SUPPORTING INFORMATION

Transcription

1 SUPPORTING INFORMATION Liquid Beam Desorption Mass Spectrometry for the Investigation of Continuous Flow Reactions in Microfluidic Chips Sandra Schulze, Maik Pahl, Ferdinand Stolz, ǂ, Johannes Appun, ȹ Bernd Abel, ǂ, Christoph Schneider, ȹ and Detlev Belder *, Institute of Analytical Chemistry, University Leipzig, Linnéstraße 3, Leipzig, Germany ǂ Wilhelm-Ostwald-Institute of Physical and Theoretical Chemistry, University Leipzig, Linnéstraße 3, Leipzig, Germany Leibniz Institute of Surface Modification (IOM), Permoserstraße 15, Leipzig, Germany ȹ Institute of Organic Chemistry, University Leipzig, Johannisallee 29, Leipzig, Germany * Phone: Fax: belder@uni-leipzig.de Table of contents: 1. Microchip Fabrication (Figure S-1) S-2 2. Liquid Beam Setup (Figure S-2) S-3 3. Microchip Emitter Characterization (Figure S-3) S-4 4. Optimization of Laser Parameters (Figure S-4) S-5 5. Spray Performance at Different Flow Rates (Figure S-5) S-6 6. Acceleration Structure (Figure S-6) S-6 7. Reaction Parameters of the Mannich Reaction (Figure S-7) S-7 References S-8 S-1

2 1. Microchip Fabrication The fabrication process started from microscope slides (Figure S-1a) of soda-lime glass of 76 mm x 26 mm size (Carl Roth, Karlsruhe, Germany) which were sputtered with a thin chrome layer (150 nm, FHR Anlagenbau GmbH, Ottendorf-Okrilla, Germany, Figure S-1b). All chemicals were purchased from Microchemicals GmbH (Ulm, Germany). A positive photoresist (AZ1518) was spin-coated on the glass slide (Spin 120 PTFE, SPS Europe, Putten, Netherlands, 4000 rpm, 1000 rpm/s, 30 s, Figure S-1c). Photomasks with the desired layout were designed, printed, fixed to glass slides and pressed in the before described manner 1 and placed on top of the glass slide (Figure S-1d). After irradation with UV light for 30 s (Flutbelichter FB5, SÜSS MicroTec AG, Garching, Germany) and developing of the photoresist in a mixture of developer (AZ351B) and water (1:4 vol%) on a rotating plate (40 U/min, 1 min) a structured photoresist is obtained (Figure S-1e). Chrome etching with ceric ammonium nitrate and perchloric acid (TechniEtch Cr01) for 2 min and etching with hydrofluoric acid for 30 min were performed in a sealed Teflon container equipped with a magnetic stirrer to remove the chrome layer and the glass respectively at the irradiated area (Figure S-1f, g). The residual photoresist and chrome layer were removed with acetone and ceric ammonium nitrate respectively (Figure S-1h). Finally, the structured bottom plate was bonded at high temperature (max. 620 C) with a cover plate in which powder-blasted holes were introduced (sandblaster Point 2, Barth Serienapparate, Königsbach-Stein, Germany) for microfluidic contacting (Figure S-1i). Figure S-1. Fabrication cycle for full glass microchips with chrome masks, wet chemical etching and bonding. S-2

3 The described protocol needs 19 h to give a bonded microchip with inlet holes. The timeand yield-depending step is the bonding where 80% yield are achieved. The manufacturing of an emitter needs additional time. The grinding step for the preparation of ground tips lasts about 30 min (100% yield) and the preparation of a tapered emitter including milling, pulling and etching as described before 2 can be performed in an academic lab at a scale of 1 h (80% yield). All in all, the time for manual fabrication of glass microchip prototypes is comparable to the fabrication time of its polymeric analogues Liquid Beam Setup The general experimental setup for liquid beam investigations with microchips and MS coupling is shown in Figure S-2. Figure S-2. Experimental setup for microchip-lilbid-ms investigations. a) Overview of the main components. b) Enlarged view of the marked area in a) with the liquid beam jetted from the microchip in front of the MS inlet. S-3

4 3. Microchip Emitter Characterization Different emitter geometries result in altered shape and size of the channel cross section. Pictures of a ground and a pulled tip can be seen in Figure S-3a and S-3b respectively. Figure S-3. Photographs (top), lightmicroscope (bottom left) and scanning electron microscope images (bottom right) of the channel cross sections of a) ground emitter tips and b) pulled emitter tips. S-4

5 4. Optimization of Laser Parameters The influence of laser power and laser wavelength on the signal intensity of microchip-lilbid- MS spectra was studied using the model analyte D-arginine in water. For this, the laser power was varied between 0 mw and 30 mw (Figure S-4a). It was obvious that the highest MS signal intensity could be reached at maximum laser power. By reducing the flash lamp energy, which is in correlation with the laser power, the signal intensity decreases as well. The laser wavelength could be adjusted between 2925 nm and 3000 nm (Figure S-4b). For further measurements the wavelength was set to 2925 nm as this resulted in the highest signal intensity because this wavelength is located in the range of the IR absorption band of the hydroxyl group stretch vibration. Figure S-4. Absolute intensities of the monomer (m/z 175.1, dark green) and dimer (m/z 349.2, light green) signal of the analyte D-arginine at varying a) laser power and b) laser wavelength after microchip-lilbid-ms. S-5

6 5. Spray Performance at Different Flow Rates The presence and shape of an ESI spray is dependent on the applied flow rate. A microchip with a pulled emitter (opening: 29 µm x 17 µm) showed a good spray performance at a flow rate of 5 µl min-1. An increase of the flow rate to 10 µl min-1 resulted in a collapse of the spray and the formation of a beam. This beam got sharper by further increasing the flow rate. Figure S-5. Photographs of the microchip in front of the MS orifice showing the electrospray performance at a pulled emitter at different flow rates. The spray is illuminated by the light of a green laser. 6. Acceleration Structure The influence of the acceleration structure on the dilution of an analyte band was studied for a microchip equipped with a tapered tip using a mixture of fluorescent dyes. Figure S-6. Microscopic image and fluorescence images of a 1 mmol L-1 fluorescein sodium salt/ 1 mmol L-1 rhodamine B mixture (1:1) in acetonitrile/water (80/20 vol%) at the acceleration structure. The indicated split ratio displays the flow rate of the reaction channel containing the sample to the acceleration channels filled with acetonitrile and gave a constant final flow rate of 125 µl min-1. S-6

7 7. Reaction Parameters of the Mannich Reaction Additionally the Mannich reaction was characterized in terms of nucleophile stability and the influence of the nucleophile and catalyst concentration on the product formation in electrospray ionization (ESI) infusion experiments. Figure S-7. Investigation of the Mannich reaction in terms of a) nucleophile stability and the influence of b) nucleophile concentration and c) catalyst concentration on the product formation. The reaction was either performed a) offline in a 3 ml reaction vessel at 1 mmol L -1 initial concentration or b, c) online in a polyetheretherketone capillary reactor of 50 µl volume at 100 µmol L -1 initial concentration and with ESI infusion. Product signal intensity (m/z 428.1) is displayed relative to the substrate signal (m/z 226.1, set to 100%, not shown). The results in Figure S-7a show that the nucleophile is stable in solution and still active after several days. A turnover of the substrate to the reaction product could be observed using a nucleophile solution of different age. When the nucleophile was used in 1 mmol L -1 hardly any product formation was observable within 10 minutes reaction time (Figure S-7b). Increasing the nucleophile concentration to 10 mmol L -1 resulted in high product signal intensity after the same reaction time. With this value the investigations moved on to study the influence of different catalyst concentrations (Figure S-7c). If the concentration was increased to 1 mmol L -1 a significant rise in product intensity was achieved. S-7

8 References 1 Hoera, C.; Ohla, S.; Shu, Z.; Beckert, E.; Nagl, S.; Belder, D. Anal. Bioanal. Chem. 2015, 407, Hoffmann, P.; Häusig, U.; Schulze, P.; Belder, D. Angew. Chem. Int. Ed. 2007, 46, Duffy, D. C.; McDonald, J. C.; Schueller, O. J.; Whitesides, G. M. Anal. Chem. 1998, 70, S-8