ASTM E2677 Limit of Detection Web Portal
Supporting Information
ASTM subcommittee E54.01 has developed a Standard Test Method for the
determination of Limit of Detection (LOD) in trace detectors, particularly
those designed for the detection of explosives and drugs of interest. The
Method was developed following ISO-IUPAC guidelines that harmonize concepts
of detection limits1 and considers the observed behaviors of
response signals in a wide range of trace detectors. Here, the
LOD90 is defined as the lowest amount of a particular substance for
which there is 90% confidence that a single measurement will have a true
detection probability of at least 90% while the true non-detection
probability of a realistic process blank is at least 90%. The LOD90
value is therefore a directly useful metric of trace detector performance
and reliability, since the value reflects the practical detection
capability of the detector system, influenced by the inherent sensitivity,
selectivity, and response variability of the system under realistic
deployment conditions.
The ASTM Standard Method was developed by a task group at NIST. The
specific statistical method for LOD determination has been
published2. In order to facilitate the calculations involved for
users of the Method, the task group has developed a web-based LOD
calculator hosted on a NIST cloud server. The LOD application utilizes
the NIST Dataplot program3 and was coded into HTML by Alan
Heckert and Keith Kwiatek.
To obtain the LOD90 value, a value of 0.10 is entered for the
confidence limit in the web form. Although 0.10 is the default, other
confidence limits may be requested. A LOD95 value may be
determined by entering a value of 0.05 for the confidence limit.
Typical values for the confidence are 0.10, 0.05, and 0.01 corresponding
to LOD90, LOD95 and LOD99, respectively. For
convenience, the documentation will simply refer to LOD90.
The web-based calculator has been developed to provide the best estimate
of the LOD90 value for a particular analyte given the quality
of the inputted data. Ideally, data should include at least ten
process blank replicates as well as detector responses from at least ten
replicates from two mass levels closely straddling the actual
LOD90 mass level. By this strategy, the Method is insensitive to
many pitfalls that are encountered in commercial trace detectors, including
detector response saturation, truncated response distributions, and
response heteroskedasticity, i.e. changes in response variation with
signal level. Practicalities dictate, however, that a limited number of
replicates be analyzed and that mass levels be selected that are wide
enough apart to guarantee the straddling of the unknown LOD90
value. By setting the minimum number of required replicates to ten, and
by utilizing a short sequence of mass levels that increase by a factor of
three, data for the calculation of an adequate LOD90 estimate may
be obtained. The web-based calculator has been tested and validated with
real and simulated data possessing several types of error structure.
To see a description of the minimum data requirements for the LOD
calculator, please see the LOD data input
page.
For questions regarding the ASTM Standard Method, please contact [email protected].
References
- Currie, L.A. (1999) Analytica Chimica Acta 391, 103-134.
- Rukhin, A.L.; Samarov, D.V. (2011) Chemometrics and Intelligent
Laboratory Systems 105, 188-194.
- Filliben, J.J.; Heckert, N.A.
https://www.itl.nist.gov/div898/software/dataplot/