Application in Petro Industry by MS5000 electron spin resonance spectrometer

Fig. 1 Spectrum of a stable free radical entailing the NO group of a nitroxyl compound (MiniScope MS100: Scan time 60 s, scan 10 mT, 9.4 GHz).

Chemical polymerisation may have a reaction mechanism involving radicals. Well known in the common laboratory practice is the preparation of polyacryl-amide gels for gel electrophoresis. The polymerisation of acrylamide is initiated either by addition of peroxodisulfate or by riboflavin and light. In both cases free radicals are generated which trigger the chain reaction. On the other hand, existing free radicals are able to interfere with or even interrupt such a process by electron pairing. In cases where polymerisation reactions are completely undesired, the addition of stable free radicals may serve as a chemical to inhibit such reactions.

As a consequence, the monitoring of the content of free radicals which may have been added as in-process inhibitors could be a valuable control instrument. The most common stable free radicals used for this purpose are nitroxyl compounds having a very characteristic ESR spectrum entailing three lines when dissolved in a liquid (Fig. 1). Automated evaluation is standard in the ESR evaluation software as well as predefined calibration curves for quantitative ESR measurements. For routine applications ESR autosampler are available for high ESR sample throughput.