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D3871-84 – Standard Test Method Technical Guide
🔍 Scope and Applicability
ASTM D3871 −84 (Reapproved 2024) specifies a dynamic headspace sampling test method for the determination of purgeable organic compounds in water. It is designed for organic compounds that boil below 200 °C and exhibit a water solubility of less than 2 %. The method targets the low µg/L to low mg/L concentration range, making it suitable for trace contaminant analysis.
Originally developed for the analysis of drinking water, the standard strongly emphasizes the need for validation when applied to environmental or waste waters. Volatile organic compounds in water at concentrations above 1000 µg/L may be determined by direct aqueous injection in accordance with Practice D2908. The user bears full responsibility for verifying the method’s validity for any untested matrix.
⚙️ Test Method and Procedure
The core of the technique relies on an inert purge gas which is bubbled through a liquid sample. This action physically strips volatile organic compounds from the aqueous phase. The effluent gas stream is then directed through a column packed with a suitable sorbent material where the analytes are trapped and concentrated.
Following the purging and trapping cycle, the sorbent column is rapidly heated. The trapped compounds are thermally desorbed and swept directly onto the head of a gas chromatographic column. Separation and measurement are then accomplished using an appropriate detector, allowing for qualitative and quantitative analysis of the purified components.
📊 Key Measured Parameters and Data Range
The following table summarizes the critical technical specifications and conditions outlined in the standard.
| 🟦 Parameter | 📐 Specification | 📏 Details |
|---|---|---|
| Boiling Point | < 200 °C | Ensures sufficient volatility for efficient purging |
| Water Solubility | < 2% | Defines the range of “purgeable” organics |
| Concentration Range | Low µg/L to low mg/L | Standard operating range for this method |
| Upper Method Threshold | > 1000 µg/L | Refer to Practice D2908 (Aqueous Injection GC) |
⚠️ Safety Precaution: This standard does not purport to address all safety concerns. It is the responsibility of the user to establish appropriate safety, health, and environmental practices. Specific precautionary statements related to the apparatus and system operation are located in Section 8.5.5.1 of the full standard.
💡 Quality Control Note: Proper validation is critical when analyzing non-potable water matrices. Users must demonstrate recovery of known concentrations of compounds of interest added to representative sample matrices. Reagent water used for blanks and standards should conform to Specification D1193.
❓ Frequently Asked Questions
🔍 What is the specific concentration range for ASTM D3871?
The test method is designed for the determination of purgeable organic compounds in the low µg/L to low mg/L concentration range. For concentrations above 1000 µg/L, direct aqueous injection per Practice D2908 is recommended.
💡 How does dynamic headspace sampling work in this context?
An inert gas is bubbled through the sample, stripping volatile compounds. These compounds are trapped on a sorbent column and subsequently thermally desorbed onto a gas chromatographic column for separation and analysis.
⚡ What types of compounds are analyzed by this method?
This method is suitable for most purgeable organic compounds, including organohalides, that boil below 200 °C and are less than 2% soluble in water.
📌 Can this method be used directly on wastewater?
Yes, but only with proper validation. The user must demonstrate the method works for the specific matrix by spiking known concentrations of target compounds into representative samples and verifying their recovery.