AOAC Final Action Methods in 2019

Figure 2017.03B. Typical blank chromatogram.

Place the flask in a refrigerator to stir overnight or until the powder dissolves (because of slow dissolution, this solution should be prepared a day before analysis is intended). Once dissolved, rinse and remove the stir bar and bring the solution to a final volume of 50 mL with water. Store frozen in separate vials. ( e ) Tryptophan standard solution .—Weigh 0.0100 ± 0.0010 g tryptophan and transfer to a 100 mL volumetric flask. Add approximately 50 mL laboratory water and dissolve the tryptophan powder by sonicating the solution (approximately 3 min). Let the solution cool to room temperature and bring to a final volume

(100 mL) using laboratory water. Store the solution frozen for future use. ( f ) Working standard solutions .—Combine the appropriate aliquot of tryptophan and internal standard stock solutions together in 50 mL volumetric flasks (one for each level; see Table 2017.03B ). Add 12.0 mL methanol to each of the flasks containing the standard–internal standard mixtures and bring to volume with laboratory water. Transfer diluted standards to autosampler vials. Store the solution frozen for future use. ( g ) Mobile phase (methanol–0.05 M buffer; 18 + 82, pH 2.3) .—Dissolve 6.9 ± 0.1 g sodium phosphate monobasic

Figure 2017.03C. Typical sample chromatogram (NIST Standard Reference Material 1849a).

© 2019 AOAC INTERNATIONAL