Porous, High Capacity Coatings for Solid Phase Microextraction by Sputtering

Abstract

We describe a new process for preparing porous solid phase microextraction (SPME) coatings by the sputtering of silicon onto silica fibers. The microstructure of these coatings is a function of the substrate geometry and mean free path of the silicon atoms, and the coating thickness is controlled by the sputtering time. Sputtered silicon structures on silica fibers were treated with piranha solution (a mixture of concd H2SO4 and 30% H2O2) to increase the concentration of silanol groups on their surfaces, and the nanostructures were silanized with octadecyldimethylmethoxysilane in the gas phase. The attachment of this hydrophobic ligand was confirmed by X-ray photoelectron spectroscopy and contact angle goniometry on model, planar silicon substrates. Sputtered silicon coatings adhered strongly to their surfaces, as they were able to pass the Scotch tape adhesion test. The extraction time and temperature for headspace extraction of mixtures of alkanes and alcohols on the sputtered fibers were optimized (5 min and 40 °C), and the extraction performances of SPME fibers with 1.0 or 2.0 μm of sputtered silicon were compared to those from a commercial 7 μm poly(dimethylsiloxane) (PDMS) fiber. For mixtures of alcohols, aldehydes, amines, and esters, the 2.0 μm sputtered silicon fiber yielded signals that were 3-9, 3-5, 2.5-4.5, and 1.5-2 times higher, respectively, than those of the commercial fiber. For the heavier alkanes (undecane-hexadecane), the 2.0 μm sputtered fiber yielded signals that were approximately 1.0-1.5 times higher than the commercial fiber. The sputtered fibers extracted low molecular weight analytes that were not detectable with the commercial fiber. The selectivity of the sputtered fibers appears to favor analytes that have both a hydrophobic component and hydrogen-bonding capabilities. No detectable carryover between runs was noted for the sputtered fibers. The repeatability (RSD%) for a fiber (n = 3) was less than 10% for all analytes tested, and the between-fiber reproducibility (n = 3) was 0-15%, generally 5-10%, for all analytes tested. The repeatabilities of our sputtered fibers and the commercial 7 μm PDMS fiber are essentially the same. Fibers could be used for at least 300 extractions without loss of performance. More than 50 compounds were identified in a gas chromatography-mass spectrometry headspace analysis of a real world botanical sample with the 2.0 μm fiber.

6‐Phenylhexyl silane derivatized, sputtered silicon solid phase microextraction fiber for the parts‐per‐trillion detection of polyaromatic hydrocarbons in water and baby formula

“…The extraction time, which ranged from 30 to 15320 s, was chosen using Fiber 1 (20 cm/2.8 μm). As observed in our previous studies [31,47], competitive extraction between LMW and HMW compounds was expected to result in displacement of the LMW compounds by the HMW ones. This type of competitive extraction has been observed in other adsorption-based SPME fibers [50].…”

“…Silicon was sputtered onto fused silica fibers using the same process applied in our previous reports, with the exception that additional deposition parameters were studied in this work [31,47]. The fused silica fibers were positioned perpendicular to the silicon target on a substrate platen.…”

“…In general, commercial SPME coatings suffer from some drawbacks, including a lack of extraction efficiency, irreproducibility, high carry over, high phase bleed instability, swelling in organic solvents, and stripping of the coating (usually observed in direct immersion [DI]) [31][32][33]. Some efforts have been made to address these issues F I G U R E 1 Structure of trichloro(6-phenylhexyl)silane by developing coatings based on functionalized silica [34], mesoporous silica nanoparticles [34], molecularly imprinted polymers [35], metal organic frameworks [36], covalent organic frameworks (COFs) [37], ionic liquids [38,39], metal oxides [40], ZnO nanorods [41], carbon nanotubes [42], graphene [43,44], biocharcoal aerogel [45], and conducting polymers [46].…”

A new holder/container with a porous cover for atomic layer deposition on particles, with transport analysis and detailed characterization of the resulting materials

“…XPS was performed with a Surface Science SSX‐100 X‐ray photoelectron spectrometer (serviced by Service Physics, Bend, OR, USA) with a monochromatic Al Kα source, a hemispherical analyzer, and a take‐off angle of 35°. Survey scans were recorded with a spot size of 800 × 800 μm and a nominal pass energy of 150 eV (instrument setting of “resolution 4”) 42 . XPS was performed on coated and uncoated zirconia particles that had been pressed into conductive carbon tape to reduce sample charging.…”

Development of a solventless stir bar sorptive extraction/thermal desorption large volume injection capillary gas chromatographic-mass spectrometric method for ultra-trace determination of pyrethroids pesticides in river and tap water samples

“…However, except SPME, these techniques are not entirely solvent free and have multistep procedures. On the other hand, SPME fibers generally suffer from drawbacks such as relatively high cost, fragility, a low limited selectivity, and swelling of the coatings in chlorinated solvents [22].…”