More Like this

1. U-Pb dating of accessory minerals by LA-ICP-MS/MS

   Stone, JS; Cruz-Uribe, AM; Brooks, HL; Walters, J (January 2019, 2019 Fall Meeting AGU)

   Titanite and apatite can incorporate significant amounts of common Pb (204Pb) into their mineral structures, which leads to uncertainty when applying the U-Pb decay series for geochronology. The isobaric interference between 204Pb and 204Hg creates an additional complexity when calculating common lead corrections. Here we investigate the removal of 204Hg interferences during titanite U-Pb dating using reaction cell gas chemistry via triple quadrupole mass spectrometry compared with traditional methods that calculate U-Pb ages using a common lead correction. U-Pb dates for titanite natural reference materials MKED-1 and BLR-1 were determined using an ESI NWR193UC excimer laser coupled with an Agilent 8900 ‘triple quadrupole’ mass spectrometer. The 8900 is equipped with an octopole collision/reaction cell, which enables online interference removal. In order to compare traditional methods for U-Pb dating with interference removal methods, two experiments were run, one in which data was collected in NoGas mode, and one in which the 8900 was run in MS/MS mode, in order to assess the feasibility of determining U/Pb ratios with mass shifted isotopes. In MS/MS mode, NH3 was flowed through the reaction cell in order to enable a charge transfer reaction between NH3 and Hg+, effectively neutralizing Hg. During spot analyses in NoGas mode, masses 202Hg, 204Hg, 204Pb, 206Pb, 207Pb, 208Pb, 232Th, 235U, and 238U were monitored. For spot analyses in MS/MS mode, Th and U isotopes were measured on-mass at 232Th, 235U, 238U and mass-shifted to 247Th, 250U, and 253U. Pb isotopes were measured on-mass since Pb does not react with NH3. Ratios for 207Pb/235U, 206Pb/238U, and 207Pb/206Pb were calculated in Iolite (v.3.7.1) using the Geochron4 DRS using MKED-1 as the primary reference material and BLR-1 as a secondary reference material. Dates were calculated using IsoplotR. Weighted mean ages for titanite BLR-1 in MS/MS mode are 1043.8 ± 10.5 Ma (2σ, MSWD=1.08) for U isotopes measured on mass, and 1039.7 ± 8.3 Ma (2σ, MSWD=1.08) for mass-shifted U isotopes. These dates are both in agreement with the TIMS 206Pb/238U date for the BLR-1 titanite of 1047.1 ± 0.4 Ma. The use of NH3 for reaction cell chemistry has the potential to enable measurement of 204Pb without needing to correct for Hg interferences. 

   more » « less
2. Direct sequencing of total S. cerevisiae tRNAs by LC-MS/MS

   https://doi.org/10.1261/rna.079656.123  

   Jones, Joshua D; Simcox, Kaley M; Kennedy, Robert T; Koutmou, Kristin S (May 2023, RNA)

   Among RNAs, transfer RNAs (tRNAs) contain the widest variety of abundant post-transcriptional chemical modifications. These modifications are crucial for tRNAs to participate in protein synthesis, promoting proper tRNA structure and aminoacylation, facilitating anticodon:codon recognition, and ensuring the reading frame maintenance of the ribosome. While tRNA modifications were long thought to be stoichiometric, it is becoming increasingly apparent that these modifications can change dynamically in response to the cellular environment. The ability to broadly characterize the fluctuating tRNA modification landscape will be essential for establishing the molecular level contributions of individual sites of tRNA modification. The locations of modifications within individual tRNA sequences can be mapped using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). In this approach, a single tRNA species is purified, treated with ribonucleases and the resulting single-stranded RNA products are subject to LC-MS/MS analysis. The application of LC-MS/MS to study tRNAs is limited by the necessity of analyzing one tRNA at a time because the digestion of total tRNA mixtures by commercially available ribonucleases produces many short digestion products unable to be uniquely mapped back to a single site within a tRNA. We overcame these limitations by taking advantage of the highly structured nature of tRNAs to prevent the full digestion by single-stranded RNA specific ribonucleases. Folding total tRNA prior to digestion allowed us to sequence S. cerevisiae tRNAs with up to 97% sequence coverage for individual tRNA species by LC-MS/MS. This method presents a robust avenue for directly detecting the distribution of modifications in total tRNAs. 

   more » « less
3. Prospects and challenges for in situ beta decay geochronology by MC-ICP-MS/MS

   Cruz-Uribe, AM; Garber, J; Arkula, C; Craig, G; Paul, B; Bouman, C (July 2024, 2024 European Workshop on Laser Ablation)
4. Investigating Byssogenesis with Proteomic Analysis of Byssus, Foot, and Mantle in Mytilus Mussels by LC‐MS/MS

   https://doi.org/10.1002/pmic.202000014  

   Sansoucy, Maxime; Tremblay, Réjean; Carrington, Emily; Marcotte, Isabelle; Sleno, Lekha (January 2021, PROTEOMICS)
5. U-Pb dating of titanite by LA-ICP-QQQ-MS

   Stone, Joshua S; Cruz-Uribe, AM; Brooks, HL (May 2019, North American Workshop on Laser Ablation 2019 Abstracts)

   Titanite has the ability to incorporate significant amounts of common Pb, which leads to uncertainty when applying the U-Pb decay series for geochronology. The isobaric interference of 204Hg on 204Pb poses an additional complexity in applying common Pb corrections. Here we investigate the removal of 204Hg interferences during titanite U-Pb dating using reaction cell gas chemistry via triple quadrupole mass spectrometry. U-Pb dates were determined for the natural titanite reference materials MKED-1 and BLR1 using an ESI NWR193UC excimer laser coupled to an Agilent 8900 ‘triple quad’ mass spectrometer. The 8900 is equipped with an octopole collision/reaction cell, which enables online interference removal. Two experiments were run, one in which we collected data in NoGas mode, and one in which NH3 was used as a reaction cell gas in MS/MS mode, in order to assess the feasibility of determining U/Pb ratios with mass shifted isotopes. In all experiments, a signal smoothing device was placed inline just before the ICP-MS interface, downstream from the addition of the Ar nebulizer gas to the He carrier gas stream. For the NoGas experiment, titanite was ablated using a 25 µm spot, with a beam energy density of 3 J/cm2, and a pulse rate of 4 Hz. In NoGas mode, signal intensities for the isotopes 201Hg, 202Hg, 204Pb, 206Pb, 207Pb, 232Th, 235U, and 238U were counted. In MS/MS mode, titanite was ablated using a 40 µm spot, with a beam energy density of 5 J/cm2, and a pulse rate of 4 Hz. A larger spot size in this experiment was used to counteract the decrease in signal intensity due to use of the reaction cell. In MS/MS mode, NH3 was flowed through the reaction cell in order to enable a charge transfer reaction between NH3 and Hg+, effectively neutralizing Hg. The isotopes 201Hg, 202Hg, 204Pb, 206Pb, and 207Pb were measured on-mass, as the isotopes of Pb are not affected by the NH3 gas. Uranium and Th both exhibit partial reaction with NH3 gas; therefore, the isotopes 232Th, 235U, and 238U were measured mass-shifted up 15 mass units, at masses 247, 250, and 253 respectively. Ratios of 207Pb/235U, 206Pb/238U, and 207Pb/206Pb were determined using the UPbGeochron4 DRS in Iolite (v.3.71) with MKED-1 as the primary reference material. Dates were calculated using IsoplotR by applying the Stacey-Kramers correction for common Pb. All isotopes of Hg were effectively neutralized by the NH3 charge transfer reaction in MS/MS mode; zero counts were detected for Hg isotopes. Dates for the BLR-1 titanite were 1050.55 ± 2.72 (2σ, n=12) Ma in NoGas mode, and 1048 ± 1.88 (2σ, n=15) Ma in MS/MS mode. These dates are in excellent agreement with the TIMS 206Pb/238U date for the BLR-1 titanite of 1047.1 ± 0.4 Ma. This method has the potential to enable measurement of 204Pb without needing to correct for Hg interferences. 

   more » « less