Recoverable Oil by Bromate Titration (Scott)

Principle
TEST METHOD NO. 9
RECOVERABLE OIL BY BROMATE TITRATION (SCOTT)
Oil recoverable by distillation from orange, tangerine, and grapefruit juices is >98%
d-limonene, which, after co-distillation with isopropanol, is determined after
acidification by titration with standard KBr-KBrO3 solution. Reaction involves release
of Br in situ and subsequent formation of limonene tetrabromide. Oil from lemon
juice contains up to 5% a-pinene and 4% citral. Since a-pinene consumes Br at
same rate, and citral at 1/2 rate, as d-limonene, method is only slightly less accurate
with lemon juice.
Comminutes may be analysed after suitable dilution.
1. Reagents
a) Potassium bromide-bromate solutions -
(1) Stock solution* - 0.099N.
(2) Standard solution - 0.0247N Dilute stock solution 1 + 3
1 ml 0.0247N KBrO3 = 0.0010 ml (equivalent to 0.00084g)
d-limonene.
Solutions are stable 6 months.
b) Methyl orange indicator - 0.1% in H2O. Use 1 drop per titration or add 5 ml
to 1 L HC1 (1 + 2).
c) 10 vol. Hydrogen Peroxide solution.
2. Apparatus
a) Electric heater - With recessed refractory top, 500-750 watts.
b) Still, all-glass - 500 ml distillation flask with T 24/40 neck; efficient condenser
with 28/15 receiving socket and drip tip; connecting bulb and adaptor. See
Fig., or use Quickfit Distillation Head SH 7/12 or 7/13 wrapped in Aluminium
foil, with 119/26 or 24/29 socket flask and 19/26 socket condenser.
c) Burette - 25 ml, 0.1 ml subdivisions; suitable for rapid and dropwise titration.

3. Determination
Preheat electric heater. Pipette sufficient sample to give a titre of not less than 10
mls nor greater than 25 mls, into distillation flask containing SiC chips or glass
beads, and add 25 ml isopropyl alcohol. If SO2 is present, add 1 drop 10 vol. H2O2.
Distil into 100 ml conical flask and continue distillation until beads of moisture appear
in bend of stillhead. Distillate volume will be approximately 25 ml. Remove flask,
leaving heater on for next determination. Add 10 ml HC1 (1 + 2) and indicator.
Titrate with standard KBr-KBrO3. Major portion of titrant may be added rapidly, but
end point (disappearance of colour) must be approached at ca 1 drop/sec. Let titre =
T1.
Determine reagent blank by titrating 3 separate mixtures of 25 ml isopropyl alcohol,
10 ml HC1 (1 + 2), and indicator without refilling the burette. Total ml titration/3 =
average blank T2.
4. Reporting
Recoverable Oil = (T1 - T2) x 0.1f
------------------- % v/v
Sample size
Where f = factor for KBr - KBrO3 reagent from 0.0247N
eg. when using 0.10N KBr - KBrO3 stock solution f = 1.012
* Use volumetric reagent of 0.1NKBr-BrO3 obtainable from chemical suppliers. If
this is not available, prepare stock solution and standardise as A.O.A.O. Analytical
methods 15 ed. 1990 947.13.
Reference AOAC 15th Ed. 1990 968.20
17 June, 1993
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