Identification strategy for unknown pollutants using high-resolution mass spectrometry: Androgen-disrupting compounds identified through effect-directed analysis

Effect-directed analysis has been applied to a river sediment sample of concern to identify the compounds responsible for the observed effects in an in vitro (anti-)androgenicity assay. For identification after non-target analysis performed on a high-resolution LTQ-Orbitrap, we developed a de novo identification strategy including physico-chemical parameters derived from the effect-directed analysis approach. With this identification strategy, we were able to handle the immense amount of data produced by non-target accurate mass analysis. The effect-directed analysis approach, together with the identification strategy, led to the successful identification of eight androgen-disrupting compounds belonging to very diverse compound classes: an oxygenated polyaromatic hydrocarbon, organophosphates, musks, and steroids. This is one of the first studies in the field of environmental analysis dealing with the difficult task of handling the large amount of data produced from non-target analysis. The combination of bioassay activity assessment, accurate mass measurement, and the identification and confirmation strategy is a promising approach for future identification of environmental key toxicants that are not included as priority pollutants in monitoring programs.     

Multidimensional computer evaluation of mass spectra

The increasing importance of spectroscopic methods as an analytical tool in industry, combined with the trend to automatize spectrometers, demands new standards in the quantity and quality of spectrum interpretation. Suitable computer programs should be able to predict structural features from mass spectral properties. The knowledge base is a structure-oriented mass spectral data collection consisting of some 42000 spectra and topologies. The comparison of selected mass spectral properties such as similarity, neutral losses and ion series of the unknown with the equivalent properties of the library spectra results in a set of corresponding structures. Subsequent substructure analysis yields a histogram of substructure frequencies containing information about their statistical relevance. The relevant substructure set may be recombined to produce a structure proposal, as is demonstrated for 1-acetyl-2-methoxy-4-trimethylsilyioxybenzene. In a second example, the relevant substructures derived by the interpretation system are used as input for the ¹³C-NMR substructure generator. This procedure reduces the solution space of the structure prediction algorithm considerably. Besides the spectrum interpretation, additional possibilities are available. The substructure search enables us, for example, to look for mass spectrometric reaction centres. Beyond that, substructure analysis is applicable to the determination of structural features typical of certain combinations of neutral losses and/or characteristic fragments.     

Semi-automated data processing of hydrogen exchange mass spectra using HX-Express

A Microsoft Excel utility, HX-Express, that significantly accelerates the analysis of hydrogen exchange mass spectrometry data is described. HX-Express generates deuterium uptake and peak width plots from peaks in mass spectral data. Data analysis is intentionally semi-automated, requiring that the user find the peaks to be analyzed. The peaks are entered in the form of x, y lists of m/z versus intensity or can be directly imported from Waters MassLynx software. Analysis of data with HX-Express provides the same results as manual data processing but is substantially faster. In addition to speed, HX-Express provides and preserves visual and numeric displays of the analysis process for quality control.     

The mass spectra of reissert compounds

A series of Reissert compounds containing the quinoline, isoquinoline and phthalazine nuclei show the common feature in their mass spectra of the initial loss of the N-substituent and either of the substituents attached to the adjacent carbon atom.     

Comparison of algorithms and databases for matching unknown mass spectra

The most used algorithms for the identification of electron-ionization mass spectra are INCOS and probability based matching (PBM). For unknown spectra of high purity, ～75% of rank 1 answers are correct for both algorithms, matched against the National Institute of Standards and Technology 62,235 spectrum database. With matching criteria that retrieve 50% of the possible correct answers from the Wiley 228,998 spectrum database, 54% of the PBM and 42% of the INCOS answers are correct; for 85% purity unknowns, 48% and 27% are correct. For an unknown spectrum of two compounds, neither was reported in the first three INCOS answers; eight of the first ten PBM answers identify both components.     

Monte-Carlo simulation of copolymer mass spectra

A computer program, MACO5, was developed which employs the Monte-Carlo approach to simulate the time-variation of the mass spectral peak intensities of a copolymer sample during the synthesis of an A/B copolyester via reactive blending of a mixture of homopolyesters A and B or when a copolymer undergoes partial degradation. The program was first used to simulate literature data consisting of a series of mass spectra of a butadiene/styrene copolymer subjected to partial ozonolysis. It was also used to investigate the role of terminal groups in reactive blending processes. Two models were developed: the first one describes inner-group ester-ester exchange reactions, the second describes the process in which and active terminal groups attacks an ester group. The predictions of the two models are compared with recent experimental mass spectral data concerning a poly(ethylene adipate-co-ethylene terephalate) copolyester.     

某些西佛碱类化合物的质谱重排反应

研究了十四种西佛碱类化合物的电子轰击质谱，利用碰撞诱导解离(CID)和B/E联动扫描技术，证实了特殊重排产物的离子结构及生成机理，并利用亚稳离子测定方式对这类化合物的主要离子进行了归属。     

Identification of unknown surfactants using electrospray mass spectrometry and NMR spectroscopy preceded by liquid ionization mass spectrometry

Commercially available but completely unknown surfactants used in the tin-lead plating industry were successfully identified by using electrospray mass spectrometry and NMR spectroscopy techniques, preceded by liquid ionization mass spectrometry used to obtain the preliminary information. The mass spectral data suggested that ethoxylated nonionic surfactants having a homologous distribution of molecular weights like 520, 564, 608, 652, 696, etc. were present. The NMR data suggested the presence of two aromatic rings and a quaternary carbon for the hydrophobe moiety instead of the well-known alkyl chains or alkylphenols. The unknown surfactants were finally concluded to be novel nonionic 4-(alpha,alpha-dimethylbenzyl)-phenol ethoxylates.     

The mass spectra of thiochromanone and related compounds

The mass spectra of thiochromanone (I), isothiochromanone (II)-2-, 3- and 8-methylthiochromanone and the sulfoxides and sulfones derived from these cyclic sulfides have been determined and the major fragmentation routes established. For the iso series loss of SO or SO₂ competes effectively with the retro-Diels-Alder reaction; however, for the thiochromanone derivatives the retro-Diels-Alder reaction is the major fragmentation route. There is no evidence for rearrangement of the sulfoxides or sulfones to sulfenates or sulfinates, respectively, prior to fragmentation.     

The mass spectra of some pyrazole compounds

The mass spectra of ten pyrazole compounds have been determined. Fragmentation schemes have been derived by means of the metastable defocusing method. The predominant process is cleavage of the nitrogen-nitrogen bond resulting in expulsion of HCN. The process second in prominence is the loss of a nitrogen molecule after initial removal of a hydrogen radical or a substituent, giving the species [C₃H₂R]⁺, probably a cyclopropenyl ion. In general, the fragmentation pattern is strongly influenced by the substituent.     

Computer-assisted library search system for identification of unknown mass spectra

The library search system described identifies a single component or two components in the unknown pure or mixture mass spectra by comparing them with a large data base of reference spectra. A preliminary search is based on the spectral interpretation and the main search is based on the probability of peak appearance. The performance of this system was tested on 254 pure spectra and 88 mixture spectra. The percentages of successful search by using the NIH/EPA/MSDC data base were 75% for the pure spectra, and 63% for both the first and second components in mixture spectra. The percentages of successful search improved to 94% for the first components of the mixture spectra and 77% for both first and second components of the mixture spectra, when conditions for measurement of reference spectra were the same as those for the unknown spectra.     

Identification of unknown compounds on the basis of retention index data in comprehensive two-dimensional gas chromatography

The identification of unknown compounds in complex samples is very difficult. Comprehensive two-dimensional gas chromatography (GC x GC) provides very good resolution and improved identification reliability. Mass spectrometry is a powerful identification tool and retention index data are another good approach to this end. In this study, a second-order polynomial was used to calculate retention index data based on n-alkanes beyond the region of the 'isovolatile' curve in GC x GC, and the results in the 2nd dimension were validated by using the same stationary phase column in one-dimensional GC. To test the usefulness of the method, volatile compounds in a tobacco leaf extract fraction were analyzed using GC x GC, and 60 compounds were identified on the basis of their retention indices.     

The mass spectra of the pyrethrins and related compounds

The mass spectra of the natural pyrethrins, allethrin, the chrysanthemic acid, and the rethrolonyl and rethronyl portions of the insecticidal esters are presented, and their main fragmentation pathways are discussed.     

The mass spectra of 1,2,4-triazines and related compounds

The mass spectra of monocyclic 1,2,4-triazines and 1,2,4-triazines fused to a pyrazole ring through a bridgehead nitrogen have been investigated: fragmentation pathways were elucidated by the use of metastable ions and high resolution mass measurements. The spectra of the monocyclic 1,2,4-triazines indicate that loss of nitrogen from the molecular ions is a relatively unimportant feature. The decomposition modes of the bicyclic pyrazolo[3,2-c]-as-triazines are sensitive to the nature of the substituent in the triazine ring.     

Doubly charged ion mass spectra of organophosphorus compounds

Doubly charged ion mass spectra have been obtained for 11 organophosphorus compounds. Methane has been used as a target gas to increase the probability of single electron transfer collisions in the first field-free region of an Hitachi RMU-7L mass spectrometer. In general, the spectra of organophosphorus compounds do not exhibit molecular ions but are dominated by fragment ions, many of which must be formed by rearrangement processes. A geometry-optimized self-consistent field molecular orbital method has been employed to compute energies and structural parameters for prominent ions. In addition, a diabatic curve crossing model has been used to examine the single electron transfer reactions responsible for intense ions in the doubly charged ion mass spectra. Appearance energies measured for ions prominent in the 2E spectra of organophosphorus compounds have ranged from 23 to 38 eV.     

The mass spectra of four-membered alicyclic sulfur compounds

The mass spectra of thietane, trimethylene sulfoxide, and trimethylene sulfone are reported. The major competing reactions are four-center fragmentation, heteroatom group elimination and rearrangement. The oxidation state of the sulfur atom has a profound effect upon the competition among these reaction channels. As the oxidation state of the sulfur increases the molecular ion becomes increasingly less stable and consequently the amount of rearrangement decreases. Elimination of the heteroatom increases as its oxidation state increases, while the amount of four-center fragmentation decreases.