A Critical Review of Surfactant-Mediated Phase Separations (Cloud-Point Extractions): Theory and Applications

Evaluation and Optimization of an On-Line Admicelle-Based Extraction-Liquid Chromatography Approach for the Analysis of Ionic Organic Compounds

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.

Simultaneous determination of 3-nitro tyrosine, o-, m-, and p-tyrosine in urine samples by liquid chromatography–ultraviolet absorbance detection with pre-column cloud point extraction

Stable 3-nitro tyrosine (3-NO(2)-Tyr), o-, m-, and p-tyrosine isomers induced by oxidation of tyrosine residues in protein were considered important biomarkers for the existence of toxic oxidizing agents peroxynitrite (ONOO(-)) and OH*, which could lead to such diseases as acute lung injury, neurodegenerative disorders, atherosclerosis, cancers and many other diseases. Therefore, development of an accurate, simple and sensitive method to simultaneously detect o-, m-, and p-tyrosine and 3-NO(2)-Tyr is necessary. Fluorescence detection is highly sensitive to o-, m-, and p-tyrosine, but it cannot be used to detect 3-NO(2)-Tyr, due to the strong fluorescence-quenching characteristic of the NO(2) group. In this study, we developed a highly sensitive reversed HPLC-UV method, combined with pre-column cloud point extraction (CPE), to simultaneously determine o-, m-, and p-tyrosine and 3-NO(2)-Tyr. The procedure included derivatization of a sample with 6-aminoquinolyl-N-hydroxy-succinimidyl carbomate (AccQ) at 0.20 mol/l borate buffer (pH 8.80) for 30 min at 70 degrees C, and pre-concentration with surfactant cloud point extraction. The surfactant-rich phase was then diluted with deionized water and injected directly into the to HPLC column for analysis. A C(18) column (3.9 mm i.d. x 300 mm) was used for gradient elution separation at 25 degrees C and the detection wavelength was at 254 nm. Nineteen general amino acids showed no interference. The detection limits of p-, o-, m-Tyr and 3-NO(2)-Tyr were between 5 and 15 nmol/l. The linear range was from 0.05 to approximately 100 micromol/l.

Potential of coacervation processes for the extraction of amphiphiles (linear alkyl benzenesulphonates) from sewage sludge samples prior to liquid chromatography

A new approach was developed for the monitoring of linear alkyl (C10-C13) benzenesulphonates (LASs) in sewage sludge. It was based on their extraction with the anionic surfactant sodium dodecanesulphonate (SDoS) that undergoes coacervation under acid conditions. The target compounds formed mixed aggregates with SDoS by ideal hydrophobic interactions which made possible the breakdown of LAS-sludge interactions and provided high extraction yields. Variables affecting extraction were optimised using a fortified dehydrated sludge. Recoveries for LASs were found independent on the length of alkyl chain. Liquid chromatography-fluorimetry was used for separation and detection of LAS homologues. Detection limit for LAS in the sludge was 5 mg/kg. Concentration levels of total LASs in activated and dehydrated sludge collected from two different sewage treatment plants were in the range 0.26-0.56 g/kg with LAS homologues ranging from 29 to 223 mg/kg. The method did not require clean-up or preconcentration steps.

Cloud point of aqueous solutions containing oxyethylated methyl dodecanoates: effects of surfactant hydrophilicity, nature of added electrolyte, and water activity

The aim of this work was to determine the cloud points of new oxyethylated methyl dodecanoates of various hydrophilicity (OMD-n, where n refers to the average degree of oxyethylation) and to correlate them with surfactant hydrophilicity and, for a given electrolyte, with water activity. Thus, it is shown that the cloud point in the absence of electrolyte (CP(0)) can be simulated by the following equation: CP(0)=165.5logn-112.0 (with R(2)=0.987). The effects of NaCl, NaHCO(3), and KSCN on the cloud point are also reported and discussed. The salting-out effect arising from the presence of NaCl or NaHCO(3) is explained by the existence of a hydration shell with enhanced water structure as well as a zone with decreased salt concentration around the -(OCH(2)CH(2))(n)- chain, as compared with the bulk. On the other hand, the salting-in effect is explained by depletion of water around the -(OCH(2)CH(2))(n)- chain. Thus, it is estimated that the number b of water molecules forced back into the bulk solution from the salt-deficient regions when the hydration shells of two -O-CH(2)-CH(2)- monomer units overlap ranges between 2 and 3 and 3 and 4 for NaCl and NaHCO(3), respectively, depending on the average degree of oxyethylation n of OMD-n. It is also shown that the water activity is a useful parameter to simulate the variation of cloud point in the presence of an electrolyte (CP) at low and moderate concentration (e.g., <1 M NaCl), CP(0)/CP approximately 1-(bR/alpha)lna(w), where R is the gas constant and alpha approximately 15 JK(-1)mol(-1). At high electrolyte concentration, the relationship between CP(0)/CP and lna(w) significantly deviates from linearity. In the particular case of KSCN, an inversion of the salt effect can be observed. The salting-in effect of KSCN increases up to about 2 M, but decreases at higher KSCN concentrations, so that KSCN can even act as a salting-out salt at high concentration (typically above 3.3 M for OMD-14).

Solid-Phase Extraction of Amphiphiles Based on Mixed Hemimicelle/Admicelle Formation: Application to the Concentration of Benzalkonium Surfactants in Sewage and River Water

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.

Prediction of the behaviour of organic pollutants using cloud point extraction

A preconcentration study based on the cloud point phenomenon was carried out for a set of triazine herbicides, three of them chloro-substituted and three of them methylthio-substituted. Concentration factors and recoveries were calculated as function of the percentage of the non-ionic surfactant Triton X-114 employed. From these values, obtained from a cloud point extraction (CPE) procedure, the distribution coefficient between the Triton X-114 micelles and water, Kc, prior to CPE was calculated for each triazine and related to the corresponding octanol-water partition coefficient, Kow. In order to confirm the results obtained with the triazine herbicides, two sets of data from chemically different organic pollutants--organophosporous and chlorophenols--obtained from the literature were assessed, concluding that they display a similar behaviour to that of the triazine herbicides. This can be used to predict the CPE behaviour of other organic pollutants from their octanol-water partition coefficients. The Kc values were compared with the analyte concentration ratio in the surfactant-rich phase and aqueous phase (Ksa) with a view to obtaining a link between the analyte behaviour prior to and after cloud point extraction procedures.

Transfer rate of several tris(β-diketonato)iron(III) complexes at the bulk aqueous–Triton X-100 micellar interface: effects of substituent groups in the extractants

The transfer rate of tris(beta-diketonato)iron(III) complexes with acetylacetone, benzoylacetone, trifluoroacetylacetone, benzoyltrifluoroacetone, and 2-thenoyltrifluoroacetone at the water-Triton X-100 micellar interface was measured by stopped-flow spectrophotometry. The forward transfer rate was first-order with respect to the micellar concentration; the rate-determining step was concluded to be the capturing process of the collided complex at the micellar surface. The value of the rate constant varied with the substituent groups in the extractants; several effects of the substituent groups on the transfer rate were observed. The "mantlephobicity" of the trifluoromethyl group because of its low wettability, the hydrophobicity of the phenyl and thienyl groups in light of their bulkiness, the dilution of the negative efficiency of the trifluoromethyl group at the capturing by enlarging the complex surface with these bulky groups, and the "mantlephilicity" of the thienyl group from its interaction with the hydrogen-bonded network of the micellar "mantle" were estimated. In contrast, the backward rate was independent of the micellar concentration, and the order could be explained by the distribution of the tris-complexes between the "core" and "mantle" of the micelle. The "core-mantle" double-layer structure of the micelle would be an important key for the behavior at the interface.

Pressurized liquid extraction of active ingredients (ginsenosides) from medicinal plants using non-ionic surfactant solutions

The feasibility of employing aqueous non-ionic surfactant solutions as an alternative solvent system in pressurized liquid extraction (PLE) is demonstrated for the first time using the roots of American ginseng as model solid samples. When compared to the use of pure water or methanol, the presence of a common non-ionic surfactant (Triton X-100) in water at a concentration above its critical micelle concentration was shown to enhance the amount of pharmacologically active ingredients (ginsenosides) extracted from ginseng roots. The advantages of using aqueous non-surfactant solutions were also demonstrated by comparing extraction performances between ultrasonic-assisted extraction and PLE methods. Furthermore, the combination of PLE and cloud point extraction was shown to be a new and effective approach for the rapid sample preconcentration of herbal materials prior to analysis by high-performance liquid chromatography.

Assessment of trace aluminium content in parenteral solutions by combined cloud point preconcentration-flow injection inductively coupled plasma optical emission spectrometry

A micelle-mediated phase separation without added chelating agents to preconcentrate trace levels of aluminium in parenteral solutions as a prior step to its determination by flow injection inductively coupled plasma optical emission spectrometry has been developed. The enrichment step is based on the cloud point extraction of aluminium with the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5). The chemical variables affecting the sensitivity of the extractive-spectrometric procedure were studied in detail. After optimization, a preconcentration factor of 200 and a %E higher than 99.9 were achieved. The detection limit (DL) value of aluminium for the preconcentration of 50 ml of parenteral solution was 0.25 microgl(-1). The calibration graph using the preconcentration system for aluminium was linear with a correlation coefficient of 0.9997 at levels near the DLs up to at least 200 microgl(-1). The developed hyphenated assay, which thoroughly satisfies the typical requirements for pharmaceutical control processes, is appropriate to monitor the aluminium concentration in parenteral nutrition.

POE chain length selectivity in the clouding of a triton surfactant

The POE chain length distribution between the coacervate and aqueous phases of a clouded Triton X-114 solution was studied. The average chain length of the surfactant in the aqueous layer was determined by HPLC and compared to the distribution in the original (unclouded) solution. Both the clouding temperature and the equilibration time were found to govern the chain length selectivity. A slight excess of longer POE chains were encountered in the aqueous layer, thus enriching the coacervate layer with shorter, less soluble chains. Chain length selection appeared to occur when the surfactant particles were dispersed in the clouded suspension, rather than after the establishment of the aqueous and coacervate layers.

In?uence of nonionic surfactants on the chromatographic behaviour of proteins in hydrophobic interaction chromatography

The chromatographic characteristics of proteins in the presence of additives of nonionic surfactants Brij-35 and Tween-80 in the conditions of descending gradient of ammonium sulfate and phenyl-coated polymeric stationary phase were investigated. It was revealed that retention factors of proteins may be regulated by use of mentioned additives. The improvement of resolution is achieved for some hardly separated pairs of proteins, viz. albumin egg/albumin bovine, aldolase/tripsin. A reversion of the elution order is observed for tripsin/chymotrypsinogen A.

Separation of phenols from aqueous micellar solutions by cloud point extraction

The cloud point technique was used to recover phenol, 4-methylphenol, and 4-nitrophenol from aqueous solutions using oxyethylated methyl dodecanoates as nonionic surfactants. Oxyethylated methyl dodecanoates are convenient nonionic surfactants for such separations. Their cloud points can be easily modified by a change in surfactant hydrophilicity or by the addition of a second nonionic surfactant and/or an electrolyte. The use of the hydrophile lipophile balance is preferred to model the cloud point of oxyethylated methyl dodecanoates and their mixtures with other surfactants. The composition of the surfactant-rich phase depends on electrolyte type and the overheating. The phase can contain only 5-15% of water. Recovery of phenols changes in the order 4-nitrophenol >4-methylphenol > phenol and is increased in the presence of sodium chloride. The presence of salting-out electrolytes is preferred both to decrease the cloud point and to increase the efficiency of extraction.

Concentration of chlorophenols in water with sodium dodecylsulfate-gamma-alumina admicelles for high-performance liquid chromatographic analysis

Chlorophenols in water were sorbed onto sodium dodecylsulfate (SDS)-alumina (gamma-form) admicelles. The extent of sorption increased with increasing amount of SDS and decreasing solution pH. Conditions for good recovery were obtained when 100 mg SDS and 1.5 g alumina was used at pH 2. However, the yield decreased with a further increase in the SDS concentration due to the formation of normal SDS micelles. The extent of sorption also increased with increasing hydrophobicity of the chlorophenol, indicating that hydrophobic interactions predominate for the collection of analytes. When a cartridge column filled with admicelles was used, >90% of tetrachlorophenol and pentachlorophenol in 200 ml of water samples were rapidly recovered. The sorbed analytes were eluted with 1 ml acetonitrile. The accuracy and precision of the present method were demonstrated for the HPLC analysis with ultraviolet (290 nm) detection of microg l(-1) levels of tetrachlorophenol and pentachlorophenol in river water samples.

Cloud-point extraction and preconcentration of cyanobacterial toxins (microcystins) from natural waters using a cationic surfactant

A new cloud-point extraction and preconcentration method using a cationic surfactant, Aliquat-336 (tricaprylylmethylammonium chloride), has been developed for the determination of cyanobacterial toxins, microcystins, in natural waters. Sodium sulfate was used to induce phase separation at 25 degrees C. The phase behavior of Aliquat-336 with respect to concentration of Na2SO4 was studied. The cloud-point system revealed a very high phase volume ratio compared to other established systems of nonionic, anionic, and cationic surfactants. At pH 6-7, it showed an outstanding selectivity in analyte extraction for anionic species. Only MC-LR and MC-YR, which are known to be predominantly anionic, were extracted (with averaged recoveries of 113.9 +/- 9% and 87.1 +/- 7%, respectively). MC-RR, which is likely to be amphoteric at the above pH range, was not detectable in the extract. Coupled to HPLC/UV separation and detection, the cloud-point extraction method (with 2.5 mM Aliquat-336 and 75 mM Na2SO4 at 25 degrees C) offered detection limits of 150 +/- 7 and 470 +/- 72 pg/mL for MC-LR and MC-YR, respectively, in 25 mL of deionized water. Repeatability of the method was 7.6% for MC-LR and 7.3% for MC-YR. The cloud-point extraction process can be completed within 10-15 min with no cleanup steps required. Applicability of the new method to the determination of microcystins in real samples was demonstrated using natural surface waters collected from a local river and a local duck pond spiked with realistic concentrations of microcystins. Effects of salinity and organic matter (TOC) content in the water sample on the extraction efficiency were also studied.

Selective recovery of lactate dehydrogenase using affinity foam

Selective isolation of lactate dehydrogenase (LDH) from porcine muscle extract was studied using foam generated from the vigorous stirring of a non-ionic surfactant, Triton X-114 derivatized with Cibacron blue. The cloud point of the surfactant-dye conjugate was higher than that of the native Triton X-114, and also the foam prepared from the affinity surfactant was more rigid taking a longer time to collapse. The equilibrium dissociation constant between pure LDH and surfactant-dye conjugate was 5.0 microM as compared to the value of 2.2 microM for the enzyme and free dye as measured by differential spectroscopy. The isolation procedure involved mixing of the porcine muscle extract with the affinity foam, separating and collapsing the foam, and warming the solution formed to 37 degrees C to yield the surfactant-dye phase and an aqueous phase containing the enzyme. The effect of surfactant concentration and protein load on enzyme recovery and purification was investigated. Under optimal conditions, LDH was quantitatively recovered with high purification factor in a very short time. Both recovery and purification were higher when foam prepared from an equivalent mixture of surfactant-dye conjugate and unmodified surfactant was used. The selectivity of interaction between LDH and detergent-dye conjugate was confirmed by lowered recovery when NADH was included during the binding step.

Use of non-ionic surfactant solutions for the extraction and preconcentration of phenolic compounds in water prior to their HPLC-UV detection

A simple and rapid HPLC method with spectrophotometric detection to determine phenolic compounds in water, including the 11 priority phenolic pollutants, is described. As they are present in low concentrations, an extraction and preconcentration step is necessary prior to their determination. A methodology based on the cloud point phenomenon is applied using the non-ionic surfactant oligoethylene glycol monoalkyl ether (Genapol X-080) as extractant. The optimum conditions for the extraction and preconcentration of phenolic derivatives have been established and detection limits lower than 10 micrograms L-1 were obtained for all studied compounds. The method has been applied to their determination in sea water and depurated waste water samples.

Copper fractionation with dissolved organic matter in natural waters and wastewater--a mixed micelle mediated methodology (cloud point extraction) employing flame atomic absorption spectrometry

A cloud point extraction-preconcentration methodology for the speciation analysis of free and organically complexed metal species in natural waters is presented. The method is based on the neutralization of the electrostatic charge of the humate-metal complexes with a positively charged surfactant in a high ionic strength solution environment. The resulting complexes are conveniently solubilized in the micelles of a non-ionic surfactant medium and are thus separated from the bulk aqueous phase. Free metal species are also determined by complexation with a conventional chelating agent under mild conditions. The overall procedure is easy, rapid and allows for a high sample throughput in terms of massive analysis of many samples in the same time period. The method offers substantially low detection limits of 8.5 and 0.9 micrograms l-1 for bound and labile species respectively, with a calibration curve rectilinear in the wide range 40-150 micrograms l-1 for the humate associated and 4-40 micrograms l-1 for the free metal species. The method is free from interferences yielding recoveries in the range 97-102% for various samples of different matrixes.

Acid-induced cloud point extraction and preconcentration of polycyclic aromatic hydrocarbons from environmental solid samples

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.

Understanding viral partitioning in two-phase aqueous nonionic micellar systems: 1. Role of attractive interactions between viruses and micelles

The partitioning behavior of viruses in the two-phase aqueous nonionic n-decyl tetra(ethylene oxide) (C10E4) micellar system cannot be fully explained by considering solely the repulsive, steric, excluded-volume interactions that operate between the viruses and the nonionic C10E4 micelles. Specifically, an excluded-volume theory developed recently by our group is not able to quantitatively predict the observed viral partition coefficients, even though this theory is capable of providing reasonable quantitative predictions of protein partition coefficients. To shed light on the discrepancy between the theoretically predicted and the experimentally measured viral partition coefficients, a central assumption underlying the excluded-volume theory that the viruses and the C10E4 micelles interact solely through repulsive, excluded-volume interactions was challenged in this study. In particular, utilizing bacteriophage P22 as a model virus, a competitive inhibition test and a partitioning study of the capsids of bacteriophage P22 were conducted. Based on the results of these two experimental studies, it was concluded that any attractive interactions between the tailspikes of bacteriophage P22 and the C10E4 micelles are negligible. Another experimental study was carried out wherein the partition coefficients of the model viruses, bacteriophages P22 and T4, were measured at various temperatures, and compared with those previously obtained for bacteriophage phiX174. This comparison also indicated that possible attractive, electromagnetic-induced interactions between the bacteriophage particles and the C10E4 micelles cannot be invoked to rationalize the observed discrepancy between the theoretically predicted and the experimentally measured viral partition coefficients.

Determination of polycyclic aromatic hydrocarbons in seawater by high-performance liquid chromatography with fluorescence detection following micelle-mediated preconcentration

In this work, the nonionic surfactant polyoxyethylene-10-lauryl ether has been used for the extraction and preconcentration of 14 polycyclic aromatic hydrocarbons, classified as priority pollutants by the US Environmental Protection Agency, from seawater samples. The cloud-point preconcentration previous separation by HPLC and quantification using fluorimetric detection and wavelength programming allow to determine these pollutants with detection limits ranging from 1.0 to 1.5 x 10(2) ng/l with RSDs better than 10.4%. The methodology is evaluated using well-established extraction and preconcentration methods and GC-MS.

Liquid-liquid extraction of palladium(II) from hydrobromic acid media by hexadecylpyridinium bromide

A simple and rapid liquid-liquid extraction of palladium has been studied involving ion-pairing of bromocomplexes of palladium(II) with hexadecylpyridinium bromide (HDPB) dissolved in chloroform. The stoichiometry and distribution of (HDP)2PdBr4 between the aqueous and organic phase was investigated by spectrophotometric mole ratio method. The extraction efficiency of palladium(II) by HDPB was studied as a function of several variables: acid, salt, surfactant concentration and equilibrium time. The results showed that PdBr4(2-) extraction could be explained by assuming the formation of (HDP)2PdBr4 complexes in the aqueous solution and transfer to organic phase. The extraction was fast and the shaking time was only a few min. The average recovery of palladium(II) from an aqueous solution containing 10 microg/ml of analyte was 99% with an RSD% of 0.95. The percentage recovery of 0.2 microg/ml palladium(II) was 96%.

Selective concentration of gold in water to a polystyrene-embedded fiber disk with polyoxyethylene(10)-p-isononylphenyl ether

A new surfactant-mediated separation method was developed for concentrating traces of gold ion in water. The methodology is based on the combination of selective complexation of gold(III) with polyoxyethylene(10)-p-isononylphenyl ether, PONPE-10, and strong binding of surfactant complex to hydrophobic polystyrene resins embedded in a PTFE fiber disk (Empore disk). A 400-fold concentration of gold(III) was achieved by 400 ml load of the sample containing 0.01% (w/v) PONPE-10 and 0.10 M nitric acid and by the subsequent elution with 1.0 ml of aqueous buffer solution of 0.01 M N-(dithiocarboxyl)sarcosine diammonium. Traces of gold (0.40 ng/l) in river water samples were successfully determined with inductively coupled plasma MS.

On-line incorporation of cloud point extraction to flow injection analysis

The on-line incorporation of cloud point extraction (CPE) to flow injection analysis (FIA) is demonstrated for the first time. The technical difficulties of inducing the cloud point phenomenon, separating the surfactant-rich phase from the aqueous phase, and detecting trace amounts of analyte(s) in the presence of the highly scattering surfactant medium in an on-line FIA system were resolved by the following: (1) mixing the sample solution containing the analyte(s) and CPE surfactant with an appropriate salting-out agent, (2) using a collection column to entrap the analyte-containing surfactant aggregates, and (3) employing the peroxyoxalate chemiluminescence reaction for the sensitive and selective determination of the analyte(s) in the presence of surfactant micelles. The figures of merit for the determination of coproporphyrin in pretreated urine samples were as follows: precision, 1.1-2.2% (RSD); limit of detection, 2.0 microg/L; and the calibration curve was linear from 46 to 2319 (micro/L (r = 0.9996).

Removal of phenols from aqueous streams by the cloud point extraction technique with oxyethylated methyl dodecanoates as surfactants

New oxyethylated methyl dodecanoates with average degrees of oxyethylation (n) ranging between 5 and 14 (denoted OMD-n) were considered as nonionic surfactants for the removal of phenol, 4-methylphenol, and 4-nitrophenol from aqueous streams by the cloud point extraction technique. The cloud point (denoted CP) strongly increases with the average degree of oxyethylation n but is independent of OMD-n concentration, except at low concentration (i.e., < 10 g.L-1). CP can be related to the surfactant hydrophilicity by the following equation: CP(degree C) = 20.27 x HLBG - 245.8 (above 10 g.L-1 and in the absence of electrolyte), where HLBG refers to the OMD-n hydrophile-lipophile balance in Griffin's scale. The presence of electrolyte such as NaCl strongly decreases the cloud point [delta CP/delta [NaCl] approximately -(9 +/- 1) degrees C-M-1]. Many parameters influence the extraction of phenols in OMD-n-rich phases, including the characteristics of phenols (hydrophobicity, hydrogen-bond acidity, hydrogen-bond basicity, etc.), the average degree of oxyethylation of OMD-n (i.e., n), the concentration of electrolyte, the settling temperature (Tset), and overheating (delta T = Tset - CP). The distribution coefficients typically range between 20 and 100. Finally, the kinetics of the separation process is limited by the slow coalescence of the fine droplets of surfactant-rich phase formed above CP.

Thermodynamics of

Formation of cobalt(II)-thiocyanato complexes in nonionic surfactant solutions of poly(ethylene oxide) type with varying poly(ethylene oxide) chain lengths of 7.5 (Triton X-114), 30 (Triton X-305), and 40 (Triton X-405) has been studied by titration spectrophotometry and calorimetry at 298 K. Data were analyzed by assuming formation of a series of ternary complexes Co(NCS)(n)Y(m)((2-n)+) (Y=surfactant) with an overall formation constant beta(nm). In all the surfactant systems examined, data obtained can be explained well in terms of formation of Co(NCS)(+) and Co(NCS)(2) in an aqueous phase (aq), and Co(NCS)(4)Y(2-) in micelles, and their formation constants, enthalpies, and entropies have been determined. The beta(41)/beta(20) ratio increases and the corresponding enthalpy becomes significantly less negative with an increasing number of ethylene oxide groups. This suggests that micelles of these nonionic surfactants have a heterogeneous inner structure consisting of ethylene oxide and octylphenyl moieties. Indeed, on the basis of molar volumes of ethylene oxide and octylphenyl groups, intrinsic thermodynamic parameters have been extracted for the reaction Co(NCS)(2)(aq)+2NCS(-)(aq)=Co(NCS)(4)Y(2-) (Delta(r)G degrees, Delta(r)H degrees, and Delta(r)S degrees ) at each moiety. The Delta(r)G degrees, Delta(r)H degrees, and Delta(r)S degrees values are -16 kJ mol(-1), -15 kJ mol(-1), and 3 J K(-1) mol(-1), respectively, for the ethylene oxide moiety, and -15 kJ mol(-1), -70 kJ mol(-1), and -183 J K(-1) mol(-1) for octylphenyl. Significantly less negative Delta(r)H degrees and Delta(r)S degrees values for ethylene oxide imply that the hydrogen-bonded network structure of water is extensively formed at the ethylene oxide moiety, and the structure is thus broken around the Co(NCS)(4)(2-) complex with weak hydrogen-bonding ability. Copyright 2001 Academic Press.

Ultrasonic extraction and field-portable anodic stripping voltammetric measurement of lead in dust wipe samples

Dust wipe samples were subjected to ultrasonic extraction (UE) in diluted nitric acid, and then analyzed for lead content using field-portable anodic stripping voltammetry (ASV). Recoveries of lead were determined from wipe materials which were spiked with certified reference materials (CRMs) containing known quantities of lead. Four different wipe materials and four different CRMs were tested, with and without filtration of aliquots of sample extract through 0.45 microm hydrophilic polytetrafluoroethylene filters. The CRMs consisted of paint, soil, particulate, and dust matrices. Wipe materials were chosen from those which have been found to meet the performance aspects of an ASTM standard specification. UE/ASV experiments were carried out in accordance with newly published ASTM procedures for on-site extraction and electroanalysis. Recoveries were found to vary for different wipe materials and CRMs. For several CRMs, quantitative (80--120%) recoveries for UE/ASV were observed for one wipe material whether filtration was used or not, while other wipe materials required filtration for quantitative recovery. In the case of one wipe material which contained detergents, quantitative recoveries could not be achieved whether filtration was used or not. The total analysis time for a sample set of 6--12 samples was 60--90 min, including extraction time and sample manipulation. The results of this work have provided information on the choice of wipe materials that can be used for quantitative lead measurements by UE/ASV in materials that are representative of sources of lead in surface dust.