## 4 Conclusions  
A sputtered carbon SPME fiber deposited at different throw distances was explored. These coatings were characterized by SEM, XPS, SE, and contact angle goniometry. The best coatings produced (11.5 \(\upmu\)m carbon, with and without PDMS) were evaluated by DI-GC-MS. Sputtered carbon SPME fibers showed similar functional group selectivity as commercial CWR fibers. However, the sputtered morphology has again shown the ability to overcome phase thickness/volume discrepancies and increase the relative recovery for some compounds. Additionally, a new SPME evaluation mix was developed, which consists of 15 compounds with different functional groups and chemical properties. Pentane, chloroform, 2-picoline, and sulfolane provided valuable insights into the coating/stationary phase behavior, which would otherwise have been missed by the traditional probe mixes. \(N\),\(N\)-dimethylamine andicyclohexylamine, which are present in the [PERSON] and [PERSON]'s test mixes, continue to show their value in the current study. The sputtered carbon fibers showed better responses per volume of the coatings than the commercial CWR fibers. Future work may include expanding the test mix to include fatty acids, nitro groups, and pesticides of interest. In addition, a more systematic exploration of this test mix with traditional SPME fibers should be performed.  
Our previous and current studies suggest that sputtered SPME fibers offer the following potential advantages, which should be further perused in future research: (i) high surface area/volume ratios afforded by their cauliflower morphology; (ii) the high surface area/volume ratio means sputtered fibers have shown a great deal of promise using very thin films of phase; (iii) as a result of the aforementioned, the fibers tend to exhibit low phase blead and low carryover; (iv) with little phase on the sputtered coatings, the phase swelling/stripping typically encountered with traditional SPME fiber phases during DI mode appears to be absent. These advantages make sputtered SPME devices very promising for DI applications, which are probably the future for SPME devices in general. Future work should also include the investigation of thicker sputtered coatings.  
The following are available online at [[https://www.mdpi.com/article/10.3390/separations8120228/s1](https://www.mdpi.com/article/10.3390/separations8120228/s1)]([https://www.mdpi.com/article/10.3390/separations8120228/s1](https://www.mdpi.com/article/10.3390/separations8120228/s1)), Figure S1: SEM images of cross section of sputtered carbon coatings with thicknesses of (a) 0.5 \(\upmu\)m, (b) 2.5 \(\upmu\)m, (c) 11.5 \(\upmu\)m, and (d) 20 \(\upmu\)m. Figure S2: XPS C 1s narrow scan of sputtered carbon coatings with and without PDMS.  
Conceptualization, D.I.P., J.S.H. and M.R.L.; investigation, D.I.P., C.M., T.R. and C.J.; resources, J.S.H. and M.R.L.; data curation, D.I.P., C.M. and J.S.H.; writing--original draft preparation, D.I.P. and J.S.H.; writing--review and editing, J.S.H. and M.R.L.; supervision, M.R.L.; project administration, M.R.L.; funding acquisition, M.R.L. All authors have read and agreed to the published version of the manuscript.  
This article was funded by 'Restek Corp'.  
Not applicable.  
Upon appropriate and timely request, the data used herein will be available.  
We acknowledge [PERSON] from Restek Corporation for his support and valuable conversations on this project.  
Conflicts of InterestSome of the authors and entities on this paper could benefit financially from the commercialization of the fibers described herein.