Investigation of impurities in Supercritical Fluid Chromatography with Trapped Ion Mobility Spectrometry – Quadrupole / Time of Flight Mass Spectrometry

Abstract

Introduction: Achieving and retaining a low background signal is essential for analytical techniques, especially for extremely accurate systems such as supercritical fluid chromatography (SFC) coupled with high-resolution mass spectrometry (HRMS) since the limits of detections are heavily dependent on the background signal.
Background: A standard option to ensure a low background signal is the usage of ultrapure reagents. These reagents avoid contaminating the system and thus increase the background signal. In this study, an increase in the background signal was observed due to impurities originating from the CO2 cylinder or the CO2 pump. No prior literature has reported impurities originating from these sources. Thus, there is a lack of knowledge about what the contaminations are, what their properties are, and how they could be efficiently analyzed.
Aims: This project aims to respond to the following questions: Do the impurities arise from the CO2 cylinder or the CO2 pump? Could the concentration of these impurities be related to the process of CO2 production? Is gas chromatography coupled with mass spectrometry (GC/MS) suitable for studying the structure and properties of these impurities?
Methods: The experimental procedure was initialized by isolating the impurities in liquid solvent by flushing CO2 from the cylinder into the solvent over a week, and injecting samples at various timepoints in trapped ion mobility spectrometry hyphenated with quadrupole time of flight mass spectrometry (tims-TOF). The last aliquot was concentrated and injected into GC/MS, before and after derivatization and at different dilutions.
Results: The aliquots collected showed that the background signal in tims-TOF increased with time while the GC/MS injections did not show any peaks for any of the samples injected.
Conclusion: The results of this study suggest that the CO2 cylinder was the source of contamination, and that GC/MS is not suitable for their analysis, probably due to poor volatility or incapability to pass the wool of the liner. Additionally, no correlation between the concentration of these impurities and the period of CO2 production could be found in the literature.

Popular Abstract

Isolation of impurities in liquid carbon dioxide and investigation of their possible sources
The development of today’s analytical chemistry techniques is focused on detection of compounds at the lowest possible concentration. To achieve that, an analytical technique must be able to distinguish the signal produced by the analyte from the background signal of the instrument. So, lower background signals allow detection of analytes in lower concentrations. If the background signal is high or increased during the analysis, then the limit of detection of the technique is compromised. In this study, higher than usual background levels were observed in a system of supercritical fluid chromatography (SFC) coupled to a high-resolution mass spectrometer (HRMS) fully obstructing the detection of the analytes. In general, SFC utilizes CO2 to separate compounds according to their polarity and then HRMS determines the mass of these molecules with accuracy up to four decimals. The increase was found to be generated by impurities emanating from either the CO2 cylinder or the CO2 pump. These sources have never caused such issues before and for that reason it is vital to find which is the exact source of these impurities and what their identity or their properties are, to avoid contamination issues in the future. Additionally, the concentration of these impurities was found to be significantly higher in summer than in fall, yielding questions about the relation between impurities levels and periods of CO2 production. The purpose of this study was to:
1. Locate the source of the impurities.
2. Investigate a possible connection between the level of the impurities and the production process of CO2, by performing a literature search.
3. Apply gas chromatography with mass spectrometry (GC/MS) to derive more information about the impurities.
To achieve the previous aims, firstly, liquid solvent was flushed with liquid CO2 to transfer the impurities into the solvent. Samples were collected over a week and then directly injected into the mass spectrometer. Afterwards the last aliquot was diluted at various ratios, derivatized to alter the volatility of the contaminants and injected into GC/MS. The experiments showed that the impurity signal increased in the mass spectrometer after 48 h, while no peaks were detected with GC/MS. In parallel, the literature survey did not yield any information on possible connections between contamination levels and CO2 production processes. These results led to the conclusions that the CO2 cylinder is the source of the contamination in the chromatography-mass spectrometry system, and that GC/MS is not a suitable technique for analyzing these impurities. Finally, the theoretical review did not give an explanation to the observed variation of the contamination levels during different seasons of CO2 production.

• author: Synefakis, Evangelos
• supervisor: Azemina Bajramova
• organization: Department of Chemistry
• course: KEMP20 20251
• year: 2025
• type: L3 - Miscellaneous, Projetcs etc.
• subject: Chemistry
• keywords: Contamination, Carbon Dioxide, Supercritical fluid chromatography, tims-TOF, Analytical chemistry
• language: English
• id: 9203932
• date added to LUP: 2025-06-24 11:55:18
• date last changed: 2025-06-24 11:55:18