Even a high-resolution mass spectrometer cannot measure drug that was discarded before injection. During development of a postmortem blood assay, Rosano and colleagues found that a weakly acidic extraction wash lost more than 90% of benzoylecgonine and its labeled internal standard. Changing the wash conditions improved recovery. The observation concerns sample preparation, not disappearance of cocaine exposure from the body.
What method was being developed?
The investigators developed a UPLC–MSE/time-of-flight method for 16 drugs and metabolites and compared it with a nominal-mass UPLC–MS/MS method. The panel included benzoylecgonine, cocaine, cocaethylene, several opioids and other frequently encountered drugs.
Quantitation used analyte-matched deuterated internal standards added before extraction. Blood underwent mixed-mode solid-phase extraction, washing, elution, evaporation and reconstitution before either instrument analyzed the extract. Every one of those stages preceded the mass measurement.
Why was benzoylecgonine vulnerable to the wash?
Benzoylecgonine has both positively and negatively ionizable groups. The authors reported that a wash at approximately pH 4.5 resulted in loss of more than 90% of benzoylecgonine and its deuterated standard during the methanol wash before the intended elution.
Reducing the wash pH to approximately 1.0 increased benzoylecgonine recovery above 90% in the development discussion. That was a specific change within this cartridge and workflow. It is not a universal instruction for every extraction system, matrix or analyte.
The loss of both analyte and labeled standard is particularly instructive. A standard can help account for matched losses, but it does not physically restore the missing material. A favorable ratio alone cannot demonstrate adequate absolute signal, detection performance or recovery. This inference should be checked against the actual method validation rather than assumed from the presence of an internal standard.
Recovery and ion suppression were tested separately
The validation used drug-negative blood from six donors at 100 and 1,000 ng/mL. Comparing samples fortified before extraction with samples fortified after extraction evaluated extraction recovery. Comparing post-extraction fortified material with neat solution evaluated matrix effects on instrument response.
These comparisons answer different questions. A low result can arise because less analyte reached the instrument or because co-extracted material altered ionization. The authors optimized chromatographic conditions separately to reduce suppression, reporting final suppression or enhancement within 20% of the neat response.
The abstract summarizes extraction recovery as above 60%, while the results discussion describes above 70% for the finalized panel and standards and above 90% for benzoylecgonine. These are reported summaries from the paper, not a basis for assigning one exact recovery percentage to every case specimen.
What quantitative performance was demonstrated?
The final method used a 25–3,000 ng/mL calibration range, a 25 ng/mL lower quantitation limit and an administratively selected 10 ng/mL detection threshold evaluated over 12 batches. Precision and bias were assessed with 16 replicate control measurements at 40, 125, 1,600 and 2,500 ng/mL. Both compared methods met the study’s CV below 15% and bias below 20% criteria, despite greater high-resolution variation for some analytes and levels.
Casework comparison involved discarded, de-identified extracts from 159 medical examiner cases. Because both instruments examined prepared extracts, agreement between them could not independently test whether a shared earlier preparation step had lost material. The study’s separate extraction experiments were therefore essential evidence.
The paper does not report one uniform blood collection site, death-to-collection interval or decomposition category for those 159 cases. Its method-development wash experiment was not an in-body stability study.
What records matter when reviewing a negative result?
Determine the analyte, extraction version, matrix, internal-standard response, recovery evidence and reporting threshold. This study demonstrates a preparation vulnerability discovered and addressed during development; it does not prove that any particular laboratory’s negative case result was wrong.
Nor does a benzoylecgonine concentration alone determine when cocaine was used, whether someone was impaired or what caused death. The extraction question complements the separate problem of drug identity when compounds share an exact mass. It also explains why validation using relevant specimens must extend beyond an instrument’s nominal capability.
Primary source
Rosano TG, Na S, Ihenetu K, Swift TA, Wood M. Multi-drug and Metabolite Quantification in Postmortem Blood by Liquid Chromatography–High-Resolution Mass Spectrometry: Comparison with Nominal Mass Technology. Journal of Analytical Toxicology. 2014;38:495–506. doi:10.1093/jat/bku066.
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