A library consisting of 3766 MS(n) spectra of 1743 compounds, including 3126 MS2 spectra acquired mainly using ion trap (IT) and triple-quadrupole (QqQ) instruments, was composed of numerous collections/sources. Ionization techniques were mainly electrospray ionization and also atmospheric pressure chemical ionization and chemical ionization. The library was tested for the performance in identification of unknowns, and in this context this work is believed to be the largest of all known tests of product-ion mass spectral libraries. The MS2 spectra of the same compounds from different collections were in turn divided into spectra of 'unknown' and reference compounds. For each particular compound, library searches were performed resulting in selection by taking into account the best matches for each spectral collection/source. Within each collection/source, replicate MS2 spectra differed in the collision energy used. Overall, there were up to 950 search results giving the best match factors and their ranks in corresponding hit lists. In general, the correct answers were obtained as the 1st rank in up to 60% of the search results when retrieved with (on average) 2.2 'unknown' and 6.2 reference replicates per compound. With two or more replicates of both 'unknown' and reference spectra (the average numbers of replicates were 4.0 and 7.8, respectively), the fraction of correct answers in the 1st rank increased to 77%. This value is close to the performance of established electron ionization mass spectra libraries (up to 79%) found by other workers. The hypothesis that MS2 spectra better match reference spectra acquired using the same type of tandem mass spectrometer (IT or QqQ) was neither strongly proved nor rejected here. The present work shows that MS2 spectral libraries containing sufficiently numerous different entries for each compound are sufficiently efficient for identification of unknowns and suitable for use with different tandem mass spectrometers. 相似文献
Structurally-related alkaloids were analyzed by electrospray ionization/multiple stage mass spectrometry (ESI/MSn) at varying collision energies to demonstrate a conceptual algorithm, precursor ion fingerprinting (PIF). PIF is a new approach
for interpreting and library-searching ESI mass spectra predicated on the precursor ions of structurally-related compounds
and their matching product ion spectra. Multiple-stage mass spectra were compiled and constructed into “spectral trees” that
illustrated the compounds’ product ion spectra in their respective mass spectral stages. The precursor ions of these alkaloids
were characterized and their spectral trees incorporated into an MSn library. These data will be used to construct a universal, searchable, and transferable library of MSn spectra. In addition, PIF will generate a proposed structural arrangement utilizing previously characterized ion structures,
which will assist in the identification of unknown compounds. 相似文献
Tandem mass spectral library searching is finding increased use as an effective means of determining chemical identity in mass spectrometry-based omics studies. We previously reported on constructing a tandem mass spectral library that includes spectra for multiple precursor ions for each analyte. Here we report our method for expanding this library to include MS2 spectra of fragment ions generated during the ionization process (in-source fragment ions) as well as MS3 and MS4 spectra. These can assist the chemical identification process. A simple density-based clustering algorithm was used to cluster all significant precursor ions from MS1 scans for an analyte acquired during an infusion experiment. The MS2 spectra associated with these precursor ions were grouped into the same precursor clusters. Subsequently, a new top-down hierarchical divisive clustering algorithm was developed for clustering the spectra from fragmentation of ions in each precursor cluster, including the MS2 spectra of the original precursors and of the in-source fragments as well as the MSn spectra. This algorithm starts with all the spectra of one precursor in one cluster and then separates them into sub-clusters of similar spectra based on the fragment patterns. Herein, we describe the algorithms and spectral evaluation methods for extending the library. The new library features were demonstrated by searching the high resolution spectra of E. coli extracts against the extended library, allowing identification of compounds and their in-source fragment ions in a manner that was not possible before.
Gas chromatography-mass spectrometry data from the analysis of complex environmental samples were converted into ASCII text and imported into a personal computer spreadsheet. A macro was written to perform mass spectral enhancement by statistical and mathematical procedures to separate the spectra of compounds of interest from interfering mass spectral responses, such as those of broadly eluting hydrocarbons. The extracted mass spectra were compared to reference spectra, with the result that usually 80–90% of the ions common to those in the reference spectra were successfully extracted by using this method. This procedure improved mass spectral quality and the ability of the data system to perform successful library searches. The fitted quality parameters showed systematic improvements after the data were subjected to the spectral enhancement procedures. These procedures could help to identify unknowns by separating their spectra from other signals, such as those of background aliphatic hydrocarbons. 相似文献
As the size of various collections of electron ionization mass spectra gets larger, there is a continuing and increasing propensity to rely on the results of computerized library searches. The results of these computerized searches do not necessarily account for a spectrum that is produced by the mixture of two or more different compounds. Sometimes the submitted spectrum is not that of a compound whose spectrum is in the library. The quality of the spectrum submitted to the library is often such that the numerical confidence level reported for the search result is so low that it will cause the result to be disregarded. When the sample spectrum is matched against library spectra that have been condensed, the search result can be misleading. Three different examples of mass spectral search results are examined: one, with a high confidence level that the unknown has been identified, but the results are incorrect; one, where the spectrum of the unknown compound is not in the library; one, where consideration of the numerical search results would cause a positive identity not to be confirmed. 相似文献
In contrast to GC-MS libraries, currently available LC-MS libraries for toxicological detection contain besides parent drugs
only some main metabolites limiting their applicability for urine screening. Therefore, a metabolite-based LC-MSn screening procedure was developed and exemplified for antidepressants. The library was built up with MS2 and MS3 wideband spectra using an LXQ linear ion trap with electrospray ionization in the positive mode and full-scan information-dependent
acquisition. Pure substance spectra were recorded in methanolic solution and metabolite spectra in urine from rats after administration
of the corresponding drugs. After identification, the metabolite spectra were added to the library. Various drugs and metabolites
could be sufficiently separated. Recovery, process efficiency, matrix effects, and limits of detection for selected drugs
were determined using protein precipitation. Automatic data evaluation was performed using ToxID and SmileMS software. The
library consists of over 700 parent compounds including 45 antidepressants, over 1,600 metabolites, and artifacts. Protein
precipitation led to sufficient results for sample preparation. ToxID and SmileMS were both suitable for target screening
with some pros and cons. In our study, only SmileMS was suitable for untargeted screening being not limited to precursor selection.
The LC-MSn method was suitable for urine screening as exemplified for antidepressants. It also allowed detecting unknown compounds based
on known fragment structures. As ion suppression can never be excluded, it is advantageous to have several targets per drug.
Furthermore, the detection of metabolites confirms the body passage. The presented LC-MSn method complements established GC-MS or LC-MS procedures in the authors’ lab. 相似文献
The infrared absorption spectra of 55 lactic acid bacteria belonging to the genera Lactobacillus, Weissella and Carnobacterium were obtained and mathematically analyzed. Sixteen reference strains and 39 food strains isolated from meat and meat products and belonging to the genera Lactobacillus (6 species), Weissella (3 species) and Carnobacterium (2 species) were processed under standardized conditions and their medium infrared spectra obtained using Fourier-transform infrared (FT-IR) spectroscopy. Reproducibility indexes and similarities between FT-IR spectra were calculated using modified correlation coefficients to detect the ranges with the best reproducibility and discrimination properties. Hierarchical cluster analysis and stepwise discriminant analysis (SDA) were subsequently carried out to detect classes and create library groups. Reference strains could be distinguished on the basis of their spectral data and their clustering was in agreement with differences in chemical composition of the cell wall. For the 39 food isolates, the capability of two identification systems was compared. Unknown strains were identified (a) using the linear functions obtained from SDA (canonical variables) of the variables that provide the best discrimination of spectra, and (b) by calculating a differentiation index when a range of the unknown's transformed IR spectrum was compared to all spectra included in a reference library. The system based on the differentiation index obtained a higher rate of identification, allowing for detection of outliers. FT-IR spectroscopy is shown to afford additional information to phenotypic and genotypic data which may help to establish a more robust taxonomic classification. 相似文献
A new method for the computerized search and identification of infrared spectra has been developed and evaluated. Based on cross-correlation, the search system utilizes all spectral information in a digitized spectrum when it attempts to match an unknown spectrum to one in a small library of known spectra. To evaluate a spectral match, the search program calculates the cross-correlation function between the unknown and known (library) spectra which indicates their degree of similarity and allows library spectra to be ranked in order of probability of match to the unknown spectrum. In this study, several small infrared spectral libraries of structurally similar compounds were searched under conditions which examined the sensitivity of the search method to chemical and instrumental variations. Because the correlation technique is slower than conventional file-searching methods, it will probably find greatest use in the search of small collections of similar spectra or as a match-ranking procedure following preliminary selection by a faster search method. 相似文献
Reproducibility of product ion spectra acquired using a liquid chromatography/triple-quadrupole mass spectrometry (LC/MS/MS) instrument over a 4-year period, and with three other LC/MS/MS instruments, one from the same manufacturer and two from a different manufacturer, was examined. The MS/MS spectra of 30 drug substances were generated in positive electrospray ionization mode at low, medium, and high collision energies (20, 35, and 50 eV). Purity and Fit score percentages against a 400-compound LC/MS/MS spectral library were calculated using an algorithm in which fragment intensity ratios and weighting factors were included. The long-term reproducibility study was conducted using a brand A instrument; after 4 years the reproducibility of the product ion spectra was still 94%, expressed as average Purity score. The inter-laboratory study involved two parts. Firstly, two LC/MS/MS spectral libraries, created independently in separate laboratories using brand A instruments, were compared with each other. The average Fit and Purity scores of spectra from one library against the other were better than 93 and 91%, respectively, when the same collision energies were used. Secondly, for the comparison of product ion spectra between brand A and brand B instruments, fragmentation conditions were first standardized for amitriptyline as the standard analyte. The average Fit scores of brand B spectra against the brand A spectral library varied between 79 and 85% at all three collision energies. These results indicate that, after standardizing the instrumental conditions, LC/MS/MS spectral libraries of drug substances are suitable for inter-laboratory use. 相似文献
Infusion-based electrospray ionization (ESI) coupled to multiple-stage tandem mass spectrometry (MSn) is a standard methodology for investigating lipid A structural diversity (Shaffer et al. J. Am. Soc. Mass. Spectrom. 18(6),
1080–1092, 2007). Annotation of these MSn spectra, however, has remained a manual, expert-driven process. In order to keep up with the data acquisition rates of modern
instruments, we devised a computational method to annotate lipid A MSn spectra rapidly and automatically, which we refer to as hierarchical tandem mass spectrometry (HiTMS) algorithm. As a first-pass
tool, HiTMS aids expert interpretation of lipid A MSn data by providing the analyst with a set of candidate structures that may then be confirmed or rejected. HiTMS deciphers
the signature ions (e.g., A-, Y-, and Z-type ions) and neutral losses of MSn spectra using a species-specific library based on general prior structural knowledge of the given lipid A species under investigation.
Candidates are selected by calculating the correlation between theoretical and acquired MSn spectra. At a false discovery rate of less than 0.01, HiTMS correctly assigned 85% of the structures in a library of 133
manually annotated Francisella tularensis subspecies novicida lipid A structures. Additionally, HiTMS correctly assigned 85% of the structures in a smaller library of lipid A species
from Yersinia pestis demonstrating that it may be used across species. 相似文献
The initial version of the new tandem mass spectral library of microcystins, toxic metabolites of cyanobacteria, and related compounds, is considered. There are 75 spectra of 28 compounds entered in the library. The library was tested by corresponding library searches which led to the true positive rate of ≥73%. A library search performance and enlargement of the library are discussed. 相似文献
Tandem mass spectral libraries are gaining more and more importance for the identification of unknowns in different fields
of research, including metabolomics, forensics, toxicology, and environmental analysis. Particularly, the recent invention
of reliable, robust, and transferable libraries has increased the general acceptance of these tools. Herein, we report on
results obtained from thorough evaluation of the match reliabilities of two tandem mass spectral libraries: the MSforID library
established by the Oberacher group in Innsbruck and the Weinmann library established by the Weinmann group in Freiburg. Three
different experiments were performed: (1) Spectra of the libraries were searched against their corresponding library after
excluding either this single compound-specific spectrum or all compound-specific spectra prior to searching; (2) the libraries
were searched against each other using either library as reference set or sample set; (3) spectra acquired on different mass
spectrometric instruments were matched to both libraries. Almost 13,000 tandem mass spectra were included in this study. The
MSforID search algorithm was used for spectral matching. Statistical evaluation of the library search results revealed that
principally both libraries enable the sensitive and specific identification of compounds. Due to higher mass accuracy of the
QqTOF compared with the QTrap instrument, matches to the MSforID library were more reliable when comparing spectra with both
libraries. Furthermore, only the MSforID library was shown to be efficiently transferable to different kinds of tandem mass
spectrometers, including “tandem-in-time” instruments; this is due to the coverage of a large range of different collision
energy settings—including the very low range—which is an outstanding characteristics of the MSforID library. 相似文献
In clinical or forensic toxicology, general unknown screening procedures are used to identify as many xenobiotics as possible,
belonging to numerous chemical classes. We present here a general unknown screening procedure based on liquid chromatography
coupled with use of a single linear ion trap mass spectrometer, and focus on the identification of pesticides and/or metabolites
in whole blood. After solid-phase extraction (SPE), the compounds of interest were separated using a reversed-phase column
and identified by the mass spectrometer operated first in the full-scan mass spectrometry (MS) mode, in the positive and negative
polarities, followed by MS2 and MS3 scanning of ions selected in data-dependent acquisition. The total scan time was 2.45 s. Two mass spectral libraries (MS2 and MS3), each of 450 spectra, were created for the 320 pesticides and metabolites detected after injection of pure solutions. Robustness
of the spectra and matrix effects were studied and were satisfactory for the present application. Detection limits for the
320 compounds were studied by extracting 1 mL spiked blood at concentrations between 10 μg/L and 10 mg/L. If necessary, it
was possible to decrease the detection limits of some compounds by 10–100-fold by scanning MS2 in only one polarity, owing to a shorter total scan time. However, at the same time, the detection specificity decreased
as no confirmation could be recorded in the following MS3 scan and no information could be registered in the other polarity. So, in these rare cases, confirmation by another method
was required. 相似文献
A new approach to the identification of microorganisms is presented. It includes the transformation of their MALDI mass spectra aimed at reducing mass scale by one order of magnitude and the use of standard software for building mass spectral libraries of low-molecular compounds and library searches. A library of 728 transformed (“rescaled”) mass spectra of 182 strains for some Streptococcus species was built. With this library, the rate of true microorganism identification was estimated by cross-comparison between library mass spectra (internal validation of the approach). The true identification rate was 84% for three Streptococcus species, which corresponds to the average trueness of species identification by MALDI as found in the literature. The proposed approach to identification can be considered as a method of choice for solving identification problems under consideration. 相似文献
Ultraperformance convergence chromatography/tandem triple quadrupole mass spectrometry (UPC2-MS/MS) is a novel tool in separation science that combines the advantages of supercritical fluid chromatography with ultraperformance liquid chromatography/MS/MS technology. The use of nontoxic CO2 fluid and a postcolumn additive to complement MS/MS allows better control of analyte retention for chiral separation and high-sensitivity determination with different chiral stationary phases. This paper reports the stereoselective separation and determination of the chiral neonicotinoid sulfoxaflor in vegetables and soil by UPC2-MS/MS. Baseline resolution (Rs?≥?1.56) of and high selectivity (LOQ?≤?1.83 μg/kg) for the four stereoisomers were achieved by postcolumn addition of 1 % formic acid–methanol to a Chiralpak IA-3 using CO2/isopropanol/acetonitrile as the mobile phase at 40 °C, 2,500 psi, and for 6.5 min in electrospray ionization positive mode. Rearranged Van’t Hoff equations afforded the thermodynamic parameters ΔHο and ΔSο, which were analyzed to promote understanding of the enthalpy-driven separation of sulfoxaflor stereoisomers. The interday mean recovery, intraday repeatability, and interday reproducibility varied from 72.9 to 103.7 %, from 1.8 to 9.2 %, and from 3.1 to 9.4 %, respectively. The proposed method was used to study the pharmacokinetic dissipation of sulfoxaflor stereoisomers in soil under greenhouse conditions. The estimated half-life ranged from 5.59 to 6.03 d, and statistically nonsignificant enantioselective degradation was observed. This study not only demonstrates that the UPC2-MS/MS system is an efficient and sensitive method for sulfoxaflor stereoseparation, but also provides the first experimental evidence of the pharmacokinetic dissipation of sulfoxaflor stereoisomers in the environment. Graphical Abstract
Chemical structure and UPC2-MS/MS separation chromatogram of sulfoxaflor. (* stereogenic center)相似文献
In clinical toxicology, fast and specific methods are necessary for the screening of different classes of drugs. Therefore,
an online extraction high-performance liquid chromatography coupled to mass spectrometry (LC-MSn) screening method using a MS2 and MS3 spectral library for the identification of xenobiotic substances has been developed and validated. Samples were run twice,
once native and once after enzymatic hydrolysis. Internal standards and buffer were added to the urine samples. Following
centrifugation, the supernatant was injected into the system. Extraction was performed by online turbulent flow chromatography.
The chromatographic separation was achieved using a Phenyl/Hexyl column. For detection, a linear ion trap, equipped with an
APCI interface, was used and the different compounds were identified using a MS2 and MS3 spectral library containing 356 compounds. The turnaround time to report the results of the screening including hydrolysis
was approximately 2 h. About 92% of the 356 substances could be identified with a limit of identification below 100 ng/ml.
The recovery and matrix effect experiments showed suitable results, and in six drug-free urine samples of healthy volunteers
analyzed for selectivity, no substances have been identified. Carryover could be well controlled, and the method had a good
reproducibility. The comparison of the results of 103 real patient urine samples showed a good agreement between the existing
GC-MS and LC-MS methods with offline extraction and the new online extraction LC-MSn screening method. The presented method allows a fast and sensitive analysis of a broad range of compounds. 相似文献