ASTM D5974 Method for Fatty and Rosin Acids in Tall Oil Fractionation Products
ASTM D5974 Standard Test Methods for Fatty and Rosin Acids in Tall Oil Fractionation Products by Capillary Gas Chromatography
PREPARATION OF METHYL ESTERS
NOTE 1 - Any of these three methods can be used, with the choice being
dependent on the factors mentioned in 3.3.

4. Conversion By Means of Tetramethylammonium Hydroxide (TMAH)
4.1 Apparatus:
4.1.1 Standard Laboratory Equipment.

4.2 Reagents and Materials:
4.2.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.

4.2.2 Tetramethylammonium Hydroxide Solution, 24 % in methanol, CAS No. 75-59-2.

4.2.3 Tetramethylammonium Hydroxide Solution, 6 % (v/v) in methanol. Dilute 25 mL of the reagent described in 4.2.2 with 75 mL of methanol.

4.2.4 Phenolphthalein Solution, 1 % (w/v) in methanol.

4.2.5 Diethyl Ether, anhydrous.

4.2.6 Methanol, anhydrous.

4.2.7 Acetic Acid, 5 % volume/volume (v/v) in methanol.

4.2.8 Toluene, optional.

4.3 Procedure:
4.3.1 Dissolve the sample from 9.2.2 or 17.1 in 0.5 to 3.0 mL of a 50:50 ether/methanol mixture, add 2 to 3 drops of phenolphthalein indicator solution, and titrate to a pH of 7.8 to 8.1 or to the very first permanent pink color, with the 6 % solution of TMAH. If the solution is overtitrated, it can be back titrated with the acetic acid in methanol solution to the end point. When the solution is injected into the heated injection port of the chromatograph, the tetramethylammonium salts are pyrolyzed to methyl esters.

NOTE 2 - For solid rosin, or other samples that are difficult to dissolve, 2 to 3 drops of toluene may be added to the vial prior to the addition of TMAH, to assist in dissolving the sample.

5. Conversion By Means of Trimethylphenylammonium Hydroxide (TMPAH)
5.1 Apparatus:
5.1.1 Standard Laboratory Equipment.

5.2 Reagents and Materials:
5.2.1 Purity of Reagents, see 4.2.1.

5.2.2 Trimethylphenylammonium Hydroxide Solution, 0.2 M or 0.1 M in methanol, CAS No. 1899-02-1.

5.2.3 Diethyl Ether, anhydrous.

5.2.4 Methanol, anhydrous.

5.2.5 Toluene, optional

5.3 Procedure:
5.3.1 Add 0.5 to 3.0 mL of a 50:50 ether/methanol, to the sample from 9.2.2 or 17.1. Add 2 to 3 drops of phenolphthalein indicator solution and titrate to the very first permanent pink color with the TMPAH in methanol solution. When the solution is injected into the heated injection port of the chromatograph, the trimethylphenylammonium salts are pyrolyzed to their respective methyl esters.

NOTE 3 - For solid rosin, or other samples that are difficult to dissolve, 2 to 3 drops of toluene may be added to the vial prior to the addition of TMPAH, to assist in dissolving the sample.

6. Conversion by Means of N,N-Dimethylformamide Dimethyl Acetal (DMF-DMA)
6.1 Apparatus:
6.1.1 Standard Laboratory Equipment.

6.2 Reagents and Materials:
6.2.1 Purity of Reagents, see 4.2.1.

6.2.2 N,N-Dimethylformamide dimethyl acetal (DMF-DMA), CAS No. 4637-24-5.

6.2.3 Methanol, anhydrous.

6.2.4 Toluene.

6.3 Procedure:
6.3.1 Place the sample from 9.2.2 or 17.1 in an appropriate anhydrous vial, and dissolve with approximately 0.5 mL of either methanol or toluene. Add approximately 1 mL of DMF-DMA, mix well, and maintain the sample at 30 - 40°C for 15 minutes.