Application of thermal ultrasound-assisted liquid–liquid micro-extraction coupled with HPLC-UV for rapid determination of synthetic phenolic antioxidants in edible oils

A simple, fast, and reliable liquid–liquid micro-extraction (LLME) method assisted by thermal ultrasound approach was developed for simultaneous determination of synthetic phenolic antioxidants (SPAs) in edible oils by high-performance liquid chromatography equipped with ultraviolet detector (HPLC-UV). The synthetic antioxidants were propyl gallate (PG), butylated hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ), and butylated hydroxyltoluene (BHT). The best extraction conditions were observed were methanol/acetonitrile (1:1, v/v) as the solvent, ultrasound at 4 min, and a temperature of 40°C. The linearity of the calibration curves for the optimum conditions were R² > 0.989 for all of the SPAs in a range from 1–200 μg ml⁻¹. Relative standard deviation (RSD %) for five analysis was in range of 2.83% to 4.21%. Limit of detection (LOD) and limit of quantification (LOQ) were obtained in range of 0.012–0.06 and 0.04–0.2 μg g⁻¹, respectively. With regard to recovery, a range of 91%–116% was calculated for the spiked edible oils.     

Response surface methodology for optimization and determination of Riluzole by microfunnel magnetic stirring-assisted liquid–liquid microextraction coupled with high-performance liquid chromatography

ABSTRACT

A rapid, simple, and highly sensitive microfunnel magnetic stirring-assisted liquid–liquid microextraction coupled with HPLC was developed for determination of Riluzole (RLZ). The main extraction parameters were screened using the Plackett–Burman design and optimized by central composite design. Under optimum conditions, the calibration curve was linear over the range of 0.2–400 ng mL^?1, and RSD of 3.21% (n = 14, 20 ng mL^?1) proved to have good reproducibility. The detection limit was 0.023 ng mL^?1 and 1.5 ng mL^?1 for aqueous and biological samples, respectively. The tap water, human plasma, and urine samples showed excellent recoveries for RLZ (97.09–101.92%) via this method.     

Flotation-assisted homogeneous liquid–liquid microextraction for determination of thorium in water samples by inductively coupled plasma–mass spectrometry and Box–Behnken design

A fast, simple, and efficient method for extraction, preconcentration, and determination of thorium in water samples with acceptable recoveries based on flotation-assisted homogenous liquid–liquid microextraction combined with inductively coupled plasma–mass spectrometry (ICP-MS) is presented. Various parameters affecting the extraction efficiency were optimized by Box–Behnken design. Under the optimum conditions (concentration of dimethyl vinyl phosphonate = 2.4 × 10^–4 mol/L, pH = 6.5, n-heptane = 150 μL, and acetonitrile = 0.5 mL), the calibration graph was linear in the range of 10.0–400.0 ng/L for thorium. The limit of detection of this method was 2.62 ng/L, and the enrichment factor was estimated to be 136 for thorium.     

Vortex-assisted dispersive liquid–liquid microextraction trace amounts of melatonin prior to HPLC determination in fruit juice samples

In the present study, a fast, simple and sensitive vortex-assisted dispersive liquid–liquid microextraction method was developed for extraction and preconcentration of trace amounts of melatonin in fruit juice samples. The extraction conditions were optimized as extraction solvent, chloroform; volume of extracting, 200.0 μL; and vortex time, 120 s. The HPLC determinations were done using ODS Waters C₁₈ column under gradient elution. The calibration curve was linear in the range of 1.0–1000.0 ng mL^–1 and detection limit was 0.23 ng mL^–1. The validated method was applied for separation and determination of melatonin in different fruit juice samples (cherry, tomato and grape).     

Application of response surface methodology for optimization and determination of palladium by in-tube ultrasonic and air-assisted liquid–liquid microextraction coupled with flame atomic absorption spectrometry

A highly sensitive, simple and rapid in-tube ultrasonic and air-assisted liquid–liquid microextraction (IT-UAA-LLME) coupled with flame atomic absorption spectrometry was developed for preconcentration and determination of palladium (Pd) in soil and water samples. The effective parameters were optimized by the Plackett–Burman (P–B) and Box–Behnken design (BBD) methods. Under the optimum conditions, the calibration graph was linear over the range of 5–800 μgL^?1 (R² = 0.998). Detection limit, relative standard deviation (RSD) and the enrichment factor were 0.94 μgL^?1, 2.64% (n = 7, C = 40 μgL^?1) and 156, respectively. The proposed method was successfully applied for the determination of trace amounts of Pd in the soil and water samples.     

Determination of gold and palladium in environmental samples by FAAS after dispersive liquid–liquid microextraction pretreatment

A new dispersive liquid–liquid microextraction (DLLME) method is proposed for rapid separation, simultaneous extraction and preconcentration of gold and palladium at ultra trace amounts. The extraction of the analytes was performed in the presence of 5-[(E)-(2,6-diaminopyridine-3-yl)diazenyl]-1,3,4-thiadiazole-2-thiol (DAT) as chelating agent. Chloroform and acetone were used as extraction and dispersive solvents, respectively. The variables affecting the complexation and extraction conditions were optimized. The calibration curves were linear in the range of 1.1–85 and 0.9–124 μg L⁻¹ with the detection limits of 0.4 and 0.6 μg L⁻¹, and with the enrichment factors of 94 and 113 for Au and Pd, respectively. The precision (RSD%) was better than 2.4%. The accuracy of the method was verified by analysing the certified standard reference material (CDN–PGMS-10). The results show that the dispersive liquid–liquid microextraction pretreatment is a sensitive, rapid, simple and safe method for the separation/preconcentration of gold and palladium.     

Microfunnel magnetic stirring-assisted liquid–liquid microextraction method for determination of trace amounts of gold after optimization employing response surface methodology

ABSTRACT

A rapid, sensitive and simple technique was proposed for the preconcentration and determination of gold in the presence of N-methyl-N,N,N-trioctylammonium chloride (Aliquat 336) as ion pair forming agent employing microfunnel magnetic stirring-assisted liquid–liquid microextraction (MF-MSA-LLME) and flame atomic absorption spectrometry. Parameters were optimized by full factorial and Box-Behnken design. Under the optimum conditions, the calibration graph was linear in the range of 2.5–800.0 ng mL?¹ (r² = 0.998). Detection limit, enrichment factor and relative standard deviation were 0.6 ng mL?¹, 240.0 and 1.4% (n = 7, C = 100 ng mL^?1), respectively. This technique was successfully applied for the determination of gold in soil and water samples.     

Interference of 7-dehydrocholesterol in α-tocopherol determination by high-performance liquid chromatography: A possible screening test for the smith-lemli-opitz syndrome

7-Dehydrocholesterol (7-DHC), a normal cholesterol precursor, accumulates in plasma and tissues of patients affected by the Smith-Lemli-Opitz (SLO) syndrome, a recessive autosomic disease characterized by mental retardation and physical malformations. In these patients, we suspected that 7-DHC interfered with α-tocopherol (α-T) determination because this steroid could be coeluted with α-tocopherol acetate (α-TA), an internal standard commonly used for α-T determination, and because the conjugated dienic structure of 7-DHC strongly absorbs at 292 nm. The aim of this work was (i) to characterize the interfering material and (ii) to evaluate the possibility of a rapid screening test for SLO syndrome identification from 7-DHC determination by reverse-phase chromatography high-performance liquid chromatography (HPLC). Human plasmas (control and SLO syndrome) were extracted with hexane after ethanol protein precipitation and addition of ascorbic acid as protective agent plus α-TA or δ-tocopherol (δ-T) as internal standards. The dry hexane extract was used for HPLC, and trimethylsilyl ethers derivatives of the extracts were submitted to gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The material interfering in the α-T determination was unambiguously identified to 7-DHC by retention time (RT) relative to standard, RT relative to δ-T, and analysis of the eluted material by GC and by GC-MS. In α-T determination, the interference can be eliminated by using δ-T as internal standard instead of α-TA. Rapid detection and evaluation of 7-DHC in plasma appear to be possible by HPLC under the conditions described; comparison with the GC reference method suggests that the rapid HPLC determination of 7-DHC in plasma can be used within the 1–40 mg/dL range, values commonly found in SLO syndrome.     

Hydrodynemics of a cocurrent upflow liquid–liquid reciprocating plate reactor for homogeneously base-catalyzed methanolysis of vegetable oils

Hydrodynamics of a continuous cocurrent two-phase upflow reciprocating plate reactor (RPR) for homogeneously base-catalyzed methanolysis of sunflower oil was studied. Here, methanol constituted the dispersed phase and sunflower oil was the continuous phase. The measurements were performed in both the non-reactive (methanol–sunflower oil) and reactive (sunflower oil–methanol–KOH) systems. The main goal was to define the effects of the vibration intensity and the important reaction operating conditions on the pressure fluctuation at the reactor bottom, the power consumption, the dispersed phase holdup, the Sauter-mean drop diameter and the specific interfacial area. The power consumption under batch, single- and two-phase flow was proved to depend on the vibration intensity. The Sauter-mean drop diameter was found to depend on the specific power consumption in accordance with the turbulent model due to the turbulent energy dissipation in well-mixed regions around perforated plates. The simplified correlation of Kumar and Hartland could be used for estimating the Sauter-mean drop diameter. The energy dissipation due to reciprocating plate motion and the superficial dispersed phase velocity affected the dispersed phase holdup and the specific interfacial area. The present results are crucial for designing RPRs for application in continuous base-catalyzed methanolysis of vegetable oils.     

Analysis of the addition products of α-tocopherol with phosphatidylcholine-peroxyl radicals by high-performance liquid chromatography with chemiluminescent detection

A chemiluminescence-based high-performance liquid chromatographic method was developed for the analysis of the addition products of α-tocopherol with phosphatidylcholine-peroxyl radicals (TOO-PC). The TOO-PC eluted from a reversed-phase column was reacted with a chemiluminescent reagent consisting of a Cypridina luciferin analog and a lipid-soluble iron chelate in acidic methanol at 50°C, and the generated chemiluminescence was monitored. The detection limit for TOO-PC by this method was about 1 pmol. This method was applied to the detection of TOO-PC in the peroxidized membranes prepared from rabbit erythrocyte ghosts. When the erythrocyte ghosts were peroxidized by the addition of a water-soluble free radical initiator, a peak corresponding to TOO-PC was detected on the chromatogram with chemiluminescent detection. The amount of TOO-PC in the erythrocyte membranes increased with the depletion of endogenous α-tocopherol. The results indicate that this method proved useful for the detection of the TOO-PC formed by the peroxyl-radical scavenging reactions of α-tocopherol in biological systems.     

Structure-retention correlation of isomeric bile acids in inclusion high-performance liquid chromatography with methyl β-cyclodextrin

The structure-retention correlation of various C₂₄ bile acid isomers was studied by the addition of methyl β-cyclodextrin (Me-β-CD) to mobile phases in reversed-phase high-performance liquid chromatography (HPLC). The compounds examined include a series of monosubstituted bile acids related to cholanoic acids differing from one another in the position and configuration of an oxygen-containing function (hydroxyl or oxo group) at the position C-3, C-6, C-7, or C-12 and the stereochemistry of the A/B-ring fusion (trans 5α-H and cis 5β-H) in the steroid nucleus. The inclusion HPLC with Me-β-CD was also applied to biologically important 4β- and 6-hydroxylated bile acids substituted by three to four hydroxyl groups in the 5β-steroid nucleus. These bile acid samples were converted into their fluorescence prelabeled 24-pyrenacyl ester derivatives and chromatographed on a Capcell Pak C₁₈ column eluted with methanol-water mixtures in the presence or absence of 5 mM Me-β-CD. The effects of Me-β-CD on the retentions of each compound were correlated quantitatively to the decreasing rate of capacity factors and the relative strength of host-guest inter-actions. On the basis of the retention data, specific and nonspecific hydrogen-bonding interactions between the bile acids and the Me-β-CD were discussed.     

Squalene in oils determined as squalane by gas—liquid chromatography after hydrogenation of methyl esters

Low levels (≤0.1%) of squalene were anticipated in oils from the blubber of the harp seal Phoca groenlandica. The traditional roule of saponification and analytical examination of the total unsaponifiables was unattractive. A method developed for squalene in olive oil, reportedly present in the range of 0.3–0.7%, was based on total conversion of the oil to methyl ester of fatty acids by alkali transesterification, followed by hydrogenation over Adam's catalyst (PtO₂). The analysis of the fully saturated methyl esters and any squalane produced concurrently was by gas—liquid chromatography. This method was satisfactory for the small amounts, 0.03% or less, of squalene in seal oil and is also illustrated for olive oil. A flame-ionization detector excessive response of approximately 25% was observed for all levels of squalene tested. The calculated factor of 1.22 should be applied to the peak area for squalane due to the higher response of hydrocarbons relative to the methyl esters of fatty acids and the system of oil components if reporting as fatty acids. Presented in part at the Annual Meeting of the Canadian Section of the American Oil Chemists' Society, London, Oct. 15–18, 1999.     

Analytical approaches for the determination of cobalt,nickel and copper by aeration-assisted homogeneous liquid–liquid microextraction and flame atomic absorption spectrometry

A new aeration-assisted homogeneous liquid–liquid microextraction using high-density solvent for determination of copper, nickel and cobalt, as a prior step to their determination, coupled to flame atomic absorption spectrometry is presented. Under the optimum conditions, the calibration graphs were linear in the range of 5.0–600.0 ng/mL for copper, 10.0–450.0 ng/mL for nickel and 8.0–500.0 ng/mL for cobalt. The limits of detection were 1.3, 3.6 and 2.7 ng/mL and the enrichment factor estimated to be 350, 340 and 360, for copper, nickel and cobalt, respectively. The proposed method was successfully applied for the determination of these cations in different samples.     

Simultaneous determination of RRR- and SRR-α-tocopherols and their quinones in rat plasma and tissues by using chiral high-performance liquid chromatography

We established a method to simultaneously determine RRR- and SRR-α-tocopherol (α-Toc) and their quinones in biological samples by chiral-phase high-performance liquid chromatography (HPLC). α-Toc had a shorter retention time than α-tocopherylquinones (α-TQ), and 2-ambo-α-Toc was completely separated into two peaks; the first peak was RRR-α-Toc and the second SRR-isomer by chiral HPLC connected Chiralcel OD-H column and Sumichiral OA4100 column. In contrast, of the two peaks of α-TQ, the first was the SRR-isomer. We also investigated differences in the distribution of RRR- and SRR-α-TQ in rat tissues after oral administration of 2-ambo-α-Toc by the above HPLC method. Rats deficient in vitamin E were divided into two groups, control and experimental, and tissues were collected at 3, 6, and 24 h after oral 2-ambo-α-Toc administration. The concentrations of RRR- and SRR-α-Toc and their quinones in plasma and each tissue were determined. The concentration of SRR-α-TQ in plasma and adrenal glands was not significantly different from RRR-α-TQ. However, the concentration of SRR-α-TQ in liver up to 6 h after oral administration was higher than that of RRR-α-TQ, and SRR- and RRR-α-TQ levels were similar at 24 h after oral administration. Therefore, we may assume that the formation of α-TQ in vivo was not different between RRR- and SRR-isomer and that it was not affected by the presence of α-Toc stereoisomers.     

Determination of (+)-, (−)-, and total gossypol in cottonseed by high-performance liquid chromatography

Gossypol, a pigment in cottonseed, is a polyphenolic, binaphthyl dialdehyde. Due to steric hindrance between the functional groups of the molecule at the bond connecting the two naphthyl rings, gossypol exists as (+)- and (−)-isomers. Gossypol is physiologically active with the (−)-isomer appearing to be more active and causing temporary infertility in males. It is thus important to know the amounts of isomers in livestock feeds. A quantitative high-performance liquid chromatography (HPLC) procedure was developed for the separation of (+)- and (−)-gossypol contained in cottonseed. This method involves derivatization of gossypol with (R)-(−)-2-amino-1-propanol followed by HPLC separation employing either a Phenomenex Prodigy (5 μ, ODS-3, 100 × 3.2 mm) or a MetaChem Inertsil (5 μ, ODS-3, 100 × 3.0 mm) reversed-phase column eluted with 80% acetonitrile and 20% 10 mM KH₂PO₄ adjusted to pH 3.0 with H₃PO₄ at 1.0 mL/min. The (+)- and (−)-gossypol-2- amino-1-propanol complexes eluted at roughly 1.4 and 2.6 min, respectively. It was found that gossypol from Upland (Gossypium hirsutum) seed was rich in the (+)-enantiomer, with the (+)- and (−)-enantiomers in a ratio of about 65:35, respectively, while gossypol from the seed of a Pima (G. barbadense) cultivar (S-6) was slightly richer in the (−)-enantiomer (46.8:53.2). Deceased.     

Numerical simulation of micro-mixing in gas–liquid and solid–liquid stirred tanks with the coupled CFD-E-model

The coupled CFD-E-model for multiphase micro-mixing was developed, and used to predict the micro-mixing effects on the parallel competing chemical reactions in semi-batch gas–liquid and solid–liquid stirred tanks. Based on the multiphase macro-flow field, the key parameters of the micro-mixing E-model were obtained with solving the Reynolds-averaged transport equations of mixture fraction and its variance at low computational costs. Compared with experimental data, the multiphase numerical method shows the satisfactory predicting ability. For the gas–liquid system, the segregated reaction zone is mainly near the feed point, and shrinks to the exit of feed-pipe when the feed position is closer to the impeller. Besides, surface feed requires more time to completely exhaust the added H⁺ solution than that of impeller region feed at the same operating condition. For the solid–liquid system, when the solid suspension cloud is formed at high solid holdups, the flow velocity in the clear liquid layer above the cloud is notably reduced and the reactions proceed slowly in this almost stagnant zone. Therefore, the segregation index in this case is larger than that in the dilute solid–liquid system.     

Preparation of melamine–formaldehyde resin grafted by (3-aminopropyl) triethoxysilane for high-performance hydrophobic materials

Aiming at meeting the specific market demands and expanding the downstream application of melamine–formaldehyde (MF) resins, a series of (3-aminopropyl) triethoxysilane (APTES) grafted MF (MF-Si) resins were synthesized via an effective method that minimized the hydrolysis of APTES and overcame the polarity discrepancy of APTES with MF resin matrix. The structure of MF-Si resins was characterized by FTIR spectroscopy, Raman spectroscopy, ¹H nuclear magnetic resonance (NMR), and solid state ¹³C NMR. It was found that APTES moieties in MF-Si materials afforded increased hydrophobicity, water resistance, and the thermal stability was not affected. With the increasing amount of APTES, the water contact angle of MF-Si films increased from 70.56 to 105.92°and the surface free energy decreased from 46.8 to 23.5 mN/m. The temperature of maximum weight loss rate (T_dmax) of MF-Si materials decreased slightly from 371.15 to 353.70 °C and the ultimate residual weight of MF-Si materials increased from 12.51 to 30.04% at 800 °C under N₂. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48664.     

Microfunnel magnetic stirring-assisted dispersive liquid–liquid microextraction-derivatization technique,for the determination of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (Mutagen X) in aqueous samples by GC-ECD

A simple, highly sensitive and reliable microfunnel magnetic stirring-assisted dispersive liquid–liquid microextraction method (MF-MSA-DLLME) was developed based on the derivatization of mutagen X in aqueous samples and determined using gas chromatography with electron capture (GC-ECD). The effects of different variables on the extraction efficiency were investigated and optimized. The calibration curve showed good linearity in the concentration range of 0.05–400 μgL^?1 (r² = 0.998) and precision (RSD = 5.0%). Under optimum conditions, the limit of detection (LOD) and the limit of quantification in drinking water were 0.015 and 0.05 µg L^?1, respectively. The developed method was successfully applied for the determination of six Mutagen X (MX) in real samples.     

Algebraic conditions,in terms of the solvent partition constants,for the separation of chemical classes by gas–liquid chromatography

The interdependence between the solvation Gibbs energy of several functional groups and the solvent partition coefficients was studied, starting from gas chromatographic data. Single-parameter relationships were derived for the –OH, -CHO, -CO, -O-,-COO (acetate), -COO (methyl ester)-, and -CN group increments. The obtained equations were found to be temperature independent, and could be successfully used for the evaluation of 19 stationary phases with respect to certain separation questions. The selectivity problem was converted into an inequality system. The graphical solution of such a system provides an image of the separation abilities of a sorbent material with respect to a given pair of solutes, and allows an efficient comparison of a great number of stationary phases. The graphs are also illustrative for the temperature effect on the selectivity features.