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# chemCal - Calibration functions for analytical chemistry
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## Overview
chemCal is an R package providing some basic functions for conveniently
working with linear calibration curves with one explanatory variable.
## Installation
From within [R](https://www.r-project.org/), get the official chemCal
release using
``` r
install.packages("chemCal")
```
## Usage
chemCal works with univariate linear models of class `lm`. Working with
one of the datasets coming with chemCal, we can produce a calibration
plot using the `calplot` function:
### Plotting a calibration
``` r
library(chemCal)
m0 <- lm(y ~ x, data = massart97ex3)
calplot(m0)
```
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### LOD and LOQ
If you use unweighted regression, as in the above example, we can
calculate a Limit Of Detection (LOD) from the calibration data.
``` r
lod(m0)
#> $x
#> [1] 5.407085
#>
#> $y
#> [1] 13.63911
```
This is the minimum detectable value (German: Erfassungsgrenze),
i.e. the value where the probability that the signal is not detected
although the analyte is present is below a specified error tolerance
beta (default is 0.05 following the IUPAC recommendation).
You can also calculate the decision limit (German: Nachweisgrenze), i.e.
the value that is significantly different from the blank signal with an
error tolerance alpha (default is 0.05, again following IUPAC
recommendations) by setting beta to 0.5.
``` r
lod(m0, beta = 0.5)
#> $x
#> [1] 2.720388
#>
#> $y
#> [1] 8.314841
```
Furthermore, you can calculate the Limit Of Quantification (LOQ), being
defined as the value where the relative error of the quantification
given the calibration model reaches a prespecified value (default is
1/3).
``` r
loq(m0)
#> $x
#> [1] 9.627349
#>
#> $y
#> [1] 22.00246
```
### Confidence intervals for measured values
Finally, you can get a confidence interval for the values measured using
the calibration curve, i.e. for the inverse predictions using the
function `inverse.predict`.
``` r
inverse.predict(m0, 90)
#> $Prediction
#> [1] 43.93983
#>
#> $`Standard Error`
#> [1] 1.576985
#>
#> $Confidence
#> [1] 3.230307
#>
#> $`Confidence Limits`
#> [1] 40.70952 47.17014
```
If you have replicate measurements of the same sample, you can also give
a vector of numbers.
``` r
inverse.predict(m0, c(91, 89, 87, 93, 90))
#> $Prediction
#> [1] 43.93983
#>
#> $`Standard Error`
#> [1] 0.796884
#>
#> $Confidence
#> [1] 1.632343
#>
#> $`Confidence Limits`
#> [1] 42.30749 45.57217
```
## Reference
You can use the R help system to view documentation, or you can have a
look at the [online documentation](https://pkgdown.jrwb.de/chemCal/).
