Calculations:

Standard Deviation:

(* see first image right*)

Ϭ = The sample standard deviation

N = The number of values in the data set

xi = An individual value of the data set

x-bar = The mean of the values in the

data set

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Method Detection Limit (MDL):

(* see second image right*)

t = “Student’s t value” for the number

of replicates at the 99% confidence level.

(Can be found in a reference table in a statistics textbook, or on the internet. The value changes with the confidence level and the number of replicates used. For this example the student’s t value equals 3.143).

Limit of Quantitation (LOQ):

(* see third image right*)

Using these calculations with the example data set:

Mean value = 21.94 mg

Standard deviation = 1.02 mg

MDL = 3.2 mg

LOQ = 10.2 mg

Since the instrument detects mass, the detection limits are in units of mass. This means that the percent moisture that can be detected is a function of the sample size. In other words the MDL for a 10-gram sample size would be 3.2 mg/10 g = 0.032%. For a 50-g sample size, the MDL would be 3.2 mg/50 g = 0.0064%. The larger the sample size, the lower the percent moisture you will be able to detect.