An automated system for liquid-liquid extraction based on a new micro-batch extraction chamber with on-line detection: Preconcentration and determination of copper(II)

An automated system to perform liquid-liquid extraction is proposed, in which the effective mixture (the intimate contact) between the aqueous phase and the organic phase, as well as the separation of the phases, are carried out in a micro-batch glass extraction chamber. Sample, reagents and organic solvent are introduced into the glass extraction chamber by a peristaltic pump using air as carrier. The detection of the extracted species from the aqueous phase is made in a small volume (120-150 μl) of isobutyl methyl ketone (MIBK). The system allows enrichment factors of 2-10-fold. The proposed automatic system was evaluated for Cu(II) extraction based on complex formation between copper(II) and 1-(2′-pyridylazo)naphthol (PAN) in MIBK. When a volumetric ration of 2:1 (aqueous:organic) was implemented, copper was detected in the concentration range of 100-1600 μg l⁻¹ (r = 0.9995) with a relative standard deviation of 2% (200 μg l⁻¹, n = 5) and a detection limit of 20 μg l⁻¹. The analytical curve was linear over the concentration range 25-500 μg l⁻¹ (r = 0.9994) when a volumetric ratio of 10:1 was employed. With this ratio, the detection limit was 5.0 μg l⁻¹ and the relative standard deviation was 6% (50 μg l⁻¹, n = 5).     

On-line liquid-liquid extraction system using a new phase separator for flame atomic absorption spectrometric determination of ultra-trace cadmium in natural waters

A robust flow injection (FI) on-line liquid-liquid extraction (LLE) preconcentration/separation system associated with a newly designed gravitational phase separator, coupled to flame atomic absorption spectrometry (FAAS) was developed. The performance of the system was illustrated for cadmium determination at the μg l⁻¹ level. The non-charged cadmium complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into isobutyl methyl ketone (IBMK). The organic phase was effectively separated from a large volume of aqueous phase and is led into a 100 μl loop of an injection valve before its introduction into the nebulizer. The system was optimized and offered good performance characteristics with unlimited life time of phase separator, greater flow rate ratios and improved flexibility, as compared with other solvent extraction preconcentration systems. With a sampling frequency of 33 h⁻¹, the enhancement factor was 155, the detection limit was 0.02 μg l⁻¹, the relative standard deviation was 3.2% at 2.0 μg l⁻¹ Cd concentration level and the calibration curve was linear over the concentration range 0.06-6.0 μg l⁻¹. The accuracy of the proposed method was evaluated by analyzing a certified reference material of water and by recovery measurements on spiked samples. Finally, it was successfully applied to the analysis of tapwater, river and seawater samples.     

Part-per-trillion determination of chlorobenzenes in water using dispersive liquid-liquid microextraction combined gas chromatography-electron capture detection

In this study, a simple, rapid and efficient method, dispersive liquid-liquid microextraction (DLLME) combined gas chromatography-electron capture detection (GC-ECD), for the determination of chlorobenzenes (CBs) in water samples, has been described. This method involves the use of an appropriate mixture of extraction solvent (9.5 μl chlorobenzene) and disperser solvent (0.50 ml acetone) for the formation of cloudy solution in 5.00 ml aqueous sample containing analytes. After extraction, phase separation was performed by centrifugation and the enriched analytes in sedimented phase were determined by gas chromatography-electron capture detection (GC-ECD). Our simple conditions were conducted at room temperature with no stiring and no salt addition in order to minimize sample preparation steps. Parameters such as the kind and volume of extraction solvent, the kind and volume of disperser solvent, extraction time and salt effect, were studied and optimized. The method exhibited enrichment factors and recoveries ranging from 711 to 813 and 71.1 to 81.3%, respectively, within very short extraction time. The linearity of the method ranged from 0.05 to 100 μg l⁻¹ for dichlorobenzene isomers (DCB), 0.002-20 μg l⁻¹ for trichlorobenzene (TCB) and tetrachlorobenzene (TeCB) isomers and from 0.001 to 4 μg l⁻¹ for pentachlorobenzene (PeCB) and hexachlorobenzene (HCB). The limit of detection was in the low μg l⁻¹ level, ranging between 0.0005 and 0.05 μg l⁻¹. The relative standard deviations (R.S.D.s) for the concentration of DCB isomers, 5.00 μg l⁻¹, TCB and TeCB isomers, 0.500 μg l⁻¹, PeCB and HCB 0.100 μg l⁻¹ in water by using the internal standard were in the range of 0.52-2.8% (n = 5) and without the internal standard were in the range of 4.6-6.0% (n = 5). The relative recoveries of spiked CBs at different levels of chlorobenzene isomers in tap, well and river water samples were 109-121%, 105-113% and 87-120%, respectively. It is concluded that this method can be successfully applied for the determination of CBs in tap, river and well water samples.     

Headspace solid-phase micro-extraction gas chromatography-mass detection method for the determination of butyltin compounds in wines

Butyltin compounds are widespread contaminants which have also been found in some wines, determined by liquid-liquid extraction followed by alkylation with a Grignard reagent and gas chromatography-mass spectrometric (GC-MS) analysis. A promising alternative to this extraction/derivatization method is the one-step tetraethylborate in situ ethylation/solid-phase micro-extraction (SPME) method. In this work, a SPME-GC-MS method for the determination of butyltin compounds in wine was optimised. The optimised parameters concerned the pre-treatment with tetramethylammonium hydroxide, matrix modification with sodium chloride, tetraethylborate concentration, extraction time and temperature, and the GC separation program. The analytical figures of merit of the optimised method (range, limit of detection (LOD) and reproducibility) were evaluated. The sensitivity (range 20-1421 kcounts μg⁻¹ l⁻¹ as Sn) and LOD (range, 0.01-0.2 μg l⁻¹ as Sn) depended greatly on the butyltin species to be measured and on the type of wine. For the tested species (monobutyltin, dibutyltin and tributyltin) the highest sensitivities were achieved for Port wine samples, followed by red wine>white wine>white Verde wine. The method allowed acceptable repeatability (relative standard deviation (R.S.D.), 6-8%; n=4) and reproducibility (R.S.D., 8-9%; n=3).     

Automatic flow procedure based on multicommutation exploiting liquid-liquid extraction for spectrophotometric lead determination in plant material

A not expensive automatic flow system based on multicommutation and exploiting the liquid-liquid extraction methodology for the determination of lead in plant material is described. The spectrophotometric procedure for lead determination was based on the reaction with dithizone followed by extraction using an organic solvent. The facilities afforded by the multicommutation approach allowed the use of an air stream as carrier, thus contributing to reduce the overall waste generation. The results obtained analysing plant materials compare very well with those obtained employing inductive coupled plasma optical emission spectrometry (ICP OES) at 90% confidence level. Others profitable features such as a linear response range between 50 and 200 μg l⁻¹ Pb (r = 0.999); a sampling rate of 15 determination per hour; a relative standard deviation of 1.8% (n = 12) for a typical sample containing 163 μg l⁻¹ Pb; a detection limit of 12 μg l⁻¹; a reagent consumption of 4.5 mg dithizone; and a waste generation of 225 μl organic solvent per determination were also achieved.     

Potentialities of two solventless extraction approaches—Stir bar sorptive extraction and headspace solid-phase microextraction for determination of higher alcohol acetates, isoamyl esters and ethyl esters in wines

A stir bar sorptive extraction with liquid desorption followed by large volume injection coupled to gas chromatography-quadrupole mass spectrometry (SBSE-LD/LVI-GC-qMS) was evaluated for the simultaneous determination of higher alcohol acetates (HAA), isoamyl esters (IsoE) and ethyl esters (EE) of fatty acids. The method performance was assessed and compared with other solventless technique, the solid-phase microextraction (SPME) in headspace mode (HS). For both techniques, influential experimental parameters were optimised to provide sensitive and robust methods. The SBSE-LD/LVI methodology was previously optimised in terms of extraction time, influence of ethanol in the matrix, liquid desorption (LD) conditions and instrumental settings. Higher extraction efficiency was obtained using 60 min of extraction time, 10% ethanol content, n-pentane as desorption solvent, 15 min for the back-extraction period, 10 mL min⁻¹ for the solvent vent flow rate and 10 °C for the inlet temperature. For HS-SPME, the fibre coated with 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) afforded highest extraction efficiency, providing the best sensitivity for the target volatiles, particularly when the samples were extracted at 25 °C for 60 min under continuous stirring in the presence of sodium chloride (10% (w/v)). Both methodologies showed good linearity over the concentration range tested, with correlation coefficients higher than 0.984 for HS-SPME and 0.982 for SBES-LD approach, for all analytes. A good reproducibility was attained and low detection limits were achieved using both SBSE-LD (0.03-28.96 μg L⁻¹) and HS-SPME (0.02-20.29 μg L⁻¹) methodologies. The quantification limits for SBSE-LD approach ranging from 0.11 to 96.56 μg L⁻and from 0.06 to 67.63 μg L⁻¹ for HS-SPME. Using the HS-SPME approach an average recovery of about 70% was obtained whilst by using SBSE-LD obtained average recovery were close to 80%. The analytical and procedural advantages and disadvantages of these two methods have been compared.Both analytical methods were used to determine the HAA, IsoE and EE fatty acids content in “Terras Madeirenses” table wines. A total of 16 esters were identified and quantified from the wine extracts by HS-SPME whereas by SBSE-LD technique were found 25 esters which include 2 higher alcohol acetates, 4 isoamyl esters and 19 ethyl esters of fatty acids. Generally SBSE-LD provided higher sensitivity with decreased analysis time.     

Headspace solid phase microextraction for the analysis of the new antifouling agents Irgarol 1051 and Sea Nine 211 in natural waters

A simple and rapid extraction method based on headspace solid phase microextraction (HS-SPME) has been developed for the analysis of two antifouling agents, currently licensed for use in marine antifouling paints. Irgarol 1051 and Sea Nine 211 were extracted from aqueous solutions using polydimethylsiloxane-divinylbenzene (PDMS-DVB) 65 μm fiber and analyzed by gas chromatography (GC) with flame thermionic, electron capture and mass spectrometric detection. The extraction time, addition of Na₂SO₄ and the influence of organic matter, such as humic acid on extraction efficiency were examined in order to achieve a sensitive method. The optimized procedure was applied to spiked natural waters, such as sea water, river water and lake water in a concentration range of 0.5-50 μg l⁻¹ in order to obtain the analytical characteristics. The linear calibration curve obtained (R²>0.990) for both analytes indicate that the presence of interfering compounds had no significant effect due to the high affinity of both analytes to the PDMS-DVB 65 μm fiber coating. Recoveries were in relatively high levels over >82% in all types of natural waters. The limits of detection (LODs) ranged from 0.002 to 0.030 μg l⁻¹, depending on the detector and the compound investigated, with relative standard deviations in the range of 3-12% at all concentration levels tested. Finally, the proposed method was applied in real water samples from different marinas of Epirus region (NW Greece) in order to investigate its performance in precise and routine environmental analysis.     

NMR investigation of acrolein stability in hydroalcoholic solution as a foundation for the valid HS-SPME/GC–MS quantification of the unsaturated aldehyde in beverages

Acrolein (propenal) is found in many foods and beverages and may pose a health hazard due to its cytotoxicity. Considerable knowledge gaps regarding human exposure to acrolein exist, and there is a lack of reliable analytical methods. Hydroalcoholic dilutions prepared for calibration purposes from pure acrolein show considerable degradation of the compound and nuclear magnetic resonance (NMR) spectroscopy showed that 1,3,3-propanetriol and 3-hydroxypropionaldehyde are formed. The degradation can be prevented by addition of hydroquinone as stabilizer to the calibration solutions, which then show linear concentration-response behaviour required for quantitative analysis. The stabilized calibration solutions were used for quantitative headspace solid-phase microextraction/gas chromatography–mass spectrometry (HS-SPME/GC–MS) determination of acrolein in alcoholic beverages with a detection limit of 14 μg L⁻¹. Of 117 tested alcoholic beverages, 64 were tested positive with the highest incidence in grape marc spirits and whiskey (100%, mean 252 μg L⁻¹), followed by fruit spirits (86%, mean 591 μg/L⁻¹), tequila (86%, mean 404 μg L⁻¹), Asian spirits (43%, mean 54 μg L⁻¹) and wine (9%, mean 0.7 μg L⁻¹). Acrolein could not be detected in beer, vodka, absinthe and bottled water. Six of the fruit and grape marc spirits had acrolein levels above the World Health Organization (WHO) provisional tolerable concentration of 1.5 mg L⁻¹.     

Determination of the steroid hormone levels in water samples by dispersive liquid-liquid microextraction with solidification of a floating organic drop followed by high-performance liquid chromatography

In this study, the steroid hormone levels in river and tap water samples were determined by using a novel dispersive liquid-liquid microextraction method based on the solidification of a floating organic drop (DLLME-SFO). Several parameters were optimized, including the type and volume of the extraction and dispersive solvents, extraction time, and salt effect. DLLME-SFO is a fast, cheap, and easy-to-use method for detecting trace levels of samples. Most importantly, this method uses less-toxic solvent. The correlation coefficient of the calibration curve was higher than 0.9991. The linear range was from 5 to 1000 μg L⁻¹. The spiked environmental water samples were analyzed using DLLME-SFO. The relative recoveries ranged from 87% to 116% for river water (which was spiked with 4 μg L⁻¹ for E1, 3 μg L⁻¹ for E2, 4 μg L⁻¹ for EE2 and 9 μg L⁻¹ for E3) and 89% to 102% for tap water (which was spiked with 6 μg L⁻¹ for E1, 5 μg L⁻¹ for E2, 6 μg L⁻¹ for EE2 and 10 μg L⁻¹ for E3). The detection limits of the method ranged from 0.8 to 2.7 μg L⁻¹ for spiked river water and 1.4 to 3.1 μg L⁻¹ for spiked tap water. The methods precision ranged from 8% to 14% for spiked river water and 7% to 14% for spiked tap water.     

Combination of dispersive liquid-liquid microextraction with flame atomic absorption spectrometry using microsample introduction for determination of lead in water samples

The dispersive liquid-liquid microextraction (DLLME) was combined with the flame atomic absorption spectrometry (FAAS) for determination of lead in the water samples. Diethyldithiophosphoric acid (DDTP), carbon tetrachloride and methanol were used as chelating agent, extraction solvent and disperser solvent, respectively. A new FAAS sample introduction system was employed for the microvolume nebulization of the non-flammable chlorinated organic extracts. Injection of 20 μL volumes of the organic extract into an air-acetylene flame provided very sensitive spike-like and reproducible signals.Some effective parameters on the microextraction and the complex formation were selected and optimized. These parameters include extraction and disperser solvent type as well as their volume, extraction time, salt effect, pH and amount of the chelating agent. Under the optimized conditions, the enrichment factor of 450 was obtained from a sample volume of 25.0 mL. The enhancement factor, calculated as the ratio of the slopes of the calibration graphs with and without preconcentration, which was about 1000. The calibration graph was linear in the range of 1-70 μg L⁻¹ with a detection limit of 0.5 μg L⁻¹. The relative standard deviation (R.S.D.) for seven replicate measurements of 5.0 and 50 μg L⁻¹ of lead were 3.8 and 2.0%, respectively. The relative recoveries of lead in tap, well, river and seawater samples at the spiking level of 20 μg L⁻¹ ranged from 93.8 to 106.2%. The characteristics of the proposed method were compared with those of the liquid-liquid extraction (LLE), cloud point extraction (CPE), on-line and off-line solid-phase extraction (SPE) as well as co-precipitation, based on bibliographic data. Operation simplicity, rapidity, low cost, high enrichment factor, good repeatability, and low consumption of the extraction solvent at a microliter level are the main advantages of the proposed method.     

Flow injection on-line solid phase extractive preconcentration of palladium(II) in dust and rock samples using exfoliated graphite packed microcolumns and determination by flame atomic absorption spectrometry

A sensitive and efficient flow injection preconcentration and matrix-separation technique using exfoliated graphite (EG) as column material was developed prior to flame atomic absorption spectrometry (FAAS) determination of palladium(II) in street/fan blade dust and rock samples. The method is based on the sorption of palladium(II)—diethylammonium dithiocarbamate chelate (which was found to be better among various thioligands) complex on to EG material and its subsequent elution with acidified methanol (0.01 M HCl in methanol). Using 8 ml of the sample, the detection limit achieved was 1.0 μg l⁻¹. The accuracy of the method developed was checked by analysing certified reference material SARM-7. The precision obtained for five successive determination of 100 μg l⁻¹ of palladium(II) was 2.4%. The performance of EG material was compared with allotropes of carbon in terms of pH, chelate concentration, weight of column material, sensitivity enhancement (w.r.t. conventional FAAS), detection limit, calibration range, selectivity and precision. Furthermore, performance of the EG material packed column was compared with commercially available C₁₈ bonded silica gel/alumina columns for on-line FIA-FAAS determination of palladium(II).     

Liquid-liquid extraction procedure exploiting multicommutation in flow system for the determination of molybdenum in plants

A liquid-liquid extraction flow analysis procedure for the spectrophotometric determination of molybdenum in plants at μg l⁻¹ level is described. The flow network comprised a set of solenoid valves assembled to implement the multicommutation approach under microcomputer control. Radiation source (LED, 475 nm), detector (photodiode) and separation chamber were nested together with the flow cell comprising a compact unit. The consumption of reagents (potassium thiocyanate and stannous chloride) and also extracting solvent (isoamyl alcohol) were optimized to 32 mg and 200 μl per determination, respectively. Accuracy was assessed by comparing results with those obtained with ICP-OES and no significant difference at 95% confidence level was observed. Other favorable characteristics such as a linear response ranging from 25 to 150 μg l⁻¹ molybdenum (r=0.999); detection limit of 4.6 μg l⁻¹ sample throughput of 25 determinations per hour and relative standard deviation of 2.5% (n=10) were also achieved.     

Ochratoxin A in wines-assessing global uncertainty associated with the results

Ochratoxin A (OTA) is a mycotoxin (potentially carcinogenic secondary metabolite derived from fungal contamination), produced by some Aspergillus and Penicillium strains. Although present and legislated in different food sources in the human diet, the regulation for wine intake is still under discussion. The Office International de la Vigne et du Vin (OIV) recommended maximum levels in wine of 2 μg l⁻¹. Some reports refer to OTA contamination in wines up to 15 μg l⁻¹ and a special incidence in red wines from the southern regions of Europe and the north of Africa, but the majority of the data available are below 1 μg l⁻¹. When working at such low concentrations, the problem of the uncertainty of the results becomes decisive towards the implementation of legal limits. In order to assess the global uncertainty associated with OTA determination in wines and widen the data set and knowledge of the situation in Portugal, 340 wines were analysed (189 Port Wine, 85 Vinho Verde and 66 wines from other regions in the country) by a high performance liquid chromatography (HPLC)-fluorescence detection (FD) method using immunoaffinity columns for clean up. OTA was detected in 69 wines by the method used, but in concentrations below 0.5 μg l⁻¹, except for two which showed levels up to a maximum of 2.1 μg l⁻¹. However, the global uncertainty for OTA is close to 37% for concentrations above 0.5 μg l⁻¹, and therefore, such value can be below or exceed the OIV limit. In the vicinity of the limit of detection, 0.084 μg l⁻¹, the global uncertainty rises exponentially to a maximum of about 70%. This can be an obstacle when discussing safety intake limits. Ethanol and glucose content did not interfere in the clean up of OTA by immunoaffinity columns.     

Flow injection wetting-film extraction system for flame atomic absorption spectrometric determination of cadmium in environmental waters

A newly simple flow injection wetting-film extraction system coupled to flame atomic absorption spectrometry (FAAS) has been developed for trace amount of cadmium determination. The sample was mixed on-line with sodium diethyl dithiocarbamate and the produced non-charged Cd(II)-diethyl dithiocarbamate (DDTC) chelate complex was extracted on the thin film of diisobutyl ketone (DIBK) on the inner wall of the PTFE extraction coil. The wetting-film with the extracted analyte was then eluted by a segment of the cover solvent, and transported directly to the FAAS for evaluation. All the important chemical and flow parameters were optimized. Under the optimized conditions an enhancement factor of 35, a sample frequency of 22 h⁻¹ and a detection limit of c_L = 0.7 μg l⁻¹ Cd(II) were obtained for 60 s preconcentration time. The calibration curve was linear over the concentration range 1.5-45.0 μg l⁻¹ Cd(II) and the relative standard deviation, R.S.D. (n = 10) was 3.9%, at 10.0 μg l⁻¹ concentration level. The developed method was successfully applied to cadmium determination in a variety of environmental water samples as well as waste-water sample.     

Detection capability of tetracyclines analysed by a fluorescence technique: comparison between bilinear and trilinear partial least squares models

According to the committee decision of 12 August 2002 (2002/657/EC) the capability of detection, CCβ, must be set in all analytical methods not only at concentration levels close to zero but also at the maximum permitted limit (PL). In this work we describe a methodology which evaluates the capability of detection of a fluorescence technique with soft calibration models (bilinear and trilinear PLS) to determine tetracyclines (group B1 substances from annex 1 of Directive 96/23/EC). Its estimation is based on the generalisation of the procedure described in International Union of Pure and Applied Chemistry and in the ISO standard 11843 for univariate signals which evaluates the probabilities of false positive (α) and false negative (β). The capability of detection, CCβ, estimated from the second-order signal and the trilinear PLS model is 9.93 μg l⁻¹ of tetracycline, 17.75 μg l⁻¹ of oxytetracycline and 26.31 μg l⁻¹ of chlortetracycline, setting α and β at 0.05. The capability of detection, CCβ, determined around the PL (100 μg kg⁻¹ in milk and muscle) with the second-order signal is 109.4 μg l⁻¹ of tetracycline, 117.0 μg l⁻¹ of oxytetracycline and 124.9 μg l⁻¹ of chlortetracycline, setting α and β at 0.05. The results were compared with those obtained with zero and first-order signals. The effect of the interferences on the capability of detection was also analysed as well as the number of standards used to build the models and their calibration range.When a tetracycline is quantified in presence of uncalibrated ones by means of the trilinear PLS model the errors oscillate between 14.70% for TC and 9.57% for OTC.     

Ligandless dispersive liquid-liquid microextraction for the separation of trace amounts of silver ions in water samples and flame atomic absorption spectrometry determination

In this article, a new ligandless dispersive liquid-liquid microextraction method has been developed for preconcentration of trace quantities of silver as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach, carbon tetrachloride and ethanol were used as extraction and dispersive solvents. Several factors that may be affected on the extraction process, like, extraction solvent, disperser solvent, the volume of extraction and disperser solvent, pH of the aqueous solution and extraction time were optimized. Under the optimal conditions, the calibration curve was linear in the range of 5.0 ng mL⁻¹ to 2.0 μg mL⁻¹ of silver with R² = 0.9995 (n = 9) and detection limit based on three times the standard deviation of the blank (3S_b) was 1.2 ng mL⁻¹ in original solution. The relative standard deviation for eight replicate determination of 0.5 μg mL⁻¹ silver was ±1.5%. The high efficiency of dispersive liquid-liquid microextraction to carry out the determination of silver in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of silver in standard and water samples with satisfactory results.     

Ultrasound-assisted dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-fluorescence detection for sensitive determination of biogenic amines in rice wine samples

Ultrasound-assisted dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography-fluorescence detection was used for the extraction and determination of three biogenic amines including octopamine, tyramine and phenethylamine in rice wine samples. Fluorescence probe 2,6-dimethyl-4-quinolinecarboxylic acid N-hydroxysuccinimide ester was applied for derivatization of biogenic amines. Acetonitrile and 1-octanol were used as disperser solvent and extraction solvent, respectively. Extraction conditions including the type of extraction solvent, the volume of extraction solvent, ultrasonication time and centrifuging time were optimized. After extraction and centrifuging, analyte was injected rapidly into high-performance liquid chromatography and then detected with fluorescence. The calibration graph of the proposed method was linear in the range of 5–500 μg mL⁻¹ (octopamine and tyramine) and 0.025–2.5 μg mL⁻¹ (phenethylamine). The relative standard deviations were 2.4–3.2% (n = 6) and the limits of detection were in the range of 0.02–5 ng mL⁻¹. The method was applied to analyze the rice wine samples and spiked recoveries in the range of 95.42–104.56% were obtained. The results showed that ultrasound-assisted dispersive liquid–liquid microextraction was a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of biogenic amines.     

Headspace liquid-phase microextraction of trihalomethanes in drinking water and their gas chromatographic determination

In the present work, a novel method for the determination of trihalomethanes (THMs) such as chloroform, dichlorobromomethane, chlorodibromomethane and bromoform in drinking water has been described. It is based on coupling headspace liquid-phase microextraction (HS-LPME) with gas chromatography-electron capture detector (GC-ECD). A microdrop of organic solvent at the tip of a commercial microsyringe was used to extract analytes from aqueous samples. Three organic solvents—xylene, ethylene glycol and 1-octanol—were compared and 1-octanol was the most sensitive solvent for the analytes. Extraction conditions such as headspace volume, extraction time, stirring rate, content of NaCl and extraction temperature were found to have significant influence on extraction efficiency. The optimized conditions were 15 ml headspace volume in a 40 ml vial, 10 min extraction time and 800 rpm stirring rate at 20 °C with 0.3 g ml⁻¹ NaCl. The linear range was 1-100 μg l⁻¹ for THMs. The limits of detection (LODs) ranged from 0.15 μg l⁻¹ (for dichlorobromomethane and chlorodibromomethane) to 0.4 μg l⁻¹ (for chloroform); and relative standard deviations (RSD) for most of THMs at the 10 μg l⁻¹ level were below 10%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 101 to 112%.     

Comparison of two extraction methods for evaluation of volatile constituents patterns in commercial whiskeys Elucidation of the main odour-active compounds

An analytical procedure based on manual dynamic headspace solid-phase microextraction (HS-SPME) method and the conventional extraction method by liquid-liquid extraction (LLE), were compared for their effectiveness in the extraction and quantification of volatile compounds from commercial whiskey samples. Seven extraction solvents covering a wide range of polarities and two SPME fibres coatings, has been evaluated. The highest amounts extracted, were achieved using dichloromethane (CH₂Cl₂) by LLE method (LLECH₂Cl₂) and using a CAR/PDMS fibre (SPME_CAR/PDMS) in HS-SPME. Each method was used to determine the responses of 25 analytes from whiskeys and calibration standards, in order to provide sensitivity comparisons between the two methods. Calibration curves were established in a synthetic whiskey and linear correlation coefficient (r) were greater than 0.9929 for LLECH₂Cl₂ and 0.9935 for SPME_CAR/PDMS, for all target compounds. Recoveries greater than 80% were achieved. For most compounds, precision (expressed by relative standard deviation, R.S.D.) are very good, with R.S.D. values lower than 14.78% for HS-SPME method and than 19.42% for LLE method. The detection limits ranged from 0.13 to 19.03 μg L⁻¹ for SPME procedure and from 0.50 to 12.48 μg L⁻¹ for LLE.A tentative study to estimate the contribution of a specific compound to the aroma of a whiskey, on the basis of their odour activity values (OAV) was made. Ethyl octanoate followed by isoamyl acetate and isobutyl alcohol, were found the most potent odour-active compounds.     

Simultaneous fluorimetric determination of glyphosate and its metabolite, aminomethylphosphonic acid, in water, previous derivatization with NBD-Cl and by partial least squares calibration (PLS)

The reactions of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with glyphosate (GLY) and with its main metabolite, aminomethylphosphonic acid (AMPA), have been studied. The resolution of binary mixtures of glyphosate and aminomethylphosphonic acid has been accomplished by partial least squares (PLS) multivariate calibration. The method of determination is based on the fluorescence emission of the derivatives formed in presence of NBD-Cl at 90 °C, in methanol and in basic medium. The dynamic ranges of the methods were comprised between 10 and 150 μg l⁻¹ for GLY and between 10 and 200 μg l⁻¹ for AMPA, being the detection limits 2 and 5.4 μg l⁻¹ for GLY and AMPA, respectively. The total luminiscence information of the derivatives has been used to optimize the spectral data set to perform the calibration, by analysis of the three-dimensional excitation-emission matrices. A comparison between the predictive ability of the multivariate calibration method, partial least squares type 1 (PLS-1), on two spectral data sets, emission and synchronous spectra, has been performed. The PLS-1 method, applied to the emission spectra, has been selected as optimum. The proposed method has been applied to the simultaneous determination of GLY and AMPA in river water. For concentrations ranging from 100 to 600 μg l⁻¹ of each compound in the samples, analytical recoveries range from 83 to 94% for GLY and from 104 to 120% for AMPA.