Direct-injection NMR

The authors constructed an 80-well hydrogenator. Fifteen catalysts were screened and the isotopic incorporation assessed by LC/MS. The regiospecificity was determined by VAST Direct Injection NMR [82] in conjunction with SPADEZ [83], a multispectrum analysis tool - this is capable of displaying and quantifying up to 96 spectra. So far it has not been possible to vary the solvents as, under the experimental conditions, the more volatile distil over into the less volatile solvents. 

Different methodologies of flow analysis were developed—FIA-NMR (Flow Injection-NMR), DI-NMR (Direct Injection-NMR) and other hybrid techniques [3]. Each technique obviously has its own set of advantages and disadvantages that need to be evaluated considering the specific problem to solve (Figure 12.2). The analysis of combichem libraries is facilitated if the sample can be employed without any pretreatment (drying to remove protonated solvents and reconstitution in deuterated solvents). This possibility not only reduces the time, cost and effort of sample handling but allows the use... 

Keifer PA, Flow injection analysis NMR (FIA-NMR) a novel flow NMR technique that complements LC-NMR and direct injection NMR (DI-NMR), Magn. Resort. Chem., 41 509-516, 2003. 

Fig. 6. H NMR spectra of a library of compounds from a 96-well microtitre plate acquired by direct-injection NMR. (Reproduced from Keifer6 with permission.)...

Direct-injection NMR (DI-NMR) capitalizes on the small-volume capacity of the flow probe and averts the disadvantages encountered in the... 

Haner RL, Llanos W, Mueller L. Small volume flow probe for automated direct-injection NMR analysis design and performance. J Magn Reson 2000 143 69-78. 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

The aliquots of the solution-state chemical synthesis samples were directly injected into a standard HPLC-NMR probe by using a robotic liquid handler. The NMR software was used to automatically find and suppress the intense NMR signals from any non-deuterated solvents used, typically using the WET sequence [5]. Unlike the characterisation of impurities in organic compounds (see the next section) or drug metabolites (see the appropriate chapter in this volume) where the proportions of the analytes can be very different, combinatorial chemistry samples tend to be all of similar quantity and this simplifies the analysis in that it is not usually necessary to worry overly about carry-over of material from sample to sample, nor it is necessary to readjust the NMR spectrometer receiver gain after every sample, thus saving considerable machine time. 

Figure 10 (A) H NMR spectrum of the trace impurity sample (200 pM atenolol and 200 mM sucrose in 50% TE/D20) from 5-mm probe. The expanded and vertically increased area is shown. Microcoil H NMR spectra shown in (B)-(D) recorded and processed with identical parameters. (B) Static NMR spectrum obtained with direct injection of 25 mM atenolol to the NMR microcoil. S/N of atenolol methyl peak is 21. (C) On-flow cITP-NMR spectrum of atenolol sample band at peak maximum during analysis of the trace impurity sample (200 pM atenolol and 200 mM sucrose in 50% TE/D20). No sucrose peaks can be observed. S/N atenolol methyl peak is 34. (D) Stopped-flow cITP-NMR spectrum of sucrose at peak maximum from the same experiment as in (C). (Adopted with the permission from Ref. 41. Copyright 1998 American Chemical Society.)...

Flow (tubeless) probe that use direct injection (manual or automatic) to deliver sample to the flow cell. Can be directly coupled with FIPLC and MS spectrometer (NMR-HPLC-MS). Is used for 96- or 384-plate analysis in a high throughput mode. 

NMR microscopy is appropriate to study the flow behavior of complex materials, the flow in complex geometric structures and processes such as extrusion, injection moulding, flow in nozzles, pipes, etc., because the velocity vectors can be directly... 

There has been significant advancement in the applications of NMR to the development of small-molecule pharmaceutical products. For example, advances in NMR automation (e.g., flow-injection analysis) and directly coupled methods (e.g., LC-MS-NMR analysis) have made analysis and characterization of small-molecule drugs much easier.23 25 These improvements have helped chemists to develop and characterize small-molecule combinatorial libraries and to screen for active compounds.4 6 It is likely some of these techniques can also be used in biopharmaceutical product development. 

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