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D2613-01 – Standard Test Method Technical Guide
ASTM D2613-01 (Reapproved 2023) provides a standardized titrimetric procedure for the quantitative determination of calcium and zinc in pure liquid paint driers. It relies on the selective chelation of these metal ions using the disodium salt of ethylenediaminetetraacetic acid dihydrate (EDTA), specifically focusing on driers that can be fully dissolved in a toluene-alcohol mixture.
📖 Scope and Summary of the Test Method
The primary application of this method is the confirmation of the manufacturer’s stated metal content in liquid calcium and liquid zinc driers used in the coatings industry. As defined in Section 3.1, the test involves dissolving the sample in toluene and ethyl alcohol, treating it with a precisely measured excess of standard 0.05 M EDTA solution, and then back-titrating the unreacted EDTA with a standard zinc chloride solution. The endpoint of this titration is detected visually using Eriochrome Black-T indicator, which undergoes a distinct color change when all excess EDTA has been complexed. It is critical to note that this method is strictly for pure driers and is not applicable to complex drier blends.
⚠️ Applicability Restriction: As explicitly stated in Section 1.2, this test method is not applicable to drier blends. It is designed for the analysis of pure liquid calcium driers or pure liquid zinc driers. Furthermore, the presence of any other cation that can be chelated by EDTA in an alkaline medium constitutes a severe interference and will invalidate the results (Section 1.3).
🧪 Reagents, Apparatus, and Standard Solutions
The accuracy of this test method is heavily dependent on the purity of the reagents and water used. All chemicals must meet reagent grade specifications, and all water used in the preparation of solutions must conform to the requirements for Type II reagent water as outlined in ASTM Specification D1193. The standard EDTA solution is prepared by dissolving exactly 18.62 grams of the disodium salt dihydrate in water and diluting to one liter to achieve a 0.05 M concentration. This solution must be stored in a polyethylene or borosilicate glass container to prevent leaching of ions. The required buffer solution is prepared by mixing 350 mL of concentrated ammonium hydroxide (sp gr 0.90) with 54 grams of ammonium chloride and diluting to one liter with water. A centrifuge capable of developing a relative centrifugal force of 1000 g to 2000 g is specified for any necessary sample clarification.
| 🟦 Reagent / Solution | ⚡ Specification | 📐 Preparation Detail |
|---|---|---|
| EDTA Standard Solution | 0.05 M | 18.62 g EDTA (disodium salt dihydrate) dissolved in water and diluted to 1 L. Store in poly or borosilicate glass. |
| Buffer Solution | Alkaline (pH ~10) | 350 mL NH₄OH (sp gr 0.90) + 54 g NH₄Cl, diluted to 1 L with Type II water. |
| Indicator | Eriochrome Black-T | Used to detect the endpoint of the back-titration of excess EDTA. |
| Zinc Chloride Back-Titrant | Standard Solution | Concentration must be accurately standardized against the 0.05 M EDTA solution. |