From b31824f420c9d904ab5f46774183a59e3b86cedd Mon Sep 17 00:00:00 2001 From: Johannes Ranke Date: Tue, 4 Oct 2016 08:45:23 +0200 Subject: Static documentation built using newer staticdocs::build_site() --- docs/lod.html | 199 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 199 insertions(+) create mode 100644 docs/lod.html (limited to 'docs/lod.html') diff --git a/docs/lod.html b/docs/lod.html new file mode 100644 index 0000000..e5eb135 --- /dev/null +++ b/docs/lod.html @@ -0,0 +1,199 @@ + + + + +lod. chemCal 0.1-37 + + + + + + + + + + + + + + + +
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+ chemCal 0.1-37 +
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+ + +
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+ +
+ +

Estimate a limit of detection (LOD)

+ +
+
+

Usage

+ 
lod(object, ..., alpha = 0.05, beta = 0.05, method = "default", tol = "default")
+ +

Arguments

+
+
object
+
+ A univariate model object of class lm or + rlm + with model formula y ~ x or y ~ x - 1, + optionally from a weighted regression. +
+
...
+
+ Placeholder for further arguments that might be needed by + future implementations. +
+
alpha
+
+ The error tolerance for the decision limit (critical value). +
+
beta
+
+ The error tolerance beta for the detection limit. +
+
method
+
+ The “default” method uses a prediction interval at the LOD + for the estimation of the LOD, which obviously requires + iteration. This is described for example in Massart, p. 432 ff. + The “din” method uses the prediction interval at + x = 0 as an approximation. +
+
tol
+
+ When the “default” method is used, the default tolerance + for the LOD on the x scale is the value of the smallest non-zero standard + divided by 1000. Can be set to a numeric value to override this. +
+
+ +
+

Value

+ +

+ A list containig the corresponding x and y values of the estimated limit of + detection of a model used for calibration. +

+ +
+ +
+

Description

+ +

The decision limit (German: Nachweisgrenze) is defined as the signal or + analyte concentration that is significantly different from the blank signal + with a first order error alpha (one-sided significance test). + The detection limit, or more precise, the minimum detectable value + (German: Erfassungsgrenze), is then defined as the signal or analyte + concentration where the probability that the signal is not detected although + the analyte is present (type II or false negative error), is beta (also a + one-sided significance test).

+ +
+ +
+

Note

+ +

- The default values for alpha and beta are the ones recommended by IUPAC. + - The estimation of the LOD in terms of the analyte amount/concentration + xD from the LOD in the signal domain SD is done by simply inverting the + calibration function (i.e. assuming a known calibration function). + - The calculation of a LOD from weighted calibration models requires + a weights argument for the internally used predict.lm + function, which is currently not supported in R.

+ +
+ +
+

References

+ +

Massart, L.M, Vandenginste, B.G.M., Buydens, L.M.C., De Jong, S., Lewi, P.J., + Smeyers-Verbeke, J. (1997) Handbook of Chemometrics and Qualimetrics: Part A, + Chapter 13.7.8

+ +

J. Inczedy, T. Lengyel, and A.M. Ure (2002) International Union of Pure and + Applied Chemistry Compendium of Analytical Nomenclature: Definitive Rules. + Web edition.

+ +

Currie, L. A. (1997) Nomenclature in evaluation of analytical methods including + detection and quantification capabilities (IUPAC Recommendations 1995). + Analytica Chimica Acta 391, 105 - 126.

+ +
+ +

Examples

+ 
data(din32645)
+m <- lm(y ~ x, data = din32645)
+lod(m)

+
$x
+[1] 0.08655484
+
+$y
+       1 
+3317.154 
+
+

+

+# The critical value (decision limit, German Nachweisgrenze) can be obtained
+# by using beta = 0.5:
+lod(m, alpha = 0.01, beta = 0.5)

+
$x
+[1] 0.0698127
+
+$y
+       1 
+3155.393 
+
+
+
+
+ + +

See also

+

Examples for din32645

+ + + + +
+
+ + +
+ + \ No newline at end of file -- cgit v1.2.1