Single injection quantification of cocaine using multiple isotopically labeled internal standards

The purity of street cocaine is an important parameter in drug research and for forensic purposes, as it can be used to group samples, determining their origin, and to assess the monetary value of a drug sample. Current methods require batch processing of samples, as calibration curves need to be run. In this paper, a method is presented for the quantification of cocaine by single injection, avoiding the need for a calibration curve by using multiple, differently isotopically labeled internal standards. Using this fast method, results can be reported immediately after analysis and fully open-access mass spectrometric analysis becomes possible. The method was fully validated, with recoveries compared to certified standards of 99–101 % and to an accredited method from an independent laboratory of 86–117 %. Precision was tested both interday and intraday on three levels and all relative standard deviations were lower than 6.1 %. A linear response was found down to a purity of 1.3 %. The total analysis time for a single sample was approximately 30 min. The method was applied to 106 cocaine samples collected from a large UK music festival. Cocaine purity ranged from 1.3 to 78.8 %, with a mean of 43.1 %. This was comparable to other studies of UK cocaine samples. Our new approach has the potential to be applied to simple quantification of a variety of analytes in biological and non-biological samples.