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D2245-90 – Standard Test Method Technical Guide
📋 Scope and Summary
This test method, designated as ASTM D2245-90 (Reapproved 2011), provides a procedure for identifying oils and oil acids present in the vehicle of solvent-reducible paints. It is based on gas chromatographic analysis of methyl esters derived from fatty acids.
Scope: The method covers the identification of oils and oil acids in vehicles separated from solvent-reducible paints. It is applicable to products containing both saturated and unsaturated fatty acids (animal or vegetable, unpolymerized or partially polymerized) with chain lengths from 8 to 20 carbon atoms. However, it is not applicable to products where fatty acids have been polymerized or oxidized to an extent that no characteristic monomeric fatty acids remain.
Summary of Test Method: The test method relies on the differential migration and partitioning of vaporized methyl esters of fatty acids between a flowing gas phase and a supported liquid phase in a gas chromatographic column. It utilizes isothermal operation and a hot wire thermal conductivity detector. The process involves: (a) separation of the vehicle from the paint by centrifugation, (b) extraction and saponification of fatty acids from the vehicle, (c) conversion of fatty acids and an added margaric acid internal standard into methyl esters, (d) preparation of a gas chromatogram, and (e) interpretation of the chromatogram. The amount of each monomeric fatty acid ester is calculated, totaled, and subtracted from 100% to determine the percentage of polymerized fatty acids.
⚙️ Apparatus, Reagents, and Calibration
Key equipment includes:
- Centrifuge for vehicle separation
- Separatory funnels with PTFE‑fluorocarbon stopcocks
- Gas chromatograph and accessories suitable for fatty acid methyl ester analysis as per Test Method D1983
Reagents:
- Hydroquinone (used to prevent oxidation)
- Margaric acid (internal standard)
Calibration and Standardization: Before analysis, optimize the gas chromatograph using known methyl ester samples as described in Test Method D1983. Prepare working standards by running known paints or vehicles through the full procedure, including the internal standard.
Referenced standards for this method are essential for proper execution:
| 📄 Standard Reference | 📌 Title | 🗂️ Status |
|---|---|---|
| D1398 | Fatty Acid Content of Alkyd Resins and Alkyd Resin Solutions | Withdrawn 2007 |
| D1983 | Fatty Acid Composition by Gas‑Liquid Chromatography of Methyl Esters | Withdrawn 2003 |
| D2372 | Separation of Vehicle From Solvent‑Reducible Paints | Active |
| D2800 | Preparation of Methyl Esters From Oils for Determination of Fatty Acid Composition by Gas‑Liquid Chromatography | Withdrawn 2007 |
Note: While some standards are withdrawn, they remain referenced for historical context and procedural continuity.
📊 Procedure and Interpretation
The complete procedure involves the following key steps:
- Separate the vehicle from the paint using centrifugation as per Practice D2372.
- Extract and saponify the fatty acids from the vehicle.
- Convert the fatty acids and a measured quantity of margaric acid into methyl esters.
- Analyze the methyl esters via gas chromatography under isothermal conditions with a thermal conductivity detector.
- Interpret the chromatogram and calculate the percentage of each monomeric fatty acid methyl ester.
- Total the monomeric esters and subtract from 100% to determine the polymerized fatty acid content.
- Compare the results with known standards to identify the specific oils or oil acids present.
This method is significant because it provides a reliable procedure to identify fatty acids in paint vehicles, aiding in quality control and formulation analysis.
For accurate results, it is crucial to use known paints or vehicles as working standards during calibration.
⚠️ Important: This test method is not applicable to products containing fatty acids that have been polymerized or oxidized to such an extent that no characteristic monomeric fatty acids remain. Ensure the sample is within the scope before proceeding.
🔬 Technical Tip: The reagent hydroquinone is used to prevent oxidation during the procedure. Handle it with care and follow appropriate safety protocols.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D2245-90?
This standard provides a test method for identifying oils and oil acids in solvent‑reducible paints by gas chromatographic analysis of methyl esters of fatty acids.
💡 Can this method be used for all types of fatty acids?
No, it is applicable only to fatty acids with 8 to 20 carbon atoms that are either saturated or unsaturated, and from animal or vegetable sources, provided they are not fully polymerized or oxidized.
⚡ What is the role of margaric acid in this test?
Margaric acid (C17:0) is used as an internal standard to quantify the fatty acid conversion and to improve accuracy in the calculation of monomeric esters.
📌 Are the referenced standards still active?
Some referenced standards, such as D1398, D1983, and D2800, have been withdrawn, but D2372 remains active. Procedural adaptations may be necessary for current compliance.