qNMR Standards

qNMR Standards for External and Internal Referencing

Quantitative 1H-NMR (qNMR) continues to be utilized with much success in the pharmaceutical, chemical, and food industries and in many facets of academic research. Regardless of the application, all qNMR methods require a calibration signal whose integrated signal intensity originates or is traceable to a known number of protons. Calibration for qNMR is made using either internal or external referencing methods. External methods rely on the use of a standard solution packaged in a defined NMR tube or capillary to obtain an integral that can be used for sample quantification, whereas internal methods rely on the use of a known amount of standard that is co-dissolved in the sample itself.

Internal Calibration Standards

The internal reference method commonly gives errors of <1% and is considered to be the most accurate and reproducible method available to obtain quantitative 1H-NMR spectra. Unfortunately, the reference standard is typically weighed into each sample solution, an action that requires time and effort, and has been reported as the largest source of error with this method.
Cambridge Isotope Laboratories, Inc. (CIL) is pleased to offer a ready-to-use DMSO-d6 solution containing a known amount of benzoic acid for internal referencing. Because this solution is preformulated, the user does not need to weigh a standard material. The elimination of this step will reduce effort and time in sample preparation and also may bring about more accurate results than if the user performs this formulation. To use this product, the sample must be soluble in DMSO-d6, physically and chemically inert toward benzoic acid, and stable in acidic pH. Ideally, there will be no resonances from the sample in the region of benzoic acid aromatic protons (7.4-8.1 ppm), HOD (~3 ppm but is variable), and DMSO-d5 (2.5 ppm). The benzoic acid concentration with associated uncertainty is presented on the certificate of analysis.

qNMR Standard for Internal Referencing

Catalogue No.DescriptionAmpouleComments
DLM- 9491D5 mM Benzoic acid in DMSO-d61 gThe benzoic acid concentration and associated uncertainty is reported
DLM-7061D15 mM Benzoic acid in DMSO-d61 gThe benzoic acid concentration and associated uncertainty is reported

External Calibration Standards

CIL is pleased to offer external calibration standards for qNMR. The standards are formulated using CIL’s high-quality DMSO-d6 and benzoic acid from NIST (SRM 350(b)), a standard reference material for acidometry. Both 5 mM and 15 mM benzoic acid concentrations are available. The concentration and associated expanded uncertainty of the benzoic acid has been accurately determined using metrological techniques and verified using qNMR. The 1H-NMR spectrum of benzoic acid in DMSO-d6 is presented in Figure 1 (see flyer).

CIL is currently offering these standards in pre-sealed NMR tubes. Please see the information below for details regarding NMR tubes and fill volumes. Other NMR tubes and concentrations may be available upon request.

qNMR Standard for External Referencing

Catalogue No.Description**NMR Tube**      Part No.Volume
DLM-9491A5 mM Benzoic acid in DMSO-d61.7 mm ODBruker part No. Z10646250 μL
DLM-9491B5 mM Benzoic acid in DMSO-d63 mm ODWilmad Part No. 335-PP-9160 μL
DLM-9491C5 mM Benzoic acid in DMSO-d65 mm ODWilmad Part No. 528-PP-8750 μL
DLM-7061A15 mM Benzoic acid in DMSO-d61.7 mm ODBruker Part No. Z10646250 μL
DLM-7061B15 mM Benzoic acid in DMSO-d63 mm ODWilmad Part No. 335-PP-9160 μL
DLM-7061C15 mM Benzoic acid in DMSO-d65 mm ODWilmad Part No. 528-PP-8750 μL

* The benzoic acid concentration and associated uncertainty are reported.
** All tubes are flame-sealed to ensure longevity.

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