AOAC 2018 Methods

(g) L-cystine (e.g. Sigma Aldrich 30199) (h) Taurine (e.g. Sigma Aldrich 86329) (i) Norvaline (e.g. Sigma Aldrich N7627) (j) Sodium hydroxide pellets, reagent grade (e.g. Merck 106498) (k) Sodium hydroxide solution, 1 M (e.g. Merck 109137) (l) Optional: Sodium hydroxide solution, 6 M (e.g. Merck 137032) (m) Hydrochloric acid fuming 37% (12 M) GR for analysis (e.g. Merck 100317)

(n) Hydrochloric acid, 1 M (e.g. Merck 109057) (o) Hydrochloric acid, 0.1 M (e.g. Merck 109060) (p) Laboratory Water Grade Type 1

D. Reagents and Standard Preparation (a) Sodium hydroxide (NaOH) solutions at 6 M, 0.2 M, and 0.05 M (b) Hydrochloric acid (HCl) solution at 0.2 M

(c) 1% DDP in 0.2 M NaOH (d) 0.1% phenol in 12 M HCl

(e) AccQ•Tag™ Ultra Derivatization kit.--Prepare the reagents included in the kit following the manufacturer’s instructions.

( 1 ) AccQ•Tag™ Ultra Borate buffer (reagent 1).--Ready-to-use solution.

Alternative reagent : 5 % (W/V) sodium tetraborate in water.

( 2 ) AccQ•Tag™ Ultra reagent (vial 2A and 2B).--Reconstitute AccQ•Tag™ Ultra reagent (vial 2A) according to the manufacturer’s instructions:

( a ) Preheat a heating block to 55 °C.

( b ) Tap vial 2A lightly before opening to ensure all AccQ•Tag™ Ultra reagent powder is at the bottom of the vial.