envalysis (version 0.3.3)

calibration: Analytical calibration functions

Description

Defines a calibration object for the calculation of concentrations from measurement signals including estimatations for the limit of detection (LOD) and limit of quantification (LOQ) in accordance with DIN 32645:2008-11.

The LOD is defined as the lowest quantity of a substance that can be distinguished from the absence of that substance (blank value) within a given confidence level (alpha). The LOQ is defined as the lowest quantity of a substance that can be quantified/distinguished from another sample given with respect to a defined confidence level (k).

Usage

calibration(formula, data = NULL, model = "lm", ...)
# S3 method for calibration
print(x, ...)
# S3 method for calibration
plot(x, interval = NULL, level = 0.95, ...)
lod(x, alpha = 0.01, level = 0.05)
loq(x, alpha = 0.01, k = 3, level = 0.05, maxiter = 10)

Arguments

formula

model formula providing the recorded signal intensities with respect to the nominal analyte concentrations in the form of signal ~ concentration or signal ~ concentraion - 1; model formulae are currently restricted to those forms, however, the possibility to use log or sqrt transformed data will be implemented in the future

data

an optional data frame containing the variables in the model

model

model class to be used for fitting; currently, lm and rlm are supported

…

further arguments passed to the sub method, i.e. the respective model environment (e.g. lm), plot, or print

x

an object of class calibration with a model formula as shown above

interval

Type of interval calculation (can be abbreviated); see predict for details

level

tolerance/confidence level; see predict and confint for details

alpha

error tolerance for the detection limit (critical value)

k

relative uncertainty for the limit of quantification (1/beta)

maxiter

a positive integer specifying the maximum number of iterations to calculate the LOQ

Value

calibration returns an object of class "calibration". print calls the function parameters together with the respective LOD and LOQ. plot plots the respective calibration curve together with the measurement values. summary may be used to retrieve the model parameters to be found as a list item called "model".

Details

If the data supplied to calibration contain more than one blank value, i.e. measurements with a nominal concentration of zero, the LOD and LOQ are calculated from the deviation of the blank samples. This method is called "blank method" according to DIN 32645:2008-11 and supposed to be more accurate than the so-called "calibration method" which will be used for the estimation of LOD and LOQ when data does not contain zero concentration measurements.

References

DIN 32645:2008-11, 2008. Chemical analysis - Decision limit, detection limit and determination limit under repeatability conditions - Terms, methods, evaluation (Technical standard). Deutsches Institut f<U+00FC>r Normung, Berlin.

Currie, L.A., 1999. Nomenclature in evaluation of analytical methods including detection and quantification capabilities: (IUPAC Recommendations 1995). Analytica Chimica Acta 391, 105<U+2013>126.

Massart, D.L., Vandeginste, B.G., Buydens, L.M.C., Lewi, P.J., Smeyers-Verbeke, J., 1997. Handbook of chemometrics and qualimetrics: Part A. Elsevier Science Inc.

See Also

icp, din32645

Examples

# NOT RUN {
data(din32645)
din <- calibration(Area ~ Conc, data = din32645)
din
plot(din, interval = "confidence")
summary(din$model)

lod(din)

loq(din)

# }