Analytical Instrument Documents

Using chemical fingerprints for timber species identification is a relatively new, but promising technique. However, little is known about the effect of pre-processing spectral data parameter settings on the timber species classification accuracy. Therefore, this study presents an extensive and automated analysis method using the random forest machine learning algorithm on a set of highly valuable timber species from the Meliaceae family. Metabolome profiles were collected using direct analysis in real-time (DART™) ionisation coupled with time-of-flight mass spectrometry (TOFMS) analysis of heartwood specimens for 175 individuals (representing 10 species). In order to analyse variability in classification accuracy, 110 sets of data pre-processing parameter combinations consisting of mass tolerance for binning and relative abundance cut-off thresholds were tested. Furthermore, for each set of parameters (designated “binning/threshold setting”), a random search for one hyperparameter of interest was performed, i.e. the number of variables (in this case ions) drawn randomly for each random forest analysis. The best classification accuracy (82.2%) was achieved with 47 variables and a binning and threshold combination of 40 mDa and 4%, respectively. Entandrophragma angolense is mostly confused with Entandrophragma candollei and Khaya anthotheca, and several Swietenia species are confused with each other due to the high similarity of their chemical fingerprints. Entandrophragma cylindricum, Entandrophragma utile, Khaya ivorensis, Lovoa trichilioides and Swietenia macrophylla are easy to discriminate and show less misclassifications. The choice of parameter settings, whether it is in the data pre-processing (binning and threshold) or classification algorithm (hyperparameters), results in variability in classification accuracy. Therefore, a preliminary parameter screening is proposed before constructing the final model when using the random forest algorithm for classification. Overall, DART-TOFMS in combination with random forest is a powerful tool for species identification.

A high throughput method for species identification and classification through chemometric processing of direct analysis in real time (DART) mass spectrometry-derived fingerprint signatures has been developed. The method entails introduction of samples to the open air space between the DART ion source and the mass spectrometer inlet, with the entire observed mass spectral fingerprint subjected to unsupervised hierarchical clustering processing. A range of both polar and non-polar chemotypes are instantaneously detected. The result is identification and species level classification based on the entire DART-MS spectrum. Here, we illustrate how the method can be used to: (1) distinguish between endangered woods regulated by the Convention for the International Trade of Endangered Flora and Fauna (CITES) treaty; (2) assess the origin and by extension the properties of biodiesel feedstocks; (3) determine insect species from analysis of puparial casings; (4) distinguish between psychoactive plants products; and (5) differentiate between Eucalyptus species. An advantage of the hierarchical clustering approach to processing of the DART-MS derived fingerprint is that it shows both similarities and differences between species based on their chemotypes. Furthermore, full knowledge of the identities of the constituents contained within the small molecule profile of analyzed samples is not required.

A new MALDI-TOF/TOF system with monoisotopic precursor selection was applied to the analysis of triacylglycerols in an olive oil sample. Monoisotopic precursor selection made it possible to obtain product-ion mass spectra without interference from species that differed by a single double bond. Complete structure determination of all triacylglycerols, including structural isomers, was made possible by interpreting the charge-remote fragmentation resulting from high-energy collision-induced dissociation (CID) of the sodiated triacylglycerols.

A Japanese lacquer film called "Urushi" is a natural polymer that has been used as a paint and adhesive for living-wares and craft-wares for approximately 8,000 years. "Urushi" has a complex structure that researchers are trying to understand using pyrolysis-gas chromatograph/mass spectrometer (Py/GC/MS) system. Recently, we developed a new gas chromatograph/high resolution time-of-flight mass spectrometer (GC/HR-TOFMS) system that can be used for comprehensive two-dimensional GC (GCxGC) measurements. Additionally, we have developed a unique combination electron ionization/photoionization (EI/PI) ion source that can be used with this GC/HR-TOFMS system. In this work, we measured "Urushi" samples using this unique Py/GCxGC/HR-TOFMS system in combination with our new combination EI/PI ion source.

Last Updated: September 2013

Since 1998 the serious public health problem in South East Asia of counterfeit artesunate, containing no or subtherapeutic amounts of the active antimalarial ingredient, has led to deaths from untreated malaria, reduced confidence in this vital drug, large economic losses for the legitimate manufacturers, and concerns that artemisinin resistance might be engendered.

Last Updated: December 2014

High-resolution mass spectrometry (HRMS) continues to play an important role in the compositional characterization of larger organic molecules. In the field of polymer characterization, however, the application of HRMS has made only slow progress because of lower compatibility between matrix-assisted laser desorption/ionization (MALDI) and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS). In this study, a newly developed type of MALDI high-resolution time-of-flight mass spectrometry (TOFMS) with a spiral ion trajectory (MALDI spiral-TOFMS) was applied to the structural and compositional characterization of polymers. To create a graphical distribution of polymer components on a two-dimensional plot converted from complex mass spectra, we adopted a slightly modified Kendrick mass defect (KMD) analysis based on accurate masses determined using spiral-TOFMS. By setting the Kendrick mass scale based on the mass of the repeating units of a given polymer, components with common repeat units lined up in the horizontal direction on the KMD plot, whereas those components with different structures were shifted vertically. This combination of MALDI spiral-TOFMS measurement and KMD analysis enabled the successful discrimination of the polymer components in a blend of poly(alkylene oxide)s, the compositional analysis of poly(ethylene oxide)/poly(propylene oxide) block copolymers, and profiling of the end-group distribution of poly(ε- caprolactone)s synthesized under different conditions.

Traceability and authenticity of olive oils in Croatia were probed by a versatile analytical approach using spiral MALDI-TOF MS system for the triacylglycerol (TAG) analysis. Molecular ion patterns were shown to represent specific data for statistical analysis, in which differences of cultivar regions of Croatian coast were recognized. This pilot project allows indications to be followed in high throughput procedures with high number of samples to get statistically relevant data for discrimination of olive oils from different geographic sites. Additionally, the fragmentation in the TOF/TOF MS provided distinct highly valuable data for assignment of acyl residues. In this way molecular species with different fatty acid substituents can be clearly assigned and possible isomeric mixtures identified.

The structural characterization of copolymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) remains a challenging task, since their random comonomer distribution creates very complicated mass spectra. In this study, a high-resolution TOF mass spectrometer with a spiral ion trajectory was applied to the structural and compositional characterization of free radical copolymerized poly(methyl methacrylate-co-tert-butyl methacrylate), poly(MMA-co-tBMA)s in ethyl lactate acting as a chain transfer agent. Virtually complete peak assignments of the isobaric components within the poly(MMA-co-tBMA)s served to identify the end-group combinations and copolymer compositions of individual copolymer components, allowing the distributions of comonomer compositions and six types of end-group combinations to be evaluated.

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