
Contents
16.2.06
AOAC Official Method 981.18
Light Filth in Tea: Flotation Method
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Published:January 2023
Cite
Light Filth in Tea: Flotation Method', in Dr. George W Latimer, Jr. (ed.), Official Methods of Analysis of AOAC INTERNATIONAL, 22nd Edition (
Extract
First Action 1981
Final Action 1988
Reagents
Sequestering agent.—Mix 50 mL Tween 80–40% isopropanol, 945.75C(x) (see 16.1.01), 50 mL Na4EDTA-40% isopropanol, 945.75C(z) (see 16.1.01), and 200 mL 40% isopropanol.
Determination
Weigh 10 g test portion into 800 mL beaker, add ca 300 mL boiling water, heat to boiling, and simmer 6 min with magnetic stirring using Teflon-coated bar. Wash material from beaker to No. 230 sieve with forcible stream of aerated water, but do not let mixture splash out of sieve. When rinse water is clear, drain residue and quantitatively transfer with 40% isopropanol to 2 L Wildman trap flask. Rinse sides of flask with 40% isopropanol, and bring total volume in flask to 900 mL with 40% isopropanol. Pour 50 mL flotation oil, 945.75C(k) (see 16.1.01), down stirring rod, with top of disk or rubber stirring stopper held just below surface of liquid. Clamp rod above liquid. Magnetically stir 6 min. Let stand 2–3 min. Pour 300 mL sequestering agent down stirring rod, with top of disk or rubber stirring stopper held just below surface of liquid. Mix 1 min by gently swirling with stirring rod beneath surface of liquid. Pour 40% isopropanol slowly down stirring rod to fill flask. Rinse rod with 40% isopropanol and clamp so that stopper is held above layer of settled material. Let stand 5 min. Rotate stopper to free settled material. Let stand 25 min and trap off, rinsing neck with isopropanol until all residue is removed. Rinse neck with 40% isopropanol and add rinse to trappings. Add 30 mL flotation oil by pouring down stirring rod into trap flask. Hand-stir 1 min to bring flotation oil down. Add 40% isopropanol to refill flask. Let stand 30 min, and trap off into same beaker of first trappings. Rinse neck with isopropanol until all residue is removed. Transfer combined trappings onto one or more ruled filter paper(s). Examine paper(s) microscopically at 30× for insect fragments and rodent hairs.
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