Surface-Assisted Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (SA-FAPA-MS)

Analytical chemistry plays a crucial role in ensuring the safety, quality, and authenticity of products and processes, e.g. in the food and beverage industry, pharmaceutical production, but also in forensics, diagnostics, and environmental sciences. One of its most powerful tools is mass spectrometry (MS) which allows scientists to selectively detect substances even at lowest amounts. Conventional MS techniques usually require extensive and complex sample preparation and additional separation procedures which make them time-consuming, resource-intensive and therefore costly. A novel approach known as ambient desorption/ionization MS (ADI-MS), offers a faster and more sustainable alternative by allowing direct analysis of samples in their original state.
This dissertation presents the development, optimization, and application of a specific ADI-MS technique termed surface-assisted flowing atmospheric-pressure afterglow MS (SA FAPA MS). This method is based on a plasma-based ionization source in combination with functionalized sample carrier surfaces and enables rapid, preparation-free detection of small molecules in matrix-containing samples, e.g. in beverages, pharmaceutical products or even body fluids.
One core goal was to improve the quantitative capabilities of SA FAPA MS as ADI MS in general faces challenges regarding signal stability and overall reproducibility. A key finding was that the choice of the sampling surface dramatically influences performance. Among the surfaces tested, cyano- and dimethyl-functionalized thin-layer chromatography (TLC) plates performed better than conventional supports such as glass or metal mesh. These surfaces enabled higher ion yields, better signal stability, and broader dynamic ranges, ultimately leading to detection limits down to the femtomole (fmol) range.
The method was successfully applied to accurately quantify model substances in beverages and electronic cigarette liquids even when matrix effects were expected. Precision and accuracy were further improved by isotopically labeled standards. Further, the semi-quantitative detection of benzocaine in human saliva demonstrated the potential for biomonitoring and diagnostic applications.
For the applications above, SA FAPA MS proves to be a fast, sensitive, and sustainable alternative to conventional MS methods. Minimal sample pre-treatment requirements, versatility, and high throughput make it very attractive for use in quality control, toxicology, diagnostics, and environmental monitoring where accurate results are required as quickly as possible.