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QS to volume with phosphate buffer (pH 5) solution. Heat and slowly stir until the
standards have completely dissolved (riboflavin dissolves more slowly) and the solution is
clear. Do not heat the solution for more than 40 minutes and do not exceed 90°C. Store
refrigerated (2˚-8˚C). Expiration: 3 months.
b)
Nicotinic Acid Stock Solution (550 mg/mL) - Accurately weigh 13.7 ± 0.1 mg USP niacin
(nicotinic acid, catalog 1461003) reference standard. Quantitatively transfer the nicotinic
acid to a 25 mL volumetric flask. Add lab water to a total volume of about 20 mL and swirl
until completely dissolved. Bring to volume with lab water. Mix well. Expiration: 3
months.
c)
Pyridoxal Stock Solution (140 mg/mL) - Accurately weigh 17.0 ± 0.5 mg pyridoxal
dihydrochloride standard. Quantitatively transfer to a 100 mL volumetric flask. Add lab
water to a total volume of about 70 mL and swirl until completely dissolved. Bring to
volume with lab water. Mix well. Expiration: 3 months.
d)
Pyridoxamine Stock Solution (160 mg/mL) - Accurately weigh 23.0 ± 0.5 mg pyridoxamine
hydrochloride standard. Quantitatively transfer to a 100 mL volumetric flask. Add lab
water to a total volume of about 70 mL and swirl until completely dissolved. Bring to
volume with lab water. Mix well. Expiration: 3 months.
9.
Mixed Working Standard (MWS) - Combine 500 μL VSSM, 25 μL pyridoxamine stock, 25 μL
pyridoxal stock, and 65 μL nicotinic acid stock solutions in a 10 mL volumetric flask containing
approximately 5 mL of 50 mM ammonium formate. Bring to volume with 50 mM ammonium
formate and mix well. Prepare fresh daily.
10.
Working Standard Solution Preparation
a)
WS1 – Add 20 μL MWS and 980 μL of 50 mM ammonium formate to a 50 mL centrifuge
tube. Add 100 μL of ISSM, and vortex to mix. Prepare fresh daily.
b)
WS2 – Add 50 μL MWS and 950 μL of 50 mM ammonium formate to a 50 mL centrifuge
tube. Add 100 μL of ISSM, and vortex to mix. Prepare fresh daily.
c)
WS3 – Add 100 μL MWS and 900 μL of 50 mM ammonium formate to a 50 mL centrifuge
tube. Add 100 μL of ISSM, and vortex to mix. Prepare fresh daily.
d)
WS4 – Add 200 μL MWS and 800 μL of 50 mM ammonium formate to a 50 mL centrifuge
tube. Add 100 μL of ISSM, and vortex to mix. Prepare fresh daily.
e)
WS5 – Add 500 μL MWS and 500 μL of 50 mM ammonium formate to a 50 mL centrifuge
tube. Add 100 μL of ISSM, and vortex to mix. Prepare fresh daily.
f)
WS6 – Add 1000 μL MWS to a 50 mL centrifuge tube. Add 100 μL of ISSM, and vortex to
mix. Prepare fresh daily.
E.
Procedure
1.
Sample preparation
a)
For powdered products, using a tarred beaker or LDPE cup, weigh 10.0 ± 0.3 g of sample.
Record the weight to at least 4 significant figures. This is the powder weight. Add room
temperature laboratory water to bring the total reconstituted sample weight (to include
the product weight) to 100 ± 2 g. Record the weight to at least 4 significant figures. This is
Candidates for 2016 Method of the Year
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