[goldy]

How do we know the purity of our compound by 1H NMR?

[AC Prabakar]

Only organic impurities (especially which is having protons) can be quantified(in other words purity of particular compound) by using H1 NMR.
But it is possible to estimate the assay of the given compound also.
To know the methodology to find purity by H1NMR refer some basic books.Even in google also you can find lot of stuff.

[orgopete]

If you weigh and add another pure compound to a weighed sample of the analyte, then you can compare the integrals of the two. If you had an equal molar quantity, then the area of 1H of the standard should result in an equal area to 1H of the analyte (but, normally the ratios are scaled to the actual weights and moles). The difference in area would be due to the presence of impurities. Obviously, the accuracy of the method would depend on the uniqueness of the peaks in question and the absence of absorbing impurities at the same chemical shift.