Chromatography-ion Trap Mass Spectrometry Research Articles

Analysis of aminoglycoside residues in bovine milk by liquid chromatography electrospray ion trap mass spectrometry after derivatization with phenyl isocyanate

A derivatization procedure using phenyl isocyanate was adapted to liquid chromatography ion trap mass spectrometry (LC–MSn) for confirmation and quantification of aminoglycoside residues in milk. Aminoglycoside residues were extracted from milk with acid and isolated from the matrix with a weak cation exchange solid-phase extraction cartridge. After isolating the compounds from the milk, derivatives of gentamicin, neomycin, and tobramycin were formed by reacting the drugs with phenyl isocyanate in the presence of triethylamine. The analytes were separated using a dilute formic acid/acetonitrile gradient on a reversed-phase LC column. The derivatized compounds were analyzed using positive ion electrospray LC–MSn with ion trap detection. Product ion spectra were generated from the derivatized protonated molecules. Specific ion transitions were evaluated for quantitative determination and qualitative confirmation of residues in milk. Using this procedure, residues were qualitatively confirmed in milk samples fortified with gentamicin and neomycin at levels ranging from 15 to 300ngmL−1. Gentamicin has four major components that were successfully separated and confirmed independently; for quantitative determination the peak areas from the four analogs were summed. Tobramycin was added as an internal standard for quantitation to mitigate the effects of matrix ion suppression and variable recoveries. Overall recoveries for this method ranged from 80% to 120% with relative standard deviations of less than 25%. The method detection limits are 9.8ngmL−1 for NEO and 12.8ngmL−1 for total GEN residues.

Antimicrobial activity in the vapour phase of a combination of cinnamon and clove essential oils

The antimicrobial activity of the vapour generated by a combination of cinnamon and clove essential oils against the growth of four Gram-negative (Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruoginosa and Salmonella choleraesuis) and four Gram-positive bacteria (Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus and Enterococcus faecalis) was assessed by means of the fractional inhibitory concentration index (FIC) of the mixture. The presence of synergism or antagonism effects depended on the reference parameter used to estimate such an index. If the minimal inhibitory concentrations were applied, the vapours of the combination of essential oils exerted an antagonistic effect on the growth of E. coli, while they wielded a synergistic effect for the inhibition of L. monocytogenes, B. cereus and Y. enterocolitica when the concentrations of maximal inhibition were used. This fact revealed a clear concentration-dependent interaction. The headspace of the cinnamon and clove essential oils and their combination was sampled by solid-phase microextraction (SPME) and the constituents identified and quantified by gas chromatography–ion trap mass spectrometry (GC/ITMS). Eugenol was the most abundant compound for the three antibacterial atmospheres. The differences in behaviour could be attributed to minor compounds. The combined headspace contained slightly larger amounts of 1,8-cineole and camphor, which are believed to enhance the eugenol activity. The mechanisms responsible for the antagonism are, however, less known and much further investigation is required. To the best of our knowledge this is the first time a combination of essential oils in the vapour phase has been tested as a preservative method to prevent microorganism proliferation.

Automated headspace solid-phase microextraction versus headspace for the analysis of furan in foods by gas chromatography–mass spectrometry

A simple, fast and fully automated method based on headspace solid-phase microextraction coupled on-line with gas chromatography–ion trap mass spectrometry (HS-SPME–GC–ITMS) is proposed for furan determination in foods. The performance of the proposed method was compared to the automated headspace-GC–MS method, proposed by the US Food and Drugs Administration (US FDA), in terms of repeatability, limits of the detection and quantification. Both methods gave similar results for furan determination in selected food samples, although slightly worse precision (RSD%, 9–12%) and higher limits of detection (from 5 to 20 times higher) were obtained by the headspace method. In addition, higher sample throughput in routine furan analysis was obtained using the proposed HS-SPME–GC–ITMS method with isotope dilution than using the US FDA method, which recommends standard addition for quantification. The proposed method provides good precision (RSD% <10%) and low limits of detection, ranging from 0.02 to 0.12 ng g −1 depending on the sample. The developed HS-SPME–GC–MS method was used to analyse furan in several Spanish food commodities and concentrations ranging from 0.1 ng g −1 to 1.1 μg g −1 were found.

Characterization of metabolites of sibutramine in primary cultures of rat hepatocytes by liquid chromatography–ion trap mass spectrometry

Liquid chromatography-ion trap mass spectrometry was used for the detection and structural characterization of metabolites of the anti-obesity drug sibutramine. Metabolites were profiled from incubations of sibutramine in primary cultures of rat hepatocytes. In addition, enantioselectivity of sibutramine metabolism was investigated by carrying out separate incubations with (R)- and (S)-sibutramine. As a result, biotransformation profile for sibutramine with rat hepatocytes is proposed. Nineteen metabolites and several of their isomers formed via demethylation, hydroxylation, dehydrogenation, acetylation, attachment of CO(2), and glucuronidation were identified in MS(2) and MS(3) experiments, though the exact position of the functionality, mostly hydroxylation, could not always be determined from the mass spectrometric information. However, clear enantioselective formation was observed for two hydroxyl derivatives and two glucuronide conjugates, indicating that the hydroxyl/glucuronic acid moiety in those structures is close to the chiral center. Most of the metabolites found in this study are new metabolites of sibutramine, which were not previously reported.

A denuder–impinger system with in situ derivatization followed by gas chromatography–mass spectrometry for the determination of gaseous iodine-containing halogen species

Reactive iodine species have been suggested to play an important role in the atmosphere (e.g. tropospheric ozone depletion, coastal new particle formation). However, there still exist major uncertainties about their atmospheric chemistry, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. In this study, 1,3,5-trimethoxybenzene (1,3,5-TMB)-coated denuder proved to be suitable for the differentiation between gaseous interhalogens (iodine monochloride (ICl), iodine monobromide (IBr)) and molecular iodine (I 2) based on a selective collection/derivatization method. The results of the denuder sampling were compared with the results of impinger sampling in water, methanol and carbon tetrachloride solutions of 1,3,5-TMB. ICl and IBr are converted into 1-iodo-2,4,6-trimethoxybenzene (1-iodo-2,4,6-TMB) and 1-bromo-2,4,6-trimethoxybenzene (1-bromo-2,4,6-TMB), respectively, in the denuder systems. The respective collection efficiency is 99.2% for ICl and 92.6% for IBr, at 500 mL min −1 gas flow rate. The collection efficiency for I 2 is lower than 1% in the same denuder system, but significantly increases to about 90% in the aqueous 1,3,5-TMB loaded impinger. The denuder–impinger coupled system was then used to differentiate and to collect the ICl, IBr and I 2 gas mixtures, followed by gas chromatography–ion trap mass spectrometry (GC–MS) determination. The precision of the method is in general better than 9.1%. The parameters affecting denuder operation including sampling flow rate, sampling duration, and relative humidity have been evaluated. The presented method provides an attractive protocol for iodine species analysis for atmospheric chemistry research.

Using liquid chromatography–ion trap mass spectrometry to determine pharmaceutical residues in Taiwanese rivers and wastewaters

To establish their environmental concentrations and to support surface water protection programs, we have undertaken a preliminary study of the concentrations of selected acidic and neutral pharmaceutical residues (clofibric acid, ketoprofen, ibuprofen, diclofenac and carbamazepine) in Taiwanese river and wastewater samples. These pharmaceutical residues were extracted from the water samples through the Oasis HLB solid-phase extraction (SPE). The analytes were then identified and quantified using liquid chromatography–ion trap mass spectrometry with dual-polarity electrospray ionization in the product ion scan mode. The limits of quantification (LOQs) ranged between 0.5 and 20 ng l −1 for 250 ml samples of water. We investigated the intra- and interbatch precision and accuracy at two levels of concentration. The selected analytes were detected at concentrations ranging from <0.5 to 960 ng l −1 in wastewater treatment plant effluents and river water samples.

Isolation and quantification by high-performance liquid chromatography–ion-trap mass spectrometry of androgen sulfoconjugates in human urine

Together with steroid glucuronides, sulfoconjugates may be used as markers of steroid administration as well as endogenous steroid production. A fast and sensitive analytical procedure has been developed for the simultaneous separation, determination and quantification of sulfate and glucuronide derivatives of testosterone (T), epitestosterone (E), androsterone (A), etiocholanolone (Etio) and dehydroepiandrosterone (DHEA) in human urine. First, a weak anion-exchange solid-phase extraction support (SPE Oasis WAX) was used for complete and rapid separation of sulfates and glucuronides in two extracts after loading of urine sample (2 mL). Then sulfates were analyzed directly by high-performance liquid chromatography–ion-trap mass spectrometry (LC–MS/MS) with electrospray ionization in negative mode. Chromatographic separation of the targeted sulfoconjugates was achieved using a Waters XBridge C 18 column (150 mm × 4.6 mm I.D., 5 μm) with gradient elution. Assay validation demonstrated good performance for instance for T sulfate (TS) and E sulfate (ES) in terms of trueness (89–107%), repeatability (3.4–22%) and intermediate precision (5.8–22%) over the range of 2–200 ng/mL (corresponding to 1.5–147 ng/mL as free steroids). Results obtained on biological samples demonstrated the suitability of this analytical strategy for direct measurement of androgen sulfoconjugates and glucuroconjugates in human urine.

Investigation of levels and fate of triclosan in environmental waters from the analysis of gas chromatography coupled with ion trap mass spectrometry

A gas chromatography–ion trap mass spectrometry method was developed and optimized for the analysis of triclosan in water. Tandem mass spectrometry, along with an isotope dilution internal standard method, was used for the quantitative analysis of triclosan in water at low ng l −1 levels. The efficiencies obtained from liquid–liquid extraction and solid-phase extraction were compared. Average recoveries by the SPE pre-concentration using a C 18 cartridge were determined as 84–90%. The limit of detection was 2 ng l −1 for triclosan in water. The accuracy represented by relative analytical errors was −16% to −10%, and the precision by relative standard deviations was 3–15% ( n = 4). The method was successfully applied to analyze triclosan at concentrations between 4.1 ng l −1 and 117 ng l −1 in environmental water samples collected from rivers and coastal water in Hong Kong.

Determination of Tertiary‐butylhydroquinone and Its Metabolites in Rat Serum by Liquid Chromatography–Ion Trap Mass Spectrometry

A new method applying sensitive and selective liquid chromatography coupled with mass spectrometry (LC/MS/MS) for analyzing tertiary-butylhydroquinone (TBHQ) and its metabolites in rat serum was validated. Using an extracted ion chromatogram (EIC) of m/z 149, free TBHQ was observed in rat serum after dosing TBHQ at 350 mg/kg to male and female Sprague-Dawley (SD) rats. Four major metabolites of TBHQ were identified-a TBHQ-sulfate, two TBHQ-sulfate-derived substances and a TBHQ-glucuronide through MS(n) spectra. Besides its simplicity, the sample treatment allows one to obtain a very good recovery of analysts, namely around 95%. This result suggests that the method described here is useful for the analysis of TBHQ and its metabolites in rat serum. Moreover, the metabolism of TBHQ was investigated using the method. After oral administration, TBHQ appear to be more completely absorbed and bio-transformed by males than females, which may result in higher acute oral toxicity of TBHQ for males than females.

A Multi-residue Method for the Analysis of Pesticides and Pesticide Degradates in Water Using HLB Solid-phase Extraction and Gas Chromatography–Ion Trap Mass Spectrometry

A method was developed for the analysis of over 60 pesticides and degradates in water by HLB solid-phase extraction and gas-chromatography/mass spectrometry. Method recoveries and detection limits were determined using two surface waters with different dissolved organic carbon (DOC) concentrations. In the lower DOC water, recoveries and detection limits were 80%-108% and 1-12 ng/L, respectively. In the higher DOC water, the detection limits were slightly higher (1-15 ng/L). Additionally, surface water samples from four sites were analyzed and 14 pesticides were detected with concentrations ranging from 4 to 1,200 ng/L.

Metabonomics in cancer diagnosis: mass spectrometry-based profiling of urinary nucleosides from breast cancer patients

Modified nucleosides are formed post-transcriptionally in RNA. In cancer disease, the cell turnover and thus RNA metabolism is increased, yielding higher concentrations of excreted modified nucleosides. In the presented study, urinary ribonucleosides were used to differentiate between breast cancer patients and healthy volunteers. The nucleosides were extracted from urine samples using affinity chromatography and subsequently analyzed via liquid chromatography ion trap mass spectrometry (LC-IT-MS). The peak areas were related to the internal standard isoguanosine and to the urinary creatinine level. For bioinformatic pattern recognition we used the support vector machine. We examined 113 urine samples from breast cancer patients (stage Tis-T4) and 99 control samples from healthy volunteers. We achieved a sensitivity of 87.67% and a specificity of 89.90% when including 31 nucleosides. The medical metabonomics concept based on the urinary nucleoside profile reveals a significantly improved classification compared with currently applied breast cancer biomarkers such as CA15-3.

N, N-Dimethyltryptamine and dichloromethane: Rearrangement of quaternary ammonium salt product during GC–EI and CI-MS–MS analysis

N, N-Dimethyltryptamine (DMT) 1 is a simple tryptamine derivative with powerful psychoactive properties. It is abundant in nature and easily accessible through a variety of synthetic routes. Most work-up procedures require the use of organic solvents and halogenated representatives are often employed. DMT was found to be reactive towards dichloromethane, either during work-up or long term storage therein, which led to the formation of the quaternary ammonium salt N-chloromethyl-DMT chloride 2. Analysis of this side-product by gas chromatography ion trap mass spectrometry (GC–MS), both in electron and chemical ionisation tandem MS modes, gave only degradation products. For example, 2 could not be detected but appeared to have rearranged to 3-(2-chloroethyl)indole 3 and 2-methyltetrahydro-β-carboline 4, whereas HPLC analysis enabled the detection of 2. GC–MS is a standard tool for the fingerprinting of drug products. The identification of a particular synthetic route is based on the analysis of impurities, provided these side products can be established to be route-specific. The in situ detection of both 3 and 4 within a DMT sample may have led to erroneous conclusions with regards to the identification of the synthetic route.

Comparison of four extraction methods for the analysis of 24 pesticides in soil samples with gas chromatography–mass spectrometry and liquid chromatography–ion trap–mass spectrometry

With a view to analyse multiresidues of pesticides in soil samples, a new ultrasonic solvent extraction (USE) was compared to the European Norm DIN 12393 for foodstuff (extraction with acetone, partitioning with ethylacetate/cyclohexane and clean-up with gel permeation chromatography (GPC)), the QuECheRS method and a pressurised liquid extraction (PLE) method. Pesticides were analysed with both GC-MS and HPLC-MS/MS. The reference materials were the EUROSOIL 7 and its subsoil SO26 as well as a sea sand. All the substances were observed to be linear in the range of 4–800 ng g −1 for the European Norm DIN 12393, 7–1400 ng g −1 for the USE method and 20–4000 ng g −1 for the QueCheRS and the PLE methods. Limits of detection (LOD) and limits of quantification (LOQ) were with HPLC between 0.006 and 0.23 ng g −1 and between 0.022 and 0.77 ng g −1, respectively, with the exception of diuron (LOD up to 11.8 ng g −1; LOQ up to 39.2 ng g −1). With GC they ranged from 3.0 to 87.5 ng g −1 and from 10 to 292 ng g −1, respectively. All substances could be recovered with USE as well as with the QuECheRS method; the European Norm DIN 12393 could not recover carbendazim and metamitron; the PLE carbendazim, metamitron and monolinuron. For the remaining substances, recoveries at a 500 ng g −1 fortification level ranged from 10.9 to 96.3% with the USE. In comparison, the QuECheRS method was the most efficient extraction method with recoveries from 27.3 to 120.9%. It was followed by the European Norm DIN 12393 with recoveries between 6.8 and 108.1% and the PLE with recoveries from 12.2 to 153.2%. Recoveries were higher from the EUROSOIL 7 than from the SO 26. The repeatability expressed in term of standard deviation was below 20% for all substances and all materials.

Cyanobacterial bacteriohopanepolyol signatures from cultures and natural environmental settings

Cyanobacteria are ubiquitous, ecologically important and phylogenetically diverse components of the phytoplankton of marine and freshwater environments, as well as some extreme settings such as hot springs, and highly saline and ice covered lakes. They have also been shown to be amongst the most prolific sources of bacteriohopanepolyols (BHPs; pentacyclic triterpenoids produced by taxa within the bacterial domain and especially in the proteobacteria) and are considered to be the most environmentally significant source of C-2 methylated hopanoids. The compounds therefore have the potential for wide application in studies of the contemporary marine carbon cycle as well as providing a means of tracking cyanobacteria back through geological history where organic matter is well preserved. Here, we have used liquid chromatography ion-trap mass spectrometry to investigate the intact BHP distributions in cultured cyanobacteria (pure cultures and enrichment cultures) and in a variety of environmental settings. We present data on the detection and characterisation of BHP structures in 26 cultured cyanobacteria (ranging from marine and freshwater species to isolates from hydrothermal systems), 10 of which have not been tested for hopanoid production. Of the 58 strains of cyanobacteria studied to date, 49 have been shown to produce BHPs and 21 of them produce C-2 methylated BHPs. We show that, paradoxically, hopanoid production appears to be absent from the most prolific marine picocyanobacteria, although two important marine nitrogen fixing species, Trichodesmium and Crocosphaera, do produce BHPs. The diversity of BHP distributions in a range of environmental samples, including lake sediments, bacterial mats from lakes and hydrothermal springs, and samples from hot and cold deserts, including endoliths, hypoliths and small stromatolitic structures is also described.

Aroma profiles of five basil ( Ocimum basilicum L.) cultivars grown under conventional and organic conditions

A headspace solid-phase microextraction (HS-SPME) method coupled to gas chromatography–ion trap mass spectrometry (GC–ITMS) has been developed and applied for profiling of volatile compounds released from five Ocimum basilicum L. cultivars grown under both organic and conventional conditions. Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC–TOFMS) was employed for confirmation of identity of volatiles extracted from the basil headspace by SPME. Linalool, methyl chavicol, eugenol, bergamotene, and methyl cinnamate were the dominant volatile components, the relative content of which was found to enable differentiating between the cultivars examined. The relative content of some sesquiterpenes, hydrocarbons benzenoid compounds, and monoterpene hydrocarbons was lower in dried and frozen leaves as compared to fresh basil leaves. A sensory analysis of the all examined samples proved the differences between evaluated cultivars.

Evaluating on-line solid-phase extraction coupled to liquid chromatography–ion trap mass spectrometry for reliable quantification and confirmation of several classes of antibiotics in urban wastewaters

This study provides an evaluation of on-line solid-phase extraction (SPE) and liquid chromatography (LC) in combination with ion trap (IT) mass spectrometry for the simultaneous routine analysis of 12 antibiotics belonging to multiple classes together with carbamazepine and propranolol in sewage treatment effluents. The on-line SPE step warranted high sensitivity and high sample throughput while IT mass detection provided high selectivity for confirmation of positive samples. A single extraction procedure resulted in recoveries ranging from 40% to 120%. Limits of detection were in the 1–46 ng/L range, which constitutes an improvement of a factor of 10 with respect to the off-line SPE procedure.

Determination of triazine herbicides in aqueous samples by dispersive liquid–liquid microextraction with gas chromatography–ion trap mass spectrometry

A simple and rapid new dispersive liquid–liquid microextraction technique (DLLME) coupled with gas chromatography–ion trap mass spectrometric detection (GC–MS) was developed for the extraction and analysis of triazine herbicides from water samples. In this method, a mixture of 12.0 μL chlorobenzene (extraction solvent) and 1.00 mL acetone (disperser solvent) is rapidly injected by syringe into the 5.00 mL water sample containing 4% (w/v) sodium chloride. In this process, triazines in the water sample are extracted into the fine droplets of chlorobenzene. After centrifuging for 5 min at 6000 rpm, the fine droplets of chlorobenzene are sedimented in the bottom of the conical test tube (8.0 ± 0.3 μL). The settled phase (2.0 μL) is collected and injected into the GC–MS for separation and determination of triazines. Some important parameters, viz, type of extraction solvent, identity and volume of disperser solvent, extraction time, and salt effect, which affect on DLLME were studied. Under optimum conditions the enrichment factors and extraction recoveries were high and ranged between 151–722 and 24.2–115.6%, respectively. The linear range was wide (0.2–200 μg L −1) and the limits of detection were between 0.021 and 0.12 μg L −1 for most of the analytes. The relative standard deviations (RSDs) for 5.00 μg L −1 of triazines in water were in the range of 1.36–8.67%. The performance of the method was checked by analysis of river and tap water samples, and the relative recoveries of triazines from river and tap water at a spiking level of 5.0 μg L −1 were 85.2–114.5% and 87.8–119.4%, respectively. This method was also compared with solid-phase microextraction (SPME) and hollow fiber protected liquid-phase microextraction (HFP-LPME) methods. DLLME is a very simple and rapid method, requiring less than 3 min. It also has high enrichment factors and recoveries for the extraction of triazines from water.

Triclosan determination in water related to wastewater treatment

Triclosan in the waste, river and sea water samples collected in Hong Kong was analyzed by using gas chromatography–ion trap mass spectrometry method. 13C 12-triclosan was used as internal standard for the quantitative analysis. Water samples were prepared and cleaned-up by using a C 18 solid-phase extraction cartridge. The recoveries of triclosan in spiked coastal water at three different concentrations ranged from 83 to 110%. The method detection limit was 0.25 ng/L for triclosan in 1-L water and the relative standard deviations and relative error were less than 11.0 and 12.3%, respectively ( n = 3). The method was successfully applied to analyze water samples collected from rivers, coastal water bodies and wastewater treatment plants at ng/L levels.

Analysis of furan in foods by headspace solid-phase microextraction–gas chromatography–ion trap mass spectrometry

A headspace-solid-phase microextraction (HS-SPME) coupled to gas chromatography–ion trap mass spectrometry (GC–IT-MS) method is proposed for the analysis of furan in different heat-treated carbohydrate-rich food samples. The extraction efficiency of six commercially available fibres was evaluated and it was found that a 75 μm carboxen/polydimethylsiloxane coating was the most suitable for the extraction of the furan. Parameters affecting the efficiency of HS-SPME procedure such as extraction temperature and time, ionic strength, headspace and aqueous volume ratio ( V h/ V w), desorption temperature and time, were optimized. Quality parameters were established using spiked water and food samples. Linearity ranged between 0.02 and 0.5 ng g −1 and run-to-run and day-to-day precisions for food samples were lower than 6% and 10%, respectively. The limit of detection (LOD) of the method is sample dependent and ranged from 8 to 70 pg g −1, while the limit of quantification is from 30 to 250 pg g −1. Isotope dilution using furan-d 4 is proposed for furan determination providing similar results to those obtained by standard addition with internal standard (US Food and Drug Administration method). The developed HS-SPME–GC–IT-MS method was applied to the analysis of furan in different Spanish food samples from a local market, and concentrations ranging from 0.17 to 2279 ng g −1 were found.

Identification and characterization of supercritical fluid extracts of Rhizoma Chuanxiong by high performance liquid chromatography ion trap mass spectrometry

The main constituents, senkyunolide A, Z-ligustilide, neocnidilide, 3-butylphthalide, and ligustilide dimers, in supercritical CO2 fluid extracts of Rhizoma Chuanxiong, a popular Chinese traditional medicine, have been identified and characterized by high performance liquid chromatography tandem mass spectrometry. Separations were carried out on an Agilent (ECLIPSE XDB) C18 analytical column by gradient elution with 0.25% acetic acid and methanol (containing 0.25% acetic acid). An Agilent 1100 series LC/MSD XCT system was operated under positive ESI and auto MS/MS modes for mass spectrometric analysis. Collision-induced dissociation (CID) fragmentations of these phthalides have been investigated and elucidated. Phthalides have primarily undergone two ESI CID pathways: side-chain cleavage with losses of alkenes and ring-opening with eliminations of H2O followed by losses of CO. Direct neutral loss of CO has not been observed. Sodium adduct ions have demonstrated completely different CID pathways.