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Stability of cocaine in formalin solution and fixed tissues
Guido Viel1, Alessandro Nalesso, Giovanni Cecchetto
1Section of Legal Medicine-Forensic Toxicology and Antidoping Unit, Department of Environmental Medicine and Public Health, Via Falloppio 50, 35121 Padova, Italy.
Forensic Science International
|October 23, 2009
Summary
Formalin fixation can impact cocaine analysis in forensic science. Cocaine rapidly degrades to benzoylecgonine in buffered formalin, complicating drug detection in tissues and solutions.
Area of Science:
- Forensic Toxicology
- Analytical Chemistry
Background:
- Formalin fixation is standard in forensic analysis but can alter drug concentrations.
- Previous research shows xenobiotic extraction and reaction during formalin fixation.
- Cocaine and its metabolite benzoylecgonine (BE) stability in formalin is not fully understood.
Purpose of the Study:
- To investigate the stability and kinetic properties of cocaine during formalin fixation.
- To determine the impact of buffered versus unbuffered formalin on cocaine and BE.
- To assess the extraction kinetics of cocaine and BE from brain and liver tissues.
Main Methods:
- Analysis of cocaine and BE in buffered (pH 7.4) and unbuffered (pH ~3.5) formalin solutions.
- Incubation of tissue samples (brain, liver) in formalin for varying durations.
- Kinetic analysis of cocaine hydrolysis and extraction using pseudo first-order kinetics.
Main Results:
- In buffered formalin (pH 7.4), cocaine rapidly hydrolyzes to BE with a half-life of approximately 7 days.
- Cocaine remains relatively stable in unbuffered formalin (pH ~3.5) for up to 30 days.
- Extraction of both cocaine and BE into formalin occurs, with higher efficiency in liver than brain tissue.
- Significant cocaine hydrolysis to BE in buffered formalin can prevent detection within 15-30 days.
Conclusions:
- Formalin-fixed tissues and solutions can be used for cocaine analysis only shortly after fixation.
- Rapid cocaine extraction and hydrolysis in buffered formalin complicate the identification and quantification of cocaine and BE.
- Unpredictable extraction rates and cocaine hydrolysis significantly affect tissue concentrations, hindering accurate interpretation of results.
