Detection of volatile organic compounds in the headspace above mold fungi by GC‐soft X‐radiation–based APCI‐MS

Mold fungi on malting barley grains cause major economic loss in malting and brewery facilities. Possible proxies for their detection are volatile and semivolatile metabolites. Among those substances, characteristic marker compounds have to be identified for a confident detection of mold fungi in varying surroundings. The analytical determination is usually performed through passive sampling with solid phase microextraction, gas chromatographic separation, and detection by electron ionization mass spectrometry (EI‐MS), which often does not allow a confident determination due to the absence of molecular ions. An alternative is GC‐APCI‐MS, generally, allowing the determination of protonated molecular ions. Commercial atmospheric pressure chemical ionization (APCI) sources are based on corona discharges, which are often unspecific due to the occurrence of several side reactions and produce complex product ion spectra. To overcome this issue, an APCI source based on soft X‐radiation is used here. This source facilitates a more specific ionization by proton transfer reactions only. In the first part, the APCI source is characterized with representative volatile fungus metabolites. Depending on the proton affinity of the metabolites, the limits of detection are up to 2 orders of magnitude below those of EI‐MS. In the second part, the volatile metabolites of the mold fungus species Aspergillus, Alternaria, Fusarium, and Penicillium are investigated. In total, 86 compounds were found with GC‐EI/APCI‐MS. The metabolites identified belong to the substance classes of alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, terpenes, and sesquiterpenes. In addition to substances unspecific for the individual fungus species, characteristic patterns of metabolites, allowing their confident discrimination, were found for each of the 4 fungus species. Sixty‐seven of the 86 metabolites are detected by X‐ray–based APCI‐MS alone. The discrimination of the fungus species based on these metabolites alone was possible. Therefore, APCI‐MS in combination with collision induced dissociation alone could be used as a supervision method for the detection of mold fungi.     

Liquid chromatography/negative ion atmospheric pressure photoionization mass spectrometry: a highly sensitive method for the analysis of organic explosives

Gas chromatography/mass spectrometry (GC/MS) is applied to the analysis of volatile and thermally stable compounds, while liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI‐MS) and liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) are preferred for the analysis of compounds with solution acid‐base chemistry. Because organic explosives are compounds with low polarity and some of them are thermally labile, they have not been very well analyzed by GC/MS, LC/APCI‐MS and LC/ESI‐MS. Herein, we demonstrate liquid chromatography/negative ion atmospheric pressure photoionization mass spectrometry (LC/NI‐APPI‐MS) as a novel and highly sensitive method for their analysis. Using LC/NI‐APPI‐MS, limits of quantification (LOQs) of nitroaromatics and nitramines down to the middle pg range have been achieved in full MS scan mode, which are approximately one order to two orders magnitude lower than those previously reported using GC/MS or LC/APCI‐MS. The calibration dynamic ranges achieved by LC/NI‐APPI‐MS are also wider than those using GC/MS and LC/APCI‐MS. The reproducibility of LC/NI‐APPI‐MS is also very reliable, with the intraday and interday variabilities by coefficient of variation (CV) of 0.2–3.4% and 0.6–1.9% for 2,4,6‐trinitrotoluene (2,4,6‐TNT). Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of hydroxylated polybrominated diphenyl ether metabolites by liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

Hydroxylated polybrominated diphenyl ether (OH‐PBDEs) metabolites have the potential to cause endocrine disruption as well as other health effects. Currently, gas chromatography/mass spectrometry (GC/MS) after derivatization is used for the analysis of OH‐PBDEs. However, there is a need for the direct analysis of OH‐PBDEs at relatively low concentrations in environmental and biological samples. Liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI‐MS/MS) was evaluated for the analysis of nine OH‐PBDEs, ranging from tri‐ to hexabrominated. Separation of the nine isomeric metabolites was achieved with reversed‐phase liquid chromatography, followed by detection by APCI‐MS in negative mode. Notably, a significant decrease in ionization was observed in 6‐hydroxyl‐substituted PBDE metabolites in the presence of an ortho‐substituted bromine, relative to the other hydroxylated metabolites. This is probably due to the formation of dioxins in the source as a result of the high‐temperature conditions, which prevented ionization by hydrogen abstraction. The MS/MS experiments also provided evidence of the neutral losses of HBr and Br₂, indicating the possible use of neutral loss scanning and selected reaction monitoring (SRM) for the screening of brominated metabolites in samples. The applicability of LC/APCI‐MS/MS was demonstrated for the analysis of metabolites of BDEs 47 and 99 formed in human liver microsomes. The LC/APCI‐MS/MS method was able to detect metabolites that had previously been identified by GC/MS following derivatization. Copyright © 2010 John Wiley & Sons, Ltd.     

Buffer gas additives (modifiers/shift reagents) in ion mobility spectrometry: Applications,predictions of mobility shifts,and influence of interaction energy and structure

Ion mobility spectrometry (IMS) is an analytical technique used for fast and sensitive detection of illegal substances in customs and airports, diagnosis of diseases through detection of metabolites in breath, fundamental studies in physics and chemistry, space exploration, and many more applications. Ion mobility spectrometry separates ions in the gas‐phase drifting under an electric field according to their size to charge ratio. Ion mobility spectrometry disadvantages are false positives that delay transportation, compromise patient's health and other negative issues when IMS is used for detection. To prevent false positives, IMS measures the ion mobilities in 2 different conditions, in pure buffer gas or when shift reagents (SRs) are introduced in this gas, providing 2 different characteristic properties of the ion and increasing the chances of right identification. Mobility shifts with the introduction of SRs in the buffer gas are due to clustering of analyte ions with SRs. Effective SRs are polar volatile compounds with free electron pairs with a tendency to form clusters with the analyte ion. Formation of clusters is favored by formation of stable analyte ion‐SR hydrogen bonds, high analytes' proton affinity, and low steric hindrance in the ion charge while stabilization of ion charge by resonance may disfavor it. Inductive effects and the number of adduction sites also affect cluster formation. The prediction of IMS separations of overlapping peaks is important because it simplifies a trial and error procedure. Doping experiments to simplify IMS spectra by changing the ion‐analyte reactions forming the so‐called alternative reactant ions are not considered in this review and techniques other than drift tube IMS are marginally covered.     

Development of two‐dimensional gas chromatography (GC×GC) coupled with Orbitrap‐technology‐based mass spectrometry: Interest in the identification of biofuel composition

Comprehensive gas chromatography (GC) has emerged in recent years as the technique of choice for the analysis of volatile and semivolatile compounds in complex matrices. Coupling it with high‐resolution mass spectrometry (MS) makes a powerful tool for identification and quantification of organic compounds. The results obtained in this study showed a significant improvement by using GC×GC‐EI‐MS in comparison with GC‐EI‐MS; the separation of chromatogram peaks was highly improved, which facilitated detection and identification. However, the limitation of Orbitrap mass analyzer compared with time‐of‐flight analyzer is the data acquisition rate; the frequency average was about 25 Hz at a mass resolving power of 15.000, which is barely sufficient for the proper reconstruction of the narrowest chromatographic peaks. On the other hand, the different spectra obtained in this study showed an average mass accuracy of about 1 ppm. Within this average mass accuracy, some reasonable elemental compositions can be proposed and combined with characteristic fragment ions, and the molecules can be identified with precision. At a mass resolving power of 7.500, the scan rate reaches 43 Hz and the GC×GC‐MS peaks can be represented by more than 10 data points, which should be sufficient for quantification. The GC×GC‐MS was also applied to analyze a cellulose bio‐oil sample. Following this, a highly resolved chromatogram was obtained, allowing EI mass spectra containing molecular and fragment ions of many distinct molecules present in the sample to be identified.     

Mass spectrometric behavior of anabolic androgenic steroids using gas chromatography coupled to atmospheric pressure chemical ionization source. Part I: Ionization

The detection of anabolic androgenic steroids (AAS) is one of the most important topics in doping control analysis. Gas chromatography coupled to (tandem) mass spectrometry (GC–MS(/MS)) with electron ionization and liquid chromatography coupled to tandem mass spectrometry have been traditionally applied for this purpose. However, both approaches still have important limitations, and, therefore, detection of all AAS is currently afforded by the combination of these strategies. Alternative ionization techniques can minimize these drawbacks and help in the implementation of a single method for the detection of AAS. In the present work, a new atmospheric pressure chemical ionization (APCI) source commercialized for gas chromatography coupled to a quadrupole time‐of‐flight analyzer has been tested to evaluate the ionization of 60 model AAS. Underivatized and trimethylsylil (TMS)‐derivatized compounds have been investigated. The use of GC–APCI–MS allowed for the ionization of all AAS assayed irrespective of their structure. The presence of water in the source as modifier promoted the formation of protonated molecules ([M+H]⁺), becoming the base peak of the spectrum for the majority of studied compounds. Under these conditions, [M+H]⁺, [M+H‐H₂O]⁺ and [M+H‐2·H₂O]⁺ for underivatized AAS and [M+H]⁺, [M+H‐TMSOH]⁺ and [M+H‐2·TMSOH]⁺ for TMS‐derivatized AAS were observed as main ions in the spectra. The formed ions preserve the intact steroid skeleton, and, therefore, they might be used as specific precursors in MS/MS‐based methods. Additionally, a relationship between the relative abundance of these ions and the AAS structure has been established. This relationship might be useful in the structural elucidation of unknown metabolites. Copyright © 2014 John Wiley & Sons, Ltd.     

固相微萃取-气相色谱/质谱测定植物叶片中的挥发性物质

采用固相微萃取（SPME)方法吸附植物叶片中的挥发性物质,然后采用气相色谱/质谱法（GC/MS）分析了挥发性物 质的成分。在45 ℃水浴温度下,采用Polyacrylate(85 μm)固相微萃取头,在广口瓶中植物叶片的上方顶空吸附60 min,然后进行GC/MS分析。结果表明,植物叶片中的挥发性物质得到了很好的分离,受山楂叶螨(Tetraychus vienneis) 危害严重的植物的完好叶片中的挥发性物质均含有顺-3-己烯-1-醇乙酸酯、顺-3-己烯-1-醇丁酸酯和α-法呢烯,且含量 较大。初步确定这些物质是对山楂叶螨具有引诱作用的主要物质,从而为利用天然生物活性物质防治山楂叶螨提供了理论 依据。     

Characterisation of the flavour profile from Graciano Vitis vinifera wine variety by a novel dual stir bar sorptive extraction methodology coupled to thermal desorption and gas chromatography–mass spectrometry

The aim of this work was to develop a new analytical technique for the study of the organoleptic compounds (flavour profile) of the Graciano Vitis vinifera wine variety. The cv. Graciano is a singular variety of red grapes with its origins in La Rioja and Navarra (northern Spain). This variety transfers an intense red colour, aroma and high acidity to musts and provides greater longevity and, consequently, a better capacity for ageing wine. A new dual-stir bar sorptive extraction approach coupled with thermal desorption (TD) and GC–MS has been used to extract the volatile and semivolatile compounds. In this extraction step, the optimal values for the experimental variables were obtained through the Response Surface Methodology (RSM). Full scan chromatogram data were evaluated with two deconvolution software tools, and the results were compared. The volatile and semivolatile components were identified with an MS match ≥80%. As a result, the flavour metabolome of the Graciano Vitis vinifera wine variety was obtained, and 205 metabolites were identified using different databases. These metabolites were grouped into esters, acids, alcohols, nitrogen compounds, furans, lactones, ketones, aldehydes, phenols, terpenes, norisoprenoids, sulphur compounds, acetals and pyrans. The majority of the metabolites observed had already been reported in the literature; however, this work also identified new, previously unreported metabolites in red wines, which may be characteristic of the Graciano variety.     

Atmospheric pressure chemical ionization in gas chromatography-mass spectrometry for the analysis of persistent organic pollutants

Atmospheric pressure chemical ionization (APCI) was primarily applied as the ion source for liquid chromatography-mass spectrometry (LC–MS). While APCI started to be used in gas chromatography-mass spectrometry (GC–MS) in 1970s, GC-APCI-MS was not widely used until recently. As a soft ionization technique, APCI provides highly diagnostic molecular ions, which is favored for the wide-scope screening. With the capability of tandem mass spectrometry (MS/MS), GC-APCI-MS methods with high sensitivity and selectivity have been developed and applied in the analysis of persistent organic pollutants (POPs) in environment and biological samples at trace levels. The present review introduces the history of the APCI source, with emphasis on mechanisms of ionization processes under the positive and negative ionization modes. Comparison between GC-APCI-MS and GC–MS with traditional electron ionization (EI) and chemical ionization (CI) are provided and discussed for selectivity, sensitivity and stability for the analyses of POPs. Previous studies found that the GC-APCI-MS methods provided limits of detection (LODs) around 10–100 times lower than other methods. An overview of GC-APCI-MS applications is given with the discussions on the advantages and drawbacks of various analytical methods applied for the analyses of POPs.     

土壤中64种痕量半挥发性有机污染物的分析方法研究

利用超声提取技术将土壤中的半挥发性有机污染物(SVOC)提取出来, 经旋转蒸发浓缩至一定体积后, 用ODSC18柱净化, 再用氮吹浓缩后, 取1.0 μL注入气相色谱中, 用DB-5 ms柱分离, 用气相色谱质谱仪(GC-MS)进行定性定量分析. 本方法研究土壤中64种半挥发性有机污染物, 其中包括苯系物、苯酚类、苯胺类、硝基芳香烃类、氯代芳烃类、多环芳烃类和酞酸酯类等物质的提取、净化方法以及回收率、精密度和检测限的测定. 该方法回收率为52.5%～105%.     

The application of gas chromatography/atmospheric pressure chemical ionisation time‐of‐flight mass spectrometry to impurity identification in Pharmaceutical Development

Accurate mass measurement (used to determine elemental formulae) is an essential tool for impurity identification in pharmaceutical development for process understanding. Accurate mass liquid chromatography/mass spectrometry (LC/MS) is used widely for these types of analyses; however, there are still many occasions when gas chromatography (GC)/MS is the appropriate technique. Therefore, the provision of robust technology to provide accurate mass GC/MS (and GC/MS/MS) for this type of activity is essential. In this report we describe the optimisation and application of a newly available atmospheric pressure chemical ionisation (APCI) interface to couple GC to time‐of‐flight (TOF) MS. To fully test the potential of the new interface the APCI source conditions were optimised, using a number of standard compounds, with a variety of structures, as used in synthesis at AstraZeneca. These compounds were subsequently analysed by GC/APCI‐TOF MS. This study was carried out to evaluate the range of compounds that are amenable to analysis using this technique. The range of compounds that can be detected and characterised using the technique was found to be extremely broad and include apolar hydrocarbons such as toluene. Both protonated molecules ([M + H]⁺) and radical cations (M^+.) were observed in the mass spectra produced by APCI, along with additional ion signals such as [M + H + O]⁺. The technique has been successfully applied to the identification of impurities in reaction mixtures from organic synthesis in process development. A typical mass accuracy of 1–2 mm/zunits (m/z 80–500) was achieved allowing the reaction impurities to be identified based on their elemental formulae. These results clearly demonstrate the potential of the technique as a tool for problem solving and process understanding in pharmaceutical development. The reaction mixtures were also analysed by GC/electron ionisation (EI)‐MS and GC/chemical ionisation (CI)‐MS to understand the capability of GC/APCI‐MS relative to these two firmly established techniques. Copyright © 2010 John Wiley & Sons, Ltd.     

High‐resolution GC/MS studies of a light crude oil fraction

The continuous development in analytical instrumentation has brought the newly developed Orbitrap‐based gas chromatography / mass spectrometry (GC/MS) instrument into the forefront for the analysis of complex mixtures such as crude oil. Traditional instrumentation usually requires a choice to be made between mass resolving power or an efficient chromatographic separation, which ideally enables the distinction of structural isomers that is not possible by mass spectrometry alone. Now, these features can be combined, thus enabling a deeper understanding of the constituents of volatile samples on a molecular level. Although electron ionization is the most popular ionization method employed in GC/MS analysis, the need for softer ionization methods has led to the utilization of atmospheric pressure ionization sources. The last arrival to this family is the atmospheric pressure photoionization (APPI), which was originally developed for liquid chromatography / mass spectrometry (LC/MS). With a newly developed commercial GC‐APPI interface, it is possible to extend the characterization of unknown compounds. Here, first results about the capabilities of the GC/MS instrument under high or low energy EI or APPI are reported on a volatile gas condensate. The use of different ionization energies helps matching the low abundant molecular ions to the structurally important fragment ions. A broad range of compounds from polar to medium polar were successfully detected and complementary information regarding the analyte was obtained.     

A derivatization and validation strategy for determining the spatial localization of endogenous amine metabolites in tissues using MALDI imaging mass spectrometry

Imaging mass spectrometry (IMS) studies increasingly focus on endogenous small molecular weight metabolites and consequently bring special analytical challenges. Since analytical tissue blanks do not exist for endogenous metabolites, careful consideration must be given to confirm molecular identity. Here, we present approaches for the improvement in detection of endogenous amine metabolites such as amino acids and neurotransmitters in tissues through chemical derivatization and matrix‐assisted laser desorption/ionization (MALDI) IMS. Chemical derivatization with 4‐hydroxy‐3‐methoxycinnamaldehyde (CA) was used to improve sensitivity and specificity. CA was applied to the tissue via MALDI sample targets precoated with a mixture of derivatization reagent and ferulic acid as a MALDI matrix. Spatial distributions of chemically derivatized endogenous metabolites in tissue were determined by high‐mass resolution and MSⁿ IMS. We highlight an analytical strategy for metabolite validation whereby tissue extracts are analyzed by high‐performance liquid chromatography (HPLC)‐MS/MS to unambiguously identify metabolites and distinguish them from isobaric compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

顶空固相微萃取-气相色谱/质谱联用法结合化学计量学分析白肋烟烘焙前后挥发性、半挥发性成分

采用顶空固相微萃取-气相色谱/质谱法（HS-SPME-GC/MS）分析了白肋烟烟叶中挥发性、半挥发性成分。20 mg烟粉在60℃条件下孵化8 min,采用聚二甲基硅氧烷/二乙烯基苯（PDMS/DVB）65 μm纤维头萃取40 min,然后在250℃解吸3 min,通过与标准品和质谱数据库进行比对,初步定性了白肋烟烟叶中122种挥发性、半挥发性成分,并采用内标法进行半定量分析。通过主成分分析（PCA）和偏最小二乘-判别分析（PLS-DA）等化学计量学方法,直观反映了白肋烟烘焙前后挥发性、半挥发性成分的变化。该方法具有样品用量小、前处理简单、灵敏度高等特点,结合化学计量学方法可用于白肋烟烘焙前后化学成分变化分析,为白肋烟烘焙条件的优化提供了科学的检测方法。     

离子淌度谱及其近年进展

近年来离子淌度谱（ＩＭＳ）在样品引入技术，信号采集和数据处理、离子源等方面都有了显著的进展，其中以ＩＭＳ作为色谱检测器（ＩＭＤ）进行的研究尤为重要，而ＩＭＳ与Ｊ民喷雾郭子化（ＥＳＩ）技术的联用扩大其在非挥发性化合物和生物物质检测方面的应用评论还综述了近年来ＩＭＳ应用于环保、化学化工、违禁药物检测、爆炸物检测以及半导体表面挥发物分析等方面的最新研究成果。     

吹扫/捕集-热脱附气质联用法对荷叶挥发油成分的对比分析

采用同时蒸馏萃取提取得到荷叶挥发油, 通过吹扫/捕集-热脱附法(P&T-TD)对上述提取物中挥发性成分进行富集, 以气质联用(GC/MS)进行定性检测, 同时与直接进样GC/MS法分析的成分进行比较. 两种方法成功分离分析出有机酸、酯、醛、醇、酚、烷烃、芳香烃、烯烃以及含氮、硫、氧杂原子的化合物等共计84种成分, 其中P&T-TD GC/MS鉴定出63种有机化合物, GC/MS鉴定出41种有机化合物, 有20种成分共同检出. 对比分析表明: P&T-TD GC/MS的吹扫/捕集-热脱附过程能富集各种组分, 相比GC/MS分析, 可以鉴定出微量成分及更多挥发性和半挥发性成分, 在精油等挥发性成分的分析检测中使用优势明显.     

Identification of organic hydroperoxides and hydroperoxy acids in secondary organic aerosol formed during the ozonolysis of different monoterpenes and sesquiterpenes by on‐line analysis using atmospheric pressure chemical ionization ion trap mass spectrometry

On‐line ion trap mass spectrometry (ITMS) enables the real‐time characterization of reaction products of secondary organic aerosol (SOA). The analysis was conducted by directly introducing the aerosol particles into the ion source. Positive‐ion chemical ionization at atmospheric pressure (APCI(+)) ITMS was used for the characterization of constituents of biogenic SOA produced in reaction‐chamber experiments. APCI in the positive‐ion mode usually enables the detection of [M+H]⁺ ions of the individual SOA components. In this paper the identification of organic peroxides from biogenic volatile organic compounds (VOCs) by on‐line APCI‐ITMS is presented. Organic peroxides containing a hydroperoxy group, generated by gas‐phase ozonolysis of monoterpenes (α‐pinene and β‐pinene) and sesquiterpenes (α‐cedrene and α‐copaene), could be detected via on‐line APCI(+)‐MS/MS experiments. A characteristic neutral loss of 34 Da (hydrogen peroxide, H₂O₂) in the on‐line MS/MS spectra is a clear indication for the existence of an organic peroxide, containing a hydroperoxy functional group. Copyright © 2009 John Wiley & Sons, Ltd.     

Ion mobility spectrometry detection for gas chromatography

The hyphenated analytical method in which ion mobility spectrometry (IMS) is coupled to gas chromatography (GC) provides a versatile alternative for the sensitive and selective detection of compounds after chromatographic separation. Providing compound selectivity by measuring unique gas phase mobilities of characteristic analyte ions, the separation and detection process of gas chromatography-ion mobility spectrometry (GC-IMS) can be divided into five individual steps: sample introduction, compound separation, ion generation, ion separation and ion detection. The significant advantage of a GC-IMS detection is that the resulting interface can be tuned to monitor drift times/ion mobilities (as a mass spectrometer (MS) can be tuned to monitor ion masses) of interest, thereby tailoring response characteristics to fit the need of a given separation problem. Because IMS separates ions based on mobilities rather than mass, selective detection among compounds of the same mass but different structures are possible. The most successful application of GC-IMS to date has been in the international space station. With the introduction of two-dimensional gas chromatography (2D-GC), and a second type of mobility detector, namely differential mobility spectrometry (DMS), GC prior to mobility measurements can now produce four-dimensional analytical information. Complex mixtures in difficult matrices can now be analyzed. This review article is intended to provide an overview of the GC-IMS/DMS technique, recent developments, significant applications, and future directions of the technique.     

Volatile constituents of Festuca nigrescens, Phleum alpinum and Poa alpina from N. W. Italian Alpine pastures

The composition of the volatile fractions of three important grasses from sub-alpine N.W. Italian pastures, namely Festuca nigrescens Lam. non Gaudin (chewing fescue), Phleum alpinum L. (alpine timothy) and Poa alpina L. (alpine bluegrass) was investigated. The fresh aerial parts were collected at the flowering stage during the summer season. The volatile oils obtained from green tissues by steam distillation in a Clevenger-type apparatus, were analyzed by GC/FID and GC/MS. The oil yield was 0.04 +/- 0.01% weight/fresh weight bases for each of the investigated species. Several classes of compounds were found in the volatile fractions, including aldehydes, alcohols, acids, hydrocarbons, esters, ketones, terpenes, and phenolics. Qualitative and quantitative differences were observed.     

Gas Chromatography‐Mass Spectrometry‐Basic Principles,Instrumentation and Selected Applications for Detection of Organic Compounds

Abstract

This mini‐review discusses the analytical technique of gas chromatography‐mass spectrometry (GC‐MS), specifically basic principles and instrumentations. The applications of GC‐MS to a number of studies for determining organic compounds from around the world are presented and highlight its universal use and acceptance. Selected applications show that GC‐MS is an integral and complimentary part of many field studies involving organic compound detection and determination.