Recent trends in trace element determination and speciation using inductively coupled plasma mass spectrometry

During the past decade, inductively coupled plasma mass spectrometry (ICPMS) has evolved from a delicate research tool, intended for the well-trained scientist only, into a more robust and well-established analytical technique for trace and ultra-trace element determination, with a few thousand of instruments used worldwide. Despite this immense success, it should be realized that in its ’standard configuration’– i.e. equipped with a pneumatic nebulizer for sample introduction and with a quadrupole filter – ICPMS also shows a number of important limitations and disadvantages: (i) the occurrence of spectral interferences may hamper accurate trace element determination, (ii) solid samples have to be taken into solution prior to analysis and (iii) no information on the ‘chemical form’ in which an element appears can be obtained. Self-evidently, efforts have been and still are made to overcome the aforementioned limitations to the largest possible extent. The application of a double focusing sector field mass spectrometer in ICPMS instrumentation offers a higher mass resolution, such that spectral overlap can be avoided to an important extent. Additionally, in a sector field instrument, photons are efficiently eliminated from the ion beam, resulting in very low background intensities, making it also very well-suited for extreme trace analysis. Also the combination of the ICP as an ion source and a quadrupole filter operated in a so-called ‘alternate’ stability region, an ion trap or a Fourier transform ion cyclotron resonance mass spectrometer allows high(er) mass resolution to be obtained. With modern quadrupole-based instruments, important types of spectral interferences can be avoided by working under ‘cool plasma’ conditions or by applying a collision cell. The use of electrothermal vaporization (ETV) or especially laser ablation (LA) for sample introduction permits direct analysis of solid samples with sufficient accuracy for many purposes. The application range of LA-ICPMS has become very wide and the introduction of UV lasers has led to an improved spatial resolution. Solid sampling ETV-ICPMS on the other hand can be used for some specific applications only, but accurate calibration is more straightforward than with LA-ICPMS. Limited multi-element capabilities, resulting from the transient signals observed with ETV or single shot LA, can be avoided by the use of a time-of-flight (TOF) ICPMS instrument. Finally, when combined with a powerful chromatographic separation technique, an ICP-mass spectrometer can be used as a highly sensitive, element-specific multi-element detector in elemental speciation studies. Especially liquid (HPLC-ICPMS) and – to a lesser extent – gas (GC-ICPMS) chromatography have already been widely used in combination with ICPMS. In speciation work, sample preparation is often observed to be troublesome and this aspect is presently receiving considerable attention. For GC-ICPMS, new sample pretreatment approaches, such as headspace solid phase microextraction (headspace SPME) and the purge-and-trap technique have been introduced. Also supercritical fluid chromatography (SFC) and capillary electrophoresis (CE) show potential to be of use in combination with ICPMS, but so far the application ranges of SFC-ICPMS and CE-ICPMS are rather limited. It is the aim of the present paper to concisely discuss the aforementioned recent ’trends’ in ICPMS, using selected real-life applications reported in the literature.     

Rearrangement Pathways of the <Emphasis Type="BoldItalic">a</Emphasis><Subscript><Emphasis Type="BoldItalic">4</Emphasis></Subscript> Ion of Protonated YGGFL Characterized by IR Spectroscopy and Modeling

The structure of the a ₄ ion from protonated YGGFL was studied in a quadrupole ion trap mass spectrometer by ‘action’ infrared spectroscopy in the 1000–2000 cm^–1 (‘fingerprint’) range using the CLIO Free Electron Laser. The potential energy surface (PES) of this ion was characterized by detailed molecular dynamics scans and density functional theory calculations exploring a large number of isomers and protonation sites. IR and theory indicate the a ₄ ion population is primarily populated by the rearranged, linear structure proposed recently (Bythell et al., J. Am. Chem. Soc. 2010, 132, 14766). This structure contains an imine group at the N- terminus and an amide group –CO–NH₂ at the C-terminus. Our data also indicate that the originally proposed N-terminally protonated linear structure and macrocyclic structures (Polfer et al., J. Am. Chem. Soc. 2007, 129, 5887) are also present as minor populations. The clear differences between the present and previous IR spectra are discussed in detail. This mixture of gas-phase structures is also in agreement with the ion mobility spectrum published by Clemmer and co-workers recently (J. Phys. Chem. A 2008, 112, 1286). Additionally, the calculated cross-sections for the rearranged structures indicate these correspond to the most abundant (and previously unassigned) feature in Clemmer’s work.     

Analysis of O-glucuronide conjugates in urine by electrospray ion trap mass spectrometry

The application of electrospray ionization (ESI) ion trap mass spectrometry in the characterization of O-glucuronide conjugates of some drugs in urine is described. The conjugated metabolites formed in rabbit and human were separated by reversed-phase high-performance liquid chromatography (HPLC) and characterized by multi-stage mass spectrometry (MSⁿ) experiments in negative ion mode. The ESI mass spectra showed a deprotonated molecule [M–H]^–, which was chosen as precursor ion. Collision-induced dissociation (CID) of [M–H]^– in MSⁿ experiments resulted in the appearance of glucuronate ‘fingerprint’ ions at m/z 175 and 113 as well as prominent aglycone ions which were the same as those produced from authentic specimens. This information can be used to identify this type of compound directly without the need for derivatization or hydrolysis of enzymes, providing a rapid and specific method for guiding the isolation and characterization of similar compounds in complex matrices with LC/MS. Received: 25 January 1999 / Revised: 19 April 1999 / Accepted: 13 May 1999     

‘Fixed charge’ chemical derivatization and data dependant multistage tandem mass spectrometry for mapping protein surface residue accessibility

Protein surface accessible residues play an important role in protein folding, protein-protein interactions and protein-ligand binding. However, a common problem associated with the use of selective chemical labeling methods for mapping protein solvent accessible residues is that when a complicated peptide mixture resulting from a large protein or protein complex is analyzed, the modified peptides may be difficult to identify and characterize amongst the largely unmodified peptide population (i.e., the ‘needle in a haystack’ problem). To address this challenge, we describe here the development of a strategy involving the synthesis and application of a novel ‘fixed charge’ sulfonium ion containing lysine-specific protein modification reagent, S,S′-dimethylthiobutanoylhydroxysuccinimide ester (DMBNHS), coupled with capillary HPLC-ESI-MS, automated CID-MS/MS, and data-dependant neutral loss mode MS³ in an ion trap mass spectrometer, to map the surface accessible lysine residues in a small model protein, cellular retinoic acid binding protein II (CRABP II). After reaction with different reagent:protein ratios and digestion with Glu-C, modified peptides are selectively identified and the number of modifications within each peptide are determined by CID-MS/MS, via the exclusive neutral loss(es) of dimethylsulfide, independently of the amino acid composition and precursor ion charge state (i.e., proton mobility) of the peptide. The observation of these characteristic neutral losses are then used to automatically ‘trigger’ the acquisition of an MS³ spectrum to allow the peptide sequence and the site(s) of modification to be characterized. Using this approach, the experimentally determined relative solvent accessibilities of the lysine residues were found to show good agreement with the known solution structure of CRABP II.     

Enhanced characterization of singly protonated phosphopeptide ions by femtosecond laser-induced ionization/dissociation tandem mass spectrometry (fs-LID-MS/MS)

To develop an improved understanding of the regulatory role that post-translational modifications (PTMs) involving phosphorylation play in the maintenance of normal cellular function, tandem mass spectrometry (MS/MS) strategies coupled with ion activation techniques such as collision-induced dissociation (CID) and electron-transfer dissociation (ETD) are typically employed to identify the presence and site-specific locations of the phosphate moieties within a given phosphoprotein of interest. However, the ability of these techniques to obtain sufficient structural information for unambiguous phosphopeptide identification and characterization is highly dependent on the ion activation method employed and the properties of the precursor ion that is subjected to dissociation. Herein, we describe the application of a recently developed alternative ion activation technique for phosphopeptide analysis, termed femtosecond laser-induced ionization/dissociation (fs-LID). In contrast to CID and ETD, fs-LID is shown to be particularly suited to the analysis of singly protonated phosphopeptide ions, yielding a wide range of product ions including a, b, c, x, y, and z sequence ions, as well as ions that are potentially diagnostic of the positions of phosphorylation (e.g., ‘a _n+1–98’). Importantly, the lack of phosphate moiety losses or phosphate group ‘scrambling’ provides unambiguous information for sequence identification and phosphorylation site characterization. Therefore, fs-LID-MS/MS can serve as a complementary technique to established methodologies for phosphoproteomic analysis.     

Gas-dynamic fluctuations and noises in the interface of an atmospheric pressure ionization ion source

The paper discusses the mechanisms of origin of ion current noise in a mass spectrometer owing to gas dynamic processes in the interface. It has been shown that the effect can be strong for a so-called ‘short’ interface, where the distance between the sampler outlet, that is, the nozzle or transportation capillary, is of the same size as the Mach barrel length, which would take place if the gas can extend freely. The spectra of gas dynamic noises have been computed in the axially symmetric approach for the above interfaces; the computed noise spectra have been shown to correlate well with those measured for total ion current to the interface skimmer.     

Dual purpose laser ablation-inductively coupled plasma mass spectrometry for pulsed laser deposition and diagnostics of thin film fabrication: Preliminary study

PLD (pulsed laser deposition) is an attractive technique to fabricate thin films with a stoichiometry reflecting that of the target material. Conventional PLD instruments are more or less black boxes in which PLD is performed virtually “blind”, i.e. without having great control on the important PLD parameters. In this preliminary study, for the first time, a 213 nm Nd-YAG commercial laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS) intended for microanalysis work was used for PLD under atmospheric pressure and in and ex situ ICPMS analysis for diagnostics of the thin film fabrication process.A PLD demonstration experiment in a He atmosphere was performed with a Sm_13.8Fe_82.2Ta_4.0 target-Ta-coated silicon wafer substrate (contraption with defined geometry in the laser ablation chamber) to transfer the permanent magnetic properties of the target to the film. Although this paper is not dealing with the magnetic properties of the film, elemental analysis was applied as a means of depicting the PLD process. It was shown that in situ ICPMS monitoring of the ablation plume as a function of the laser fluence, beam diameter and repetition rate may be used to ensure the absence of large particles (normally having a stoichiometry somewhat different from the target). Furthermore, ex situ microanalysis of the deposited particles on the substrate, using the LA-ICPMS as an elemental mapping tool, allowed for the investigation of PLD parameters critical in the fabrication of a thin film with appropriate density, homogeneity and stoichiometry.     

Analysis of monomolecular layers of solids by the static method of secondary ion mass spectroscopy (SIMS)

The mass spectrum of secondary ions emitted from a solid surface under ion bombardment is characteristic of the composition of the superficial monolayers. By the use of very low primary ion current densities and highly sensitive detection techniques, analysis can be performed without measurable disturbance of the original first monolayers. Some results demonstrating the capabilities of this ‘static’ method of secondary ion mass spectrometry (SIMS) are presented.     

Actinide bioassays by ICPMS

The ever-increasing sensitivity of ICPMS continues to expand the technique’s application in the field of health physics. Enhancements in sample introduction and instrument design over the last few years have resulted in improving the ICPMS detection limit from ∼10 ng/l to≤0.1 ng/l. This additional sensitivity provides greater flexibility in the analysis of long-lived radionuclides in biological fluids, and requires only minimal sample preparation of urine for uranium analysis; the described 3-minute abbreviated matrix separation provides detection limits that are comparable to or better than alpha counting. For urine samples tested having concentrations that exceed the accepted administrative limit for total uranium (0.2 μg/day), isotopic analysis by ICPMS (e.g., determining the presence of²³⁶U, or measuring appropriate uranium isotope ratios) provides a reliable indication of occupational exposure. Our laboratory also utilizes ICPMS in a study examining uranium dissolution rate classification of dust collected at the perimeter of a nuclear facility. Specific details regarding these and other health physics applications are featured, including our group’s participation in assisting the DOE with the evaluation of ICPMS as a cost-effective alternative to fission-track analysis for the routine determination of²³⁹Pu in urine.     

Comparison of electron ionization mass spectra of some organic compounds (MW < 200 Da) recorded on mass spectrometers of various types

Low-resolution electron ionization mass spectra recorded on various types of mass spectrometers (time-of-flight, quadrupole, and three-dimensional ion trap) were compared. A model mixture of 10 organic compounds (MW < 200 Da) was analyzed by gas chromatography-mass spectrometry. Pure mass spectra of analytes were extracted using the AMDIS software. The best repeatability was achieved for the time-of-flight mass spectrometer. The mass spectra recorded by a quadrupole and a time-of-flight mass spectrometer were quite similar. In the case of these instruments, library search using a commercial mass spectral data base (NIST’05) gave satisfactory result for each analyte (rank 1 or 2 in the “hit list”; Match > 900). In some cases, the mass spectra of model compounds recorded by the ion trap mass spectrometer differed in intensity of certain mass spectral peaks (but not in the set of peaks) from the mass spectra presented in the library and from the experimental mass spectra recorded by the time-of-flight and quadrupole instruments.     

Operation and application of a new time-of-flight e-gas secondary neutral mass spectrometer (ToF–SNMS)

The low-pressure rf plasma of a secondary neutral mass spectrometer (e-gas SNMS) was connected with a time-of-flight (ToF) mass spectrometer for the first time. As opposed to ToF–SIMS in e-gas SNMS, the primary ion pulse cannot be used for triggering the flight time measurement. Therefore, an extraction pulse is used which at a defined time loads an ion package from the beam of the post-ionised particles into the ToF spectrometer. The newly developed ToF–SNMS system is described, and first experimental results are presented.     

SOME PHILOSOPHICAL INFLUENCES ON ILYA PRIGOGINE’S STATISTICAL MECHANICS

During a long and distinguished career, Belgian physical chemist Ilya Prigogine (1917–2003) pursued a coherent research program in thermodynamics, statistical mechanics, and related scientific areas. The main goal of this effort was establishing the origin of thermodynamic irreversibility (the ‘‘arrow of time’’) as local (residing in the details of the interaction of interest), rather than as global (being solely a consequence of properties of the initial singularity – the ‘‘Big Bang’’). In many publications for general audiences, he stated the opinion that this scientific research had great philosophical importance. Prigogine and his colleagues considered that the most recent stages of this research program have been successful, so that the local origins of the arrow of time are now established. There is no scientific consensus as to whether or not this claim is valid. Similarly, there is no consensus on whether the competing global (initial singularity) explanation has been proven.     

Ethylene oxide-bridged bipyridine oligomers that function as selective host molecules for the encapsulation of small alkali cation guests

Two novel ethylene oxide-bridged bipyridine oligomers were synthesized that contain host pockets with four (1) or six (2) oxygen donor atoms and a pyridyl nitrogen donor. The alkali picrate extracting ability and selectivity of these free ligands was investigated using a liquid–liquid dichloromethane–water extraction study. Both open-chain oligomer frameworks display unexpectedly high extraction efficiency (EE) values for specific guest ions (EE = 57% Na⁺ extracted by 1, and EE = 39% Cs⁺ extracted by 2). These extraction values are comparable to macrocyclic analogues and their ion selectivities follow the ‘same-fit’ concept that has been extensively reported for fixed pocket systems. The shorter chain oligomer (1) binds ions in the series (Na⁺ > K⁺ > Cs⁺), while the larger oligomer (2) binds ions in the reverse order (Cs⁺ > K⁺ > Na⁺). Formation of the host–guest ligand–ion complexes were verified by ¹H NMR spectroscopy and MALDI-TOF mass spectrometry experiments. A Job’s plot analysis based on UV spectral data also supported the 1:1 (oligomer to ion) complexation observed in the MALDI mass spectra.     

Expansion Cooling in the Matrix Plume is Under-Recognized in MALDI Mass Spectrometry

Time-of-flight (TOF) mass spectra for a peptide (Y₆) were obtained by utilizing matrix-assisted infrared laser desorption ionization (IR-MALDI) with glycerol as the matrix and by ultraviolet MALDI with α-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA), and 2,5-dihydroxybenzoic acid (DHB). Collisional activation during ion extraction and exothermicity in the gas-phase proton transfer were found to be unimportant as the driving forces for in-source (ISD) and post-source (PSD) decays, indicating that the thermal energy acquired during photo-ablation is responsible for their occurrence. The temperatures of [Y₆ + H]⁺ in the ‘early’ and ‘late’ matrix plumes were estimated by the kinetic analysis of the ISD and PSD yields, respectively. The order of the temperatures was glycerol < DHB ≈ SA < CHCA in the early plume and glycerol < DHB < SA < CHCA in the late plume. For each matrix, the temperature in the late plume was lower than in the early plume by 300–400 K, which was attributed to expansion cooling. The model (thermalization followed by expansion cooling) proposed to explain the occurrence of both rapid ISD and slow PSD is not only in sharp contrast with but also mutually exclusive with the prevailing explanation that the exothermicity in proton transfer and in-plume collisional activation are the driving forces for ion fragmentation in MALDI. The model also explains why MALDI is more successful for mass spectrometry of labile molecules than other desorption techniques that do not utilize a matrix. Factors affecting the plume temperature are also discussed.     

Hydroxyl orientations in cellobiose and other polyhydroxyl compounds: modeling versus experiment

Theoretical and experimental gas-phase studies of carbohydrates show that their hydroxyl groups are located in homodromic partial rings that resemble cooperative hydrogen bonds, albeit with long H…O distances and small O–H…O angles. On the other hand, anecdotal experience with disaccharide crystal structures suggested that these clockwise ‘c’ or counter-clockwise (reverse ‘r’) sequences are not prevalent in the crystalline state. The situation was clarified with quantum mechanics calculations in vacuum and in continuum solvation, as well as Atoms-In-Molecules analyses. From the experimental side, the Cambridge Structural Database was searched. Geometric criteria for these sequences were developed. A criterion based on 120° ranges of hydroxyl orientations accepted 4% of sequences as having ‘c,c’ or ‘r,r’ orientations instead of the 7% expected based on chance. Criteria based on an O–H…O angle > 90° and a 90° lower limit of the absolute value of the H–O–C…H improper torsion accepted 7.0% of the 358 sequences as ‘c,c’ or ‘r,r’. Highly variable orientation of the hydroxyl groups in crystals was seen to depend mostly on strong inter-residue or intermolecular hydrogen bonds. That lack of specific orientation in general for the crystal structures was supported by the solvated calculations that showed very little variation in the energy when one of the hydroxyl groups in 1,2-dihydroxycyclohexane was rotated. The vacuum calculations found the energy to vary with rotation by more than 4 kcal/mol, confirming the gas-phase experiments and calculations on more complicated molecules. Molecules examined in some detail include scyllo inositol and native and methylated cellobiose.     

Comparison of atomic absorption,mass and X-ray spectrometry techniques using dissolution-based and solid sampling methods for the determination of silver in polymeric samples

In this work, the capabilities and limitations of solid sampling techniques – laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), wavelength dispersive X-ray fluorescence spectrometry (WD-XRFS) and solid sampling electrothermal atomic absorption spectrometry (SS-ETAAS) – for the determination of silver in polymers have been evaluated and compared to those of acid digestion and subsequent Ag determination using pneumatic nebulization ICPMS (PN-ICPMS) or flame AAS (FAAS).     

Fractionation of nano- and microparticles in a rotating conoidal coiled column

A method for the continuous-flow fractionation of particles in a transverse centrifugal field in a rotating conoidal coiled (RCC) column has been developed. A model of a planetary centrifuge with a conoidal drum of a special construction has been tested. The effects of the rotation and revolution speed of the conoidal RCC, as well as the direction and pumping rate of the mobile phase on the behavior of particles smaller than 1 μm have been studied. The conditions have been selected and optimized for the retention and elution of spherical particles of the ‘150 nm’, ‘400 nm’, and ‘900 nm’ standard samples of silica gel (Polyscience Inc.). The possibility of using RCC for the analysis and production of monodisperse standard particle samples has been demonstrated. In particular, the ‘900 nm’ particles have been separated from admixtures of small (100–200 nm) particles and nonspherical 1–2 μm particles present in the sample. The separated fractions have been characterized by electron microscopy.     

Marked individual variability in the levels of trimethylselenonium ion in human urine determined by HPLC/ICPMS and HPLC/vapor generation/ICPMS

Selenium species were determined using HPLC/ICPMS and HPLC/vapor generation/ICPMS in the urine from seven human volunteers investigated at background selenium concentrations and at slightly elevated concentrations after ingestion of 200 μg Se as a selenite supplement. Trimethylselenonium ion (TMSe) was present, together with selenosugars, in the urine samples, a result that dispels recent doubts about its possible previous misidentification with a cationic selenosugar. Although TMSe was present as only a trace metabolite in urine from five of the seven volunteers (0.02–0.28 μg Se/L, equivalent to 1–5% of the sum of selenosugars and TMSe), it was a significant metabolite (up to 4.6 μg Se/L, 22%) in one volunteer, and it was the major identified metabolite (up to 15 μg Se/L, 53%) in another volunteer. This marked individual variability in the formation of TMSe was maintained in a duplicate investigation of urine from the same seven volunteers.     

<Superscript>239, 240, 241</Superscript>Pu fingerprinting of plutonium in western US soils using ICPMS: solution and laser ablation measurements

Sector field inductively coupled plasma mass spectrometry (SF-ICPMS) has been used with analysis of solution samples and laser ablation (LA) of electrodeposited alpha sources to characterize plutonium activities and atom ratios prevalent in the western USA. A large set of surface soils and attic dusts were previously collected from many locations in the states of Nevada, Utah, Arizona, and Colorado; specific samples were analyzed herein to characterize the relative contributions of stratospheric fallout vs. Nevada Test Site (NTS) plutonium. This study illustrates two different ICPMS-based analytical strategies that are successful in fingerprinting Pu in environmental soils and dusts. Two specific datasets have been generated: (1) soils are leached with HNO₃-HCl, converted into electrodeposited alpha sources, counted by alpha spectrometry, then re-analyzed using laser ablation SF-ICPMS; (2) samples are completely dissolved by treatment with HNO₃-HF-H₃BO₃, Pu fractions are prepared by extraction chromatography, and analyzed by SF-ICPMS. Optimal laser ablation and ICPMS conditions were determined for the re-analysis of archived alpha spectrometry “planchette” sources. The best ablation results were obtained using a large spot size (200 μm), a defocused beam, full repetition rate (20 Hz) and scan rate (200 μm s⁻¹); LA-ICPMS data were collected with a rapid electrostatic sector scanning experiment. Less than 10% of the electroplated surface area is consumed in the LA-ICPMS analysis, which would allow for multiple re-analyses. Excellent agreement was found between ^239+240Pu activities determined by LA-ICPMS vs. activity results obtained by alpha spectrometry for the same samples ten years earlier. LA-ICPMS atom ratios for ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu range from 0.038–0.132 and 0.00034–0.00168, respectively, and plot along a two-component mixing line (²⁴¹Pu/²³⁹Pu = 0.013 [²⁴⁰Pu/²³⁹Pu] – 0.0001; r ² = 0.971) with NTS and global fallout end-members. A rapid total dissolution procedure, followed by extraction chromatography and SF-ICPMS solution Pu analysis, generates excellent agreement with certified ^239+240Pu activities for standard reference materials NIST 4350b, NIST 4353, NIST 4357, and IAEA 385. ^239+240Pu activities and atom ratios determined by total dissolution reveal isotopic information in agreement with the LA-ICPMS dataset regarding the ubiquitous mixing of NTS and stratospheric fallout Pu sources in the regional environment. For several specific samples, the total dissolution method reveals that Pu is incompletely recovered by simpler HNO₃-HCl leaching procedures, since some of the Pu originating from the NTS is contained in refractory siliceous particles.     

Determination of ethylphenols in wine by in situ derivatisation and headspace solid-phase microextraction–gas chromatography–mass spectrometry

Contamination by Brettanomyces is a frequent problem in many wineries that has a dramatic effect on wine aroma and hence its quality. The yeast Brettanomyces/Dekkera is involved in the formation of three important volatile ethylphenols—4-ethylphenol, 4-ethylguaiacol and 4-ethylcatechol—that transmit an unpleasant aroma to wine that has often been described as ‘medicinal’, ‘stable’ or ‘leather’. This study proposes an in situ derivatisation and headspace solid-phase microextraction– gas chromatography coupled to mass spectrometry method to determine the three ethylphenols in red Brettanomyces-tainted wines. The most important variables involved in the derivatisation (acetic anhydride and base concentration) and the extraction (extraction temperature and salt addition) processes were optimised by experimental design. The optimal conditions using 4 mL of wine in 20-mL sealed vials were 35 μL of acetic anhydride per millilitre of wine, 1 mL of 5.5% potassium carbonate solution and 0.9 g of sodium chloride and the extraction was performed with a divinylbenzene–carboxen–poly(dimethylsiloxane) fibre at 70 °C for 70 min. Then, the performance characteristics were established using wine samples spiked with the ethylphenols. For all compounds, the detection limits were below the odour threshold reported in the literature and they were between 2 and 17 μg L⁻¹ for 4-ethylguaiacol and 4-ethylphenol, respectively. Intermediate precision (as relative standard deviation) was acceptable, with values ranging from 0.3 to 12.1%. Finally, the method was applied in the analysis of aged Brettanomyces-tainted wines.