Result and Discussion:

In SPME process, there are some factors that

need to be considered such as the thickness of

fibre, agitation method and the conditioning of

fibre. Longer extraction time needed with the

use of thicker fibre but it provide better

recoveries. The extraction time and the relative

number of analytes extracted are independent of

the concentration of the analytes (Vas and

Vékey, 2004). The extraction time can be

reduced with use of proper agitation method

such as stirring, ultrasonics and heating. With

the use of proper agitation, the extraction time

depends on the geometry of the fibre and the co-

efficiency of the analyte diffusion in the fibre.

Before the extraction proceeded, the PDMS

fibre needs to be conditioned in a GC injection

port. In this experiment, the PDMS fibre was

conditioned at 250˚C for 10 minutes (Dr.

Nor'ashikin et al, 2012). This step is necessary

as it can remove any contaminants at the fibre.

The chromatograms obtained from the

experiments concerning the influence of type of

accelerant are shown in Figures 2 – 4.

Figure 1: GC-MS chromatogram of blank cotton cloth sample.

Figure 2: (Top) Chromatogram of a petrol standard. (Bottom) Chromatogram of a petrol fire debris sample

Figure 3: (Top) Chromatogram of a diesel standard. (Bottom) Chromatogram of a diesel fire debris sample

Figure 4: (Top) Chromatogram of a kerosene standard. (Bottom) Chromatogram of a kerosene fire debris sample

SPME extracts of the simulated fire debris samples produced acceptable and identifiable

chromatograms. However, it is difficult to characterize petrol and kerosene in fire debris based

on the chromatogram only because the chromatogram obtained was not identical to the standards

and too complex. The complexity of the chromatogram in Figure 2 indicates that petrol is

composed of a wide range of different compounds. Petrol was seen to be composed of aliphatic

and aromatic hydrocarbons. The chromatograms obtained for diesel standard remain

recognizable, but differ slightly for fire debris samples.

For each accelerant, five major volatile compounds with high quality were selected based

on the library search of mass spectrometry. The different volatile organic profiles characterized

the accelerants are presented in Table 1 – 7.

Table 1: Volatile profile of blank by SPME-GC-MS

Retention time (tR)

Volatile Compounds

Area (%)

Quality (%)

9.474 Benzoic acid 6.55 90

9.726 Naphthalene 5.83 93

12.449 Biphenyl 6.24 93

14.064Phenol, 2,4-bis (1,1-dimethylethyl)

13.34 97

17.290 Phenanthrene 3.93 96

Unsoaked cotton cloth was set as a blank in this analysis to ensure that materials other than the

material being analysed do not contribute to the identification. Table 1 simplify the five major

compounds found in blank fire debris.

Table 2: Volatile profile of standard petrol by SPME-GC-MS

Retention time (tR)

Volatile Compounds

Area (%)

Quality (%)

4.109Benzene, 1,3-dimethyl

1.06 97

5.952Benzene, 1-ethyl-2-methyl

0.71 95

6.189Benzene, 1,3,5-trimethyl

4.73 94

12.650Naphthalene, 2,6-dimethyl

1.81 97

16.5831,4,5,8-Tetramethyl

naphthalene0.67 93

Table 3: Volatile profile of fire debris sample soaked in petrol by SPME-GCMS

Retention time (tR)

Volatile Compounds

Area (%)

Quality (%)

4.835Benzene, 1,3-dimethyl

0.75 97

6.214Benzene, 1-ethyl-2-methyl

2.95 94

6.500Benzene, 1,3,5-trimethyl

0.70 91

12.794Naphthalene, 2,6-dimethyl

0.63 97

16.0211,4,5,8-Tetramethyl

naphthalene0.13 97

In the chromatograms of petrol fire debris, signals of alkyl derivate of benzene were

observed to have high peak area. This is similar to the standard petrol as shown in Table 2. The

volatile compounds found in standard petrol have large area compared to one in fire debris. It

can be said that some of the compound has been used up for combustion.

Table 4: Volatile profile of standard diesel by SPME-GCMS

Retention time (tR)

Volatile Compounds

Area (%)

Quality (%)

6.210Benzene, 1,2,2-trimethyl

0.56 90

7.889 Undecane 2.40 95

12.214 Tetradecane 4.72 94

13.510 Pentadecane 3.52 96

14.988 Hexadecane 1.13 94

Table 5: Volatile profile of fire debris sample soaked in diesel by SPME-GCMS

Retention time (tR)

Volatile Compounds

Area (%)

Quality (%)

6.722Benzene, 1,2,2-trimethyl

0.18 95

8.370 Undecane 1.11 93

12.667 Tetradecane 4.88 89

13.926 Pentadecane 3.22 94

15.093 Hexadecane 2.30 94

Major volatile compound found in diesel fire debris are alkanes such as Undecane,

Tetradecane, Pentadecane and Hexadecane as listed in Table 4. Examination of fire debris

revealed the presence of residual diesel in different relative amounts and retention time as

compared to the standard diesel oil.

Table 6: Volatile profile of standard kerosene by SPME-GCMS

Retention time (tR)

Volatile Compounds

Area (%)

Quality (%)

4.038 o-Xylene 3.20 95

4.412Benzene, 1,3-dimethyl

1.31 97

6.100Benzene, 1,2,4-trimetyl

2.67 90

6.182 Decane 3.38 78

7.332Benzene, 1,2,4-trimetyl

1.81 91

Table 7: Volatile profile of fire debris sample soaked in kerosene by SPME-GCMS

Retention time (tR)

Volatile Compounds Area (%) Quality (%)

4.735 o-Xylene 0.49 89

5.089 Benzene, 1,3-dimethyl 0.19 68

6.892 Benzene, 1,2,4-trimetyl 4.66 43

6.892 Decane 4.66 55

12.574Decahydro-4,4,8,9,10-pentamethyl

naphthalene1.07 97

For kerosene, differences in quantitative ratios of alkyl derivates of benzene can be observed.

This can be explained by the influence of fire conditions or, more probably, by changes in

kerosene composition. Still, the characteristic pattern of alkyl derivates benzene, considered

being kerosene’s ‘fingerprint’, thats enabling identification.