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D3697-17 – Standard Test Method Technical Guide
📐 Scope and Applicability
ASTM D3697-17 specifies a test method for determining dissolved and total recoverable antimony in water by atomic absorption spectroscopy. The validated concentration range is 1 to 15 µg/L, extendable by sample dilution or reduced scale expansion.
Precision and bias data were generated from tests on reagent water, tap water, salt water, and two untreated wastewaters. Caution is necessary when applying these statements to other water matrices without verification.
💡 Technical Tip: The detection limit and working range can be adjusted using sample dilution or less scale expansion. Users must verify performance for specific sample matrices. Practice D2777 provides the standard protocol for determining precision and bias.
⚙️ Test Method Principle and Procedure
This procedure uses chemical digestion and hydride generation atomic absorption spectrophotometry. Organic antimony compounds are decomposed by digesting with sulfuric and nitric acids to sulfur trioxide fumes. The antimony is then reduced sequentially with potassium iodide and stannous chloride, followed by sodium borohydride to generate stibine (SbH₃) gas. The stibine is purged from the solution by a nitrogen flow and swept into a hydrogen flame for atomic absorption measurement at 217.6 nm.
⚠️ Safety Warning: Stibine gas (SbH₃) is highly toxic. Concentrated acids are used during digestion. All steps involving hydride generation and acid handling must be conducted in a properly functioning fume hood. Always follow laboratory safety protocols.
📊 Key Terminology and Quality Control
The standard defines several critical quality control terms. The continuing calibration blank checks for baseline drift and carryover. The continuing calibration verification standard assesses instrument drift across the calibration curve. The laboratory control sample containing a certified antimony concentration validates the accuracy of the digestion and analysis. The term total recoverable antimony is defined as the concentration determinable by this specific digestion procedure, noting that some organic antimony compounds may not be fully recovered.
| 🟦 Parameter | 📐 Specification / Value |
|---|---|
| Analytical Wavelength | 217.6 nm |
| Validated Range | 1 – 15 µg/L |
| Hydride Generation | NaBH₄ reduction to Stibine (SbH₃) |
| Carrier / Purge Gas | Nitrogen (N₂) |
| Sample Digestion | H₂SO₄ / HNO₃ to SO₃ fumes |
| 🎯 QC Element | ⚡ Requirement |
|---|---|
| Continuing Calibration Blank | Verifies blank response and freedom from carryover |
| Continuing Calibration Verification | Known concentration covering the calibration curve range; verifies drift is minimal |
| Laboratory Control Sample | Certified antimony concentration solution for accuracy assessment |
❓ Frequently Asked Questions
🔍 What is the analytical range for antimony in ASTM D3697-17?
The method is applicable for antimony concentrations from 1 to 15 µg/L. This range can be extended by using less scale expansion on the instrument or by diluting the sample.
💡 On what water matrices was the precision and bias established?
The precision and bias data were obtained using reagent water, tap water, salt water, and two untreated wastewaters. Users should verify performance for other water types.
⚡ What detection technique is used for antimony in this method?
Antimony is measured by atomic absorption spectrophotometry at 217.6 nm. The element is first converted to stibine gas (SbH₃) using sodium borohydride, which is then swept into a hydrogen flame.
📌 What does “total recoverable antimony” encompass in this standard?
It represents the antimony species that are determinable by the method’s specific digestion procedure. Some organic antimony compounds may not be completely recovered and are excluded from this definition.