
SMART3 Soil Colorimeter 9.18 9
STATISTICAL & TECHNICAL DEFINITIONS RELATED TO
PRODUCT SPECIFICATIONS
Method Detection Limit (MDL): “The method detection limit (MDL) is defined as the
minimum concentration of a substance that can be measured and reported with 99%
confidence that the analyte concentration is greater than zero and is determined
from analysis of a sample in a given matrix containing the analyte.”1Note 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.3The 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.4For 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.5A 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 defined 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.
1CFR 40, part 136, appendix B
2Statistics in Analytical Chemistry: Part 7 – A Review, D. Coleman and L Vanatta,
American Laboratory, Sept 2003, P. 31.
3Skoog, D.A., West, D. M., Fundamental of Analytical Chemistry, 2nd ed., Holt Rinehart
and Winston, Inc, 1969, p. 26.
4Statistics in Analytical Chemistry: Part 7 – A Review, D. Coleman and L Vanatta,
American Laboratory, Sept 2003, P. 34.
5Jeffery G. H., Basset J., Mendham J., Denney R. C., Vogel’s Textbook of Quantitative
Chemical Analysis, 5th ed., Longman Scientific & Technical, 1989, p. 130.
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