Laser-ablation for the analysis of anthropological evidence
Mauro Martinez, Matthieu Baudelet
National Center for Forensic Science and Chemistry Department, University of Central Florida
The study of anthropological evidence has seen a new dimension with elemental analysis. For a long time, it relied on XRF and/or ICP-MS. The introduction of laser-ablation has given the opportunity to reduce sample preparation while having full access to the whole periodic table with limits of detection from ppb’s to %. This talk will show the use of Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation ICP-MS (LA-ICP-MS) for anthropological materials, from the cultural to the forensic point of view. We consider anthropological evidence in a general sense (not only bones but also hair and teeth).
Bone analysis has mainly relied on osteology and is based on the practitioner’s experience, or consist in the use with empirical mathematical formulas and comparison in databases. This talk will present new approaches for the use of LIBS and results that extend the capability of elemental analysis for forensic analysis.
Teeth are great indicators in the human body for growth, evolution of diet and even geographical movements. This information can be extracted from LA-ICP-MS elemental maps. Information on the history and cultural distribution of an archaeological population will be discussed.
DNA is not easy to recover from hair, preventing sex determination in some cases. Using LIBS on the hair, we identified different minor elements of interest that can reflect the metabolism change in the body that can be different between male and female individuals. This study substantiates the potential of the elemental analysis of hair as a proxy for human sex determination.
Mass Selection of Van der Waals-Tagged Ions within a Cryogenic Linear Ion Trap
Larry Tesler; Nicolas C. Polfer
University of Florida, Department of Chemistry
Infrared ion spectroscopy has the potential to become a gold standard technique for molecular identification in mass spectrometry;1 however, the low duty cycle of the technique, where only one analyte is probed at one laser wavelength at one time, imposes a significant impediment for analytical applications. Prior work showed that using a cryogenic linear ion trap (cryoLIT), multiple solvent-tagged ions can be mass-isolated, irradiated, and mass detected in a multiplexed manner and thus significantly improving throughput;2,3 however, the solvent-tagged ions require multiple photons to lose their tags leading to band broadening and shifting, and the polar solvent molecules will perturb the IR spectrum of the analyte4. Tagging the analyte ions, through van der Waals interactions, with an inert gas (i.e. N2) is preferable as it is in principle a more innocent tag that only requires a single photon to evaporate off the analyte.3 With that in mind, N2-tagged infrared photodissociation will be the focus of this talk.
The cryoLIT is a cryogenic linear ion trap extension to a custom mass spectrometer (ESI-QMF-QIT-TOF).2 The cryoLIT is cooled by a temperature-controlled cryostat with the temperature monitored at the coldfinger and one of the DC endplates. Tagging and collisional-cooling gas is introduced into the trap via a solenoid pulse valve. Tagged ions are mass selected via a stored waveform inverse Fourier Transform (SWIFT) excitation, followed by irradiation with a tunable optical parametric oscillator (OPO) light source (LaserVision) from 2000 to 4000 cm-1 to induce infrared photodissociation (IRPD), which manifests itself by loss of the tag. The relative populations of untagged and tagged ions are detected through a resonant mass instability scan.
As of now, N2-tagged ions have been observed for several ion species; when obtaining a mass spectrum of loperamide (m/z 477), the singly (m/z 505) and doubly (m/z 535) tagged ions are observed with a singly tagged efficiency of 11% at trap temperature of 23K. Using a SWIFT waveform, the singly tagged loperamide ion was mass isolated from the untagged and doubly tagged ions, demonstrating that IRPD experiments are possible with N2-tagged ions. N2-tagging has also been observed for tryptophan (m/z 205), and an IRPD spectrum of the N2-tagged molecule has been reported.3 Further investigation of N2-tagging within the cryoLIT will be done by looking at N2-tagging of RRL4G (polypeptide) and its fragments; tagging yields will be analyzed to determine how N2-tagging behaves as a function of trap temperature and molecular properties (i.e. mass, charge, collisional cross-section).
(1) J. Am. Soc. Mass Spectrom., 27, 757 (2016)
(2) J. Mass Spectrom., 52, 720 (2017)
(3) Analyst, 143, 1615 (2018)
(4) M. R. Bell, W. D. Vinicius, A. P. Cismesia, L. F. Tesler, A. E. Roitberg and N. C. Polfer, In Preparation.
Fabric Phase Sorptive Extraction: a Unique Integration of Solid Phase Extraction (SPE) and Solid Phase Microextraction (SPME)
Abuzar Kabir and Kenneth G. furton
Florida International University
Sample preparation remains as the bottleneck in the analytical workflow. As such, the significant improvements in chromatographic separation and mass-spectrometric detection in recent years have not been fully exploited. Among the conventional sample preparation techniques, SPE utilizes exhaustive extraction principle and generally employed small ligands such as C8, C18 bonded to silica particles. SPME, on the other hand, utilizes equilibrium driven extraction principle and primarily employs long-chain organic polymers, immobilized on a fused silica fiber. Although, SPE and SPME are different in principle and applications, both require sample pretreatment processes such as filtration, centrifugation, protein precipitation etc., prior to analyte extraction. These extra steps are laborious, time consuming, and often results in significant analyte loss.
Fabric sorptive extraction (FPSE) is developed to prepare samples containing high volume of interferents without any sample pretreatment. The FPSE device utilizes a piece of fabric as the substrate to chemically bind polymeric sorbent via sol-gel reaction. The sol-gel sorbent provides unique selectivity, sponge-like porous sorbent allows rapid mass transfer of the analyte for analyte-sorbent interaction and the fabric substrate acts as a bait via hydrophilic interactions to lure the target analyte(s). As a result, FPSE provides a near exhaustive extraction in a relatively short period.
After the extraction, the device is exposed to a small volume of organic solvent for analyte back-extraction. Finally, the sample can be injected simultaneously into LC/GC/CE for complementary information. Several recent applications of FPSE for extracting a number of important analytes from different sample matrices will be presented.
Manganese Dioxide Nanoparticle Formation and Electrochemical Characterization
Juliette Experton, Xiaojian Wu, Gelan Wang, Charles R. Martin
Department of Chemistry, University of Florida, Gainesville, FL 32611
Manganese dioxide is an environmentally abundant material that shows considerable interest for energy-related applications, such as supercapacitor and cathode material in batteries. However, its use is currently limited by its poor cyclability and its low ionic and electronic conductivities. To overcome these limitations, many strategies have been centered on the design of MnO2 nanoparticles to reduce the diffusion distance for the insertion cations. We have developed a method to grow MnO2 nanoparticles on gold nanotubes in the absence of a direct electrical contact. This method entails using gold nanotubes as bipolar electrode. A voltage of 2 V is applied across a gold nanotube membrane to generate redox reactions, one cathodic and one anodic, at either end of the tubes. The anodic reaction is chosen such that it forms MnO2 nanoparticles at one opening of the nanotubes. We describe here the mechanism of electrodeposition of these MnO2 nanoparticles. Furthermore, electrochemical measurements of conductivity and permselectivity are presented to address the performance of MnO2 as a cathode material in lithium-ion batteries.
Avoiding misidentification of phosphopeptides: Exploring the factors that enhance and inhibit phosphate scrambling in peptide sequencing
Laura S. Baileya, Melanie Alvasb, Nicolas Galyc, Amanda L. Patricka, Nicolas C. Polfera
a University of Florida, Department of Chemistry, Gainesville, FL, USA
b Sorbonne Université, Paris, France
c Université Paul Sabatier, Toulouse, France
Phosphorylation is one of the most ubiquitous post-translational modifications (PTM) in proteins, and thus plays a critical factor in many regulatory mechanisms. Although this PTM is most commonly found on serine (90%), threonine (10%), and tyrosine (0.05%), it has also been found on histidine and arginine (mainly in eukaryotes) . Mass spectrometry-based sequencing is the key technology for peptide/protein identification, as well as identification of any PTMs. This typically involves peptide fragmentation via collision-induced dissociation (CID). However, the high lability of PTMs often leads to uninformative fragmentation, such as loss of these groups. Even more worryingly, phosphate groups may be subject to intramolecular transfer—often referred to as sequence “scrambling”— which may result in incorrect sequencing . In a systematic study, we aim to determine the mechanism behind phosphate scrambling and if this transfer can be minimized.
Our template sequence G[B]AXDAAPAAXAPAA[B]AAR (where XD is phosphorylated donor tyrosine or serine residue, XA is a non-phosphorylated acceptor residue, and [B] represents where a basic residue may be added) was simplified from Cui and Reid’s work. The most scrambled Reid sequence, GRApSpSPVPAPSSGLHAAVR, showed an average rearrangement of 42.3% (defined as the number of scrambled fragments verses the sum of scrambled and un-scrambled fragments), and similar sequences showed scrambling ratios ranging from 10% to 50% ; however, our simplified alanine version only showed 2% scrambling. In a systematic study of 13 sequences, we investigated how several parameters affected phosphate scrambling, including the phosphate donor and acceptor identity (tyrosine vs. serine), the number of donors and acceptors (1:1, 1:2, and 2:2 donor:acceptor ratios), the contribution of basic residues, and the position of the basic residue near either the carboxy- or amino-terminus. While the number and identity of donors and acceptors had little effect on scrambling (scrambling ratios of 0.1-5%), higher scrambling ratios were observed when a basic residue was added near the carboxy-terminus (14% for arginine and 30% for histidine).
Secondly, we sought to inhibit the intramolecular transfer, thereby eliminating the appearance of scrambled fragments. Towards this end, appearance of scrambled fragments was investigated based on the timescale of activation (i.e., slow vs. fast), location of fragmentation (i.e., trap vs. collision cell), and charge state. Fast activation nearly eliminated scrambling in the histidine sequence (2% scrambling). Further, increasing the charge state decreased the appearance of scrambled fragments from 30% ([y11+HPO3]+1) for a charge state of +2 to 15% ([y10+HPO3]+2) for the +3 charge state and 5% ([y7+HPO3]+2) for the +4 charge state. Therefore, while histidine appears necessary for the transfer of phosphate, the specificity of conditions (especially the protonation of the mediating residue) would indicate it’s an uncommon occurrence in proteomics.
 Proteomics 2013, 13 (6), 910–931.  J. Mass Spectrom. 2009, 44 (6), 861–878.  Proteomics 2013, 13 (6), 964–973.
USF Human Donation Program: Experimental Research in Decomposition
Erin H. Kimmerle, Ph.D.
Florida Institute for Forensic Anthropology and Applied Science, University of South Florida
In 2016, USF initiated a human donation program for experimental research in forensic anthropology, outdoor crime scenes, legal medicine, and related forensic sciences. The 3.5-acre Adam Kennedy Memorial Forensic Field, established for outdoor research utilizes donors for research in forensic anthropology, geochemistry, geophysics, biochemistry, ecology, and forensic art. Currently, numerous projects investigating human decomposition, the effects of scavenging, geochemical analysis for human identification, and various methods of remote sensing for locating and documenting clandestine graves are underway. There have been 21 donors and more than 75 pre-donors register. The establishment of this program and the preliminary areas of research will be discussed. More specifically, the research on progressive decomposition to establish baseline rates in Florida shows that the effects of vulture and opossum scavenging on remains plays a significant role in the rate of decomposition, more than any other variable. The scavengers can also cause skeletal fractures and damage that mimics trauma and unexpected alterations to the body and scene.