Continuous Liquid-liquid Extraction Research Articles

Determination of antioxidant potential of volatile extracts isolated from various herbs and spices.

Antioxidant activities of volatile extracts isolated from thyme, basil, rosemary, chamomile, lavender, and cinnamon were evaluated by two independent assays: the aldehyde/carboxylic acid assay and the conjugated diene assay. The volatile extracts were prepared from dried herbs and spices using liquid-liquid continuous extraction following steam distillation under reduced pressure (55 degrees C and 95 mmHg). The antioxidant activities of the extracts decreased in the following order in both of the lipophilic assay systems: thyme > basil > rosemary > chamomile > lavender and cinnamon. Thyme and basil extracts inhibited the oxidation of hexanal for 40 days at the levels of 10 microg/mL and 50 microg/mL, respectively. The extracts of thyme and basil were effective in retarding methyl linoleate deterioration at 40 degrees C, with activity increasing with concentration in the range 10-200 microg/mL. At a concentration of 50 microg/mL, thyme extract was similar in antioxidant activity to BHT and alpha-tocopherol in the conjugated diene assay. The antioxidant potentials of the volatile extracts used in this study were accurately measured by the lipophilic systems, such as the aldehyde/carboxylic acid assay and the conjugated diene assay.

Antioxidative activity of volatile chemicals extracted from beer.

Volatile chemicals obtained from a commercial beer by liquid-liquid continuous extraction were evaluated for antioxidant activity. The inhibitory ability of this extract toward the conversion of hexanal to hexanoic acid was monitored over a 35-day period. The volatile extract demonstrated >99% effectiveness at inhibiting hexanal oxidation at 50 microg/mL, comparable to that of the natural antioxidant alpha-tocopherol (vitamin E). Volatile compounds contained in the extract were isolated and identified by gas chromatography-mass spectrometry (GC-MS). From the volatile constituents identified in beer extract, phenylethyl alcohol, maltol, and 2-furanmethanol were examined for antioxidative activities. At a concentration of 500 microg/mL, maltol and 2-furanmethanol demonstrated approximately 95 and 100% inhibition of hexanal oxidation over 35 days, respectively. Phenylethyl alcohol did not show any appreciable level of inhibition of hexanal oxidation. Heterocyclic compounds, some of which are known to possess antioxidative activities, were also identified in the volatile extract.

Odour-impact compounds of Gorgonzola cheese.

Volatile concentrates were obtained by vacuum distillation from both natural and creamy Gorgonzola cheese and isolated by continuous liquid-liquid extraction. Both were analysed by high resolution gas chromatography (HRGC), HRGC-mass spectrometry and HRGC-olfactometry. A total of 63 components were identified in the neutral extract of the natural type (21 esters, 13 ketones, 14 alcohols, 5 aldehydes, 1 sulphur compound, 7 aromatic compounds and 2 terpenes) and 52 in the creamy type (17 esters, 12 ketones, 10 alcohols, 5 aldehydes, 1 sulphur compound, 5 aromatic compounds and 2 terpenes). Ketones, whose major components were 2-nonanone and 2-heptanone, were the predominant constituents of the neutral fraction. By olfactometric analysis of the neutral extracts, 23 odour-impact compounds were found in the natural and 21 in the creamy Gorgonzola cheese. 1-Octen-3-ol, ethyl hexanoate, 2-nonanone, 2-heptanone, 2-heptanol, ethyl butanoate, 2-nonanol and 4-methylanisole were the key odorants of the natural cheese, whereas 2-heptanone, 2-heptanol, ethyl butanoate, 3-methyl thiopropanal and an unidentified constituent with a fruity odour were characteristic of the creamy Gorgonzola cheese. On the basis of high odour unity values, 2-nonanone, 1-octen-3-ol, 2-heptanol, ethyl hexanoate, methylanisole and 2-heptanone were the most important odorants of natural and creamy Gorgonzola cheese aroma.

Trace-level determination of 1,4-dioxane in water by isotopic dilution GC and GC-MS.

The volatile and polar solvent 1,4-dioxane has recently been reported as a contaminant of ground and surface waters, establishing the need to determine this substance in drinking water. This investigation established that 1,4-dioxane can be determined in water by various techniques including direct aqueous injection (DAI) gas chromatography (GC) and purge and trap GC-mass spectrometry (MS). Purge and trap GC-MS is limited by 1,4-dioxane's poor purge efficiency, resulting in detection limits up to 100 times greater than the efficiently purged volatile organic compounds. To attain the sensitivity required for drinking water monitoring, a method based on continuous liquid-liquid extraction with dichloromethane was developed. Isotope dilution was more accurate and reproducible than quantification with external standards, and the improvement in precision led to a lower method detection limit, 0.2 microgram L-1, using a quadrupole ion trap instrument in the electron ionization mode. Isotope dilution accuracy approached 100% in ppb determinations. Isotopic dilution quantification was also possible using a non-selective GC detector owing to the high efficiency of capillary GC columns that resolve the deuterium-labeled solvent from the natural isotopes.

Purification of Natural Amorphous Graphite Using an Oscillating Liquid-Liquid Continuous Extraction Apparatus.

Through a flushing process, natural amorphous graphite was highly purified using a commercial oscillating liquid-liquid continuous-extraction apparatus. Aqueous slurries of raw graphite with a mean particle size of 2μm were conditioned at pH 4.2 in the presence of chelating and reducing reagents, and the graphite particles were extracted using a kerosene-based oil phase. The graphite particles in the oil phase were returned to an aqueous dispersion with the addition of a nonionic surfactant and sodium carbonate, and were recovered by centrifugation. The ash in the graphite decreased from 16 to 2mass% as a result of the separation of clayey impurities. The excellent functionality of the extractor for refining amorphous graphite was attributed especially to its perforated cylinder-shaped impeller capable of inducing a high shearing stress. Not only are fine oil droplets created, which are favorable for the collection of graphite particles, but the aggregates of raw graphite are also released as individual particles.

Flow Injection Continuous Liquid-Liquid Extraction Using a Hollow Fiber Membrane Separator for Determination of Copper in Water

ABSTRACT A simple flow injection photometric method for the determination of copper was developed based on the formation and liquid-liquid extraction of the analyte-bathocuproine-perchlorate ternary complex. The analytical reaction of complex formation is integrated with the continuous liquid-liquid extraction procedure. A hollow fiber-type membrane separator was specially constructed for the determination. The analytical properties like sensitivity, precision, accuracy and rapidity were evaluated. The sensitivity of the method depends on the injection volume. By using an injection volume of 0.6 ml, the detection limit (3σ) found was 15 ng ml−1 copper, with a determination range of 48 - 3000 ng/ml. The repeatability of the method, expressed as the relative standard deviation, was in all instances less than 3.0%. The sampling rate was of 20 h−1. The accuracy of the method was tested with certified reference materials, and the mean error was calculated to be less than 5%. The method was successfully applied to the determination of copper in river water.

The use of high temperature gas chromatography to study the biodegradation of high molecular weight hydrocarbons

A consequence of the biodegradation of petroleum is that lower molecular weight compounds are removed preferentially to higher molecular weight (HMW) compounds greater than triacontane ( n-C 30). The extent to which the latter compounds are biodegraded has rarely been studied. Reasons for this include the technical difficulties associated with carrying out biodegradability tests with solid, water-insoluble substances and the limits of the analytical techniques, such as gas chromatography (GC). A quantitative high temperature GC (HTGC) method was developed to monitor the biodegradation of the aliphatic fraction of a waxy Indonesian oil by Pseudomonas fluorescens. Recoveries of over 90% were obtained for n-alkanes up to hexacontane (C 60) using liquid-liquid continuous extraction. After only 14 days, 80% of the aliphatic hydrocarbons had been degraded. At the end of the 136-day study, 14% of the original fraction remained. This comprised mainly C 40+ compounds. No decrease in the concentrations of compounds above C 45 was observed. However, the use of a rapid screening biodegradation method provided tentative proof that Pseudomonas fluorescens was capable of utilising n-alkanes up to C 60 once the bacteria had acclimated to HMW alkanes.

Determination of morphine and its analogues in urine by on-line coupled reversed-phase liquid chromatography-gas chromatography with on-line derivatization

An on-line coupled reversed-phase liquid chromatography-gas chromatography (RPLC-GC) method requiring minimal manual sample preparation was developed for the determination of morphine, codeine, heroin, dihydrocodeine and ethylmorphine in urine. A loop-type interface and concurrent eluent evaporation technique were used in the coupling, and the aqueous phase was changed to organic solvent by continuous liquid-liquid extraction before transfer to the GC. The two phases were separated with a sandwich-type phase separator. The analytes were also derivatized on-line before GC separation. The LC was used for clean-up, and the GC for the final separation and detection of the analytes. Total analysis time was less than 60 min, which is much shorter than with traditional analysis methods. A marked increase in the recoveries in liquid-liquid extraction (LLE) was obtained by heating the aqueous eluent and the extraction coil. Linearity and repeatability of the method were good and the limits of quantification for the analytes were between 61 and 92 ng/ml.

Residence time model for assessing liquid-liquid extraction systems

A model based on the residence time of solvent in the extraction system may be used to describe the dynamic operation of a continuous liquid-liquid extractor. It is proposed that optimum performance occurs when the extract exiting from the contactor is near equilibrium with the solution being extracted. This approach was tested on two commercially available continuous extraction systems. The difference in their performance was found to be related to the level of agitation of the two contactor vessels: the stirred system was approximately six times more efficient than the simple column continuous extractor. The stirred system achieved a near equilibrium analyte distribution between the solvent and sample and could be described accurately in terms of residence time theory. This was in marked contrast to its unmixed counterpart where the analyte distribution between solvent and sample reached 14% of its equilibrium value during its residence in the contactor. The effect of dead volume of solvent within the extraction assembly on the extraction rate was also apparent; its main effect was to delay the extraction process.

Speciation of mercury by continuous flow liquid-liquid extraction and inductively coupled plasma atomic emission spectrometry detection

An accurate, precise, sensitive and automated non-chromatographic method for methylmercury speciation based on a selective continuous liquid-liquid extraction of methylmercury, into xylene, as bromide and cold mercury vapour generation directly from the organic phase and final ICP-AES mercury detection is proposed. Both separation steps, liquid-liquid and gas-liquid are accomplished in a continuous mode and on line with ICP-AES as detector. The detection limit attained for methylmercury was 4ng·ml−1 (as mercury). The precision of the determination at a concentration level around 20 times the detection limit was +-5%. The proposed methodology has been applied successfully to the speciation of methylmercury and inorganic mercury in spiked sea water and spiked urine samples.

Analysis of extractable organic compounds in water by gas chromatography mass spectrometry: applications to surface water

Contamination of water by organic pollutants is a common environmental problem. Over a period of 1 year, the surface water of a canal network (Languedoc-Roussillon area, France) was analysed in order to identify organic compounds and to monitor its quality. Pollutants were extracted from 19 l of raw water using methylene chloride in a continuous countercurrent liquid-liquid extractor with a pulsed column. The extraction was performed at a pH above 11 and again at a pH below 2 according to U.S. Environmental Protection Agency method 625. The extract was analysed by gas chromatography/mass spectrometry, using two ionization techniques, namely electron ionization and chemical ionization. Mass spectra obtained by electron ionization were compared with those in a database (NIST). Some natural compounds and micropollutants were identified. Their structures were confirmed by chemical ionization (methane). One hundred and ten substances, making up the broad spectrum of extractable compounds in the surface water studied, were found by this method at a nanogram per litre concentration level. Among them, 13 are priority pollutants. These specific pollutants were qualified.

An automated flow-reversal injection/liquid—liquid extraction approach to the direct determination of total free fatty acids in olive oils

A continuous liquid-liquid extraction system based on an automated, simplified single-channel flow-reversal injection mode involving no segmentation or separation unit is proposed for the direct determination of total free fatty acids (FFA) in olive oils. It relies on the reaction between the Cu 2+-pyridine complex and FFA, which takes place at the organic-aqueous interface, the Cu 2+-FFA complex (copper soap) thus formed being extracted into the organic phase during the flow-reversal process. Continuous monitoring of the organic phase at 716 nm by means of a photometer located in the middle of the injection loop provides a multi-peak absorbance-time profile representing multiple reversals in the dynamic extraction process. Total FFA can thus determined in contents from 0.01 to 1.5% (3.5 × 10 −4 − 5.3 × 10 −2, M) for oleic acid in toluene-diluted oil samples (corresponding to 0.06–9.0% of FFA for original samples) with relative standard deviations in the range 4.9–7.8% and a sampling frequency of 12 h −1. The results provided by the proposed method are in accordance with those obtained with a manual procedure and comparable to those afforded by a standard acid-base titration method after appropriate correction.

Sb(III) and Sb(V) separation and analytical speciation by a continuous tandem on-line separation device in connection with inductively coupled plasma atomic emission spectrometry.

A sensitive, precise and automated non-chromatographic method for Sb(III) and Sb(V) analytical speciation based on a continuous tandem on-line separation device in connection with inductively coupled plasma-atomic emission (ICP-AES) detection is proposed. Two on-line successive separation steps are included into this method: a continuous liquid-liquid extraction of Sb(III) with ammonium pyrrolidine dithiocarbamate (APDC) into methylisobuthylketone (MIBK), followed by direct stibine generation from the organic phase. Both separation steps are carried out in a continuous mode and on-line with the ICP-AES detector. Optimization of experimental conditions for the tandem separation and ICP-AES detection are investigated in detail. Detection limits for Sb(III) were 3 ng.mL(-1) and for Sb(V) 8 ng.mL(-1). Precisions observed are in the range +/- 5%. The proposed methodology has been applied to Sb(III) and Sb(V) speciation in sea-water samples.

Analysis of Wine Aroma by Direct Injection in Gas Chromatography without Previous Extraction

A method is proposed which allows the direct gas chromatographic analysis of real-life samples of wine (i.e., without the need of preliminary sample preparation) just by using a programmed temperature vaporizer injector operated in a modified solvent elimination mode. The procedure presented is ecologically beneficial as no solvent is required for its performance; it is not expensive since it does not demand a special methodology; and it might be used as a quick screening in several fields. A comparison of the proposed method with other isolation techniques (i.e., continuous liquid-liquid extraction and simultaneous distillation-extraction) usually employed for the concentration of volatile components is also included

Continuous liquid‐liquid extraction combined on‐line with capillary gas chromatography‐atomic emission detection for environmental analysis

AbstractThe on‐line coupling of a liquid‐liquid extraction system with capillary gas chromatography using atomic emission detection (GC‐AED) has been studied. The required large volumes of about 100 μl of an iso‐octane solution can be introduced into the GC‐AED system by using the AED solvent vent and a solvent vapor exit in front of the capillary analytical column. Test solutions containing several pesticides were detected using the carbon, chlorine, nitrogen and sulfur channels. Analyte detectability (in concentration units) was improved significantly and low concentractions of the test compounds could be determined (1–5 ng/ml). Aqueous samples were on‐line extracted and analyzed. The precision of the large‐volume injection itself as well as the total extraction‐GC‐AED system was satisfactory (RSD of ca. 2 and 4%, respectively). As a real‐life application, several ground water samples were screened.

Gaschromatographic determination of phenol, methylphenols, chlorophenols, nitrophenols and nitroquinones in water at 0.1 μ g l −1

A sensitive method for the analysis of phenol, 2 monomethylphenols, 8 chlorophenols and 7 nitrophenols in minor polluted waters at 0.1 and 0.25 μg l −1 concentration is reported involving continuous liquid-liquid extraction with a light phase rotary perforator, derivatisation either with diazomethane or with trimethylsulfonium hydroxide (TMSH) and analysis by GC-MS. Emphasis was laid on simple derivatisation procedures. The reaction yields with diazomethane in the presence of catalytical amounts of methanol were higher than 85% for all compounds except phenol, the methylphenols and nitrohydroquinone. TMSH gave high reaction yields for the chlorophenols only. The combination of rotary perforator extraction and diazomethane methylation ensured generally high recoveries from a drinking water matrix and may be carried out in routine work. Solid phase extraction with commercial RP-C18 cartridges (1 g, 11 water sample) with and without addition of 30 g l −1 sodium chloride to the sample yielded generally lower recoveries, especially for phenol, the methylphenols and some of the nitrophenols.

Phase Discrimination in Continuous Liquid-Liquid Extraction with Diode Array Photometric Detection

A high-resolution phase-discrimination approach for use in continuous liquid-liquid extraction monitoring is reported that uses any available diode array spectrophotometer to monitor the segmented flow at three wavelengths: one for discriminating the phases involved, another for monitoring the target species, and the third for correction of signal fluctuations. Two sizes of organic-aqueous-phase segmentation are produced along the dynamic system: short segment lengths favoring mass transfer between the immiscible phases and longer segments formed at the expense of the shorter ones in a grouping chamber in order to allow one of the phases to fully occupy the flow cell path length line during monitoring. The proposed approach was successfully used for continuous monitoring of both aqueous and the organic phases, as well as liquid-liquid extraction processes involving chemical derivatization reactions

Continuous liquid-liquid extraction for preconcentration with on-line monitoring

Continuous liquid-liquid extraction for preconcentration with on-line monitoring

Identifying Volatiles in Soursop and Comparing Their Changing Profiles during Ripening

The volatile compounds in soursop (Annona muricata L.) were obtained by a liquid-liquid continuous extraction procedure from the aqueous solution of blended soursop pulp and analyzed by gas chromatography (GC) and GC-mass spectrometry (MS). Twelve volatiles were identified by comparing their mass spectra and Kovats retention indexes with those of standard compounds: five were identified tentatively from MS data only, eight are being reported for the first time. (Z) -3-hexen-l-ol was the main volatile present in mature-green fruit, while methyl (E) -2-hexenoate, methyl (E) -2-butenoate, methyl butanoate, and methyl hexanoate were the four main volatiles present in ripe fruit. Concentrations of these five volatiles decreased and several other unidentified volatiles appeared when the fruit became overripe.

Chemical analysis and sensory evaluation of hydrolysis products of humulene epoxides II and III

An analytical method was developed for authentic beer samples to identify hydrolysis and isomerization products of humulene epoxides II and III. This method involved a continuous liquid-liquid extraction, cleanup and concentration procedure, and analysis by GC/MS. Twelve compounds were identified in the concentration range from 0.002 to 2.8 mg/l in pilot brew and commercial beer samples. Seven of these compounds have not been found in beer before. A variety of hop essential oils, obtained by steam distillation, also was analyzed by GC/MS. In addition to humulene monoepoxides I-III, compounds 8 and 9 were found in the hop oils. Compound 9 has not been reported as a hop oil component previously