Division 7.3.1 Use of the lower band of the 95 % prediction interval at the decision limit of the confirmatory method

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Cut-off value = {BEQ}_{DL} - s_{y,x} \times t_{α,f = m - 2} \sqrt{1 ∕ n + 1 ∕ m + {(x_{i} - \bar{x})}^{2} ∕ Q_{xx}}

with:

BEQ_DL

BEQ corresponding to the decision limit of the confirmatory method, being the ML taking into account the expanded measurement uncertainty

s_y,x

residual standard deviation

t _{α,f = m – 2}

student factor (α = 5 %, f = degrees of freedom, single-sided)

total number of calibration points (index j)

number of repetitions on each level

x_i

sample concentration (in TEQ) of calibration point I determined by a confirmatory method

\bar{x}

mean of the concentrations (in TEQ) of all calibration samples

$Q_{xx} = \sum_{j = 1}^{m} {(x_{i} - \bar{x})}^{2}$ square sum parameter

index for calibration point i