Exhaled nitric oxide (eNO) is a useful biomarker of various physiological conditions, including asthma and other pulmonary diseases. Herein a fast and sensitive analytical method has been developed for the quantitative detection of eNO based on extractive electrospray ionization mass spectrometry (EESI-MS). Exhaled NO molecules selectively reacted with 2-phenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) reagent, and eNO concentration was derived based on the EESI-MS response of 1-oxyl-2-phenyl-4, 4, 5, 5-tetramethylimidazoline (PTI) product. The method allowed quantification of eNO below ppb level (~0.02 ppbv) with a relative standard deviation (RSD) of 11.6%. In addition, eNO levels of 20 volunteers were monitored by EESI-MS over the time period of 10 hrs. Long-term eNO response to smoking a cigarette was recorded, and the observed time-dependent profile was discussed. This work extends the application of EESI-MS to small molecules (<30 Da) with low proton affinity and collision-induced dissociation efficiency, which are usually poorly visible by conventional ion trap mass spectrometers. Long-term quantitative profiling of eNO by EESI-MS opens new possibilities for the research of human metabolism and clinical diagnosis.

The PVF Tedlar is widely used for gas collection in clinical diagnostics and environmental research. However, sample collection is frequently associated with the degradation, adsorption, or transformation of sensitive chemicals. Here, we explore to what extent the Tedlar bag collection effects the composition of expired breath samples. Collected breath samples were analyzed using the EESI-MS technique after the storage time of 30 min, 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h, respectively. Our results demonstrated the gradual MS signal decay after 3 h storage. The decay rate of 3 h is about 45% and 6 h is about 88%. Therefore, the Tedlar bag is suggested as a reliable breath holder on the time scale of <3 h.

Using a solid-state reaction strategy, nominal Li3TiO3F oxyfluorides ceramics were fabricated, and its sintering behavior, microstructure, phase assemblages, as well as microwave dielectric performances were all investigated. The main phase of Li3TiO3F with cubic structures accompanied with small amounts of the LiF or Li2TiO3 secondary phase was identified by XRD analysis. SEM analysis showed that a uniform and dense microstructure was obtained for 750 °C-sintered samples. The dielectric constant (εr) and quality factor (Q × f) were found to be strongly correlated with porosity and grain size distribution, whereas the temperature coefficient of resonance frequency (τf) was mainly dominated by the phase assemblages. In particular, the 750 °C-sintered Li3TiO3F samples exhibited good microwave dielectric performances: εr = 18, Q × f = 57,300 GHz (under 9.2 GHz), τf = −43.0 ppm/°C.

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