3 research outputs found
DART-MS: A New Analytical Technique for Forensic Paint Analysis
Automotive paint evidence is one
of the most significant forms
of evidence obtained in automotive-related incidents. Therefore, the
analysis of automotive paint evidence is imperative in forensic casework.
Most analytical schemes for automotive paint characterization involve
optical microscopy, followed by infrared spectroscopy and pyrolysis-gas
chromatography mass spectrometry (<i>py</i>-GCMS) if required.
The main drawback with <i>py</i>-GCMS, aside from its destructive
nature, is that this technique is relatively time intensive in comparison
to other techniques. Direct analysis in real-time–time-of-flight
mass spectrometry (DART-TOFMS) may provide an alternative to <i>py</i>-GCMS, as the rapidity of analysis and minimal sample
preparation affords a significant advantage. In this study, automotive
clear coats from four vehicles were characterized by DART-TOFMS and
a standard <i>py</i>-GCMS protocol. Principal component
analysis was utilized to interpret the resultant data and suggested
the two techniques provided analogous sample discrimination. Moreover,
in some instances DART-TOFMS was able to identify components not observed
by <i>py</i>-GCMS and vice versa, which indicates that the
two techniques may provide complementary information. Additionally,
a thermal desorption/pyrolysis DART-TOFMS methodology was also evaluated
to characterize the intact paint chips from the vehicles to ascertain
if the linear temperature gradient provided additional discriminatory
information. All the paint samples were able to be discriminated based
on the distinctive thermal desorption plots afforded from this technique,
which may also be utilized for sample discrimination. On the basis
of the results, DART-TOFMS may provide an additional tool to the forensic
paint examiner
Development of “Laser Ablation Direct Analysis in Real Time Imaging” Mass Spectrometry: Application to Spatial Distribution Mapping of Metabolites Along the Biosynthetic Cascade Leading to Synthesis of Atropine and Scopolamine in Plant Tissue
Methods
for the accomplishment of small-molecule imaging by mass
spectrometry are challenged by the need for sample pretreatment steps,
such as cryo-sectioning, dehydration, chemical fixation, or application
of a matrix or solvent, that must be performed to obtain interpretable
spatial distribution data. Furthermore, these steps along with requirements
of the mass analyzer such as high vacuum, can severely limit the range
of sample types that can be analyzed by this powerful method. Here,
we report the development of a laser ablation-direct analysis in real
time imaging mass spectrometry approach which couples a 213 nm Nd:YAG
solid state UV laser to a direct analysis in a real time ion source
and high-resolution time-of-flight mass spectrometer. This platform
enables facile determination of the spatial distribution of small-molecules
spanning a range of polarities in a diversity of sample types and
requires no matrix, vacuum, solvent, or complicated sample pretreatment
steps. It furnishes high-resolution data, can be performed under ambient
conditions on samples in their native form, and results in little
to no fragmentation of analytes. We demonstrate its application through
determination of the spatial distribution of molecules involved in
the biosynthetic cascade leading to formation of the clinically relevant
alkaloids atropine and scopolamine in <i>Datura leichhardtii</i> seed tissue
Molecular Characterization of Volatiles and Petrochemical Base Oils by Photo-Ionization GC×GC-TOF-MS
The characterization
of organic mixtures by comprehensive two-dimensional
gas chromatography (GC×GC) coupled to electron impact (EI) ionization
time-of-flight mass spectrometry (TOF-MS) allows the detection of
thousands of compounds. However, owing to the exhaustive fragmentation
following EI ionization, despite the use of mass spectral libraries,
a majority of the compounds remains unidentified because of the lack
of parent ion preservation. Thus, soft-ionization energies leading
to organic compounds being ionized with limited or no fragmentation,
retaining the molecular ion, has been of interest for many years.
In this study, photoionization (PI) was evaluated as the ion source for GC×GC-TOF-MS measurements.
First, capabilities and limitations of PI were tested using an authentic
mixture of compounds of several chemical classes. Ionization energy
exhibited by PI, equivalent to 10.8 eV, resulted in significant retention
of molecular ion information; [M]<sup>+•</sup> for alkanes,
ketones, FAMEs, aromatics, [M–H]<sup>+•</sup> for chloroalkanes,
and [M–H<sub>2</sub>O]<sup>+•</sup> for alcohols. Second,
considering the potential of PI for hydrocarbons, base oils, complex
mixtures of saturated and unsaturated hydrocarbons blended for finished
lubricant formulations, were extensively evaluated. Several chemical
classes of hydrocarbons were positively identified including a large
number of isomeric compounds, both aliphatics and cyclics. Interestingly,
branched-alkanes were ionized with lower excess internal energy, not
only retaining the molecular ions but also exhibiting unique fragmentation
patterns. The results presented herein offer a unique perspective
into the detailed molecular characterization of base oils. Such unprecedented
identification power of PI coupled with GC×GC-TOF-MS is the first
report covering volatiles to low-volatile organic mixtures