AOAC RI ERP E-Book - DS DF

OMAMAN-38 A: Collaborative Study Manuscript Expert Review Panel Use Only September, 2017

Proceed to step [I(a)] for calculations.

(h)

H. Determination of SDFS Proper deionization of the filtrate is an essential part of obtaining quality chromatographic data on SDFS. Refer to ( Figure 2017.xxE ) to see patterns of glycerol and D-glucose in the presence and absence of buffer salts. To ensure that the resins being used are of adequate deionizing capacity, add 0.1 mL of protease suspension [C(f)] to 40 mL of either maleate buffer [C(j)] or MES buffer [C(k)] along with 3.0 mL of 0.75 M Tris base solution [C(l)] , 4.0 mL of 2M acetic acid [C(m)] , 1 mL of glycerol internal standard (100 mg/mL) [C(g)] and 1 mL of D-glucose solution (100 mg/mL). Concentrate this solution to dryness on a rotary evaporator and re-dissolve the residue in 32 mL of deionised water. To 5 mL of this solution in a 13 mL polypropylene tube [ B (s)] add 1.5 g of Amberlite ® FPA53 (OH − ) resin and 1.5 g of Ambersep ® 200 (H + ) and swirl the contents regularly over 5 min. Allow the resin to settle and remove the supernatant (1.5-2.0 mL) with a syringe [ B (cc)] and filter through a polyvinylidene fluoride filter, pore size 0.45 μm [ B (z)] . Inject an aliquot (50 L) of this solution onto the TSK columns (Bio-Rad ® de-ashing pre-cartridges in place). No salt peaks should be seen on HPLC. ( a) Filtrate recovery, desalting, and LC analysis.— (Set aside the filtrate from one of the sample duplicates [G(c)] to use in case of spills or if duplicate LMWDF data is desired. Transfer the filtrate [G(c)] into a 500 mL measuring cylinder. Adjust the volume to 300 mL with 78 % v/v aqueous ethanol [ C (b)], transfer to a 1 L beaker and mix thoroughly. Transfer ~ 75 mL (~ 25 %) of this solution to a 500 mL evaporator flask, and concentrate with a rotary evaporator to dryness at 50°C. [Note: it is not essential to quantitatively transfer all solution because SDFS is determined by the ratio of these peaks on HPLC to that of glycerol internal standard]. (b) Desalting of sample.— Dissolve the residue in the evaporator flask in 8 mL of deionized water and transfer most of this solution to a 40 mL polypropylene container (apparatus 19). Transfer 5 mL of this solution to a 13 mL polypropylene tube (apparatus 19) containing 1.5 g of Amberlite ® FPA53 (OH − ) resin and 1.5 g of Ambersep ® 200 (H + ) (Fig. 5). Cap the container and invert the contents regularly over 5 min. Alternatively, if the ammonium AOAC Research Institute ERP Use Only

Method updated 2008--08-10 This copy printed 22 August 2017

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