Aerospace Medicine Technical Reports
FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute
Report No: DOT/FAA/AM-07/23
Title and Subtitle: Intensity of the Internal Standard as the Basis for Reporting a Test Specimen as Negative or Inconclusive
Report Date: August 2007
Authors: Ray H. Liu, Chih-Hung Wu, Yi-Jun Chen, Chiung-Dan Chang, Jason G. Linville, Dennis V. Canfield
Abstract: Under normal circumstances, a test specimen is reported as �negative� when the response of the analyte is absent. However, if the intensity of the internal standard (IS) is low, indicating interference factors, the test could be considered �inconclusive.�
A quantitative hypothesis, A = (R�I�S)/L, serves as the �cutoff� for the acceptable signal-to-noise (S/N) ratio for the IS in making �negative/inconclusive� decisions, where A: acceptable S/N ratio for internal standard; R: relative response of the IS and the analyte (same concentration); I: concentration of the IS; S: (minimal S/N ratio); and L: limit of detection. The hypothesis was empirically tested using 9-carboxy-11-nor-Delta9-tetrahydrocannabinol (THC-COOH) analyte, THC-COOH-d3 IS, and ibuprofen and hydrogen peroxide (H2O2) as interference factors.
Urine specimens containing 0�5 ng/mL of THC-COOH were spiked with various quantities of ibuprofen or H2O2, followed by liquid-liquid extraction, derivatization, and GC-MS analysis under selected-ion-monitoring mode. Among the �adulterated� test specimens evaluated, those with a S/N for the internal standard below the acceptable IS S/N �A,� the quantitative criterion was indeed found to provide a useful guide for making negative/inconclusive decisions. This equation could be programmed into the instrument software to flag results as being inconclusive when they do not meet the criteria described in this paper.
Key Words: True Negative, Drug, Equation, Interpretation, Interfernce
No. of Pages: 12
Civil Aerospace Medical Institute
Report No: DOT/FAA/AM-07/23
Title and Subtitle: Intensity of the Internal Standard as the Basis for Reporting a Test Specimen as Negative or Inconclusive
Report Date: August 2007
Authors: Ray H. Liu, Chih-Hung Wu, Yi-Jun Chen, Chiung-Dan Chang, Jason G. Linville, Dennis V. Canfield
Abstract: Under normal circumstances, a test specimen is reported as �negative� when the response of the analyte is absent. However, if the intensity of the internal standard (IS) is low, indicating interference factors, the test could be considered �inconclusive.�
A quantitative hypothesis, A = (R�I�S)/L, serves as the �cutoff� for the acceptable signal-to-noise (S/N) ratio for the IS in making �negative/inconclusive� decisions, where A: acceptable S/N ratio for internal standard; R: relative response of the IS and the analyte (same concentration); I: concentration of the IS; S: (minimal S/N ratio); and L: limit of detection. The hypothesis was empirically tested using 9-carboxy-11-nor-Delta9-tetrahydrocannabinol (THC-COOH) analyte, THC-COOH-d3 IS, and ibuprofen and hydrogen peroxide (H2O2) as interference factors.
Urine specimens containing 0�5 ng/mL of THC-COOH were spiked with various quantities of ibuprofen or H2O2, followed by liquid-liquid extraction, derivatization, and GC-MS analysis under selected-ion-monitoring mode. Among the �adulterated� test specimens evaluated, those with a S/N for the internal standard below the acceptable IS S/N �A,� the quantitative criterion was indeed found to provide a useful guide for making negative/inconclusive decisions. This equation could be programmed into the instrument software to flag results as being inconclusive when they do not meet the criteria described in this paper.
Key Words: True Negative, Drug, Equation, Interpretation, Interfernce
No. of Pages: 12
Last updated: Friday, June 1, 2012