(a)
Extraction solution
.—0.2% citric acid [w/v, 40 g/20 L deionized (DI) water].
(b) Polyester fiber (available in fabric or craft stores).
(c) 250 mL amber HDPE (high density polyethylene) wide-mouth bottles for sample storage.
(d) Cupric sulfate solution stabilizer (20 g CuSO4 5H2O/L 1 + 1 HCl).
(e) Calibration standard, 500 mg N/L, matrix-matched to the
liquid extracts for AOAC
993.13
.
(f) Matrix-matched (–7 + 9 mesh IBDU) internal reference material.
(f) 2% HCl/DI water solution for cleanup of equipment and
tubing.
E. Sample Preparation of Granular Materials
(a)
Homogeneous or blended materials (coated N-P-Ks, granulations, or blends)
.—Reduce via
gated riffle splitter (Jones Micro-Splitter SP-171X; Gilson Co., Inc., Lewis Center, OH) to 30.0 ± 1.0
g unground test portion. Place 3 (±0.2) g fiber 2–3 cm above the bottom of column (do not pack),
and insert PTFE rod (ThermoFisher Scientific, Pittsburgh, PA). Using powder funnel, add test
portion, and place 3 (±0.2) g fiber near top of column below O-ring, but not directly on top of
test portion. Ensure no test portion or fibers foul O-ring seals.
(b)
Pellets, spikes, briquettes, etc
.—If larger than 2.5 cm, crack, crush, or break to yield pieces
as large as possible that fit column (<2.5 cm). Use largest pieces equaling 30.0 ± 1.0 g, and weigh
to ±.01 g. Place 3 (±0.2) g fiber approximately 2–3 cm above bottom of column (do not pack),
insert polyethylene rod, add test portion, place 3 (±0.2) g fiber near top of column, but not on top
of test portion. Ensure no fibers foul O-ring seals.
F. Extraction
Extraction sequence (examples in parenthesis)—
Day 1
.—
Extraction 1
.—2 h at 25°C (e.g., Mon. 9:00 am– 11:00 am).
Extraction 2
.—2 h at
50°C. Begin 1 h following extraction 1 (e.g., Mon. 12:00 pm–2:00 pm).
Extraction 3
.—20 h at
55°C. Begin 1 h following extraction 2 (e.g., Mon. 3:00 pm– 11:00 am Tues.).
Day 2
.—
Extraction 4
.—50 h at 60°C. Begin 1 h following extraction 3 (e.g., Tues. 12:00 pm–2:00
pm Thurs.).
Day 4
.—
Extraction 5 (if needed).—
94 h at 60°C complete extraction 4 (e.g., Thurs. 3:00 pm).
Begin extraction 5 one hour following extraction 4 (e.g., Thurs. 4:00 pm–2:00 pmMon.).
Candidates for 2016 Method of the Year
212