In: Chemistry
A plot of detector signal versus ppm Ca2+ yielded a best fit straight line with a slope of 0.13 volts/ppm. Multiple blank measurements resulted in a standard deviation of 0.18 volts. Using a 2:1 signal-to-noise ratio criteria, calculate the detection limit for Ca2+ in ppm when this method is employed.
LOD (limit of detection)
The detection limit of an individual analytical procedure is the
lowest amount of analyte in a sample which can be detected but not
necessarily quantitated as an exact value. Several approaches for
determining the detection limit are possible.
Based on visual evaluation: The detection limit is determined by
the analysis of samples with known concentrations of analyte and by
establishing the minimum level at which the analyte can be reliably
detected.
Based on Signal-to-Noise Approach: Determination of the
signal-to-noise ratio is performed by comparing measured signals
from samples with known low concentrations of analyte with those of
blank samples and by establishing the minimum concentration at
which the analyte can be reliably detected. A signal-to-noise ratio
between 3 or 2:1 is generally considered acceptable for estimating
the detection limit.
Based on the Standard Deviation of the Response and the Slope:
The detection limit (DL) may be expressed as:=3X STANDRD DEVIATION OF LOW CONCEN/ SLOPE OF THE CALIBRATION LINE
The detection limit = 3*0.18volts/0.13volts/ppm =4.154 ppm