Pressure Chemical Ionization Mass Research Articles

Tribological study of borated hydroxyalkyldithiocarbamate as additive for environmentally adapted lubricants

PurposeThe fast growing concern for maintaining integrity of the environment has built up development of environmentally‐adapted lubricants. Because of their toxicity, most of the traditional lubricating additives cannot be used in this kind of lubricant. The purpose of this paper is to find a borate ester derivative which can be used as a multifunctional additive in rapeseed oils (RSO).Design/methodology/approachA borated S‐2‐hydroxypropyl N, N‐dibutyl dithiocarbamate (BDTC) was synthesized and characterized. Its tribological properties in rapeseed oil as multifunctional additive were evaluated, using a four‐ball tribometer and compared with one kind of commercial MoDTC. In addition, its thermal stability was identified using TGA and antioxidative ability tested by PDSC. The action mechanism of BDTC was studied by X‐ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atmospheric pressure chemical ionization mass spectrometer (APCI/MS) analysis.FindingsResults show that BDTC exhibits high thermal stability, possesses comprehensive tribological performance in rapeseed oil, and has evident effect in controlling the oxidation of RSO. Analysis of worn surface indicates that BDTC was decomposed and reacted with metal during the friction process. The lubricating film mainly contains inorganic boron compound (B2O3), organic nitrogen derivatives and FeSO4.Originality/valueThis paper provides a borate ester derivative which possesses excellent tribological properties and can be used as a multifunctional ashless additive in environmentally‐adapted lubricants. Furthermore, an innovative method, APCI/MS, was used to analyze the tribo‐fragmentation behavior of BDTC.

Characterization of Triacylglycerol Enantiomers Using Chiral HPLC/APCI-MS and Synthesis of Enantiomeric Triacylglycerols

In this work, the first systematic characterization of triacylglycerol (TG) enantiomers in real samples using chiral high-performance liquid chromatography (HPLC) with atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is performed. Our chiral HPLC/APCI-MS method is based on the use of two cellulose-tris-(3,5-dimethylphenylcarbamate) columns connected in series using a gradient of hexane-2-propanol mobile phase. All TG enantiomers containing 1-8 DBs and different fatty acyl chain lengths are separated using our chiral HPLC method except for TGs having a combination of saturated and di- or triunsaturated fatty acyls in sn-1 and sn-3 positions. In our work, the randomization reaction of monoacyl TG standards is used for the preparation of all TG enantiomers and regioisomers in a mixture, while the stereospecific esterification of 1,2- or 2,3-isopropylidene-sn-glycerols by selected fatty acids is used for the synthesis of TG enantiomers. The composition of TG enantiomers and regioisomers in hazelnut oil and human plasma samples is determined. Unsaturated fatty acids are preferentially esterified in sn-2 position in hazelnut oil, while no significant preference of saturated or unsaturated fatty acyls is observed in case of human plasma sample. Fatty acids with the higher number of DBs are preferred in sn-1 position of TG enantiomers in hazelnut oil unlike to moderate sn-3 preference in human plasma. The characterization of cholesteryl esters from TG fraction of human plasma sample using our chiral HPLC/APCI-MS method is presented as well.

Differential Analysis of Camphor Wood Products by Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

In the course of this study, desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS) was applied to readily acquire the mass spectral fingerprints of camphor wood and other wood samples under ambient conditions. Characteristic natural analytes, such as camphor and geraniol, were successfully detected in their protonated form and then identified by tandem mass spectrometry (MS(n)). Further principal component analysis (PCA) and cluster analysis (CA) of the mass spectrometric results allow a confident discrimination of camphor wood products from inferior/fake ones. These experimental findings demonstrate that DAPCI-MS is a valuable tool for differential analysis of untreated camphor wood products with sufficient sensitivity and high throughput.

Collision‐induced dissociation of aflatoxins

The aflatoxin mycotoxins are particularly hazardous to health when present in food. Therefore, from an analytical point of view, knowledge of their mass spectrometric properties is essential. The aim of the present study was to describe the collision-induced dissociation behavior of the four most common aflatoxins: B1, B2, G1 and G2. Protonated aflatoxins were produced using atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) combined with high-performance liquid chromatography (HPLC). For the tandem mass spectrometry (MS/MS) experiments nitrogen was used as the collision gas and the collision energies were varied in the range of 9-44 eV (in the laboratory frame). The major APCI-MS/MS fragmentations of protonated aflatoxins occurred at 30 eV collision energy. The main fragmentation channels were found to be the losses of a series of carbon monoxide molecules and loss of a methyl radical, leading to the formation of radical-type product ions. In addition, if the aflatoxin molecule contained an ether- or lactone-oxygen atom linked to a saturated carbon atom, loss of a water molecule was observed from the [M + H](+) ion, especially in the case of aflatoxins G1 and G2. A relatively small modification in the structure of aflatoxins dramatically altered the fragmentation pathways and this was particularly true for aflatoxins B1 and B2. Due to the presence of a C = C double bond connected to the ether group in aflatoxin B1 no elimination of water was observed but, instead, formation of radical-type product ions occurred. Fragmentation of protonated aflatoxin B1 yielded the most abundant radical-type cations.

Vitamin D, season, and risk of prostate cancer: a nested case-control study within Norwegian health studies

It is biologically plausible that vitamin D might prevent prostate cancer. However, recent meta-analyses concluded that there is no consistent relation between circulating 25-hydroxyvitamin D [25(OH)D] concentrations and prostate cancer, and several large studies have actually reported an increased risk of prostate cancer associated with high 25(OH)D. We aimed to assess the prospective relations between serum 25(OH)D, serum retinol, and risk of prostate cancer. In this nested case-control study, Norwegian men who participated in population-based health studies between 1981 and 1991 were followed with respect to prostate cancer throughout 2006. For each case (n = 2106), a matched control was selected. Stored serum was analyzed for 25(OH)D by using HPLC atmospheric pressure chemical ionization mass spectrometry. We showed a positive relation between an increasing 25(OH)D concentration and prostate cancer risk [rate ratio (RR): 1.15 (95% CI: 1.04, 1.27) per 30-nmol/L increase in 25(OH)D concentration]. Predefined analyses stratified by season showed no relation for subjects with serum collected during winter and spring (RR: 1.00 per 30-nmol/L increase), whereas a strengthened positive association [RR: 1.27 (95% CI: 1.09, 1.47) per 30-nmol/L increase] was observed in men with serum collected during the summer and autumn. There was no relation between serum retinol and prostate cancer. The cause for increased risk of prostate cancer related to a high 25(OH)D concentration only during the summer and autumn is not obvious. The effect may be related to vitamin D itself or to other factors associated with sun exposure.

Rapid Screening of Sulfur Fumigated Chinese Star Anises by Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Without any sample pretreatment,the mass spectral fingerprints of sulfur fumigated Chinese star anises and untreated samples were rapidly obtained in either a positive or negative ion detection mode with a home-made surface desorption atmospheric pressure chemical ionization(DAPCI) source.The DAPCI-MS raw data were further analyzed by principal component analysis(PCA) and cluster analysis(CA),and several unknown samples were successfully discriminated using the PCA model.The results showed that the DAPCI-MS was able to detect some characteristic chemicals from the Chinese star anises' surface and identify the components by tandem mass spectrometry(MS/MS).The further principal component analysis(PCA) and cluster analysis(CA) of MS fingerprints allow a confident discrimination of sulfur fumigated star anise samples from the non-sulfur fumigated samples.The method developed here is attractive to provide a fast and effective way to screen sulfur fumigated products with sufficient sensitivity and no toxin pollution.This method is expected to be applied to rapid identification of the sulfur fumigated product on the market in future.

Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry for Rapid Analysis of Capmhor Wood Products

Without sample pretreatment,a home-made surface desorption atmospheric pressure chemical ionization mass spectrometry(SDAPCI-MS) was used to obtain the fingerprint of camphor wood and common wood sample.The MS data were further analyzed by principal component analysis(PCA).The results show that the SDAPCI-MS is able to detect some characteristic chemicals such as camphor and geraniol from the wood surface and identify the components by tandem mass spectrometry(MS/MS).PCA of the mass spectral fingerprint data was used to differentiate the samples from category and quality.The method developed here is attractive by showing the advantages of no sample pretreatment,high sensitivity and high analytical speed(less than 3min per sample),and thus provides a fast and effective method to screen wood quality.

A Rapid and Sensitive LC–MS/MS Assay for the Quantitation of Bromantane in Human Plasma

The purpose of this study was to develop and validate a high-performance liquid chromatographic–tandem mass spectrometric (LC–MS/MS) method for analysis of the bromantane in human plasma. The analyte and Internal Standard (IS), selenox, were extracted from human plasma by solid-phase extraction and separated on a Zorbax SB-C18 column using methanol–0.2% formic acid as mobile phase. Detection was performed using an atmospheric pressure chemical ionization source and mass spectrometric positive Multi-Reaction-Monitoring-Mode (+MRM) at an ion voltage of +2000 V. The assay was linear over the concentration range 1–500 ng/mL with the Lowest Limit of Quantification (LLOQ) of 1 ng/mL. The method also afforded satisfactory results in terms of the sensitivity, specificity, precision (intra- and inter-day, CV<10%), accuracy, recovery as well as the stability of the analyte under various conditions. The method can be applied to pharmacokinetic and toxicological studies.

Simultaneous quantification of vinblastine and desacetylvinblastine concentrations in canine plasma and urine samples using LC–APCI–MS/MS

A highly sensitive and specific liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (LC/APCI–MS/MS) method has been developed and validated for simultaneous quantification of vinblastine and its metabolite, desacetylvinblastine, in canine plasma and urine samples. Plasma and urine samples were processed by a solid phase extraction procedure. The optimal chromatographic behavior of these analytes was achieved on pentafluorophenyl (PFP) propyl analytical column (5μm, 50×2.1mm) under isocratic elution of 0.75mL/min with a mobile phase of 5mM ammonium acetate and methanol. The samples were analyzed in positive ion, multiple reaction monitoring mode. The calibration curves were linear over 0.125–2ng/mL (lower calibration curve); 2–100ng/mL (higher calibration curve) and 0.125–5ng/mL for vinblastine and desacetylvinblastine in plasma, and over 1–2000ng/mL and 0.5–100ng/mL for vinblastine and desacetylvinblastine in urine samples, respectively. The limits of quantitation of vinblastine and desacetylvinblastine were 0.125ng/mL in both matrices. The intra and interday accuracy was above 89% and precision below 8.6% for both analytes in both matrices. The developed method was successfully applied to ongoing in vivo vinblastine pharmacokinetic studies in dogs.

Quantification of β-carotene, retinol, retinyl acetate and retinyl palmitate in enriched fruit juices using dispersive liquid–liquid microextraction coupled to liquid chromatography with fluorescence detection and atmospheric pressure chemical ionization-mass spectrometry

A detailed optimization of dispersive liquid–liquid microextraction (DLLME) was carried out for developing liquid chromatographic (HPLC) techniques, using both fluorescence and atmospheric pressure chemical ionization mass spectrometric (APCI-MS) detection, for the simultaneous analysis of preforms of vitamin A: retinol (R), retinyl acetate (RA), retinyl palmitate (RP) and β-carotene (β-C). The HPLC analyses were carried out using a mobile phase composed of methanol and water, with gradient elution. The APCI-MS and fluorescence spectra permitted the correct identification of compounds in the analyzed samples. Parameters affecting DLLME were optimized using 2mL of methanol (disperser solvent) containing 150μL carbon tetrachloride (extraction solvent). The precision ranged from 6% to 8% (RSD) and the limits of detection were between 0.03 and 1.4ngmL−1, depending on the compound. The enrichment factor values were in the 21–44 range. Juice samples were analyzed without saponification and no matrix effect was found when using fluorescence detection, so calibration was possible with aqueous standards. However, a matrix effect appeared with APCI-MS, in which case it was necessary to apply matrix-matched calibration. There was great variability in the forms of vitamin A present in the juices, the most abundant ester being retinyl acetate (0.04 to 3.4μgmL−1), followed by the amount of retinol (0.01 to 0.16μgmL−1), while retinyl palmitate was not detected, except in the milk-containing juice, in which RP was the main form. The representative carotenoid β-carotene was present in the orange, peach, mango and multifruit juices in high amounts. The method was validated using two certified reference materials.

Nanoparticles and nanocrystals of a new bidentate nickel(II) complex of N-[ethyl(propan-2-yl)carbamothioyl]-4-nitrobenzamide: synthesis, characterization, and crystal structures

The nickel(II) complex of N-[ethyl(propan-2-yl)carbamothioyl]-4-nitrobenzamide has been synthesized and characterized by Fourier transform-infrared spectroscopy, elemental analysis, nuclear magnetic resonance spectroscopy, and mass spectrometry (atmospheric pressure chemical ionization mass spectrometry). The single-crystal X-ray structures of N-[ethyl(propan-2-yl)carbamothioyl]-4-nitrobenzamide (1) and bis[N-[ethyl(propan-2-yl)carbamothioyl]-4-nitrobenzamide]nickel(II) (2) have been determined from single-crystal X-ray diffraction data. Loss of the N–H proton resonance and the N–H stretching vibration and the shift of the νC=O and νC=S stretching vibrations confirm formation of the metal complex. These studies show that the metal complex is neutral in cis-configuration. The complex has been used as a single-source precursor for the deposition of nickel sulfide nanocrystals by thermolysis. The nickel sulfide nanocrystals were characterized by X-ray powder diffraction and transmission electron microscopy.

Fragmentation patterns of protonated amino acids formed by atmospheric pressure chemical ionization

Dissociation reactions of protonated amino acids (AAs) can be used as models for the fragmentation of protonated peptides. Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) provides a great deal of structural information in a short analysis time. In APCI-MS, the fragmentation patterns can be obtained by varying the cone voltage and some fragment ions are produced that can be used to identify the structure of an analyte. In general, the fragmentation of AAs has used liquid chromatography/tandem mass spectrometry (LC/MS/MS). However, we studied the fragmentation of protonated AAs using a single quadrupole mass spectrometer. The principal fragment ions were [M + H - H(2)O - CO](+), [M + H - H(2)O](+), and [M + H - NH(3)](+). AAs that only generated [M + H - H(2)O - CO](+) were alanine, glycine, histidine, isoleucine, leucine, proline, phenylalanine, and valine. AAs that generated [M + H - H(2)O](+) and [M + H - H(2)O - CO](+) were aspartic acid, glutamic acid, serine, and threonine, while AAs that generated [M + H - NH(3)](+) and [M + H - H(2)O - CO](+) were asparagine, cysteine, glutamine, methionine, tryptophan, and tyrosine. Arginine and lysine generated [M + H - H(2)O](+) and [M + H - NH(3)](+). The relative abundances of the fragment ions increased with increase in the cone voltage. The experimental results were explained by the favorability of the intermediate structure and the stability of the fragment ion structure. The specific fragmentation patterns could be used for differentiating underivatized AAs.

Human plasma quantification of fludrocortisone using liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry after low-dosage administration

BackgroundFludrocortisone acetate is given at very low dosage (50μg) to patients suffering from septic shock with controversial clinical results. However, it is not clear if absorption is effective in these patients. MethodsAn analytical method based upon liquid chromatography coupled to triple quadrupole spectrometry detection with atmospheric pressure chemical ionization interface has been developed for the identification and quantification of fludrocortisone, the active molecule circulating in human plasma. A solid phase extraction of plasma was used after addition of fludrocortisone-D2 as internal standard. Compounds were separated on a C18 column with a gradient of methanol–formate buffer. The ion transitions used to monitor analytes were m/z 381→239 and m/z 381→181 for fludrocortisone and m/z 383→239 and m/z 383→181 for fludrocortisone-D2. ResultsRetention times were 4.0min for both compounds. Calibration curves were linear for fludrocortisone in the 0.1–25ng/ml range. The limits of detection and quantification were 0.05ng/ml and 0.1ng/ml, respectively. The intra- and inter-assay precisions were lower than 10.9% and the recovery was 101.8%. A slight matrix effect by about 10% was observed. Application of the method to a patient in septic shock treated with one 50-μg dose of fludrocortisone acetate has shown a maximal plasma concentration of 0.36ng/ml obtained after 2h. ConclusionThis method allows fludrocortisone pharmacokinetic/pharmacodynamic studies when given at low dosage in an intensive care unit in case of adrenal insufficiency during a septic shock.

Fast Screening of Authentic Ginseng Products by Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Surface desorption atmospheric pressure chemical ionization mass spectrometry was developed as a rapid online detection technology for the chemical fingerprints of ginseng products without any sample pretreatment. More than 20 ginsenosides were detected in the ginseng tissue and identified by their tandem mass spectrometry. Data were well matched with their reference compounds. Herein, surface desorption atmospheric pressure chemical ionization mass spectrometry was first applied to study the nonvolatile compounds in ginseng. White and red ginseng have been successfully differentiated from their counterfeits using some ginsenosides as chemical markers. Ginsenoside can be used to differentiate between white ginseng, red ginseng, unboiled ginseng, and their counterfeits. Ginsenosides Ra1-3, Rb2-3, and Rc might be used to differentiate between white ginseng and boiled ginseng. Our result showed that surface desorption atmospheric pressure chemical ionization mass spectrometry not only could be used for fast screening authentic ginseng products but also might become a useful promising technique for the characterization of nonvolatile compounds in medicinal herbs to save researchers the laborious effort of sample pretreatment.

Characterization and quantification of triacylglycerols in peanut oil by off‐line comprehensive two‐dimensional liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry

The complexity of natural triacylglycerols (TAGs) in various edible oils is prodigious due to the hundreds of set is of TAG compositions, which makes the identification of TAGs quite difficult. In this investigation, the off-line 2D system coupling of nonaqueous RP and silver-ion HPLC with atmospheric pressure chemical ionization MS detection has been applied to the identification and quantification of TAGs in peanut oil. The method was successful in the separation of a high number of TAG solutes, and the TAG structures were evaluated by analyzing their atmospheric pressure chemical ionization mass spectra information. HPLC and MS conditions have been optimized and the fragmentation mechanisms of isomers have been validated. In addition, an internal standard approach has been developed for TAG quantification. Then this system was applied in peanut oil samples and there was a total of 48 TAGs including regioisomers that have been determined and quantified.

Characteristics of Low-Temperature Plasma Ionization for Ambient Mass Spectrometry Compared to Electrospray Ionization and Atmospheric Pressure Chemical Ionization

Ambient desorption/ionization mass spectrometry (ADI-MS) is an attractive method for direct analysis with applications in homeland security, forensics, and human health. For example, low-temperature plasma probe (LTP) ionization was successfully used to detect, e.g., explosives, drugs, and pesticides directly on the target. Despite the fact that the field is gaining significant attention, few attempts have been made to classify ambient ionization techniques based on their ionization characteristics and performance compared to conventional ionization sources used in mass spectrometry. In the present study, relative ionization efficiencies (RIEs) for a large group of compound families were determined with LTP-Orbitrap-MS and compared to those obtained with electrospray ionization mass spectrometry (ESI-MS) and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). RIEs were normalized against one reference compound used across all methods to ensure comparability of the results. Typically, LTP analyte ionization through protonation/deprotonation (e.g., 4-acetamidophenol) was observed; in some cases (e.g., acenaphthene) radicals were formed. Amines, amides, and aldehydes were ionized successfully with LTP. A benefit of LTP over conventional methods is the possibility to successfully ionize PAHs and imides. Here, the studied model compounds could be detected by neither APCI nor ESI. LTP is a relatively soft ionization method because little fragmentation of model compounds was observed. It is considered to be an attractive method for the ionization of low molecular weight compounds over a relatively wide polarity range.

Determination of Melamine and Derivatives in Foods by Liquid Chromatography Coupled to Atmospheric Pressure Chemical Ionization Mass Spectrometry and Diode Array Detection

Two liquid chromatographic methods based on atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS) and diode array detection (DAD) are evaluated for the rapid determination of melamine (MEL) and structurally related compounds, including ammeline (AMN), ammelide (AMD), and cyanuric acid (CA) in foods. Both procedures used ion-exchange LC and isocratic elution. Samples were extracted by homogenization with acetonitrile/water/diethylamine. Specificity was demonstrated for LC-MS by the retention characteristics and MS spectra, by comparing with commercial standards. Specificity was only demonstrated in the case of LC-DAD for MEL and AMN, considering the retention characteristics and UV spectra. The recoveries obtained for spiked samples were satisfactory for all the analytes with LC-MS. The proposed procedure, LC-APCI-MS, was successfully applied to the analysis of different baby foods, including infant formula and breakfast cereal, and samples of rice flour, potato starch, soya drink, and coconut drink.

Headspace delivery of limonene from the serum and non-serum fractions of orange juice in-vitro and in-vivo

The impact of orange juice pulp on the physical release of limonene to the headspace of freshly prepared orange juice was evaluated both in-vitro and in-vivo. Atmospheric pressure chemical ionization mass spectrometry was used to analyse the impact of the matrix on the dynamic release of the volatile aroma compound, limonene, in orange juice. Pulp and aqueous serum was isolated (by centrifugation and filtration) from freshly prepared orange juice and subsequently reconstituted at varying pulp addition levels in serum (0g/100 g–20g/100 g, wwb). The addition of pulp significantly enhanced the static headspace concentration of limonene with a 210 fold increase with 10g/100 g pulp addition. In addition, pulp enhanced the ability of the orange juice serum to replenish limonene in the headspace after dynamic headspace dilution. The release of limonene was studied under realistic consumer consumption conditions (In-nose delivery) by atmospheric pressure chemical ionisation-mass spectrometry; pulp significantly enhanced the amount of limonene exhaled in the nasal airflow (retronasal delivery). Surprisingly, given the variations in limonene concentration, naïve consumers did not perceive samples as significantly different on consumption. This is presumably due to the wide range of other aroma compounds not evaluated in this study that contribute to the perceived aroma.

Formation of the Ions of Methylindoles in APCI Mass Spectrometry

Indoles are common building blocks of new pharmacologically active chemical entities in drug discovery and development. Due to their poor ionization in electrospray ionization mass spectrometry, atmospheric pressure chemical ionization (APCI) is the method of choice for LC-MS analysis of simple indoles. Three types of ions, including [M − 1]+, , and [M + H]+, can be observed in APCI but the relative intensities of these ions may vary depending upon the structural properties of the indoles and the mass spectral source conditions. We report in this paper the observation of [M − 1]+ ions for methylindoles in an Agilent multimode ion source and the investigation into their formation. By means of tandem mass spectrometric experiments performed on a Thermo Fisher Scientific LTQ ion trap mass spectrometer equipped with an APCI source, it was found that [M − 1]+ ions can be generated from ions upon-collision induced dissociation. This suggests that the [M − 1]+ ions might be the in-source fragmentation product of ions. It was proposed that both [M − 1]+ and ions are probably generated through a charge transfer mechanism while [M + H]+ ions are the product of proton transfer. The basicity of the analytes might play an important role in dictating which ionization mechanism is operative. For 3-methylindole, the charge transfer process appears to be more dominant than for 2-methylindole since the former is less basic. As expected, substituting electron withdrawing groups on 3-methylindole, such as fluorine, promotes charge transfer and vice versa. Therefore, it is expected that formation of the [M − 1]+ ions is more pronounced for less basic methylindoles.

Effects of Ethanol and Long-Chain Ethyl Ester Concentrations on Volatile Partitioning in a Whisky Model System

Ethanolic atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was used to analyze the headspace concentrations of a test set of 14 whisky volatile compounds above a series of aqueous ethanolic solutions differing in alcohol content (5-40% ABV) and with regard to concentration of ethyl hexadecanoate (0-500 mg/L). The latter was selected to represent the long-chain ethyl esters found at various concentrations in new-make spirit. Headspace ion intensities were modeled against ethanol and ethyl hexadecanoate concentrations as factors. A separate model was prepared for each compound. Not surprisingly, ethanol content in the range of 5-40% ABV had a significant effect (P < 0.0001) on headspace volatile concentrations of all volatile compounds, whereas the ethyl hexadecanoate concentration had a selective effect of reducing headspace concentrations of the more hydrophobic compounds (log P > 2.5). This finding is discussed in terms of the "structuring" effects of ethyl hexadecanoate when present above critical micelle concentration, leading to the selective incorporation of hydrophobic volatile compounds into the interior of micelle-like structures. Data presented illustrate that dilution of whiskies to 23% ABV for "nosing" in the presence of long-chain ethyl esters is likely to change the balance of volatile compounds in the headspace and thus the perceived aroma character.