Nitric oxide-assisted atmospheric pressure corona discharge ionization for the analysis of automobile hydrocarbon emission species

Abstract

Nitric oxide reagent gas has been found to improve the sensitivity and robustness of the atmospheric pressure corona discharge ionization (APCDI) process. Sensitivity has been increased by a factor of 20-100, depending on the compound, over APCDI without nitric oxide. The robustness (defined as the sensitivity to matrix interferences) of APCDI in the presence of water has been improved by a factor of 3 over normal APCDI. These improvements are due in part to a modification of the commercial inlet system and ionization chamber that allows the chamber and sample gases to be heated to 100 and 350°C, respectively. Nitric oxide was chosen as the reagent gas because of the variety and selectivity of its interaction with hydrocarbons with differing functional groups. Product ions of nitric oxide ionization and their subsequent tandem mass spectra are presented and discussed for selected alkanes; alkenes, alkylbenzenes, alcohols; aldehydes, and an ether. A tandem mass spectrometry (unique parent ion-daughter ion transition) method was developed to quantify compounds of specific interest in vehicle emissions. The absolute sensitivity for these compounds, under ideal conditions, was determined and ranges from 0.006 ppb for xylene (most sensitive) to 80 ppb for C8 (or larger) normal alkanes. Routine sensitivity for real-world samples was in the single parts per billion range for aromatic and olefinic species. Potential applications include the real-time, on-line monitoring of selected hydrocarbons in automobile exhaust.

Direct atmospheric pressure chemical ionization-tandem mass spectrometry for the continuous real-time trace analysis of benzene, toluene, ethylbenzene, and xylenes in ambient air

“…The same ionic species are observed in the non-subtract background full-scan mass spectra of BTEX at concentrations determined to be the method LODs (Figure 3). These observations all argue that our approach helps to overcome the inhibition of chemical ionization of low levels of BTEX usually observed for direct APCI [16]. Table 1 summarizes precursor ions, major product ions and SRM parameters optimized for each compound.…”

“…These ions make the overall ionization complex and nonquantitative for some compounds, including BTEXspecies, particularly at low levels. In addition, at low parts per million concentrations, water inhibits chargetransfer ionization of BTEX-hydrocarbons by solvating reagent ions and thus reduces their ability to interact with hydrophobic molecules [16]. Our approach overcomes these drawbacks by enhancing the efficiency of the chemical ionization of BTEX molecules.…”

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

“…As ESI, MALDI and other ionization methods that solely rely on protonation or deporotonation typically have a strong bias toward the most basic or acidic analytes, APCI is more generally applicable . However, APCI produces a wider variety of different types of ions from a given analyte than ESI and MALDI, often including protonated [MH] + and deprotonated molecules [M–H] – as well as molecular ions [M] +• , their fragment ions and ions resulting from hydride abstraction, i.e., [M–H] + (a process attributed mainly to NO + commonly present in the ion source) . This situation arises from the complex ion formation processes involved in APCI, which are different from those associated with ESI and MALDI.…”

The Controversy Persists: Is There a Qualification Criterion to Utilize Inhaled Nitric Oxide in Pre-term Newborns?

“…Nitic oxide (NO) is a known free radical important as a chemical intermediate in multiple environmental reactions (1)(2)(3)(4). In the 1990's, Nitric oxide's function was better elucidated as an endothelium-derived relaxing factor and signaling molecule (5,6).…”