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D1628-94 – Standard Test Method Technical Guide
📐 Scope and Reagent Specifications
Standard D1628-94 outlines standard test methods for the chemical analysis of solid chromated copper arsenate (CCA) and its solutions. The procedures specifically cover the determination of Pentavalent Arsenic (calculated as As2O5), Copper (calculated as CuO), and Hexavalent Chromium (calculated as CrO3).
Section 5 of the standard strictly governs the purity of reagents. All chemicals must be reagent grade, conforming to the specifications of the Committee on Analytical Reagents of the American Chemical Society where available. Water used in the procedures must meet the requirements of Specification D 1193 for reagent water, ensuring no lessening in the accuracy of the determination.
⚙️ Test Procedure and Analysis Overview
The analytical procedures are conducted in a specific order to ensure accurate results. The summary of the test method involves a critical aeration step. According to Section 3, 20 mL of tartaric acid solution is added to a 250-mL Erlenmeyer flask, followed by 2 mL of the ACA concentrate, yielding a light blue-green solution. After adding 20 mL of sodium bicarbonate solution, the solution turns light blue. Following the addition of the starch indicator, one drop of iodine solution is added from a buret. The completion of aeration—which converts trivalent arsenic to pentavalent arsenic—is confirmed when the solution turns a stable dark blue.
Accurate sampling is paramount, as defined in Section 6. For water solutions, the material must be mixed thoroughly to ensure uniformity. A representative sample of at least 0.45 L (preferably 0.9 L) should be taken using a “thief” or other appropriate device and stored in properly closed glass containers.
| 🟦 Determination | 📐 Calculated As | ⚡ Standard Sections |
|---|---|---|
| Pentavalent Arsenic | As2O5 | 7 – 9 |
| Copper | CuO | 10 – 13 |
| Hexavalent Chromium | CrO3 | 14 – 16 |
📊 Sampling Requirements and Data
The standard emphasizes representative sampling for accurate analysis. The following table summarizes the key sample requirements for water solutions of chromated copper arsenate as outlined in Section 6.
| 📏 Parameter | 🎯 Specification |
|---|---|
| Sample Type | Water solution |
| Minimum Volume | 0.45 L |
| Preferred Volume | 0.9 L |
| Collection Device | “Thief” or other device |
| Storage Container | Glass or other suitable material |
⚠️ Safety Considerations: Section 1.3 of the standard explicitly notes that it does not address all associated safety concerns. Users are responsible for establishing appropriate safety and health practices. Specific precautionary statements are located in sections 8.2 and 12.1.2 of the standard.
💡 Reagent Purity: To maintain the integrity of the analytical results, always verify that reagent grade chemicals conform to the specifications of the American Chemical Society (Section 5.1). Using lower grades of chemicals may lessen the accuracy of the determination.
❓ Frequently Asked Questions
🔍 What is the primary purpose of the aeration step described in Section 3?
The aeration step is used to chemically convert trivalent arsenic to pentavalent arsenic, which is a necessary preparation for the titration process. The endpoint is reached when the solution turns a stable dark blue upon the addition of iodine solution.
💡 Into what oxide forms are the key elements calculated?
The standard specifies that Pentavalent Arsenic is calculated as As2O5, Copper is calculated as CuO, and Hexavalent Chromium is calculated as CrO3.
⚡ What type of water is specified for preparing reagents?
According to Section 5.2, all references to water in the test methods assume the use of reagent water conforming to ASTM Specification D 1193.
📌 What is the minimum required sample volume for analyzing a water solution?
Section 6 specifies that the sample shall be thoroughly mixed and at least 0.45 L, preferably 0.9 L, collected in a properly closed glass container.