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D4765-13 – Standard Test Method Technical Guide
📋 Scope and Application
This test method, designated ASTM D4765-13 (Reapproved 2018), covers the simultaneous collection and separate measurement of gaseous fluorides (e.g., hydrogen fluoride) and particulate fluorides in industrial workplace atmospheres. It is applicable for industrial hygiene evaluation and control, with a recommended range of 0.005 to 5 mg F⁻/m³ air. The method does not apply to gaseous fluoro compounds such as fluorocarbons or fluorosulfur compounds. All values are in SI units, and users must establish appropriate safety, health, and environmental practices.
🔬 Summary of Test Method
Particulate fluorides from a measured air volume are collected on a membrane filter, while gaseous fluorides are absorbed by an alkali-impregnated cellulose pad placed behind the filter. The collected particulate matter is made alkaline, ashed, and fused to release fluoride, which is then quantified using a fluoride ion-selective electrode. Gaseous fluorides are determined from an aqueous extract of the cellulose pad using the same electrode technique. This approach allows separate measurement of both fluoride forms.
⚠️ Interferences and Quality Assurance
Insoluble or complexed fluorides must be liberated via fusion, pH adjustment, and complexing agents due to the ion-selective electrode’s response to ionic activity. Not all filter materials are suitable; mixed-cellulose ester membrane filters are recommended for particulate sampling, and each filter batch must be quality-checked. The pH and ionic strength of fluoride standard solutions must be matched to samples to ensure accurate electrode readings.
| 🔍 Key Parameter | 📏 Specification |
|---|---|
| Measurement Range | 0.005 to 5 mg F⁻/m³ air |
| Particulate Collection | Mixed-cellulose ester membrane filter |
| Gaseous Collection | Alkali-impregnated cellulose pad |
| Analytical Technique | Fluoride ion-selective electrode |
💡 Technical Note: Prepare standard solutions with the same pH and ionic strength as samples to minimize electrode drift and interference.
⚠️ Quality Check: Verify the quality of each membrane filter batch before sampling, as some filters may introduce contamination or interference.
❓ Frequently Asked Questions
🔍 What is the recommended measurement range for this test method?
The method is suitable for fluoride concentrations from 0.005 to 5 mg F⁻ per cubic meter of air, typical in industrial atmospheres.
💡 How are particulate and gaseous fluorides collected separately?
Particulate fluorides are captured on a membrane filter, while gaseous fluorides pass through and are absorbed by an alkali-impregnated cellulose pad placed behind it.
⚡ What filter materials are recommended?
Mixed-cellulose ester membrane filters are recommended for their low interference and efficient capture of particulate fluorides in workplace air.
📌 What interferences must be addressed during analysis?
Insoluble and complex fluoride forms require fusion and pH adjustment; also, the ionic strength of standards and samples must be matched for accurate electrode response.