Carbon detection

DEPT (distortionless enhancement by polarization transfer) A onedimensional C-NMR experiment commonly used for spectral editing that allows us to distinguish between CH, CH2, CH, and quaternary carbons. Detectable magnetization The magnetization processing in the x y -plane induces a signal in the receiver coil that is detected. Only single-quantum coherence is directly detectable. 

Carbon formation/deposition is a difficult deactivation mechanism to characterize on cobalt-based FTS catalysts. This is due to the low quantities of carbon that are responsible for the deactivation (<0.5 m%) coupled with the presence of wax that is produced during FTS. Furthermore, carbon is only detrimental to the FT performance if it is bound irreversibly to an active site or interacts electronically with it. Hence, not all carbon detected will be responsible for deactivation, especially if the carbon is located on the support. 

To continue the investigation, carbon detected proton T relaxation data were also collected and were used to calculate proton T relaxation times. Similarly, 19F T measurements were also made. The calculated relaxation values are shown above each peak of interest in Fig. 10.25. A substantial difference is evident in the proton T relaxation times across the API peaks in both carbon spectra. Due to spin diffusion, the protons can exchange their signals with each other even when separated by as much as tens of nanometers. Since a potential API-excipient interaction would act on the molecular scale, spin diffusion occurs between the API and excipient molecules, and the protons therefore show a single, uniform relaxation time regardless of whether they are on the API or the excipients. On the other hand, in the case of a physical mixture, the molecules of API and excipients are well separated spatially, and so no bulk spin diffusion can occur. Two unique proton relaxation rates are then expected, one for the API and another for the excipients. This is evident in the carbon spectrum of the physical mixture shown on the bottom of Fig. 10.25. Comparing this reference to the relaxation data for the formulation, it is readily apparent that the formulation exhibits essentially one proton T1 relaxation time across the carbon spectrum. This therefore demonstrates that there is indeed an interaction between the drug substance and the excipients in the formulation. 

Fabbrizzi L, Leone A, Taglietti A (2001) A chemosensing ensemble for selective carbonate detection in water based on metal-ligand interactions. Angew Chem Int Ed 40 3066-3069... 

With the use of cryogenic probes, carbon detection becomes possible in protein NMR experiments [23]. This may be required for perdeuterated proteins or when signal loss in INEPT transfer steps becomes prohibitively large. 

C ZDDP + polyisobutylene succinimide dispersant + calcium carbonate-phenate [Ca] = 4220 ppm Low-molecular weight phosphates, short chain ortho- and pyro-phosphates ( 50% of zinc replaced by calcium in phosphate film some carbonates detected in tribofilm)... 

Subsequently, Uhrinova et al.29 reconsidered the problem using both proton-and carbon-detected experiments. For example, couplings of anomeric carbons were measured from the 13C satellites in proton NMR spectra. The critical factor in these methods is the suppression of signals from protons bound to, 2C atoms. In the pulse-sequence proposed, these protons were selectively inverted by a BIRD (Bilinear Rotation Decoupling) pulse,30 and the spin-echo method introduced by Bendall et al.31 was used. 

Solvent-soluble organics Extraction and carbon detection differential thermal analysis... 

There is a carbon detected analogue of the HMBC experiment called COLOC (Correlated spectroscopy for Long range Couplings) that predated the experiment treated here. The COLOC is not used much any more and we will not give any examples. 

Figure 2 2D C-"B correlation [13] of l,7-dicarba-c/o50-dodecaborane(12) with carbon detection using the polarization transfer experiment. A non-degassed, saturated solution in CDC was used. Relaxation time 3 s measurement time 10 h...

Figure 5 C- Te correlation spectrum of the compoimd shown, a degassed and sealed saturated solution in tetrahydrofuran-c, using a relaxation time of 3 s. The polarization method under carbon detection was used the evolution time was adjusted to 300 Hz total measurement time 14 h...

Gloor, R., Leidner, H., Wuhrmann, K., and Fleischmann, T. H. (1981). Exclusion chromatography with carbon detection. A tool for further characterization of dissolved organic carbon. Water Res. 15, 457-462. 

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