# Passive Sampling and Analysis of Naphthalene
## 5 Conclusions  
The new method for quantification of TWA concentrations of naphthalene in exhaust gases using retracted SPME fibers and GC-MS was developed. The following conclusions can be made about the effects of sampling parameters on the SPME method:  
1. The effects of variability of SPME fibers quality on mass extracted are significant. ANOVA showed no effect on mass extracted by randomly selected PA and DVB fiber coating, while randomly selected PDMS fibers extract significantly different masses of analytes. However, reproducible results with lower than 5% RSD were obtained with PDMS coating, which was chosen as an optimal fiber for further experiments.
2. Losses during sample storage time ranged from \(\sim\)0.2 \(\pm\) 0.07%/min and 0.4 \(\pm\) 0.07%/min sample losses for 23 \({}^{\circ}\)C and 0 \({}^{\circ}\)C, respectively. Storage temperature had no influence on sample recovery from SPME fiber coating. Sample storage in cool temperatures does not appear to have practical benefits.
3. SPME fiber coating was saturated by using a sampling time of longer than 1440 min.
4. Effects of gas concentrations on naphthalene mass extracted with TWA-SPME were linear in the whole studied concentration range (0.1-12 ppm) with R\({}^{2}\) > 0.99. Mean masses extracted by SPME were lower than predicted by theory by 54%. It was likely due to a saturation of SPME fiber when subjected to \(Cg\) = 4 ppm. The mean % difference for (lower range) \(Cg\) < 4 ppm was 49% for naphthalene. The mean % difference for (higher range) \(Cg\) > 4 ppm was 60%.
5. Effects of fiber retraction depth % of naphthalene mass were calculated by dividing mass extracted by \"broken\" fiber to the total mass extracted by SPME assembly (coating + metallic parts). Percent difference between experimental and theoretical mass was 39%. It is recommended using a shorter \(Z\) to minimize the % contribution by metallic parts of SPME fiber.
6. The interfering contribution of extraction by (adsorption to) metallic parts of SPME needle assembly itself was reproducible and ranged from 26% to 43% for shorter sampling time (<540 min) and was virtually constant (16%) for sampling time longer than 540 min.
7. The new method was verified on exhaust gases from idling pickup truck and a tractor and compared side-by-side with a direct injection of sampled exhaust gas method. DI analysis was below method detection limits.
8. The TWA-SPME approach can be considered for adoption to a wide range of measurements involving volatile organic compounds (VOCs) and semivolatile organics, a condition that careful method development focuses on the variability of SPME fibers, fiber coatings, and quantifying the contribution of extraction (adsorption) to SPME metallic parts.  
The following are available online at [[http://www.mdpi.com/2073-4433/8/7/130/s1](http://www.mdpi.com/2073-4433/8/7/130/s1)]([http://www.mdpi.com/2073-4433/8/7/130/s1](http://www.mdpi.com/2073-4433/8/7/130/s1)), Figure S1: Calibration of MS detector for naphthalene, Figure S2: Side-by-side vehicle exhaust gas sampling using (a) passive sampling with retracted SPME fibers in triplicates and (b) dynamic sampling into a Tedlar bag.  
This research has been supported by the grant from the U.S. Civilian Research & Development Foundation (CRDF) Global Program \"2014 Kazakhstan collaborative research travel fellowship\" (award number GISX-14-60330-0) and the grant 4185/GF4 of the Ministry of Education and Science of the Republic of Kazakhstan (2015-2017). Authors would like to thank [PERSON] for technical support.  
[PERSON] and [PERSON] conceived and designed the experiments. [PERSON] performed the experiments and analyzed the data. [PERSON], [PERSON] and [PERSON] wrote the paper. All authors contributed to shaping the content of the paper during the revisions. All authors have read and approved the final manuscript.  
The authors declare no competing financial interests.