Hach DR/850 Procedures Manual page 45

CHEMICAL ANALYSIS INFORMATION
5. Compute the MDL using the appropriate Student's t value (see table
below) and the standard deviation value:
MDL = Student's t x s
For example:
The EDL for measuring iron using the FerroZine method is 0.003 mg/L.
An analyst accurately prepared 1 liter of a 0.010 mg/L (about 3x the EDL)
laboratory standard by diluting a 10-mg/L iron standard in iron-free
deionized water.
Eight portions of the standard were tested according to the FerroZine
method with the following results:
Using a calculator program, the average concentration = 0.010 mg/L and
the standard deviation (s) = 0.0009 mg/L
Based on the USEPA's definition, calculate the MDL as follows:
MDL for FerroZine method = 2.998 (Student's t ) x 0.0009 (s)
MDL = 0.003 mg/L (agrees with initial estimate)
, continued
Number of Test Portions
7
8
9
10
Sample #
1
2
3
4
5
6
7
8
45
Student's t Value
3.143
2.998
2.896
2.821
Result (mg/L)
0.009
0.010
0.009
0.010
0.008
0.011
0.010
0.009