Irradiation, Dosimetry, Oxymetry, Membrane Fluidity

Fig. 1 ESR-spectrum of an irradiated alanine powder sample. (MiniScope MS100: Scan time 11 s, scan 15 mT, 9.4 GHz, modulation amplitude 1 mT)

Structural elucidation studies are a classical field of application for the MS5000 in combination with autosampler. ESR spectroscopy contributes in a different way to many areas such as biophysics wherever radicals may play a chemical role or may be used as labels or probes. Since this spectroscopic method is able to „see“ the unpaired electron, and nothing else, it is an unique way to detect and measure radicals directly. Minimum requirement is the presence of a sufficiently high concentration of radicals, due to the high sensitivity of miniscope 5000 ESR spectrometer reaching down to nanomolar range.

Depending on the specific problem to be solved different methods of measuring radicals are available which are presented with the help of practical examples:

  • Radicals induced by radiation can be detected directly even at reactions speeds down to 2µs due to the high speed kinetic option of the MS5000.

  • Radicals derived from dry alanine powder persist for very long periods this material can be used efficiently for dosimetry.

  • Radical existing only for a short period may be trapped by so-called spin traps. The unpaired electron is preserved for measurement in an adduct compound of the spin trap as a standard application for MS5000 EPR spectrometer

  • Certain radicals stable for a long time period, so-called spin labels, can be used as probes for the fluidity or viscosity of the phase environmental to the unpaired electron.

  • Since the line width in a spectrum of a spin label depends on the content of molecular oxygen within the sample this effect can be used to quantify oxygen (oximetry).

In the absence of water radicals induced by radiation will survive for months, even years. The existence of radicals in dried food (e.g. spices) can proof radiation treatment. Another practical application of measuring radiation induced radicals is alanine dosimetry.

Since radicals are the agents making oils and fats rancid antioxidative substances are of broad interest as protective additives within the food and cosmetic industry. The efficiency of such additives are tested MS5000 EPR spectroscopy after incubation with reactive radicals. Four routine applications combination of ESR spectrometer with autosampler makes it an efficient equipment for high throughput.