Repeated lyophilization: A neo-method for urine-based reference materials preparation.

Area of Science:

• Forensic Toxicology
• Analytical Chemistry
• Clinical Chemistry

Background:

• Urine drug testing relies on cut-off values to classify samples as positive or negative.
• Reference materials are crucial for standardizing results across laboratories.
• Urine's biological nature presents challenges for its use as a stable reference matrix.

Purpose of the Study:

• To develop improved, stable, and accurate urine matrix reference materials (mRMs) for drug testing.
• To optimize the preparation process using repeated lyophilization.
• To evaluate the stability and storage conditions of the prepared mRMs.

Main Methods:

• Selected target analytes including morphine, nitrazepam, lorazepam, buprenorphine, zolpidem, midazolam, diazepam, and clozapine.
• Optimized sample preparation through repeated lyophilization.
• Investigated optimal urine density (1.010-1.017 kg/m³).

Main Results:

• Repeated lyophilization yielded denser powders, reducing sample collapse and improving quality.
• Lyophilized urine mRMs demonstrated improved stability and accuracy.
• Storage stability: one month at room temperature, six months at 4°C.

Conclusions:

• Repeated lyophilization is an effective method for preparing high-quality urine matrix reference materials.
• Lyophilized urine mRMs offer enhanced stability and accuracy for drug testing.
• These mRMs provide a reliable tool for improving consistency in forensic and clinical toxicology.