SOFT/TIAFT 98 - Long Term Stability of Abused Drugs and Anti-Abuse ...

SOFT - TIAFT 1998

Poster Session 3

Thursday October 8, 1998

LONG TERM STABILITY OF ABUSED DRUGS AND ANTI-ABUSE CHEMOTHERAPEUTICAL AGENTS STORED AT -20°C

David E. Moody, Kim Monti and Alan C. Spanbauer

Center for Human Toxicology, University of Utah, Salt Lake City, UT 84112, USA

Stability is an important consideration in the use of specimens for accurate determination of analyte concentrations. To determine the long-term stability for analytes routinely analyzed by mass spectrometry in this laboratory, quality control (QC) results were plotted versus time. The time required for the initial concentration to reach a specified level of deviation (i.e. 10%) was then determined from the slopes. QCs were prepared at 3 concentrations in drug-free matrix and stored at approximately -20°C; urines were fortified with 2% sodium fluoride; plasmas (except for those containing cocaine) were prepared with heparin; those used for cocaine and metabolites were fortified with sodium flouride and potassium citrate. Data are summarized below for the low concentration QCs.

Analyte	Maximum Days of Storage	Intercept (ng)(mL)^-1	Slope (ng)(mL)^-1(day)^-1	Days to Reach 10% Deviation
Cocaine (plasma)	765	26.0	0.00428	608
Benzoylecgonine (plasma)	765	26.4	-0.00269	981
Ecgonine Methyl Ester (plasma)	765	26.0	-0.00338	769
Norcocaine (plasma)	765	24.0	0.00229	1048
Ibogaine (plasma)	475	25.7	0.00298	863
Methadone (urine)	384	25.8	-0.00564	457
EDDP (urine)	280	25.6	0.02505	102
EMDP (urine)	280	23.5	-0.00293	802
LAAM (plasma)	650	10.1	0.00053	1906
norLAAM (plasma)	650	10.8	0.00070	1543
dinorLAAM (plasma)	650	10.3	0.00052	1981

Both positive and negative slopes were found. With the exception of EDDP concentrations were within 10% of initial for at least one year, and in many cases, several years.

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