## 2 Results and Discussion
### The Effect of SPME Fiber Coating on Analytical Results
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c} \hline \hline _Aldehyde and ketone_ & & & & & & & & & & & & \\ Benzaldehyde & 100-52-7 & 962/962 [25] & 97 & MS,RLS & 0.73 & 0.26 & 0.47 & ND & 0.31 & ND & ND & ND \\ benzacetaldehyde & 122-78-1 & 1046/1046 [78] & 78 & MS,RLS & 0.17 & 0.10 & ND & ND & ND & ND & ND \\ \(\mathrm{2}\)-Permonate & 107-87-9 & 689/867 [67] & 70 & MS,RRI & 0.31 & 0.23 & 0.13 & ND & ND & ND & ND \\ \(\mathrm{2}\)-Heptonne & 110-43-0 & 891/890 [31] & 83 & MS,RLS & 0.21 & ND & ND & ND & ND & ND & ND \\ \(\mathrm{2}\)-Methyl-2- & 1120-73-6 & 907/914 [39] & 74 & MS,RI & 0.12 & ND & ND & ND & ND & ND & ND \\ cyclopenten-1-one & & Total & & 1.54 & 0.59 & 0.60 & 0 & 0.31 & 0 & 0 & 0 \\ Sal/_dale_ & & & & & & & & & & & \\ Dimethyl disulfide & 624-92-0 & 743/742 [39] & 98 & MS,RLS & 6.52 & 6.10 & 7.98 & 5.32 & 5.20 & 3.99 & 6.92 & 12.36 \\ Dimethyl trisulfide & 3658-80-8 & 971/972 [32] & 94 & MS,RLS & 14.55 & 12.62 & 17.12 & 11.93 & 5.83 & 6.51 & 9.44 & 16.88 \\ Methyl (methylthio) & 42474-44-2 & 1129/1139 [31] & 86 & MS,RI & 0.19 & 0.11 & 0.13 & 0.21 & ND & ND & ND & ND \\ methyl disulfide & 5756-24-1 & 1221/1220 [32] & 93 & MS,RI & 1.53 & 2.83 & 13.16 & 5.03 & 4.10 & 5.84 & 6.69 & 4.16 \\ \(\mathrm{2}\)-Terrythema & & Total & & & 22.79 & 21.66 & 38.39 & 22.49 & 15.13 & 16.34 & 23.05 & 33.40 \\ \(\mathrm{2}\)-Terrythema & 3777-69-3 & 992/992 [32] & 87 & MS,RI & 0.34 & 0.07 & 0.21 & 0.13 & 0.25 & ND & ND & ND \\ \(\mathrm{2}\)-Terrythiophene & 4861-58-9 & 163/1164 [33] & 83 & MS,RI & 0.09 & ND & 0.17 & ND & ND & ND & ND & ND \\ Indide & 120-72-9 & 1304/1303 [34] & 97 & MS,RLS & 36.76 & 31.01 & 38.64 & 37.38 & 64.79 & 45.55 & 19.78 & 21.00 \\ Total & & & & 3.719 & 31.08 & 39.02 & 37.51 & 65.04 & 45.55 & 19.78 & 21.00 \\ \(\mathrm{4}\)\(\mathrm{\check{k}}\)\(\mathrm{\check{e}}\) & & & & & & & & & & & \\ Limenene & 138-86-3 & 1030/1030 [35] & 95 & MS,RI & 0.14 & ND & ND & ND & ND & ND & ND \\ Coquene & 3856-25-5 & 1382/1382 [34] & 96 & MS,RI & 0.31 & 0.35 & ND & ND & ND & ND & ND & ND \\ alphus-Cayophyllene & 6753-98-6 & 1468 & 95 & MS & 0.49 & 0.62 & ND & ND & ND & 1.59 & ND & ND \\ Avoundardone & 101191-91.7 & 1475/1470 [37] & 76 & MS,RI & 0.20 & 0.28 & ND & ND & ND & 0.55 & ND & ND \\ alpha-Pansinssen & 56633-28-4 & 1532 & 94 & MS & 0.29 & 0.44 & ND & ND & ND & 1.16 & ND & ND \\ Total & & & & 1.43 & 1.69 & 0 & 0 & 0 & 3.30 & 0 & 0 \\ \(\mathrm{Others}\) & & & & & & & & & & & & \\ Dimethylamine & 124-40-3 & \(<\)604 & 72 & MS & 0.17 & ND & ND & ND & ND & 0.82 & 0.01 \\ Exalyptol & 470-82-6 & 1033/1033 [38] & 98 & MS,RLS & 0.05 & ND & 0.13 & 0.34 & ND & ND & ND & 0.61 \\  & & Total & & & 0.22 & 0 & 0.13 & 0.34 & 0 & 0 & 0.82 & 0.62 \\  & All total & & & & 92.60 & 89.35 & 96.40 & 98.72 & 95.06 & 84.26 & 88.65 & 97.94 \\ \hline \end{tabular}  
* \({}^{\mathrm{a}}\) RI: retention index, RI*: retention index from literature; \({}^{\mathrm{b}}\) Qual: the similar degree of their mass spectra comparing with those contained in the Nist08 database; \({}^{\mathrm{c}}\) Identification method: MS, compared with Nist 08 Mass Spectral Database; RI, agrees with retention index of literatures; S, agrees with mass spectrum of authentic standards; ND; not detected.  
\end{table} 
Table 2: _Cont._The extract efficiency of Carboxen/PDMS and PDMS/DVB on carboxylic acids is close; the sum of relative peak area of fatty acids in FST2 is larger than that in FST1. However, when PDMS was used, the sum of relative peak area of fatty acids in FST2 is smaller than that in FST1. We think there may be two reasons. One is that PDMS is the best fiber for extracting carboxylic acids; the other is that the value of peak area is relative. When more constituents are identified, the peak area of every constituent is smaller. Among the four fibers, the number of constituents identified in FST1 is the least by using PDMS. The extraction efficiencies of Carboxen/PDMS and DVB/CAR/PDMS on esters and PDMS/DVB and PDMS on esters are close.