Chiral amino acid analysis of vinegars using gas chromatography – selected ion monitoring mass spectrometry

 Twenty-five vinegars were examined quantitatively for their content of free amino acid (AA) enantiomers using chiral gas chromatography/mass spectrometry. Vinegars manufactured from grape must contained l-proline (l-Pro) as the major AA. Balsamic vinegars (aceto balsamico di Modena), with one exception, contained the highest amounts of l-AAs (861–2000 mg l^–1) as well as d-AAs (46–361 mg l^–1). The amounts of d-Pro and d-alanine (d-Ala) increased in the course of maturation. Sherry vinegars had a AA pattern similar to that of balsamic vinegars but with much lower amounts: concentrations of l-AAs were 244 mg l^–1 and 456 mg l^–1 and of d-AAs were 18 mg l^–1 and 19 mg l^–1. The l-AA content of cider vinegars was very low (34 mg l^–1 and 44 mg l^–1) and only traces of d-AAs (<2 mg l^–1) were found. In spirit vinegars few d-AAs and low amounts of most l-AAs were detected, with the exception of l-glutamic acid (l-Glu) (210–847 mg l^–1), probably added as a flavour enhancer. The AA content of spirit vinegars blended with wine vinegar was influenced by the portion of wine vinegar added. Rice vinegars had concentrations of l-AAs from as low as 36 mg l^–1 to as high as 6860 mg l^–1, and the concentrations of d-AAs ranged from 6 mg l^–1 to 531 mg l^–1. All vinegars declared as "produced by microbial fermentation" contained d-Ala, d-aspartic acid, and d-Glu as typical bacterial markers. From the data it is concluded that chiral AA analysis can be used to distinguish among fermented and synthetic vinegars and to identify raw materials used for their production. In particular, the amount of d-Pro can be used as proof of the maturation process of balsamic vinegar. Received: 11 December 1997 / Revised version: 12 May 1998     

Comprehensive authenticity assessment of lavender oils using multielement/multicomponent isotope ratio mass spectrometry analysis and enantioselective multidimensional gas chromatography–mass spectrometry

¹³C_V-PDB, ²H_V-SMOW and ¹⁸O_V-SMOW multielement isotope ratio mass spectrometry analysis of linalool and linalyl acetate, the main components of lavender oils, is reported. Self-prepared and commercially available lavender oils, as well as samples of linalool and linalyl acetate labelled as synthetic and natural products respectively, were investigated. Multielement/multicomponent isotope ratio mass spectrometry analysis and—as far as possible—in conjunction with enantioselective analysis is judged to be the most comprehensive basis of authenticity assessment in flavour and essential oil analysis.     

Confirmatory analysis of steroids in muscle using liquid chromatography–tandem mass spectrometry

A method is described for screening and confirmation of synthetic and endogenous steroids in muscle tissue. The method is sensitive, selective, and rapid and the consumption of organic solvents is low, compared to previously published methods. The procedure involves hydrolysis, defattening with heptane and final clean up with SPE using C₁₈ cartridge. After filtration, the analytes are analysed by LC/MS/MS and quantification is performed using deuterated internal standards. Decision limits (CCα) varied from 0.02 to 0.33?µg?kg^?1 and the detection capabilities (CCβ) were <0.50?µg?kg^?1. The mean within-laboratory reproducibility ranged 5–22% (%RSD_IR). Endogenous steroids (e.g. testosterone, epitestosterone and androstenedione) have been included in the method, to provide an insight into their levels, as the presence of these steroids was detected several times during analysis of imported meat.     

Detection of pyrrolizidine alkaloids in commercial honey using liquid chromatography–ion trap mass spectrometry

Pyrrolizidine alkaloids (PAs) are known secondary plant metabolites which can cause hepatotoxicity in both humans and livestock. PAs can be consumed through the use of plants for food, medicinal purposes and as contaminants of agricultural crops and food. PA contaminated grain has posed the largest health risk, although any PA contamination in our food chain should be recognised as a potential health threat. For this purpose, retail honeys were tested by LC–MS/MS. The method allows for specific identification of toxic retronecine and otonecine-type PAs by comparison to reference compounds via a spectral library. In total, 50 honey samples were matched to the reference spectra within a set of tolerance parameters. Accurate data analysis and quick detection of positive samples was possible. Positive samples contained an average PA concentration of 1260 μg kg^?1 of honey. Good linear calibrations were obtained (R² > 0.991). LOD and LOQ ranged from 0.0134 to 0.0305 and 0.0446 to 0.1018 μg mL^?1, respectively.     

Quantification of N-carboxymethyl-lysine in selected chocolate-flavoured drink mixes using high-performance liquid chromatography–linear ion trap tandem mass spectrometry

N^ε-carboxymethyl-lysine (CML) is considered to be an important marker of the Maillard reaction. In the present investigation a liquid chromatography coupled to ion trap tandem mass spectrometry has been developed for the analysis of CML and lysine in drink mixes. To ensure the best specificity of the method, porous graphitic carbon packing material was used for the chromatographic separation and two transition reactions were recorded per analyte. With the stable-isotope dilution technique employed in this method the recovery ranged from 100% to 111.4% for CML. All other performance characteristics tested were also satisfactory. The method was applied to the analysis of chocolate-flavoured drink mixes after sodium borohydride reduction and acid hydrolysis. In this food category, CML content varied from 8.1 to 131.9 μg/g powder or 95 to 3527 μg/g protein. Among the food items analysed by different laboratories chocolate-flavoured drink mixes appear to have one of the highest CML contents.     

Determination of phthalate esters in wine using solid-phase extraction and gas chromatography–mass spectrometry

A method for the determination of six phthalate esters in wine samples has been developed. The phthalates were extracted from wine samples with an optimised solid-phase extraction method on C18 column and quantification was achieved via gas chromatography coupled with a mass spectrometer. The method was linear between 0.015 and 5.000 μg mL⁻¹ for DMP, DEP and DEHP and between 0.018 and 5.000 μg mL⁻¹ for iBP, DBP and BBP. The LOQs of DMP, DEP and DEH were 0.024 μg mL⁻¹ while those of iBP, DBP and BBP were 0.029 μg mL⁻¹. The intra-day method repeatability was between 10% and 15% RSD, whereas the inter-day method repeatability was between 13% and 21% RSD. A survey was performed on white and red wines (n = 62) from the market, winemakers and an experimental pilot plant. All the analysed samples were phthalate contaminated. Commercial wine showed higher detection frequency and level of total phthalate, DBP and BBP than those produced in a pilot plant. iBP and DEHP concentrations were similar in all the groups of samples. iBP concentration was higher in red wines than in white ones.     

Characterization of the volatile profile of thistle honey using headspace solid-phase microextraction and gas chromatography–mass spectrometry

In this study, a headspace solid-phase microextraction method was developed for the characterization of the volatile fraction of thistle honey and compared with a dynamic headspace extraction method. A DVB/CAR/PDMS fibre was used. The effects of extraction time, equilibration time and salt addition on extraction yield were evaluated. The volatile fraction of seven Italian thistle honey samples was extracted under the optimized conditions and analyzed by gas chromatography–mass spectrometry. Characterization of the volatile profile was performed in terms of nature and relative amount of the extracted compounds. A total of 40 compounds, belonging to different chemical classes, were identified. The relative amounts of 16 compounds found in all the analyzed thistle honeys, i.e. nonanal, furfural, decanal, 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran, benzaldehyde, α-linalool, lilac aldehyde (isomer IV), hotrienol, phenylacetaldehyde, 4-oxoisophorone, benzyl alcohol, 2-phenylethanol, a not identified compound, octanoic acid, nonanoic acid and methyl anthranilate, were calculated and submitted to statistical analysis, in order to define for each compound a typical range. On the basis of the obtained data, a characteristic set of values was defined for thistle honey volatile fingerprint. The developed model proved to be effective in recognizing the botanical origin of thistle honey.     

Analysis of pesticide residues in seaweeds using matrix solid-phase dispersion and gas chromatography–mass spectrometry detection

Products containing organophosphates, carbamates and pyrethroids pesticides, employed as chemotherapeutants in aquaculture, can remain as residues in the marine environment. Matrix solid-phase dispersion (MSPD) was developed to extract seventeen pesticides from seaweed samples using Florisil and graphitized carbon black as clean-up adsorbents prior to gas chromatography–mass spectrometry (GC–MS) determination. The extraction has been optimised by a Box–Behnken design. The optimal conditions were 1 g of seaweed sample, 4 g of anhydrous sodium sulphate as dispersant, 3.6 g of Florisil and 0.4 g of GCB and an elution volume of 14 mL of a hexane:ethyl acetate mixture containing 40% ethyl acetate. The recoveries ranged from 81.6% to 113.2% with relative standard deviations (RSDs) ranging from 1.6% to 13.2%. The limits of detection (LOD) ranged from 0.5 to 2.9 ngg⁻¹. Internal quality control was successfully carried out to verify the quality of the data obtained in the analysis of these pesticides in seaweed samples.     

Determination of biogenic diamines with a vaporisation derivatisation approach using solid-phase microextraction gas chromatography–mass spectrometry

A gas-phase on-fibre derivatisation method for the determination of putrescine and cadaverine by gas chromatography/mass spectrometry using trifluoroacetylacetone (TFAA) has been studied and optimised. Small amounts (2 μl) of putrescine, cadaverine and TFAA standards were vaporised at high temperature in a 20 cm³ closed SPME vial. The subsequent derivatives were recovered from the headspace of the vial using a PDMS/DVB fibre. The optimised mole ratio for [TFAA]/[Putrescine + Cadaverine] reaction was 22.3/1 with a derivatisation and extraction temperature of 120 ^oC and an extraction time of 20 min. The retention times for the derivatised putrescine and cadaverine were 20.5 and 22.2 min, respectively on a capillary column, CP-Sil 8CB; 30 m length × 0.25 mm i.d. × 0.25 μm film thickness. The correlation coefficients (R²) of calibration curves for putrescine and cadaverine were 0.999 and 0.997, respectively over a range of sample masses of 20–350 ng, using nonadecane as an internal standard. Putrescine and cadaverine recoveries were determined to be 93.9% and 103.3%, respectively. The method was found to be a straightforward single step procedure that was unaffected by complex sample matrices and was successfully tested on samples of meat, vegetables and cheese.     

Exploring stingless bee honey from selected regions of Peninsular Malaysia through gas chromatography–mass spectrometry–based untargeted metabolomics

Volatile organic compounds in honey are known for their considerable impact on the organoleptic properties of honey, such as aroma, flavor, taste, and texture. The type and composition of volatile organic compounds are influenced by entomological, geographical, and botanical origins; thus, these compounds have the potential to be chemical markers. Sixty-two volatile compounds were identified using gas chromatography–mass spectrometry from 30 Heterotrigona itama (H. itama) honey samples from 3 different geographical origins. Hydrocarbons and benzene derivatives were the dominant classes of volatile organic compounds in the samples. Both clustering and discriminant analyses demonstrated a clear separation between samples from distant origins (Kedah and Perak), and the volcano plot supported it. The reliability and predictability of the partial least squares–discriminant analysis model from the discriminant analysis were validated using cross-validation (R²: 0.93; Q²: 0.83; accuracy: 0.97) and the permutation test (p < 0.001), and the output depicted that the model is legitimate. In combination with the variable importance of projection (VIP > 1.0) and the Kruskal–Wallis test (p < 0.01), 19 volatile organic compounds (encompassed aldehydes, benzene derivatives, esters, hydrocarbons, and terpenoids) were sorted and named potent chemical markers in classifying honey samples from three geographical origins. In brief, this study illustrated that volatile organic compounds of stingless honey originated from the same bee species, but different geographical origins could be applied as chemical markers.     

Application of dispersive liquid–liquid microextraction for the determination of selected organochlorine pesticides in honey by gas chromatography–mass spectrometry

Dispersive liquid–liquid microextraction (DLLME) is a rapid and easy technique that consumes minute amounts of organic solvents. In this work, we present chemometric study on optimization of DLLME parameters for the extraction of aldrin, endrin, lindane, α-endosulfan, 4,4′-DDT and its metabolites from honey matrix. Method quantification limits (MQLs) vary between 0.3 ng/g for 2,4′-DDE and 4,4′-DDE to 13.2 ng/g for α-endosulfan and enable determination at levels below EU-established Maximum Residue Limits. The developed method is linear (R ² > 0.994) in the investigated range (MQL—100 ng/g), with preconcentration factors of 13.2–30.5 and good repeatability (CV ≤ 17%). A comparison with other available methods reported in the last decade is provided. The method has been applied to 19 real samples from Poland, and the results show that organochlorine pesticides (OCPs) are present in analysed honeys at levels not posing threat to human health (below 14 ng/g for sum of 4,4′-DDT and metabolites and below 5 ng/g for aldrin, endrin and lindane). To the best of our knowledge, this is the first reported application of DLLME for the determination of OCPs in honey.     

Quantitative analysis of glycoconjugate precursors of guaiacol in smoke-affected grapes using liquid chromatography–tandem mass spectrometry based stable isotope dilution analysis

Guaiacol has been shown to accumulate in glycoconjugate forms in the fruit and leaves of grapevines following vineyard exposure to bushfire smoke. To investigate the glycosylation of guaiacol in smoke-affected grapes, a quantitative stable isotope dilution analysis method using liquid chromatography-tandem mass spectrometry was developed and validated, using the [²H₄]-labelled analogue of guaiacol β-d-glucopyranoside as internal standard. The method was subsequently applied to the analysis of grapes sampled from grapevines exposed to either bushfire or experimental smoke, enabling compositional comparisons of guaiacol glycoconjugates in smoke-affected grapes from different varieties to be determined, for the first time.     

Determination of 3-MCPD in grilled meat using pressurized liquid extraction and gas chromatography–high resolution mass spectrometry

An analytical method for the determination of free 3-monochloropropane-1,2-diol (3-MCPD) in grilled meat using pressurized liquid extraction, derivatisation using phenylboronic acid, and gas chromatography/high resolution mass spectrometry was developed. The limit of quantification was 1???g/kg. Using this method, the contents of 3-MCPD in grilled steaks (collar) were analysed for different grilling conditions. Charcoal, an electric grill, and a gas grill were used for grilling collars. Further parameters investigated were the pre-treatment of meat (untreated, salted, marinated with oil or emulsion marinade), the use of aluminium grill trays, and a lid. For grilled steaks, contents of 3-MCPD in the range of <1 to 365???g/kg (median 16???g/kg) were detected. The highest contamination was found for a steak pre-treated with an oily marinade grilled on a charcoal grill with a closed lid. Consuming such a steak will exhaust the tolerable daily intake of 2???g/kg body weight for 3-MCPD to about 26?%.     

Microwave pretreatment and gas chromatography–mass spectrometry determination of herbicide residues in onion

A rapid multi-residue method was developed for the determination of 16 herbicides in onion. The analytical procedure was based on preventing formation of sulfur-containing compounds in onion by microwave inactivation of the enzyme alliinase. The onion samples which had been pretreated were extracted with acetonitrile and cleaned by solid-phase extraction. The herbicide residues in onion were detected by gas chromatography/mass spectrometry with selected ion monitoring. The recoveries of 16 herbicides ranged from 69.2% to 105.0% with the relative standard deviations (RSD) below 10.7%. The limit of quantitation (LOQ) ranged from 0.003 to 0.015 mg kg⁻¹. The method was applied to the analysis of herbicide residues in onion samples.     

Identification of pyrazine derivatives in a typical maple syrup using headspace solid-phase microextraction with gas chromatography–mass spectrometry

Headspace solid-phase microextraction combined with gas chromatography–mass spectrometry was applied to identify pyrazines in a typical maple syrup characterised by plant ligneous or sawdust flavour. Carboxen/polydimethylsiloxane (85 μm) fibre and Supelcowax 10 column were selected instead of Carbowax/divinylbenzene (65 μm) fibre and VF-5ms column, respectively, because of their high capacity to extract and separate pyrazines. A total of 27 pyrazines were identified. To our knowledge, about half of these compounds had not previously been detected in maple syrup and 15 pyrazines were flavour components.     

Flavour profiling by gas chromatography–mass spectrometry and sensory analysis of yoghurt derived from ultrasonicated and homogenised milk

The odour, flavour, taste, sensory and volatile components profile of yoghurt, derived from milk homogenised by ultrasound or pressure were compared. The ultrasonication of milk led to yoghurts with lower degree of likeness (DOL) and off-flavours compared with those of yoghurts from pressure treated milk; also, burned, pungent and fatty flavour characteristics were more intense. The volatile components were identified by solid phase microextraction–gas chromatography–mass spectrometry (SPME–GC–MS). Both homogenisation treatments lead to chromatograms with similar peak areas of 2,3-butadione, 3-hydroxy-2-butanone, delta-decalactone, while the chromatogram peak areas of acetone, 2-butanone, 2-heptanone, bicyclo[2,2,1]-heptan-2-one, 2-nonanone, 2-undecanone, butanoic acid, hexanoic acid, octanoic acid, n-decanoic acid, hexadecanoic acid, acetaldehyde, hexanal, 1-buten-3-yne, heptane and dimethylsulphide were higher for the ultrasonicated samples. Sensory characteristics and GC–MS profiles were correlated with DOL and two models created with PLS regression. Both models included the appropriate variables and showed adequate ability to describe DOL by sensory characteristics or volatile components.     

Optimization of gas chromatography–single quadrupole mass spectrometry conditions for multiresidue analysis of pesticides in grapes in compliance to EU-MRLs

A single quadrupole GC–MS method was optimized for multiresidue determination of 47 pesticides in grapes with limit of quantifications of each compound in compliance with the EU-MRL requirements. Sample preparation involved extraction of 10 g sample with 10 ml ethyl acetate (+10 g sodium sulphate) by homogenization at 15,000 rpm followed by centrifugation at 3000 rpm. The supernatant was cleaned by dispersive solid phase extraction with primary secondary amine and acidified with 0.1% formic acid. Residues were estimated in selected ion monitoring mode with programmable temperature vaporizer-large volume injection (8 μl). All the GC and MS parameters were thoroughly optimized to achieve satisfactory linearity (R² > 0.99) within 0.01–0.25 mg kg⁻¹ with minimum matrix interferences. Recoveries at 0.01 and 0.02 mg kg⁻¹ were within 67–120% with associated precision RSD below 19%. The method was successfully applied for analysis of the real world samples for incurred residues.     

Degradation study of enniatins by liquid chromatography–triple quadrupole linear ion trap mass spectrometry

Enniatins A, A₁, B and B₁ (ENs) are mycotoxins produced by Fusarium spp. and are normal contaminants of cereals and derivate products. In this study, the stability of ENs was evaluated during food processing by simulation of pasta cooking. Thermal treatments at different incubation times (5, 10 and 15 min) and different pH (4, 7 and 10) were applied in an aqueous system and pasta resembling system (PRS). The concentrations of the targeted mycotoxins were determined using liquid chromatography coupled to tandem mass spectrometry. High percentages of ENs reduction (81–100%) were evidenced in the PRS after the treatments at 5, 10 and 15 min of incubation. In contrast to the PRS, an important reduction of the ENs was obtained in the aqueous system after 15 min of incubation (82–100%). In general, no significant differences were observed between acid, neutral and basic solutions. Finally, several ENs degradation products were identified using the technique of liquid chromatography–triple quadrupole linear ion trap mass spectrometry.     

Characterisation of the glycerophospholipid fraction in flaxseed oil using liquid chromatography–mass spectrometry

A high-performance liquid chromatographic method coupled with mass spectrometry was used to characterise the natural phospholipid (PL) classes and molecular species in flaxseed oils. The PL fraction included phosphatidylethanolamine (PE) (27–40%), phosphatidylinositol (PI) (29–32%), phosphatidylcholine (PC) (7–18%), lysophosphatidylcholine (LPC) (8–21%), phosphatidylglycerol (PG) (1–4%) and phosphatidic acid (PA) (1–9%). The distribution of fatty acids was found to differ between phospholipids. Stearic acid was mainly present in the form of PC and LPC. Palmitic acid was present in the most abundant molecular species in PI, PG and PA whereas linoleic acid formed the most abundant molecular species in PE.