8 February / March 2016
Figure 7: Result of the breakthrough experiment, showing no significant residue was in the 2nd thermal desorption rube
solvent. This demonstrates that non-detectable breakthrough of the residue occurred even for hexane, the most volatile component.
Quantitative Results
There are no certified reference materials (CRM) for the quantitation of hydrocarbon residue (C6
plus) in LPG; therefore, a Quality
Control (QC) sample was prepared in LPG and quantitated from the calibration curve
Analyte LPG
Sample Weight (g)
0.4088 0.4140 0.4317 0.4269 0.4274 0.4143
Std Dev 0.0093 Average 0.4205 % RSD 2.21
LPG
Sample Weight (g)
0.4088 0.4140 0.4317 0.4269 0.4274 0.4143
Std Dev 0.0093 Average 0.4205 % RSD 2.21
Calculated Amount (µg/g)
2.00 2.06 1.93 2.00 1.98 2.00
0.0418 1.9950 2.10
Toluene
Calculated Amount (µg/g)
1.8 1.8 1.7 1.7 1.7 1.8
0.0548 1.7500 3.13
Actual Amount (µg/g)
1.8 1.8 1.8 1.8 1.8 1.8
% Dev
0.0 0.0
-5.6 -5.6 -5.6 0.0
Hexane
Actual Amount (µg/g)
1.8 1.8 1.8 1.8 1.8 1.8
% Dev
Calculated Amount (µg/g)
11.1 14.4 7.2
11.1 10.0 11.1
1.6 1.6 1.5 1.5 1.5 1.5
0.0516 1.5333 3.37
Diesel and Compressor Oil
Calculated Amount (µg/g)
114 113 102 107 104 108
4.7749 108 4.4
Table 4: Quantitative data for six separate tube injections of a QC sample made in LPG
Actual Amount (µg/g)
132 132 132 132 132 132
% Dev
-14 -14 -23 -19 -21 -18
created in pentane. To demonstrate the accuracy and precision of this new gas chromatography method and sampling technique, six separate injections of the QC standard were made onto six tubes, and the masses recorded. The results in µg/g in the LPG are shown in Table 4. The accuracy (% deviation) is demonstrated by the difference between the actual and the calculated result, while the repeatability of the injection technique and method is
Iso-Octane
Actual Amount (µg/g)
1.6 1.6 1.6 1.6 1.6 1.6
% Dev
Calculated Amount (µg/g)
0 0
-6.25 -6.25 -6.25 -6.25
1.7 1.7 1.6 1.7 1.7 1.7
0.0408 1.6833 2.43
shown by the average of the six results and the standard deviation. Based on this data set, it can be seen that the recoveries are all very acceptable, while the detection limit for total residues in LPG is on the order of 10 µg/g. However, it was observed that there was a slight loss in targets above C34
(diesel
and compressor oil) for the results using LPG as the solvent, which can be explained by pentane having greater solvation capability for these high boiling point components
Heptane
Actual Amount (µg/g)
1.7 1.7 1.7 1.7 1.7 1.7
% Dev
0.00 0.00
-5.88 0.00 0.00 0.00
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