Ultrasound-assisted extraction of volatile compounds from wine samples: optimisation of the method

This study describes a liquid–liquid extraction technique for extracting volatile compounds from wine using dichloromethane and ultrasounds. This technique permits the simultaneous extraction of different samples with high reproducibility. After the preliminary tests, several parameters (sample volume, solvent volume and extraction time) were optimised using a factorial design to obtain the most relevant variables. The analytical characteristics were obtained such as calibration graphs, detection limits ranging from 0.0238 mg L⁻¹ for 1-pentanol to 0.261 mg L⁻¹ for octanoic acid, quantification limits and relative standard deviation from 2.1 to 6.2%. Extraction yields were calculated giving a range 9.16–1.2%. The optimised conditions were applied to the extraction of samples of young wines from the Denominación de Origen Calificada Rioja category using gas chromatography and a flame ionisation detector.     

Improvement of the chromatographic separation of several 1,4-dihydropyridines calcium channel antagonist drugs by experimental design

A high-performance liquid chromatographic method with diode array detection has been developed and optimized for the separation of five calcium channel blockers belonging to the 1,4-dihydropyridine subgroup (nifedipine and related drugs). The possibility of the simultaneous drug analysis allows a decrease of time during the assay as well as a saving of reagents and solvents. In this work, the effect of four experimental parameters (organic modifier percentage, pH value, concentration of the buffer in the mobile phase, and column temperature) on the chromatographic resolution are investigated by experimental design in order to optimize the chromatographic separation of five 1,4-dihydropyridines (amlodipine, nitrendipine, felodipine, lacidipine, and lercanidipine). Fractional factorial design, central composite design, and finally the Multisimplex program are used to establish the optimal conditions in terms of resolution and minimum analysis time. Optimal separation of the five compounds under study is achieved in less than 12 min using a Sulpecosil LC-ABZ+Plus C18 column, a composition of mobile phase of acetonitrile-10mM acetic acid acetate buffer pH 5 (72:28, v/v) at a flow rate of 1 mL/min, a column temperature of 30 degrees C +/- 0.1 degrees C, and a detection wavelength of 238 nm.     

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–flame ionization detection (GC–FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 μL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 μL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04–1000.25 and 54.76–74.02%, respectively. The linear range was (0.005–16 μg mL⁻¹) and limits of detection were between 0.005 and 0.01 μg mL⁻¹ for each of the analytes. The relative standard deviations (R.S.D.) for 4 μg mL⁻¹ of TCAs in water were in the range of 5.6–6.4 (n = 6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma.     

Pressurized liquid extraction in determination of polychlorinated biphenyls and organochlorine pesticides in fish samples

Pressurized liquid extraction (PLE) is a relatively new technique applicable for the extraction of persistent organic pollutants from various matrices. The main advantages of this method are short time and low consumption of extraction solvent. The effects of various operational parameters (i.e. temperature of extraction, number of static cycles and extraction solvent mixtures) on the PLE efficiency were investigated in this study. Fish muscle tissue containing 3.2% (w/w) lipids and native polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and other related compounds was used for testing. Purification of crude extracts was carried out by gel permeation chromatography employing Bio-Beads S-X3. Identification and quantitation of target indicator PCBs and OCPs was performed by high-resolution gas chromatography (HRGC) with two parallel electron-capture detectors (ECDs). Results obtained by the optimized PLE procedure were compared with conventional Soxhlet extraction (the same extraction solvent mixtures hexane–dichloromethane (1:1 v/v) and hexane–acetone (4:1 v/v) were used). The recoveries obtained by PLE operated at 90–120 °C were either comparable to “classic” Soxhlet extraction (for higher-chlorinated PCB congeners and DDT group) or even better (for lower chlorinated analytes). The highest recoveries were obtained for three static 5 min extraction cycles.     

Trace analysis of chlorobenzenes in water samples using headspace solvent microextraction and gas chromatography/electron capture detection

In the present work, a rapid method for the extraction and determination of chlorobenzenes (CBs) such as monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene and 1,2,4-trichlorobenzene in water samples using the headspace solvent microextraction (HSME) and gas chromatography/electron capture detector (ECD) has been described. A microdrop of the dodecane containing monobromobenzene (internal standard) was used as extracting solvent in this investigation. The analytes were extracted by suspending a 2.5 μl extraction drop directly from the tip of a microsyringe fixed above an extraction vial with a septum in a way that the needle passed through the septum and the needle tip appeared above the surface of the solution. After the extraction was finished, the drop was retracted back into the needle and injected directly into a GC column. Optimization of experimental conditions such as nature of the extracting solvent, microdrop and sample temperatures, stirring rate, microdrop and sample volumes, the ionic strength and extraction time were investigated. The optimized conditions were as follows: dodecane as the extracting solvent, the extraction temperature, 45 °C; the sodium chloride concentration, 2 M; the extraction time, 5.0 min; the stirring rate, 500 rpm; the drop volume, 2.5 μl; the sample volume, 7 ml; the microsyringe needle temperature, 0.0 °C. The limit of detection (LOD) ranged from 0.1 μg/l (for 1,3-dichlorobenzene) to 3.0 μg/l (for 1,4-dichlorobenzene) and linear range of 0.5–3.0 μg/l for 1,2-dichlorobenzene, 1,3-dichlorobenzene and from 5.0 to 20.0 μg/l for monochlorobenzene and from 5.0 to 30 μg/l for 1,4-dichlorobenzene. The relative standard deviations (R.S.D.) for most of CBs at the 5 μg/l level were below 10%. The optimized procedure was successfully applied to the extraction and determination of CBs in different water samples.     

Low-temperature clean-up method for the determination of pyrethroids in milk using gas chromatography with electron capture detection

This paper describes a new gas-chrormatography with electron capture detection (GC-ECD) method for determination of some pyrethroids in milk samples. The extraction of the pyrethroids was carried out by liquid–liquid extraction with clean-up by precipitation at low temperature, without additional stages for removal of fat interferences. The method was efficient with recoveries of 93.0 ± 0.1% for cipermethrin and 84.0 ± 0.3% for deltamethrin. The quantification limits were 0.75 μg L⁻¹ for both pyrethroids. The method was simple, of easy execution, and used only small quantities of organic solvent. After optimization and validation, the method was used for the determination of residues of the pyrethroids cipermethrin and deltamethrin in milk and in lactea drink commercialized in Viçosa (MG, Brazil). Some samples presented contamination with deltamethrin at levels below the maximum contamination limits established by the FAO.     

Pressurized solvent extraction and monolithic column-HPLC/DAD analysis of anthocyanins in red cabbage

The aim of this work was to develop a fast method for extraction and analysis of anthocyanins in red cabbage. Pressurized hot water containing 5% of ethanol was used as an extremely efficient extraction solvent. HPLC/DAD with a monolithic column was used to accomplish a fast analysis—24 anthocyanin peaks within 18 min. Statistical design was used to optimize the studied extraction parameters: temperature (80–120 °C); sample amount (1–3 g); extraction time (6–11 min); concentration of formic acid in the extraction solvent (0–5 vol.%). The best extraction conditions for a majority of the anthocyanin peaks were 2.5 g of sample, 99 °C (at 50 bar), 7 min of extraction and a solvent composition of water/ethanol/formic acid (94/5/1, v/v/v).     

New applications of azamacrocyclic ligands in ion recognition, transport and preconcentration of palladium

This work deals with the evaluation of a synthesized 15-membered triolefinic azamacrocycle containing a NH group, (E,E,E)-1,6-bis(p-tolylsulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-triene (R₂NH), for the selective extraction of palladium and platinum from aqueous chloride matrices prior their analysis by ICP-AES. The optimal conditions for liquid–liquid experiments have been evaluated, with special emphasis given to the selection of the organic solvent and the optimal aqueous chloride concentration for the extraction of PdCl₄²⁻ and PtCl₆²⁻. The selective transport and separation of palladium(II) from a mixture of Pd(II) and Pt(IV) was accomplished by means of a supported liquid membrane system containing the macrocycle as carrier dissolved in anethol and 0.5 M thyocianate solution as stripping solution. A C18 cartridge has been activated with the reagent R₂NH in order to test the feasibility of achieving the preconcentration of palladium solutions. Enrichment factors close to the theoretical ones were obtained with the designed system and using thiourea as eluting solution.     

Immunochemical determination of dioxins in sediment and serum samples

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are considered highly toxic contaminants and the environmental and biological monitoring of these compounds is of great concern. Immunoassays may be used as screening methods to satisfy the growing demand for rapid and low cost analysis. In this work, we describe the application of an immunoassay that uses 2,3,7-trichloro-8-methyldibenzo-p-dioxin (TMDD) as a surrogate standard for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to sediment and human serum samples. Sample extraction and preparation methods were developed with the aim to establish the simplest, cost-effective and efficient removal of the matrix interferences in the enzyme-linked immunosorbent assay (ELISA). The overall method for sediments is based on a hexane extraction; clean up by a multilayered silica gel column and an activated carbon column; an organic solvent exchange with DMSO–Triton X-100 and ELISA measurement. The gas chromatography–high resolution mass spectrometry (GC–HRMS) validation studies (n = 13) revealed that the method is suitable for the toxic equivalents (TEQ) screening of dioxin in sediments with a method detection limit of about 100 pg g⁻¹ dry sediment with a precision of 13–33% R.S.D. The analysis of a large number of samples originating from different sources would be required to establish more precisely the screening level, as well as the number of false positives and negatives of dioxin TEQ by the immunoassay for sediments. The immunoassay method for sediment analysis offers improvement in speed, sample throughput, and cost in comparison to GC–HRMS. Dioxins were determined in serum samples after a simple liquid–liquid extraction and solvent exchange into DMSO–Triton X-100 without further dilution. The current method (approximate method LOQ of 200 pg ml⁻¹ serum) is not sufficiently sensitive for the determination of dioxins in serum to measure acceptable exposure limit.     

Extraction and determination of papaverin in pericarpium papaveris using aqueous two-phase system of poly(ethylene glycol)-(NH4)2SO4 coupled with high-performance liquid chromatography

Based on aqueous two-phase system (ATPS) of poly(ethylene glycol) (PEG)–(NH₄)₂SO₄, a simple pretreatment approach was developed for the extraction and determination of papaverin in pericarpium papaveris. The influence factors on phase behavior of the ATPS and partition behavior of papaverin was investigated, and partition mechanism based on the hydrophobic interaction between PEG and analyte molecules was proposed. Under the optimal conditions, the extraction efficiencies for papaverin were 93–96%, and the recoveries of the added standard were 97–106% with relative standard deviations of 1.8–2.5%. Combined with a high-performance liquid chromatography (HPLC) method, this extraction technique has been successfully applied to the determination of papaverin in pericarpium papaveris with the detection limit of 2 ng mL⁻¹ and the linear range of 0.10–10 μg mL⁻¹. Compared with the conventional liquid–liquid extraction or solid-phase extraction, this method was more environmentally benign, more cost effective and much simpler due to the direct injection of the upper phase into HPLC system.     

Supported liquid membranes for the determination of vanillin in food samples with amperometric detection

A supported liquid membrane system has been developed for the extraction of vanillin from food samples. A porous PTFE membrane is impregnated with an organic solvent, which forms a barrier between two aqueous phases. The analyte is extracted from a donor phase into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor. The determination (100–1400 μg ml⁻¹ vanillin) was performed using a PVC-graphite composite electrode versus Ag/AgCl/3MKCl at +0.850 V placed in a wall-jet flow cell as amperometric detector. The solid sample is directly placed in the membrane unit without any treatment, and the analyte was extracted from the sample, passes through the membrane and conduced to the flow cell by the acceptor stream. The limit of detection (3σ) was 44 μg ml⁻¹. The method was applied to the determination of vanillin (9–606 μg g⁻¹) in food samples.     

Ultrasound-assisted dynamic extraction of valuable compounds from aromatic plants and flowers as compared with steam distillation and superheated liquid extraction

A method for the extraction of valuable compounds from plants and flowers (viz. laurel, rosemary, thyme, oregano and tuberose) is proposed. The dynamic approach allows go-and-backward circulation of the extractant (ethanol) through the solid sample subjected to the action of an ultrasound probe (thus reducing sample amount and avoiding overpressure). A multivariate optimisation study and application of the optimum values of the variables to kinetics studies show that 10 min is sufficient to obtain extraction efficiencies that greatly surpass those provided by steam distillation for essential oils or superheated liquid extraction for these oils and other valuable compounds, with lower costs and higher quality of the extract. The extraction time of the proposed method is 176–165 min shorter than steam distillation and 31–20 min shorter than superheated liquid extraction, depending on the target compound.     

Comparison of extraction techniques of robenidine from poultry feed samples

In this paper, effectiveness of six different commonly applied extraction techniques for the determination of robenidine in poultry feed has been compared. The sample preparation techniques included shaking, Soxhlet, Soxtec, ultrasonically assisted extraction, microwave – assisted extraction and accelerated solvent extraction. Comparison of these techniques was done with respect to the recovery extraction, temperature and time, reproducibility and solvent consumption. Every single extract was subjected to clean – up using aluminium oxide column (Pasteur pipette filled with 1 g of aluminium oxide), from which robenidine was eluted with 10 ml of methanol. The eluate from the clean-up column was collected in a volumetric flask, and finally it was analysed by HPLC–DAD–MS. In general, all extraction techniques were capable of isolating of robenidine from poultry feed, but the recovery obtained using modern extraction techniques was higher than that obtained using conventional techniques.

In particular, accelerated solvent extraction was more superior to other techniques, which highlights the advantages of this sample preparation technique. However, in routine analysis, shaking and ultrasonically assisted extraction is still the preferred method for the solution of robenidine and other coccidiostatics.     

Off-line coupling of pressurized liquid extraction and LC/ED for the determination of retinyl acetate and tocopherols in infant formulas

An analytical methodology including pressurized liquid extraction (PLE) as sample treatment to isolate retinyl acetate and tocopherols from infant formulas has been developed. The milk extracts were kept at −18 °C for 30 min and after filtration could be injected directly into the chromatographic system. Thus, a rapid and simple routine control method of these products is possible.

The parameters affecting both the extraction process and the liquid chromatography (LC) system were optimized. PLE was performed using one cycle of extraction during a static time of 5 min. Methanol was chosen as the extraction solvent for a temperature of 50 °C. Chromatographic separation was accomplished using a RP-18 column; the mobile phase used was methanol–water (94:6, v/v) containing 2.5 mM acetic acid/sodium acetate buffer. Electrochemical detection in amperometric mode with a glassy carbon electrode at +1100 mV was applied. The proposed methodology was successfully used for the determination of retinyl acetate, δ-tocopherol, (β + γ)-tocopherol and -tocopherol in different infant formulas. The analytes were evaluated in the same chemical form present in the samples. Recoveries were between 92 and 106%. A certified reference material of milk powder was also analyzed.     

Analysis for chloroanisoles and chlorophenols in cork by stir bar sorptive extraction and gas chromatography–mass spectrometry

A complete methodology for the determination of chloroanisoles and chlorophenols in cork material is proposed. The determination is accomplished by means of a previous liquid–solid extraction followed by stir bar sorptive extraction (SBSE) coupled to gas chromatography–mass spectrometry (GC–MS). Two different liquid–solid extraction experiments were conducted and eight compounds considered (2,6-dichloroanisole, 2,4-dichloroanisole, 2,4,6-trichloroanisole, 2,4,6-trichlorophenol, 2,3,4,6-tetrachloroanisole, 2,3,4,6-tetrachlorophenol, pentachloroanisole and pentachlorophenol). From the results obtained we can conclude that high volume extraction extending extraction time up to 24 h is the best choice if we have to release compounds from the inner surfaces of cork stoppers. Recovery percentages ranged from 51% for pentachloroanisole to 81% for 2,4-dichloroanisole. This method allows the determination of an array of compounds involved in cork taint at very low levels from 1.2 ng g⁻¹ for 2,4,6-tricholoroanisole to 23.03 ng g⁻¹ for 2,3,4,6-tetrachlorophenol.     

Liquid–liquid equilibria of water/1-propanol/methyl ethyl ketone/potassium chloride

The liquid–liquid equilibrium of water/1-propanol/methyl ethyl ketone (MEK) at 25°C was significantly modified by the presence of dissolved potassium chloride. Water is salted out of the organic phase while MEK is more preferentially salted out of the aqueous phase than 1-propanol. These results in considerable enlargement of the two-phase region and enhancement of the extractive efficiency of MEK for the separation of 1-propanol from its aqueous mixture. Good correlation of the liquid–liquid equilibria (LLE) of the system in the presence of potassium chloride up to saturation was obtained with Tan’s modified NRTL phase model for multicomponent solute–solvent mixtures with the solute–solvent interaction parameters expressed as a third-order polynomial function in salt concentration. Similar to the observation reported for vapour–liquid equilibrium (VLE) of solvent–solute mixtures, salting-in and salting-out of the solvent components from the respective phases can be predicted according to the relative solute–solvent interaction parameters of the solvent components in the two phases.     

On-line sample treatment and FT-IR determination of doxylamine succinate in pharmaceuticals

A low solvent consumption method for Fourier transform infrared spectroscopy (FT-IR) determination of doxylamine succinate in pharmaceuticals has been developed. The analyte was continuous and selectively extracted with a 13% (v/v) ethanol:chloroform solvent mixture, recirculating the solvent through the sample and monitoring the process by FT-IR. Doxylamine succinate was determined by on-line standard addition measuring the peak area in the regions 1730–1710 and 1485–1462 cm⁻¹ corrected with a two-point baseline established between 2000 and 1800 cm⁻¹. This new method implies low volumes of chloroformic solvent mixture, only 2.6 mL per sample, in front of classical batch FT-IR methods, improving analytical efficiency and reducing waste generation. The on-line extraction and standard addition determination of doxylamine succinate allowed a throughput of 10 h⁻¹.     

Rapid reversed-phase liquid chromatographic determination of patulin in apple juice

A rapid, simple and economical method using a limited amount of organic solvent is described for the determination of patulin in apple juice. The sample was extracted with ethyl acetate and the extract was cleaned up by extraction with sodium carbonate solution. Patulin was then determined by reversed-phase liquid chromatography using a MicroPak C₁₈ column and a variable-wavelength UV-Vis detector set at 276 nm. Patulin and 5-hydroxymethylfurfural were completely resolved by using water- acetonitrile (99:1, v/v) as the mobile phase at a flow-rate of 1.0 ml/min. The detection limit was <5 μg/1 and the recovery was 98%.     

Determination of epichlorohydrin in water and sewage samples

The simple, quick and effective methods for the analysis of epichlorohydrin (ECH) in water and sewage samples with the use of gas chromatography have been presented. From among all the methods developed, the procedures for monitoring drinking-water quality and the methods which allow the determination of epichlorohydrin in sewage samples have been selected.

The limits of ECH detection have been determined by direct aqueous injection (DAI) into the chromatographic column and an analysis with the application of a flame ionization detector (FID), a mass spectrometry detector (MS), an electron capture detector (ECD) and atomic emission detection (AED) detectors. The method allows the determination of ECH in water samples at the concentration level of 0.1 mg l⁻¹. Moreover, the developed methods of water samples preparation for chromatographic analysis using the following extraction methods: headspace (HS), stripping with adsorption on solid phase, liquid–liquid extraction (LLE), solid phase extraction (SPE) and solid phase microextraction (SPME) have been evaluated. The limits of ECH detection for each procedure with the application of gas chromatography (GC) combined with various detectors have been determined and their statistical evaluation has been presented. The SPME method allowed us to determine ECH in water samples at the concentration levels of 1.0 ng l⁻¹.

The results of studies on the choice of the selective methods allowing ECH analysis in sewage samples have been demonstrated. The applied SPME method was found to be a quick and effective technique to determine micro trace amounts of ECH in samples containing high amounts of various organic compounds.     

Ultrasound-assisted extraction of capsaicinoids from peppers

The development of a rapid, reproducible and simple method of extraction of the majority capsaicinoids (nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin and homodihydrocapsaicin) present in hot peppers by the employment of ultrasound-assisted extraction is reported. The study has covered four possible solvents for the extraction (acetonitrile, methanol, ethanol and water), the optimum temperature for extraction (10–60 °C), the extraction time (2–25 min), the quantity of sample (0.2–2 g), and the volume of solvent (15–50 mL). Under the optimum conditions of the method developed, methanol is employed as solvent, at a temperature of 50 °C and an extraction time of 10 min. The repeatability and reproducibility of the method (R.S.D. < 3%) have been determined. The capsaicinoids extracted have been analysed by HPLC with fluorescence detection and using monolithic columns for the chromatographic separation. The method developed has been employed for the quantification of the various capsaicinoids present in different varieties of hot peppers cultivated in Spain.