The Degraded Sample
A liquid sample in a sealed vial arrives at the lab 11 days after seizure. The submitting agency stored it in a vehicle glovebox in summer heat before delivery. The liquid is slightly cloudy and has a distinct odor. You are asked to quantify the active compound (a substituted amphetamine) by GC-MS. Your calibration curve is valid for the range 0.05–2.0 mg/mL. The sample, diluted 1:10, gives a peak area corresponding to 0.03 mg/mL on the curve - below the lowest calibrator. The chromatogram also shows several small unidentified peaks.
1. What is the analytical problem with reporting 0.03 mg/mL, and what should you do?
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0.03 mg/mL falls below the lowest calibration standard (0.05 mg/mL), so it is outside the validated range; reporting it as a quantitative result extrapolates the curve and is not defensible. Options: (1) re-run undiluted or with a smaller dilution to bring the analyte into range; (2) prepare a lower calibrator and validate linearity at that level; (3) if neither is possible, report the result as 'less than the limit of quantitation' with the LOQ stated, not as a number. Do not report 0.03 as a measured concentration.
2. How does the storage history affect interpretation of the result and the unidentified peaks?
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Heat and delay can degrade the analyte and produce breakdown products, which may explain the cloudiness, odor, and extra peaks. The measured concentration reflects the sample as received, not necessarily as seized. State the storage conditions and elapsed time in the report and qualify the result accordingly. The unidentified peaks should be reported as unidentified, not assigned without data. If degradation is suspected, note that the original concentration may have been higher and that the result is a lower-bound estimate at best.