Homogeneous liquid–liquid extraction combined with high performance liquid chromatography–fluorescence detection for determination of polycyclic aromatic hydrocarbons in vegetables

In this article, homogeneous liquid–liquid extraction (HOLLE), combined with HPLC-fluorescence detector (HPLC-FLD), has been developed for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) in vegetables. ACN was used as extraction solvent for the extraction of target analytes from vegetables. When the previous extraction process was over, the ACN extract was transferred to the water-immiscible organic phase, tetrachloroethane, used as extraction solvent in HOLLE procedures. Under the optimum conditions, repeatability was carried out by spiking PAHs at concentration level of 12.5 μg/kg, the RSDs varied between 1.1 and 8.5% (n = 3). The LODs, based on S/N of 3, ranged from 0.025 to 0.25 μg/kg. Relative recoveries of PAHs from cucumber and long crooked squash samples were in the range of 72.4–104.9% and 65.5–119.3%, respectively. Compared with the conventional extraction method, the proposed method has the advantage of being quick, easy to operate, and having low consumption of organic solvent.     

Accurate mass determination,quantification and determination of detection limits in liquid chromatography–high-resolution time-of-flight mass spectrometry: Challenges and practical solutions

Uniform guidelines for the data processing and validation of qualitative and quantitative multi-residue analysis using full-spectrum high-resolution mass spectrometry are scarce.     

Novel algorithm for simultaneous component detection and pseudo-molecular ion characterization in liquid chromatography–mass spectrometry

Resolving components and determining their pseudo-molecular ions (PMIs) are crucial steps in identifying complex herbal mixtures by liquid chromatography–mass spectrometry. To tackle such labor-intensive steps, we present here a novel algorithm for simultaneous detection of components and their PMIs. Our method consists of three steps: (1) obtaining a simplified dataset containing only mono-isotopic masses by removal of background noise and isotopic cluster ions based on the isotopic distribution model derived from all the reported natural compounds in dictionary of natural products; (2) stepwise resolving and removing all features of the highest abundant component from current simplified dataset and calculating PMI of each component according to an adduct-ion model, in which all non-fragment ions in a mass spectrum are considered as PMI plus one or several neutral species; (3) visual classification of detected components by principal component analysis (PCA) to exclude possible non-natural compounds (such as pharmaceutical excipients). This algorithm has been successfully applied to a standard mixture and three herbal extract/preparations. It indicated that our algorithm could detect components’ features as a whole and report their PMI with an accuracy of more than 98%. Furthermore, components originated from excipients/contaminants could be easily separated from those natural components in the bi-plots of PCA.     

Simultaneous determination of valproic acid and its main metabolite in human plasma using a small scale dispersive liquid–liquid microextraction followed by gas chromatography–flame ionization detection

A simple, sensitive, and rapid analytical method has been developed and validated for the extraction and quantification of valproic acid and its main metabolite (3-heptanone) in human plasma. Initially, the proteins of plasma were precipitated with trifluoroacetic acid. Then a very small volume of a water-immiscible extractant and acetonitrile was mixed and rapidly injected into the pre-treated plasma sample. For further turbidity (dispersion of the extractant into sample solution), the cloudy solution was vortexed. After centrifugation, the settled phase was injected into gas chromatography-flame ionization detection. The effective parameters, such as type and volume of extraction and disperser solvents, vortex time, and pH were studied and optimized. The limits of detection of valproic acid and 3-heptanone were obtained, 0.065 and 0.015 mg L^?1, respectively. An acceptable precision was obtained for a concentration of 2 mg L^?1 of each analyte (relative standard deviation?≤?8%). The average absolute recoveries (n?=?3) of valproic acid and 3-heptanone were 52?±?2 and 42?±?1%, respectively. The validated method has been successfully used in analysis of the analytes in human plasma samples.     

Analysis of acrylamide in coffee and cocoa by isotope dilution liquid chromatography–tandem mass spectrometry

An accurate and precise method for the quantification of acrylamide using stable isotope dilution liquid chromatography–tandem mass spectrometry was developed and used to measure acrylamide in coffee and cocoa samples. The sample preparation involved extraction of the analyte and its internal standard, ¹³C₃-acrylamide, into water and subsequent defatting of the aqueous extract with dichloromethane. An aliquot of the resulting aqueous extract was then azeotropically dried under reduced pressure and subsequently purified using an aminopropyl-bonded silica cartridge. The purified extracts were then chromatographed on a 5-μm 2.1×150 mm Hypercarb column, the effluent of which was monitored for the analyte and its internal standard using positive-ion APCI-selected reaction monitoring. The intra-laboratory reproducibility of the method, expressed as a relative coefficient of variation (%, n=5), was determined at four levels of concentration (12.3, 42.3, 139.3 and 464.8 μg kg⁻¹) and was found to vary between 0.6–2.5%. The accuracy of the method was assessed using a reference sample of coffee. The average result obtained using our method differed from the assigned value of the reference material by less than 1%. An analysis of a cocoa sample revealed that the method is capable of precisely estimating acrylamide in challenging matrices down to a level of at least 12.3 μg kg⁻¹.     

Simultaneous determination of 1,1-dimethylhydrazine and products of its oxidative transformations by liquid chromatography–tandem mass spectrometry

A liquid chromatography–tandem mass spectrometry method is proposed for the simultaneous determination of 1,1-dimethylhydrazine, methylhydrazine, N,N-dimethylformamide, 1-methyl-1H-1,2,4-triazole, dimethylguanidine, N-nitrosodimethylamine and 1,1,4,4-tetramethyltetrazene, important rocket fuel pollutants of soils. Chromatographic separation was conducted according to previously published results in an isocratic mode on an analytical column with a Nucleosil-100–5SA sulfo-cation-exchanger. The mobile phase composition was optimised in order to achieve effective separation of all analytes and provide high sensitivity of mass spectrometric detection – an ammonium acetate buffer solution (50 mM, pH 5.4) containing methanol (25%) was used. Detection was performed in the positive electrospray ionisation mode with multiple reaction monitoring (MRM). The parameters of ion source, ion optics, the inlet potentials of the quadrupoles and the collision energy for the detection of the found product ions were optimised. Calibration dependences for all compounds are linear in wide concentration ranges, covering 3–4 orders of magnitude. The detection limits vary from 40 pg mL^?1 for dimethylguanidine to 18 ng mL^?1 for methylhydrazine. No significant matrix effects were observed in the analysis of acid peaty soil extracts. The method was validated and successfully used to analyse a real soil sample collected at the place of impact of the first stage of a carrier rocket.     

Trace determination of dichlorodiphenyltrichloroethane and its main metabolites in environmental water samples with dispersive liquid–liquid microextraction in combination with high performance liquid chromatography and ultraviolet detector

Dichlorodiphenyltrichloroethane,1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its main metabolites have been paid much more attention, and present paper describes a new process for the rapid determination of such pollutants in environmental water samples based on dispersive liquid–liquid microextraction (DLLME) and high performance liquid chromatography with ultraviolet detector, which has merits such as high enrichment factor and sensitivity, low cost and easy to operate. Significant parameters such as extraction solvent and dispersive solvent type and volume, pH, extraction time and centrifuging time, which would have important impact on the enrichment of target pollutants, have been investigated in detail. The results exhibited that excellent performance could be achieved with carbon tetrachloride and acetonitrile as the extraction solvent and dispersive solvent, respectively. Under the optimal conditions, excellent linear relationship was gained in the range of 1.0–50 μg L⁻¹, and detection limits were in the range of 0.32–0.51 μg L⁻¹. The precisions of the proposed method were in the range of 2.80–7.50% (RSD). The proposed method was validated with real water samples, and the results indicated the spiked recoveries were in the range of 85.58–119.6% and the established method was very good and competitive in the determination of DDT and its metabolites.     

Ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction and high-performance liquid chromatography for determination of ketoconazole and econazole nitrate in human blood

A simple and efficient method, based on ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction (UESA-DLLME) followed by high-performance liquid chromatography (HPLC) has been developed for extraction and determination of ketoconazole and econazole nitrate in human blood samples. In this method, a common cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used as dispersant. Chloroform (40 μL) as extraction solvent was added rapidly to 5 mL blood containing 0.068 mg mL⁻¹ CTAB. The mixture was then sonicated for 2 min to disperse the organic chloroform phase. After the extraction procedure, the mixture was centrifuged to sediment the organic chloroform phase, which was collected for HPLC analysis. Several conditions, including type and volume of extraction solvent, type and concentration of the surfactant, ultrasound time, extraction temperature, pH, and ionic strength were studied and optimized. Under the optimum conditions, linear calibration curves were obtained in the ranges 4–5000 μg L⁻¹ for ketoconazole and 8–5000 μg L⁻¹ for econazole nitrate, with linear correlation coefficients for both >0.99. The limits of detection (LODs, S/N = 3) and enrichment factors (EFs) were 1.1 and 2.3 μg L⁻¹, and 129 and 140 for ketoconazole and econazole nitrate, respectively. Reproducibility and recovery were good. The method was successfully applied to the determination of ketoconazole and econazole nitrate in human blood samples.     

Simultaneous screening of homotaurine and taurine in marine macro-algae using liquid chromatography–fluorescence detection

Simultaneous analysis of homotaurine and its homologous, taurine, is a highly challenging issue, especially in matrices they exist simultaneously. A simple precolumn derivatization procedure combined with high-performance liquid chromatography–fluorescence detection was developed for simultaneous determination of homotaurine and taurine in marine macro-algae. The analytes were derivated with o-phthalaldehyde at an ambient temperature and alkaline medium. Calibration curves were linear in the ranges of 50–2500 µg L^?1 for homotaurine and 100–2500 µg L^?1 for taurine with the coefficients of determination higher than 0.998. Limits of detection of homotaurine and taurine were 15 and 30 µg L^?1, respectively. Intraday (n = 6) and inter-day (n = 4) precisions of the method were satisfactory with relative standard deviations less than 6.0%. Good recoveries (>94%) were acquired by the method for extraction of homotaurine and taurine from algae matrices. Liquid chromatography–mass spectrometry was also used to confirm detection of the analytes in algae samples. The data suggest that the method was successfully applied to simultaneous determination of homotaurine and taurine in algae samples.     

Simultaneous determination of NNK and its seven metabolites in rabbit blood by hydrophilic interaction liquid chromatography–tandem mass spectrometry

A hydrophilic interaction liquid chromatographic–tandem mass spectrometric (HILIC–MS–MS) method for investigation of the in vivo metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent carcinogen, in rabbit blood has been developed and validated. This method achieved excellent repeatability and accuracy. Recovery ranged from 76.9 to 116.3 % and precision (as RSD) between 0.53 and 6.52 %. Linearity was good for all compounds (R ²?>?0.9990) and the limit of detection (LOD) ranged from 0.016 to 0.082 ng mL^?1. Pharmacokinetic analysis indicated that NNK was rapidly eliminated in vivo in rabbit blood and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) was the major metabolite. The hydroxy acid, keto acid, and NNAL-N-oxide were also important metabolites in rabbit blood. It is probable that α-methylene hydroxylation was the major pathway of α-hydroxylation of NNK and NNAL in the rabbit.

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV–Vis detection

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 L phosphoric acid 1 mol L^–1 at a controlled room temperature of 15°C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C₁₈ column, using methanol/LiCl_(aq) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV–Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3–300 mg L^–1 per injection (20 L) and the limit of detection (LOD) for acetaldehyde was 2.03 g L^–1, with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n=5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7–102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.     

Development of a liquid–chromatography tandem mass spectrometry and ultra-high-performance liquid chromatography high-resolution mass spectrometry method for the quantitative determination of zearalenone and its major metabolites in chicken and pig plasma

A sensitive and specific method for the quantitative determination of zearalenone (ZEN) and its major metabolites (α-zearalenol (α-ZEL), β-zearalenol (β-ZEL), α-zearalanol (α-ZAL), β-zearalanol (β-ZAL) and zearalanone (ZAN)) in animal plasma using liquid chromatography combined with heated electrospray ionization (h-ESI) tandem mass spectrometry (LC–MS/MS) and high-resolution Orbitrap^® mass spectrometry ((U)HPLC–HR–MS) is presented. The sample preparation was straightforward, and consisted of a deproteinization step using acetonitrile. Chromatography was performed on a Hypersil Gold column (50 mm × 2.1 mm i.d., dp: 1.9 μm, run-time: 10 min) using 0.01% acetic acid in water (A) and acetonitrile (B) as mobile phases.     

Dispersive liquid–liquid microextraction coupled to liquid chromatography for thiamine determination in foods

A miniaturized dispersive liquid–liquid microextraction (DLLME) procedure coupled to liquid chromatography (LC) with fluorimetric detection was evaluated for the preconcentration and determination of thiamine (vitamin B₁). Derivatization was carried out by chemical oxidation of thiamine with 5 × 10⁻⁵ M ferricyanide at pH 13 to form fluorescent thiochrome. For DLLME, 0.5 mL of acetonitrile (dispersing solvent) containing 90 μL of tetrachloroethane (extraction solvent) was rapidly injected into 10 mL of sample solution containing the derivatized thiochrome and 24% (w/v) sodium chloride, thereby forming a cloudy solution. Phase separation was carried out by centrifugation, and a volume of 20 μL of the sedimented phase was submitted to LC. The mobile phase was a mixture of a 90% (v/v) 10 mM KH₂PO₄ (pH 7) solution and 10% (v/v) acetonitrile at 1 mL min⁻¹. An amide-based stationary phase involving a ligand with amide groups and the endcapping of trimethylsilyl was used. Specificity, linearity, precision, recovery, and sensitivity were satisfactory. Calibration graph was carried out by the standard additions method and was linear between 1 and 10 ng mL⁻¹. The detection limit was 0.09 ng mL⁻¹. The selectivity of the method was judged from the absence of interfering peaks at the thiamine elution time for blank chromatograms of unspiked samples. A relative standard deviation of 3.2% was obtained for a standard solution containing thiamine at 5 ng mL⁻¹. The esters thiamine monophosphate and thiamine pyrophosphate can also be determined by submitting the sample to successive acid and enzymatic treatments. The method was applied to the determination of thiamine in different foods such as beer, brewer’s yeast, honey, and baby foods including infant formulas, fermented milk, cereals, and purees. For the analysis of solid samples, a previous extraction step was applied based on an acid hydrolysis with trichloroacetic acid. The reliability of the procedure was checked by analyzing a certified reference material, pig’s liver (CRM 487). The value obtained was 8.76 ± 0.2 μg g⁻¹ thiamine, which is in excellent agreement with the certified value, 8.6 ± 1.1 μg g⁻¹.     

Sensitive determination of nitrophenol isomers by reverse-phase high-performance liquid chromatography in conjunction with liquid–liquid extraction

A method for the highly sensitive determination of 2-, 3- and 4-nitrophenols was developed using reverse-phase high-performance liquid chromatography (RP-HPLC) with a UV photodiode array detector. Using a reverse-phase column and 40% aqueous acetonitrile as an eluent (i.e. isocratic elution), the integrated peak area of detector output was linear up to 300 mg/L and the detection limit was 150 µg/L. The sensitivity of this detection method was improved by pretreating the sample solutions with a solvent extraction procedure that makes use of the high partition coefficient of ethyl acetate (EA)/water system. To find an optimum condition for the extraction procedure, this process was simulated by plotting the concentration of nitrophenol extracted in organic solvent against the volume multiplication factor at various partition coefficient of solute. This simulation demonstrated that EA is a superior extractant to other organic solvents. With the newly developed method, the detection limit was extended to 0.3 µg/L. This method offers fast, reliable and more sensitive determination of nitrophenol isomers than any other HPLC method.     

Determination of organochlorine pesticides in river water using dispersive liquid–liquid microextraction and gas chromatography–electron capture detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–electron capture detection (GC–ECD), has been developed for the extraction and determination of 14 organochlorine pesticides (hexachlorocyclohexanes (α-HCH, β-HCH and δ-HCH), Lindane (γ-HCH), Aldrin, Dieldrin, Endrin, Heptachlor, Heptachlor epoxide, α-Chlordane, β-Chlordane and p,p′-DDT, p,p′-DDD, p,p′-DDE) in river water samples. Factors relevant to the microextraction efficiency, such as the kind of extraction and disperser solvent, their volume and the salt effect was investigated and optimised. In this method the appropriate mixture of extraction solvent (13.5 µL carbon disulphide) and disperser solvent (0.50 mL acetone) were rapidly injected into the aqueous sample by syringe. The values of the detection limit of the method were in the range of 0.05–0.001 µg L^?1, while the relative standard deviations for five replicates varied from 2.7 to 9.3%. A good linearity (0.9894 ≤ r ² ≤ 0.9998) and a broad linear range (0.01–200 µg L^?1) were obtained. The method exhibited enrichment factors ranging from 647 to 923, at room temperature. The relative standard deviations varied from 2.7 to 9.3% (n = 5). The relative recoveries of each pesticide from water samples at spiking levels of 2.00 and 10.0 µg L^?1 were 88.0–111.0% and 95.8–104.1%, respectively. Finally, the proposed method was successfully utilised for the preconcentration and determination of the organochlorine pesticides in the Jajrood River water samples.     

Simultaneous quantitative determination of liraglutide and insulin degludec in rat plasma by liquid chromatography–tandem mass spectrometry method and its application

A simple, fast and high-throughput LC–tandem mass spectrometry method was developed and validated to simultaneously measure liraglutide and insulin degludec in rat plasma. After protein precipitation, plasma samples were subjected to gradient elution using an InertSustain Bio C₁₈ column with 1000/20/1 water/acetonitrile/formic acid (v/v/v) and 1000/1 acetonitrile/formic acid (v/v) as the mobile phase. The method was validated from 1.00 to 500 ng/mL of liraglutide and insulin degludec. Further, the extraction recovery from the plasma was 41.8%–49.2% for liraglutide and 56.5%–69.7% for insulin degludec. Intra- and inter-day precision of liraglutide was 3.5%–9.4% and 8.4%–9.8%, respectively, whereas its accuracy was between −12.6% and −1.3%. Intra- and inter-day precision of insulin degludec was 5.2%–13.6% and 11.8%–19.1%, respectively, showing an accuracy between −3.0% and 9.9%. As a result, the method was successfully applied to a pharmacokinetics study of liraglutide and insulin degludec following a single-dose subcutaneous administration to rats.     

Gas chromatography–electron capture detection determination of Dacthal and its di-acid metabolite in soil after ultrasound-assisted extraction and in situ focused microwave-assisted derivatization

A quantitative method for the determination of Dacthal and its di-acid metabolite in soil has been developed by coupling ultrasound-assisted extraction and microwave-assisted derivatization of the analytes prior to gas chromatography–electron capture detection for individual separation and measurement. The main factors affecting both extraction efficiency and derivatization were optimized by experimental design methodology. The proposed approach allows extraction of these pollutants from spiked sediment and soil with efficiencies similar to those provided by the reference method but with a drastic reduction of both the extraction and derivatization times. The repeatability of the analyses, expressed as RSD, of Dacthal and its di-acid metabolite was 4.6% and 5.4%, respectively; meanwhile, the RSD for within-laboratory reproducibility was 8.7% and 9.2%, respectively.     

Comparison of dispersive liquid–liquid microextraction and hollow fiber liquid–liquid–liquid microextraction for the determination of fentanyl,alfentanil, and sufentanil in water and biological fluids by high-performance liquid chromatography

Dispersive liquid–liquid microextraction (DLLME) and hollow fiber liquid–liquid–liquid microextraction (HF-LLLME) combined with HPLC–DAD have been applied for the determination of three narcotic drugs (alfentanil, fentanyl, and sufentanil) in biological samples (human plasma and urine). Different DLLME parameters influencing the extraction efficiency such as type and volume of the extraction solvent and the disperser solvent, concentration of NaOH, and salt addition were investigated. In the HF-LLLME, the effects of important parameters including organic solvent type, concentration of NaOH as donor solution, concentration of H₂SO₄ as acceptor phase, salt addition, stirring rate, temperature, and extraction time were investigated and optimized. The results showed that both extraction methods exhibited good linearity, precision, enrichment factor, and detection limit. Under optimal condition, the limits of detection ranged from 0.4 to 1.9 μg/L and from 1.1 to 2.3 μg/L for DLLME and HF-LLLME, respectively. For DLLME, the intra- and inter-day precisions were 1.7–6.4% and 14.2–15.9%, respectively; and for HF-LLLME were 0.7–5.2% and 3.3–10.1%, respectively. The enrichment factors were from 275 to 325 and 190 to 237 for DLLME and HF-LLLME, respectively. The applicability of the proposed methods was investigated by analyzing biological samples. For analysis of human plasma and urine samples, HF-LLLME showed higher precision, more effective sample clean-up, higher extraction efficiency, lower organic solvent consumption than DLLME.     

Dispersive liquid–liquid–liquid microextraction combined with liquid chromatography for the determination of chlorophenoxy acid herbicides in aqueous samples

A novel sample preparation method “Dispersive liquid–liquid–liquid microextraction” (DLLLME) was developed in this study. DLLLME was combined with liquid chromatography system to determine chlorophenoxy acid herbicide in aqueous samples. DLLLME is a rapid and environmentally friendly sample pretreatment method. In this study, 25 μL of 1,1,2,2-tetrachloroethane was added to the sample solution and the targeted analytes were extracted from the donor phase by manually shaking for 90 s. The organic phase was separated from the donor phase by centrifugation and was transferred into an insert. Acceptor phase was added to this insert. The analytes were then back-extracted into the acceptor phase by mixing the organic and acceptor phases by pumping those two solutions with a syringe plunger. After centrifugation, the organic phase was settled and removed with a microsyringe. The acceptor phase was injected into the UPLC system by auto sampler. Fine droplets were formed by shaking and pumping with the syringe plunger in DLLLME. The large interfacial area provided good extraction efficiency and shortened the extraction time needed. Conventional LLLME requires an extraction time of 40–60 min; an extraction time of approximately 2 min is sufficient with DLLLME. The DLLLME technique shows good linearity (r² ≥ 0.999), good repeatability (RSD: 4.0–12.2% for tap water; 5.7–8.5% for river water) and high sensitivity (LODs: 0.10–0.60 μg/L for tap water; 0.11–0.95 μg/L for river water).