High concentration aqueous sodium fluoride certified reference materials for forensic use certified by complexometric...

Area of Science:

• Analytical Chemistry
• Forensic Science
• Metrology

Background:

• Sodium fluoride (NaF) at 1-2% prevents ethanol formation in forensic blood and urine samples.
• South African laboratories must verify NaF concentration (>1 g/100 ml) in blood samples using fluoride ion-selective electrodes.
• Certified NaF reference solutions are essential for accurate calibration and forensic testing.

Purpose of the Study:

• To describe the preparation and certification of sodium fluoride (NaF) reference materials.
• To validate a classical complexometric method for NaF concentration verification.
• To ensure traceability and uncertainty calculations for certified reference materials (CRMs).

Main Methods:

• Preparation of aqueous sodium fluoride solutions (0.3-3.0 g/100 ml).
• Certification via precipitation of fluoride as lead chlorofluoride (PbClF).
• Back-titration of excess lead with ethylenediamine tetraacetic acid (EDTA) using a photometric electrode.

Main Results:

• The study successfully applied a complexometric method for NaF CRM certification.
• Procedures for preparation, concentration verification, homogeneity, and stability were established.
• Traceability and uncertainty were calculated, ensuring CRM quality.

Conclusions:

• The described complexometric method provides a reliable means for certifying sodium fluoride reference materials.
• These CRMs are vital for accurate calibration in forensic ethanol analysis.
• The methodology ensures the quality and reliability of forensic testing in South Africa.