Development of a Tube Plasma Ion Source for Gas Chromatography–Mass Spectrometry Analysis and Comparison with Other Atmospheric Pressure Ionization Techniques

Abstract

A tube plasma ionization (TPI) open-air source for gas chromatography−mass spectrometry (GC−MS) was developed. This source is based on an inverse low temperature plasma configuration where the pin inner electrode is applying the high voltage and the grounded electrode is the housing itself. The ionization possibilities were tested by using an EPA mix of priority contaminants, showing that 68% of the analytes could undergo both proton-transfer and charge-exchange reactions. The potential of using different discharge gases (He and Ar) to ionize the analytes and auxiliary gases (He, N 2 , O 2, and synthetic air) to transport the ions toward the MS was carefully investigated. Additionally, the addition of water was also tested to show the different ionization trends in the TPI source. Finally, the ionization by TPI under both dry and wet conditions was compared with other gas-phase atmospheric pressure ionization sources showing TPI could ionize a wider range of compounds (97%) than atmospheric pressure chemical ionization (APCI, 95%) and atmospheric pressure photoionization (APPI, 87%). Besides, the detection capability of TPI was better than APCI and APPI, achieving instrumental limits of detection down to 3 fg on column, which demonstrates the great potential of this ionization source for GC−MS determinations.

Comprehensive two-dimensional gas chromatography with flow modulator coupled via tube plasma ionization to an atmospheric pressure high-resolution mass spectrometer for the analysis of vermouth volatile profile

“…Considering that the peaks are modulated at least 3–4 times, around 20–30 spectra per 1 D peak can be expected, which is high enough to carry out the identification of VOCs in vermouth. Additionally, the outstanding detection capability that TPI has shown for a wide range of analytes [ 14 ] may ensure the detection of flavoring compounds even at low concentration ranges. The repeatability of the HS-SPME GC × GC-TPI-qTOF-MS methodology has been evaluated by measuring the area of the internal standard (1,4-dichlorobenzene) in the sample ( n = 3).…”

“…The GC was coupled to a flame ionization detector (FID, Agilent Technologies) for both sample extraction and chromatographic separation optimizations. Additionally, for the identification of the aroma profile, the gas chromatograph was coupled to a 6546 LC/Q-TOF high-resolution mass spectrometer (Agilent Technologies) interfaced with the homemade TPI source described elsewhere [ 14 ]. Briefly, the TPI source is based on an inverse low-temperature plasma configuration.…”

“…Although plasma-based sources have been widely used for ambient ionization mass spectrometry [ 13 ], their application using GC-HRMS is still quite limited. Recently, our research group has developed a tube plasma ionization (TPI) source for GC-qTOF-MS coupling which allows the determination of a wide range of compounds [ 14 ]. Moreover, the operation of this source at atmospheric pressure conditions could help to improve the performance of flow modulators for GC × GC analysis since the 2 D flowrate is negligible compared with the high flows required in the source, thus avoiding the split of the eluate before the MS determination.…”

Detailed comparison of Xenon APPI (9.6/8.4 eV), Krypton APPI (10.6/10.0 eV), APCI, and APLI (266 nm) for gas chromatography high resolution mass spectrometry of standards and complex mixtures

“…2,3,4 Electrospray ionisation (ESI), desorption ionisation techniques, atmospheric pressure chemical ionisation (APCI), atmospheric pressure photoionisation (APPI), and atmospheric pressure laser ionisation (APLI) are well-established techniques in a broad variety of application fields, such as environmental applications, drug and pharmaceutical analysis, life sciences, or petroleomics. 2,4,5 Developments on API techniques are still ongoing 6 and novel methods, such as plasma ionisation based on dielectric barrier discharge ionisation (DBDI) 7 or lowtemperature plasma (LTP) 8 , soft X-ray-based APPI 9 , and atmo-spheric pressure single photon laser ionisation (APSPLI) 10 , were recently introduced.…”

“…• Ionisation in APCI is induced by corona discharge, where primary radical cations are formed by the makeup gas that is commonly nitrogen (7)(8). The primary ions then react with traces of water in the ion source and form charged water clusters (9)(10)(11).…”