Radiometric methods layer

The adsorption of ions and the formation of the electric double layer at water/oxide interface are the physical phenomena the importance of which in life and technology can hardly be overestimated. So, no surprise that the mechanism of the formation of the electric double layer at water/oxide interfaces has been studied thoroughly in hundreds of papers and it would take far too long to review even the most fundamental of them. Various techniques have been used to measure proton and accompanying ion adsorption on the outermost surface oxygens of oxides. The most popular of these techniques are potentiometric titration and (-potential measurements. Then, radiometric methods allow the adsorption of individual ions to be monitored. 

Chemical test reagents can be applied also to thin-layer chromatograms which contain radioactive substances. In addition, various procedures for detection and quantitative determination of labelled compounds can be employed. Both chemical and radiometric methods of detection should always be used on the same thin-layer chromatogram this yields information about both the chemical and radiochemical purity of the sample studied. 

Measurement of labelling yield and subsequent radiochemical purity requires a suitable analytical technique, and the method of choice for radio-labelled peptides is reversed phase HPLC with on-line UV and radiometric detection. It is important to use as stringent a separation method as possible with isocratic or slow mobile phase composition gradients over the peptide peak. Ideally, more than one mobile phase system should be used (e.g. a phosphate buffer-methanol system in addition to the standard water-acetonitrile system), since these may show the presence of new impurities. It is important to recognize that HPLC analyses only measure those components that elute from the column. Insoluble, highly lipophilic or positively charged species may bind to the solid phase. It is very important to verify the absence of these species by a complimentary technique such as thin layer chromatography (TLC) and to ensure that the two techniques produce similar results. 

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