Identification of compounds from Etonia rosemary (Conradina etonia)

Mosquitoes transmit pathogens that result in diseases harmful to human, livestock, and wildlife hosts. Numerous measures can be used to reduce insect-borne disease risk to humans, and one approach is the use of topical repellents to prevent host-seeking arthropods from taking a blood meal. A current emphasis in the development of new repellents is that they be safe. Therefore, natural products sources are increasingly being explored. Compounds from plants of the mint family (Lamiaceae) have been demonstrated to be insect repellents. This study examines compounds from Etonia rosemary (Conradina etonia) to identify compounds for examination as insect repellents. Samples of Etonia rosemary were passively extracted with hexane, dichloromethane, and methanol and analyzed by GC/MS. This extraction method was chosen to eliminate thermal degradation of plant components that can occur during the distillation procedure. Additional headspace volatile compounds from this plant were identified using microscale purge-and-trap GC/MS. A variety of terpenes, terpenic alcohols, ketones, and aldehydes were identified in the extracts with terpenes and short-chained aldehydes detected in greatest abundance.     

Analysis of the essential oil from aerial parts of Eupatorium cannabinum subsp. corsicum (L.) by gas chromatography with electron impact and chemical ionization mass spectrometry

Eupatorium cannabinum subsp. corsicum (L.), an aromatic plant, is an endemic subspecies from Corsica. The essential oil from aerial parts of E. cannabinum subsp. corsicum was studied by GC, GC/MS and 13C NMR. One hundred and forty-seven components were identified representing 93.6% of the total amount. The main constituents are germacrene D (28.5%), alpha-phellandrene (19.0%) and para-cymene (5.2%). A particularity of this essential oil is the presence of monoterpene esters derived from nerol, lavandulol, borneol, thymol and 8,9-dehydrothymol. These compounds have been investigated using GC/MS in different ionization modes like electron impact (EI), positive chemical ionization (PCI) and negative chemical ionization (NCI).     

A simple, rapid and sensitive method for determination of aldehydes in human blood by gas chromatography/mass spectrometry and solid-phase microextraction with on-fiber derivatization

Aldehydes are considered potential markers for enhanced oxidative stress and have been proposed as a diagnostic measure of cancer status. Do to their volatility and activity, it is very difficult to accurately measure aldehydes in human blood. In the present work, gas chromatography/mass spectrometry (GC/MS) and solid-phase microextraction (SPME) with on-fiber derivatization was developed for determination of aldehydes in human blood. O-(2,3,4,5,6-Pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) in aqueous solution was first adsorbed by a SPME fiber, and then the aldehydes in blood samples were headspace extracted by the SPME fiber and rapidly derivatized with PFBHA on the SPME fiber. Finally, the oximes formed were desorbed and detected by GC/MS in electron ionization (EI) mode. Validation of the present method was carried out, and the method was applied to quantitative analysis of the aldehydes in lung cancer blood. The results demonstrated that GC/MS and SPME with on-fiber derivatization is a simple, rapid, sensitive and solvent-free method for the determination of aldehydes in human blood.     

Headspace solid-phase microextraction combined with GC×GC-TOFMS for the analysis of volatile compounds of Coptis species rhizomes

In this study, the investigation of the volatile compounds of dried rhizomes of Coptis chinensis Franch, C. deltoidea C. Y. Cheng et Hsiao, and C. teeta Wall was carried out to complete the chemical composition of these valuable natural products. Volatile profiles were established and compared after headspace solid-phase microextraction (HS-SPME) using a polydimethylsiloxane/divinylbenzene (PDMS/DVB, 65 μm) fibre coupled to comprehensive 2D gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS). Analyses were performed and compared on two column-phase combinations (non-polar/polar and polar/non-polar). The majority of the identified compounds eluted as well-separated (pure) components as a result of high-resolution capability of the GC×GC method, which significantly reduces co-elution. Therefore, this increases the likelihood that pure mass spectra can be obtained. More than 290 volatile and semi-volatile organic compounds were tentatively characterized by means of GC×GC in tandem with TOFMS detection. Improved result interpretations were obtained in terms of compound classification based on the organized structure of the peaks of structurally related compounds in the GC×GC contour plot. These compounds are distributed over the chemical groups of hydrocarbons, acids, alkenes, alkynes, aldehydes, ketones, alcohols, esters, furans, and terpenoids. Among all the chemical groups, terpenoids present the higher number of identified compounds (44), alkenes (41), and aldehydes and ketones (28). This study completed the volatile phytochemical analysis of the headspace composition of various Coptis species rhizomes, and should serve as a means to identify the difference between the rhizomes and may also be useful to confirm individual species based on their volatile chemical profile.     

两种离子源技术气相色谱-质谱法检测茶叶中酰胺类除草剂的残留量

采用电子轰击(EI)和负化学(NCI)离子源两种离子源技术气相色谱-质谱联用法(GC     

High Sensitivity Negative Ion GC-MS Method for Detection of Estrogens in Urine

A sensitive negative chemical ionization (NCI) gas-chromatography/mass spectrometry (GC/MS) method for the detection of estrogens is described. After hydrosis and clean-up by C₁₈ ODS solid phase extraction (SPE) cartridge, the extracts obtained were derivatized with heptafluorobutyric anhydride and analyzed in the negative ion mode by GC/MS. Stability of derivatives was good. Selected ion monitoring (SIM) mode was applied to increase the sensitivity and, when possible, the higher m/z ions were selected to improve identification. The detection limit of the HFB esters in NCI using SIM was below 10 femtograms.     

Development of a multiresidue method for analyzing herbicide and fungicide residues in bovine milk based on solid-phase extraction and liquid chromatography-tandem mass spectrometry

The adverse effect of reactive chemical residues on the quality of drug products has necessitated the determination of low-molecular-weight aldehydes in pharmaceutical excipients. An analytical methodology for the detection of trace amounts of C1-C8 aliphatic aldehydes and benzaldehyde in excipients is described. The proposed procedure is based on the derivatization of aldehydes in aqueous solution with O-2,3,4,5,6-(pentafluorobenzyl) hydroxylamine hydrochloride (PFBHA), followed by static headspace gas chromatographic (SHS-GC) analysis of PFBHA aldehyde oximes with negative chemical ionization (NCI) MS detection. The method developed was demonstrated to be simple, selective, sensitive, and was successfully applied to the screening of aldehydes at sub-microg/g levels in over 30 typical excipients. The most abundant aldehydes found in the samples were formaldehyde and acetaldehyde, for which a rapid and reliable routine quantification method by readily available SHS-GC instrumentation coupled with flame-ionization detection was also developed and validated.     

Simple and sensitive method for determination of nitrated polycyclic aromatic hydrocarbons in diesel exhaust particles by gas chromatography-negative ion chemical ionisation tandem mass spectrometry

An extremely simple and sensitive method was developed for determination of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs; mono-nitro-PAHs and dinitropyrenes) in diesel exhaust particles (DEPs) by gas chromatography-negative ion chemical ionisation tandem mass spectrometry (GC/NCI/MS/MS). We used two types of column in GC/NCI/MS/MS analysis. A polar column was used for determination of mono-nitro-PAHs, and a non-polar column was used for determination of dinitropyrenes and mono-nitro-PAHs except nitrofluoranthenes. The proposed method requires no clean-up procedure. The limits of detection ranged from 0.01 to 0.09 pg for all compounds tested. The applicability of the method to DEP samples was validated using diesel particulate standard reference materials (SRMs). Although DEPs contain complex matrices, all compounds could be detected easily in SRM2975 (diesel particulate matter) and SRM1975 (diesel particulate extract) without a clean-up procedure. The RSDs were less than 5% for all compounds examined. The quantitative results for SRMs exhibited good agreement with the available data in the literature. These results indicate that the proposed GC/NCI/MS/MS method is useful for determination of nitro-PAHs in DEP samples.     

微波辅助萃取-气相色谱-负化学电离/电子轰击电离-飞行时间质谱法测定烟草中农药残留

建立了微波辅助萃取结合气相色谱-飞行时间质谱(GC-TOF MS)技术在负化学电离(NCI)源和电子轰击电离(EI)源两种模式下测定烟草中24种农药残留的分析方法。烟叶样品于100℃下用二氯甲烷-正己烷(3:1, v/v)混合溶剂微波萃取10 min,萃取液经弗罗里硅土固相萃取柱净化后进行检测分析。在NCI源和EI源质谱模式下,24种农药的线性关系均良好(r²>0.99),相对标准偏差分别小于8.6%和9.1%,定量限分别为0.3~6.9 μg/kg和10.2~44.9 μg/kg,加标回收率分别为75.2%~94.8%和75.0%~95.1%。比较两种离子源模式下的色谱图和质谱图,NCI源模式较EI源模式的选择性好、灵敏度高、基质干扰小、图谱简单易于解析,检出限低一个数量级以上,在分析低含量、复杂基质的样品时更具优势。     

Analysis of aldehydes in excipients used in liquid/semi-solid formulations by gas chromatography-negative chemical ionization mass spectrometry

Monitoring of low-molecular-weight aldehyde levels in excipients used in liquid/semi-solid based capsule (LFC) dosage forms plays a critical role in the development of these pharmaceutical products. A simple, sensitive and specific method based on gas chromatography coupled with mass spectrometry (GC-MS) utilizing an Rtx-5MS capillary column was developed and validated for the detection and quantification of C1-C8 aliphatic aldehydes in LFC excipients at sub-microg/g levels. The proposed procedure is based on the derivatization of aldehydes in 10:1 (v/v) acetonitrile:water with O-2,3,4,5,6-(pentafluorobenzyl) hydroxylamine hydrochloride (PFBHA), followed by direct GC analysis of aldehyde-PFBHA-oxime derivatives with negative chemical ionization (NCI) MS detection. The method developed was successfully applied to the analysis of short chain aldehydes in 30 typical LFC excipients. An example case study on the formation and growth of aldehydes in these excipients under accelerated storage conditions is also reported.     

Determination of anabolic steroids by gas chromatography/negative-ion chemical ionization mass spectrometry and gas chromatography/negative-ion chemical ionization tandem mass spectrometry with heptafluorobutyric anhydride derivatization

A gas chromatography/mass spectrometry (GC/MS) method is described which uses negative ion chemical ionization (NCI) and tandem mass spectrometry (MS/MS) for the determination of eight anabolic steroids in human urine. Eight anabolic steroids were derivatized by heptafluorobutyric anhydride (HFBA), and were determined using GC/NCI-MS and GC/NCI-MS/MS. The linear correlation coefficients for calibration in NCI-MS/MS were in the range 0.9880-0.9988. This method of derivatization with HFBA for use with GC/NCI was useful in determinations of 19-norandrosterone, boldenone, 19-noretiocholanolone, 2-methylandrosterone, nandrolone, 1-methyleneandrosterone, 1-methylandrosterone, 4-dihydroboldenone and mesterolone. The detection limits of this procedure were 5-20 ppb at a signal-to-noise (S/N) ratio of 3.     

固相萃取-气相色谱/负化学电离-质谱法测定酸水解植物蛋白及酱油中的3-氯-1,2-丙二醇

建立了酸水解植物蛋白及酱油中3-氯-1,2-丙二醇(3-MCPD)的固相萃取-气相色谱/质谱测定方法。样品经Aoisa-HBL固相萃取柱萃取,正己烷-乙酸乙酯净化提取,七氟丁酰咪唑衍生,衍生物经气相色谱/负化学电离-质谱（GC/NCI-MS）选择离子模式(SIM)检测,外标法定量。3-MCPD的定量检测限为0.5 μg/kg,平均回收率为92.2%～97.4%,相对标准偏差为3.6%～10.9%。该方法检测灵敏度高,定性定量准确。     

Comparison of different extraction methods: steam distillation, simultaneous distillation and extraction and headspace co-distillation, used for the analysis of the volatile components in aged flue-cured tobacco leaves

Steam distillation (SD), simultaneous distillation and extraction (SDE) and headspace co-distillation (HCD) were compared here for their effectiveness in the extraction of volatile compounds from tobacco. The different grades of aged flue-cured tobacco leaves extracted by the three methods respectively were analyzed using GC-MS. Mass spectra or authentic compounds were used to identify around 408 components in various volatile fractions. On the one hand, the qualitative comparison showed that more compounds were detected in HCD extract (391 components) than in SDE extract (377 components), and the approximately quantitative analysis showed that the total amount of volatile components in SDE extract (445.48 microg/g) was much more than that in HCD extract (315.72 microg/g). But on the other hand, HCD was the most efficient for nearly all the highly volatile compounds among the three methods. As to low-volatile compounds such as lactones, long chain aldehydes, ketones, alcohols, and esters, more was detected in SDE extract than in HCD extract. The SD method (322 components, total amount 228.42 microg/g) was the lowest sensitive to all compounds except semi-volatile fatty acids among the three methods.     

Identification of volatile components in yak butter using SAFE, SDE and HS-SPME-GC/MS

The volatile components of yak butter were isolated by solvent-assisted flavour evaporation (SAFE), simultaneous distillation extraction (SDE; dichloromethane and diethyl ether as solvent, respectively) and headspace solid-phase microextraction (HS-SPME; CAR/PDMS, PDMS/DVB and DVB/CAR/PDMS fibre extraction, respectively) and were analysed by GC/MS. A total of 83 volatile components were identified under six different conditions, including 28 acids, 12 esters, 11 ketones, 10 lactones, 10 alcohols, 4 other compounds, 2 aldehydes, 2 unsaturated aldehydes, 1 furan, 1 sulphur-containing compound, 1 unsaturated alcohol and 1 unsatruated ketone. Among them, 51 were identified by SAFE, 58 by SDE (45 with dichloromethane as solvent and 41 with diethyl ether as solvent) and 40 by HS-SPME (26 with CAR/PDMS; 26 with PDMS/DVB and 32 with DVB/CAR/PDMS). Three pretreatment methods were compared to show that the volatile components obtained using different methods varied greatly, both in terms of categories and in content. Therefore, a multi-pretreatment method should be adopted, together with GC/MS. A total of 25 aroma-active compounds were detected by gas chromatography-olfactometry, among which 20 aroma-active compounds were found by SDE (14 with dichloromethane as solvent and 14 with diethyl ether as solvent) and 17 by SAFE.     

Headspace solid-phase microextraction combined with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry for the determination of volatile compounds from marine salt

In this work, a methodology to characterise the volatile and semi-volatile compounds from marine salt by headspace solid-phase microextraction (HS-SPME) and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC/TOFMS) was developed. Samples from two saltpans of Aveiro, in Portugal, with diverse locations, obtained over three years (2004, 2005, and 2007) were analysed. A 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane SPME fibre was used. The volatiles present in the headspace of the solid salt samples (crystals) were equilibrated overnight at 60 °C and extracted for 60 min prior to injection in the GC × GC/TOFMS. 157 compounds, distributed over the chemical groups of hydrocarbons, aldehydes, esters, furans, haloalkanes, ketones, ethers, alcohols, terpenoids, C₁₃ norisoprenoids, and lactones were detected across the samples. Furans, haloalkanes and ethers were identified for the first time in marine salt. The large number of co-elutions on the first column that were resolved by the GC × GC system revealed the complexity of marine salt volatile composition. The existence of a structured 2D chromatographic behaviour according to volatility, in the first dimension (¹D), and primarily polarity, in the second dimension (²D), was demonstrated, allowing more reliable identifications. The resolution and sensitivity of GC × GC/TOFMS enabled the separation and identification of a higher number of volatile compounds compared to GC–qMS, allowing a deeper characterisation of this natural product.     

Identification of volatiles from pineapple (Ananas comosus L.) pulp by comprehensive two-dimensional gas chromatography and gas chromatography/mass spectrometry

Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications.     

Unambiguous detection of astaxanthin and astaxanthin fatty acid esters in krill (Euphausia superba Dana)

HPLC atmospheric pressure chemical ionization (APCI)/MS, GC MS, HPLC diode array detection (DAD), and NMR were used for the identification of astaxanthin and astaxanthin fatty acid esters in krill (Euphausia superba Dana). Matrix solid phase dispersion was applied for the extraction of the carotenoids. This gentle and expeditious extraction technique for solid and viscous samples leads to distinct higher enrichment rates than the conventional liquid-liquid extraction. The chromatographic separation was achieved employing a C30 RP column that allows the separation of shape-constrained geometrical isomers. A methanol/tert-butylmethyl ether/water gradient was applied. (all-E) Astaxanthin and the geometrical isomers were identified by HPLC APCI/MS, by coelution with isomerized authentical standard, by UV spectroscopy (DAD), and three isomers were unambiguously assigned by microcoil NMR spectroscopy. In this method, microcoils are transversally aligned to the magnetic field and have an increased sensitivity compared to the conventional double-saddle Helmholtz coils, thus enabling the measurement on small samples. The carotenol fatty acid esters were saponified enzymatically with Lipase type VII from Candida rugosa. The fatty acids were detected by GC MS after transesterification, but also without previous derivatization by HPLC APCI/MS. C14:0, C16:0, C16:1, C18:1, C20:0, C20:5, and C22:6 were found in astaxanthin monoesters and in astaxanthin diesters. (all-E) Astaxanthin was identified as the main isomer in six fatty acid ester fractions by NMR. Quantitation was carried out by the method of internal standard. (13-cis) Astaxanthin (70 microg/g), 542 microg/g (all-E) astaxanthin, 36 microg/g unidentified astaxanthin isomer, 62 microg/g (9-cis) astaxanthin, and 7842 microg/g astaxanthin fatty acid esters were found.     

Analysis of aldehydes and ketones from beer as O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine derivatives

O-(2,3,4,5,6-pentafluorobenzyl)Hydroxylamine (PFBOA) was used as a derivatization reagent for carbonyl compounds in beer. Derivatization was carried out in aqueous solution without extraction or concentration of the sample. The effects of antifoam agent, reaction time and pH on the reaction efficiency were studied. Antifoam RD, a silicone polymer-based antifoam reagent, was the best antifoaming agent since it did not cause interferences. Reaction time studies showed that the yield of aldehydes increased up to 12 hr and then decreased slightly. The yield of 3-hydroxybutanone, a test compound for ketones, increased throughout the 48 hr test period. The natural pH of beer (ca. 4.5) was favourable for the determination of carbonyl compounds as PFBOA derivatives. Higher pH values caused yield losses and some compounds, such as butanedione, 2,3-pentanedione and 5-hydroxymethyl-2-furfural, could not be measured at all in neutral or basic conditions. Carbonyl compounds were identified by GC-MS, using three different ionization techniques, electron impact ionization, chemical ionization, and negative chemical ionization. The formation of the protonated molecules by ammonia chemical ionization and formation of the negative molecular ions and [M - HF](-.) ions by negative chemical ionization permitted reliable identification of the various carbonyl compounds studied. Sixteen carbonyl compounds from the 32 standard compounds were identified in beer and 11 of the most significant were quantitated using GC-ECD. Reproducibility of quantitation for beer samples was good, the relative standard deviations varied between 2.7 and 6.7 %. The estimated detection limits of the PFBOA derivatives of the carbonyl compounds in beer varied in the range of 0.01-1 microg/dm(3).     

Enhanced signal generation for use in the analysis of synthetic pyrethroids using chemical ionization tandem quadrupole ion trap mass spectrometry

Synthetic pyrethroids fragment extensively under electron ionization (EI) conditions to give low mass ions, most of them with the same m/z ratios. This fragmentation is primarily due to the labile ester linkage found in these compounds. In this research we established the best gas chromatography (GC) conditions in the EI mode that served as a benchmark in the development of a chemical ionization (CI) protocol for ten selected synthetic pyrethroids. Based on proton affinity data, several reagent gases were evaluated in the positive CI ionization mode. Methanol was found to produce higher average ion counts relative to the other gases evaluated, which led to the development of an optimized method consisting of selective ejection chemical ionization (SECI) and MS/MS. Standard stainless steel ion trap electrodes produced significant degradation of chromatographic performance on late eluting compounds, which was attributed to electrode surface chemistry. A dramatic improvement in signal-to-noise (S/N) ratios was observed when the chromatographically inert Silcosteel® coated electrodes were used. The resulting method, that has significant S/N ratio improvements resulting from a combination of septum programmable injections (SPI), optimized CI and inert Silcosteel®-coated electrodes, was used to determine instrument detection limits.     

GC-MS/MS multi-residue method for the determination of organochlorine pesticides,polychlorinated biphenyls and polybrominated diphenyl ethers in human breast tissues

In this work, a multiresidue method for the quantification and confirmation of around 30 organohalogenated compounds in human breast tissue samples has been developed. Analytes tested included organochlorine (OC) (pesticides and polychlorinated biphenyls) and organobromine (OBr) (polybrominated diphenyl ether) compounds. The approach is based on a simple extraction with hexane, followed by a SPE clean-up using silica cartridges and final measurement by GC coupled to triple quadrupole MS. Analyses were performed in both ionizations, electron impact (EI) (selected reaction monitoring (SRM) mode) and negative chemical ionization (NCI) (selected ion recording (SIR) mode). Three isotopically labeled standards were added before extraction and used as surrogates: HCB-¹³C₆, lindane-D₆ and p,p′-DDE-D₈. The method was validated in terms of accuracy, precision, LOQ and LOD and confirmation reliability, using breast tissue spiked at three concentration levels in the range 1–100 ng/g for OC compounds and at two levels 0.1 and 10 ng/g for OBr compounds (0.5 and 50 ng/g for BDE 209). The usefulness of the developed method was tested by the analysis of real human samples, giving as a result the detection of several OC and OBr compounds in different samples analyzed. The acquisition of at least two SRM transitions (in EI) or ions (in NCI) per analyte allowed positive findings to be confirmed by accomplishment of ion ratios between the quantification and the confirmation transitions or ions.