Chasin A.A.M.^*, Midio A.F.^**

^*Medical Legal Institute of Sao Paulo, Brazil
^**Department of Toxicology - University of Sao Paulo - FCF-USP cx postal 66355 - cep 05389-920, Sao Paulo, Brazil

The coingestion of cocaine (COC) and ethanol is a very frequent occurrence and is known to increase the risk of morbidity and mortality. Along with this interaction, there is a formation of a transesterification product, the cocaethylene (CE), which is even more lethal than cocaine having lower levels of LD₅₀. In order to study the role of ethanol in lethal intoxication and to establish its influence in post mortem cocaine concentrations, an ion-trap chromatographic-mass spectrometric method (GC/MS) was developed to simultaneously quantify this agent and its biotransformation products: benzoylecgonine (BE), ecgonine methyl ester (EME) and the "biomarker" of this interaction, the CE in the whole blood.
Deuterated internal standards were added to 2 mL of postmortem whole blood. Extraction was performed with Bond Elut Certify columns and the residues were evaporated and derivatized with MTBSTFA (N-methyl-N-t-butildimethylsilil trifluoroacetamide). The extracts were analyzed with a Varian Saturn 3 mass spectrometer linked to a Varian Model 3400 gas chromatograph, equipped with dimethylsilicone capillary column (DB5) using a temperature program. Detection was performed by electron impact. The monitored ions were m/z 82/85 for EME-TBDMS/D₃EME-TBDMS; 182/185 for COC/D₃COC; 196/199 for CE/D₃CE and 282/285 for BE-TBDMS/D₃BE-TBDMS. The limits of detection and quantification were found to be 25 and 50 ng mL^-1, respectively for COC and CE and 50 and 100 ng mL^-1 for BE and EME. The accuracy was different for each of the compounds, varying from 65 to 98%. The dynamic range of the assay was 50 to 3500 ng mL^-1. This method of analysis was useful intending for cocaine abuse and in overdose cases.