Direct Detection of Inorganic Nitrate Salts by Ambient Pressure Helium-Plasma Ionization Mass Spectrometry

Abstract

Inorganic nitrates in solid deposits were detected directly by ambient-pressure helium-plasma ionization-mass spectrometry (HePI-MS), without the need for extensive sample preparation. Nitrates were detected even from complex matrices such as meats and fruit juices. Any electrospray-ionization mass spectrometer can be modified to perform ambient-pressure HePI-MS by simply passing helium through the metal capillary intended for liquid-sample delivery. Nitrates on paper strips, glass slides, or cotton swabs (sometimes wetted with a mineral acid) were inserted directly into the ambient-pressure HePI source. The spectra acquired under negative-ion generating conditions showed a peak at m/z 62 for the nitrate ion, along with a lower-intensity peak at m/z 125 for the nitrate adduct of nitric acid. Apparently, it is nitric acid that is initially transferred to the gas phase, forming an ion-molecule complex with hydroxyl anions present in the plasma. The ion-neutral complex then dissociates by eliminating water to produce gaseous NO(3)(-) ions. This hypothesis was supported by the observation that certain solid nitrate salts, which were not readily amenable to HePI (notably the alkali nitrates), were immediately detected as m/z 62 and 125 ions upon acidification by a strong acid. Quantitative evaluations showed that the nitrate-signal response versus the deposited mass is linear for over 3 orders of magnitude. With the use of (15)N-labeled nitrate (m/z 63), the limit of detection was determined to be as low as 200 fg.

In-source collision induced dissociation of inorganic explosives for mass spectrometric signature detection and chemical imaging

“…These HMEs and IED components include unstable primary explosives (e.g., peroxides [31][32][33][34], azides, and fulminates), fuel-oxidizer and self-initiating mixtures, nitrated sugar alcohols, and radiological dispersion devices (RDDs) [34][35][36][37]. In the present work, we focus on the detection of inorganic explosives and components, a rising area of research.…”

Screening freshness of seafood by measuring trimethylamine (TMA) levels using helium-plasma ionization mass spectrometry (HePI-MS)

“…HePI is a versatile ambient-ionization MS technique, applicable to the analysis of a wide variety of samples, both organic and inorganic. It has been applied, for example, to the analysis of energetic materials (Yang et al 2012), pharmaceutical preparations (Attygalle et al 2014a, 2014b, Xia et al 2016, halobenzenes (Attygalle et al 2014a(Attygalle et al , 2014bGangam et al 2015), phenolics and quinones (Hassan et al 2017), inorganic nitrates (Pavlov and Attygalle 2013), and inorganic mercury compounds (Weerasinghe et al 2014). A major advantage of HePI is that it is highly portable and adaptable: any mass spectrometer with an electrospray ion source can be transformed into an ambient HePI instrument with ease, and no extensive hardware modifications are necessary (see Experimental Section).…”

Rapid detection and isotopic measurement of discrete inorganic samples using acoustically actuated droplet ejection and extractive electrospray ionization mass spectrometry

“…These analyses comprise of elemental and molecular speciation as well as isotopic distribution measurements. Typical inorganic mass spectrometric methods include inductively coupled plasma (ICP)‐MS, secondary ion mass spectrometry (SIMS), thermal ionization mass spectrometry (TIMS), and, more recently, ambient ionization mass spectrometry (AI‐MS) . The recent development of a plethora of atmospheric pressure and ambient ionization techniques has facilitated an array of approaches for efficiently generating gas‐phase ions for MS analysis.…”