Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D4766-21 – Standard Test Method Technical Guide
The ASTM D4766-21 standard, originally approved in 1988 and revised in 2021, specifies a test method for determining vinyl chloride monomer (VCM) in workplace atmospheres using a modified charcoal tube method. It is designed for personal or stationary monitoring with low-flow rate pumps and provides time-weighted average concentrations over a range from approximately 0.03 to 100 ppm (v).
📘 Scope and Summary of Test Method
This test method covers the determination of VCM in workplace air by sampling through activated charcoal tubes, as described in Practice D3686. The method is suitable for low-flow rate sampling and provides time-weighted average results. It cannot be used for instantaneous concentration measurements. The range is from the limit of quantitation (approximately 0.03 ppm (v)) to 100 ppm (v). The method references Terminology D1356 and Practice E355 for definitions. The standard is under the jurisdiction of ASTM Committee D22 on Air Quality.
⚙️ Sampling and Analytical Procedure
The sampling procedure uses glass or metal tubes packed with activated charcoal in two sections: a front section for adsorption and a backup section to capture any breakthrough. Known volumes of air are passed through the tube at low flow rates. After sampling, the charcoal is desorbed with carbon disulfide (CS2). The desorbed solution is analyzed using a gas chromatograph equipped with a flame ionization detector (GC-FID). To ensure accuracy, two or more different chromatographic columns are used to detect interferences. The method is compatible with personal sampling equipment and provides time-weighted average samples.
| 🟦 Component | 📏 Specification |
|---|---|
| Sampling Tube | Glass or metal, with front and backup sections of activated charcoal |
| Flow Rate | Low-flow rate, compatible with personal pumps |
| Desorption Solvent | Carbon disulfide (CS2) |
| Analytical Instrument | Gas chromatograph with flame ionization detector |
📊 Calibration and Performance
Calibration is performed using standard solutions of vinyl chloride in carbon disulfide at known concentrations. Adsorption/desorption efficiencies are determined through standard addition techniques. The method’s performance is validated for the range of 0.03 to 100 ppm (v) as time-weighted averages. The use of multiple columns helps in identifying any interferences. The limit of quantitation is approximately 0.03 ppm (v), and the method provides reliable measurements for workplace exposure monitoring.
| 🎯 Performance Parameter | ⚡ Value |
|---|---|
| Quantitation Range | 0.03 to 100 ppm (v) |
| Sampling Type | Time-weighted average |
| Detection Method | GC-FID with multiple columns |
Technical Tip: For accurate results, ensure that charcoal tubes are stored in airtight containers before and after sampling. Desorption with carbon disulfide should be performed in a well-ventilated area due to its toxicity and flammability.
Safety Alert: Refer to Section 9, 10.2.3, and 11.1.3 of the standard for specific hazards associated with vinyl chloride and carbon disulfide. Always use appropriate personal protective equipment (PPE).
❓ Frequently Asked Questions
🔍 What is the purpose of the backup section in the charcoal tube? The backup section captures any vinyl chloride that breaks through the front section, ensuring complete collection and accurate measurements.
💡 How is vinyl chloride desorbed from the charcoal? It is desorbed using carbon disulfide (CS2), which is a common solvent for organic compounds in charcoal tube methods.
⚡ What concentration range does this method cover? The method covers concentrations from approximately 0.03 ppm (v) to 100 ppm (v) based on time-weighted average sampling.
📌 Why are multiple GC columns recommended? Multiple columns help identify interferences that might co-elute with vinyl chloride, improving the accuracy and reliability of the analysis.