High-Accuracy Determination of Potassium and Selenium in Human Serum by Two-Step Isotope Dilution ICPMS

Table 5

Sources of uncertainty in the determination of K.

Sources of uncertainty	K
	Level 1		Level 2		Level 3
	Value (xi)	uc (xi)	Value (xi)	uc (xi)	Value (xi)	uc (xi)
Type A uncertainties
RY	0.041	0.00017	0.041	0.00017	0.041	0.00017
Rz	11	0.063	11	0.063	11	0.063
RBc	0.97	0.0014	1.0	0.0015	1.1	0.0018
RB	0.93	0.0013	1.0	0.0015	0.91	0.0014
CB/mg kg^−1	0.14	0.16	0.16	0.16	0.21	0.16
K	—	—	—	—	—	—
Type B uncertainties
Cz/mg kg^−1	46	0.10	46	0.10	46	0.10
mzc/mg	3.3 × 10^3	0.040	3.3 × 10^3	0.040	3.3 × 10^3	0.040
mYc/mg	3.4 × 10^3	0.040	3.4 × 10^3	0.040	3.4 × 10^3	0.040
mY/mg	3.4 × 10^3	0.040	3.4 × 10^3	0.040	3.4 × 10^3	0.040
mx/mg	2.1 × 10^3	0.040	1.1 × 10^3	0.040	8.0 × 10^2	0.040
Combined type A and type B	—	0.22	—	0.34	—	0.37
Degrees of freedom (Veff)		11		11		11
Coverage factor (k)	—	2	—	2	—	2
Measured value/mg kg^−1	136.8	—	178.0	—	252.3	—
Expanded uncertainty (U ())	—	0.14	—	0.21	—	0.23