Journal of Analytical Toxicology, VoL 18, November/December 1994
Stability of Drugs of Abuse in Urine Samples Stored
S. Dugan and S. Bogema
American Medical Laboratories, 14225 Newbrook Drive, Chantilly, VA 22021
George Washington University School of Medicine, Washington, DC 20052
Department of Forensic Sciences, George Washington University, Washington, DC 20052
Isolated studies of the stability of individual drugs of abuse have
been reported. However, few have evaluated stability in frozen
urine samples stored for 12 months. We have determined the
stability of 11-nor-9-carboxy-Ag-tetrahydrocannabinol (9-COOH-
THC), amphetamine, methamphetamine, morphine, codeine,
cocaine, benzoylecgonine, and phencyclidine in 236 physiological
urine samples. Following the initial quantitative analysis, the
samples were stored at -20~ for 12 months and then reanalyzed.
All drug concentrations were determined by gas
chromatographic-mass spectrometric methods with cutoff
concenlrations of 5 ng/mt for 9-COOH-THC and phencyclidine
and 100 ng/mL for each of the other drugs. The average change in
the concentrations of these drugs following this long-term storage
was not exlensive except for an average change of -37% in
The Department of Health and Human Services issued
mandatory guidelines for federal workplace drug-testing pro-
grams in April, 1988 (1). These guidelines require that drug-
testing laboratories shall retain all confirmed drug-positive
urine samples for one year in frozen storage. During this year
of storage, retesting may be requested at any time. As a result
of storage, it is possible that the drug concentrations differ
from the initial results. Although storage studies of drugs have
been reported, generally they are restricted to a few drugs, are
short-term studies, or do not evaluate drug stability in frozen
urine. Therefore, this study was undertaken in order to eval-
uate the stability of drugs of abuse following 12 months of
Materials and Methods
Cocaine hydrochloride, codeine sulfate, d-amphetamine sul-
*Author to whom correspondence should be addressed.
fate, methamphetamine hydrochloride, morphine sulfate
pentahydrate, and phencyclidine hydrochloride were obtained
from The United States Pharmacopeial Convention (Rockville,
MD). Benzoylecgonine tetrahydrate was obtained from ADRI
(Park Forest, IL) and Sigma Chemical Co. (St. Louis, MO). 11-
nor-9-Carboxy-Ag-tetrahydrocannabinol (9-COOH-THC) was
obtained from Research Triangle Institute (Research Triangle
Park, NC). Morphine glucuronide was obtained from Supelco
Benzoylecgonine-d3, cocaine-d3, d-amphetamine-d3, and
methamphetamine-d5 were obtained from Sigma. 9-COOH-
THC-d3 was obtained from Research Triangle Institute. Phen.
cyclidine-d s was obtained from Radian Corp. (Austin, TX).
Codeine-d 3 and morphine-d3 were obtained from MSD Iso-
topes, Merck and Co. (Rahway, NJ).
Standards and solutions
A stock methanolic solution of 9-COOH-THC (100 lJg/mL)
was purchased from Research Triangle Institute. A stock solu-
tion of each of the other drugs (1 mg/mL) was prepared with
HPLC grade methanol and stored at -20~ Methanolic solu-
tions used as calibration standards were prepared at the fol-
lowing concentrations: amphetamine, methamphetamine, co-
caine, benzoylecgonine, codeine, and morphine, 1000 ng/mL;
9-COOH-THC, 80 ng/mL; and phencyclidine, 87 ng/mL.
Urine controls and blanks
DPC CON-DOA drugs-of-abuse urine controls, levels 1 and 3,
were obtained from Diagnostic Products Corp. (Los Angeles,
CA). We prepared blank negative urine control from samples
that had been analyzed and found to be drug free. National In-
stitute of Standards and Technology (NIST) 9-COOH-THC ref-
erence material was obtained from NIST (Gaithersburg, MD).
Cocaine reference material was obtained from the College of
American Pathologists (Chicago, IL), Both positive and nega-
tive quality-control urine samples were analyzed daily.
Chemicals and reagents
4-Carbethoxyhexafluorobutyryl chloride (4-CEHBC) was
purchased from PCR, Inc. (Gainesville, FL). N,O-bis-(Tri-
Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission.
Journal of Analytical Toxicology, Vol. 18, November/December 1994
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Manuscript received April I0, 1992;
revision received March 14, 1994.