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1670 Butler-Thompson et al. : J ournal of AOAC I nternational V ol. 98, N o. 6, 2015

Table 2011.18B. SLV accuracy (spike recovery) data for myo-inositol

No. of replicates (duplicates on multiple days)

Native level, mg/100 g RTF

Spike level, mg/100 g RTF Recovery, % RSD, %

Sample type

Free myo-inositol

Child formula powder, unfortified Infant formula powder soy-based

12 12 12 12

0.0426

1.89 14.9 15.2 1.74 1.09

101 98.2 102 93.9 93.2 90.2 101 96.3 77.1 87.3 90.0 81.9 79.9 72.8 75.7

2.78 2.47 3.00 3.00 1.54 3.14 2.64 3.27 13.2 6.88 15.7 0.21 7.51 5.18 3.23

4.18 3.35 0.00 0.00 0.00

Infant formula powder partial hydrolyzed milk-based

Infant elemental powder, unfortified Infant elemental powder, unfortified Infant elemental powder, unfortified Adult nutritional powder milk-based Adult nutritional RTF high protein

6 6

0.390

12 12

0.409 0.042

65.0 61.4

Myo-inositol bound as phosphatidylinositol

11.1 a 0.00 0.443

7.3

Infant formula (NIST SRM 1849a) Infant elemental powder, unfortified

6 6 6 6 6 6 6

0.294 0.340

Child formula powder

Infant formula powder soy-based

2.48

3.22

Infant formula powder partial hydrolyzed milk-based Infant formula powder partial hydrolyzed soy-based

0.247

0.152

1.94 1.43

2.47 1.54

Adult nutritional powder milk-based

a  Results in mg/kg powder.

into a 100 mL volumetric flask and record the weight to the nearest 0.0001 g. For powdered products that do not require reconstitution, accurately weigh 0.25–1.5 g powder into a 100 mL volumetric flask and record the weight to the nearest 0.0001 g. Add approximately 10 to 15 mL laboratory water to the volumetric flask and swirl or stir to completely dissolve the powder. For powdered products that are not homogeneous at the subgram level, reconstitute following the product label instructions and accurately weigh 0.5 to 5 g reconstituted product into a 100 mL volumetric flask. Record the weight to the nearest 0.0001 g. Add enough 0.5% hydrochloric acid to each sample to adjust the sample pH to 4.5 ± 0.2 and swirl to mix. Allow the samples to react with 0.5% hydrochloric acid for a minimum of 2 min and then dilute to volume with laboratory water. Mix well. Filter samples through Whatman 2V filter paper into 125 mL Erlenmeyer flasks or appropriate glassware. ( Note : Although some samples will filter cloudy, the filtrates can still be used.) Filter an aliquot of sample filtrate through a 0.45 μm syringe filter into an autosampler vial. (b)  Sample preparation for myo-inositol bound as phosphatidylinositol determinations.— ( 1 )  Extraction .—Weigh 4 g (±10%) liquid or reconstituted powder product or 1 g (±10%) homogeneous powder into a 50 mL centrifuge tube and record the weight to the nearest 0.0001 g. Add 4 mL laboratory water to 1 g homogeneous powder samples. In a fume hood, add 10 mL methanol and stir for at least 20 min or vortex for at least 1 min and allow samples to set for at least 20 min. Add 20 mL chloroform and stir for at least 5 min or vortex for at least 1 min and allow samples to set for at least 5 min. If large clumps form when chloroform is added, cap tube and shake well for at least 1 min to mix sample. Add 5 mL 6% metaphosphoric acid and

( Note : It is important that the sodium hydroxide does not absorb carbon dioxide from the air.) Swirl to mix well. Dilute to volume with water and mix well. Expiration: 1 month. (g)  Sodium hydroxide, 4.0% or 1 M (Pump 2). —Quickly weigh 160 (±3) g 50% sodium hydroxide into a 2000 mL volumetric flask containing approximately 1900 mL water. ( Note : It is important that the sodium hydroxide does not absorb carbon dioxide from the air.) Swirl to mix well. Dilute to volume with water and mix well. Expiration: 1 month. (h)  6%Metaphosphoric acid. —Weigh 6.0 g metaphosphoric acid into a 100 mL volumetric flask. Dissolve and dilute to volume with laboratory water. Mix well. Store refrigerated. Expiration: 1 week. (i)  Phosphatidylinositol extraction solutions. —Prepare fresh on day of use. ( 1 )  Chloroform–methanol (2 + 1). —Mix 60 mL chloroform and 30 mL methanol. ( 2 )  Hexane–diethyl ether (80 + 20) .—Mix 80 mL hexane and 20 mL diethyl ether. ( 3 )  Hexane–diethyl ether (50 + 50) .—Mix 50 mL hexane and 50 mL diethyl ether. ( 4 )  Methanol–chloroform–water (75 + 15 + 10).— Mix 75 mL methanol, 15 mL chloroform, and 10 mL water. E. Sample Preparation and Extraction (a)  Sample preparation for free myo-inositol determinations. — Prepared samples that are constantly stored at 1–8°C in closed containers are stable for up to 5 days. After 5 days, samples must be prepared again. Thoroughly mix or stir products prior to sampling. For liquid products, accurately weigh 0.5 to 5 g (±10%) product