We present atmospheric pressure laser-induced acoustic desorption chemical ionization (AP/LIAD-CI) with O2 carrier/reagent gas as a powerful new approach for the analysis of saturated hydrocarbon ...mixtures. Nonthermal sample vaporization with subsequent chemical ionization generates abundant ion signals for straight-chain, branched, and cycloalkanes with minimal or no fragmentation. M – H+ is the dominant species for straight-chain and branched alkanes. For cycloalkanes, M+• species dominate the mass spectrum at lower capillary temperature (<100 °C) and M – H+ at higher temperature (>200 °C). The mass spectrum for a straight-chain alkane mixture (C21–C40) shows comparable ionization efficiency for all components. AP/LIAD-CI produces molecular weight distributions similar to those for gel permeation chromatography for polyethylene polymers, Polywax 500 and Polywax 655. Coupling of the technique to Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) for the analysis of complex hydrocarbon mixtures provides unparalleled mass resolution and accuracy to facilitate unambiguous elemental composition assignments, e.g., 1754 peaks (rms error = 175 ppb) corresponding to a paraffin series (C12–C49, double-bond equivalents, DBE = 0) and higher DBE series corresponding to cycloparaffins containing one to eight rings. Isoabundance-contoured plots of DBE versus carbon number highlight steranes (DBE = 4) of carbon number C27–C30 and hopanes of C29–C35 (DBE = 5), with sterane-to-hopane ratio in good agreement with field ionization (FI) mass spectrometry analysis, but performed at atmospheric pressure. The overall speciation of nonpolar, aliphatic hydrocarbon base oil species offers a promising diagnostic probe to characterize crude oil and its products.
Rising from the Ashes Willard, William; Marshall, Alan G; Pearson, J. Diane
2020, 2020-06-01
eBook
Rising from the Ashes explores continuing Native American political, social, and cultural survival and resilience with a focus on the life of Numiipuu (Nez Perce) anthropologist Archie M. Phinney. He ...lived through tumultuous times as the Bureau of Indian Affairs implemented the Indian Reorganization Act, and he built a successful career as an indigenous nationalist, promoting strong, independent American Indian nations. Rising from the Ashes analyzes concepts of indigenous nationalism and notions of American Indian citizenship before and after tribes found themselves within the boundaries of the United States. Collaborators provide significant contributions to studies of Numiipuu memory, land, loss, and language; Numiipuu, Palus, and Cayuse survival, peoplehood, and spirituality during nineteenth-century U.S. expansion and federal incarceration; Phinney and his dedication to education, indigenous rights, responsibilities, and sovereign Native Nations; American Indian citizenship before U.S. domination and now; the Jicarilla Apaches’ self-actuated corporate model; and Native nation-building among the Numiipuu and other Pacific Northwestern tribal nations. Anchoring the collection is a twenty-first-century analysis of American Indian decolonization, sovereignty, and tribal responsibilities and responses.  
•Applied top-down LC-MS to diagnose β-thalassemia using relative quantitation of intact subunits.•Successfully distinguished the impact of heterozygous Hb variants.•Using ion-ion reaction (PTR-PIP) ...to improve the sensitivity and specificity of the LC-MS methods.
β-thalassemia is a quantitative hemoglobin (Hb) disorder resulting in reduced production of Hb A and increased levels of Hb A2. Diagnosis of β-thalassemia can be problematic when combined with other structural Hb variants, so that the separation approaches in routine clinical centers are not sufficiently decisive to obtain accurate results. Here, we separate the intact Hb subunits by high-performance liquid chromatography, followed by top-down tandem mass spectrometry of intact subunits to distinguish Hb variants. Proton transfer reaction-parallel ion parking (PTR-PIP), in which a radical anion removes protons from multiply charged precursor ions and produces charge-reduced ions spanning a limited m/z range, was used to increase the signal-to-noise ratio of the subunits of interest. We demonstrate that the δ/β ratio can act as a biomarker to identify β-thalassemia in normal electrospray ionization MS1 and PTR-PIP MS1. The application of PTR-PIP significantly increases the sensitivity and specificity of the HPLC-MS method to identify δ/β ratio as a thalassemia biomarker.
We determine the elemental compositions of aromatic nitrogen model compounds as well as a petroleum sample by atmospheric pressure photoionization (APPI) and electrospray Ionization (ESI) with a 9.4 ...Tesla Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. From the double-bond equivalents calculated for the nitrogen-containing ions from a petroleum sample, we can infer the aromatic core structure (pyridinic versus pyrrolic nitrogen heterocycle) based on the presence of M
+
·
(odd-electron) versus M+H
+ (even-electron) ions. Specifically, nitrogen speciation can be determined from either a single positive-ion APPI spectrum or two ESI (positive- and negative-ion) spectra. APPI operates at comparatively higher temperature than ESI and also produces radical cations that may fragment before detection. However, APPI fragmentation of aromatics can be eliminated by judicious choice of instrumental parameters.
At currently achievable Fourier transform ion cyclotron resonance broadband mass spectrometry resolving power (m/ Δ m 50% > 350 000 for 200 < m/z < 1000), it would be necessary to spread out a ...conventional mass spectrum over ∼200 m in order to provide visual resolution of the most closely resolved peaks. Fortunately, there are natural gaps in a typical mass spectrum, spaced 1 Da apart, because virtually no commonly encountered elemental compositions yield masses at those values. Thus, it is possible to break a broadband mass spectrum into 1-Da segments, rotate each segment by 90°, scale each segment according to its mass defect (i.e., difference between exact and nominal mass), and then compress the spacing between the segments to yield a compact display. For hydrocarbon systems, conversion from IUPAC mass to “Kendrick” mass (i.e., multiplying each mass by 14.00000/14.01565) further simplifies the display by rectilinearizing the peak patterns. The resulting display preserves not only the “coarse” spacings (e.g., ∼1 Da between odd and even masses, corresponding to either even vs odd number of nitrogens or 12C c vs 12C c - 1 13C1 elemental compositions of the same molecule; ∼2-Da separations, corresponding to a double bond or ring; ∼14 Da separations, corresponding to one CH2 group) but also the “fine structure” (i.e., different mass defects for different elemental compositions) across each 1-Da segment. The method is illustrated for experimental electrospray ionization FTICR ultrahigh-resolution mass spectra of a petroleum crude oil. Several thousand elemental compositions may be resolved visually in a single one-page two-dimensional display, and various compound familiesclass (N n O o S s ), type (Z in C c H2 c + Z N n O o S s ), and alkylation seriesmay be identified visually as well.
We identify water-soluble (23 °C) crude oil NSO nonvolatile acidic, basic, and neutral crude oil hydrocarbons by negative-ion ESI and continuous flow FD FT-ICR MS at an average mass resolving power, ...m/Δm 50% = 550 000. Of the 7000+ singly charged acidic species identified in South American crude oil, surprisingly, many are water-soluble, and much more so in pure water than in seawater. The truncated m/z distributions for water-soluble components exhibit preferential molecular weight, size, and heteroatom class influences on hydrocarbon solubility. Acidic water-soluble heteroatomic classes detected at >1% relative abundance include O, O2, O3, O4, OS, O2S, O3S, O4S, NO2, NO3, and NO4. Parent oil class abundance does not directly relate to abundance in the water-soluble fraction. Acidic oxygen-containing classes are most prevalent in the water-solubles, whereas acidic nitrogen-containing species are least soluble. In contrast to acidic nitrogen-containing heteroatomic classes, basic nitrogen classes are water-soluble. Water-soluble heteroatomic basic classes detected at >1% relative abundance include N, NO, NO2, NS, NS2, NOS, NO2S, N2, N2O, N2O2, OS, O2S, and O2S2.
Solution-phase hydrogen/deuterium exchange (HDX) monitored by high-resolution Fourier transform ion cyclotron resonance (FTICR) mass spectrometry offers a rapid method to study protein conformations ...and protein−protein interactions. Pepsin is usually used to digest proteins in HDX and is known for lack of cleavage specificity. To improve digestion efficiency and specificity, we have optimized digestion conditions and cleavage preferences for pepsin and protease type XIII from Aspergillus saitoi. A dilution series of the proteases was used to determine the digestion efficiency for several test proteins. Protease type XIII prefers to cleave on the C-terminal end of basic amino acids and produced the highest number of fragments and the best sequence coverage compared to pepsin or protease type XVIII from Rhizhopus. Furthermore, protease type XIII exhibited much less self-digestion than pepsin and thus is superior for HDX experiments. Many highly overlapped segments from protease type XIII and pepsin digestion, combined with high-resolution FTICR mass spectrometry, provide high sequence resolution (to as few as one or two amino acids) for the assignment of amide hydrogen exchange rate. Our H/D exchange results correlate well with the secondary and tertiary structure of myoglobin. Such assignments of highly overlapped fragments promise to greatly enhance the accuracy and sequence resolution for determining conformational differences resulting from ligand binding or protein−protein interactions.
The diminishing clean oil reserve is driving the search for new or improved ways to reduce the level of NSO-containing species found in high abundance in heavy crude oils. Hydrotreatment is the ...currently preferred technique to remove those polar species. Unfortunately, nitrogen-containing compounds cause coke formation on the surface of the hydrotreatment catalyst, leading to partial or complete deactivation. Here, positive- and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) identify those nitrogen compounds that resist hydrotreatment. ESI preferentially ionizes polar (e.g., heteroatom-containing) species: basic molecules are detected as positive ions and acidic/neutral molecules as negative ions. FT-ICR MS resolves thousands of species in a single mass spectrum, allowing for unambiguous determination of elemental composition, C
c
H
h
N
n
O
o
S
s
, for identification of compound “class” (numbers of N, O, S heteroatoms, “type” (rings plus double bonds), and carbon number (revealing the extent of alkylation). We find that hydrotreatment-resistant compounds typically contain a single nitrogen atom, both pyridinic benzalogs and pyrollic benzalogs. Compounds with more than one heteroatom, such as O
x
, N
x
O
y
, N
x
S
y
and N
x
, are partially removed. Compound classes with lower double bond equivalents or fewer CH
2 groups are preferentially removed. Species that contain O
x
S
y
are fully removed by hydrotreatment.
Electrospray ionization (ESI) combined with ultrahigh resolution Fourier Transform-Ion Cyclotron Resonance mass spectrometry (FT-ICR MS) at 9.4 Tesla has been shown to be an ideal tool for the ...molecular characterization of dissolved natural organic matter (DOM). Here, we apply this technique for tracing DOM as it moves from mangrove porewaters into a Brazilian estuary and assess the changes that occur in the initial stages of outwelling. Comparisons of molecular features of DOM from the porewater and two sites within the adjacent estuary revealed that mass spacing patterns were far more pronounced in the mangrove porewater DOM, and the average molecular weights of estuarine DOM were lower. Calculation of double bond equivalents and Kendrick mass analysis normalized for both methylene (-CH
2−) and oxygen (O) substitution indicated that the lower molecular weights observed in the estuarine DOM were due primarily to loss of high molecular weight, highly unsaturated and/or aromatic components observed in the porewater DOM. Photodegradation is suggested as one mechanism that removes these high molecular weight components once mangrove-derived DOM reaches the estuary. The mass analyses were supported by UV–Vis and 3-D synchronous scanning fluorescence spectroscopy measurements to aid in the characterization of DOM in this unique ecosystem.
Electrospray ionization (ESI) was combined with ultrahigh-resolution Fourier transform-ion cyclotron resonance mass spectrometry (FTICR MS) to characterize complex humic and fulvic acid mixtures. ...Lower than expected molecular weight distributions previously observed for humics when analyzed by ESI-MS have fueled speculation about a bias in favor of low molecular weight. Multiply charged ions, ionization suppression, and sample fragmentation have all been suggested as sources of this low molecular weight bias. In this work, resolution of the individual components of humic mixtures within a 1 mass-to-charge unit window was accomplished by FTICR MS at 9.4 T. At mass resolving powers between 60 000 (high mass) and 120 000 (low mass), it was possible to determine that virtually all ions present in spectra of Suwannee River fulvic and humic acid are singly charged, thus eliminating inadequate accounting for multiply charged ions as a primary source of any low molecular weight bias. The high-resolution mass spectra also revealed the presence of molecular families containing ions that differ from each other in degree of saturation, functional group substitution (primarily CH vs N and CH4 vs O), and number of CH2 groups. Ionization suppression and ion fragmentation were addressed for humic and fulvic acid mixtures and well-characterized poly(ethylene glycol) (PEG) mixtures with average molecular weights of 8000 and 10 000. Although these high molecular weight PEG mixtures fragment extensively under traditional positive-ion mode ESI conditions, similar fragmentation could not be confirmed for humic and fulvic acid mixtures.
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