Polar Effects Control the Gas-Phase Reactivity of para-Benzyne Analogs.

We report herein a gas-phase reactivity study on a para-benzyne cation and its three cyano-substituted, isomeric derivatives performed using a dual-linear quadrupole ion trap mass spectrometer. All four biradicals were found to undergo primary and secondary radical reactions analogous to those observed for the related monoradicals, indicating the presence of two reactive radical sites. The reactivity of all biradicals is substantially lower than that of the related monoradicals, as expected based on the singlet ground states of the biradicals.

Polar Effects Control the Gas-phase Reactivity of Charged -Benzyne Analogs.

The gas-phase reactivity of charged -benzynes is entirely unexplored as they and/or their precursors tend to undergo ring-opening upon their generation. We report here a gas-phase reactivity study of two such benzynes, the 2,5-didehydropyridinium and 5,8-didehydroisoquinolinium cations, generated in a modified dual-linear quadrupole ion trap (DLQIT) mass spectrometer. Both biradicals were found to form diagnostic products with organic molecules, indicating the presence of two radical sites.

A differentially pumped dual linear quadrupole ion trap (DLQIT) mass spectrometer: a mass spectrometer capable of MS(n) experiments free from interfering reactions.

A novel differentially pumped dual linear quadrupole ion trap (DLQIT) mass spectrometer was designed and built to facilitate tandem MS experiments free from interfering reactions. The instrument consists of two differentially pumped Thermo Scientific linear quadrupole ion trap (LQIT) systems that have been connected via an ion transfer octupole encased in a machined manifold. Tandem MS experiments can be performed in the front trap and then the resulting product ions can be transferred via axial ejection into the back trap for further, independent tandem MS experiments in a differentially pumped area.

Experimental and computational studies on the formation of three para-benzyne analogues in the gas phase.

Experimental and computational studies on the formation of three gaseous, positively-charged para-benzyne analogues in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer are reported. The structures of the cations were examined by isolating them and allowing them to react with various neutral reagents whose reactions with aromatic carbon-centered σ-type mono- and biradicals are well understood. Cleavage of two iodine-carbon bonds in N-deuterated 1,4-diiodoisoquinolinium cation by collision-activated dissociation (CAD) produced a long-lived cation that showed nonradical reactivity, which was unexpected for a para-benzyne.

Reactivity of the 4,5-didehydroisoquinolinium cation.

The chemical properties of a 1,8-didehydronaphthalene derivative, the 4,5-didehydroisoquinolinium cation, were examined in the gas phase in a dual-cell Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. This is an interesting biradical because it has two radical sites in close proximity, yet their coupling is very weak. In fact, the biradical is calculated to have approximately degenerate singlet and triplet states.

Differentiation of protonated aromatic regioisomers related to lignin by reactions with trimethylborate in a Fourier transform ion cyclotron resonance mass spectrometer.

Several lignin model compounds were examined to test whether gas-phase ion-molecule reactions of trimethylborate (TMB) in a FTICR can be used to differentiate the ortho-, meta-, and para-isomers of protonated aromatic compounds, such as those formed during degradation of lignin. All three regioisomers could be differentiated for methoxyphenols and hydroxyphenols. However, only the differentiation of the ortho-isomer from the meta- and para-isomers was possible for hydroxyacetophenones and hydroxybenzoic acids.

Carbon disulfide reagent allows the characterization of nonpolar analytes by atmospheric pressure chemical ionization mass spectrometry.

While atmospheric pressure ionization methodologies have revolutionized the mass spectrometric analysis of nonvolatile analytes, limitations native to the chemistry of these methodologies hinder or entirely inhibit the analysis of certain analytes, specifically, many nonpolar compounds. Examination of various analytes, including asphaltene and lignin model compounds as well as saturated hydrocarbons, demonstrates that atmospheric pressure chemical ionization (APCI) using CS(2) as the reagent produces an abundant and stable molecular ion (M(+•)) for all model compounds studied, with the exception of completely saturated aliphatic hydrocarbons and the two amino acids tested, arginine and phenylalanine. This reagent substantially broadens the applicability of mass spectrometry to nonvolatile nonpolar analytes and also facilitates the examination of radical cation chemistry by mass spectrometry.

Reactions of an aromatic σ,σ-biradical with amino acids and dipeptides in the gas phase.

Gas-phase reactivity of a positively charged aromatic σ,σ-biradical (N-methyl-6,8-didehydroquinolinium) was examined toward six aliphatic amino acids and 15 dipeptides by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR) and laser-induced acoustic desorption (LIAD). While previous studies have revealed that H-atom and NH(2) abstractions dominate the reactions of related monoradicals with aliphatic amino acids and small peptides, several additional, unprecedented reaction pathways were observed for the reactions of the biradical. For amino acids, these are 2H-atom abstraction, H(2)O abstraction, addition - CO(2), addition - HCOOH, and formation of a stable adduct.

Identification of the carboxylic acid functionality by using electrospray ionization and ion-molecule reactions in a modified linear quadrupole ion trap mass spectrometer.

A mass spectrometric method has been developed for the identification of the carboxylic acid functional group in analytes evaporated and ionized by electrospray ionization (ESI). This method is based on gas-phase ion-molecule reactions of ammoniated ([M + NH4]+) and sodiated ([M + Na]+) analyte molecules with trimethyl borate (TMB) in a modified linear quadrupole ion trap mass spectrometer. The diagnostic reaction involves addition of the deprotonated analyte to TMB followed by the elimination of methanol.

Assessment of trueness of a glucose monitor using interstitial fluid and whole blood as specimen matrix.

Background: Interstitial fluid (ISF) is a specimen of increasing interest for glucose measurements because it can be obtained in a minimally invasive manner. Our previous study showed that sufficient ISF can be obtained using microneedles to measure glucose with a conventional electrochemical glucose monitor. The aim of this study was to assess the trueness of this glucose monitor using split-sample comparison with whole blood.

Assessment of microwave-assisted enzymatic digestion by measuring glycated hemoglobin A1c by mass spectrometry.

Enzymatic digestion of proteins and analysis of the resulting peptides by mass spectrometry is an established approach in proteomics and in clinical and environmental chemistry. The long digestion times of several hours prevent the fast turnover of samples and results. Qualitative applications showed that microwave radiation profoundly shortens enzymatic digestion.

Variability among five over-the-counter blood glucose monitors.

Background: The American Diabetes Association recommends that people with diabetes use self-monitoring to control their blood glucose concentration. To assess the need for standardization, we evaluated the variability among 5 of the most common monitors: MediSense Precision Xtra, Ascencia Dex, Prestige Smart System, OneTouch Ultra, and Accu-Chek Advantage.

Methods: We took steps to minimize preanalytical variation.

Assessment of trueness of glucose measurement instruments with different specimen matrices.

Background: The trueness of glucose monitors is commonly assessed using whole-blood samples and a clinical analyzer as a comparison method. In this study, the effect of specimen matrix on trueness of one clinical analyzer and one glucose monitor was compared with a gas chromatography-mass spectrometry (GC/MS) reference method, using split-sample comparison with capillary whole blood (CWB), venous whole blood (VWB), and plasma (PL).

Methods: CWB was analyzed by the glucose monitor and the GC/MS reference method.