AOAC SPIFAN Nutrients ERP-Final Review (Jan. 2019)

1248  D raher & W hite : J ournal of AOAC I nternational V ol . 101, N o . 4, 2018

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

and <1.26 for 5-methyl-tryptophan. Excessive tailing indicates the need for a new column to restore expected performance. ( 3 ) Residual error of linear regression .—The residual error for any one point of the 4-point linear regression must not exceed 5%. In the event of excessive error, repeat the analysis with fresh standard solutions. References: (1) AOAC SMPR2014.013 J. AOAC Int . 98 , 1073(2015)

if the areas agree within approximately 1%. If not equilibrated, an additional middle standard injection should be added and the system rechecked for area agreement. This is a prerun suitability check only. ( c ) Once the system is equilibrated, order the sequence with the four standard levels (high to low is recommended), blanks Figure 2017.03B , and samples, and then the bracketing standard injections. Repeat the calibration after approximately 20 sample injections. Following the sample analysis, rinse the analytical column with a solution of approximately 25% methanol in water. For longer storage, the column is best left in 60–80% organic solvent, preferably acetonitrile. ( d ) System suitability requirements .—( 1 ) Resolution .—In the laboratory control sample, see Figure 2017.03C , the resolution of the Trp peak and the small interference peak after the Trp peak must be >1.25. ( 2 ) USP tailing .—The USP tailing factor can be calculated within the chromatography software and should be <1.59 for Trp

DOI: 10.5740/jaoac.int.SMPR2014.013 (2) Narahashi, Y., & Yanagita, M. (1967) J. Biochem . 62 , 633–641 (3) Yamaskov, I.A., Tichonova, T.V., & Davankov, V.A. (1986) Enzyme Microb. Tech . 8 , 241–244 J. AOAC Int. (future issue) DOI: 10.5740/jaoacint.17-0257