Research Article
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 × 103 | 0.040 | 3.3 × 103 | 0.040 | 3.3 × 103 | 0.040 | | mYc/mg | 3.4 × 103 | 0.040 | 3.4 × 103 | 0.040 | 3.4 × 103 | 0.040 | | mY/mg | 3.4 × 103 | 0.040 | 3.4 × 103 | 0.040 | 3.4 × 103 | 0.040 | | mx/mg | 2.1 × 103 | 0.040 | 1.1 × 103 | 0.040 | 8.0 × 102 | 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 |
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