1.0 OBJECTIVE
To provide the procedure for the Chromatographic Peak Purity interpretation
2.0 SCOPE
This procedure is Applicable to the Chromatographic Peak Purity interpretation
3.0 RESPONSIBILITY
3.1 QC-Chemist
4.0 ACCOUNTABILITY
4.1 Executive – Quality
control
4.2 Head – Quality
control
5.0 PROCEDURE
5.2 UV spectra are taken at various points across a chromatographic peak and compared. If the spectra are sufficiently alike, the peak is considered pure; if the differences in spectra are large enough, the peak is not pure.
5.3 With some peak-purity outputs, all you get is an indication of the peak purity, sometimes called a match angle or purity angle.
5.4 With sophisticated peak-deconvolution
software, the peaks can be measured separately, in much the same manner as an
LC-MS detector can distinguish between two co-eluting peaks of different
molecular weights.
5.5 Peak purity analysis must be performed for both Drug substance as well as for
Impurities. Both must pass the test.
5.6 For Empower 3 /2
5.61 When an impurity is
detected, the purity plot rises above the threshold line. This indicates
spectral differences beyond noise contributions and implies the presence of
more than one compound in the chromatographic peak. In the example below, the
coeluting impurity is in the leading edge of the peak.
5.6.2 The above figure is the peak purity plot for a chemically pure chromatographic peak. Notice there are no valleys or shoulders on the peak. The thick solid line represents the spectral differences across the peak. The reference point is the apex spectrum. Most of the spectra in the peak are close to zero difference, which is characteristic with a pure compound. At low absorbances the baseline noise contributes to spectral differences
5.6.3 The purity of the entire peak is determined by the purity angle and the threshold angle.
5.6.4 Purity angle:
The average value of the
angle between each spectrum of the peak and the spectrum at the top of the
peak. In other words, the purity of the entire peak can be determined by this
value.
・
If <0.2
The detection limit of
this method is about 0.1 to 0.2. Therefore, it can be concluded that the peak
for which the purity values below 0.2 consists of almost the same spectral
components.
The measurement
precision of this is better than the visual check (up to 1 angle).
・If
> 1
Although there are
differences in shape that can be observed by the visual check, the purity angle
alone does not mean that components with other spectra have co-eluted.
This is because other than the co-elution of other components, the noise included in the spectra can also cause the differences. This should be noted especially with low-concentration components.
・If purity angle < purity threshold angle
If the purity angle is
larger than the threshold angle indicating the shape differences of the spectra
caused by noise, there is a spectra difference exceeding the effect of noise.
It is highly likely that components with different spectra are co-eluting.
6.0 ANNEXURES
Nil
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