Ionization of semi-fluorinated n‐alkanes in controlled atmosphere using flexible micro-tube plasma (FμTP) ionization source with square- and sine-wave voltage

• Published in: Talanta (Oxford) 2022-11, Vol.249, p.123662-123662, Article 123662
• Main Authors: Tian, Caiyan, Speicher, Luisa, Xue, Dengqi, Moreno-González, David, Marggraf, Ulrich, Ahlmann, Norman, Brandt, Sebastian, Franzke, Joachim, Niu, Guanghui
• Format: Article
• Language: English
• Subjects: Controlled atmosphere; Flexible micro-tube plasma (FμTP); Semi-fluorinated n-alkanes (SFAs); Sine-wave voltage; Square-wave voltage
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/j.talanta.2022.123662

Non-thermal plasma-based ionization sources have been widely used and shown excellent soft ionization performance in mass spectrometry. Despite their extensive application, the ionization mechanisms of these sources are of great interest for further exploring their full potential. A controlled atmosphere can provide a clean and controllable ionization environment and is beneficial for studying the ionization mechanism. The plasma source itself also has a significant impact on the ionization mechanism of the analyte, and the voltage waveform is one of the key parameters for controlling the plasma source. In this paper, a miniature flexible micro-tube plasma (FμTP) ionization source was sustained using both square and sine-wave voltage. The ionization processes of typical semi-fluorinated n-alkanes (SFAs) were investigated in the controlled atmosphere filled with 80% N2 and 20% O2. The main mass peaks using both square and sine-wave voltages are found to be [M-mH]+ and [M-mH+nO]+ (m = 1, 3; n = 0, 1, 2). However, for the square-wave voltage, the [M-H+O]+ species are the most abundant while [M−H]+ species are dominant for the sine-wave voltage, showing that the plasma generated with sine-wave voltage is somewhat “softer” than the one with square-wave voltage for SFAs. With the assistance of optical spectroscopy, the plasma developments in one discharge cycle for both voltage waveforms were obtained. Only one discharge can be found in each half cycle for square-wave voltage while several for the sine-wave voltage. These would be responsible for the different ionization behaviors in these two cases. This work provides more insight into the ionization mechanism of SFAs and more understanding of plasma-based soft ionization. In addition, the analytical performance was evaluated to be comparable when using these two voltage generators with a big difference in cost, which will benefit the instrumental development. [Display omitted] •SFAs was analyzed using mass spectrometry with miniature FμTP as ionization source in controlled atmosphere.•The ionization mechanism of SFAs was found to be the same while different pathways for square- and sine-wave voltage.•Square- and sine-wave voltage sustained FμTP ionization sources give high-sensitive and comparable analytical performance.•The ionization source sustained by sine-wave voltage is somewhat “softer” than that by square-wave voltage for SFAs.