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D2373-05 – Standard Test Method Technical Guide
📐 Scope and Significance
ASTM D2373-05 (Reapproved 2011) specifies a titrimetric method for determining cobalt in liquid paint driers that are soluble in glacial acetic acid. The procedure employs the disodium salt of ethylenediaminetetraacetic acid dihydrate (EDTA) for complexation. This test method is intended for pure cobalt driers used in oxidizing-type coatings, where cobalt content directly affects drying properties. It is not applicable to drier blends or samples containing other cations that can be titrated with EDTA under alkaline conditions, as they may interfere. All values are reported in SI units.
⚙️ Reagents and Apparatus
Reagents must meet ACS specifications, and water should conform to Type II of Specification D1193. Key reagents include a buffer solution at pH 10.0 and a standard cupric sulfate solution (0.05 M). A centrifuge capable of 1000 to 2000 g is required for sample preparation.
| 🧪 Reagent | 📏 Preparation Specifications |
|---|---|
| Buffer Solution (pH 10.0) | Dissolve 67.5 g of ammonium chloride (NH4Cl) in water, add 570 mL of ammonium hydroxide (NH4OH, sp gr 0.90), and dilute to 1 L. |
| Cupric Sulfate Standard Solution (0.05 M) | Dissolve 12.5 g of cupric sulfate pentahydrate (CuSO4·5H2O) in water and dilute to 1 L. |
⚡ Test Procedure and Key Measured Properties
The liquid drier sample is dissolved in glacial acetic acid, then diluted with isopropyl alcohol and water. An excess of standard EDTA solution is added to chelate cobalt ions. The excess EDTA is back-titrated with standard cupric sulfate solution using PAN (1-(2-pyridylazo