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D2352-85 – Standard Test Method Technical Guide
📐 Scope and Significance of the Standard
ASTM D2352 – 85 (Reapproved 2015) outlines the test method for determining the sulfur dioxide (SO₂) content in white pigments that have been separated from solvent-reducible paints. This method is particularly significant for monitoring calcium sulfate pigments, such as titanium-calcium composites, which are commonly used to modify the properties of paint systems. The standard is designed to help formulators and users precisely control the pigment composition of their end products. It is important to note that this method is not applicable in the presence of sulfides that decompose under the specified test conditions. All reported values are standardized in SI units, with values in parentheses provided for information only.
⚠️ Safety Information: Per Section 1.4 of the standard, this document does not address all safety concerns. Users must establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to handling the reagents required by the procedure.
⚙️ Summary of the Test Method and Reagent Preparation
Principle of the Analysis: The extracted white pigment is placed in a reaction flask. Dilute hydrochloric acid (1+3) is added to release sulfur dioxide gas. The evolved SO₂ is bubbled through an absorption vessel containing a standard 0.05 N iodine solution and potassium iodide (KI). The unreacted iodine is then determined by back-titration using a standardized 0.05 N sodium thiosulfate (Na₂S₂O₃) solution, employing starch as the endpoint indicator. A reagent blank is run concurrently under the same conditions without the pigment, and the blank titration value is subtracted from the sample value to determine the precise SO₂ content.
Critical Reagent Formulations: All reagents must be of ACS reagent grade, and water is understood to mean Type II reagent grade water in accordance with ASTM D1193. The table below provides the exact specifications for preparing the key reagent solutions.
| 🧪 Reagent | ⚗️ Preparation Specification | 📏 Exact Ratio / Normality |
|---|---|---|
| Hydrochloric Acid (HCl) | Mix 1 volume of concentrated HCl (sp gr 1.19) with 3 volumes of reagent water. | (1 + 3) Dilution |
| Iodine Solution (for SO₂) | Dissolve 15–20 g of pure KI in minimal water, add ~6.4 g of resublimed iodine, dilute to 1 L with water, and mix. Standardize against 0.05 N Na₂S₂O₃. | 0.05 N |
| Potassium Iodide (KI) | Dissolve 100 g of pure KI in reagent water and dilute to 1 L. | 100 g/L |
| Sodium Thiosulfate (for SO₂) | Dissolve 12.
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