Journal of Analytical Methods in Chemistry

Research Article

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.