Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D1105-21 – Standard Test Method Technical Guide
The ASTM D1105-21 standard establishes a definitive method for removing extractives from wood samples prior to chemical analysis. This ensures that subsequent tests accurately reflect the structural polymer components (cellulose, hemicellulose, and lignin) of the wood rather than its soluble extraneous materials.
📜 Scope and Significance
According to D1105-21, extractives are materials soluble in neutral solvents that are not part of the wood polymer structure. These include waxes, fats, resins, gums, tannins, sugars, starches, and coloring matter. The test method covers the preparation of extractive-free wood and is specifically applicable to all North American woods. Removing these components is a critical prerequisite for any accurate chemical analysis of the wood’s structural components.
🧪 Apparatus, Reagents, and Sample Preparation
The standard specifies a glass Soxhlet extraction apparatus. Fritted-glass filters, cellulose, or Alundum extraction thimbles of medium to coarse porosity are recommended. The sample must consist of air-dry sawdust passed through a Wiley mill. The required particle size must pass through a 250-μm (No. 60 mesh) sieve and be retained on a 180-μm (No. 80 mesh) sieve.
Two primary solvents are required: 95% ethanol, and an ethanol-toluene mixture prepared by combining exactly 1.0 L of absolute ethanol with 427 mL of toluene.
⚠️ Critical Safety Precaution: The ethanol-toluene mixture presents significant health hazards. The standard explicitly warns: “Avoid inhalation of vapors and contact with skin.” Perform all extraction steps in a well-ventilated fume hood.
| 📏 Parameter | 📐 Specification |
|---|---|
| 🟦 Sample Particle Size | Pass No. 60 (250 µm), Retain No. 80 (180 µm) |
| 🧪 Solvent 1 Mixture | 1.0 L Ethanol + 427 mL Toluene |
| ⏱️ Minimum Siphoning Rate | 4 siphonings per hour |
| ⏱️ Solvent 1 Extraction Time | 4 hours |
| ⏱️ Solvent 2 Extraction Time | 4 hours (minimum, or until colorless) |
| 🎯 Sample State | Air-dry |
🔄 Step-by-Step Extraction Procedure
The procedure involves a sequential two-step solvent extraction to ensure complete removal of all classes of extractives. The extraction rate must be carefully maintained.
- Ethanol-Toluene Extraction: Place the prepared sample in the extraction thimble, ensuring it does not extend above the level of the top of the siphon tube. Extract for 4 hours with the ethanol-toluene mixture at not less than four siphonings per hour. A thin wire screen disk over the material prevents channeling by dripping condensate.
- Solvent Removal and Wash: Transfer the wood to a Büchner funnel, remove the excess solvent with suction, and wash the thimble and wood thoroughly with ethanol to remove all traces of toluene.
- Ethanol Extraction: Return the wood to the extractor and continue the extraction with 95% ethanol for 4 hours. The endpoint is confirmed when the ethanol siphons over completely colorless. Extraction may be continued longer if necessary.
- Final Drying: Remove the extractive-free wood from the thimble, spread it in a thin layer, and allow it to dry in the air until free of ethanol before proceeding with subsequent chemical analysis.
💡 Technical Best Practice: Maintaining a consistent condensation and siphon rate is critical for the validity of the extraction. A rate of fewer than four siphonings per hour does not conform to the standard. If the thimble is nearly full, a Gooch crucible placed in the rim of the thimble can help keep the sample together during the process.
❓ Frequently Asked Questions
🔍 What specific materials are classified as extractives in this standard?
Extractives are defined as materials soluble in neutral solvents that are not part of the wood polymer structure. According to the standard, ethanol-toluene extracts waxes, fats, some resins, and portions of wood gums. Hot water extracts tannins, gums, sugars, starches, and coloring matter.
⚠️ What safety precautions are specified for the solvent mixture?
The standard provides a clear warning (Section 4.2) for the ethanol-toluene mixture: “Avoid inhalation of vapors and contact with skin.” It is the responsibility of the user to establish appropriate safety, health, and environmental practices, including the use of fume hoods and personal protective equipment.
📌 What is the required particle size for the wood sample?
The sample must be reduced by means of a Wiley mill to pass through a 250-µm (No. 60 mesh) sieve and be retained on a 180-µm (No. 80 mesh) sieve. The milled sample should then be air-dried before the extraction procedure begins.
💡 When is the ethanol extraction step considered complete?
The standard specifies that the ethanol extraction must run for a minimum of 4 hours. However, if the ethanol is still colored, the extraction must continue. The definitive endpoint is reached when the ethanol siphons over from the sample completely colorless.