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Solid-phase microextraction (SPME) is a solvent-free sample preparation technique in which a fused silica fiber coated with polymeric organic liquid is introduced into the sample. In this paper, theoretical aspects, operating models, factors of influencing sensitivity, applications and future development are introduced briefly with 19 references.
Dried whey and whey protein are important food ingredients. Functionality of whey products has been studied extensively. Flavor inconsistency and flavors which may carry through to the finished product can limit whey ingredient applications in dairy and nondairy foods. The goal of this research was to determine the flavor and flavor variability of commercially produced liquid Cheddar cheese whey. Liquid Cheddar cheese whey from five culture blends from two different stirred-curd Cheddar cheese manufacturing facilities was collected. Whey flavor was characterized using instrumental and sensory methods. Wide variation in whey headspace volatiles was observed between different manufacturing facilities (P < 0.05). Hexanal and diacetyl were two key volatiles that varied widely (P < 0.05). FFA profiles determined by solid-phase microextraction and degree of proteolysis of the whey samples were also different (P < 0.05). Differences in whey flavor profiles were also confirmed by descriptive sensory analysis (P < 0.05). Differences in liquid whey flavor were attributed to differences in milk source, processing and handling and starter culture blend. The flavor of liquid Cheddar cheese whey is variable and impacted by milk source and starter culture rotation. Results from this study will aid future studies that address the impact of liquid whey flavor variability on flavor of dried whey ingredients.
The development, optimization, and application of a novel method for arsenic speciation based on capillary gas-liquid chromatography with simultaneous quadrupole ion-trap mass spectrometric (MS) detection and pulsed flame photometric detection (PFPD) is described. The method couples the sensitive arsenic-selectivity of PFPD with the structure elucidation capability of molecular MS detection for the determination of trace levels of unknown organoarsenicals in complex matrices. The conditions that affect the PFPD response in the presence of interfering species were optimized using the sequential Simplex algorithm for three key factors: gate delay (18.3 ms), gate width (9.1 ms), and combustion gas composition (16.6 ml/min H2). Complete discrimination in the PFPD of the arsenic signal from interfering S-, C-, and OH-emitting species that are problematic in existing methods was achieved. Additionally, a revised interpretation of our previously reported mechanism [J. Chromatogr. A 807 (1998) 253] for the dithiol derivatization and subsequent GC-MS determination of dimethylarsinic acid is presented.
A high-performance liquid chromatographic method for the analysis of oxaprozin in the presence of ketoprofen (the internal standard) was developed. Sample preparation involved macro- and microextraction procedures. An octadecylsilane reversed-phase system with an acetonitrile-phosphate buffer (pH 3.9) mobile phase was used to separate the compounds from the extracted plasma components and the oxaprozin metabolites. Linear UV detector response over a wide concentration range resulted in rapid and reproducible quantitation.
The evaluation of solid-phase microextraction (SPME) for analysis of flavor compounds produced by bacteria has been studied. First, it was necessary to determine the optimal conditions to extract the different volatile compounds in dilute aqueous solutions. For this, the effects of salt, headspace, and liquid samplings and two coating phases [poly(dimethylsiloxane) (PDMS) and poly(acrylate) (PA)] were tested. The addition of salt enhanced SPME absorption of all the compounds. Ethyl ester was better extracted in liquid sampling with PDMS phase, whereas all of the other compounds were better extracted in headspace sampling at 80 degrees C with PA phase. The SPME technique was applied to the analysis of bacterial metabolites. It has been shown that Staphylococcus xylosus (16) and Staphylococcus carnosus (833) were able to produce esters and to catabolize leucine and that S. carnosus (833) limited the oxidation of free fatty acids.
Fatty acid ethyl esters (FAEE) are known to be formed in blood and almost all human tissues after alcohol consumption and to be incorporated from sebum into hair where they can be used as long-term markers for excessive alcohol consumption. In order to examine whether skin surface lipids which consist mainly of sebum are an equally useful matrix for measurement of FAEE as alcohol abuse markers, samples were collected by a wipe-test from the forehead of 13 teetotallers, 16 social drinkers, 10 death cases with known recent alcohol misuse and five death cases without indications of alcohol misuse. The samples were analysed by headspace solid-phase microextraction and gas chromatography-mass spectrometry for ethyl myristate, ethyl palmitate, ethyl oleate and ethyl stearate and by high performance liquid chromatography with photodiode array detector for squalene, (SQ), as a natural reference substance which the FAEE concentrations were related to. The ratio mFAEE/mSQ ranged between 0.16 and 1.12 ng/microg (mean 0.34 ng/microg) for the teetotallers and between 0.08 and 0.94 ng/microg (mean 0.37 ng/microg) for the social drinkers with no significant difference between both groups. For the alcoholics 2.4-24.2 ng/microg (mean 13.1 ng/microg) were found. For two volunteers the course of mFAEE/mSQ 2 weeks before and 3 weeks after a single high alcohol dose was pursued by daily wipe tests. A strong increase of mFAEE/mSQ occurred between 7 and 12 days after the drinking event. This delay can be explained by the transition time of about 8 days between sebum production and its appearance on the skin surface known from literature. For seven social drinkers skin surface lipid samples were also collected using drug of abuse patches of the firm PharmCheck. The ratios mFAEE/mSQ in these samples were in the same range as from the wipe-test. The comparison with the self-reported ethanol amounts consumed the week before and during the test gave no good correlation (R2 = 0.42). It can be concluded from the results that FAEE in skin surface lipids can be used for medium-term retrospective detection of heavy drinking.
The importance of sample preparation methods as the first stage in an analytical procedure is emphasised and examined. Examples are given of the extraction and concentration of analytes from solid, liquid and gas phase matrices, including solvent phase extractions, such as supercritical fluids and superheated water extraction, solid-phase extraction and solid-phase microextraction, headspace analysis and vapour trapping. The potential role of selective extraction methods, including molecular imprinted phases and affinity columns, are considered. For problem samples alternative approaches, such as derivatisation are discussed, and potential new approaches minimising sample preparation are noted.
The presence of flavins in the retina has been known for some time. However, the small size of the tissue has made it difficult to quantify the levels of the individual flavins, riboflavin (RB), FMN, and FAD without pooling large numbers of retinas. A procedure to extract and quantitate RB, FMN, and FAD in retinal tissue from as few as four rat retinas has been developed. The procedure resolves these three classes of flavins and provides a recovery near 100%. For the analysis, HPLC using a reverse-phase column with cyclohexyl functional groups was coupled to a fluorescence detector. The microextraction-HPLC procedure was reproducible for the quantitative analysis of flavins in the retina and equally applicable for analysis of flavins in liver and plasma.
Pharmaceuticals have become major targets in environmental chemistry due to their presence in aquatic environments (following incomplete removal in wastewater treatment or point-source contaminations), threat to drinking water sources and concern about their possible effects to wildlife and humans. Recently several methods have been developed for the determination of drugs and their metabolites in the lower nanogram per litre range, most of them using solid-phase extraction (SPE) or solid-phase microextraction (SPME), derivatisation and finally gas chromatography mass spectrometry (GC-MS), gas chromatography tandem mass spectrometry (GC-MS/MS) and liquid chromatography electrospray tandem mass spectrometry (LC-ES/MS/MS). Due to the elevated polarity of non-steroidal anti-inflamatory drugs (NSAIDs), analytical techniques based on either liquid chromatography coupled to mass spectrometry (LC-MS) and gas chromatography coupled to mass spectrometry (GC-MS) after a previous derivatisation step are essential. The most advanced aspects of current GC-MS, GC-MS/MS and LC-MS/MS methodologies for NSAID analysis are presented.
A novel solid-phase extraction element is developed for sorptive enrichment of dilute analytes from liquid samples with high extraction efficiencies due to its larger amounts of polydimethylsiloxane (PDMS) absorbent than the conventional syringe type of solid-phase microextraction (SPME). The extraction element is made of titanium (Ti) open tubular tube (30 mm x 1.2 mm i.d. x 1.6 mm o.d.) coated with a chemically bonded layer of PDMS (500 microm in thickness). The extraction element combined with thermal desorption-gas chromatography-mass spectrometry using a pyrolysis-gas chromatography-mass spectrometry system was used to extract and analyze a typical herbicide, bethrodine in water samples over a concentration range from 2.5 to 2.5 x 10(4) ng/l. Thus obtained calibration curve showed good linearity for the tested whole concentration range with regression coefficient of 0.992. Detection limit of 0.5 ng/l level was achieved and the reproducibility of the measurements for bethrodine at 10 ng/l level was found to be fairly good with relative standard deviation below 7.5%.
A gas chromatographic method, along with a headspace solid-phase microextraction (HS-SPME), was developed for the determination of acrylamide formed in Maillard reaction model systems. The developed method was validated by liquid chromatography/mass spectrometry. A headspace sample was collected from an aqueous acrylamide solution (100 microg/mL) by SPME and directly injected into a gas chromatograph equipped with a nitrogen-phosphorus detector. The recovery of acrylamide from an aqueous solution was satisfactory, i.e, >93% under the conditions used. Acrylamide formed in an asparagine/D-glucose (molar ratio, 1/2) Maillard reaction model system heated at 150 and 170 degrees C for 20 min was collected and analyzed by the newly developed method using gas chromatography with nitrogen-phosphorus detection and HS-SPME. The amounts of acrylamide were 318 +/- 33 microg/g asparagine from a sample heated at 150 degrees C and 3329 +/- 176 microg/g asparagine from a sample heated at 170 degrees C. Addition of cysteamine or glutathione to the above model system reduced acrylamide formation. Acrylamide formation was not observed when cysteamine or glutathione was added to asparagine in the above model systems to obtain equimolar concentrations of both compounds. This newly developed method is simple and sensitive, and requires no solvent extraction.
On-line coupling of solid phase microextraction (SPME) and capillary electrophoresis (CE) is highly desirable due to the apparent advantages of the two techniques particularly in the context of microanalysis. However, the hyphenation is a significant challenge, because of band broadening and analyte carryover caused by the slow kinetics of analyte desorption in liquid phase. A novel strategy was presented in this study to overcome these problems. Analytes desorbed from an SPME fiber, which was held by an adapter, were first transferred by electrophoretic migration into a short piece of microdialysis hollow fiber, which was located at the inlet of a CE system. Analytes with molecular weights greater than the molecular weight cut-off of the microdialysis material were trapped in the microdialysis hollow fiber due to the dialysis effect. Then, under another electric field with different electrode polarity, the analytes trapped in the microdialysis hollow fiber migrated into the separation capillary and were separated. In the coupling approach, the microdialysis hollow fiber functioned as a macromolecule trap and a sample pre-concentrator as well. Band broadening was eliminated because the initial sample volume was very small (at nL level). Meanwhile, analyte carryover was eliminated because the desorption time could be as long as needed. Coupling of SPME with CE including two modes, capillary zone electrophoresis (CZE) and capillary isoelectric focusing (CIEF), was successfully demonstrated with proteins as test analytes. High efficiency and high resolution were obtained. The detection limits with UV absorbance whole-column imaging detection were 3.0 x 10(-7) and 3.0 x 10(-8) M (S/N = 3) for beta-lactoglobulin A and ovalbumin, respectively.
High performance liquid chromatography coupled with liquid-liquid-liquid microextraction was developed for the simultaneous determination of sildenafil and vardenafil in human plasma. The effects of extraction solvent, the volume of organic solvent, dropsize of acceptor phase, stirring rate and extraction time on the enrichment factors of analytes were investigated. The optimized experimental conditions, 300 microL toluene as the organic phase, 2 microL 0.2 mol/L HCl as the acceptor phase, 600 r/min of the stirring rate, and 40 min of the extraction time, were gotten. Under these conditions, high enrichment factors were obtained. The linear range of studied analytes was from 5 microg/L to 1.0 mg/L. The relative standard deviation was lower than 5%. The limits of detection were 1 microg/L for sildenafil and 0.5 microg/L for vardenafil at signal-to-noise ratio of 3. The method with little solvent consumption may provide high analyte preconcentration and excellent sample clean-up, and it is a sensitive and suitable method for simultaneous determination of the above two substances in human plasma.
Sample preparation (SP) is an integral and important part of an analytical process. Lately, SP has been the topic of increased interest in research and development of novel advanced technologies. Major needs in this aspect are miniaturization, automation, and enrichment. Among other methodologies, flow techniques can be conveniently and effectively coupled to liquid-phase separation technologies for on-line sample preparation. This paper reviews the current trends in on-line automated sample preparation by flow-through techniques prior to liquid-phase separations. Strategies and interfaces developed to couple flow techniques with liquid chromatography, capillary electrophoresis, and mass spectrometry are described. Advantages and limitations of the coupling are discussed. The paper also highlights certain selected applications of these coupled systems.
A novel dispersive solid-phase microextraction approach utilizing a magnetic molecularly imprinted polymer (MMIP) integrated with HPLC-UV detection was developed for the concurrent quantification of catechin and myricetin in herbal extracts and aqueous samples. The sorbent was engineered as a core-shell nanocomposite, consisting of a selective polymer layer deposited onto Fe3O4@SiO2-APTMS magnetic nanoparticles. Dual-template imprinting using catechin and myricetin generated complementary binding cavities within the polymer framework. Experimental variables influencing extraction were systematically screened and subsequently optimized. A Plackett-Burman design was first applied to identify the most influential factors, with pH and sorption time identified as the dominant variables. These parameters were subsequently fine-tuned using a central composite design, and the optimization process was completed in only 30 experimental runs. The sorption characteristics of the imprinted sorbent (MMIP) were compared with those of its non-imprinted counterpart (MNIP). The MMIP demonstrated markedly higher maximum binding capacities (Qmax), reaching 119.3 mg g-1 for myricetin and 112.1 mg g-1 for catechin, whereas the corresponding values for the MNIP were 32.55 and 32.08 mg g-1, respectively. Moreover, the affinity constants (KL = 0.760-0.950 L mg-1) were approximately 2.3-fold higher for the MMIP, confirming its stronger and more selective interactions with the target analytes. The selectivity coefficients for the targeted flavonoids relative to structurally related compounds, including ferulic acid, p-coumaric acid, melatonin, and curcumin, exceeded 3.5 for the MMIP, whereas the corresponding values for the MNIP were close to 1.1, demonstrating the high molecular recognition capability of the imprinted sorbent. Method validation demonstrated limits of detection (LODs) of 0.33-0.59 ng mL-1 and limits of quantification (LOQs) of 1.10-1.96 ng mL-1, and excellent linearity over the concentration range of 5.0-5500 ng mL-1 (R2 > 0.998). The method achieved recoveries of 93.96% to 105.69% with RSDs below 5.5%, while the preconcentration factors ranged from 209 to 229. Furthermore, the sorbent retained more than 95% of its extraction efficiency after four consecutive reuse cycles and more than 80% after six cycles, demonstrating excellent stability and reusability. The proposed method was successfully applied to the analysis of six medicinal plant extracts and water samples, showing negligible matrix interference and superior sensitivity, selectivity, and operational simplicity compared with conventional solid-phase extraction methods.
This paper reviews the practical applications of solid-phase microextraction (SPME) in the analysis of organic vapours which are pollutants of atmospheric air, indoor air and workplace air. Applications to headspace of solids and liquids such as different waters, soils, food, etc., are also included. Problems related to calibration in SPME analysis of gaseous matrices are also dealt with. Calibration procedures and apparatus for generation of standard gaseous mixtures are described. Advantages and limitations of SPME based gas chromatographic methods of air organic pollutants are discussed.
Headspace sorptive extraction (HSSE) and stir bar sorptive extraction (SBSE), two recently introduced solventless enrichment techniques, have been applied to the analysis of the headspace of Arabica roasted coffee and of the headspace of the brew and of the brew itself. In both HSSE and SBSE enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnet incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace (gas phase extraction or HSSE) or by immersing it in the liquid (liquid phase extraction or SBSE). The stir bar is then thermally desorbed on-line with capillary GC-MS. The performance of HSSE and SBSE have been compared through the determination of the recoveries and relative abundances of 16 components of the coffee volatile fraction to classical static headspace (S-HS) and to headspace and in-sample solid phase microextraction (HS-SPME and IS-SPME, respectively) applying the fibers PDMS 100 microm, Carbowax/divinylbenzene 65 microm (CW/DVB), Carboxen/PDMS 75 microm(CAR/PDMS), polyacrylate 85 microm(PA), PDMS/divinylbenzene 65 microm(PDMS/DVB), and Carboxen/divinylbenzene/PDMS 50-30 microm(CAR/PDMS/DVB). In all cases, HSSE and SBSE gave higher recoveries, and this is entirely due to the high amount of PDMS applied.
Methyl salicylate (MeSA) in many plants is a important signaling compound, which plays an important role in a pathogen-induced defense response. In this paper, gas chromatography-mass spectrometry (GC-MS) with headspace solid-phase microextraction (HS-SPME) was developed for determination of MeSA and other volatile compounds in leaves of a tomato plant (Lycopersicon esculentum). Tomato leaves were ground under liquid nitrogen and sampled by HS-SPME, with a 100 microm polydimethylsiloxane fiber, and finally analyzed by GC-MS. Eighteen compounds in the leaves of tomato plant infested by tobacco mosaic virus (TMV) were separated and identified, among them MeSA, which was quantitatively analyzed by the standard addition method. MeSA concentrations higher than 2.0 microg g(-1) fresh weight accumulated in leaves of TMV-infested tomato plant as the defense response to TMV. A similar concentration of MeSA in the leaves of MeSA-treated tomato plant was also found. No MeSA in leaves of control tomato plant was detected. These findings suggest that MeSA might be a signaling compound in the tomato plant response to TMV. The present method for determination of MeSA required only simple sample preparation and no organic solvent, and provided an excellent relative standard deviation of less than 5.0% and a low detection limit of 10 ng g(-1) fresh weight for MeSA. These results show that GC-MS-HS-SPME is a simple, rapid and sensitive method for determination of MeSA and other plant-signaling compounds in plant tissues.