In the series Distinguishing Impurities, Part 1 pointed to certain signs in which an elucidator can differentiate a signal as pertaining to an impurity and not to the main unknown. Part 1 also made reference to using 2D NMR data as a practical approach to ascertain whether a signal from a 1H NMR was an impurity. With so many choices for 2D NMR experiments, the question is which one(s) will offer the best chance to assist with this method.
The diagram below is a 1H -13C HSQC spectrum related to the 1H NMR spectrum shown in Part 1. Originally flagged as possible impurities based on the 1H NMR data, the singlets at 1.68 and 2.14 ppm show a H-C correlation as do the remaining 1H signals. Based on this example, the HSQC data cannot differentiate any impurities from the main unknown.