An ultrasensitive SPI/PAI ion source based on a high-flux VUV lamp and its applications for the online mass spectrometric detection of sub-pptv sulfur ethers.

Single-photon ionization mass spectrometry (SPI-MS) is an attractive analytical technique for the online detection of volatile organic compounds; however, the low photon flux of the vacuum ultraviolet (VUV) lamp commonly used in the SPI ion source and the corresponding low detection sensitivity remain a constraint to its wide field applications. In this study, a new VUV lamp-based SPI ion source was developed. By increasing the discharging volume and optimizing the configuration of the lens and ionizer, the photon flux of the VUV lamp and the sensitivity of the ion source were significantly improved. The VUV lamp output was 2.8 × 1015 photons s-1, which was focused into the small ionization zone, and the ion intensity of gaseous benzene under SPI achieved 1.7 × 104 counts per second per pptv (cps pptv-1). This ion source can also function in photoinduced associative ionization (PAI) mode by introducing gaseous CH2Cl2 to initiate an associative ionization reaction. Because of the high efficiency of the ion source, the amount of doped CH2Cl2 needed for PAI was greatly reduced (∼2.5% of that used in previous experiments). PAI exhibited an outstanding protonation effect on monosulfur ethers (CnH2n+1S). The signal intensities of the protonated molecular ions (MH+) were 46-128 times higher than those of the molecular ions (M+) produced by SPI. Since monosulfur ethers generally have lower SPI cross-sections than polysulfur ethers (CnH2n+1S2 or CnH2n+1S3), the PAI and SPI modes were selected for the online measurement of a series of mono- and polysulfur ethers, respectively. The obtained detection sensitivity of the mono- and polysulfur ethers reached 476.5 ± 1.72-2835.1 ± 99.5 and 47.9 ± 0.4-105.1 ± 2.3 counts pptv-1, respectively, in 10 s of sampling time. The corresponding 3σ limits of detection (LODs) were 0.12-0.71 and 0.06-0.14 pptv, respectively. This study provides advances in the development of a high-flux VUV lamp and a highly efficient SPI/PAI ion source, as well as an ultrasensitive analytical method for detecting sulfur ethers.

Exploring breath biomarkers in BLM-induced pulmonary fibrosis mice with associative ionization time-of-flight mass spectrometry.

Pulmonary fibrosis (PF) is a common but fatal disease that threatens human health worldwide. Developing effective diagnostic methods is of great importance for the early detection of PF in patients. In this study, bleomycin (BLM) was used in mice to mimic idiopathic pulmonary fibrosis (IPF). The exhaled breath of BLM-induced PF, PF plus DDAH1 overexpression, and healthy control mice were analyzed in real-time using a newly developed associative ionization time-of-flight mass spectrometry method (AI-TOFMS), which is uniquely sensitive, especially to oxygenated volatile organic compounds (VOCs). Multivariate data analyses and discriminant modeling analyses revealed that four exhaled compounds, i.e., acrolein, ethanol, nitric oxide, and ammonia, had a strong correlation with PF symptoms. An Orthogonal Partial Least Square Discriminant Analysis (OPLS-DA) score plot showed an excellent separation between these three groups. The area under the receiver operating characteristic (ROC) curve for these four compounds distinguished PF mice from healthy controls at 0.989. In addition, the degrees of acute inflammation and fibrosis were assessed with Hematoxylin and Eosin (H&E) staining and Masson's Trichrome staining. Finally, combined with pathological characteristics and mRNA expression levels, the formation of the above-mentioned volatile compounds was explored. The obtained experimental results indicated that these four breath compounds, acrolein, ethanol, nitric oxide, and ammonia, were potential exhaled biomarkers for pulmonary fibrosis.

Ultrasensitive detection of trace chemical warfare agent-related compounds by thermal desorption associative ionization time-of-flight mass spectrometry.

A thermal desorption associative ionization time-of-flight mass spectrometer was developed for ultrasensitive detection of semi-volatile chemical warfare agents (CWAs). The excited-state CH2Cl2-induced associative ionization method presented a soft ionization characterization and an excellent sensitivity towards CWAs. The detection sensitivities of the investigated nine CWA-related substances were 2.56 × 105-5.01 × 106 counts ng-1 in a detection cycle (30 s or 100 s). The corresponding 3σ limits of detection (LODs) were 0.08-3.90 pg. Compared with the best-documented LODs via the dielectric barrier discharge ionization (DBDI) and secondary electrospray ionization (SESI), the obtained LODs of the investigated compounds were improved by 2-76 times. Additionally, the measured sensitivity of 2-Chloroethyl ethyl, a proxy for mustard gas, is 550 counts pptv-1, which exceeds the DBDI and SESI's corresponding values (4.4 counts pptv-1 and 6.5 counts pptv-1) nearly by two orders of magnitude. A field application simulation was conducted by putting a strip of PTFE film contaminated with the CWA-related agent into the thermal desorption unit. The simulation showed that the sensitivities of the instrument via swipe surveying could achieve 2.19 × 105 to 5.23 × 106 counts ng-1. The experimental results demonstrate that the excited-state CH2Cl2-induced associative ionization is an ultrasensitive ionization method for CWAs and reveal a prospect for improving the detection of CWA species future.