Hydrophilic Solvents Research Articles

Green solvents for the selective extraction of bioactive compounds from by-products of the coffee production chain

Approximately 15–20 million tonnes of by-products were generated globally in the coffee production chain during the 2020/21 season. The current uses for these by-products are inadequate or contribute to environmental degradation. This work reports the screening of hydrophilic and hydrophobic solvents, including deep eutectic solvents (DES), for their ability to extract the valuable metabolites caffeine and chlorogenic acid (markers in commercial extraction) from four coffee-related by-products. Water was the best solvent for recovering caffeine and chlorogenic acid from defective green coffee beans, while all hydrophilic DES surpassed water in the extraction of chlorogenic acid from coffee pulp. For the two remaining by-products, at least one DES was as good or better at extracting the caffeine or chlorogenic acid compared to water. The array of hydrophobic solvents tested here showed different selectivities, allowing the annotation of 12 compounds that have not been previously reported in coffee by-products. These results demonstrate the ability to obtain a new and controllable range of extracts from coffee by-products using green and functional solvents.

Combination of switchable hydrophilic solvent liquid-liquid microextraction with QuEChERS for trace determination of triazole fungicide pesticides by GC-MS.

This work first proposed a novel green and efficient method based on Quick, Easy, Cheap, Efficient, Rugged, and Safe pretreatment (QuEChERS) combined with switchable hydrophilic solvent homogeneous liquid-liquid microextraction (SHS-HLLME) for trace determination of triazole fungicides (TFs) in agricultural products such as vegetables and fruits by gas chromatography-mass spectrometry (GC-MS). N,N-Dimethyl benzylamine was used for the synthesis of SHS. Box-Behnken design was applied for the optimization of extraction conditions and a mathematical model was obtained. Ultimately, 0.50mL SHS, 1.0mL 10molL-1 sodium hydroxide, and 45s ultrasonic time were determined as optimal conditions for the SHS-HLLME method. The limit of detection and limit of quantification determined using the optimal method (SHS-HLLME/GC-MS) were 0.13-0.27ngmL-1 and 0.43-0.90ngmL-1, respectively. In addition, the SHS-HLLME method under optimal conditions was combined with the traditional QuEChERS method to realize the advancement of the SHS-HLLME method from simple to complex matrix analysis, and the QuEChERS-SHS-HLLME method was successfully applied to the analysis of TFs in cucumbers, tomatoes, watermelon and grapes in agricultural products. Matrix-matched calibration standards were used to improve the accuracy of TFs in spiked cucumber samples to obtain recovery results close to 100%. It was shown that the new method is green and rapid, enabling fast and inexpensive sample pretreatment with up to 100-fold enrichment factor and low detection limit compared with the original QuEChERS method.

Impact of organic solvents on the catalytic performance of halohydrin dehalogenase

Biocatalytic transformations in organic synthesis often require the use of organic solvents to improve substrate solubility and promote the product formation. Halohydrin dehalogenases (HHDHs) are enzymes that catalyze the formation and conversion of epoxides, important synthetic class of compounds that are often sparingly soluble in water and prone to hydrolysis. In this study, the activity, stability, and enantioselectivity of HHDH from Agrobacterium radiobacter AD1 (HheC) in form of cell-free extract were evaluated in various aqueous-organic media. A correlation was discovered between the enzyme activity in the ring-closure reaction and logP of the solvent. Knowledge of such a relationship makes biocatalysis with organic solvents more predictable, which may reduce the need to experiment with a variety of solvents in the future. The results revealed a high enzyme compatibility with hydrophobic solvents (e.g., n-heptane) in terms of activity and stability. Regarding the HHDH applicability in an organic medium, inhibitions by a number of solvents (e.g., THF, toluene, chloroform) proved to be a more challenging problem than the protein stability, especially in the ring-opening reaction, thus suggesting which solvents should be avoided. In addition, solvent tolerance of the thermostable variant ISM-4 was also evaluated, revealing increased stability and to a lesser extent enantioselectivity compared to the wild-type. This is the first time such a systematic analysis has been reported, giving insight into the behavior of HHDHs in nonconventional media and opening new opportunities for the future biocatalytic applications. KEY POINTS: • HheC performs better in the presence of hydrophobic than hydrophilic solvents. • Enzyme activity in the PNSHH ring-closure reaction is a function of the logP. • Thermostability of ISM-4 variant is accompanied by superior solvent tolerance.

Comparison of the effect of zinc oxide nanoparticles and extract of Acorus calamus applied topically on surgical wounds inflicted on the skin of rabbits.

Antibiotics are used for postsurgical wound healing purposes but unfortunately, resistance against them demands some alternatives for quick recovery. Sepsis of wounds is a challenge for medical as well as veterinary professionals. Nanoparticles have significant advantages in wound treatment and drug resistance reversal. This study was conducted to appreciate emerging alternates of antibiotics like zinc oxide nanoparticles and plant extracts in topical application. Zinc oxide is considered a good wound healer and its nanoparticles are easy to access. So, the efficacies of zinc oxide nanoparticles and sweet flag plant extract ointments were tested to compare modern and traditional therapeutics as sweet flag is considered a pure medicinal plant. Rabbits were selected for this study due to the healing properties of their skin. Wounds were inflicted on the thoracolumbar region and treated for 29 days post-surgically daily with normal saline and the ointment of zinc oxide nanoparticles and sweet flag extract ointment, prepared in a hydrophilic solvent. Wound shrinkage was observed daily and histopathological analysis was made and results were compared. Zinc oxide nanoparticles ointment showed the most satisfactory results for every parameter included in the study. No side effects of its topical application were observed. Healing was normal without any complications. The preparations of zinc oxide nanoparticles may help in the era of antibiotic resistance as topical drugs in the future.

Performance of hydrophobic physical solvents for pre-combustion CO2 capture at a pilot scale coal gasification facility

Here, we present the first pilot plant data for hydrophobic physical solvents for CO2 and H2S removal from coal-derived H2-rich syngas. Four physical solvents were tested under pre-combustion CO2 capture conditions at bench scale and pilot plant scale: one baseline hydrophilic solvent and three hydrophobic solvents. The solvents were: (1) polyethylene-glycol-dimethyl ether (PEGDME), a hydrophilic solvent analog for the commercial process Selexol, (2) tributyl- phosphate (TBP), a commercially available hydrophobic solvent, (3) polyethylene glycol-poly(dimethylsiloxane) (PEG-PDMS-3), and (4) diethyl sebacate (CASSH-1), a novel, computationally screened hydrophobic solvent developed by the National Energy Technology Laboratory (NETL). All solvents were studied under pure gas (CO2/N2/H2/CH4) equilibrium conditions at NETL followed by pilot plant testing with syngas at the University of North Dakota Energy & Environmental Research Center (UND EERC). Long term performance of CASSH-1 and PEDGME was then assessed with results compared to process simulation predictions. Within experimental uncertainties, all solvents showed comparable CO2 absorption performance at above room temperature operation while the hydrophobic solvents had limited water uptake and low vapor pressure, which alleviates concerns related to corrosion, water absorption, and solvent loss to evaporation. These results indicate low viscosity, low vapor pressure hydrophobic solvents are a promising option for lower cost CO2 capture from high pressure syngas applications.

Switchable hydrophilicity solvent based microextraction of mercury from water, fish and hair samples before its spectrophotometric detection

Mercury is highly toxic even at trace levels and causes severe health problems in human beings. Therefore, proper extraction, preconcentration and quantification of Hg2+ in different samples are highly important. The present work is based on the preconcentration of Hg2+ in water, hair and fish samples using switchable hydrophilicity solvent-based liquid-liquid microextraction (SHS-LLME) before its quantification by UV–visible spectrophotometry. 2-(5-Bromo-2-pyridylzo-5-(diethylamino)phenol) (5-Br-PADAP) was used to form colored complex with Hg2+. Optimization studies show that at pH 8 maximum % recovery of the Hg2+ was obtained with 400 μL of extraction solvent. The amount of 5-Br-PADAP (20 μg) was enough for the complete derivatization of Hg2+ to Hg2+-5-Br-PADAP. The maximum volume of the sample was optimized as 20 mL up to which the analyte can be quantitatively extracted. Figures of merits like detection and quantification limits (n = 7) were calculated as 0.014 ng mL−1 and 0.048 ng mL−1, respectively. The relative standard deviation was determined as 5.6 for (n = 7) repeated determinations. Preconcentration and enhancement factors originated as 50 and 48, respectively. Validation was done using certified reference materials like TMDA 53.3 water and NCS ZC81002B human hair and water, hair and fish samples.

Dissolution dynamics of a binary switchable hydrophilicity solvent-polymer drop into an acidic aqueous phase.

Switchable hydrophilicity solvents (SHSs) are solvents defined by their ability to switch from their hydrophobic form to a hydrophilic form when brought into contact with an acidic trigger such as CO2. As a consequence, SHSs qualify as promising alternatives to volatile organic compounds during industrial solvent extraction processes, as greener and inexpensive methods can be applied to separate and recover SHSs. Furthermore, because of their less volatile nature, SHSs are less flammable and so increase the safety of a larger scale extraction process. In this work, we study the dynamics and in-drop phase separation during the dissolution process of a drop composed of a SHS and a polymer, triggered by an acid in the surrounding aqueous environment. From 70 different experimental conditions, we found a scaling relationship between the drop dissolution time and the initial volume with an overall scaling coefficient of ∼0.53. We quantitatively assessed and found a shorter dissolution time related to a decrease in the pH of the aqueous phase or an increase in the initial polymer concentration in the drop. Examining the internal state of the drop during the dissolution revealed an in-drop phase separation behavior, resulting in a porous morphology of the final polymer particle. Our experimental results provide a microscopic view of the SHS dissolution process from droplets, and findings may help design SHS extraction processes for particle formation from emulsions.

One-step effervescence tablet-assisted switchable hydrophilic solvent microextraction combined with micro spectrophotometry for the determination of copper in Salvia yunnanensis and environmental samples

In this work, an efficient one-step effervescence tablet-assisted switchable hydrophilic solvent microextraction (ETA-SHS-ME) method was developed and firstly combined with micro ultraviolet-visible (micro UV-Vis) spectrophotometry for the determination of trace copper (Cu) in natural medicine Salvia yunnanensis and environmental samples (water and soil). The extraction was rapidly accomplished in one step by transferring the effervescence tablet into the aqueous sample, the proton donor agent (malonic acid) contained in the tablet reacted simultaneously with the organic phase source (sodium nonanoate) and the effervescent agent (sodium bicarbonate, NaHCO3) to produce the extractant nonanoic acid and CO2. The in situ generated CO2 promoted the dispersion of nonanoic acid in the aqueous sample and improved the extraction efficiency of the analytical method. Under the optimal conditions, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.01 and 0.04 μg/L, respectively, and the enhancement factor (EF) was 76.3. The developed method was successfully applied to the analysis of trace Cu in natural medicine and environmental samples. The one-step extraction method coupled with portable spectrophotometer has a good prospect for application in field analysis.

Green approach to extract bioactive compounds from orange peel employing hydrophilic and hydrophobic deep eutectic solvents

Consumer interest in natural products with advantageous biological impacts on their health has increased in recent years. Therefore, academic and industrial communities have concentrated their research on developing sustainable techniques for extracting bioactive compounds from natural resources. In the present study, extracts rich in bioactive compounds from orange peel were obtained using novel hydrophilic and hydrophobic deep eutectic solvents (DESs). Bioactive compounds such as carotenoids and polyphenols, their stability, antioxidant capacity, permeability, and biological activity were determined to consider their inclusion in food formulations. The results demonstrated that the highest total carotenoid values were obtained with hydrophobic DESs using DL-Menthol: camphor (163.5 ± 1.1 mg/100gfw), DL-Menthol: Eucalyptol (168.7 ± 1.7mg/100gfw), and lauric acid: octanoic acid (153.1 ± 7.1 mg/100gfw). Total polyphenols were higher in hydrophilic DESs such as proline: malic acid (282.8 ± 7.3 mg/100gfw). The antioxidant values showed that hydrophobic extracts have higher antioxidant activity than traditional solvents. Carotenoid stability was also improved using DL-Menthol: camphor, while lactic acid: glucose and proline: malic acid showed a better capacity to stabilize polyphenols. To simulate carotenoid and polyphenol permeation, the Parallel Artificial Membrane Permeability Assay (PAMPA) was used and demonstrated that DESs can enhance the permeability of these bioactive compounds. Biological tests were also performed, and the antiproliferative effect in HeLa cells showed only 26.70% cell viability in DL-Menthol: camphor extracts. Based on the presented results, DESs can be used to extract hydrophilic and hydrophobic compounds from orange peels, and the obtained extracts could be included in food formulations, avoiding the solvent elimination process.

An innovative simplified one-pot process for Astaxanthin purification from Paracoccus carotinifaciens

Astaxanthin (ASX) is a carotenoid with several applications in the food and pharmaceutical fields which is recognised as having a higher physiological and commercial value when it is biologically rather than chemically sourced. This work experimentally investigates the bio-fractionation of biomass of the Paracoccus carotinifaciens bacterium by extraction with the switchable hydrophilicity solvent N,N-dimethyl cyclohexylamine (DMCHA) to obtain ASX and related carotenoids in separate form. This is done by means of a sequential process carried out in a single apparatus. DMCHA gave an extraction yield in terms of equivalent ASX extracted per unit mass of processed dry microbial biomass (62.5 %) higher than acetone (48 %) and ethanol (14 %). After the DMCHA was washed from the extract with carbonated water, 88.2 % of the extracted ASX was recovered. The possibility of extracting carotenoids with recycled solvent with a minor (-7.7%) efficiency drop was also demonstrated, as was the lower energy footprint of DMCHA-based than competing volatile solvent-based extraction processes.

Selective Conversion of Glucose to Levulinic Acid Catalyzed by HPAs/MOF-5 in a Hydrophilic Eutectic Solvent System

Selective Conversion of Glucose to Levulinic Acid Catalyzed by HPAs/MOF-5 in a Hydrophilic Eutectic Solvent System

Evaluation of Antioxidant Capacity (ABTS and CUPRAC) and Total Phenolic Content (Folin-Ciocalteu) Assays of Selected Fruit, Vegetables, and Spices.

Antioxidant (AOX) capacity assays are important analytical tools, used worldwide to measure the AOX capacities of various food commodities. Although numerous protocols have been published to ascertain AOX capacities, there are increasing concerns about the reliability of many of these assays. Poor correlation of results between various assays, as well as problems with reproducibility, consistency, and accuracy, is to blame. Published AOX assays also differ markedly from each other by employing different reaction conditions, using different extracting solvents, and applying dissimilar quantification methods. In this study, AOX capacities of a range of fruit, vegetables, and spices, commonly consumed and of commercial importance in Australia and worldwide, were measured in both hydrophilic and lipophilic solvents by using two different assay systems. As the polyphenolic compounds present in any sample matrix are the main contributors to its AOX properties, the commodities were also analysed for total phenolic content (TPC), again using both solvent systems. Analysis of the results from the current study with values from the published literature exposed the challenges that make direct comparison of any quantitative results difficult. However, a strong mutual correlation of our assay results facilitated a meaningful comparison of the data within the laboratory. Concurrent use of lipophilic and hydrophilic solvents made the results more reliable and understandable. Findings from this study will aid to address the existing challenges and bring a more rational basis to the AOX capacities. This unique analytical approach also provided a platform to build an internal reference database for the commonly consumed and commercially important food commodities with the potential to broaden the scope into a database for similar food matrices.

FORMULATION AND EVALUATION OF PARENTERAL IN-SITU FORMING BIODEGRADABLE IMPLANT FOR CONTROLLED RELEASE OF LEVOTHYROXINE SODIUM

Objective: The objective of present research work is formulation and evaluation of parenteral in-situ forming biodegradable implant for controlled release of levothyroxine sodium. Material and Method: The present study used N-Methyl pyrrolidone (NMP) and triacetin as solvents and PLGA as a biodegradable polymer to manufacture two biodegradable polymeric drug delivery systems, in-situ forming implant (ISFI) and in-situ micro particles (ISM). Other evaluation tests, such as sterility, percent drug entrapment capacity, and so on, were also carried out. ISFI and ISM were tested for up to one month at three different temperatures (4ºC, 25ºC, and 40ºC). Result and Discussions: The drug release from both systems was compared. The polymer content, type of solvent (hydrophilic or hydrophobic), and implant morphology all contributed to increased burst release in the ISFI formulation. Burst release was decreased using a combination of hydrophilic and hydrophobic solvents (NMP and Triacetin). When compared to other formulations, ISM had the lowest burst release. Both the ISFI and ISM formulations might deliver medications for up to 30 days. Long-acting Levothyroxine sodium formulations (ISFI & ISM) may be a superior option for hypothyroidism treatment. Keyword: In-situ Implant, Biodegradable polymers, PLGA, Long term release, Solvent exchange technique, ISFI, ISM.

Partition of Amino Acids in Aqueous Two-Phase Systems Comprising Hydrophilic Organic Solvents and Salts

An aqueous two-phase system (ATPS) comprising a hydrophilic organic solvent and inorganic salt is advantageous because of its high polarity, low viscosity, and low cost. In this work, nine amino acids were partitioned in an ATPS that comprised hydrophilic organic solvents (2-methyl-2-propanol, tetrahydrofuran, and 2-propanol) and salts (Na2SO4, K2HPO4, and (NH4)2SO4). Amino acids were successfully extracted using different combinations of solvents and salts. The distribution ratio of amino acids in the ATPS containing ammonium sulfate increased with an increase in their hydrophobicity, except for that of alanine. The specific extraction of alanine was observed because of its salting-out effect in ammonium sulfate solution. The sulfate salts of amino acids exhibited higher extractability than amphoteric amino acids.

Preparation of Surface-Supported Polylactide Spherical-Cap Particles.

Biodegradable polymer particles are of considerable importance due to their multiple applications in medical diagnostics and therapy. Spherical-cap particles have been prepared in a very general and simple method by melting a thin polymer film supported on a solid substrate that is in contact with a hydrophilic solvent. The melted polymer forms droplets which transform into solid particles attached to the surface after cooling down the sample. This approach has been demonstrated for polylactide adlayers on glass, which, when melted in glycerol, produce an array of polymer particles supported on the surface. The size of the particles depends on the experimental conditions and ranges from tens of nanometers to several micrometers. The particles can be employed to incorporate guest species, for example, drug molecules or inorganic nanoparticles. This has been confirmed herein through entrapment of an anticancer drug (doxorubicin) and radiogold (Au-198) nanoparticles. The resulting structures have been examined using a number of complementary physicochemical techniques including scanning and transmission electron microscopy, atomic force and optical microscopy as well as Raman and fluorescence spectroscopy.

Evaluation of blood lead levels in opium addicts and healthy control group using novel deep eutectic solvent based dispersive liquid-liquid microextraction followed by GFAAS.

Today, drug dealers and sellers add lead compounds to these substances to get more profit. As a result, drug users are heavily exposed to lead, and lead poisoning is clearly seen in most of them. Therefore, it is especially important to check the blood lead levels in these people. In this research, an efficient and eco-friendly pretreatment method was established by deep eutectic solvent for dispersive liquid-liquid microextraction (DES - DLLME) followed by graphite furnace atomic absorption spectrometry (GFAAS) analysis. The selected hydrophilic deep eutectic solvent consists of l-menthol and (1S)-( +)-camphor-10-sulfonic acid (CSA) at a 5:1 molar ratio as a green solvent instead of traditional toxic organic solvents. Under the optimal extraction conditions, the introduced method exhibited good linearity with coefficient of determination (r2) 0.9975 and an acceptable linear range of 0.3-80µg L-1. Accordingly, the detection limit was 0.1µg L-1 (S/N = 3) for lead ions, and the high enrichment factor (240) was obtained. The proposed method was successfully applied to analysis lead ions in real blood samples, which is a promising technique for biological samples. The case samples were classified and analyzed based on age, duration of consumption, and type of substance. The results showed that there was no significant difference between blood lead levels in different age groups and different duration of use, while blood lead levels were higher in opium residue (shireh) users than in opium users.

Volumetric and transport properties of switchable-hydrophilicity solvent systems: N,N-Dimethylbutylamine, water and carbon dioxide

Switchable-hydrophilicity solvents (SHSs) are an emerging class of solvents with switchable phase behavior. They can be used as a substitute for volatile solvents and can be removed from organic products without distillation. However, the detailed physical properties data of SHSs are still very scarce in the literature. In this work, the experimental values densities, dynamic viscosities, refractive indices as well as conductivities of switchable hydrophilicity solvent (SHS)systems (N,N-Dimethylbutylamine (DMBA), water, and carbon dioxide) are investigated at temperatures (283.15, 288.15, 293.15, 298.15, 303.15 and 308.15) K and at atmospheric pressure. VLE of the CO2 loaded DMBA solutions are measured at 298.15 K over the partial pressure range of carbon dioxide from 17.0 to 98.0 kPa. Density data have been used to calculate the apparent molar volumes (Vϕ), limiting apparent molar volumes (Vϕ0) and limiting partial molar expansivity of solute (Eϕ0). The Jones-Dole coefficients B, the Gibbs free energies of activation of viscous flow per mole of solvent (Δμ10≠) and per mole of solute (Δμ20≠), entropies (ΔS20≠) and enthalpies (ΔH20≠) of activation of viscous flow were calculated from experimental viscosity data and discussed in terms of transition state theory. The Walden's product was calculated from the conductance and dynamic viscosity data. The results are valuable sources of information on the design and development of SHSs for novel industrial applications.

Oil-Based Drilling Cuttings from Shale Gas Wells Treated with CO2 Switchable Hydrophilic Solvents: Priority Pollutant Migration and Produced Wastewater Assessment

The exploitation of shale gas resources brings in abundant hazardous oil-based drilling cuttings (ODBCs). Herein, N, N-Dimethylcyclohexylamine (DMCHA) acted as the CO2 switchable hydrophilic solvents (SHSs), and the OBDCs treated with DMCHA were studied, especially priority pollutant migration and produced wastewater assessment during the extraction process. The petroleum hydrocarbon content of OBDCs decreased from 10.73 to 0.84 wt% after the DMCHA extraction was conducted at a DMCHA/OBDCs liquid–solid ratio of 20:1, 35 °C, and 200 rpm for 30 min. Using the CO2 switchability of SHSs, the petroleum hydrocarbon and DMCHA were recovered. There was wastewater, which was produced after recovering DMCHA, and the produced wastewater assessment showed that chemical oxygen demand, 5-day biochemical oxygen demand, total nitrogen, total organic carbon, and petroleum were 561.00, 238.00, 40.60, 309.00, and 0.27 mg/L, respectively. Meanwhile, phenols (0.0031 mg/L), naphthalene (0.0000129 mg/L), phenanthrene (0.000059 mg/L), anthracene (0.000058 mg/L), as well as heavy metal ions such as Cu (0.01 mg/L) could be detected in the produced wastewater. As a result, a priority pollutant migration mechanism from ODBCs to the produced wastewater was proposed. This would be helpful for the better management policy making of the ODBCs treated by using CO2 SHSs and the produced wastewater.

Dispersive Liquid‐Liquid Microextraction (DLLME) Based on Solidification of Switchable Hydrophilicity Solvent Coupled with High‐Performance Liquid Chromatography (HPLC) with Photodiode Array (PDA) Detection for the Determination of Pyrethroid Pesticides in Grains

Rapid dispersive liquid-liquid microextraction (DLLME) based on the solidification of a switchable hydrophilicity solvent (SHS) was established for the preconcentration of pyrethroid pesticides from grain prior to determination using high‐performance liquid chromatography (HPLC) with photodiode array (PDA). Lauric acid was selected to be the switchable hydrophilicity solvent due to its conversion between hydrophobic and hydrophilic forms and solidification at low temperature, thereby avoiding a time-consuming centrifugation step. The results show that the optimal conditions for pyrethroid pesticides included 30 mmol/L lauric acid, hydrochloric acid as the hydrogen donor, a 1:1.8 stoichiometric ratio of sodium laurate and hydrochloric acid, an extraction temperature of 50 °C, an extraction time of 8 min, and a solidification time of 3 min. Under the optimal conditions, this approach provided a high enrichment factor (308.4 to 330.2), a short pretreatment period of less than 15 min, and sensitive detection limits from 5 to 20 ng/g suitable for the analysis of food. The method was employed for the determination of pyrethroid pesticides in grain. The recoveries were 84.3% to 115.7%, and the relative standard deviation was less than 9.9%.

Ultrasonic-assisted dispersive liquid–liquid microextraction based on hydrophilic deep eutectic solvents: Application to lead and cadmium monitoring in water and food samples

A green and innovative ultrasonic-assisted dispersive liquid–liquid microextraction using hydrophilic deep eutectic solvents (UA-HDES-DLLME) was developed for the selective and simultaneous extraction and enrichment of Pb (II) and Cd (II) in water and food samples for flame atomic absorption spectrometry. Several natural deep eutectic solvents (NADES) were used for the preparation of six different HDES and methyl violet was used as chelating reagent. Effective parameters such as pH, sonication time, methyl violet amount, DES type, dispersive solvent types, etc were optimized. Relative standard deviation (RSD) and preconcentration factor (PF) were 4.0% and 80. Low limits of detection (LOD, 1.3 ng mL−1 for Pb (II) and 0.33 ng mL−1 for Cd (II)) and quantification (LOQ, 4.0 ng mL−1 for Pb (II) and 1.0 ng mL−1 for Cd (II)) were found. The method accuracy was confirmed with analyses of certified reference materials.