qNMR has been attracting considerable attention across a broad spectrum of chemical analytical laboratories, as it provides accurate quantitative information without the requirement of reference compounds or predetermined response factors for every analyte.
NMR spectra provide various types of information, usually focused on the identification of the compounds contained in a sample; however, it’s well-known that quantitative data can also be obtained.
There are in fact two types of quantitative analysis in NMR:
In the relative quantitation method, the NMR signal intensities are expressed as shown in Equation 1. The purity of the target sample can then be calculated using Equation 2 as long as the sample is correctly prepared* with an internal standard material of known purity.
Fig.1 shows a 1H NMR spectrum of diethyl phthalate (DEP) with bistrimethylsilyl benzene (1,4-BTMSB-d4 ) as an internal standard. The standard used should yield an NMR signal that will not overlap with the target signals and also has a known purity. 1,4- BTMSB-d4 with SI-traceability from Wako Pure Chemical Industries, Ltd. was chosen.
Fig.1 1H NMR spectrum of DEP and 1,4-BTMSB-d4 (Spectrometer: JNM-ECS400)
Note: *Weighing is necessary for proper sample preparation.