Combination of dispersive liquid–liquid microextraction and solid–phase microextraction: An efficient hyphenated sample preparation method

A configuration for cooling assisted organic solvent coated thin film microextraction after dispersive liquid-liquid microextraction method: A microextraction method for ultra-trace analyzing of volatile sample

A combination of the dispersive liquid-liquid microextraction (DLLME) method based on the total vaporization procedure and cooling-assisted organic solvent-coated thin film microextraction (TFME) was applied for extracting chlorpyrifos (as the model compound). Based on the high thermal conductivity, a nickel foam thin film with the dimensions of 5.0 mm × 5.0 mm was used as a substrate for holding the organic solvent. Supporting thin film by organic solvent increases the thickness and contact area of the film relative to TFME or single drop microextraction (SDME) alone, resulting in a dramatic increase in the extraction efficiency. To protect the organic solvent and enhance the analyte distribution coefficient between the film and the vapor phase, a cooling system was applied. The proposed design was effective due to condensing the target analyte only on the uniform cooled thin film and not on the other regions in the extraction chamber. A corona discharge ionization source-ion mobility spectrometer was employed to identify the analyte. After optimizing the effective parameters, the limits of quantification (S/N = 10) and detection (S/N = 3) were calculated 0.1 and 0.03 μg L-1, respectively, and the dynamic range was measured between 0.1 and 7.0 μg L-1, with a determination coefficient of 0.9997. For three concentration levels of 0.1, 3.0, and 7.0 μg L-1, the relative standard deviations (n = 3) as the repeatability index were to be 6 %, 5 %, and 4 % for intra-day and 9 %, 6 %, and 5 % for inter-day, respectively. The enrichment factor was also calculated to be 3630 for the analyte concentration of 1.0 μg L-1. Well water, potato, and agricultural wastewater were analyzed as the real samples and the relative recovery values were measured between 92 % and 99 %. The accuracy of the proposed technique was validated by the European Standards EN 12393 method. In this approach, two steps of analyte extraction (DLLME and TFME) were used consecutively, resulting in better preconcentration and reduced matrix interference during cleaning-up.

Development of dispersive liquid-liquid microextraction with solid-phase evaporation as a novel hyphenated method prior to ion mobility spectrometry and its application for trace analysis of fluoxetine

For the hyphenating of dispersive liquid-liquid microextraction (DLLME) with nano mesoporous solid-phase evaporation (SPE_V) as a novel method, MCM-41@SiO₂ was synthesized and used as a nano mesoporous adsorbent for coating on the solid-phase fiber, preconcentration of fluoxetine antidepressant drug (as a model compound), and total evaporation of the extraction solvents obtained by the DLLME method. To detect the analyte molecules, a corona discharge ionization-ion mobility spectrometer (CD-IMS) was applied. In order to increase the extraction efficiency and the IMS signal of the fluoxetine drug, some variables including extraction solvent and its volume, disperser solvents and its volume, sample solution pH, desorption temperature, and evaporation time of the solvent from the solid-phase fiber were chosen and optimized. Some analytical parameters including limit of detection (LOD), limit of quantification (LOQ), linear dynamic range (LDR) with determination coefficient, and relative standard deviations (RSDs) were calculated under the optimized conditions. LOD (S/N = 3), 3 ng mL^-1; LOQ (S/N = 10), 10 ng mL^-1; LDR, 10-200 ng mL^-1; and intra- and inter-day RSDs (n = 3), 2.5% and 9.6% for 10 ng mL^-1, and 1.8% and 7.7% for 150 ng mL^-1, respectively. To investigate the ability of the hyphenated method to determine fluoxetine in real samples, fluoxetine tablets, and some biological samples such as human urine and blood plasma were selected and the relative recovery values were calculated to be 85-110%. The accuracy of the proposed method was compared with that of the HPLC standard method.

Centrifuge-free dispersive liquid-liquid microextraction coupled with thin-film microextraction for the preconcentration of molinate in real samples by ion mobility spectrometry

A tandem microextraction method, centrifuge free dispersive liquid-liquid microextraction and thin-film microextraction (DLLME-TFME), was used for analyzing molinate in environmental samples by ion mobility spectrometry (IMS). Considering the IMS as a competitive detection system, coupling these two popular sample preparation methods reduces the effect of solvent interference and improves the sensitivity of the technique. Trichloromethane and methanol were used as the extraction, and dispersive solvents for the DLLME method and electrospun polyacrylonitrile/copper-benzene-1,4-dicarboxylic acid fibers were used as a sorbent in the TFME method. Some effective experimental variables influencing the extraction efficiency of an analyte such as type and volume of dispersive and extraction solvents, solution pH, ionic strength, sonication time, and extraction time were studied. The linear dynamic range of 0.5-50 μg L^-1 and the limit of detection of 0.1 μg L^-1 were obtained under optimized conditions. The relative standard deviations for intra-and inter-day analysis were calculated less than 10%. The present method was used for the determination of molinate in different real samples such as agricultural wastewater, well water, river water, and apple, and the recovery was obtained between 82% and 113%, for the spiked samples.

Z-sep+ based QuEChERS technique for the pre-concentration of malathion pesticide in fruits followed by analysis using UV-Vis spectroscopy

In this work, the concentrations of malathion in fruits were determined using UV-Vis spectrophotometry prior to pre-concentration using QuEChERS. The Z-sep⁺/PSA sorbent combination was used for the d-SPE clean-up and extraction was done using acetonitrile during QuEChERS. The absorbance of malathion was measured using a UV-Vis spectrophotometer at a wavelength of 415 nm. The QuEChERS parameters, which included type and volume of extraction solvent, type and mass of sorbents, and centrifugation rate, were optimised prior to application of the developed method to real fruit samples. The linear range was from 0.1 to 0.9 mg kg^-1 while the coefficient of determination (R²) was 0.9999. The limit of detection (LOD) for malathion was found to be 0.017 mg kg^-1 and the limit of quantification was 0.05 mg kg^-1. Orange samples were found to have no malathion residues when the developed method was applied to them while the concentrations of malathion in apple and pear samples were 0.07 mg kg^-1 and 0.09 mg kg^-1 respectively.

Deep eutectic solvent-based dispersive liquid-liquid micro-extraction of pesticides in food samples

Deep eutectic solvents are versatile, green and new generation solvents that can be used during dispersive liquid-liquid micro-extraction techniques for pesticides. They have tunable physico-chemical properties that can be easily changed by varying the ratios of hydrogen bond donors and hydrogen bond acceptors in their structures. Deep eutectic solvents are non-flammable, chemically and thermally stable solvents with low vapour pressure. Thus, they have characteristics that are similar to those of ionic liquids. However, they have simpler synthetic procedures, less expensive and are more biodegradable than ionic liquids. One of the limitations of deep eutectic solvents is their toxicity to the environment but they are less toxic than ionic liquids. This paper gives a focused and comprehensive recent review on the applications of deep eutectic solvents during dispersive liquid-liquid micro-extraction of pesticides in food samples for the period starting from 2016 to 2020. Emphasis was placed on the modifications done to the deep eutectic solvent-based dispersive liquid-liquid micro-extraction techniques in order to enhance their greenness during pesticide pre-concentration in food samples. In addition, hyphenated dispersive liquid-liquid micro-extraction techniques were also reviewed and lastly, the paper outlined the challenges associated with the use of DESs during the DLLME techniques.

Novel sample preparation approaches in gas chromatographic analysis: Promising ideas

The development of sample preparation procedures is still a dynamic process despite a number of already proposed techniques. The main challenge in this research field is to fully replace classical procedures like liquid-liquid extraction and solid-phase extraction in gas chromatographic analysis. Some progress has been already achieved for the last 20 years when miniaturized techniques were incorporated in ISO standards. The current review is focused on novel approaches in sample treatment that appeared since 2010. It includes research studies describing non-conventional instrumental design available to inspire future progress in the field. A combination of a few extraction principles and supporting with additional treatment are the main core suggested for improvement of sample preparation efficiency. This requires good compatibility of extraction media, assessment of multiple experimental parameters, and potential automatization possibilities.

Green pre-concentration techniques during pesticide analysis in food samples

The ever-increasing demand for determining pesticides at low concentration levels in different food matrices requires a preliminary step of pre-concentration which is considered a crucial stage. Recently, the parameter of "greenness" during sample pre-concentration of pesticides in food matrices is as important as selectivity in order to avoid using harmful organic solvents during sample preparation. Developing new green pre-concentration techniques is one of the key subjects. Thus, to reduce the impact on the environment during trace analysis of pesticides in food matrices, new developments in pre-concentration have gone in three separate directions: the search for more environmentally friendly solvents, miniaturization and development of solvent-free pre-concentration techniques. Eco-friendly solvents such as supercritical fluids, ionic liquids and natural deep eutectic solvents have been developed for use as extraction solvents during pre-concentration of pesticides in food matrices. Also, miniaturized pre-concentration techniques such as QuEChERS, dispersive liquid-liquid micro-extraction and hollow-fiber liquid-phase micro-extraction have been used during trace analysis of pesticides in food samples as well as solvent-free techniques such as solid-phase micro-extraction and stir bar sorptive extraction. All these developments which are aimed at ensuring that pesticide pre-concentration in different food matrices is green are critically reviewed in this paper.

Online extraction of antihypertensive drugs and their metabolites from untreated human serum samples using restricted access carbon nanotubes in a column switching liquid chromatography system

A novel analytical method was developed to determine 5 antihypertensive drugs of different pharmacological classes (angiotensin-converting enzyme inhibitors, calcium channel blockers, α-2 adrenergic receptor agonists, angiotensin II receptor blockers, and aldosterone receptor antagonists) and some of their metabolites in human serum. The untreated samples were directly analyzed in a column switching system using an extraction column packed with restricted access carbon nanotubes (RACNTs) in an ultra-high performance liquid chromatography coupled to a mass spectrometer (UHPLC-MS/MS). The RACNTs column was able to exclude approximately 100% of proteins from the samples in 2.0min, maintaining the same performance for about 300 analytical cycles. The method was validated in accordance with Food and Drug Administration (FDA) guidelines, being linear for all the determined analytes in their respective analytical ranges (coefficients of determination higher than 0.99) with limits of detection (LODs) and quantification (LOQs) ranging from 0.09 to 10.85μgL^-1 and from 0.30 to 36.17μgL^-1, respectively. High recovery values (88-112%) were obtained as well as suitable results for inter and intra-assay accuracy and precision. The method provided an analytical frequency of 5 samples per hour, including the sample preparation and separation/detection steps. The validated method was successfully used to analyze human serum samples of patients undergoing treatment with antihypertensive drugs, being useful for pharmacometabolomic, pharmacogenomic, and pharmacokinetic studies.