Untreated and hydrotreated nitrogen-concentrated distillation fractions (483−504 °C) from Syncrude oil have been analyzed by electron ionization, field desorption ionization, and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The routinely attainable mass resolving power ≥300 000 at m/z 300 and sub-ppm mass accuracy allowed for resolution and elemental compositional assignment of various compound classes. Multiple closely spaced mass doublets (with mass differences <10 mDa) were detected. Although hydrotreatment reduced the relative abundances of several heteroatomic classes (N2, S3, NS2, NOS, O3, OS2, and O2S) below detectability, N-, S-, O-, O2-, OS-, and NO-containing compounds survived hydrotreatment. Analysis of N-, S-, and O-containing compounds and hydrocarbon compounds at the molecular level exposes compositional changes and reveals the effectiveness of the hydrotreating process.

We analyzed three vacuum gas oil distillation fractions, 295−319 °C, 319−456 °C, and 456−543 °C, with a home-built external electron ionization (EI) 7 T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. EI at 10 eV allows soft ionization of aromatic compounds in the vacuum gas oil range. Unambiguous elemental composition assignment provides insight into compositional variations at the molecular level; for example, ultrahigh resolving power (m/Δm 50% ≈ 300 000 at m/z 300) and mass accuracy (<0.4 ppm) readily resolve C3/SH4 doublets (3.4 mDa mass difference) across the full m/z range of interest. To our knowledge, this is the first time that hydrocarbons and sulfur-containing hydrocarbons have been completely mass-resolved across the full VGO range. Aromatic hydrocarbons are the major detected components in all three samples. In addition, many sulfur-, nitrogen-, and oxygen-containing compounds were directly observed. The concentrations of the heteroatomic species increase with boiling point. Detailed data analysis revealed compound types (rings plus double bonds) and their carbon number distributions for hydrocarbon and heteroatomic compounds in the distillation fractions and increasing average molecular weight (or carbon number distribution) and aromaticity with increasing boiling temperature of the petroleum fractions. The present analysis requires only micrograms of sample, is fast (single time-domain data set acquired in a few seconds), and highly reproducible.

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The conventional colloidal gold immunochromatographic assay (AuNP-ICA) cannot meet the requirements for the rapid and sensitive detection of Escherichia coli (E. coli) O157:H7 because of its poor sensitivity. Herein, a novel two-step cascade signal amplification strategy that integrates in situ gold growth and nanozyme-mediated catalytic deposition was proposed to enhance the detection sensitivity of conventional AuNP-ICA dramatically. The enhanced strip displayed ultrahigh sensitivity in E. coli O157:H7 detection and had a detection limit of 1.25 × 101 CFU/mL, which is approximately 400-fold lower than that of traditional AuNP-ICA (5 × 103 CFU/mL). The amplified strip had no background signal in the T-line zone in the absence of E. coli O157:H7 even after one round of cascade signal amplification. The enhanced strip demonstrated excellent selectivity against E. coli O157:H7 with a negligible cross-reaction to nine other common pathogens. Intra-assays and interassays showed that the improved strip has acceptable accuracy and precision for determining E. coli O157:H7. The average recoveries in a real milk sample ranged from 87.33 to 112.15%, and the coefficients of variation were less than 10%. The enhanced strip also showed great potential in detecting a single E. coli O157:H7 cell in a 75 μL solution.

We have designed and constructed a linear quadrupole ion trap for the measurement of laser-induced fluorescence (LIF) of mass selected gas-phase ions produced by electrospray ionization. The instrument consists of a simple electrospray source, radiofrequency octopole guide, a dc quadrupole bender, a quadrupole mass filter, the linear quadrupole trap (which is equipped with optics for LIF collection and a channeltron ion detector), and several multielement focusing lenses. With this instrument, the LIF decay lifetime of gas-phase Rhodamine 640 radical cations is determined for the first time.

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A 193 nm laser photofragmentation time-of-flight mass spectrometric study of chloroiodomethane J. Chem. Phys. 123, 174316 (2005); 10.1063/1.2074507 5.6 tesla Fourier transform ion cyclotron resonance mass spectrometer for analysis of volatile complex mixtures Rev.An external electron ionization ͑EI͒ source has been interfaced to a 7 T Fourier transform ion cyclotron resonance mass spectrometer and tested for volatile complex mixture analysis. A new Sulfinert ® -deactivated inlet system provides continuous stable sample flow to the EI source, leading to stable ion signal ͑±10% deviation͒ for 2 h from a 200 nL mixture of 15 n-alkylbenzenes. Ultrahigh-mass resolving power, m / ⌬m 50% Ϸ 735 000, was obtained for 1-bromo-2-chlorobenzene with accurate isotopic ratio measurement. Base line resolution was observed for two of the closest commonly encountered mass doublets, C 3 /SH 4 ͑m 2 − m 1 = 3.4 mDa at m / z = 190͒ and SH 3 13 C/C 4 ͑m 2 − m 1 = 1.1 mDa at m / z = 190͒. Although hydrocarbons dominate the positive-ion 18 eV EI Fourier transform ion cyclotron resonance mass spectrum from diesel fuels, many sulfur-, nitrogen-, and oxygen-containing compounds were readily observed without prior fractionation. By comparing 18 eV EI Fourier transform ion cyclotron resonance mass spectra of unprocessed and processed diesel fuels, we were able to identify which heteroatom-containing species were removed by processing.

PurposeTryptophan’s (Trp) unique hydrophobic and structural properties make it an important antigen binding motif when positioned in complementarity-determining regions (CDRs) of monoclonal antibodies (mAbs). Oxidation of Trp residues within the CDR can deleteriously impact antigen binding, particularly if the CDR conformation is altered. The goal of this study was to evaluate the conformational and functional impact of Trp oxidation for two mAb subtypes, which is essential in determining the structure-function relationship and establishing appropriate analytical control strategies during protein therapeutics development.MethodsSelective Trp oxidation was induced by 2,2′-Azobis(2-amidinopropane) dihydrochloride (AAPH) treatment in the presence of free methionine (Met). The native and chemically oxidized mAbs were characterized by hydrogen-deuterium exchange mass spectrometry (HDX-MS) for conformational changes and surface plasmon resonance (SPR) for antigen-antibody binding.ResultsTreatment of mAbs with AAPH selectively oxidized solvent accessible Trp residues. Oxidation of Trp within or in proximity of CDRs increased conformational flexibility in variable domains and disrupted antigen binding.ConclusionsTrp oxidation in CDRs can adversely impact mAbs’ conformation and antigen binding. Trp oxidation should be carefully evaluated as part of critical quality attribute assessments. Oxidation susceptible Trp should be closely monitored during process development for mAbs to establish appropriate analytical control for manufacturing of drug substance and drug product.Electronic supplementary materialThe online version of this article (10.1007/s11095-018-2545-8) contains supplementary material, which is available to authorized users.