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1580
H
aselberger
&
J
acobs
:
J
ournal of
AOAC I
nternational
V
ol
. 99, N
o
. 6, 2016
H
ase berger & Jacobs:
J
urnal of
AOAC I
nternational
V
ol.
99, N
o
. 6, 2016
5
proven adequate for the qualitative determination required
here, including for matrices containing maltodextrins (which
tend to be the most problematic, in particular with respect to
determining presence of GF
3
and/or GF
4
). If necessary, it is
acceptable to modify the Part I separation conditions to optimize
resolution.
(b)
Electrochemical detector parameters.—
This method
utilizes the carbohydrate triple waveform per Table
2016.06F
.
Note
: This waveform is not appropriate for disposable gold
electrodes. The reference electrode is set to AgCl mode.
(c)
Injection.—
Make a single 4 µL injection of each
sample test solution. At the start of each sequence, make six
equilibration injections (one may use laboratory water or extra
standards for the equilibration injections) to ensure that system
is stable, followed by the two retention time standards. Bracket
samples with standards after every six injections. Maintain
autosampler sample compartment at 10°C.
G. Data Interpretation and Assignment of
Commodity Factors (CF)
Using chromatograms from analysis of the RT standards for
reference, determine whether GF
3
, GF
4
, and higher DP fructan
forms (evidenced by peaks after ~36 min) are present in the test
sample(s). Assign commodity factors based on the following
rules:
(1) Presence of either GF
3
and/or GF
4
, but no fructan peaks
after ~36 min
.—CF = 1.233.
(2)
Presence of either GF
3
and/or GF
4
, along with fructan
peaks after ~36 min
.—CF = 1.068.
(3)
Absence of GF
3
and GF
4
and presence of fructan peaks
after ~36 min
.—CF = 0.9526.
Discrete ingredient commodity examples are shown in
Figures
2016.06A–C
. Oligofructose containing materials
derived from the partial hydrolysis of chicory inulin often
display a characteristic peak with significant tailing at ~5 min,
as illustrated in Figure
2016.06B
. If identification of fructan
type is difficult, it may be helpful to also inject a selection of
different commodities for direct comparison.
Part II – Quantitative Determination
of Total Fructan
H. Apparatus and Materials
(a)
LC system.—
One biocompatible gradient pump;
biocompatible refrigerated autosampler capable of injecting
4 μL; electrochemical detector with gold electrode capable of
pulsed amperometric detection. For example, Dionex ICS-3000
or 5000 consisting of an SP, DP, WPS-3000 (TB; P or S type),
and an electrochemical cell with a conventional gold working
electrode and combination pH Ag/AgCl reference electrode or
equivalent.
(b)
Analytical column set
.
—
Analytical column, Thermo
CarboPac PA1, 250 × 4 mm; borate trap (replaces guard
column), Thermo Part No. 047078 or equivalent.
(c)
Analytical balance.—
Readable to 0.01 mg.
(d)
pH meter.—
Readable to ±0.01.
(e)
Water bath, 40°C.—
Maintained at 40 ± 2°C.
(f)
Syringe filter.—
0.45 µm nylon.
(g)
Volumetric flasks.—
Glass, Class A, assorted sizes.
(h)
Volumetric pipets.
—Glass, Class A, assorted sizes.
(i)
Centrifuge tube.—
5 mL plastic (or greater, extra volume
allows for room to neutralize excess reagent).
(j)
Microcentrifuge tubes.—
Assorted sizes.
(k)
Polypropylene beaker.—
100 mL.
(l)
Screw capped vials.—
No metal lined caps.
(m)
Graduated cylinders.—
Glass, assorted sizes.
Table 2016.06F. PAD waveform
Time, s
Potential, V
Integration
0.00
+0.05
0.20
+0.05
Begin
0.40
+0.05
End
0.41
+0.75
0.60
+0.75
0.61
–0.15
1.00
–0.15
Figure 2016.06A. scFOS chromatogram (Part I).
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
22.0
24.0
26.0
28.0
30.0
32.0
34.0
36.0
38.0
40.0
42.0
44.0
46.0
48.0
50.0
52.0
54.0
56.0
58.0
60.0
-5
10
20
30
40
50
60
70
80
90
100
110
125 111815-fructanqual ID #7
FOS
ED_1
nC
min
1 - 2.250
2 -GF3 - 2.650
3 -GF4 - 3.350
4 - 3.600
5 - 4.517
6 - 4.867
7 - 6.417
8 - 42.500
25