Extraction Efficiency Evaluation In order to validate the use of acetonitrile in place of the pyridine in the extraction system for disperse dyes, an efficiency evaluation was performed. The relative efficiency of the acetonitrile versus pyridine was determined by integrating the peaks over a selected wavelength range. A ratio of the area under the curve for the acetonitrile divided by that for the pyridine was calculated. One dye, C.I. Disperse Blue 60, showed anomalous variability in the calculated ratios, the cause of which was unknown. To address this anomaly, all extractions were considered individually and a range was calculated in order to compare the extraction systems. Each dye standard was extracted with both solvents and ratios of each combination were calculated (see Table 3). TABLE 3—Efficiency of relative extraction calculated from the spectrophotometer.Sample acn1/pyr1 acn1/pyr2 acn2/pyr1 acn2/pyr2 Range DY42 1.00 1.18 0.90 1.06 0.90–1.18 DB60 0.94 1.03 0.77 0.85 0.77–1.03 DO25 1.12 1.09 1.07 1.05 1.05–1.12 acn1, first acetonitrile extract; acn2, second acetonitrile extract; pyr1, first pyridine extract; pyr2, second pyridine extract. From Table 3, it can be seen that the disperse dyes, C.I. Disperse Yellow 42, C.I. Disperse Blue 60, and C.I. Disperse Orange 25, had a comparable extraction whether acetonitrile or pyridine was used. C.I. Disperse Blue 60 showed different absorbance peak shapes depending on the extraction solvent. These differences may be because of solute–solvent interactions such as hydrogen bonding and Van der Waals forces between a highly polar dye and the polar solvent. There were no shifts in λmax or peak shapes for the other disperse dyes. Although the peak shape for Blue 60 changed, the wavelength range selected for integration continued to describe the absorbance. Thus, the area under the curve could still be used for calculations. The result, an average ratio of 1.01, demonstrates that the acetonitrile system is as efficient at removing the disperse dyes from polyester as the pyridine system. The relative extraction efficiency of pyridine to acetonitrile was also evaluated using the DAD. Calculations were performed in a similar manner, using the area under the curve and calculating a ratio for the acetonitrile response versus the pyridine response. The diode array for the LC/MS showed an extraction efficiency of c. 62% (see Table 4). Again, this result demonstrates that acetonitrile is an appropriate substitute for pyridine in the extraction system.
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