Sputtered Silicon Solid Phase Microextraction Fibers with a Polydimethylsiloxane Stationary Phase with Negligible Carry-Over and Phase Bleed

Authors: Tuhin Roychowdhury2,  Dhananjay Patel2, Dhruv Shaha2, Anubhav Diwan3, Massoud Kaykhaii4,
Jason Herrington1, David  Bell1,  Matthew Linford2

1. Restek Corporation, 2. Department of Chemistry & Biochemistry, Brigham Young University, 3. Moxtek, Inc.,
4. Department of Chemistry, Faculty of Sciences, University of Sistan and Baluchestan

Published By: Journal of Chromatography A

Year of Publication: 2020

Link: https://doi.org/10.1016/j.chroma.2020.461065

Abstract:
We report the preparation of high performance, sputtered, polydimethylsiloxane (PDMS)-coated solid phase microextraction (SPME) fibers that show negligible carry-over and phase bleed. This process involves sputtering silicon onto silica fibers and functionalizing the resulting porous nanostructures with ultrathin films of vapor-deposited PDMS. Different thicknesses of silicon (0.25, 0.8, and 1.8 µm) and PDMS (8, 16, and 36 nm) were produced and their extraction efficiencies evaluated. The deposition of PDMS was confirmed by time-of-fight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and contact angle goniometry on model, planar silicon substrates. These fibers were investigated using direct immersion SPME coupled with gas chromatography-mass spectrometry (GC-MS) analysis of a series of polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic pollutants. The 1.8 µm thick silicon coating with 16 nm of PDMS (Si (1.8 µm)/PDMS (16 nm)) produced the best response among the combinations tested. Conditions for the extraction of PAHs with this fiber were optimized and its extraction performance was compared to that of a commercial 7 μm PDMS fiber. The linearity (1 – 110 µgL−1), repeatability (RSD%, n=3) (17% ave.), and minimum detection limits (0.6 – 1.5 µgL−1) of the sputtered fibers were determined and found to be superior to the commercial 7µm PDMS fiber in many respects. Carry-over and phase bleed from commercial PDMS-based SPME fibers are two of their major drawbacks, which decrease their lifetimes and usefulness. Minimal carry-over and phase bleed were observed for our sputtered PDMS-coated fibers. In particular, our fiber only shows 12 % of the phase bleed of the comparable commercial fiber. In addition, it shows no carry-over for analytes with retention times greater than pyrene, and only 5 % of the carry-over of the other analytes. Our fibers could be used for at least 300 injections without any significant loss of performance.