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(A) C (B) C
Elution Counts, E [min] Elution Counts, E1 [min]
Figure 15.2 (A) Synchronous and (B) asynchronous correlation maps for stage I,
60-180 s. The solid line indicates positive peaks, and the broken line indicates negative peaks. (Reproduced with permission from Ref. No. 1. Copyright (2002) American Chemical Society.)
2D Correlation Gel Permeation Chromatography
role in the overall reduction in intensity. The signs of the two cross peaks arising from bands E and F are negative, reflecting an increase in population of the precursors II and III present among three monomeric species (PFOTHS, PFODHS and PFOMHS).
In the asynchronous 2D correlation map (Figure 15.2(B)) obtained from the time-resolved GPC profiles in stage I (60-180 s), we find a relatively strong cross peak at coordinate (13.00, 11.52), which correlates elution band A with band C. The signs of both synchronous and asynchronous cross peaks at the same coordinate are positive. Therefore, the variation in intensity of band A occurs before that of band C. This order of events implies that consumption of PFOTHS monomers, produced by the hydrolysis reaction in the earlier step (0-60 s), occurs during this stage (60-180 s) before further hydrolysis reaction of PFOTES. Since the asynchronous correlation between band E or F and band A provides the negative cross peak at coordinates (13.00, 10.84) or (13.00, 10.34), the variation in intensity of band A occurs after that for bands E or F. Therefore, in stage I, consumption of components II and III occurs before that of PFOTHS.
18.104.22.168 Stage II
The 2D correlation spectra for stage II (240-360 s) are shown in Figure 15.3(A) and (B). In the synchronous correlation map (Figure 15.3(A)), new autopeaks and cross peaks appear, in addition to the auto- and cross peaks found in the synchronous map for stage I. The connection of two autopeaks with two cross
Elution Counts, E1 [min]
Elution Counts, E-| [min]
Figure 15.3 (A) Synchronous and (B) asynchronous correlation maps for stage II,
240-360 s. (Reproduced with permission from Ref. No. 1. Copyright (2002) American Chemical Society.)
Extension of 2D Correlation Analysis to Other Fields
peaks provides at least six correlation squares. We may classify these correlation squares into three classes: class 1 (CSq2, CSq3, and CSq4), class 2 (CSq5 and CSq6) and class 3 (CSq7). In class 1, the correlation square CSq2 indicates correlation between bands A and C. Furthermore, two correlation squares (CSq3 and CSq4) in class 1 imply correlation between band A and another band, either E or F. In particular, we note that the signs of the two cross peaks, which constitute the CSq3 and CSq4 squares, are negative, indicating that the intensity of band A decreases while those of bands E and F increase. Class 2 contains two squares, CSq5 and CSq6, which reflect a reduction in intensity of band C and an increase in intensity of bands E or F. The correlation square CSq7, in class 3, reveals that the intensities of bands E and F increase together as a function of sampling time.
The asynchronous 2D correlation spectrum, obtained from the GPC data in stage II, is shown in Figure 15.3(B). When band A on the E1 axis is compared with bands C and D on the E2 axis, the signs of both the asynchronous and synchronous cross peaks are all positive. Therefore, in stage II, the decrease in intensity of band A occurs first followed by a decrease in intensity of bands C and D. For the contour maps constructed from band A on the E1 axis and bands E and F on the E2 axis, the signs of both the synchronous and asynchronous cross peaks are negative. The increase in intensity of bands E and F occurs first and is followed by the reduction in intensity of band A. The correlation of band C with the polymeric components provides at least five positive cross peaks, demonstrating the resolution-enhancing characteristic of the asynchronous correlation map. Band C decreases in intensity as a consequence of hydrolysis, and the decrease is then followed by the variation in intensity of the polymeric component bands. This resolution-enhancement characteristic of 2D GPC analysis provides further details of subtle changes in GPC profiles in terms of the presence of cross peaks at coordinates (11.12, 10.88) and (11.20, 10.24-10.49). The existence of these cross peaks might be considered to imply the existence of another band between bands D and E and its correlation with the polymeric components. However, the former cross peak can be assigned to the correlation peak between the low-elution component (DL) of band D and the high-elution component (EH) of band E, while assignment of the latter cross peak is to correlation between the high-elution component (DH) of band D and the polymeric component (discussed in stage III). Furthermore, splitting of bands E and F also occurs during this stage, thus providing the high- and low-elution bands (coordinates: EH (E1 = 10.92), EL (E1 = 10.76), FH (E1 = 10.44) and FL (E1 = 10.24)).