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D4901-99 – Standard Test Method Technical Guide
📋 Scope and Significance of D4901-99
ASTM Standard Practice D4901-99 (Reapproved 2020) outlines the method for preparing a solution of liquid vegetable tannin extracts for use in tannin analysis. The primary objective is to achieve a standardized concentration of 4 g tannin per liter, critical for accurate testing. This practice accounts for the complex solubility behavior of vegetable tannin extracts, which are heterogeneous mixtures influenced by temperature and concentration, affecting the degree of dispersion and size of component particles. By dissolving the extract in hot water and cooling slowly, the procedure ensures proper dispersion and equilibrium for reliable analysis.
🧪 Apparatus, Reagents, and Specimen Requirements
The following equipment and reagents are specified:
| 🟦 Item | 📏 Specification |
|---|---|
| Volumetric Flask | 1 L, Class A, with upper bulb in neck |
| Formaldehyde | 40% solution |
| Toluene | Assay ≥99.5% |
The test specimen must be prepared from a sample following Practice D6404. It should be an aliquot that, when dissolved, yields a tannin concentration of 4 g/L, with an acceptable range of 3.75 to 4.25 g/L. The sample must be thoroughly mixed at room temperature, and the specimen weighed to the nearest 0.1 mg.
| 🎯 Parameter | ⚡ Requirement |
|---|---|
| Tannin Concentration Target | 4 g/L |
| Acceptable Range | 3.75 to 4.25 g/L |
| Mixing Method | Mechanical shaking for 10 min; stirrer for viscous extracts |
| Weighing Accuracy | Nearest 0.1 mg |
⚙️ Procedure for Solution Preparation
Begin by preparing the liquid extract sample as detailed in Practice D6404. Allow it to reach room temperature, then mix thoroughly. Transfer the specimen to a tared container and stopper it to prevent moisture loss. Weigh the container and specimen to the nearest 0.1 mg. Do not return any material removed from the sample for other tests, and avoid contamination from dried material on the stopper.
Pour approximately 200 mL of distilled water at 95°C into a 1 L volumetric flask and immediately transfer the specimen. The solution should then be cooled slowly to standard room temperature, following Practice D4904 for analytical cooling. Note that hand shaking is rarely sufficient; mechanical shaking for 10 minutes is recommended. For viscous extracts, a stirrer may be used, but care must be taken to avoid moisture loss.
💡 Tip: Always use mechanical shaking for consistency. For very viscous extracts, a stirrer is necessary, but cover the container to minimize moisture loss.
⚠️ Warning: The water temperature must be precisely 95°C to ensure proper dissolution. Deviations can affect solubility and introduce errors in the tannin analysis.
❓ Frequently Asked Questions
🔍 What is the purpose of this standard?
ASTM D4901-99 specifies the practice for preparing a standardized solution from liquid vegetable tannin extracts for accurate tannin analysis.
💡 How is the specimen concentration determined?
The specimen must provide a solution with 4 g tannin per L, within the range of 3.75 to 4.25 g/L, by taking an appropriate aliquot from the sample.
⚡ What is the critical water temperature for dissolution?
Distilled water heated to 95°C is required for dissolving the extract, followed by slow cooling to room temperature for consistent results.
📌 Which flask is recommended for this practice?
A 1 L Class A volumetric flask with an upper bulb in the neck is especially suitable for this preparation.