facing the mass spectrometer inlet capillary and a diffuse ring from the outer droplet of the electrospray forming mainly in that same direction, similar to that described by Green et al. 31. The footprint of the commercial sprayer showed a homogenous edge all around with a diffuse ring in all directions with only a slight sideways bias, which suggests a less directional and less focussed electrospray (see Figure 2 B). Such differences could potentially have an impact on desorption efficiency of molecules from tissue and spatial resolution during DESI-MS imaging. Laser light sheet visualisation was used to investigate the primary electrospray of each sprayer and images are shown in Figure 2 D. It was observed that the droplet emission from the inner capillary is similar for both, with the emission concentrated towards the edge furthest from the spectrometer inlet (or, in this case, the simulated inlet) and closer to the surface (right edge in Figure 2 B). For the in-house sprayer, the inner capillary is set in the forward direction, which is presumably enhanced by the gas flow. Since the capillary is asymmetrically aligned there is a higher gas flow along the far edge. This has the effect of pushing in, or focusing, the edge of the emission cone. In contrast, the commercial source has a smaller diameter nebulising gas exit orifice and has a more symmetric alignment and consequently a more symmetric emission cone, but also a broader spray cone. The experiments were performed at relatively low solvent flow rate (1.5 µl/min) and high gas pressure (7 bars). The spreading effect is likely to be enhanced if the solvent flow rate is increased or the gas pressure is lowered. Figure 2: Comparison of the in-house built and commercial DESI sprayers. A: schematic diagram of the in-house built sprayer, consisting of two fused silica capillaries and the commercial sprayer, consisting of a stainless steel gas nozzle and a fused silica solvent capillary; B,C: Negative ion spectra from pork liver and corresponding desorption areas for 30 s dwell time on coated rhodamine for the in-house built and commercial sprayer for the first and second experiment; BPI: base peak intensity; D: laser sheet visualisation of the electrospray emitted by the in-house built and commercial sprayers, respectively.
facing the mass spectrometer inlet capillary and a diffuse ring from the outer droplet of the electrospray forming mainly in that same direction, similar to that described by Green et al. 31. The footprint of the commercial sprayer showed a homogenous edge all around with a diffuse ring in all directions with only a slight sideways bias, which suggests a less directional and less focussed electrospray (see Figure 2 B). Such differences could potentially have an impact on desorption efficiency of molecules from tissue and spatial resolution during DESI-MS imaging. Laser light sheet visualisation was used to investigate the primary electrospray of each sprayer and images are shown in Figure 2 D. It was observed that the droplet emission from the inner capillary is similar for both, with the emission concentrated towards the edge furthest from the spectrometer inlet (or, in this case, the simulated inlet) and closer to the surface (right edge in Figure 2 B). For the in-house sprayer, the inner capillary is set in the forward direction, which is presumably enhanced by the gas flow. Since the capillary is asymmetrically aligned there is a higher gas flow along the far edge. This has the effect of pushing in, or focusing, the edge of the emission cone. In contrast, the commercial source has a smaller diameter nebulising gas exit orifice and has a more symmetric alignment and consequently a more symmetric emission cone, but also a broader spray cone. The experiments were performed at relatively low solvent flow rate (1.5 µl/min) and high gas pressure (7 bars). The spreading effect is likely to be enhanced if the solvent flow rate is increased or the gas pressure is lowered. Figure 2: Comparison of the in-house built and commercial DESI sprayers. A: schematic diagram of the in-house built sprayer, consisting of two fused silica capillaries and the commercial sprayer, consisting of a stainless steel gas nozzle and a fused silica solvent capillary; B,C: Negative ion spectra from pork liver and corresponding desorption areas for 30 s dwell time on coated rhodamine for the in-house built and commercial sprayer for the first and second experiment; BPI: base peak intensity; D: laser sheet visualisation of the electrospray emitted by the in-house built and commercial sprayers, respectively.