Published: Journal of Analytical Toxicology, Volume 20, Number 4, July/August 1996, pp. 275-276.

Stability of 11-Nor-D⁹-Tetrahydrocannabinol in Negative Human Urine in High-Density Polyethylene (Nalgene®)
N.J. Giardino

To the Editor:
Unlike many other drugs of abuse, 11-nor-D⁹-tetrahydrocannabinol (THC) and its urinary metabolite, 11-nor-D⁹-tetrahydrocannabinol-9-carboxylic acid (TCHA), are particularly lipophilic and may stick to plastic container walls when in solution in negative human urine. THCA in negative human urine has been shown to be stable in high-density polyethylene for up to two years at a concentration of 15 ng/mL (1). The current study demonstrated the feasibility of storing a THC-urine solution (75 ng/mL) in high-density polyethylene Nalgene container for up to 40 days. This study is significant in that there is a dearth of literature on this topic. THC and several drugs of abuse have been added to negative human urine and stored in 20-L high-density polyethylene carboys for use in positive blind and control preparation (2). This is common practice in high-production drug testing laboratories, even though the stability of THC concentration over time has not been investigated.

This could be a very useful storage method for the Air Force Drug Testing Division (AFDTD). Urinalysis testing for all Air Force members would require 50,000 members per month to be tested for drugs of abuse by the AFDTD. The most frequently detected drug of abuse in the Air Force is marijuana (THC).

A THC concentration of 75 ng/mL was made using 1L of UTAK® liquid urine (75 ng/mL), which is the highest concentration of THC in use at the AFDTD. This prepared single liter of spiked urine was then stored in a 2-L Nalgene container, which is normally used to ship negative urine, at 2–8°C. No special preparatory procedures were done to the commercially obtained negative human urine, such as freezing, then thawing, and then filtering precipitate. Filtering of precipitate is usually done and can be quite time consuming. Sterile technique was used in solution preparation and handling (3).
The use of a 2-L container was convenient for this study because there were no 20-L carboys available. The 2-L container was a rectangle, as were the 20-L carboys. The 2-L container has a surface area to volume ratio that is approximately 1.3 times that of a 20-L carboy. This 30% difference is not anticipated to have an appreciable affect on changes in concentration over time in a 20-L carboy. Also, it is reasonable to assume that the solutions inside the 2-L and 20-L container are well-mixed, resulting in uniform concentration, and that the solution is in constant contact with the interior walls of the container.

Each month, duplicate 5-mL samples were tested in a similar fashion. The container was allowed to warm to room temperature. THC was then measured in urine by an assay, which involves solid-phase extraction and derivatization of the drug from urine. The extract was then analyzed using capillary gas chromatography and electron ionization mass spectrometry. A deuterated analogue of THC, d3-THC, was added to the specimen as an internal standard. Analysis was accomplished using selected ion monitoring (SIM) of three ions for the drug and two ions for the deuterated analogue. Quantitation was based upon the peak-area ratios of the 372 amu THC ion and the corresponding 375 amu d₃-THC ion. The system was calibrated during each analytical run with a 15 ng/mL standard. The Department of Defense defined the cutoff concentration for THC, and blind control samples were also evaluated with each run. If any of these control samples gave unacceptable results, the run was repeated. The system linearity was evaluated by analyzing control samples containing THC at concentrations above and below the cutoff level. System linearity was demonstrated up to 1,000 ng/mL (4).
Table I shows the duplicate measurements taken; time was measured in days.

All results were certified within plus or minus 20% of 75 ng/mL as was required by AFDTD standard operating procedure. A slight downward trend in THC concentration was observed after day 42 (see Table I).

This study illustrates that a solution of THC in negative human urine at approximately 75 ng/mL can be stored in Nalgene containers with minimal decrease in concentration over an extended period. No special preparatory procedures were performed on the commercially obtained negative human urine, such as freezing then thawing and filtering precipitate prior to making up the THC solution, which can be time consuming. Storing THC in 20-L Nalgene carboys could offer obvious advantages for military and private sector laboratories that perform large numbers of specimen urinalysis in terms of convenience by reducing the number of times a standard would need to be prepared. This could also improve the consistency of results.

Nicholas J. Giardino
AL/AOT
2601 West Road
Suite 117
Brooks AFB, Texas 78235-5240

References

1. L. Fuhrman and V.S. Szasz. Long Shelf Life of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic-acid standard (THCA). Report from the U.S. Army Forensic Toxicology Drug Testing Laboratory, Weisbaden, West Germany, February 1990.
2. P. Underwood. Ft. Meade, MD, Personal communication, 1995.
3. D.A. Skoog and D.M. West. Fundamentals of Analytical Chemistry, Saunders and Golden Series, Philadelphia, Pennsylvania, 1976, pp 10-15.
4. R.L. Hawks and C.N. Chiang, Eds. Examples of Drug Assays, Urine Testing for Drugs of Abuse, A Research Monograph (73), Rockville, MD, 1986.

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