A Study of the Critical Uncertainty Contributions in the Analysis of PCBs in Ambient Air
Table 3
(a) Table calculating the uncertainty in the mass fraction of PCB in the SRM using (1) and the gravimetric approach (mass fraction domain).
Quantity
Symbol
Value
Sensitivity coefficient
Uncertainty
Probability distribution
Divisor
Contribution to standard uncert
Mass fraction of PCB in the extract (ng⋅g−1)
8.244
2.97
0.857
Normal
1
2.545
Total mass of extract (g)
1.0322
23.7
0.0005
Normal
1
0.010
Bias correction (no units)
0.775
31.6
0
Normal
1
0.000
Extraction efficiency (no units)
0.679
−36.1
0.029
Normal
1
−1.030
Mass of SRM extracted (g)
0.397
−61.6
0.001
Normal
1
−0.031
Mass fraction of PCB in the SRM (ng⋅g−1)
24.475
—
—
Normal
1
2.746
(b) Table calculating the uncertainty in the measured mass fraction of PCB in the extract using (2) and the gravimetric approach (mass fraction domain).
Quantity
Symbol
Value
Sensitivity coefficient
Uncertainty
Probability distribution
Divisor
Contribution to standard uncert
Average injection standard corrected peak area of PCB in the extract (no units)
0.0213
387
0.0021
Normal
1
0.824
Gradient of the calibration curve for the PCB (g⋅ng−1)
0.00258
−3191
0.00007
Normal
1
−0.236
Measured mass fraction of PCB in the extract (ng⋅g−1)
8.244
—
—
Normal
1
0.857
(c) Table calculating the uncertainty in extraction efficiency using (3) and the gravimetric approach (mass fraction domain).
Quantity
Symbol
Value
Sensitivity coefficient
Uncertainty
Probability distribution
Divisor
Contribution to standard uncert
Average, injection standard-corrected, peak area of the internal standard in the extract (no units)
0.298
2.28
0.007
Normal
1
0.017
Mass fraction of the internal standard in a calibration solution (ng⋅g−1)
58.90
0.012
0.45
Normal
1
0.005
Bias correction (no units)
0.775
0.876
0
Normal
1
0.000
Average, injection standard-corrected, peak area of the internal standard in a calibration solution (no units)
0.489
−1.79
0.012
Normal
1
−0.022
Theoretical mass fraction of the internal standard in the extract (assuming complete recovery) (ng⋅g−1)
41.03
−0.021
0.27
Normal
1
−0.006
Extraction efficiency (no units)
0.679
—
—
Normal
1
0.029
(d) Table calculating the uncertainty in the bias correction to account for differences between the densities of the analysed extracts and calibration solutions using (4) and the gravimetric approach (mass fraction domain).
Quantity
Symbol
Value
Sensitivity coefficient
Uncertainty
Probability distribution
Divisor
Contribution to standard uncert
Density of calibration solution (g⋅mL−1)
0.659
1.18
0.001
Normal
1
0.002
Density of extract (g⋅mL−1)
0.850
−0.912
0.070
Rectangular
√3
−0.064
Bias correction (no units)
0.775
—
—
—
—
0*
*As discussed in the main text, the standard uncertainty in has been assigned to be zero.