FIGURE 2
Response Curve of Irganox 1010 CAD Response
FIGURE 3
Response Curve of Bisphenol A CAD Response
Compounds
Bisphenol A
Dioctyl phthalate
Ultranox
Erucamide
Irgafos 168
Irganox 245
Palmitic acid
Irganox 1076
Irganox 1010
Stearic acid
Summary of Response Curves
TABLE 4
Equation of Quadratic (Second Order) Fit
y = -508x + 56,596x + 6,739
2
y = -323x + 42,735x - 13,423
2
y = -357x + 51,339x + 17,665
2
y = -291x + 77,057x + 4,818
2
y = -312x + 80,592x + 9,717
2
y = -322x + 50,284x + 27,365
2
y = -619x + 39,712x - 117,255
2
y = -457x + 83,398x + 22,715
2
y = -315x + 62,534x + 28,621
2
y = -307x + 68,241x - 144,756
2
R
2
0.9998
0.9989
0.9985
0.9996
0.9980
0.9973
0.9999
0.9989
0.9981
0.9998
elastomer curing process.
The most critical aspect of using a
known surrogate standard to quantitate
unknown extractables and leachables is
that they have similar response factors.
Representative compounds from different
extractables and leachables categories,
such as antioxidants (BHT, Irganox 1010,
Irganox 1076, Irganox 245, Irgafos 168,
Ultranox 626), platicizers
(dioctylphthalate, diethyl phthalate), fatty
acids and related compounds (stearic acid,
palmitic acid, erucamide), monomers and
oligomers (Bisphenol A, caprolactam,
cBT oligomers) were evaluated for their
peak area response relative to Irganox
1010 at 10 ppm. The evaluation includes
three different elution conditions: (1) A
gradient from 25% ACN to 100% ACN;
( 2) Isocratic with 5% water and 95%
acetonitrile; and ( 3) Isocratic with 100%
acetonitrile. Table 2 compares the CAD
relative response factor (RRF) with the
UV RRF for each compound. Figure 1
presents a representative chromatogram.
Some of the relatively volatile
compounds, such as caprolactam, BHT,
and diethyl phthalate, were not detected
with CAD. The reason for this is when
the eluent enters the detector, it is
nebulized with nitrogen, and the resulting
droplets are dried to remove mobile phase
and produce analyte particles. During this
process, relatively volatile compounds are
also evaporated. Although this is a
limitation of CAD, relatively volatile
compounds can be detected and
quantitated with complementary
techniques, such as GC/FID or GC/MS.
The RRFs of all the detected
compounds are within a narrow range,
especially for the isocratic conditions
with RRF %RSD of all compounds at
about 22% and 23%. The variation in
RRF for the gradient condition is greater
than with the isocratic conditions because
of the desolvation differences of the
mobile phase in the detector. Compounds
that elute earlier (when the mobile phase
Drug Delivery Technology March 2009 Vol 9 No 3
