Carbon Nanotube Templated- Microfabricated Thin Layer Chromatography Plates

Transcription

1 Carbon Nanotube Templated- Microfabricated Thin Layer Chromatography Plates David S. Jensen, 1 Supriya Kenyal, 1 Ricky Wyman, 1 Robert Davis, 1 Richard Vanfleet, 1 Andrew Dadson, 2 Michael Vail, 2 Matthew R. Linford 1* 1 Brigham Young University, Provo, UT, USA 2 US Synthetic Corporation, Orem, UT, USA

2 Presentation Outline Current TLC technology Why produce a microfabricated TLC plate How the TLC plates are fabricated Studies using a diamond geometry patterned surface Studies using a zigzag patterned surface Comparison with current HPTLC and UTLC plates Further work

3 Properties of Si 60 TLC and HPTLC plates

4 Why microfabricate a TLC plate TLC and HPTLC plates are produced by creating a slurry of adsorbent and then smearing the slurry across the backing. This produces a random bed of adsorbent The SiO 2 adsorbent is bound together by a low concentration of low molecular weight polymer or calcium sulfate (gypsum) Why microfabrication? Goal: create a separation medium that will significantly reduce analyst time and improve chromatographic characteristics. Theoretical studies show that an increase in the homogeneity of the adsorbent bed improves the chromatographic efficiency for pressure driven systems. 1,2 Microfabrication allows for precise placement of the chromatographic adsorbent. 1. De Smet, J. et al. Anal. Chem. 2004, 76, Billen, J. et al. J. Chromatogr. A 2007, 1168, 73-99

5 Fabrication Scheme After Reduce reducing the patterned the iron iron catalyst with and H 2 forming argon while the temperature is nanoparticles ramped up to the 750 C. This process carbon forms nanotubes iron nanoparticles. (CNTs) are grown with C 2 H 4, H 2, and Ar as the processing gases. Heights can range from 10 µm to 2 mm. Iron catalyst Al 2 O 3 (Diffusion barrier, limits the formation of iron silicide) Backing Material (Silicon wafer)

6 Coating the CNTs with silicon SiH4(g) Si(g) + 2H2(g) TEM image showing the silicon used encapsulated as the CNTS SiH4 is processing reagent to coat CNT the CNTs with amorphous silicon. This is a low Si coating pressure chemical deposition process at a temperature of 530 CSEM micrograph of silicon coated CNTs. This process produces a mechanically stable material. However, the material at this point is dark and is difficult to see separated analytes Al2O3 (Diffusion barrier, limits the formation of iron silicide) Backing Material (Silicon wafer)

7 Converting the Silicon to Silica Oxidation of the of material the material in in atmosphere 1000 C removes at 1000 C removes the CNTs and converts the silicon to the silica. CNTs After and which converts the material the silicon is to hydrated silica. with After an which acidic solution the material (1:1 is hydrated 0.1 M HCl:MeOH) with an prior acidic to solution chromatography (1:1 0.1 M HCl:MeOH) to increase the silanol content prior to chromatography

8 Microfabrication Process Scheme at a Glance Backing Material Photolithography Barrier Layer Al 2 O 3 (30 nm) Catalytic Material Iron (6 nm) Remove Photo Resist CNT Growth CVD Process LPCVD Process Infiltrate with Silicon Oxidize CNTs out Oxidize Si to SiO 2 After the fabrication process the silanol content of the adsorbent needs to be increased. The TLC plate is placed into a bath of 1:1 HCl(0.1 M):Methanol at reflux temperatures for overnight. After the rehydration process the TLC plate is rinsed thoroughly with water to remove any residual acid. Then the plate is dried at 110 C and is now ready for chromatography.

9 SEM micrographs of the final product Side image Top View

10 Microfabrication process: Placement of the Iron catalyst Photolithography was used to place the iron catalyst 10 x 5 µm diamond geometry Sight the paper that speaks about the theoretical use of the diamond geometry and the other microfluidic devices that have used this type of design

11 2:1 Aspect Ratio Diamond Geometry Bird s eye view of the TLC plate Different channel widths create different flow velocities and distorts the chromatography Dimensions: 10 x 5 µm pillar 4 µm bed spacing 100 µm tall When the CNT features were grown tall they tend to lean This creates inhomogenaties for solvent flow

12 Chromatography A test dye mixture from CAMAG (Muttenz, Switzerland) was used for chromatographic evaluation Mobile phase was toluene The plate has chromatographic abilities! The analytes wander during the separation process The chromatography does suffer from this random adsorbent bed created from the mechanical instability of the CNTs

13 What needs to be fixed? The mechanical strength of the CNT framework needs to be increased. This has been done by the use of a zigzag pattern. The zigzag pattern approximates a parallel plate geometry which has shown to give the best theoretical plate height in chromatography. 1,2 1. De Smet, J. et al. Anal. Chem. 2004, 76, Billen, J. et al. J. Chromatogr. A 2007, 1168, 73-99

14 Run Time 12 mins 37 sec Mobile Phase: Toluene (3mL) Migration distance: 45 mm Relative Humidity: 42% CAMAG Test Dye Mixture III Dispersed in Hexanes 3%v/v and 10% v/v Finish Plate I Prior Oxidation Dimensions Adsorbent layer thickness: 50 µm Nominal Hedge Thickness: 5 µm Nominal Channel Width: 9 µm After oxidation Hedge With: 8.3 ± 0.4 µm: Channel Width: Closed off These plate number are comparable to HPTLC plates Channels are closed off Start 3% 3% 10% 10% and 3% are v/v of CAMAG test dye into hexanes Features are closed off, this leads to a slow development time of ca. 12 minutes

15 Run Time 2 mins 59 sec Mobile Phase: Toluene (3mL) Migration distance: 45 mm Relative Humidity: 41% CAMAG Test Dye Mixture III Dispersed in Hexanes 3%v/v and 10% v/v Plate II Prior Oxidation Dimensions Adsorbent layer thickness: 50 µm Nominal Hedge Thickness: 5 µm Nominal Channel Width: 11 µm After oxidation Hedge With: 7.2± 0.3 µm: Channel Width: 4.8 ± 2.0 µm Finish Start The features are now opened introducing faster capillary flow giving a development time of 3 minutes 3% 3% 10%

16 Run Time 2 mins 20 sec Mobile Phase: Toluene (3mL) Migration distance: 45 mm Relative Humidity: 42% CAMAG Test Dye Mixture III Dispersed in Hexanes 3%v/v and 10% v/v Plate III Finish Start 3% 3% 10% Prior Oxidation Dimensions Adsorbent layer thickness: 50 µm Nominal Hedge Thickness: 5 µm Nominal Channel Width: 13 µm After oxidation Hedge With: 7.4.± 0.2 µm: Channel Width: 6.7 ± 1.9 µm Development time: 2 minutes and 20 seconds

17 Run Time 2 mins 4 secs Mobile Phase: Toluene (3mL) Migration distance: 45 mm Relative Humidity: 42% CAMAG Test Dye Mixture III Dispersed in Hexanes 3%v/v and 10% v/v Plate IV Finish Prior Oxidation Dimensions Adsorbent layer thickness: 50 µm Nominal Hedge Thickness: 5 µm Nominal Channel Width: 15 µm After oxidation Hedge With: 7.4 ± 0.2 µm: Channel Width: 7.0 ± 2.7 µm Start Development time: 2 minutes and 4 seconds 3% 3% 10%

18 van Deemter like plots

19 UTLC by Merck Chromatography was preformed under the same conditions that were used for the microfabricated TLC plates. Development time: 22 min 10 sec SiO 2 -layer of 10 µm has mesopores of 3-4 nm and macropores of 1-2µm

20 HPTLC LiChrospher from Merck Chromatography was preformed under the same conditions that were used for the microfabricated TLC plates. Layer thickness: 200 µm Particles: Spherical with a mean PSD of 7 µm The chromatography doesn t have baseline separation. There is also binder that is included as seen in this SEM micrograph

21 Run Times: 2 min 20 sec Comparison of R f and development times 22 min 10 sec 4 min 28 sec 4 min 30 sec Plate III CNT-M TLC Merck UTLC (baseline separation) (baseline separation but long development time) LiChrospher HPTLC (no baseline separation) Merck TLC (no baseline separation)

22 Areas of Improvement A reduction in the width of the adsorbent is effectively decreasing the particle size. There are significant improvements that can still be made. H = A + B/u + Cu Understanding how a change in the channel width effects the flow velocity and chromatographic abilities. Surface silanization will be possible to produce different phases C 18, -C 8, -C 4, -NH 2, -diol, etc.

23 Acknowledgements Brigham Young University Department of Chemistry and Biochemistry The Linford group US Synthetic Corporation For Financial Support

24 Questions?

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