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D5655-95 – Standard Test Method Technical Guide
📖 Scope and Test Summary
ASTM D5655-95 (Reapproved 2000) specifically covers the colorimetric analysis of Copper Dimethyldithiocarbamate (CDDC) in treated wood. CDDC is a naturally colored compound that can be quantitatively determined following solvent extraction. All values stated in SI units are regarded as the standard, with inch-pound units provided for reference. The standard establishes a conformance test for CDDC used in the preservative treatment of wood.
⚙️ Apparatus, Reagents, and Sampling
The accuracy of this test method depends on precise equipment and high-purity solvents. The sample preparation must also strictly follow the defined drying conditions to preserve the integrity of the active compound.
| 🟦 Apparatus / Reagent | 📐 Key Specification |
|---|---|
| Spectrophotometer | Any good quality model capable of reading at 435 nm (e.g., Beckman Model 35, B/L Spectronic 20). |
| Grinding Mill | A typical Wiley mill capable of reducing wood to 30 mesh particle size. |
| Reflux Apparatus | Per ASTM Methods D 147 or equivalent. |
| Filtration System | Buchner funnel and filter flask using Whatman #425 filter paper. |
| Extraction Azeotrope | 12.6% MeOH / 87.4% CHCl₃ (w/w), Spectro Grade. |
| Analytical Standard | Copper Dimethyldithiocarbamate, purity >99%. |
⚠️ Safety Advisory: Chloroform and methanol are hazardous. All work using the extraction azeotrope must be conducted in a certified fume hood. Review the Safety Data Sheets (SDS) and your organization’s chemical hygiene plan before proceeding.
Sampling Requirement: Increment borings must be oven-dried at 60°C or less to prevent thermal degradation of the CDDC active ingredient.
📊 Colorimetric Procedure and Standard Curve
🧪 Calibration Standards
Analytical grade CDDC (>99%) is dissolved in the extraction azeotrope to produce a standard curve for quantification.
| 🎯 Calibration Parameter | ⚡ Required Value / Specification |
|---|---|
| Standard Concentration Range | 0 to 25 ppm |
| Detection Wavelength | 435 nm |
| Standard Curve Plot | Known concentration (ppm) vs. Absorbance |
🪵 Test Execution
The ground wood sample is extracted with the chloroform/methanol azeotrope using the reflux apparatus. The extract is vacuum filtered through a Buchner funnel with Whatman #425 paper. The absorbance of the clear filtrate is measured at exactly 435 nm. The concentration of CDDC in the treated wood is determined by comparing the sample absorbance against the prepared standard curve.
💡 Analytical Tip: The composition of the extraction azeotrope (12.6% MeOH / 87.4% CHCl₃) creates a critical polarity balance. Verify the composition of your prepared solvent mixture regularly to ensure maximum and consistent extraction efficiency from the wood matrix.
❓ Frequently Asked Questions
🔍 What kind of spectrophotometer is acceptable?
Any good quality spectrophotometer capable of accurately reading absorbance at 435 nm is suitable. Instruments such as the Beckman Model 35 and B/L Spectronic 20 are specifically listed in the standard as common examples.
💡 What particle size is required for the ground wood?
The grinder (e.g., a Wiley mill) must reduce the wood sample to a particle size of 30 mesh. This provides the surface area necessary for thorough solvent extraction.
⚡ What is the correct composition of the extraction solvent?
The extraction solvent is an azeotrope composed of 12.6% Methyl Alcohol and 87.4% Chloroform (by weight). The standard specifies that both solvents must be Spectro Grade to avoid baseline interference at the test wavelength.
📌 What temperature is critical for sample drying?
The increment borings must be oven-dried at 60°C or less. Drying at higher temperatures can thermally degrade the CDDC compound, leading to erroneously low analytical results.