LaMotte SMART3 Colorimeter - Manual (Page 8)

 STATISTICAL & TECHNICAL DEFINITIONS RELATED TO
PRODUCT SPECIFICATIONS
Method Detection Limit (MDL): “The method detection limit (MDL) is defi ned
as the minimum concentration of a substance that can be measured and
reported with 99% confi dence that the analyte concentration is greater than
zero and is determined from analysis of a sample in a given matrix containing
the analyte.” 1 Note that, “As Dr. William Horwitz once stated, ‘In almost all cases
when dealing with a limit of detection or limit of determination, the primary
purpose of determining that limit is to stay away from it.’” 2
Accuracy: Accuracy is the nearness of a measurement to the accepted or true
value. 3 The accuracy can be expressed as a range, about the true value, in
which a measurement occurs (i.e. ±0.5 ppm). It can also be expressed as the
% recovery of a known amount of analyte in a determination of the analyte (i.e.
103.5 %).
Resolution: Resolution is the smallest discernible difference between any
two measurements that can be made. 4 For meters this is usually how many
decimal places are displayed. (i.e. 0.01). Note that the resolution many change
with concentration or range. In some cases the resolution may be less than the
smallest interval, if it is possible to make a reading that falls between calibration
marks. A word of caution, that resolution has very little relationship to accuracy
or precision. The resolution will always be less than the accuracy or precision
but it is not a statistical measure of how well a method of analysis works. The
resolution can be very, very good and the accuracy and precision can be very
bad! This is not a useful measure of the performance of a test method.
Repeatability: Repeatability is the within-run precision.
5 A run is a single data
set, from set up to clean up. Generally, one run occurs on one day. However,
for meter calibrations, a single calibration is considered a single run or data set,
even though it may take 2 or 3 days.
Reproducibility: Reproducibility is the between-run precision.
6
Detection Limit (DL): The detection limit (DL) for the 2020we/wi
is defi ned as the minimum value or concentration that can be determined by the
meter, which is greater than zero, independent of matrix, glassware, and other
sample handling sources of error. It is the detection limit for the optical system of
the meter.
1 CFR 40, part 136, appendix B
2 Statistics in Analytical Chemistry: Part 7 – A Review, D. Coleman and L Vanatta,
American Laboratory, Sept 2003, P. 31.
3 Skoog, D.A., West, D. M., Fundamental of Analytical Chemistry, 2 nd ed., Holt
Rinehart and Winston, Inc, 1969, p. 26.
4 Statistics in Analytical Chemistry: Part 7 – A Review, D. Coleman and L Vanatta,
American Laboratory, Sept 2003, P. 34.
6 SMART3 Colorimeter 11.10