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Optimising the experimental parameters

The nature of the NMR lineshape means that to integrate a peak accurately the integral width either side of peak must be substantial - approximately 300 times the peak width in both directions to obtain 99.9% of the tme area. This kind of integral width is usually impractical and the only way that quantitative NMR produces acceptable results is that the errors on each peak cancel each other out. However, integral widths large enough to provide meaningful results will [Pg.141]

Baseline and phase correction are also important factors in determining the accuracy of the NMR result - it is usually the case that these have to be done manually to obtain best results. It is also quite likely that different operators will perform these functions differently and this may be a cause of reproducibility problems (see Section 4.4.5 below). A recent paper [199], though not aimed at quantitation directly, has a useful discussion of the difficulties of obtaining precise integrals, particularly with respect to the phasing of signals. [Pg.142]

Lastly, the assignment of the spectrum should indicate some protons which should not be used for quantitation - those labile NH and OH protons which are exchange broadened and therefore more difficult to integrate accurately, but which may also partially deuterate in solvents such as D2O or CD3OD. Keto-enol tautomerism may also cause exchange for aliphatic protons beta to a carbonyl group, for example, and some aromatic protons may also be surprisingly labile, as shown in Fig. 4.10. [Pg.142]

All the considerations above apply especially to assay by NMR, that is, strength determinations, usually using a well-characterised internal standard. Minimisation of errors leads to strength precision of 1% [196]. Other literature too demonstrates that good precision can be obtained. For example, the fluoroquinolones pefloxacin, norfloxacin, ofloxacin have been assayed by both and F NMR in commercial preparations [201] with good recoveries for [Pg.142]


Method development in CE involves optimising the experimental parameters such as pH, organic modifiers, surfactant additives, ion-pair reagents, cyclo-dextrins, polymer additives, complexation agents and combinations of these additives. The use of pH is a very powerful tool for manipulating and influencing... [Pg.55]

Liu et al combined LIBS and a neuro-genetic method to analyse heavy metals (Cr, Pb, Cu, Ni, Cd and Zn) in soils. The neuro-genetic method was applied to optimise the experimental parameters of the LIMS in order to maximise the signal-to-background ratio for all heavy metals simultaneously. [Pg.405]


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