AOAC OMA# 2017.03 (Final Action)-OMB

D raher & W hite : J ournal of AOAC I nternational V ol . 101, N o . 4, 2018  1247

Figure 2017.03A. Typical medium standard chromatogram.

( b ) Remove the samples from the incubation unit after a minimum of 16 h. Allow samples to cool to room temperature. Remove the caps and add 12 mL methanol to each tube. Dilute each tube to a 50 mL volume with laboratory water. ( c ) Cap the tubes and mix thoroughly by inversion. Attach a 0.45 μm filter to a 3 cc syringe and transfer several milliliters of each sample to the syringe. Filter the samples into an

fluorescence detector lamp is designed to be on during analysis only due to the near-instant warm-up of the lamp. ( b ) Load standards, enzyme blanks, and samples onto the autosampler tray. The sequence includes a minimum of four initial injections for equilibration. The first of the four injections is a high standard to check that the Trp peak response does not exceed approximately 50% of full scale. (If significantly over 50%, lower the PMT gain by 1 unit. This will decrease the signal by about one-half. Results are best with a high standard between 20 and 50% of full scale.) The remaining three precision injections are 5.0/50 medium standard Figure 2017.03A and provide a check of system equilibration by calculating the percent difference in the last two middle standard injection Trp peak areas. The system is considered equilibrated

autosampler vial, cap, and analyze the samples. L. Instrumental Analysis and System Suitability

( a ) Set the HPLC pump to a 0.5 mL/min flow rate and equilibrate the analytical column with mobile phase for 30 min. Set the column oven to 30°C. The instrument method designates an λ ex of 295 nm and λ em of 345 nm. The Agilent G1321A

Figure 2017.03B. Typical blank chromatogram.