Quantitative 13C NMR spectroscopy using refocused constant-time INEPT, Q-INEPT-CT

Quantitative NMR spectroscopy is a useful tool for the analysis of various mixtures. Usually 1H NMR is used for quantitative measurements, but in many cases the better signal dispersion offered by 13C NMR is beneficial. However, the low natural abundance of 13C and long T1 relaxation times make the acquisition of quantitative 13C spectra with adequate signal-to-noise ratio time-consuming. The use of polarization transfer experiments such as DEPT or INEPT can offer improved signal intensity and faster repetition rate, but yield non-quantitative results. In this paper we present a pulse sequence based on constant-time INEPT, Q-INEPT-CT, which is capable of producing quantitative carbon spectra with better sensitivity and/or in less time than traditional quantitative 13C. Additionally, the constant length of the sequence means that signal loss due to relaxation effects can be relatively easily corrected. Thus, the presented sequence is a valuable tool when quantitative carbon data is required quickly and/or low-concentration samples are involved.