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D3694-96 – Standard Test Method Technical Guide
ASTM D3694-96 (Reapproved 2024) provides standardized practices for the preparation of sample containers and preservation of organic constituents in water samples. These practices ensure sample integrity from collection to analysis, covering various methods specific to different analytical tests.
🧪 Container Preparation Practices
Proper container preparation is critical to avoid contamination. Containers must be cleaned with appropriate solvents and, in some cases, baked at high temperatures to remove organic residues. The choice of container material, such as glass or fluoropolymer, depends on the target analytes. Glass containers with PTFE-lined caps are commonly used for organic sample collection, and cleaning procedures often include detergent washes, acid rinses, and solvent rinses with organic-free water.
🛡️ Preservation of Organic Constituents
Preservation methods are tailored to the specific analysis, and the standard provides guidance to choose the minimum number of practices for multiple analyses. Common techniques include refrigeration at 4°C, acidification to pH<2 with sulfuric acid, and addition of preservatives. The preservation method for waterborne oils is specifically given in Practice D3325. Section 9 of the standard details preservation practices for various test methods, as summarized in the following table.
| 🧪 Constituent | 🛡️ Preservation Method | 📊 Applicable Test |
|---|---|---|
| Phenolic Compounds | Acidify to pH<2 with H₂SO₄, store at 4°C | D1783 |
| Cyanides | Add NaOH to pH>12, store at 4°C | D2036 |
| Oil and Grease | Acidify to pH<2, store at 4°C | D3921 |
| Volatile Organics | Zero headspace, store at 4°C | D2908, D3871 |
| Total Kjeldahl Nitrogen | Acidify to pH<2 with H₂SO₄, store at 4°C | D3590 |
⚠️ Safety and Quality Assurance
Users must establish appropriate safety, health, and environmental practices as per Section 1.4. Specific hazard statements are noted in sections 6.7, 6.24, and 8.1.3. The standard emphasizes compliance with regulatory limits and adherence to internationally recognized standardization principles. For further considerations, the Manual on Water is referenced.
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