skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Toward high-resolution NMR spectroscopy of microscopic liquid samples

Abstract

A longstanding limitation of high-resolution NMR spectroscopy is the requirement for samples to have macroscopic dimensions. Commercial probes, for example, are designed for volumes of at least 5 mL, in spite of decades of work directed toward the goal of miniaturization. Progress in miniaturizing inductive detectors has been limited by a perceived need to meet two technical requirements: (1) minimal separation between the sample and the detector, which is essential for sensitivity, and (2) near-perfect magnetic-field homogeneity at the sample, which is typically needed for spectral resolution. The first of these requirements is real, but the second can be relaxed, as we demonstrate here. By using pulse sequences that yield high-resolution spectra in an inhomogeneous field, we eliminate the need for near-perfect field homogeneity and the accompanying requirement for susceptibility matching of microfabricated detector components. With this requirement removed, typical imperfections in microfabricated components can be tolerated, and detector dimensions can be matched to those of the sample, even for samples of volume << 5 uL. Pulse sequences that are robust to field inhomogeneity thus enable small-volume detection with optimal sensitivity. We illustrate the potential of this approach to miniaturization by presenting spectra acquired with a flat-wire detector that canmore » easily be scaled to subnanoliter volumes. In particular, we report high-resolution NMR spectroscopy of an alanine sample of volume 500 pL.« less

Authors:
ORCiD logo; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1371965
Report Number(s):
PNNL-SA-126952
Journal ID: ISSN 1463-9076; PPCPFQ; 49151; 49164
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 19; Journal Issue: 22
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Environmental Molecular Sciences Laboratory

Citation Formats

Butler, Mark C., Mehta, Hardeep S., Chen, Ying, Reardon, Patrick N., Renslow, Ryan S., Khbeis, Michael, Irish, Duane, and Mueller, Karl T.. Toward high-resolution NMR spectroscopy of microscopic liquid samples. United States: N. p., 2017. Web. doi:10.1039/c7cp01933e.
Butler, Mark C., Mehta, Hardeep S., Chen, Ying, Reardon, Patrick N., Renslow, Ryan S., Khbeis, Michael, Irish, Duane, & Mueller, Karl T.. Toward high-resolution NMR spectroscopy of microscopic liquid samples. United States. doi:10.1039/c7cp01933e.
Butler, Mark C., Mehta, Hardeep S., Chen, Ying, Reardon, Patrick N., Renslow, Ryan S., Khbeis, Michael, Irish, Duane, and Mueller, Karl T.. 2017. "Toward high-resolution NMR spectroscopy of microscopic liquid samples". United States. doi:10.1039/c7cp01933e.
@article{osti_1371965,
title = {Toward high-resolution NMR spectroscopy of microscopic liquid samples},
author = {Butler, Mark C. and Mehta, Hardeep S. and Chen, Ying and Reardon, Patrick N. and Renslow, Ryan S. and Khbeis, Michael and Irish, Duane and Mueller, Karl T.},
abstractNote = {A longstanding limitation of high-resolution NMR spectroscopy is the requirement for samples to have macroscopic dimensions. Commercial probes, for example, are designed for volumes of at least 5 mL, in spite of decades of work directed toward the goal of miniaturization. Progress in miniaturizing inductive detectors has been limited by a perceived need to meet two technical requirements: (1) minimal separation between the sample and the detector, which is essential for sensitivity, and (2) near-perfect magnetic-field homogeneity at the sample, which is typically needed for spectral resolution. The first of these requirements is real, but the second can be relaxed, as we demonstrate here. By using pulse sequences that yield high-resolution spectra in an inhomogeneous field, we eliminate the need for near-perfect field homogeneity and the accompanying requirement for susceptibility matching of microfabricated detector components. With this requirement removed, typical imperfections in microfabricated components can be tolerated, and detector dimensions can be matched to those of the sample, even for samples of volume << 5 uL. Pulse sequences that are robust to field inhomogeneity thus enable small-volume detection with optimal sensitivity. We illustrate the potential of this approach to miniaturization by presenting spectra acquired with a flat-wire detector that can easily be scaled to subnanoliter volumes. In particular, we report high-resolution NMR spectroscopy of an alanine sample of volume 500 pL.},
doi = {10.1039/c7cp01933e},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
number = 22,
volume = 19,
place = {United States},
year = 2017,
month = 1
}
  • Quantitative analysis of individual compounds in complex mixtures using high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) is complicated by differences in the ionization efficiencies of analyte molecules in the mixture, resulting in signal suppression during ionization. However, the ability to obtain concentration estimates of compounds in an environmental sample is important for data interpretation and comparison. We introduce an approach for estimating mass concentrations of analytes observed in a multicomponent mixture by HR-ESI-MS, without prior separation. The approach relies on a calibration of the instrument using appropriate standards added to the mixture of studied analytes. An illustration of how the proposedmore » calibration can be applied in practice is provided for aqueous extracts of isoprene photooxidation organic aerosol, with multifunctional organic acids standards. We show that the observed ion sensitivities in ESI-MS are positively correlated with the “adjusted mass,” defined as a product of the molecular mass and the H/C ratio in the molecule (adjusted mass = H/C x molecular mass). The correlation of the observed ESI sensitivity with adjusted mass is justified by considering trends of the physical and chemical properties of organic compounds that affect ionization in the positive ion mode, i.e., gas-phase basicity, polarizability, and molecular size.« less
  • High-resolution X-ray absorption spectroscopy is a powerful diagnostic tool for probing chemical and physical properties of the interstellar medium (ISM) at various phases. We present detections of K transition absorption lines from the low-ionization ions of O I, O II, Ne I, Ne II, and Ne III, and the high-ionization ones of O VI, O VII, O VIII, Ne IX, and Mg XI, as well as details of neutral absorption edges from Mg, Ne, and O in an unprecedented high-quality spectrum of the low-mass X-ray binary Cyg X-2. These absorption features trace the intervening ISM which is indicated by themore » unshifted line centroids with respect to the rest-frame wavelengths of the corresponding atomic transitions. We have measured the column densities of each ion. We complement these measurements with the radio H I and optical H{alpha} observations toward the same sight line and estimate the mean abundances of Ne, O, and Mg in the cool phase to Ne/H = 0.84{sup +0.13} {sub -0.10} x 10{sup -4}, O/H = 3.83{sup +0.48} {sub -0.43} x 10{sup -4}, and Mg/H = 0.35{sup +0.09} {sub -0.11} x 10{sup -4}, and O and Mg in the hot phase to O/H = 5.81{sup +1.30} {sub -1.34} x 10{sup -4} and Mg/H = 0.33{sup +0.09} {sub -0.09} x 10{sup -4}, respectively. These results indicate a mild depletion of oxygen into dust grains in the cool phase and little or no depletion of magnesium. We also find that absorption from highly ionized ions in the hot Galactic disk gas can account for most of the absorption observed toward the extragalactic sight lines like Mrk 421. The bulk of the observed O VI likely originates from the conductive interfaces between the cool and hot gases, from which a significant amount of N V and C IV emission is predicted.« less
  • Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentrations of ionic liquids, has been challenging. In the present work the 13C, 15N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid-protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C 4-mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6-3.5 M, whichmore » corresponds to 10-60% v/v). Interactions between GB1 and [C 4-mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in 15N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C 4-mim]Br were assigned using 3D methods under HR-MAS conditions. Furthermore, HR-MAS NMR is a viable tool that could aid in elucidation of molecular mechanisms of ionic liquid-protein interactions.« less
  • Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentrations of ionic liquids, has been challenging. In the present work the 13C, 15N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid-protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C 4-mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6-3.5 M, whichmore » corresponds to 10-60% v/v). Interactions between GB1 and [C 4-mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in 15N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C 4-mim]Br were assigned using 3D methods under HR-MAS conditions. Furthermore, HR-MAS NMR is a viable tool that could aid in elucidation of molecular mechanisms of ionic liquid-protein interactions.« less
  • We have used high-resolution stimulated Brillouin gain spectroscopy to search for evidence of a {open_quotes}structural transition{close_quotes} within the liquid phase of benzene. On the basis of previous measurements of depolarized light scattering intensities and Brillouin line shifts, it has been proposed that such a transition occurs in the temperature range 42-48 {degrees}C. Our highly accurate Brillouin shift measurements show a linear dependence on temperature from 24 to 69 {degrees}C, with no sign of any anomaly. 23 refs., 2 figs.