Solution 6.5 - Chemometrics: Data Analysis for the Laboratory and Chemical Plant

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  • Published: Jan 1, 2000
  • Channels: Chemometrics & Informatics

The scores and loadings are as follows.

2. The graph is given below, there is no special significance to the scales.

The two graphs follow very similar trends suggesting that the first PC mainly measures magnitude. This is entirely typical for uncentred data.

3. The graph is given below.

It appears that there is one species at low pH below 2.24, with pure spectra at the first two points in the titration, another between pH 5.40 and 8.51 (remember that each correlation is between two successive points) and a third one above pH 10.57. It is possible, but unlikely, that there is a fourth component at low pH, the correlation coefficients will be very susceptible to noise when the spectra change with pH.

4. The graphs are as follows.

PC 2 v 1

PC3 v 1

PC3 v 2

The region between pH 4.77 and 8.12 is clearly featured in the last two graphs and corresponds primarily to the pure region for the middle eluting compound, or the plateau in the correlation curve. The PC2 v 1 graph suggests that the spectrum at pH 6.25 is the extreme point in the plot, and so corresponds best to the pure compound. This corresponds quite closely to the correlation plot where the highest correlation coefficient is between spectra at pH 6.49 and 6.85. Because of noise it is not possible to obtain an correspondence. Notice that the last two PC plots curl round at pH 11.27 which might suggest that this rather than the final pH is the best for the species formed under basic conditions, noise of other species taking over at very high pH values.

5. The graph is as follows

The points must fall on a circle of radius 1, as they are normalised to constant sum of squares of 1. The points due to each pure component cluster together.

6. There is no completely correct answer, but pHs 2.15, 6.25 and 11.27 are good choices given the discussion above. The spectra are presented below.

Although the spectra are not very different there are some significant peak shifts.

7. The pH profiles are given below.

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