Cloud point extraction

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

In this study we examined the influence of concentration conditions, acidity of solutions, and electrolytes inclusions on the liophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 at the cloud point temperature. The liophilic properties of micellar phases formed under different conditions were determined by the estimation of effective hydration values and solvatation free energy of methylene and carboxyl groups at cloud-point extraction of aliphatic acids. It was demonstrated that micellar phases formed from the low concentrated aqueous solutions of the surfactant have more hydrophobic properties than the phases resulting from highly concentrated solutions. The influence of media acidity on the liophilic properties of the surfactant phases was also exposed. 

For fluorescence PAH determination in tap water acid-induced cloud point extraction was used. This kind of extraction based on the phase separation into two isotropic liquid phases a concentrated phase containing most of the surfactant (surfactant-rich phase), where the solubilised solutes are exttacted, and an aqueous phase containing a surfactant concenttation closes to the critical micellar concentration. 

Hydrophobicity inflkence. Despite of the diphilic character of the NS-rich phase the efficiency of micellar extraction raises with general substrate hydrophobicity increase. The hydrophobicity of ligand is the main factor, which determines the cloud point extraction of complexes. 

Strkcttire inflkence. The specificity of interphase transfer in the micellar-extraction systems is the independent and cooperative influence of the substrate molecular structure - the first-order molecular connectivity indexes) and hydrophobicity (log P - the distribution coefficient value in the water-octanole system) on its distribution between the water and the surfactant-rich phases. The possibility of substrates distribution and their D-values prediction in the cloud point extraction systems using regressions, which consider the log P and values was shown. Here the specificity of the micellar extraction is determined by the appearance of the host-guest phenomenon at molecular level and the high level of stmctural organization of the micellar phase itself. 

THE CLOUD-POINT EXTRACTION OF ALIPHATIC AMINES INTO THE NON-IONIC SURFACTANT-RICH PHASES... 

ACID-BASED SURFACTANT CLOUD POINT EXTRACTION AND PRECONCENTRATION OF POLYCYCLIC AROMATIC HYDROCARBONS PRIOR TO FLUORESCENCE DETERMINATION... 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

Sodium dodecylsulphate was selected as an anionic surfactant Factors affecting acid-induced cloud point extraction including surfactant, hydrochloric acid, PAHs, and electrolyte concentration, centrifugation have been examined. Finally, we applied the optimized acid-induced CPE system for combination of the extraction and preconcentration steps with fluorimetric determination of some representatives of PAHs. Suggested means was used for PAHs determination in tap water. 

This phenomenon can be exploited for separation and concentration of solutes. If one solute has certain affinity for the micellar entity in solution then, by altering the conditions of the solution to ensure separation of the micellar solution into two phases, it is possible to separate and concentrate the solute in the surfactant-rich phase. This technique is known as cloud point extraction (CPE) or micelle-mediated extraction (ME). The ratio of the concentrations of the solute in the surfactant-rich phase to that in the dilute phase can exceed 500 with phase volume ratios exceeding 20, which indicates the high efficiency of this technique. Moreover, the surfactant-rich phase is compatible with the micellar and aqueous-organic mobile phases in liquid chromatography and thus facilitates the determination of chemical species by different analytical methods [104]. 

The most important advantage of cloud point extraction is that only small amounts of nonionic or zwitterionic surfactants are required and consequently the procedure is less costly and more environmentally benign than other conventional extraction techniques such as liquid-liquid extraction and solid liquid extraction [107,108]. Moreover, CPE offers the possibility of combining extraction and preconcentration in one step. 

Fig. 13.5 Steps involved in cloud point extraction (CPE) prior to HPLC, GC, and CE analysis.

Applications of Cloud Point Extraction to the Analysis of Selected Samples... 

Cloud point extraction has been applied to the separation and preconcentration of analytes including metal ions, pesticides, fungicides, and proteins from different matrices prior to the determination of the analyte by techniques such as atomic absorption, gas chromatography, high performance liquid chromatography, capillary zone electrophoresis, etc. 

Cloud point extraction of metal ions. The use of cloud point extraction as a separation technique was first introduced by Watanabe for the extraction of metal ions forming sparingly water soluble complexes [109], Since then, the technique has been applied successfully to the extraction of metal chelates for spectrophotometric, atomic absorption, or flow injection analysis of trace metals in a variety of samples [105-107,110]. Other metal complexes such as AUCI4 or thiocyanato-metal complexes can be extracted directly using nonionic surfactants such as polyoxyethylene... 

Cloud point extraction from biological and clinical samples. The most frequent use of CPE is for the separation and purification of biological analytes, principally proteins. In this way, the cloud point technique has been used as an effective tool to isolate and purify proteins when combined with chromatographic separations. Most of the applications deal with the separation of hydrophobic from hydrophilic proteins, with the hydrophobic proteins having more affinity for the surfactant-rich phase, and the hydrophilic proteins remaining in the dilute aqueous phase. The separation of biomaterials and clinical analytes by CPE has been described [105,106,113]. 

Table 13.2 Summary of Cloud Point Extractions of Metals Chelates Using Nonionic... 

Most proteins must be folded into a specific three-dimensional conformation to express their specificity and activities, which comphcates the DSP [212]. Researchers in the area of RME of proteins/enzymes have reafized this and directed more efforts in developing novel and imaginative techniques in RME as well as coupling the existing techniques such as chromatography, electrophoresis, and membrane extractions with RME. Such promising techniques developed in the recent past have been discussed in this section. Apart from these techniques, use of novel surfactants in the RME and surfactant based separation processes (e.g., cloud-point extraction) are also considered. 

Aqueous micellar solutions of many nonionic surfactants, with an increase in temperature, become turbid over a narrow temperature range, which is referred to as their cloud-point [17,277]. Above the cloud-point temperature, such solutions separate into two isotropic phases. Cloud-point extraction (CPE) is also referred to as a particular case of ATPE [278,279] and more specifically as aqueous micellar two-phase systems [10,277]. Very recently, in an extensive review, Quina and Hinze [280] have discussed in detail the emergence of CPE as an environmentally benign separation process, highlighting the basic features, experimental protocols, recent applications, and future trends in this area. 

M. A. Bezerra, A. L. B. Conceicao and S. L. C. Ferreira, Doehlert matrix for optimisation of procedure for determination of nickel in saline oil-refinery effluents by use of flame atomic absorption spectrometry after preconcentration by cloud-point extraction. Anal. Bioanal. Chem., 378(3), 2004, 798-803. 

Sicilia, D., S. Rubio, D. Perez-Bendito, N. Maniasso, and E.A.G. Zagatto. 1999. Anionic surfactants in acid media A new cloud point extraction approach for the determination of polycyclic aromatic hydrocarbons in environmental samples. Anal. Chim. Acta 392 29-38. 

Cloud point phenomenon (cloud point extraction—CPE) Extracting analytes (both organic and inorganic) from water samples 58-65... 

A plot of the temperatures required for clouding versus surfactant concentration typically exhibits a minimum in the case of nonionic surfactants (or a maximum in the case of zwitterionics) in its coexistence curve, with the temperature and surfactant concentration at which the minimum (or maximum) occurs being referred to as the critical temperature and concentration, respectively. This type of behavior is also exhibited by other nonionic surfactants, that is, nonionic polymers, // - a I k y I s u I Any lalcoh o I s, hydroxymethyl or ethyl celluloses, dimethylalkylphosphine oxides, or, most commonly, alkyl (or aryl) polyoxyethylene ethers. Likewise, certain zwitterionic surfactant solutions can also exhibit critical behavior in which an upper rather than a lower consolute boundary is present. Previously, metal ions (in the form of metal chelate complexes) were extracted and enriched from aqueous media using such a cloud point extraction approach with nonionic surfactants. Extraction efficiencies in excess of 98% for such metal ion extraction techniques were achieved with enrichment factors in the range of 45-200. In addition to metal ion enrichments, this type of micellar cloud point extraction approach has been reported to be useful for the separation of hydrophobic from hydrophilic proteins, both originally present in an aqueous solution, and also for the preconcentration of the former type of proteins. 

Delgado, B., V. Pino, J.H. Ayala, V. Gonzalez, and A.M. Alfonso. 2004. Nonionic surfactant mixtures A new cloud-point extraction approach for the determination of PAHs in seawater using HPLC with fluori-metric detection. Anal. Chim. Acta 518 165-172. 

Yuan, Ch. G., G.B. Jiang, B. He, and J.F. Liu. 2005. Preconcentration and determination of tin in water samples by using cloud point extraction and graphite furnace atomic absorption spectrometry. Microchim. Acta 150 329-334. 

Carabias-Martinez, R., E. Rodriquez-Gonzalo, J. Dominiquez-Alvaro, C. Garcia Pinto, and J. Hemandez-Mendez. 2003. Prediction of the behaviour of organic pollutants using cloud point extraction. J. Chromatogr. A 1005 23-34. 

Giokas, D.L., J. Antelo, E.K. Paleologos, F. Arce, and M.I. Karayannis. 2002. Copper fractionation with dissolved organic matter in natural waters and wastewater-a mixed micelle mediated methodology (cloud point extraction) employing flame atomic absorption spectrometry. J. Environ. Monit. 4 505-510. 

Farajzadeh, M.A. and M.R. Fallahi. 2006. Simultaneous cloud-point extraction of nine cations from water samples and their determination by flame atomic absorption spectrometry. Anal. Sci. 22 635-640. 

Shemirani, R, R.R. Kozani, and Y. Assai. 2007. Development of a cloud point extraction and preconcentration method for silver prior to flame atomic absorption spectrometry. Microchim. Acta 157 81-85. 

The advantages cited for the described nonionic micellar cloud point extraction schemes include the following (1) ability to concentrate a variety of analytes (with concentration factors of 10-75), (2) safety and cost benefits (i.e. the use of small amounts of nonionic surfactant as an extraction solvent obviates the need to handle the usually large volumes of organic solvent required in traditional liquid-liquid extractions so that the volatility, flammability, and cost are reduced), (3) easy disposal of the nonionic surfactant extraction solvent (i.e. the nonionic surfactant solution is reportedly easily burned in the presence of waste... 

Table 6.11 Examples of application of cloud point extraction in trace analysis...

Made], K. Microwave-assisted and cloud point extraction in determination of drugs and other bioactive compounds. Trends Anal. Chem. 28, 436-446 (2009)... 

Paleologos, E.K., Giokas, L., Karayannis, M.I. Micelle-mediated separation and cloud-point extraction. Trends Anal. Chem. 24, 426-436 (2005)... 

Hinze, W.L., Pramauro, E. A critical review of surfactant-mediated phase separations (cloud point extractions) theory and applications. Crit. Rev. Anal. Chem. 24, 133-177 (1993)... 

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