NMR Solvents and Consumables

Standards for qNMR

The Production and Use of a NIST-Traceable Standard Solution for Quantitative NMR Applications

Kris Dziewiszek1, Kevin Millis1*, Joe Ray2, Tim Eckersley1
1. Cambridge Isotope Laboratories, Inc., Tewksbury, MA USA
2. Baxter Healthcare Corporation, Round Lake, IL USA
 

  • The Production and Use of a NIST-Traceable Standard Solution for Quantitative NMR Applications
  • qNMR Reference 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.

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.
 
CIL is currently offering these standards in presealed 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
Catalog No. Description** NMR Tube**       Part No. Volume
DLM-9491A 5 mM Benzoic acid in DMSO-d6 1.7 mm O.D. Bruker part No. Z106462 50 μL              
DLM-9491B 5 mM Benzoic acid in DMSO-d6 3 mm O.D. Wilmad Part No. 335-PP-9 160 μL
DLM-9491C 5 mM Benzoic acid in DMSO-d6 5 mm O.D. Wilmad Part No. 528-PP-8 750 μL
DLM-7061A 15 mM Benzoic acid in DMSO-d6 1.7 mm O.D. Bruker Part No. Z106462 50 μL
DLM-7061B 15 mM Benzoic acid in DMSO-d6 3 mm O.D. Wilmad Part No. 335-PP-9 160 μL
DLM-7061C 15 mM Benzoic acid in DMSO-d6 5 mm O.D. Wilmad Part No. 528-PP-8 750 μL

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

 

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 to the largest source of error with this method.
 
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
Catalog No.     Description Ampoule      Comments 
DLM- 9491D 5 mM Benzoic acid in DMSO-d6                                    1 g The benzoic acid concentration and associated uncertaintly is reported 
DLM-7061D 15 mM Benzoic acid in DMSO-d6 1 g             The benzoic axid concentration and associated uncertaintly is reported