AOAC OMB Final Action Recommendation (December 2019)-2016.14

2016.14 (October 2019) – FOS-03 METHOD

FOR ERP USE ONLY DO NOT DISTRIBUTE

(m) Sodium chloride solution (1 M) for graphitized carbon SPE column .—Into a 100-mL volumetric flask

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weigh 5.8 g NaCl and dissolve with 90 mL of water. Make up to the mark with water. Stable for 6

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months at room temperature.

(n) Elute solution for graphitized carbon SPE column (TFA 0.05 % in acetonitrile 25 % (v/v)) .—Into a

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100-mL volumetric flask, add 25 mL of acetonitrile and 50 μL of TFA. Make up to the mark with

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water. Stable for 6 months at room temperature.

E.

Mobile Phase Preparation (Using CarboPac PA20 column or Equivalent)

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If using a CarboPac PA1 column (or equivalent), skip this section and go directly to section F . 158

(a) Mobile phase A for CarboPac PA20, sodium hydroxide solution (600 mM).— Into an eluent bottle,

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introduce 970 mL of water C(a) and degas with helium for 20 min. Add (using a single-use plastic

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pipette) 31.2 mL of 50 % (w/w) NaOH solution C(j) . Degas with helium for 20 min and protect the

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eluent from exposure to carbon dioxide until, and during use by suitable means (e.g. by keeping

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under a blanket of helium). Stable for 1 week at room temperature.

(b) Mobile phase B for CarboPac PA20, deionised water resistivity ≥18 MΩ.— Into an eluent bottle,

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introduce 2000 mL of water C(a) and degas with helium for 20 min. Thereafter protect the eluent

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from exposure to carbon dioxide until, and during use by suitable means (e.g. by keeping under a

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blanket of helium). Stable for 4 days at room temperature.

(c) Mobile phase C for CarboPac PA20, sodium hydroxide solution (30 mM).— Into an eluent bottle,

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introduce 1000 mL of water C(a) and degas with helium for 20 min. Add (using a single-use plastic

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pipette) 1.6 mL of 50 % (w/w) NaOH solution C(j) . Degas with helium for 20 min and protect the

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eluent from exposure to carbon dioxide until, and during use by suitable means (e.g. by keeping

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under a blanket of helium). Stable for 1 week at room temperature.

(d) Post-column addition reagent, sodium hydroxide solution (300 mM).— Into an eluent bottle,

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introduce 985 mL of water C(a) and add (using a single-use plastic pipette) 15.6 mL of 50 % (w/w)

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