Survey and qualification of internal standards for quantification by 1H NMR spectroscopy

Study of Karstedt's Catalyst for Hydrosilylation of a Wide Variety of Functionalized Alkenes with Triethoxysilane and Trimethoxysilane

“…The purity P x which stands for the yield was calculated for each isomer and the ratio of γ-to β-isomers was correspondingly determined. In the work, 2,4,6-trichloronitrobenzene was used as the internal standard from 1 H NMR spectrum with the 1 H chemical shift at δ 7.46 (t, 2H), [18] the 1 H chemical shift of Si-CH 2 at δ 0.45-0.65 (m, 2H) was chosen as the characteristic peak of γ-isomer, the 1 H chemical shift of Si-CH-CH 3 at δ 0.90-1.05 (m, 3H) was chosen as the characteristic peak of β-isomer. [19] As can be seen from Table 1, the yields of the hydrosilylation of the aminated alkenes with trimethoxysilane and triethoxysilane using Karstedt's catalyst were higher than 90%.…”

Quantitative NMR spectroscopy of biologically active substances and excipients

“…A study of the Swedish medical products agency pointed out, that after 3 years storage in a dry environment and in their original containers with tightly closed caps lower contents of frequently used reference substances were obtained than at the time of delivery [39]; thus, it is necessary to verify the purity of these compounds in routine work on a regular basis.…”

“…Internal standard substances According to many papers a suitable internal standard should meet the following criteria: (1) readily available in a highly pure form, (2) inexpensive, (3) stable and chemical inert, (4) nonvolatile and nonhygroscopic, (5) soluble in most of the NMR solvents, (6) simple 1 H NMR spectra are preferred, (7) easily weighable, and (8) optimal molecular weight [32,34,39]; the spin-lattice relaxation time is usually disregarded, even though the measurement time of a 1 H NMR experiment depends on the longest T 1 relaxation time of resonances of interest. In order to avoid distortion of integrated signal intensity due to relaxation effects, it is essential to delay the application of the next pulse by five times the longest T 1 relaxation time (90°pulse) to ensure full relaxation of the excited nuclei (99.3% of the equilibrium magnetization is measured after 5×T 1 [41]).…”

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“…A combination of LC-QTOF-MS and NMR was proven to be very effective when screening for adulterants in pharmaceutical tablets and capsules, herbal food supplements, ointments, and creams. The procedure was made easiest when LC-QTOF-MS only generated one peak, the MS spectrum generated only one hit in the database search, LC retention time with a reference compound and/or UV spectrum confirmed the hit, and identification was made with MS. NMR can readily confirm the identity and can be followed up with quantitative determination of the adulterant content in the product by qNMR [86,87]. However, this was not the case most of the time and other routes had to be taken in order to identify the adulterants.…”