## 4 Conclusions  
SPME is a sorbent-based VOC collection technique that has gained widespread popularity across many life science applications due to its ability to focus and enrich the sample using minimal specialized equipment. SPME Arrow offers these same advantages, yet with an increase in sorbent phase volume and alterations to the SPME fiber design that have the ability to increase its mechanical robustness. As such, many life scientists may desire more information about the resulting effects of advancing to an SPME Arrow approach in the future. This study provides foundational data on the sampling dynamics of commercially-available SPME Arrow in biological applications. The CWR/PDMS fiber was found to be a suitable fiber type for the expected range of volatiles. A sampling extraction time was optimized at 5 min (room temperature) with a 3 min inlet desorption time. Carryover of VOCs was not observed using the optimized method. A significant increase in recovery was observed for most analytes using the CWR/PDMS SPME Arrow. For some compounds where a significant increase was not observed (e.g., benzene, naphthalene), recovery was found to be comparable to the traditional SPME fiber and remained above sufficient levels for analysis. The optimized method produced intraday repeatability values of peak area less than 10% and interday repeatability values of peak area less than 15%, indicating sufficient precision for monitoring longitudinal trends in biological applications. Finally, the optimized SPME Arrow method was applied to _B. subtilis_ cultures and monitored over a five-day period. A total of 25 VOCs were identified across three longitudinal trend categories. In the 'produced VOCs' category, compounds were detected higher in abundance in the bacterial samples than in the control samples over time. In the 'consumed VOCs' category, compounds were detected in lower abundance in the bacterial samples than in the control samples over time. In the 'equilibrated VOCs' category, compounds were either higher or lower in the bacterial samples initially, and eventually equilibrated with levels in the control samples. Compounds in the 'produced VOCs' and 'consumed VOCs' categories generally represented compounds that exhibited a significant difference between the two types of samples, while 'equilibrated VOCs' did not. The SPME Arrow method allowed for a sensitive, selective, and repeatable VOC sampling methodology to be used on bacterial samples, which is imperative to future quantitative approaches using SPME Arrow for microbiological VOC monitoring. **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2297-8739/5/3/45/s1](http://www.mdpi.com/2297-8739/5/3/45/s1)]([http://www.mdpi.com/2297-8739/5/3/45/s1](http://www.mdpi.com/2297-8739/5/3/45/s1)), Figure S1: Category 1 compounds ('produced VOCs') detected from the headspace of _B. subtilis_ samples incubated at 24 \({}^{\circ}\)C and monitored over a five day period using the optimized SPME Arrow method, Figure S2: Category2 compounds (\"consumed VOCs\") detected from the headspace of _B. subtilis_ samples incubated at 24 \({}^{\circ}\)C and monitored over a five day period using the optimized SPME Arrow method, Figure S3: Category 3 compounds ('equilibrated VOCs') detected from the headspace of _B. subtilis_ samples incubated at 24 \({}^{\circ}\)C and monitored over a five day period using the optimized SPME Arrow method, Table S1: Tabulated average peak area, standard deviation (s), and % relative standard deviation (% RSD) for intraday and interday repeatability for reference volatile organic compounds using the optimized SPME Arrow method. Conceptualization, K.E.E., D.O.C., and K.A.P. ; Data curation, K.E.E., D.O.C., and K.A.P. ; Formal analysis, K.E.E., D.O.C., and K.A.P. ; Funding acquisition, K.A.P. ; Methodology, D.O.C. ; Project administration, K.A.P. ; Resources, D.O.C. ; Supervision, K.A.P. ; Writing--original draft, K.E.E. and K.A.P. ; Writing--review & editing, K.E.E., D.O.C., and K.A.P.