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Papers by soledad rubio
Acid-induced cloud point extraction and preconcentration of polycyclic aromatic hydrocarbons from environmental solid samples
Journal of Chromatography A, 2002
The effectiveness of the acid-induced phase separation of anionic surfactants (acid-induced cloud... more The effectiveness of the acid-induced phase separation of anionic surfactants (acid-induced cloud point extraction, ACPE) to extract polycyclic aromatic hydrocarbons (PAHs) from different environmental samples (soils, sediments and sludges), prior to chromatographic analysis, was evaluated. Variables affecting the ACPE efficiency were optimised using a natural matrix (a harbour sediment, CRM 535). Temperature, surfactant concentration and stirring were of primary importance to maximise recovery, whereas temperature and surfactant/hydrochloric acid concentration influenced the volume of the surfactant-rich phase and therefore the preconcentration factor achieved. The optimal conditions (2% sodium dodecanesulphonate (SDoS), 4.2 M HCl, 60 degrees C, 1 h) were applied to the extraction of PAHs from various matrices and the ACPE recoveries compared to certified results from Soxhlet extractions. Recoveries obtained for four to five aromatic ring PAHs ranged from 71 to 98%. Uncertainties obtained using ACPE were similar to or lower than those provided for the certified values. The volume of the extracts ranged from 1 to 2 ml. The method did not require additional clean-up or preconcentration steps.
Analytica Chimica Acta, 2005
Hemimicelles-based solid-phase extraction was proposed for the concentration of high volume commo... more Hemimicelles-based solid-phase extraction was proposed for the concentration of high volume commodity phthalates from wastewater samples prior to their separation and quantitation by liquid chromatography/atmospheric pressure chemical ionization in positive mode, ion trap mass spectrometry. Di-(2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP) and di-n-butyl phthalate (DBP) were concentrated on hemimicelles of sodium dodecyl sulphate (SDS) produced on alumina on the basis of hydrophobic interactions. The recovery of the target compounds was found quantitative under a wide range of experimental conditions (15-255 mg SDS g −1 alumina, pH 2-6 and sample loading volume up to 1 L). Concentration factors of 2500 were achieved by SPE of 0.5 L of sewage samples. The method detection limits found for BBP, DBP and DEHP were 7, 15 and 16 pg, respectively. The relative standard deviation ranged from 2 to 5%, which indicated good method precision. The approach developed was applied to the determination of phthalates in raw and treated sewage samples.
SolidPhase Extraction of Amphiphiles Based on Mixed Hemimicelle/Admicelle Formation: Application to the Concentration of Benzalkonium Surfactants in Sewage and River Water
Analytical Chemistry, 2003
The capability of surfactant-coated mineral oxides to aid the solid-phase extraction (SPE) of amp... more The capability of surfactant-coated mineral oxides to aid the solid-phase extraction (SPE) of amphiphiles based on the formation of mixed hemimicelles/admicelles was investigated. The approach is illustrated by studying the adsolubilization of benzalkonium homologue (C(12), C(14), C(16)) surfactants (BAS) on sodium dodecyl sulfate (SDS)-coated alumina. These oppositely charged surfactants form mixed aggregates on alumina causing retention of BAS by strong hydrophobic and ionic interactions. The recovery of BAS was found quantitative and independent of the alkyl chain length under a wide range of experimental conditions (3-200 mg of SDS/g of alumina; pH 2-11; sample flow rate 3-20 mL/min, and sample loading volume 0.025-1 L). Anionic and nonionic surfactants and electrolytes did not interfere to the levels found in raw sewage. Combination of BAS adsolubilization-based SPE with liquid chromatography/electrospray ionization in positive ion mode/ion trap mass spectrometry permitted the quantification of BAS with detection limits of 4 ng/L and their identification by isolation and subsequent fragmentation in the ion trap. The approach developed was applied to the determination of BAS in raw and treated sewage and river samples. The concentrations of benzalkonium surfactants found ranged between 0.1 and 49 microg/L.
Evaluation and Optimization of an On-Line Admicelle-Based Extraction-Liquid Chromatography Approach for the Analysis of Ionic Organic Compounds
Analytical Chemistry, 2004
Admicelles-based solid-phase extraction (SPE) was on-line coupled with liquid chromatography/elec... more Admicelles-based solid-phase extraction (SPE) was on-line coupled with liquid chromatography/electrospray ionization/ion trap mass spectrometry, and it was proposed for the extraction of ionic organic compounds based on the formation of surfactant-analyte ion pairs. The approach was illustrated by studying the preconcentration of quaternary ammonium herbicides (quats) on sodium dodecyl sulfate (SDS) admicelles produced on alumina. Optimization of the parameters affecting SPE were studied on the basis that admicelles are dynamic entities in equilibrium with the aqueous phase. Some general guidelines could be established for method development from the results obtained. Factors influencing on-line operation were elucidated. On-line regeneration of the sorbent in each run was easily achieved by disruption of SDS admicelles with methanol and posterior coating of the alumina with SDS. The recovery of quats from drinking water samples were found quantitative for paraquat, diquat, and difenzoquat and above to 70% for chlormequat and mepiquat. Concentration factors of about 250, using sample volumes of 50 mL, were achieved. The detection limits ranged from 10 to 30 ng/L. The approach developed permits compliance with the directives of the European Community for drinking waters (100 ng/L) and goes deeply into the basis of solid-phase extractions that use surfactant-coated mineral oxide as sorbents.
Determination of non-ionic polyethoxylated surfactants in wastewater and river water by mixed hemimicelle extraction and liquid chromatography–ion trap mass spectrometry
Journal of Chromatography A, 2005
The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospher... more The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospheric pressure chemical ionisation in positive mode, ion trap mass spectrometry (LC/(APCl+-IT)-MS) for the concentration, separation and quantitation of non-ionic surfactants has been investigated. Concentration was based on the formation of mixed aggregates of analytes [alkylphenol ethoxylates (APE, octyl and nonyl) and alkyl ethoxylates (AE, C12-C16)] with the anionic surfactant sodium dodecyl sulphate (SDS) that is adsorbed on alumina. Parameters affecting SPE were investigated on the basis that hemimicelles are dynamic entities in equilibrium with the aqueous phase. The performance of ion trap mass spectrometry for MS and MS/MS quantitation of non-ionic homologues was assessed. Recoveries of analytes from wastewater influent and effluent and river water samples ranged between 91 and 98% and were found independent on the length of the alkyl chain under the optimised conditions. Anionic surfactants did not interfere to the levels found in environmental samples. The detection limits ranged between 14 and 111 ng/l for wastewater influent, 10 and 40 for wastewater effluent and 4 and 35 for river water, after concentration of 250, 500 and 750 ml of sample, respectively. The approach was applied to the determination of AE and APE in influent and effluent samples from four wastewater treatment plants and four river samples. The concentrations of individual non-ionic surfactants found ranged between 0.3 and 373 microg/l.
Supramolecular systems-based extraction-separation techniques coupled to mass spectrometry
Journal of Separation Science, 2005
The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas... more The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas-phase fundamental studies of host–guest complexes and supramolecular assemblies. Mass spectrometric analysis has also benefited from the ability of supramolecular systems to behave as pseudophases in which solutes partition from the bulk solvent phase. Supramolecular systems-based extraction and concentration schemes and separation techniques have been widely used in different fields of analytical chemistry and are ideally suited for coupling with MS. This review describes the present status of the application of supramolecular chemistry in mass spectrometric analysis and includes topics such as the use of coacervative liquid–liquid extraction and hemimicelle/admicelle-based SPE of organic compounds prior to chromatography and electrophoresis. It also discusses the recent advances in enantioselective analysis using CD in electrophoresis- and chromatography-MS. The potential and analytical challenges of these approaches in environmental and bioanalytical chemistry, where one can expect significant developments in the future, are outlined.
Water Research, 2000
AbstractÐMany aromatic compounds are oxidized but not completely mineralized by Fenton's reagent.... more AbstractÐMany aromatic compounds are oxidized but not completely mineralized by Fenton's reagent. Little attention has so far been given to the identi®cation of residual organic matter and the evaluation of its toxicity. In this work, the oxidation of metol [N-methyl-p-aminophenol] by Fe 2+ /H 2 O 2 in the dark as a model for aromatic amines and alcohols was examined. Analysis of oxidized solutions was performed by both LC-electron impact (EI)-MS and LC-electrospray ionization (ESI)-MS. It was checked that the degradation of metol takes place via direct oxidation by Fe 3+ and OH Á attack. Intermediates amenable to oxidation by OH Á are basically partially oxygenated aromatic species, dimerization products and polymers. End products not amenable to oxidation by this radical are ferrycarboxylate complexes, which are non-toxic to UC581 bacterial cells. These complexes can be completely destroyed by irradiation with light. The photo-Fenton reaction is therefore an eective choice for the in situ treatment of industrial euents containing aromatic amines and hydroxylated species. 7
Trends in Analytical Chemistry, 2003
Supramolecular assemblies have been used largely in analytical extraction and concentration schem... more Supramolecular assemblies have been used largely in analytical extraction and concentration schemes. Their ability to form a phase with regions of different polarities, acidities and viscosities, where solutes of very different structure can be solubilized, has encouraged this use. At present, the basis, characteristics and scope of extraction techniques, such as cloud point, are well established. However, they have not been accepted in routine analysis, despite the demonstrated advantages of surfactant-mediated separations over other conventional extraction techniques. This article deals with the challenges in making these extraction techniques competitive and explores the potential for using other phenomena and materials where supramolecular assemblies are involved, such as coacervation, hemimicelles/admicelles and amphiphilic-templated mesoporous silicas, for the extraction/concentration of organic compounds. #
Analytica Chimica Acta, 2004
The surfactant-dye binding degree (SDBD) method was extended to the determination of amphiphilic ... more The surfactant-dye binding degree (SDBD) method was extended to the determination of amphiphilic drugs. This new methodology was based on the effect of amphiphilic compounds on the degree of binding of a surfactant to dye molecules. The dye induces the formation of surfactant aggregates and allows this process to be monitored from changes in their spectral features. The interaction between the anionic dye Coomassie Brilliant Blue G (CBBG) and the cationic surfactant didodecyldimethylammonium bromide (DDABr) was used for the sensitive determination of phenamic acids (meclophenamic, mephenamic, fluphenamic and niflumic acid), non-steroidal anti-inflammatory drugs. The addition of phenamic acid to the dye-surfactant mixture resulted in the formation of drug-DDABr aggregates with well-defined stoichiometries (between 1:1 and 1:3) and, hence, in decreased interactions between the dye and the cationic surfactant. Mixtures of drug-surfactant were demonstrated to behave as those made up of pure surfactant, and, therefore, the expression previously derived for determining surfactants could be used to quantify amphiphilic drugs. The proposed method permitted the determination of phenamic acids at the mg l −1 level with the precision required for quality control (the relative standard deviation for 7 mg l −1 of meclophenamic acid was 1.1%). Pharmaceutical preparations were analysed directly after dissolution of the samples in ethanol.
Water Research, 1997
The potential of the oxidation of various carcinogenic aromatic amines by Fenton's reagent [Fe(II... more The potential of the oxidation of various carcinogenic aromatic amines by Fenton's reagent [Fe(II) + H202] for liquid waste treatments was assessed. The insoluble products yielded were amenable to oxidation to ring-cleavage products and ultimately to carbon dioxide. Mineralization was confirmed by mass spectrometry. The kinetics of precipitation was determined from scattering measurements, at 500 nm, of the insoluble substance produced as a function of time. The influence of experimental variables on the removal of aromatic amines from aqueous solutions by formation of insoluble products and ring-cleavage products was established. Complete removal took about 1 and 3 h of treatment overall for the formation of insoluble products and ring-cleavage products, respectively. Residual hydrogen peroxide, iron(It) concentration, chemical oxygen demand and chromatographic techniques were used to determine when the reaction was finished. The iron(II) concentration was found to be crucial to the nature of the end products obtained (insoluble products, ring-cleavage products, C02). © 1997 Elsevier Science Ltd
Kinetic determination of Hg(II) based on its accelerating effect on the reaction between hexacyanoferrate(II) and 1,10-phenanthroline catalysed by micelles
Talanta, 1991
A kinetic-photometric method for the determination of Hg(II) over the range 10-80 ng/ml is propos... more A kinetic-photometric method for the determination of Hg(II) over the range 10-80 ng/ml is proposed. It is based on the accelerating effect of this ion on the reaction between hexacyanoferrate(II) and 1,10-phenanthroline which is monitored via the ferroin complex formed. Anionic sodium dodecyl sulphate (SDS) micelles, which catalyse the reaction, allow the ferroin complex to be formed under more acidic conditions. Combination of this pH shift and the development of the reaction in the vicinity of micelles results in improved selectivity in the determination of Hg(II) compared to the reaction occurring in an aqueous medium. Some observations on the effect of SDS on the reaction are reported.
Journal of Chromatography A, 2003
Alkyl ammonium surfactants were extracted and concentrated from sludge samples using the acid-ind... more Alkyl ammonium surfactants were extracted and concentrated from sludge samples using the acid-induced cloud-point extraction (ACPE) technique. Reversed-phase liquid chromatography-electrospray ionization in positive ion mode ion-trap mass spectrometry was then used for the separation, quantitation and identification of single homologues of the cationic surfactants. Variables affecting the ACPE efficiency were optimized using a spiked activated sludge. Total method recoveries ranged from 91 to nearly 100%. Detection limits for cationics in the sludge were between 40 and 75 ng / g. The analysis of cationic surfactants in activated and dehydrated sludge collected from two different sewage treatment plants revealed the presence of dialkyldimethyl, alkylbenzyldimethyl and alkyltrimethyl ammonium in the concentration range from 0.1 to 34 mg / kg. Alkylpyridinium surfactants were not detected. The persistence of alkyl ammonium surfactants in sewage sludge after treatments applied at municipal sewage plants was confirmed.
Determination of non-ionic polyethoxylated surfactants in sewage sludge by coacervative extraction and ion trap liquid chromatography–mass spectrometry
Journal of Chromatography A, 2004
The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospher... more The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospheric pressure chemical ionisation in positive mode, ion trap mass spectrometry (LC/(APCl+-IT)-MS) for the concentration, separation and quantitation of non-ionic surfactants has been investigated. Concentration was based on the formation of mixed aggregates of analytes [alkylphenol ethoxylates (APE, octyl and nonyl) and alkyl ethoxylates (AE, C12-C16)] with the anionic surfactant sodium dodecyl sulphate (SDS) that is adsorbed on alumina. Parameters affecting SPE were investigated on the basis that hemimicelles are dynamic entities in equilibrium with the aqueous phase. The performance of ion trap mass spectrometry for MS and MS/MS quantitation of non-ionic homologues was assessed. Recoveries of analytes from wastewater influent and effluent and river water samples ranged between 91 and 98% and were found independent on the length of the alkyl chain under the optimised conditions. Anionic surfactants did not interfere to the levels found in environmental samples. The detection limits ranged between 14 and 111 ng/l for wastewater influent, 10 and 40 for wastewater effluent and 4 and 35 for river water, after concentration of 250, 500 and 750 ml of sample, respectively. The approach was applied to the determination of AE and APE in influent and effluent samples from four wastewater treatment plants and four river samples. The concentrations of individual non-ionic surfactants found ranged between 0.3 and 373 microg/l.
Water-Induced Coacervation of Alkyl Carboxylic Acid Reverse Micelles: Phenomenon Description and Potential for the Extraction of Organic Compounds
Analytical Chemistry, 2007
Coacervates made up of alkanoic (C8-C16) and alkenoic (C18) acid reverse micelles were described ... more Coacervates made up of alkanoic (C8-C16) and alkenoic (C18) acid reverse micelles were described for the first time, and their potential for the extraction of organic compounds prior to liquid chromatography was examined. The coacervation process occurred in miscible binary mixtures of water and a variety of protic and aprotic solvents. The phase behavior of alkyl carboxylic acids was found to be a function of both the Hildebrand solubility parameter, delta, and the hydrogen-bonding capability of the solvent. The best solvents for analytical extractions were those featuring the lowest delta values. The phase behavior of alkyl carboxylic acid/water/tetrahydrofuran (THF) ternary systems as a function of component concentration, pH, ionic strength, and temperature was investigated. The efficiency and the time required for phase separation depended on the experimental procedure used (i.e., standing, centrifugation, stirring, and sonication). The formation of alkyl carboxylic acid reverse micelles in THF was proven using both hydrophilic fluorescent probes and scattered light measurements. The structure of the coacervates consisted of spherical droplets dispersed in a continuous phase. Phase volume ratios were a function of both alkyl carboxylic acid and THF concentration. The low volume obtained (e.g., 1.5 microL per mg of decanoic) compared to that obtained by other coacervates (e.g., 5.1 microL per mg of dodecane sulfonic acid and 11.3 microL per mg of Triton X-114) greatly improved the concentration factors reached by coacervation-based extractions. Parameters affecting the extraction efficiency were assessed. Analytes in a wide range of polarity were efficiently extracted on the basis of the hydrophobic (e.g., PAHs) and hydrogen bond (e.g., chlorophenols, bisphenols, pesticides, phthalates, nonionic surfactants, dyes, and photographic developers) interactions that reverse micelles can establish. The coacervates were compatible with the chromatographic determination of analytes following UV or MS detection. They were successfully applied to the extraction of alkylphenol ethoxylates (octyl and nonyl) and alcohol ethoxylates (C12-C16) from influent and effluent wastewater and river water samples. Nonionic surfactants in the coacervate were directly separated and quantified by liquid chromatography-ion trap mass spectrometry. Concentration factors were around 160. The recovery of nonionics in the environmental water samples ranged from 90 to 104%.
An Acid-Induced Phase Cloud Point Separation Approach Using Anionic Surfactants for the Extraction and Preconcentration of Organic Compounds
Analytical Chemistry, 1999
The acid-induced liquid-liquid phase separation of anionic surfactants in aqueous solutions, and ... more The acid-induced liquid-liquid phase separation of anionic surfactants in aqueous solutions, and its applicability to cloud point extraction methodology, were examined. The phase diagrams obtained (eg,[HCl] vs [surfactant]) consisted of three regions: a homogeneous ...
Water Research, 2000
AbstractÐThe potential of the Fenton's reagent for oxidation of p-aminophenols, which are the mai... more AbstractÐThe potential of the Fenton's reagent for oxidation of p-aminophenols, which are the main developers used in white and black processes, was assessed. Metol [N-methyl-p-aminophenol] was chosen as a model. Degradation of this compound by Fenton's reagent was examined under dark conditions as a function of reagent concentrations and pH used in batch treatments. Under optimal conditions, 0.2 M H 2 O 2 , 9.0 Â 10 À4 M Fe 2+ , pH 3±5 and room temperature, the initial COD of a 5 Â 10 À3 M metol solution was reduced by about 50% within 2 h. After this time, additional COD reduction was very slow (about 20% in ®ve days). No aromatic compounds were detected about 4 h of reaction indicating that residual organic matter was mainly made up of ring cleavage products. Metol conversion behaved as a ®rst-order reaction with respect to metol and Fe 2+ . Complete destruction of residual organic matter could be achieved at high temperatures (about 608C) or by using the photo-Fenton reaction, which thus opens up prospects for an eective treatment of p-aminophenols in euents from photographic processes. #
Evaluation of the factors affecting extraction of organic compounds based on the acid-induced phase cloud point approach
Analytica Chimica Acta, 2002
On the basis of a better analytical exploitation of acid-induced cloud point approach, a systemat... more On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic ...
Journal of Chromatography A, 2009
Food constitutes the primary route for human exposure to bisphenol A (BPA), one of the highest vo... more Food constitutes the primary route for human exposure to bisphenol A (BPA), one of the highest volume chemicals produced worldwide. The estrogenic properties of BPA, its wide dispersive use and the recent extensive literature describing low-dose BPA effects in animals, have raised concerns about its possible adverse effects on human health. A reliable health risk assessment of BPA relies basically on its unambiguous identification and accurate quantification in food, and the aim of the present review is to give an overview of the analytical methods reported so far for the determination of BPA in these matrices. Emphasis is placed on the main strategies developed for sample treatment, which usually consists of several laborious and time-consuming steps in order to achieve the required sensitivity and selectivity. Separation, identification and quantitation of BPA is today reliably made with mass spectrometric methods, namely liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), and thus main attention is devoted to these techniques, but other methods using LC coupled to fluorescence or electrochemical detection, as well as immunochemical methods are also covered. Recent and expected future developments are discussed.
Analytica Chimica Acta, 2006
Sodium dodecyl sulphate (SDS)-coated alumina was used for the extraction/preconcentration of benz... more Sodium dodecyl sulphate (SDS)-coated alumina was used for the extraction/preconcentration of benzimidazolic pesticides (BFs) [carbendazim (CB), thiabendazole (TB) and fuberidazole (FB)] from river and underground water. SDS admicelles were required to get quantitative retention of BFs. Adsolubilization of analytes occurred through hydrophobic and electrostatic interactions. Methanol (1 ml) provided quantitative elution of the target analytes for all the samples analyzed. The high breakthrough volumes obtained (400 ml for CB and 1 l for BF and FB) and the low eluent volume used resulted in very high preconcentration factors (between 400 and 1000). Calcium was found to decrease BFs retention due to the disruption of SDS admicelles; however, this interference was easily removed by precipitation with SDS prior to BFs adsolubilization. The accuracy of the proposed method was assessed by studying recoveries of BFs in natural waters at two spiking concentration levels (80, 40 and 4 ng l −1 , and 400, 200 and 20 ng l −1 for CB, TB and FB, respectively); mean recoveries in the intervals 96-105% and 98-108% were obtained for river and underground water samples, respectively. (D. Pérez-Bendito). dently of the detection technique used. Liquid-liquid extraction is the classical approach for pesticide extraction from water samples [3]; however, because of its disadvantages, it has been widely replaced by solid-phase extraction (SPE). The most classical sorbent material, C 18 -bonded silica, is limited for the extraction/preconcentration of polar pesticides because of the early breakthrough of water-soluble analytes . Although polymeric materials (e.g. styrene-divinylbenzene) provide higher retention of polar analytes , the reduction of the volume of organic extract by evaporation is generally required to reach high preconcentration factors, which is timeconsuming and results in losses for some analytes (e.g. carbendazim ). Finally, carbon-based sorbents have a great capacity for the preconcentration of highly polar pesticides [9-11], but very high standard deviations [3] and some effect of irreversible adsorption [9,10] have been described.
Journal of Chromatography A, 2005
Supramolecular sorbents (hemimicelles/admicelles) are proposed for the extraction/preconcentratio... more Supramolecular sorbents (hemimicelles/admicelles) are proposed for the extraction/preconcentration of bisphenols from aqueous environmental samples prior to their liquid chromatography/fluorimetric determination. A comparative study on the use of cetyltrimethylammonium bromide (CTABr)-coated silica and sodium dodecyl sulphate (SDS)-coated ␥-alumina as sorbent materials, is presented. Bisphenol A (BPA) and bisphenol F (BPF) were quantitatively retained on CTABr admicelles. Addition of tetrabutylammonium chloride (TBAC) to water samples was required to completely retain bisphenols on SDS-␥-alumina. Retention on both sorbents occurred through hydrophobic and pi-cation interactions between the quaternary ammonium head group of the cationic amphiphile (CTABr or TBAC) and the aromatic rings of the target analytes. TBAC-SDS-␥alumina was the sorbent selected for the SPE of bisphenols on the basis of the lower elution volume required (1 ml of methanol) and the greater breakthrough volume allowed (400 ml), which permitted to reach practical detection limits of 10 and 15 ng/l for BPF and BPA, respectively. The proposed method was used to quantify bisphenol A and bisphenol B in wastewater samples from four sewage treatment plants. Recoveries obtained ranged between about 99 and 105% for raw wastewater and between 96 and 106% for treated wastewater.
Acid-induced cloud point extraction and preconcentration of polycyclic aromatic hydrocarbons from environmental solid samples
Journal of Chromatography A, 2002
The effectiveness of the acid-induced phase separation of anionic surfactants (acid-induced cloud... more The effectiveness of the acid-induced phase separation of anionic surfactants (acid-induced cloud point extraction, ACPE) to extract polycyclic aromatic hydrocarbons (PAHs) from different environmental samples (soils, sediments and sludges), prior to chromatographic analysis, was evaluated. Variables affecting the ACPE efficiency were optimised using a natural matrix (a harbour sediment, CRM 535). Temperature, surfactant concentration and stirring were of primary importance to maximise recovery, whereas temperature and surfactant/hydrochloric acid concentration influenced the volume of the surfactant-rich phase and therefore the preconcentration factor achieved. The optimal conditions (2% sodium dodecanesulphonate (SDoS), 4.2 M HCl, 60 degrees C, 1 h) were applied to the extraction of PAHs from various matrices and the ACPE recoveries compared to certified results from Soxhlet extractions. Recoveries obtained for four to five aromatic ring PAHs ranged from 71 to 98%. Uncertainties obtained using ACPE were similar to or lower than those provided for the certified values. The volume of the extracts ranged from 1 to 2 ml. The method did not require additional clean-up or preconcentration steps.
Analytica Chimica Acta, 2005
Hemimicelles-based solid-phase extraction was proposed for the concentration of high volume commo... more Hemimicelles-based solid-phase extraction was proposed for the concentration of high volume commodity phthalates from wastewater samples prior to their separation and quantitation by liquid chromatography/atmospheric pressure chemical ionization in positive mode, ion trap mass spectrometry. Di-(2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP) and di-n-butyl phthalate (DBP) were concentrated on hemimicelles of sodium dodecyl sulphate (SDS) produced on alumina on the basis of hydrophobic interactions. The recovery of the target compounds was found quantitative under a wide range of experimental conditions (15-255 mg SDS g −1 alumina, pH 2-6 and sample loading volume up to 1 L). Concentration factors of 2500 were achieved by SPE of 0.5 L of sewage samples. The method detection limits found for BBP, DBP and DEHP were 7, 15 and 16 pg, respectively. The relative standard deviation ranged from 2 to 5%, which indicated good method precision. The approach developed was applied to the determination of phthalates in raw and treated sewage samples.
SolidPhase Extraction of Amphiphiles Based on Mixed Hemimicelle/Admicelle Formation: Application to the Concentration of Benzalkonium Surfactants in Sewage and River Water
Analytical Chemistry, 2003
The capability of surfactant-coated mineral oxides to aid the solid-phase extraction (SPE) of amp... more The capability of surfactant-coated mineral oxides to aid the solid-phase extraction (SPE) of amphiphiles based on the formation of mixed hemimicelles/admicelles was investigated. The approach is illustrated by studying the adsolubilization of benzalkonium homologue (C(12), C(14), C(16)) surfactants (BAS) on sodium dodecyl sulfate (SDS)-coated alumina. These oppositely charged surfactants form mixed aggregates on alumina causing retention of BAS by strong hydrophobic and ionic interactions. The recovery of BAS was found quantitative and independent of the alkyl chain length under a wide range of experimental conditions (3-200 mg of SDS/g of alumina; pH 2-11; sample flow rate 3-20 mL/min, and sample loading volume 0.025-1 L). Anionic and nonionic surfactants and electrolytes did not interfere to the levels found in raw sewage. Combination of BAS adsolubilization-based SPE with liquid chromatography/electrospray ionization in positive ion mode/ion trap mass spectrometry permitted the quantification of BAS with detection limits of 4 ng/L and their identification by isolation and subsequent fragmentation in the ion trap. The approach developed was applied to the determination of BAS in raw and treated sewage and river samples. The concentrations of benzalkonium surfactants found ranged between 0.1 and 49 microg/L.
Evaluation and Optimization of an On-Line Admicelle-Based Extraction-Liquid Chromatography Approach for the Analysis of Ionic Organic Compounds
Analytical Chemistry, 2004
Admicelles-based solid-phase extraction (SPE) was on-line coupled with liquid chromatography/elec... more Admicelles-based solid-phase extraction (SPE) was on-line coupled with liquid chromatography/electrospray ionization/ion trap mass spectrometry, and it was proposed for the extraction of ionic organic compounds based on the formation of surfactant-analyte ion pairs. The approach was illustrated by studying the preconcentration of quaternary ammonium herbicides (quats) on sodium dodecyl sulfate (SDS) admicelles produced on alumina. Optimization of the parameters affecting SPE were studied on the basis that admicelles are dynamic entities in equilibrium with the aqueous phase. Some general guidelines could be established for method development from the results obtained. Factors influencing on-line operation were elucidated. On-line regeneration of the sorbent in each run was easily achieved by disruption of SDS admicelles with methanol and posterior coating of the alumina with SDS. The recovery of quats from drinking water samples were found quantitative for paraquat, diquat, and difenzoquat and above to 70% for chlormequat and mepiquat. Concentration factors of about 250, using sample volumes of 50 mL, were achieved. The detection limits ranged from 10 to 30 ng/L. The approach developed permits compliance with the directives of the European Community for drinking waters (100 ng/L) and goes deeply into the basis of solid-phase extractions that use surfactant-coated mineral oxide as sorbents.
Determination of non-ionic polyethoxylated surfactants in wastewater and river water by mixed hemimicelle extraction and liquid chromatography–ion trap mass spectrometry
Journal of Chromatography A, 2005
The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospher... more The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospheric pressure chemical ionisation in positive mode, ion trap mass spectrometry (LC/(APCl+-IT)-MS) for the concentration, separation and quantitation of non-ionic surfactants has been investigated. Concentration was based on the formation of mixed aggregates of analytes [alkylphenol ethoxylates (APE, octyl and nonyl) and alkyl ethoxylates (AE, C12-C16)] with the anionic surfactant sodium dodecyl sulphate (SDS) that is adsorbed on alumina. Parameters affecting SPE were investigated on the basis that hemimicelles are dynamic entities in equilibrium with the aqueous phase. The performance of ion trap mass spectrometry for MS and MS/MS quantitation of non-ionic homologues was assessed. Recoveries of analytes from wastewater influent and effluent and river water samples ranged between 91 and 98% and were found independent on the length of the alkyl chain under the optimised conditions. Anionic surfactants did not interfere to the levels found in environmental samples. The detection limits ranged between 14 and 111 ng/l for wastewater influent, 10 and 40 for wastewater effluent and 4 and 35 for river water, after concentration of 250, 500 and 750 ml of sample, respectively. The approach was applied to the determination of AE and APE in influent and effluent samples from four wastewater treatment plants and four river samples. The concentrations of individual non-ionic surfactants found ranged between 0.3 and 373 microg/l.
Supramolecular systems-based extraction-separation techniques coupled to mass spectrometry
Journal of Separation Science, 2005
The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas... more The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas-phase fundamental studies of host–guest complexes and supramolecular assemblies. Mass spectrometric analysis has also benefited from the ability of supramolecular systems to behave as pseudophases in which solutes partition from the bulk solvent phase. Supramolecular systems-based extraction and concentration schemes and separation techniques have been widely used in different fields of analytical chemistry and are ideally suited for coupling with MS. This review describes the present status of the application of supramolecular chemistry in mass spectrometric analysis and includes topics such as the use of coacervative liquid–liquid extraction and hemimicelle/admicelle-based SPE of organic compounds prior to chromatography and electrophoresis. It also discusses the recent advances in enantioselective analysis using CD in electrophoresis- and chromatography-MS. The potential and analytical challenges of these approaches in environmental and bioanalytical chemistry, where one can expect significant developments in the future, are outlined.
Water Research, 2000
AbstractÐMany aromatic compounds are oxidized but not completely mineralized by Fenton's reagent.... more AbstractÐMany aromatic compounds are oxidized but not completely mineralized by Fenton's reagent. Little attention has so far been given to the identi®cation of residual organic matter and the evaluation of its toxicity. In this work, the oxidation of metol [N-methyl-p-aminophenol] by Fe 2+ /H 2 O 2 in the dark as a model for aromatic amines and alcohols was examined. Analysis of oxidized solutions was performed by both LC-electron impact (EI)-MS and LC-electrospray ionization (ESI)-MS. It was checked that the degradation of metol takes place via direct oxidation by Fe 3+ and OH Á attack. Intermediates amenable to oxidation by OH Á are basically partially oxygenated aromatic species, dimerization products and polymers. End products not amenable to oxidation by this radical are ferrycarboxylate complexes, which are non-toxic to UC581 bacterial cells. These complexes can be completely destroyed by irradiation with light. The photo-Fenton reaction is therefore an eective choice for the in situ treatment of industrial euents containing aromatic amines and hydroxylated species. 7
Trends in Analytical Chemistry, 2003
Supramolecular assemblies have been used largely in analytical extraction and concentration schem... more Supramolecular assemblies have been used largely in analytical extraction and concentration schemes. Their ability to form a phase with regions of different polarities, acidities and viscosities, where solutes of very different structure can be solubilized, has encouraged this use. At present, the basis, characteristics and scope of extraction techniques, such as cloud point, are well established. However, they have not been accepted in routine analysis, despite the demonstrated advantages of surfactant-mediated separations over other conventional extraction techniques. This article deals with the challenges in making these extraction techniques competitive and explores the potential for using other phenomena and materials where supramolecular assemblies are involved, such as coacervation, hemimicelles/admicelles and amphiphilic-templated mesoporous silicas, for the extraction/concentration of organic compounds. #
Analytica Chimica Acta, 2004
The surfactant-dye binding degree (SDBD) method was extended to the determination of amphiphilic ... more The surfactant-dye binding degree (SDBD) method was extended to the determination of amphiphilic drugs. This new methodology was based on the effect of amphiphilic compounds on the degree of binding of a surfactant to dye molecules. The dye induces the formation of surfactant aggregates and allows this process to be monitored from changes in their spectral features. The interaction between the anionic dye Coomassie Brilliant Blue G (CBBG) and the cationic surfactant didodecyldimethylammonium bromide (DDABr) was used for the sensitive determination of phenamic acids (meclophenamic, mephenamic, fluphenamic and niflumic acid), non-steroidal anti-inflammatory drugs. The addition of phenamic acid to the dye-surfactant mixture resulted in the formation of drug-DDABr aggregates with well-defined stoichiometries (between 1:1 and 1:3) and, hence, in decreased interactions between the dye and the cationic surfactant. Mixtures of drug-surfactant were demonstrated to behave as those made up of pure surfactant, and, therefore, the expression previously derived for determining surfactants could be used to quantify amphiphilic drugs. The proposed method permitted the determination of phenamic acids at the mg l −1 level with the precision required for quality control (the relative standard deviation for 7 mg l −1 of meclophenamic acid was 1.1%). Pharmaceutical preparations were analysed directly after dissolution of the samples in ethanol.
Water Research, 1997
The potential of the oxidation of various carcinogenic aromatic amines by Fenton's reagent [Fe(II... more The potential of the oxidation of various carcinogenic aromatic amines by Fenton's reagent [Fe(II) + H202] for liquid waste treatments was assessed. The insoluble products yielded were amenable to oxidation to ring-cleavage products and ultimately to carbon dioxide. Mineralization was confirmed by mass spectrometry. The kinetics of precipitation was determined from scattering measurements, at 500 nm, of the insoluble substance produced as a function of time. The influence of experimental variables on the removal of aromatic amines from aqueous solutions by formation of insoluble products and ring-cleavage products was established. Complete removal took about 1 and 3 h of treatment overall for the formation of insoluble products and ring-cleavage products, respectively. Residual hydrogen peroxide, iron(It) concentration, chemical oxygen demand and chromatographic techniques were used to determine when the reaction was finished. The iron(II) concentration was found to be crucial to the nature of the end products obtained (insoluble products, ring-cleavage products, C02). © 1997 Elsevier Science Ltd
Kinetic determination of Hg(II) based on its accelerating effect on the reaction between hexacyanoferrate(II) and 1,10-phenanthroline catalysed by micelles
Talanta, 1991
A kinetic-photometric method for the determination of Hg(II) over the range 10-80 ng/ml is propos... more A kinetic-photometric method for the determination of Hg(II) over the range 10-80 ng/ml is proposed. It is based on the accelerating effect of this ion on the reaction between hexacyanoferrate(II) and 1,10-phenanthroline which is monitored via the ferroin complex formed. Anionic sodium dodecyl sulphate (SDS) micelles, which catalyse the reaction, allow the ferroin complex to be formed under more acidic conditions. Combination of this pH shift and the development of the reaction in the vicinity of micelles results in improved selectivity in the determination of Hg(II) compared to the reaction occurring in an aqueous medium. Some observations on the effect of SDS on the reaction are reported.
Journal of Chromatography A, 2003
Alkyl ammonium surfactants were extracted and concentrated from sludge samples using the acid-ind... more Alkyl ammonium surfactants were extracted and concentrated from sludge samples using the acid-induced cloud-point extraction (ACPE) technique. Reversed-phase liquid chromatography-electrospray ionization in positive ion mode ion-trap mass spectrometry was then used for the separation, quantitation and identification of single homologues of the cationic surfactants. Variables affecting the ACPE efficiency were optimized using a spiked activated sludge. Total method recoveries ranged from 91 to nearly 100%. Detection limits for cationics in the sludge were between 40 and 75 ng / g. The analysis of cationic surfactants in activated and dehydrated sludge collected from two different sewage treatment plants revealed the presence of dialkyldimethyl, alkylbenzyldimethyl and alkyltrimethyl ammonium in the concentration range from 0.1 to 34 mg / kg. Alkylpyridinium surfactants were not detected. The persistence of alkyl ammonium surfactants in sewage sludge after treatments applied at municipal sewage plants was confirmed.
Determination of non-ionic polyethoxylated surfactants in sewage sludge by coacervative extraction and ion trap liquid chromatography–mass spectrometry
Journal of Chromatography A, 2004
The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospher... more The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospheric pressure chemical ionisation in positive mode, ion trap mass spectrometry (LC/(APCl+-IT)-MS) for the concentration, separation and quantitation of non-ionic surfactants has been investigated. Concentration was based on the formation of mixed aggregates of analytes [alkylphenol ethoxylates (APE, octyl and nonyl) and alkyl ethoxylates (AE, C12-C16)] with the anionic surfactant sodium dodecyl sulphate (SDS) that is adsorbed on alumina. Parameters affecting SPE were investigated on the basis that hemimicelles are dynamic entities in equilibrium with the aqueous phase. The performance of ion trap mass spectrometry for MS and MS/MS quantitation of non-ionic homologues was assessed. Recoveries of analytes from wastewater influent and effluent and river water samples ranged between 91 and 98% and were found independent on the length of the alkyl chain under the optimised conditions. Anionic surfactants did not interfere to the levels found in environmental samples. The detection limits ranged between 14 and 111 ng/l for wastewater influent, 10 and 40 for wastewater effluent and 4 and 35 for river water, after concentration of 250, 500 and 750 ml of sample, respectively. The approach was applied to the determination of AE and APE in influent and effluent samples from four wastewater treatment plants and four river samples. The concentrations of individual non-ionic surfactants found ranged between 0.3 and 373 microg/l.
Water-Induced Coacervation of Alkyl Carboxylic Acid Reverse Micelles: Phenomenon Description and Potential for the Extraction of Organic Compounds
Analytical Chemistry, 2007
Coacervates made up of alkanoic (C8-C16) and alkenoic (C18) acid reverse micelles were described ... more Coacervates made up of alkanoic (C8-C16) and alkenoic (C18) acid reverse micelles were described for the first time, and their potential for the extraction of organic compounds prior to liquid chromatography was examined. The coacervation process occurred in miscible binary mixtures of water and a variety of protic and aprotic solvents. The phase behavior of alkyl carboxylic acids was found to be a function of both the Hildebrand solubility parameter, delta, and the hydrogen-bonding capability of the solvent. The best solvents for analytical extractions were those featuring the lowest delta values. The phase behavior of alkyl carboxylic acid/water/tetrahydrofuran (THF) ternary systems as a function of component concentration, pH, ionic strength, and temperature was investigated. The efficiency and the time required for phase separation depended on the experimental procedure used (i.e., standing, centrifugation, stirring, and sonication). The formation of alkyl carboxylic acid reverse micelles in THF was proven using both hydrophilic fluorescent probes and scattered light measurements. The structure of the coacervates consisted of spherical droplets dispersed in a continuous phase. Phase volume ratios were a function of both alkyl carboxylic acid and THF concentration. The low volume obtained (e.g., 1.5 microL per mg of decanoic) compared to that obtained by other coacervates (e.g., 5.1 microL per mg of dodecane sulfonic acid and 11.3 microL per mg of Triton X-114) greatly improved the concentration factors reached by coacervation-based extractions. Parameters affecting the extraction efficiency were assessed. Analytes in a wide range of polarity were efficiently extracted on the basis of the hydrophobic (e.g., PAHs) and hydrogen bond (e.g., chlorophenols, bisphenols, pesticides, phthalates, nonionic surfactants, dyes, and photographic developers) interactions that reverse micelles can establish. The coacervates were compatible with the chromatographic determination of analytes following UV or MS detection. They were successfully applied to the extraction of alkylphenol ethoxylates (octyl and nonyl) and alcohol ethoxylates (C12-C16) from influent and effluent wastewater and river water samples. Nonionic surfactants in the coacervate were directly separated and quantified by liquid chromatography-ion trap mass spectrometry. Concentration factors were around 160. The recovery of nonionics in the environmental water samples ranged from 90 to 104%.
An Acid-Induced Phase Cloud Point Separation Approach Using Anionic Surfactants for the Extraction and Preconcentration of Organic Compounds
Analytical Chemistry, 1999
The acid-induced liquid-liquid phase separation of anionic surfactants in aqueous solutions, and ... more The acid-induced liquid-liquid phase separation of anionic surfactants in aqueous solutions, and its applicability to cloud point extraction methodology, were examined. The phase diagrams obtained (eg,[HCl] vs [surfactant]) consisted of three regions: a homogeneous ...
Water Research, 2000
AbstractÐThe potential of the Fenton's reagent for oxidation of p-aminophenols, which are the mai... more AbstractÐThe potential of the Fenton's reagent for oxidation of p-aminophenols, which are the main developers used in white and black processes, was assessed. Metol [N-methyl-p-aminophenol] was chosen as a model. Degradation of this compound by Fenton's reagent was examined under dark conditions as a function of reagent concentrations and pH used in batch treatments. Under optimal conditions, 0.2 M H 2 O 2 , 9.0 Â 10 À4 M Fe 2+ , pH 3±5 and room temperature, the initial COD of a 5 Â 10 À3 M metol solution was reduced by about 50% within 2 h. After this time, additional COD reduction was very slow (about 20% in ®ve days). No aromatic compounds were detected about 4 h of reaction indicating that residual organic matter was mainly made up of ring cleavage products. Metol conversion behaved as a ®rst-order reaction with respect to metol and Fe 2+ . Complete destruction of residual organic matter could be achieved at high temperatures (about 608C) or by using the photo-Fenton reaction, which thus opens up prospects for an eective treatment of p-aminophenols in euents from photographic processes. #
Evaluation of the factors affecting extraction of organic compounds based on the acid-induced phase cloud point approach
Analytica Chimica Acta, 2002
On the basis of a better analytical exploitation of acid-induced cloud point approach, a systemat... more On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic ...
Journal of Chromatography A, 2009
Food constitutes the primary route for human exposure to bisphenol A (BPA), one of the highest vo... more Food constitutes the primary route for human exposure to bisphenol A (BPA), one of the highest volume chemicals produced worldwide. The estrogenic properties of BPA, its wide dispersive use and the recent extensive literature describing low-dose BPA effects in animals, have raised concerns about its possible adverse effects on human health. A reliable health risk assessment of BPA relies basically on its unambiguous identification and accurate quantification in food, and the aim of the present review is to give an overview of the analytical methods reported so far for the determination of BPA in these matrices. Emphasis is placed on the main strategies developed for sample treatment, which usually consists of several laborious and time-consuming steps in order to achieve the required sensitivity and selectivity. Separation, identification and quantitation of BPA is today reliably made with mass spectrometric methods, namely liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), and thus main attention is devoted to these techniques, but other methods using LC coupled to fluorescence or electrochemical detection, as well as immunochemical methods are also covered. Recent and expected future developments are discussed.
Analytica Chimica Acta, 2006
Sodium dodecyl sulphate (SDS)-coated alumina was used for the extraction/preconcentration of benz... more Sodium dodecyl sulphate (SDS)-coated alumina was used for the extraction/preconcentration of benzimidazolic pesticides (BFs) [carbendazim (CB), thiabendazole (TB) and fuberidazole (FB)] from river and underground water. SDS admicelles were required to get quantitative retention of BFs. Adsolubilization of analytes occurred through hydrophobic and electrostatic interactions. Methanol (1 ml) provided quantitative elution of the target analytes for all the samples analyzed. The high breakthrough volumes obtained (400 ml for CB and 1 l for BF and FB) and the low eluent volume used resulted in very high preconcentration factors (between 400 and 1000). Calcium was found to decrease BFs retention due to the disruption of SDS admicelles; however, this interference was easily removed by precipitation with SDS prior to BFs adsolubilization. The accuracy of the proposed method was assessed by studying recoveries of BFs in natural waters at two spiking concentration levels (80, 40 and 4 ng l −1 , and 400, 200 and 20 ng l −1 for CB, TB and FB, respectively); mean recoveries in the intervals 96-105% and 98-108% were obtained for river and underground water samples, respectively. (D. Pérez-Bendito). dently of the detection technique used. Liquid-liquid extraction is the classical approach for pesticide extraction from water samples [3]; however, because of its disadvantages, it has been widely replaced by solid-phase extraction (SPE). The most classical sorbent material, C 18 -bonded silica, is limited for the extraction/preconcentration of polar pesticides because of the early breakthrough of water-soluble analytes . Although polymeric materials (e.g. styrene-divinylbenzene) provide higher retention of polar analytes , the reduction of the volume of organic extract by evaporation is generally required to reach high preconcentration factors, which is timeconsuming and results in losses for some analytes (e.g. carbendazim ). Finally, carbon-based sorbents have a great capacity for the preconcentration of highly polar pesticides [9-11], but very high standard deviations [3] and some effect of irreversible adsorption [9,10] have been described.
Journal of Chromatography A, 2005
Supramolecular sorbents (hemimicelles/admicelles) are proposed for the extraction/preconcentratio... more Supramolecular sorbents (hemimicelles/admicelles) are proposed for the extraction/preconcentration of bisphenols from aqueous environmental samples prior to their liquid chromatography/fluorimetric determination. A comparative study on the use of cetyltrimethylammonium bromide (CTABr)-coated silica and sodium dodecyl sulphate (SDS)-coated ␥-alumina as sorbent materials, is presented. Bisphenol A (BPA) and bisphenol F (BPF) were quantitatively retained on CTABr admicelles. Addition of tetrabutylammonium chloride (TBAC) to water samples was required to completely retain bisphenols on SDS-␥-alumina. Retention on both sorbents occurred through hydrophobic and pi-cation interactions between the quaternary ammonium head group of the cationic amphiphile (CTABr or TBAC) and the aromatic rings of the target analytes. TBAC-SDS-␥alumina was the sorbent selected for the SPE of bisphenols on the basis of the lower elution volume required (1 ml of methanol) and the greater breakthrough volume allowed (400 ml), which permitted to reach practical detection limits of 10 and 15 ng/l for BPF and BPA, respectively. The proposed method was used to quantify bisphenol A and bisphenol B in wastewater samples from four sewage treatment plants. Recoveries obtained ranged between about 99 and 105% for raw wastewater and between 96 and 106% for treated wastewater.