ASTM subcommittee E54.01 has developed a Standard Test Method for the determination of Limit of Detection (LOD) in trace explosive detectors. The Method was developed following ISO-IUPAC guidelines that harmonize concepts of detection limits 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. Although this standard was developed in the context of detecting trace explosives, it should be applicable in many other applications.
The ASTM Standard Method was developed by a task group at NIST led by Michael Verkouteren. The specific statistical method for LOD determination has been published in the following paper: Rukhin, A.L.; Samarov, D.V. (2011), Chemometrics and Intelligent Laboratory Systems, 105, 188-194. This method is based on censored normal distributions.
A unique feature of this standard is that the task group has developed a web-based LOD calculator hosted on a NIST cloud server. The web-based LOD calculator utilizes the NIST Dataplot program to perform the LOD calculations.
This page provides links to a Fortran routine for performing the LOD computations. Although the Fortran code can be used as a stand-alone program, it can also serve as a template for implementing the LOD computations in your own preferred software. In addition, there are links to several test data sets with the corresponding output. Specifically, in the download section below, the following files are available
- dplod2.f90 - Fortran source code for performing the LOD computations
- lod_test.f90 - a test Fortran driver program for dplod2.f90
- std_lod.xlsx - an Excel file containing several sample data sets
- std_ascii.zip - a zip file containing the test data sets in an ASCII file (std_lod.txt), the Dataplot output for these test files (std_lod.out), and the Dataplot macro that generated the sample output (std_lod.dp)