## 3 Results and Discussion
### Quantification of the Odor-Active Compounds with FD Factors \(\geq\)32 or 50
Four odorants, including ethyl butanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate and octanal, had lower concentrations in six CSSs, and their values were less than 1 ug/L. The odorants quantitated could be grouped into eight categories according to their chemical structures, that is, alcohols, carboxylic acids, esters, aldehydes, ketones, phenols, pyrazines and sulfur-containing compounds. Among these eight categories, the total concentrations of carboxylic acids in all of six CSSs were higher than those of the other seven categories, and the values ranged from 62,711 ug/L to 413,936 ug/L. The value of the total concentrations of all the quantitated odorants in J3 (542,622 ug/L) was the highest, and that in J1 (74,373 ug/L) was the lowest. Of the six CSSs, the total concentrations of ketones (61,452 ug/L) and esters (58.69 ug/L) were the highest in C1; those of alcohols (45,928 ug/L), phenols (4884 ug/L) and pyrazines (582 ug/L) were the highest in C3; and carboxylic acids (413,936 ug/L), sulfur-containing compounds (25,775 ug/L) and aldehydes (25,368 ug/L) had their highest concentrations in J3. C2 contained the lowest concentrations of both sulfur-containing compounds (2029 ug/L) and aldehydes (593 ug/L). In J1, the concentrations of carboxylic acids (62,711 ug/L), alcohols (1694 ug/L), ketones (4638 ug/L), phenols (408 ug/L) and esters (19.05 ug/L) were the lowest among the six samples. The lowest concentration of pyrazines (115 ug/L) was found in J2. These results showed that there were great differences in the concentrations of odor-active compounds among the six samples. \begin{table}
\begin{tabular}{c c c c c}
**No.** & **Compound** & **Quantified Ion** & **Standard Curves** & **R\({}^{2}\)** \\ \hline
3 & 2-methylbutanal & 57 & y = 0.0069x + 1.4039 & 0.999 \\
3 & 3-methylbutanal & 71 & y = 0.0027x + 1.0098 & 0.996 \\
6 & ethyl 2-methylpropanoate & 71 & y = 0.1264x + 0.0185 & 0.998 \\
8 & ethyl butanoate & 71 & y = 0.6002x\(-\)0.0036 & 0.995 \\
10 & ethyl 2-methylbutanoate & 102 & y = 0.7420x\(-\)0.0164 & 0.995 \\
11 & ethyl 3-methylbutanoate & 88 & y = 0.5337x\(-\)0.0065 & 0.994 \\
13 & 3-methylbutanol & 55 & y = 0.0016x\(-\)0.0079 & 0.999 \\
14 & octanal & 84 & y = 0.3571x + 0.0137 & 0.991 \\
19 & dimethyl trusulfide & 126 & y = 1.0809x\(-\)0.1085 & 0.998 \\
22 & 2,3,5-trimethylpyrazine & 122 & y = 0.0449x\(-\)0.6999 & 0.995 \\
23 & acetic acid & 60 & y = 0.0002x\(-\)1.0603 & 0.993 \\
24 & methional & 48 & y = 0.0006x + 0.0061 & 0.997 \\
25 & 2-ethyl-3,5-dimethylpyrazine & 135 & y = 0.2299x\(-\)0.1852 & 0.994 \\
28 & ethyl 2-hydroxy-4-methylpentanoate & 69 & y = 0.0425x\(-\)0.1146 & 0.993 \\
35 & butanoic acid & 60 & y = 0.0017x\(-\)0.6759 & 0.990 \\
36 & benzeneacetaldehyde & 91 & y = 0.0299x\(-\)1.0006 & 0.998 \\
37 & 3-methylbutanoic acid & 73 & y = 0.0034x\(-\)0.8599 & 0.994 \\
38 & 2-furanmethanol & 98 & y = 0.0005x + 0.01316 & 0.994 \\
39 & methionol & 106 & y = 0.0003x + 0.0056 & 0.999 \\
45 & guaiacol & 109 & y = 0.0618x + 0.0339 & 0.999 \\
46 & phenethyl alcohol & 91 & y = 0.0297x\(-\)0.0239 & 0.992 \\
47 & maltol & 126 & y = 0.4418x\(-\)0.4070 & 0.998 \\
48 & 4-ethylguaiacol & 137 & y = 0.4116x + 0.2833 & 0.994 \\
49 & 4-hydroxy-2,5-dimethyl-3(2H)-furanone & 128 & y = 0.1502x + 0.4608 & 0.992 \\
50 & 5-ethyl-4-hydroxy-2-methyl-3(2H)-furanone & 125 & y = 0.0780x + 0.2168 & 0.991 \\
51 & 4-ethylphenol & 107 & y = 0.1818x\(-\)0.0239 & 0.997 \\
52 & 2,6-dimethoxyophenol & 154 & y = 0.0016x\(-\)0.0140 & 0.998 \\
55 & phenylacetic acid & 91 & y = 0.4581x + 1.6573 & 0.998 \\ \end{tabular}
\end{table} 
Table 3: Standard curves of 28 odor-active compounds quantitated in six CSS samples.