# Solid-Phase Microextraction Arrow for the Sampling of Volatile Organic Compounds in Milk Samples
## 3 Results and Discussion
### Evaluation of Sensitivity and Reproducibility for SPME Arrow and Conventional SPME Procedures  
In order to compare the sensitivity of the two examined sample preparation techniques, comparison of SPME Arrow and Conventional SPME procedures took place with regard to cumulative VOC areas. For this purpose, five replicate analyses of the same milk sample took place under optimized sample preparation conditions and the average peak areas for 2-heptanone, \(\alpha\)-pinene and dodecane, as well as the total volatiles in milk samples were calculated. It is known that the higher the cumulative area, the higher the fiber sensitivity toward the same number of accumulated analytes [13]. Figure 6 shows the results for sensitivity comparison obtained for the two different methods. As can be observed, higher average peak areas were observed for 2-heptanone, dodecane and total volatiles with the use of CAR/PDMS SPME Arrow fiber, while only for \(\alpha\)-pinene was the average peak area higher with the use of conventional CAR/PDMS SPME fiber. With the use of CAR/PDMS SPME Arrow fibers a 1.4-fold increase in the peak areas for total volatiles was observed, while for 2-heptanone and dodecane the increase was 2.6- and 2.1-fold, respectively. A two-way \(t\)-test assuming unequal variances was employed (\(p<0.05\)) in order to test the significance of the observed differences. It was found in all four cases that the differences were statistically significant. The results were similar to those obtained by [PERSON] et al. [18] that reported an up to 2-fold increase with SPME Arrow fiber in the determination of biogenic volatile organic compounds in the atmosphere compared to conventional SPME fiber. As it can be concluded, higher sensitivity in terms of average peak areas of total VOCs can be achieved when using CAR/PDMS SPME Arrow fibers.  
Figure 6: Sensitivity comparison for Carbon wide range (WR) SPME Arrow/polydimethylsiloxane (CAR/PDMS) SPME Arrow fiber and conventional CAR/PDMS SPME fiber.  
Moreover, in order to compare the reproducibility of the two examined sample preparation techniques, a comparison of SPME Arrow and conventional SPME procedures was conducted on the basis of average relative standard deviation (RSD) values for the peak areas. For this purpose, five replicate analyses of the same milk sample were conducted under optimized sample preparation conditions [13]. Figure 7 shows the results for reproducibility comparison obtained for the two different methods. Subsequently, the RSD values for 2-heptanone, \(\alpha\)-pinene and dodecane, as well as the total volatiles in milk samples were calculated. It was found that the RSD of the total volatiles for conventional SPME procedure was 12.5%, while for SPME Arrow was 6.2%. For 2-heptanone, the RSD of the replicate analysis with conventional SPME procedure was 7.8%, while for SPME Arrow it was 3.3%. For \(\alpha\)-pinene, the RSD of the replicate analysis with a conventional SPME procedure was 10.3%, while for SPME Arrow it was 4.7%. For dodecane, the RSD of the replicate analysis with a conventional SPME procedure was 13.3%, while for SPME Arrow it was 7.5%. It can be concluded that the use of SPME Arrow CAR/PDMS fiber provides more reproducible results compared to the use of conventional CAR/PDMS SPME fibers.