reference material (SRM: 2668 level I, Urine).

Analysis of Phthalate Esters in Mammalian Cell Culture Using a Microfluidic Channel Coupled with an Electrochemical Sensor

An analytical tool to monitor trace phthalate was developed using a microfluidic channel device coupled with a novel electrochemical biosensor. At first, the electrochemical sensor was constructed with biomimetic layers to reveal a large hydrogen over potential by controlling the surface charge and hydrophobicity through assembling with a lipid (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) and a cationic molecule (toluidine blue O) bonded to a conductive polymer. The modified electrode possessing a highly negative polarization potential (approximately -1.8 V vs Ag/AgCl) can uptake sparingly soluble phthalate ester (PEs) compounds in aqueous media. Each sensor probe material was characterized employing SEM, AFM, XPS, QCM, TEM, UV-visible, and impedance spectroscopy. The microfluidic channel is used first to concentrate and separate trace amounts of phthalates, and then the sensor probe is installed at the end of channel. Experimental variables affecting the PEs analysis were assessed and optimized in terms of biomimetic layer composition and analytical conditions. The linear dynamic range and detection limits of the PEs were 0.15 nM-10.0 μM and ∼12.5 pM with relative standard deviations <5%. The proposed method was applied to evaluate the effect of endocrine disruptors on mammalian kidney cells, where the cell samples show in-taking percentages between 1.8 and 7.0% to the total PEs according to the incubation time.

Multi-residue method for determination of 58 pesticides, pharmaceuticals and personal care products in water using solvent demulsification dispersive liquid-liquid microextraction combined with liquid chromatography-tandem mass spectrometry

A rapid and efficient sample pretreatment using solvent-based de-emulsification dispersive liquid-liquid microextraction (SD-DLLME) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was studied for the extraction of 58 pharmaceuticals and personal care products (PPCPs) and pesticides from water samples. Type and volume of extraction and disperser solvents, pH, salt addition, amount of salt and type of demulsification solvent were evaluated. Limits of quantification (LOQ) in the range from 0.0125 to 1.25 µg L(-1) were reached, and linearity was in the range from the LOQ of each compound to 25 μg L(-1). Recoveries ranged from 60% to 120% for 84% of the compounds, with relative standard deviations lower than 29%. The proposed method demonstrated, for the first time, that sample preparation by SD-DLLME with determination by LC-MS/MS can be successfully used for the simultaneous extraction of 32 pesticides and 26 PPCPs from water samples. The entire procedure, including the extraction of 58 organic compounds from the aqueous sample solution and the breaking up of the emulsion after extraction with water, rather than with an organic solvent, was environmentally friendly. In addition, this technique was less expensive and faster than traditional techniques. Finally, the analytical method under study was successfully applied to the analysis of all 58 pesticides and PPCPs in surface water samples.