Appendix I: Further comments about ρ
The most similar test and reference spectra were those of Viagra 50 mg, which showed a difference of about 1%. Over the range
400–2500 nm, ρm = 0.0122 and δa = 1.21. Because of high-profile similarity above and below 800 nm, the exclusion of 400–800-nm data had essentially no effect
on ρm or δa for Viagra 50 mg. Because of the high-profile similarity above 800 nm for Viagra 100 mg and the modest difference in visual
tablet colors, ρm and δa for Viagra 100 mg were larger when 400–800-nm data were included. Figure 10 shows slight visual-color difference between
test and referenceViagra 100 mg. The TLC results showed a single spot from test and reference Viagra products that agreed
with the TLC results from the sildenafil citrate API.
Figure 10. Photograph of test (left) and reference (right) 100-mg Viagra tablets. The test and reference products were of
slightly different visual color, as reflected in the 400–800-nm range in Figure 9.
The authors acknowledge the assistance of Mary Lego, education manager at Foss NIR Systems, in acquiring the spectra on a
Foss NIRSystems RCA XDS NIR spectrometer.
James E. Polli* is a professor, and Stephen W. Hoag is an associate professor, both at the University of Maryland School of Pharmacy, 20 Penn St., Baltimore, MD 21201, firstname.lastname@example.org
. Polli is also a member of Pharmaceutical Technology's editorial advisory board. Sharon Flank is CEO of InfraTrac.
*To whom all correspondence should be addressed.
Submitted: Oct. 1, 2008. Accepted: Dec. 15, 2008.
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