Figure 3: Raw diffuse transmission spectra of calibration tablets.
Twelve batches of tablets that are 0.25 in. in diameter with a nominal weight of100 mg were formulated with a label claim
of 10.0 mg phenylephrine hydrochloride (PE–HCl) and 4.0 mg chlorpheniramine maleate (CPM). The CPM and PE–HCl were varied
by ± 20% of this label claim in a fractional factorial design of experiments (DOE). The lactose excipient was varied to maintain
constant weight (see Table I). The tablets were compressed on a rotary tablet press (HT-AP 18 SS-U/I, Elizabeth Hata International)
at the University of Tennessee's Pharmaceutical Sciences Department, the Memphis College of Pharmacy.
Figure 4: Second derivative math pretreatment of calibration spectra.
NIR method. The NIR instrument used in the study was an XDS MasterLab (FOSS NIRSystems). This instrument was used in the diffuse-transmission
mode and sequentially measured multiple tablets positioned in a custom tray specifically designed for the tablets under test
(see Figure 1). The tray was machined for 0.25-in. diameter tablets with +0.004-in. oversize tolerance for ease of fit and
tablet placement without allowing stray light to pass around the tablet. Stray light is spectral energy that does not interact
with the sample and therefore dilutes absorbance and reduces the sensitivity and linearity of the measurements. The MasterLab
uses a standard indium–gallium–arsenide detector that has a dynamic range of more than 5.0 absorbance units. This absorbance
range is required for measuring in the transmission mode through solid dosage forms. Maintaining low stray light is most important
at these high absorbance levels (i.e., low light levels).
Figure 5: Predicted residual error sum of squares (PRESS) plot of partial least squares factors used to predict chlorpheniramine
maleate concentration with seven factors.
The tray used for this study had 31 tablet positions and was loaded to scan 10 tablets from each batch. The 10 tablets were
scanned in less than 3 min., taking a reference spectrum before scanning each batch. Spectra were collected from 800 nm to
1650 nm with 0.5-nm data intervals. Thirty-two spectral scans of each tablet were coadded to produce a single spectrum to
enhance the signal-to-noise ratio.
Figure 6: Partial least squares loadings that indicate where chlorpheniramine maleate is highly correlated with spectral data.
The structure of chlorpheniramine is superimposed.
HPLC method. HPLC analysis of the same tablets measured by NIR was performed at the University of Tennessee Pharmaceutical Sciences Department
in the Memphis College of Pharmacy laboratory. The HPLC system was a Shimadzu vp series provided with an LC-10AD vp pump,
an automatic injector SIL-10AD vp, an SPD-M10A vp diode array detector, and a DGU-14A degasser. The chromatographic analysis
was performed on a 5-µm particle Luna C18 column (150 × 4.6 mm) (Phenomenex) kept in a CTO-10A vp column oven (Shimadzu) at
35 °C. Final chromatographic condition was an isocratic elution, and the mobile phase was methanol: acetonitrile: tri ethyl
amine: 0.4 % sodium lauryl sulphate in the ratio of 350:300:1.5:350.
Figure 7: Calibration set. CPM is chlorpheniramine maleate, HPLC is high-performance liquid chromatography, and NIR is near
infrared. R2 = 0.9811, Standard error of calibration = 0.0739 mg, Standard error of cross validation = 0.0901 mg.
The mobile phase pH was adjusted to 3.8 with o-phosphoric acid. The flow rate was 1 mL/min, and the injection volume was 20
µl. Absorbance was measured at 215 nm, the wavelength of highest sensitivity for both phenylephrine and chlorpheniramine.
Individual tablets were sonicated in methanol and with the mobile phase. The suspension was filtered using 0.22-µm PTFE syringe
filters. The samples were diluted with the mobile phase before being injected on to chromatography. The Shimadzu CLASS-VP
software was used for analysis. Figure 2 is a representative chromatogram.