Lock solvents

The increased solvent requirements for LC-NMR over tube NMR make the technique expensive if fully deuterated solvents are used. D2O is usually substituted for H2O in the eluent, mainly because of its low cost ( 150 per 1), but also because it provides a lock solvent for the NMR. Fully deuterated organic modifiers such as 3-acetonitrile may not be absolutely required, but in practice they are often also used in many pharmaceutical laboratories as they give reduced solvent signals. This reduces the need for solvent suppression, which lessens the risk that diagnostic resonances are also suppressed in error. 

The goal of this research was to shed further light on the solution chemistry of amic acid and imide materials using F-NMR. Several immediate advantages of this technique were obvious in advance. Studies could be performed in any solvent desired, with no spectral interference from the solvents. Industry has demonstrated a preference for W-methylpyrrolidinone (NMP) as a solvent for PAA and, in the case of soluble Pis, for the final polymer. Utilization of an external lock solvent and fluorinated standards would allow the investigations to be carried out in an uncontaminated NMP setting. 

Use the measured value (in the appropriate lock solvent) in calculating the observation frequency for other nuclides on the lUPAC scale. Best of all, add TMS to the sample of interest (if it s compatible) and record a H NMR spectrum as well. 

An alternative to adding additional reference materials is to use a so-called external reference. Here the spectrum of a separate reference substance is acquired before and/or after the sample of interest and the spectrum reference value carried over. Identical field settings should be used for both which, on some older instruments, requires the same lock solvent, or an additional correction to the spectrum reference frequency must be used to compensate any differences. This restriction does not arise on instruments that use shifting of the lock transmitter frequency to establish the lock condition. 

Sample preparation Benzaldehyde (2.50 mL) was added to a 10mm constricted NMR tube. Tetramethylurea (TMU, 0.30 mL) was used as internal standard and hexaflurobenzene (0.05 mL) as locking solvent. The tube was flame sealed and tlie contents were mixed tlioroughly before analysis. 

Figure 1 -1-11. A H NMR spectrum of the POAC-Z>-PSt micelles after the reaction with benzyl alcohol. Solvent CCU with benzene-Je as the lock solvent and diethyl ether as the standard to estimate the conversion.

Two C-13 NMR experimental parameters were found to be particularly important. One is the temperature, for which the effects have been well illustrated in this report. We have found that 40 C is low enough for neutral solutions of PAm and yet still different enough from room temperature to allow close regulation. The other is the use of lock solvent. If the lock solvent is directly mixed into the solution, proton-deuterium exchange reactions are known to take place that could cause NOE differences. A better way is to use lock solvent in an insert. 

This chapter describes the development of H HR MAS NMR single seed measurements and the analysis will be exemplified in studies of wheat and barley. In order to assign H NMR signals to the various metabolites within the seed, both one-dimensional (ID) and two-dimensional (2D) NMR measurements were performed however, only ID spectra are presented in this chapter. Considerations about spinning rate, temperature and locking solvent are discussed, as these experimental parameters may influence the... 

All other sPP and the catalyst samples were recorded with a Varian VXR-5000 spectrometer. The polymers were 5-10% (w/w) solutions in TCB with dg-benzene added as a lock solvent. C-13 NHR spectra were obtained at 75.43 HHz and 120 C using SCpulse width and a 15 second delay time. Inverse gated decoupling with Waltz modulation was used to suppress NOE s for purposes of quantitation. The LAB ONE curve fitting program from New Methods Research Inc. (NHRi) in New York was used to quantify the SPP rr centered methyl pentads and hexads in the SPP spectra. 

Nuclear Magnetic Resonance (NMR) Spectroscopy. NMR spectra were recorded using a Bruker Aspect 3000, AM-360 MHz spectrometer (Bruker Instruments Inc., Manning Park, Billerica, MA). Si H NMR spectra were obtained with the spectrometer operating at 59.6 MHz and using a 32000 Hz spectral width, a relaxation delay of 15 s, a pulse width of 58 , and 32 K data points. The samples were dissolved in EG. CeDe and tetramethylsilane, in a sealed inner tube, served as lock and reference materials respectively. Al NMR spectra were obtained with the spectrometer operating at 93.8 MHz and using a 41000 Hz spectral width, a relaxation delay of 0.2 s and a pulse width of 13 . The samples were dissolved in EG. D O in a sealed inner tube served as the lock solvent and a IM solution of... 

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