3.5. Quantitative NMR Analysis

The most important fundamental relation of qNMR is the signal response (integrated signal area) I_x in a spectrum that is directly proportional to the number of nuclei N_x generating the corresponding resonance line [27,28]:

K_s is an unknown spectrometer constant, which is a constant for all resonance lines in the same ¹H single-pulse NMR spectrum. Accordingly, the determination of the relative area ratios I_x/I_y is the most efficient way to obtain quantitative results by using Equation (5) when K_s cancels for the ratio:

For the purity determination of a substance, an internal standard with known purity is needed. Based on Equation (5), the component purity can be calculated from the NMR intensity via Equations (6) and (7):

W_x and P_x represent the mass and purity of the analyte. M_x and M_Std are the molar masses of the analyte and the standard (3,4,5-trichloropyridine: 182.44 g/mol). m is the weighed mass of the investigated sample. m_Std and P_Std are the weighed mass and the purity (99.5%) of the standard. N_Std and I_Std correspond to the number of protons for the standard (in this experiment is 2) and the integrated signal area of a typical NMR line (which was 2 in this experiment). N_x and I_x correspond to the number of protons for the analyte ¹H.