Characterization of a Direct Sample Analysis (DSA) Ambient Ionization Source

Abstract

Abstract. Water cluster ion intensity and distribution is affected by source conditions in direct sample analysis (DSA) ionization. Parameters investigated in this paper include source nozzle diameter, gas flow rate, and source positions relative to the mass spectrometer inlet. Schlieren photography was used to image the gas flow profile exiting the nozzle. Smaller nozzle diameters and higher flow rates produced clusters of the type [H + (H 2 O) n ] + with greater n and higher intensity than larger nozzles and lower gas flow rates. At high gas flow rates, the gas flow profile widened compared with the original nozzle diameter. At lower flow rates, the amount of expansion was reduced, which suggests that lowering the flow rate may allow for improvements in sampling spatial resolution.

Advances in Ionization for Mass Spectrometry

“…Usmanov and Hiraoka also reported on the use of a soleniod pulsed valve for reducing the gas load on the mass analyzer using atmospheric pressure ionization methods . Winter and co-workers characterized a direct sample analysis (DSA) source that is a modified APCI . Wachsmuth et al redesigned an APCI source for coupling to gas chromatography and achieved a 4-fold decrease in detection limits and narrower elution peaks relative to earlier versions .…”

“…215 Winter and co-workers characterized a direct sample analysis (DSA) source that is a modified APCI. 216 Wachsmuth et al redesigned an APCI source for coupling to gas chromatography and achieved a 4-fold decrease in detection limits and narrower elution peaks relative to earlier versions. 217 This improvement led to more than a doubling of peaks above a S/N of 20 extracted from metabolite fingerprints of pancreatic cancer cell supernatants.…”

Molecular Ionization-Desorption Analysis Source (MIDAS) for Mass Spectrometry: Thin-Layer Chromatography

“…The source is aligned coaxially with the inlet of the mass spectrometer. Schlieren photographs taken of the heated nitrogen gas flow from the DSA revealed that the gas flow profile widened as it left the nozzle [32]. By adapting nozzles of smaller internal diameter, more uniform gas flow was achieved [32].…”

“…The development of MIDAS stems from our previous work studying the direct sample analysis (DSA) platform [32]. The DSA is a combined source and sampling platform.…”

“…Schlieren photographs taken of the heated nitrogen gas flow from the DSA revealed that the gas flow profile widened as it left the nozzle [32]. By adapting nozzles of smaller internal diameter, more uniform gas flow was achieved [32]. These observations as well as a desire to make a device capable of analyzing planar and/or irregular surfaces (currently a limitation of the DSA) spurred the development of MIDAS.…”