Modern Extraction Techniques - American Chemical Society

Jul 16, 2004 - “Where shall I start?” asked Piglet. “How about at the beginning,” Pooh replied. (The Adventures of Winnie the Pooh, A. A. Miln...
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Anal. Chem. 2004, 76, 4659-4664

Modern Extraction Techniques Douglas E. Raynie*

Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota 57007 Review Contents Fluid-Phase Partitioning Methods Supercritical and Pressurized Liquid Extraction Microwave-Assisted Extraction Other Methods Sorptive Extractions Solid-Phase Extraction Solid-Phase Microextraction Restricted Access Media Membrane Extraction Other Sorptive Methods Proteins and Biomolecules Conclusion Literature Cited

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“Where shall I start?” asked Piglet. “How about at the beginning,” Pooh replied. (The Adventures of Winnie the Pooh, A. A. Milne). Preparing an inaugural biennial review covering a field as broad as “extraction” or “sample preparation” is a rather daunting task. Where does one begin? How should the topic be defined? What combination of breadth versus depth is needed? After careful consideration, this biennial review addresses “modern extraction methods” applied as analytical sample preparation tools. Even with this limitation, a significant level of discretion needs to be used in this subjective review. The review covers those articles abstracted during the calendar years of 2002 and 2003, with preference given to articles introducing new forms of analytical extraction and fundamental developments in extraction and related methodologies. Applications discussed are only those that are unique. Following the rapid development of analytical techniques in the post-World War II era, increasing demands are placed on sample quality, and thus extraction as a sample preparation tools akin to the computer-programming mantra “garbage in, garbage out.” These demands include sample integrity, throughput, and compatibility with subsequent analysis. Thus, during this review period, trends in analytical extraction have been a movement toward less (organic) solvent consumption, faster extraction time, improved quantification (i.e., higher recoveries, better reproducibility, and a drive to ever lower method detection limits), and automation. In many instances, the underlying goals are achieved through miniaturization, including the direct coupling of extraction procedures to small-scale separation and analysis methods. Improved extraction selectivity is often a secondary goal since analytical selectivity is typically achieved through subsequent separations methods, selective analytical methods, or both. * Phone: 605-688-4549. Fax: 605-688-6364. E-mail: [email protected]. 10.1021/ac040117w CCC: $27.50 Published on Web 07/16/2004

© 2004 American Chemical Society

The trends mentioned above are primarily met through the manipulation of the physical properties of the extracting solvent (as in supercritical fluid extraction (SFE) or pressurized liquid extraction (PLE)) or the application of selective sorbents (including restricted access media (RAM) and molecularly imprinted polymers (MIP)). Trends in improving extraction throughput are met by either decreasing the actual extraction time or via process improvements, such as parallel processing. The move toward increased extraction yield (by manipulation of solvent properties) is a concern primarily for the isolation of analytes from a solid sample. On the other hand, selectivity concerns (via selective sorbents) become an issue mostly for liquid samples. Following a general review, the two approaches of solvent manipulation and selective adsorbents will be discussed individually. Since the field of biological macromolecular analysis (such as proteomics) can place unique demands on sample preparation steps, this area will be addressed separately. Due to their primary nature as an enabling tool, analytical sample preparation and extraction suffer from the lack of a specific, dedicated journal. Hence, advances in the field are typically found in general analytical chemistry journals, such as this journal, or in chromatography journals. One regular resource is the column prepared by Ron Majors for LC/GC magazine. In December 2002, Majors (1) reported results of a users’ survey of trends in sample types and characteristics, sample preparation (and extraction) techniques, and emerging techniques. Majors found that the demand for extracting liquid samples (78% of survey respondents) was essentially the same as the demand for the extraction of solid samples (67% survey response), especially if one includes gels and semisolid samples (20%), which are largely treated as solids. A trend noted when comparing to a previously survey conducted five years earlier showed a 3-fold increase in the number of analysts concerned with both sample volumes of less than 1 mL and with sample concentrations less than one part-per-billion. An extensive review (2) of analytical extractions covered operational aspects and the fundamental aspects of equilibrium and the kinetics of mass transfer necessary for the development of methods employing the more recently developed extraction techniques. The review addressed special considerations with extractions conducted on-site or in situ. Smith (3) and Saito and Jinno (4) reviewed extraction as the primary sample preparation technique prior to chromatographic separations. Smith provided examples of a variety of methods, such as sorbent-based methods, headspace sampling, pressurized solvent methods (including SFE and superheated, or subcritical, water extraction (SWE)), and selective methods (like MIP), applied to solid, liquid, and gaseous samples. Saito and Jinno discussed the role of miniaturization and sorptive phases (and subsequent desorption) in liquid-phase separations, including on-line coupling. Analytical Chemistry, Vol. 76, No. 16, August 15, 2004 4659

Environmental applications continue to drive the development of many extraction procedures. Petrovic and Barcelo (5) presented a discussion of sample collection and preservation, as related to the extraction of nonionic surfactants in environmental solids. Sturgeon et al. (6) reported an interlaboratory comparison of the determination of tributyltin in marine sediment. Participating laboratories used mechanical shaking, sonication, PLE, microwaveassisted extraction (MAE), and in situ derivatization and found substantial agreement between the methods. Similarly, a separate report (7) compared SFE, PLE, SWE, MAE, and traditional methods for the determination of acidic herbicides in soils. Other general environmental extractions investigated miniaturized sample preparation methods (8) and the recovery of semivolatile organic compounds during the sample preparation of particulate matter (9). The analysis of foods and natural products also provides an avenue for the development of extraction technologies, especially involving wet or pulpy samples. Bjoerklund et al. (10) reviewed SFE, MAE, and PLE for the fast analysis of polychlorinated biphenyls (PCB) in food. Their treatment investigated subsequent analysis by immuno- and bioassay, in addition to conventional chromatographic procedures. Buldini et al. (11), Huie (12), and Zygmunt and Namiesnik (13) also discussed the extraction of plant material, such as foods and natural products. Volatile analytes are often determined through characterization of the sample headspace, that is, the gaseous layer in immediate proximity to the solid or liquid sample. Augusto et al. (14) compared analytical distillation, headspace-manipulation methods, liquid-liquid extraction (LLE), solid-phase extraction (SPE), and SFE for the analysis of aromas and fragrances. The review provided 66 references. Ortega-Heras et al. (15) also studied aromas, exploring the aroma composition of wines using LLE and static headspace sampling, as did Wanakhachornkrai and Lertsiri (16), who looked at the volatiles in Thai soy sauce by dynamic headspace sampling, direct solvent extraction, and vacuum simultaneous steam distillation-extraction. Bouche et al. (17) took a minimalist approach for the forensic characterization of light hydrocarbons in inhalation intoxication cases. FLUID-PHASE PARTITIONING METHODS As stated earlier, the physical properties of extracting solvents, especially temperature and pressure, can be externally manipulated to enhance their ability to extract analytes from a wide variety of, primarily solid, sample matrixes. The solvent manipulations can result in a supercritical fluid (SFE), can be from direct heating above the normal boiling point (PLE), may be heated with microwave energy (MAE), or can have an input of ultrasonic energy. This manipulation of physical properties can result in lower surface tension, increased solute solubilities, higher diffusion, and even some alteration of solvent polarity. Supercritical and Pressurized Liquid Extraction. While generally considered as two distinct methods, from a physical (including instrumental) viewpoint, the technologies share significant similarities. SFE typically involves carbon dioxide as the primary extraction solvent. The carbon dioxide is pressurized to about 50 atm if used as a liquid or above 75 atm when used as a supercritical fluid. Precise temperature control is also necessary, at temperatures generally in the range of 35-200 °C for super4660

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critical carbon dioxide and lower for the liquid. Through alteration of the applied temperature-pressure combination, some alteration of the solvent properties is achieved. Solvent polarity is “modified” through the addition of up to 20% of organic cosolvent. The advantages and analytical uses of SFE are well-established. PLE is similar in the use of temperatures above the atmospheric boiling point, typically in the range of 100-200 °C. However, the pressures are usually inconsequential, as long as sufficient pressure to maintain the liquid state of the extracting solvent is applied. Pressures around 100 atm are usually applied. Any aqueous or organic solvent can conceivably be used with PLE. The use of heated, pressurized water for extraction, SWE, is a hybrid between SFE and PLE. While most laboratories that perform SWE approach the technique from an SFE point of view, from the physical properties and chemical phase point of view, SWE is more similar to PLE. In addition to all of the advantages of the other types of pressurized fluids, SWE allows some control over effective solvent polarity, via controlled changes in temperature, with a completely aqueous solvent. While no commercial systems dedicated entirely to SWE exist, both SFE and PLE equipment can be used with minimal modification. Of particular interest with SFE is the ability to extract labile compounds. Halasz et al. (18) demonstrated this capability with the isolation of polynitro organic explosives from soil. Another unique feature of SFE is the capacity of directly coupling the technique with chromatography. Ashraf-Khorassani et al. (19) reported a rapid and quantitative analysis time for the on-line SFEliquid chromatography (LC) characterization of polymer additives. Zhu and Lee (20) improved the analytical time, by the elimination of multiple sample preparation steps, for the determination of PCB in pine needles with SFE and gas chromatography-mass spectrometry. Ramos et al. (21) thoroughly reviewed the role of both SWE and PLE in environmental analysis. They focused on the parameters influencing extraction yield and selectivity, noting the use of the techniques for class separations. Other articles compared PLE with other extraction techniques in environmental analysis. De la Cal et al. (22) compared PLE with a combined SoxhletSPE procedure for the quantitative recovery of polybrominated diphenyl ether congeners in sediment samples. Interestingly, they performed an on-line cleanup procedure by placing a sorbent inside the PLE cell with the sample. On the other hand, Aguera et al. (23) performed SPE after the PLE of triclosan and related antibiotics from marine sediments, as did Datta et al. (24) with the PLE and LC-fluorescence determination of alkoxyphenols in fish tissue. Croce et al. (25) also determined alkoxyphenols, comparing PLE, Soxhlet, automated Randall, MAE, and surfactant solution extraction of river sediments. The researchers claimed comparable results between the techniques and recommended choice of extraction method based on cost. PLE is also being applied to the natural products arena, with Dawidowicz et al. (26) optimizing the extraction conditions prior to the LC analysis of rutin and isoquercitrin in black elder flowers, leaves, and berries. Papagiannopoulos and Mellenthin (27) sequentially used solvents of increasing polarity to purify and separate polyphenols important in the brewing process. Others (28) used the postextraction SPE cleanup method to simplify the

time for the determination of multiple pesticide residues in tobacco. Microwave-Assisted Extraction. Conceptually, MAE is similar to PLE. That is, liquid solvents are heated to temperatures beneficial to analytical extractions. In the case of MAE, the heating is due to irradiation with microwave energy and this irradiation serves only to heat the sample + solvent system. Practically, several differences exist between MAE and other forms of extraction. The solvent or the sample must possess a dipole (i.e., are polar) in order to absorb microwave energy. The heating due to microwave irradiation can be much more rapid than heating with conventional means. The development of MAE followed from the development of microwave sample digestions and MAE exists in multimode and focused-radiation formats and open- and closedvessel configurations. Reviews (29, 30) discuss the approaches and strategies for MAE. One use of MAE gaining popularity is to use the microwave irradiation to drive volatile analytes into the headspace for subsequent sampling with solid-phase microextraction (SPME). The research group of Jen (31-33) in Taiwan developed this approach for the analysis of aqueous and soil-bound chlorophenols. They examined the effects of pH, sample polarity, salt addition, microwave power, and irradiation time, the SPME desorption parameters to create a “solventless” sample preparation system. Hydrolysis and derivatization chemistries can also be combined with MAE. Carro et al. (34) used an experimental design approach for the microwave extraction and saponification of organochlorine pesticides in oyster samples. The variables they examined included solvent volume, extraction time and temperature, acetone addition, sample amount, and sodium hydroxide volume, with the extraction time and temperature having the greatest effect. Gfrerer and Lankmayr (35) took a similar approach in developing a validated method for the determination of polycyclic aromatic hydrocarbons in pumpkin seed oils. Vryzas et al. (36) used an MAE-acid hydrolysis procedure to convert dithiocarbamate fungicides on tobacco and peaches to CS2. The evolved CS2 was trapped in a layer of isooctane, a nonpolar “microwave-transparent” solvent. Other Methods. Extractions from solids may also be accelerated through the application of ultrasonic energy. Hardcastle and Compton (37) demonstrated that ultrasound energy maintained a high surface area between phases when extracting copper from blood. Other applications, such as the isolation of neuroleptic compounds from hair (38) and the determination of selenium in seafood (39), show the ability of sonoextraction to speed analytical schemes. Unique geometries can also be applied to provide a diffusive aspect to liquid-liquid extractions. Jandik et al. (40) used an H filter to study the laminar fluid diffusion of antibiotics from blood into a receiver fluid. Jonsson and Nilsson (41) demonstrated an XT tube extractor for bioanalytical sample preparation. Syringebased construction also found utility. Shen and Lee (42) used the organic solvent film formed in a microsyringe body as the extraction interface in the headspace sampling of chlorobenzenes, and Psillakis and Kalogerakis (43) reviewed the development of single-drop microextraction.

Unique solvent properties are also of interest in developing extraction procedures. Takagai and Igarashi (44) presented the mechanism of phase separation and applications of homogeneous liquid-liquid extraction. While becoming increasingly discussed as a “green” solvent by the engineering community, ionic liquids are used rather sparingly in analytical chemistry. Liu et al. (45) investigated these solvents for both direct immersion and headspace liquid-phase microextraction. Grob et al. (46) compared volatile solvents with acids for the extraction of cellular nucleotides prior to capillary electrophoretic characterization. Paixao and Stamford (47) investigated solvent combinations with saponification for the quantitative improvement of the removal of analytes from emulsified fat products. SORPTIVE EXTRACTIONS Initially borrowing from column chromatography and applying modern chromatographic stationary phases, a variety of sorptive extraction techniques have been developed. The use of cartridgebased SPE is well-established. The same sorption chemistry is applied in new configurations, on fibers and stir bars, inside capillary tubes, on membranes, and elsewhere. The selective nature of the sorbent drives the extraction and new phases, especially molecularly imprinted polymers and other types of restricted access media, are being developed. Solid-Phase Extraction. The heart of SPE is the selective sorptive phase. While siloxane-based chromatography phases are well-established and widely used, work is still underway in characterizing these phases. Decaestecker et al. (48) compared a range of commercial SPE sorbentssapolar, mixed mode, and polymericsfor their suitability in cleaning toxicological samples. Grey et al. (49) evaluated alkyl-silica sorbents, mixed mode, and polymeric phases in both conventional and multilayer cartridge formats for the determination of paraquat and diquat in environmental waters and vegetables. Mueller et al. (50) investigated the effects of mixed-mode SPE and protein precipitation on ion suppression during subsequent electrospray ionization MS, as did Briem et al. (51). Both groups found that SPE had a greater impact on reducing ion suppression. Specialty applications are also important in evaluating SPE sorbents. Iha et al. (52) explored SPE in the enantioselective analysis of atenolol in biological fluids, while Vera-Avila et al. (53) examined commercial immunosorbent cartridges specific for phenylurea pesticides. Another trend in SPE is to move beyond the traditional cartridge format. Koster et al. (54) developed instrumentation for placing SPE in-line with LC and Focant and de Pauw (55) used disposable, multilayer silica for a robust in-line SPE cleanup of pollutants from biological fluids. While SPE in the format of 96well plates has been commercially available, Berna et al. (56) thoroughly investigated the collection, storage, and filtration of samples associated with this SPE approach. Broyles et al. (57) explored the same parameters for SPE microfabricated for microfluidic (so-called “lab on a chip”) devices. Sample characteristics can also play an important role in the success of SPE. Reddersen and Heberer (58) demonstrated the matrix-dependent formation of artifacts during the acidic extraction of environmental waters for chlorinated antibiotics. Iwase (59) and Thomsen et al. (60) evaluated optimal SPE conditions for use with emulsified samples, such as milk. Analytical Chemistry, Vol. 76, No. 16, August 15, 2004

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Solid-Phase Microextraction. A miniaturized version of SPE, where the sorbent phase is coated on the outside of a fiber or the inside of a tube, known as SPME, has shown increasing applicability. One review (61) concentrated on the passive sampling of gasphase contaminants with SPME. Saito and Jinno (62) reviewed the on-line coupling of SPME with microcolumn separation techniques, while Kumazawa et al. (63) discussed application of the technique to LC for drug analysis. Chen et al. (64) extended the fundamental understanding of the technique for use in onsite analysis. We have already seen the use of this technique for headspace sampling coupled with microwave irradiation. Pinho et al. (65) investigated the use of SPME for conventional headspace sampling of cheeses. They explored the addition of water on the release of free fatty acids, the linear relationship between SPME adsorption and analyte concentration in the cheese sample, and competitive adsorption on the fiber. Ezquerro et al. (66) found that SPME headspace sampling was superior to static methods for studying thermooxidative degradation of packaging materials. Blood analysis (67) required salting out to extract headspace alcohols by SPME in a validated method. The study of phases for SPME, as with SPE, assisted in the development of applications of the technique. Mullett and Pawliszyn (68) reviewed the selectivity and biocompatibility of SPME phases, including MIP. Goncalves and Alpendurada (69) looked at six different SPME fibers for development of a multiresidue method for the simultaneous determination of four different classes of pesticides. Others (70, 71) also compared commercial SPME phases for environmental samples. Meanwhile, Cai et al. (72) used sol-gel technology to develop a dibenzo-18-crown-6 SPME coating. The novel coating proved both sensitive and selective for aliphatic amines. Configurations designed as alternatives to the conventional fiber-coated SPME are being investigated. Kataoka (73) reviewed the in-tube approach to SPME. Morishima et al. (74) used polyetheretherketone (PEEK), rather that fused silica, for in-tube SPME connected directly on-line with microcolumn LC. The same group (75) previously examined the roles of extraction time, flow rate, and the desorption process for fused-silica-based in-tube SPME on-line with LC. Walles et al. (76) investigated the automation of in-tube SPME with the quantitative LC-MS of drug metabolites. Saito et al. (77) approached in-tube SPME by packing several hundreds of fine fibrous, coated materials longitudinally into a fused-silica capillary. They obtained limits of quantification down to 1 ng/mL. Restricted Access Media. Not long ago, MIP and RAM drew praises for the high selectivity inherent in their use. Just as quick, these phases started to fall from favor since new phases had to be custom synthesized for each set of analytes. Walles et al. (78) presented pharmaceutical applications of RAM. Molinelli et al. (79) claimed the first report of combining MIP with SPE for beverage analysis. Mullet et al. (80) developed an alkyl-diol-silica RAM for in-tube SPME, the approach being the first of its kind. Membrane Extraction. Membrane extraction takes advantage of potentially high surface areas, as well as unique selectivities, to achieve favorable results. Depending on their configurations, membrane extractors may not have a selective sorptive phase, but since they do not manipulate solvent properties in the manner 4662

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of SFE, PLE, or MAE, they will be discussed here. Jonsson and co-workers (81, 82) reviewed membrane extraction approaches, describing the method principles as a practical guide. One type of membrane extraction is the use of hollow fiber membranes, including the XT tube extractor previously discussed (41). Jonsson et al. (83) further developed the XT tube extractor for bioanalytical use and explored the effects of sample pH, organic solvents, sample flow rate, and fiber lengths on extraction efficiency. Khrolenko et al. (84) combined the supported liquid membrane method with SPME for the determination of microgram levels of pesticide in fruit juices. Norberg et al. (85) used robotics to automate supported liquid membrane extraction. Chimuka et al. (86) utilized the selectivity of supported liquid membranes to remove uranium ions from complex samples. Other reports (87, 88) showed the simplicity of hollow fiber membranes for microscale extractions. Other membrane methods were utilized for their selective nature. Ultrafiltration found use in the characterization of human plasma (89, 90). Hennion and Pichon (91) reviewed antigenantibody interactions, multiresidue extractions, immunosorbents, and on-line chromatographic coupling when discussing immunobased sample preparation. Others (92-94) directly coupled membrane extractions with GC, LC, or both. Other Sorptive Methods. Baltussen et al. (95) reviewed sorptive sample preparation and noted the need for liquid polymer sorbents to eliminate irreversible adsorption and incomplete desorption. Two newer approaches to sorptive extraction expected to make major advances are matrix solid-phase dispersion (MSPD) and stir bar sorptive extraction. Sandra and David (96) applied MSPD with ultrasound extractions to over 50 food samples per day during the 1999 “Belgian dioxin food crisis”. Applications of MSPD to animal (97) and plant (98) tissues have also been reported. The group of Sandra (99) coated magnetic stir bars with the same coatings used in SPME and achieved significantly higher phase ratios. They applied the technique to samples as diverse as biological fluids (100) and malted beverages (101) for a variety of different analytes. PROTEINS AND BIOMOLECULES The needs of proteomics and similar bioanalytical schemes place a special demand on sample preparation in this arena. Wells et al. (102) reviewed automated sample preparation approaches as applied to genomics, while Terry et al. (103) investigated the critical parameters important to the detection of genetically modified organisms. Several investigators reported the unique solvent effects toward biological molecules. Castellanos-Serra and Paz-Lago (104) examined detergents and other solutions to inhibit unwanted proteolysis during sample preparation procedures. Ho and Hsu (105) studied variations in protein patterns to identify microorganisms. Dernovics et al. (106) utilized cell wall digesting enzymes to improve the isolation of selenium in mushrooms. Borderies et al. (107) performed a multiple sequence procedure to isolate cell wall proteins in genome sequencing. Reyes et al. (108) reviewed microfluidic sample preparation systems for protein analysis. Microchip approaches to proteometic sample preparation are reported (109-111), whereas the SPE disk approach was reported (112) to be more universal. Perhaps the

most novel approach to automated sample preparation for nucleic acid and protein extraction that bears watching is pressure cycling technology (113). In this technique, samples are exposed to rapidly cycled pressures, from ambient up to 35 000 psi in 5 s, to control molecular interactions as the extract passes into a lysis buffer. CONCLUSION Fundamental developments in the areas of fluid-phase partitioning methods, selective sorbent extractions, and membranebased extractions are continuing. As development continues and applications are reported, the marketplace will respond with suitable systems and supplies to drive this once neglected analytical field. Douglas Raynie is an Assistant Professor in the Department of Chemistry and Biochemistry at South Dakota State University. Prior to joining SDSU, he was employed for eleven years as a Senior Scientist at Procter and Gamble’s Corporate Research Division. He earned his Ph.D. at Brigham Young University under the direction of Dr. Milton L. Lee. His undergraduate degree is from Augustana (South Dakota) College, with majors in chemistry and biology. Dr. Raynie’s research interests include high-resolution chromatography (including high-temperature LC and SFC), chromatographic sample preparation (including ASE, SFE, SPME, and SPE), chromatography theory, sustainable and green chemistry, and problem-based learning in analytical chemistry. At P&G, he introduced ASE to industry as one of the world’s first practitioners of the technique.

LITERATURE CITED (1) (2) (3) (4) (5) (6)

(7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27)

Majors, R. E. LC/GC 2002, 20, 1098-1113. Pawliszyn, J. Anal. Chem. 2003, 75, 2543-2558. Smith, R. M. J. Chromatogr., A 2003, 1000, 3-27. Saito, Y.; Jinno, K. J. Chromatogr., A 2003, 1000, 53-67. Petrovic, M.; Barcelo, B. Chromatographia 2002, 56, 535-544. Sturgeon, R. E.; Wahlen, R.; Brandsch, T.; Fairman, B.; WolfBriche, C.; Garcia Alonso, J. I.; Rodriguez Gonzalez, P.; Ruiz Encinar, J.; Sanz-Medel, A.; Inagaki, K.; Takatsu, A.; Lalere, B.; Monperrus, M.; Zuloaga, O. Anal. Bioanal. Chem. 2003, 376, 780-787. Macutkiewicz, E.; Rompa, M.; Zygmunt, B. Crit. Rev. Anal. Chem. 2003, 33, 1-17. Saito, Y.; Kawazoe, M.; Imaizumi, M.; Morihima, Y.; Nakao, Y.; Hatano, K.; Hayashida, M.; Jinno, K. Anal. Sci. 2002, 18, 7-17. Swartz, E.; Stockburger, L.; Gundel, L. A. Environ. Sci. Technol. 2003, 37, 597-605. Bjoerklund, E.; von Holst, C.; Anklam, E. Trends Anal. Chem. 2002, 21, 39-52. Buldini, P. L.; Ricci, L.; Sharma, J. L. J. Chromatogr., A 2002, 975, 47-70. Huie, C. W. Anal. Bioanal. Chem. 2002, 373, 23-30. Zygmunt, B.; Namiesnik, J. J. Chromatogr. Sci. 2003, 41, 109116. Augusto, F.; Leite e Lopes, L.; Zini, C. A. Trends Anal. Chem. 2003, 22, 160-169. Ortega-Heras, M.; Gonzalez-San Jose, M. L.; Beltran, S. Anal. Chim. Acta 2002, 458, 85-93. Wanakhachornkrai, P.; Lertsiri, S. Food Chem. 2003, 83, 619629. Bouche, M.-P. L. A.; Lambert, W. E.; van Bocxlaer, J. F. P.; Piette, M. H.; de Leenheer, A. P. J. Anal. Toxicol. 2002, 26, 35-42. Halasz, A.; Groom, C.; Zhou, E.; Paquet, L.; Beaulieu, C.; Deschamps, S.; Corriveau, A.; Thiboutot, S.; Ampleman, G.; Dubois, C.; Hawari, J. J. Chromatogr., A 2002, 963, 411-418. Ashraf-Khorassani, M.; Nazem, N.; Taylor, L. T. J. Chromatogr., A 2003, 995, 227-232. Zhu, X. R.; Lee, H. K. J. Chromatogr., A 2002, 976, 393-398. Ramos, L.; Kristenson, E. M.; Brinkman, U. A. T. J. Chromatogr., A 2002, 975, 3-29. de la Cal, A.; Eljarrat, E.; Barcelo, D. J. Chromatogr., A 2003, 1021, 165-173. Aguera, A.; Fernandez-Alba, A. R.; Piedra, L.; Mercua, M.; Gomez, M. J. Anal. Chim. Acta 2003, 480, 193-205. Datta, S.; Loyo-Rosales, J. E.; Rice, C. P. J. Agric. Food Chem. 2002, 50, 1350-1354. Croce, V.; Patrolecco, L.; Polesello, S.; Valsecchi, S. Chromatographia 2003, 58, 145-149. Dawidowicz, A. L.; Wianowska, D.; Gawdzik, J.; Smolarz, D. H. J. Liq. Chromatogr. Relat. Technol. 2003, 26, 2381-2397. Papagiannopoulos, M.; Mellenthin, A. J. Chromatogr., A 2002, 976, 345-348.

(28) Haib, J.; Hofer, I.; Renaud, J.-M. J. Chromatogr., A 2003, 1020, 173-187. (29) Nobrega, J. A.; Trevizan, L. C.; Araujo, G. C. L.; Nogueira, A. R. A. Spectrochim. Acta, B 2002, 57B, 1855-1876. (30) Luque-Garcia, J. L.; Luque de Castro, M. D. Trends Anal. Chem. 2003, 22, 90-98. (31) Wei, M. C.; Jen, J. F. Chromatographia 2002, 55, 701-706. (32) Chen, Y. I.; Su, Y. S.; Jen, J. F. J. Chromatogr., A 2002, 976, 349-355. (33) Wei, M. C.; Jen, J. F. J. Chromatogr., A 2003, 1012, 111-118. (34) Carro, N.; Garcia, I.; Igacio, M.-C.; Llompart, M.; Yebra, M.-C.; Mouteira, A. Anal. Bioanal. Chem. 2002, 374, 547-553. (35) Gferer, M.; Lankmayr, E. J. Sep. Sci. 2003, 26, 1230-1236. (36) Vryzas, Z.; Papadakis, E. N.; Papadopoulou-Mourkidou, E. J. Agric. Food Chem. 2002, 50, 2220-2226. (37) Hardcastle, J. L.; Compton, R. G. Electroanalysis 2002, 14, 753759. (38) Weinmann, W.; Mueller, C.; Vogt, S.; Frei, A. J. Anal. Toxicol. 2002, 26, 303-307. (39) Mendez, H.; Alava, F.; Lavilla, I.; Bendicho, C. Anal. Chim. Acta 2002, 452, 217-222. (40) Jandik, P.; Weigl, B. H.; Kessler, N.; Cheng, J.; Morris, C. J.; Schulte, T.; Avdalovic, N. J. Chromatogr.m A 2002, 954, 33-40. (41) Jonsson, O. B.; Nilsson, U. L. Anal. Bioanal. Chem. 2003, 377, 182-188. (42) Shen, G.; Lee, H. K. Anal. Chem. 2003, 75, 98-103. (43) Psillakis, E.; Kalogerakis, N. Trends Anal. Chem. 2002, 21, 5363. (44) Takagai, Y.; Igarashi, S. Am. Lab. 34 (15), 29-20. (45) Liu, J. F.; Jiang, G. B.; Chi, Y. G.; Cai, Y. Q.; Zhou, Q. X.; Hu, J. T. Anal. Chem. 2003, 75, 5870-5876. (46) Grob, M. K.; O’Brien, K.; Chu, J. J.; Chen, D. D. Y. J. Chromatogr., B: Anal. Technol. Biomed. Life Sci. 2003, 788, 103-111. (47) Paixao, J. A.; Stamford, T. L. M. J. Liq. Chromatogr. Relat. Technol. 2002, 25, 217-239. (48) Decaestecker, T. N.; Coopman, E. M.; van Peteghem, C. H.; van Bocxlaer, J. F. J. Chromatogr., B: Anal. Technol. Biomed. Life Sci. 2003, 789, 19-25. (49) Grey, L.; Nguyen, B.; Yang, P. J. Chromatogr., A 2002, 958, 2533. (50) Mueller, C.; Schaefer, P.; Stoertzel, M.; Vogt, S.; Weinmann, W. J. Chromatogr., B: Anal. Technol. Biomed. Life Sci. 2002, 773, 47-52. (51) Briem, S.; Eklund, E.; Williams, G.; Brunvall, J. Chromatographia 2002, 55(Suppl.), S35-S39. (52) Iha, M. M.; Martinez, A. S.; Bonato, P. S. J. Chromatogr. B: Anal. Technol. Biomed. Life Sci. 2002, 767, 1-9. (53) Vera-Avila, L. E.; Rangel-Ordonez, L.; Covarrubias-Herrera, R. J. Chromatogr. Sci. 2003, 41, 480-488. (54) Koster, E.; Ooms, B.; Sarlin, F.; Giaquinta, B. Spectra Anal. 2002, 31(229), 19-31. (55) Focant, J.-F.; de Pauw, E. J. Chromatogr., B: Anal. Technol. Biomed. Life Sci. 2002, 776, 199-212. (56) Berna, M.; Murphy, A. T.; Wilken, B.; Ackermann, B. Anal. Chem. 2002, 74, 1197-1201. (57) Broyles, B. S.; Jacobson, S. C.; Ramsey, J. M. Anal. Chem. 2003, 75, 2761-2767. (58) Reddersen, K.; Heberer, T. J. Chromatogr., A 2003, 1011, 221226. (59) Iwase, H. J. Chromatogr., A 2003, 1008, 81-87. (60) Thomsen, C.; Leknes, H.; Lundanes, E.; Becher, G. J. Anal. Toxicol. 2002, 26, 129-137. (61) Hook, G. L.; kimm, G. L.; Hall, T.; Smith, P. A. Trends Anal. Chem. 21, 534-543. (62) Saito, Y.; Jinno, K. Anal. Bioanal. Chem. 2002, 373, 325-331. (63) Kumazawa, T.; Lee, X. P.; Sato, K.; Suzuki, O. Anal. Chim. Acta 2003, 492, 49-67. (64) Chen, Y.; Koziel, J. A.; Pawliszyn, J. Anal. Chem. 2003, 75, 64856493. (65) Pinho, O.; Ferreira, I. M. P. L. V. O.; Ferreira, M. A. Anal. Chem. 2002, 74, 5199-5204. (66) Ezquerro, O.; Pons, B.; Tena, M. T. J. Chromatogr., A 2002, 963, 381-392. (67) Zuba, D.; Parczewski, A.; Reichenbaecher, M. J. Chromatogr., B: Anal. Technol. Biomed. Life Sci. 2002, 773, 75-82. (68) Mullett, W. M.; Pawliszyn, J. J. Sep. Sci. 2003, 26, 251-260. (69) Gonclaves, C.; Alpendurada, M. F. J. Chromatogr., A 2002, 968, 177-190. (70) Hook, G. L.; Kimm, G.; Betsinger, G.; Savage, P. B.; Swift, A.; Logan, T.; Smith, P. A. J. Sep. Sci. 2003, 26, 1091-1096. (71) Alonso, A.; Fernandez-Torroba, M. A.; Tena, M. T.; Pons, B. Chromatographia 2003, 57, 369-378. (72) Cai, L. S.; Zhao, Y. Y.; Gong, S. L.; Dong, L.; Wu, C. Y. Chromatographia 2003, 58, 615-621. (73) Kataoka, H. Anal. Bioanal. Chem. 2002, 373, 31-45. (74) Morishma, Y.; Saito, Y.; Fujimoto, C.; Takeichi, T.; Jinno, K. Chromatographia 2002, 56, 585-590. (75) Saito, Y.; Nakao, Y.; Imaizumi, M.; Morishima, Y.; Kiso, Y.; Jinno, K. Anal. Bioanal. Chem. 2002, 373, 81-86. (76) Walles, M.; Mullett, W. M.; Levsen, K.; Borlak, J.; Wuensch, G.; Pawliszyn, J. J. Pharm. Biomed. Anal. 2002, 30, 307-319.

Analytical Chemistry, Vol. 76, No. 16, August 15, 2004

4663

(77) Saito, Y.; Nojiri, M.; Imaizumi, M.; Nakao, Y.; Morishima, Y.; Kanehara, H.; Matsuura, H.; Kotera, K.; Wada, H.; Jinno, K. J. Chromatogr., A 2002, 975, 105-112. (78) Walles, M.; Borlak, J.; Levsen, K. Anal. Bioanal. Chem. 2002, 374, 1179-1186. (79) Molinelli, A.; Weiss, R.; Mizaikoff, B. J. Agric. Food Chem. 2002, 50, 1804-1808. (80) Mullett, W. M.; Levsen, K.; Lubda, D.; Pawliszyn, J. J. Chromatogr., A 2002, 963, 325-334. (81) Jonsson, J. A.; Mathiasson, L.; Majors, R. E. LC-GC 2003, 21, 424+. (82) Jonsson, J. Chromatographia 2003, 57 (Suppl.), S317-S324. (83) Jonsson, O. B.; Nordlof, U.; Nilsson, U. L. Anal. Chem. 2003, 75, 3506-3511. (84) Khrolenko, M.; Dzygiel, P.; Wieczorek, P. J. Chromatogr., A 2002, 975, 219-227. (85) Norberg, J.; Tiruye, D.; Mathiasson, L.; Jonsson, J. A. J. Sep. Sci. 2002, 25, 351-355. (86) Chimuka, L.; Cukrowska, E.; Soko, L.; Naicker, K. J. Sep. Sci. 2003, 26, 601-608. (87) Basheer, C.; Lee, H. K.; Obbard, J. P. J. Chromatogr., A 2002, 968, 191-199. (88) de Jager, L.; Andrews, A. R. J. Anal. Chim. Acta 2002, 458, 311320. (89) Majcherczyk, P. A.; Moreillon, P.; Decosterd, L. A.; Sanglard, D.; Bille, J.; Glauser, M. P.; Marchetti, O. J. Pharm. Biomed. Anal. 2002, 28, 645-651. (90) Dawidowicz, A. L.; Kalitynski, R. Biomed. Chromatogr. 2003, 17, 447-452. (91) Hennion, M.-C.; Pichon, V. J. Chromatogr., A 2003, 1000, 2952. (92) Sandahl, M.; Mathiasson, L.; Jonsson, J. A. J. Chromatogr., A 2002, 975, 211-217. (93) Kaykhaii, M.; Sarafraz-Yazdi, A.; Chamsaz, M.; Pawliszyn, J. Analyst 2002, 127, 912-916. (94) Koeller, G.; Popp, P.; Weingart, K.; Hauser, B.; Herrmann, W. Chromatographia 2003, 57 (Suppl.), S229-S233. (95) Baltussen, E.; Cramers, C. A.; Sandra, P. J. F. Anal. Bioanal. Chem. 2002, 373, 3-22.

4664

Analytical Chemistry, Vol. 76, No. 16, August 15, 2004

(96) Sandra, P.; David, F. J. Chromatogr. Sci. 2002, 40, 248-253. (97) Lagana, A.; Bacaloni, A.; Castellano, M.; Curini, R.; de Leva, I.; Faberi, A.; Meterazzi, S. J. AOAC Int. 2003, 86, 729-736. (98) Ziakova, A.; Brandsteterova, E.; Blahova, E. J. Chromatogr., A 2003, 983, 271-275. (99) David, F.; Tienport, B.; Sandra, P. LC-GC Eur. 2003, 16, 410+. (100) Tienport, B.; David, F.; Desmet, K.; Sandra, P. Anal. Bioanal. Chem. 2002, 373, 46-55. (101) Demyttenaere, J. C. R.; Sanchez Martinez, J. I.; Verhe, R.; Sandra, P.; de Kimpe, N. J. Chromatogr., A 985, 221-232. (102) Wells, D. A.; Herron, L. L.; Majors, R. E. LC-GC 2002, 20, 416+. (103) Terry, C. F.; Harris, N.; Parkes, H. C. J. AOAC Int. 2002, 85, 768-774. (104) Castellanos_Serra, L.; Paz-Lago, D. Electrophoresis 2002, 23, 1745-1753. (105) Ho, Y. P.; Hsu, P. H. J. Chromatogr., A 2002, 976, 103-111. (106) Dernovics, M.; Stefanka, Z.; Fodor, P. Anal. Bioanal. Chem. 2002, 372, 473-480. (107) Borderies, G.; Jamet, E.; Lafitte, C.; Rossignol, M.; Jauneau, A.; Boudart, G.; Monsarrat, B.; Esquerre-Tugaye, M.-T.; Boudet, A.; Pont-Lezica, R. Electrophoresis 2003, 24, 3421-3432. (108) Reyes, D. R.; Iossifidis, D.; Auroux, P. A.; Manz, A. Anal. Chem. 2002, 74, 2637-2652. (109) Ekstrom, S.; Malmstrom, J.; Wallman, L.; Lofgren, M.; Nilsson, J.; Laurell, T.; Marko-Varga, G. Proteomics 2002, 2, 413-480. (110) Breadmore, M. C.; Wolfe, K. A.; Arcibal, I. G.; Leung, W. K.; Dickson, D.; Giordano, B. C.; Power, M. E.; Ferrance, J. P.; Feldman, S. H.; Norris, P. M.; Landers, J. P. Anal. Chem. 2003, 75, 1880-1886. (111) Bergkvist, J.; Ekstrom, S.; Wallman, L.; Lofgren, M.; MarkoVarga, G.; Nillson, J.; Laurell, T. Proteomics 2002, 2, 422-429. (112) Pappsilber, J.; Ishihama, Y.; Mann, M. Anal. Chem. 2003, 75, 663-670. (113) Schumacher, R. T.; Manak, M.; Gerrett, P.; Miller, W.; Lawrence, N.; Tao, F. Am. Lab. 2002, 34 (16), 38+.

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