Electrospray ionization mass spectral studies of N,N-dialkylaminoethane-2-sulphonic acids

Oxidative reactions of VX type compounds and N,N-dialkylaminoethane-2-thiols that are precursors for VX compounds produce N,N-dialkylaminoethane-2-sulphonic acids, N(R(1))(R(2))-CH(2)-CH(2)SO(3)H (where R(1) and R(2) = methyl, ethyl, n-propyl and isopropyl, 1-10), as the degradation products, and these degradation products are considered as markers for the detection of chemicals listed in the schedules of Chemical Weapons Convention (CWC) chemicals. Off-site detection of such degradation products in aqueous samples is an important task in the verification of CWC-related chemicals. Here we report a simple method involving the direct analysis of aqueous samples using positive and/or negative ion electrospray ionization (ESI) for the screening, detection and identification of N,N-dialkylaminoethane-2-sulphonic acids, avoiding sample preparation and chromatographic steps. The positive ion ESI mass spectra of all the compounds result in abundant [M+Na](+) ions, and the negative ion spectra show abundant [M-H](-) ions to confirm their molecular weight. The collision-induced dissociation spectra of [M+Na](+) and [M-H](-) give characteristic product ions by which it is easy to detect and identify all the studied N,N-dialkylaminoethane-2-sulphonic acids including those of isomeric compounds. The method is successfully applied to detect the spiked chemical, N,N-diisopropylaminoethane-2-sulphonic acid, present in a water sample received in a proficiency test.     

Gas chromatography/mass spectrometric analysis of N,N-dialkylaminoethyl-2-chlorides and trimethylsilyl derivatives of N,N-dialkylaminoethan-2-ols for verification of the Chemical Weapons Convention

Gas chromatography/electron ionization mass spectrometry (GC/EI-MS) of N,N-dialkylaminoethyl-2-chlorides (DAAECls) and trimethylsilyl (TMS) derivatives of N,N-dialkylaminoethan-2-ols (DAAEAs) has been carried out. GC/EI-MS data of these compounds are of importance for verification of the Chemical Weapons Convention (CWC). Based on these EI mass spectra, generalized fragmentation routes are proposed that rationalize most of the characteristic ions.     

Identification of iso- and n-propylphosphonates using liquid chromatography-tandem mass spectrometry and gas chromatography-Fourier transform infrared spectroscopy

Organophosphorus nerve agents and their precursors, specifically listed in the schedules of chemicals in the Annex to the Chemical Weapons Convention (CWC), include analogues with C1-C3 alkyl groups on phosphorus. The Organisation for the Prohibition of Chemical Weapons (OPCW) requires designated laboratories to unequivocally identify isomeric propyl groups bonded to phosphorus in analytes that may be present in samples submitted for analysis. Homologous series of isomeric pairs of dialkyl iso- and n-propylphosphonates, alkyl iso- and n-propylphosphonochloridates, and alkyl iso- and n-propylphosphonofluoridates, have been analysed by liquid chromatography-ion trap tandem mass spectrometry and/or by gas chromatography-Fourier transform infrared spectroscopy. The results show that P-propyl isomers can be reliably differentiated by collision induced dissociation (CID) of selected fragment ions and by their infrared P=O stretching and C-H deformation frequencies.     

Fragmentation pathways of O-alkyl methylphosphonothionocyanidates in the gas phase: Toward unambiguous structural characterization of chemicals in the Chemical Weapons Convention framework

The electron-impact (EI) mass spectra of a series of O-alkyl methylphosphonothionocyanidates were studied for Chemical Weapons Convention (CWC) purposes. General EI fragmentation pathways were constructed and discussed, and collision-induced dissociation studies of the major EI ions were performed to confirm proposed fragment structures by analyzing fragment ions of deuterated analogs and by use of density functional theory (DFT) calculations. Thiono–thiolo rearrangement, McLafferty-type rearrangement, and a previously unknown intramolecular electrophilic aromatic substitution reaction were observed and confirmed. The study also focused on differentiation of isomeric compounds. Retention indices for all compounds, and an electrophilicity index for several compounds, are reported and interpreted.     

Use of a hand-portable gas chromatograph-toroidal ion trap mass spectrometer for self-chemical ionization identification of degradation products related to O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX)

The chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX) and many related degradation products produce poorly diagnostic electron ionization (EI) mass spectra by transmission quadrupole mass spectrometry. Thus, chemical ionization (CI) is often used for these analytes. In this work, pseudomolecular ([M+H]⁺) ion formation from self-chemical ionization (self-CI) was examined for four VX degradation products containing the diisopropylamine functional group. A person-portable toroidal ion trap mass spectrometer with a gas chromatographic inlet was used with EI, and both fixed-duration and feedback-controlled ionization time. With feedback-controlled ionization, ion cooling (reaction) times and ion formation target values were varied. Evidence for protonation of analytes was observed under all conditions, except for the largest analyte, bis(diisopropylaminoethyl)disulfide which yielded [M+H]⁺ ions only with increased fixed ionization or ion cooling times. Analysis of triethylamine-d₁₅ provided evidence that [M+H]⁺ production was likely due to self-CI. Analysis of a degraded VX sample where lengthened ion storage and feedback-controlled ionization time were used resulted in detection of [M+H]⁺ ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample.     

Rapid screening of N-oxides of chemical warfare agents degradation products by ESI-tandem mass spectrometry

Rapid detection and identification of chemical warfare agents and related precursors/degradation products in various environmental matrices is of paramount importance for verification of standards set by the chemical weapons convention (CWC). Nitrogen mustards, N,N-dialkylaminoethyl-2-chlorides, N,N-dialkylaminoethanols, N-alkyldiethanolamines, and triethanolamine, which are listed CWC scheduled chemicals, are prone to undergo N-oxidation in environmental matrices or during decontamination process. Thus, screening of the oxidized products of these compounds is also an important task in the verification process because the presence of these products reveals alleged use of nitrogen mustards or precursors of VX compounds. The N-oxides of aminoethanols and aminoethylchlorides easily produce [M + H]⁺ ions under electrospray ionization conditions, and their collision-induced dissociation spectra include a specific neutral loss of 48 u (OH + CH₂OH) and 66 u (OH + CH₂Cl), respectively. Based on this specific fragmentation, a rapid screening method was developed for screening of the N-oxides by applying neutral loss scan technique. The method was validated and the applicability of the method was demonstrated by analyzing positive and negative samples. The method was useful in the detection of N-oxides of aminoethanols and aminoethylchlorides in environmental matrices at trace levels (LOD, up to 500 ppb), even in the presence of complex masking agents, without the use of time-consuming sample preparation methods and chromatographic steps. This method is advantageous for the off-site verification program and also for participation in official proficiency tests conducted by the Organization for the Prohibition of Chemical Weapons (OPCW), the Netherlands. The structure of N-oxides can be confirmed by the MS/MS experiments on the detected peaks. A liquid chromatography-mass spectrometry (LC-MS) method was developed for the separation of isomeric N-oxides of aminoethanols and aminoethylchlorides using a C18 Hilic column. Critical isomeric compounds can be confirmed by LC-MS/MS experiments, after detecting the N-oxides from the neutral loss scanning method.

Why are electron capture negative ion mass spectra not reproducible? An ion source problem

Differences in the electron capture negative ion mass spectra of environmentally related organic compounds acquired on a VG 30-250 triple quadruple mass spectrometer and on an HP 5985B gas chromatography/mass spectrometry system were investigated with respect to the ion formation process. Neither ion source temperature nor pressure was responsible for the differences. The populations of thermal electrons in both ion sources were experimentally determined and found to be similar, suggesting that electron capturing reactions should proceed with comparable efficiencies in both ion sources. The ion extraction efficiencies of the two instruments were examined by monitoring the transmission profiles of low- and high-mass ions as a function of lens potentials. Results indicated that the HP 5985B extraction lens significantly suppressed low-mass ions. Further, theoretical evaluation of ion trajectories using SIMION suggested that on the HP 5985B, low-mass ions entered the mass analyzer as a defocused beam, but high-mass ions entered the analyzer as a well-collimated beam. On the VG 30–250, low- and high-mass ions were transmitted to the analyzer with equal efficiency by the ion extraction system.     

Microsynthesis and mass spectral study of Chemical Weapons Convention related 2‐alkyl‐1,3,6,2‐dioxathiaphosphocane‐2‐oxides

Chemical Weapons Convention (CWC)‐related compounds where the phosphorus atom is part of a ring have very limited representation in mass spectral libraries and the open literature. Here we report electron ionization (EI), chemical ionization (CI) and electrospray ionization tandem mass spectrometry (ESI‐MSⁿ) spectra and retention indices for 2‐alkyl‐1,3,6,2‐dioxathiaphosphocane‐2‐oxides (alkyl C₁ to C₃) which are new cyclic chemicals covered under the CWC. The EI mass spectra show a pattern of ion fragmentation that is similar to that of other cyclic phosphonates in that loss of the alkylphosphonic acid as a neutral loss is more important than the presence of the protonated alkylphosphonic acid. In contrast to other cyclic phosphonates, the 2‐alkyl‐1,3,6,2‐dioxathiaphosphocane‐2‐oxides show almost no protonated alkylphosphonic acid and as a result the spectra do not carry the same distinctive signature of the phosphorus–carbon bond that is required for the chemical to be covered under the CWC. Copyright © 2008 John Wiley & Sons, Ltd.     

Atmospheric pressure ionisation mass spectrometric fragmentation pathways of noscapine and papaverine revealed by multistage mass spectrometry and in-source deuterium labelling

Two opium alkaloids, noscapine and papaverine, show good response as [M+H]+ ions in positive ion electrospray mass spectrometry and atmospheric pressure chemical ionisation mass spectrometry. The two compounds exhibit markedly different fragmentation pathways and behaviour under multistage mass spectrometry (MSn), with papaverine displaying a wealth of ions in MS2 and noscapine providing a single dominant ion at each stage of MSn prior to MS4. Elucidation of the fragmentation pathways using the MSn capability of the ion trap was aided by spraying the analytes in 2H2O to incorporate an isotopic label. Simplex optimisation allowed optimum trapping and fragmentation parameters to be determined, leading to a six-fold improvement in response for one transition and a seven-fold improvement for one transition sequence.     

Investigations of the fragmentation pathways of benzylpyridinium ions under ESI/MS conditions

Benzylpyridinium ions are often used as ‘thermometer ions’ in order to evaluate the internal energy distribution of the ions formed in sources of mass spectrometers. However, the detailed fragmentation pathways of these parent ions were not well established. In particular, fragmentation involving a rearrangement (RR) process may be influencing the simulated distribution curves. In a previous study, we suggested that such RR actually occurred under electrospray ionization/mass spectrometry (ESI/MS) and fast atom bombardment/mass spectrometry (FAB/MS) experiments. Here, we present a systematic study of different substituted benzylpyridinium ions. Theoretical calculations showed that RR fragmentation leading to substituted tropylium ions could occur under ‘soft ionization’ conditions, such as ESI or FAB. Experimental results obtained under gas‐phase reactivity conditions showed that some substituted benzylpiridinium compounds actually undergo RR fragmentations under ESI/MS conditions. Mass‐analyzed kinetic experiments were also carried out to gain information on the reaction pathways that actually occur, and these experimental results are in agreement with the reaction pathways theoretically proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Microsynthesis and gas chromatography/electron ionization mass spectrometric and tandem mass spectrometric analysis of cyclic alkylphosphonates for verification of the Chemical Weapons Convention

We describe the microsynthesis and gas chromatography/mass spectrometric (GC/MS) analysis of cyclic alkylphosphonates (CAPs), which are included in schedule 2B4 chemicals in the Chemical Weapons Convention (CWC). The reported microsynthesis is efficient in comparison with traditional synthesis. GC/MS and GC/tandem mass spectrometric (MS/MS) analysis of a variety of CAPs revealed that their fragmentations were dominated by alpha-cleavages, alkene eliminations and hydrogen rearrangements. Based on the obtained mass spectra and precursor and product ion analysis of five-, six- and seven-membered cyclic alkylphosphonates, the proposed fragmentation routes rationalize most of the characteristic ions.     

Analysis of O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its degradation products by packed capillary liquid chromatography-electrospray mass spectrometry

Packed capillary column liquid chromatography (LC)-electrospray mass spectrometry (ESI-MS) was used for the first time to detect and identify O-ethyl, S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its degradation products, including compounds containing a P-CH3 bond, bis(diisopropylamino)thioalkanes and ureas commonly employed as VX stabilizers. The reported ESI-MS data were generally acquired with a higher sampling cone voltage, a setting that promoted collisionally activated dissociation, and resulted in the acquisition in informative mass spectra containing both molecular and product ion information. The developed method appears to be an attractive alternative to GC-MS for the analysis of aqueous sample containing the degradation products of VX, since they may be analysed directly with little risk of thermal decomposition and without the need for additional sample handling or derivatization. Application of this method to a degraded VX sample resulted in the detection of a number of novel polar and higher-molecular-mass degradation products, not previously associated with VX during GC-MS analysis.     

剧毒性Ⅱ型核糖体失活蛋白蓖麻毒素和相思子毒素的检测鉴定方法研究进展

Ⅱ型核糖体失活蛋白(RIPs)是一类重要的蛋白毒素,该类毒素大都具有一对二硫键连接的A-B链结构特征,B链具有半乳糖结合特性,能够与真核细胞膜表面受体特异性结合,将具有N-糖苷酶活性的A链导入细胞,与核糖体特定位点发生脱嘌呤作用使核糖体失活,最终通过抑制蛋白质合成而展现出细胞毒性。Ⅱ型RIPs毒素毒性极强,来源于植物的蓖麻毒素(ricin)和相思子毒素(abrin)的毒性分别是神经性毒剂维埃克斯(Vx)的385倍和2885倍。同时,该类毒素来源广泛、易于制备、稳定性好,成为一类潜在化生恐怖战剂,受到国内外广泛关注,其中蓖麻毒素作为唯一的蛋白毒素被收录于禁止化学武器公约禁控清单。近年来发生的多次蓖麻毒素邮件恐怖事件,进一步促进了有关Ⅱ型RIPs毒素的准确、灵敏、快速的检测鉴定技术的发展。剧毒性Ⅱ型RIPs毒素的检测鉴定方法主要涉及免疫分析法为代表的特异性识别和生物质谱分析为主的定性定量检测方法,以及基于脱嘌呤反应活性和细胞毒性的毒素活性检测方法。基于抗原-抗体作用的免疫检测法及基于寡核苷酸适配体的特异性识别检测法具有速度快、灵敏度高的优势,但对于复杂样品中高度同源蛋白的检测,易产生假阳性结果。随着生物质谱技术的快速发展,电喷雾离化(ESI)或基质辅助激光解吸离化(MALDI)等技术广泛应用于蛋白质的准确鉴定,不仅能够提供蛋白毒素的准确分子量和结构序列信息,而且能够实现准确定量。酶解质谱法是应用最为广泛的检测鉴定方法,通过酶解肽指纹谱分析,实现蛋白毒素的准确鉴定;对于复杂样品中蛋白毒素的分析,通过多种蛋白酶酶解策略获得丰富的特异性肽段标志物,然后进行肽段标志物的靶向质谱分析从而获得准确的定性及定量信息,方法有效提升了Ⅱ型RIPs毒素鉴定的准确度和灵敏度。免疫分析法和生物质谱法能够准确鉴定Ⅱ型RIPs毒素,但无法识别毒素是否还保持毒性。对于Ⅱ型RIPs毒素的活性分析,主要包括基于N-糖苷酶活性的脱嘌呤反应测定法和细胞毒性测定法,两种方法均可实现毒素毒性的简便、快速、灵敏的分析检测,是Ⅱ型RIPs毒素检测方法的有效补充。由于该类毒素的高度敏感性,国际禁止化学武器组织(OPCW)对相关样品中Ⅱ型RIPs毒素的分析提出了唯一性鉴定的技术要求。该文引用了Ⅱ型RIPs毒素及其检测方法相关的70篇文献,综述了以上Ⅱ型RIPs毒素的结构性质、中毒机理及典型剧毒性Ⅱ型RIPs毒素检测方法的研究进展,对不同检测方法的特点和应用潜力进行了总结,并结合OPCW对Ⅱ型RIPs毒素唯一性鉴定的技术需求,展望了未来Ⅱ型RIPs毒素检测技术研究的发展趋势。     

Electrospray ionization mass spectra of amino acid phosphoramidates of adenosine

Amino acid phosphoramidates of adenosine were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated. In the positive ion mass spectra abundant characteristic fragment ions appeared, and many complementary ions were found. In the negative ion mass spectra only a few fragment ions were observed, and most of them contained phosphoryl groups. The results show that ESI-MS is a useful tool for structural determination of amino acid phosphoramidates of nucleosides.     

药物泰瑞沙的质谱分析及其未知杂质的结构解析

利用气相色谱-质谱法在电子电离源下对用于治疗肺癌的药物泰瑞沙(Tagrisso)进行分析,对主成分奥斯替尼(Osimertinib)在质谱中产生的主要的碎片离子进行归属,推测其可能的质谱裂解途径。参考主成分奥斯替尼的质谱裂解方式,由质谱裂解机理的角度出发对该药物中的4个未知的关键杂质的结构进行有效解析。此外,发现奥斯替尼及其个别杂质在质谱裂解过程中出现了显著的违背偶电子规则的碎片离子。通过对药物泰瑞沙的质谱分析期望能够提供一些分析、解析药物中未知杂质的思路和方法。     

Study of the fragmentation pathway of α-aminophosphonates by chemical ionization and fast atom bombardment mass spectrometry

The diastereoisomers of α-aminophosphonates are key intermediates in the synthesis of enantiomerically pure α-aminophosphonic acids, which are analogs of α-amino acids. Although several methods have been reported for the diastereoselective synthesis of α-aminophosphonates, their mass spectrometry (MS) fragmentation patterns have not yet been fully investigated. The work described here involved a detailed study of the fragmentation of enriched α-aminophosphonate diastereoisomers by chemical ionization (CI-MS) and fast atom bombardment (FAB)-MS. The complete characterization of the different conventional MS fragmentation pathways is represented and this intriguing exercise required the use of tandem mass spectrometry (MS/MS) experiments and high-resolution accurate mass measurements. All α-aminophosphonates gave prominent pseudomolecular ions, protonated molecules [MH](+) , and their fragmentations mainly showed a loss of dimethyl phosphite to give the corresponding iminium ions as base peaks for α-aminophosphonates bearing methylbenzyl and 2,2-dimethylbutyl fragments. The loss of the chiral fragment from the iminium ions bearing the (S)-1-(1-naphthyl)ethyl group gave rise to a base peak due to aryl cations. The nature of all fragment ions were confirmed by high-resolution mass spectrometry (HRMS).     

Characterization of VX on concrete using ion trap secondary ionization mass spectrometry

The nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) was analyzed on the surface of concrete samples using an ion trap secondary ion mass spectrometer (IT-SIMS). It was found that VX could be detected down to an absolute quantity of 5 ng on a concrete chip, or to a surface coverage of 0.0004 monolayers on crushed concrete. To achieve these levels of detection, the m/z 268-->128 ion fragmentation was measured using MS2, where m/z 268 corresponds to [VX + H]+, and 128 corresponds to a diisopropylvinylammonium isomer, that is formed by the elimination of the phosphonothiolate moiety. Detection at these levels was accomplished by analyzing samples that had been recently exposed to VX, i.e., within an hour. When the VX-exposed concrete samples were aged, the SIMS signature for intact VX had disappeared, which signaled the degradation of the compound on the concrete surface. The VX signature was replaced by ions which are interpreted in terms of VX degradation products, which appear to be somewhat long lived on the concrete surface. These compounds include ethylmethylphosphonic acid (EMPA), diisopropyl taurine (DIPT), diisopropylaminoethanethiol (DESH), bis(diisopropylaminoethane) disulfide [(DES)2], and a particularly tenacious compound that may correspond to diisopropylvinylamine (DIVA), or an isomer thereof. It was found that the thiolamine-derived degradation products DIPT, DESH, and (DES)2 were removed with isopropyl alcohol extraction. However, the DIVA-related degradation product was observed to strongly adhere to the concrete surface for longer than one week. Although quantitation was not possible in this set of experiments, the results clearly show the rapid degradation of VX on concrete, as well as the surface sensitivity of the IT-SIMS for intact VX and its adsorptive degradation products.     

Synthesis and Electrospray Ionization Mass Spectra of N-（1,3, 2-Dioxaphosphorinan-2-ylmethyl）thiophosphoramidates

N-（1,3,2-Dioxaphosphorinan-2-ylmethyl）thiophosphoramidates were synthesized and determined by NMR spectra and positive ion electrospray ionization mass spectrometry （ESI-MS） in conjunction with tandem mass spectrometry （MS/MS）. The fragmentation pathways were investigated. The results show that these characteristic ions in ESI mass spectra are useful in the structural determination of N-（1,3,2-dioxaphosphorinan-2-ylmethyl）- thiophosphoramidates.     

Fragmentation and reactions of two isomeric O-alkyl S-(2-dialkylamino)ethyl methylphosphonothiolates studied by electrospray ionization/ion trap mass spectrometry

An initial investigation into the electrospray ionization ion trap mass spectrometry (ESI/ITMS) of simple organophosphorus compounds [1] demonstrated that detailed structural information could be obtained by sequential fragmentation of the ions using collision induced dissociation (CID). Several novel fragmentations/rearrangements were observed and it was apparent that the full potential of this approach could not be exploited until a more detailed understanding of the ion fragmentations was obtained. Such an understanding will only result from a detailed study of a wide range of compounds. The present paper describes the investigation of two isomeric organophosphates of particular relevance to chemical warfare convention (CWC) considerations.     

Application of cation-exchange solid-phase extraction for the analysis of amino alcohols from water and human plasma for verification of Chemical Weapons Convention

The analysis of nitrogen containing amino alcohols, which are the precursors and degradation products of nitrogen mustards and nerve agent VX, constitutes an important aspect for verifying the compliance to the CWC (Chemical Weapons Convention). This work devotes on the development of solid-phase extraction method using silica- and polymer-based SCX (strong cation-exchange) and MCX (mixed-mode strong cation-exchange) cartridges for N,N-dialkylaminoethane-2-ols and alkyl N,N-diethanolamines, from water. The extracted analytes were analyzed by GC-MS (gas chromatography-mass spectrometry) in the full scan and selected ion monitoring modes. The extraction efficiencies of SCX and MCX cartridges were compared, and results revealed that SCX performed better. Extraction parameters, such as loading capacity, extraction solvent, its volume, and washing solvent were optimized. Best recoveries were obtained using 2 mL methanol containing 10% NH(4)OH and limits of detection could be achieved up to 5 x 10(-3) microg mL(-1) in the selected ion monitoring mode and 0.01 microg mL(-1) in full scan mode. The method was successfully employed for the detection and identification of amino alcohol present in water sample sent by Organization for Prohibition of Chemical Weapons (OPCW) in the official proficiency tests. The method was also applied to extract the analytes from human plasma. The SCX cartridge showed good recoveries of amino alcohols from human plasma after protein precipitation.