Potential of GC-Combustion-MS as a Powerful and Versatile Nitrogen-Selective Detector in Gas Chromatography

Abstract

Here, we show the potential and applicability of the novel GC-combustion-MS approach as a nitrogen-selective GC detector. Operating requirements to achieve reproducible and compound-independent formation of volatile NO species as a selective N-signal during the combustion step are described. Specifically, high temperatures (≥1000 °C) and post-column O2 flows (0.4 mL min–1 of 0.3% O2 in He) turned out to be necessary when using a vertical oven without makeup flow (prototype #1). In contrast, the use of a horizontal oven with 1.7 mL min–1 He as an additional makeup flow (prototype #2) required milder conditions (850 °C and 0.2 mL min–1). A detection limit of 0.02 pg of N injected was achieved, which is by far the lowest ever reported for any GC detector. Equimolarity, linearity, and peak shape were also adequate. Validation of the approach was performed by the analysis of a certified reference material obtaining accurate (2% error) and precise (2% RSD) results. Robustness was tested with the analysis of two complex samples with different matrices (diesel and biomass pyrolysis oil) and N concentration levels. Total N determined after the integration of the whole chromatograms (524 ± 22 and 11,140 ± 330 μg N g–1, respectively) was in good agreement with the reference values (497 ± 10 and 11,000 ± 1200 μg N g–1, respectively). In contrast, GC-NCD results were lower for the diesel sample (394 ± 42 μg N g–1). Quantitative values for the individual and families of N species identified in the real samples by parallel GC–MS and additional GC × GC–MS analyses were also obtained using a single generic internal standard.

Sensitive Detection and Quantification of Oxygenated Compounds in Complex Samples Using GC-Combustion-MS

“…The resulting volatile combustion species are then brought to a manually actuated high-temperature six-way valve, installed inside the GC, which in turn allows directing them to the ion source of the MS instrument. Such a valve allows also bypassing the combustion furnace when necessary, which enables the setup to work under GC–MS (Figure S1A) or GC-combustion-MS (Figure S1B) configurations . The expected products for a complete oxidation of organic compounds with O 2 as the oxidant would then comprise C a H b O c + ( a + b 4 − c 2 ) O 2 → 800 ° normalC a C normalO 2 + true b 2 normalH 2 O Of course, other N- and S-containing volatile species would be formed at high temperatures (i.e., NO x or SO x ) if present in the compound.…”

“…Applications can be foreseen in a wide variety of fields, ranging from the petroleum and chemical (polymer and plastic) industries to quantitative metabolomics, where the determination of the great and rising variety of O-containing compounds is increasingly important. This work is the last step in the development of an innovative multipurpose GC detection system (GC-comb-MS) featuring element-selective detection (C, H, N, S, and O) with generic quantification in complex samples, while maintaining the structural elucidation power of mass spectrometry. , In fact, it can be regarded as the first approach that enables the online and simultaneous ultrasensitive elemental quantification of every individual volatizable (GC) organic compound present in complex samples. Of course, such tremendous potential to provide elemental fingerprints for individual compounds in complex samples will be boosted even further when combined with the huge separation power of multidimensional GC.…”

“…Helium (purity 99.999%) was purchased from Air Liquide. Two different gas mixtures were used as the combustion gas, 16 O 2 /He (0.3%, v/v) from Linde and 18 O 2/ He (1% v/v, 97% 18 O 2 enriched) from Westfalen AG. Real samples were provided by TotalEnergies Raffinage Chimie, a hydrotreated diesel sample, and aliquots from effluents were taken at different times along the hydrotreatment of a wood biooil.…”

“…Such a valve allows also bypassing the combustion furnace when necessary, which enables the setup to work under GC−MS (Figure S1A) or GC-combustion-MS (Figure S1B) configurations. 18 The expected products for a complete oxidation of organic compounds 19 with O 2 as the oxidant would then comprise…”

“…In this work, we have developed a highly sensitive instrumental approach to detect selectively and quantify Ocontaining compounds in complex samples without the need to resort to specific standards. Our approach makes use of isotopically enriched 18 O 2 during the combustion step that takes place between the GC separation and the ionization in the MS instrument. The proof-of-concept strategy to stand out the O-containing compounds from the organic crowd and perform their accurate quantification is demonstrated.…”