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ESR spectroscopy

Researchers: Adriana Paula Popa, Dana Toloman

Keywords: Electron Spin Resonance, ESR , paramagnetic species, transition metals, free radicals

Description

Electron Spin Resonance Spectroscopy (ESR) is an analytical technique for analyzing organic or inorganic materials, the signal being generated by unpaired electronic species. The ESR spectrum is obtained by sweeping a magnetic field while the sample is subjected to a microwave field of given frequency.

The specific ESR parameters are:

  • g-factor – characteristic of the type of paramagnetic ion in the sample,
  • line width – influenced by magnetic and crystalline interactions,
  • signal intensity – due to the concentration of spins in the sample,
  • hyperfine constant – determined by the molecular and local structure of the paramagnetic ion.

Typical systems that can be studied by ESR are:

  1. transition metal and rare earth ions
  2. free radicals
  3. point defects (localized crystal imperfections)

ESR spectra allow the identification of paramagnetic species both qualitatively and quantitatively, provide information on local structure and spin dynamics.

Primary information, such as the identification of paramagnetic species, can be obtained by room temperature measurements in X-band.

Complex information related to the local structure and interactions in the system is obtained by measurements: (i) at varying temperatures (4K-500K); (ii) in multi-frequency and (iii) by applying the magnetic field at different angles to the sample surface.

Depending on the complexity of the system, the interpretation of the results can be immediate or more laborious, requiring the combination of various computational techniques – fits, theoretical simulations of experimental spectra.

 Applications

Areas of application: R&D, optimization of industrial processes/products, biomedical and environmental.

Systems:

  1. nanomaterials, nanocomposites, glasses and ceramics, conducting and semiconducting materials, superconductors
  2. free radicals, organo-metallic compounds and zeolites, polymers
  3. spin markers, antioxidants and contrast agents, free radicals in tissues, oxygen and nitrogen radicals in biological systems; radicals generated in photochemical reactions

Industries: food industry, chemical industry, environment/cleaning, pharmaceutical industry, health-nanomedicine.

 Infrastructure

The ESR spectroscopy laboratory is equipped with a Bruker ELEXSYS E 500 spectrometer dedicated to both solid and liquid samples.

The spectrometer is equipped with two microwave bridges:

  • X-band (9 GHz) and Q-band (35 GHz);
  • an electromagnet generating a maximum field strength of 1 T (X-band) and 1.5 T (Q-band) respectively;
  • goniometer which allows the sample to rotate in the magnetic field;
  • two variable temperature units allowing measurements in the range 4K-300K and 77K-500K respectively.

The following cavities required for different applications are available:

(i) standard cavity operating in the temperature range 4-500K;

(ii) high sensitivity cavity for both solid and liquid samples;

(iii) dual-mode cavity, dedicated to the investigation of forbidden transitions in transition metal and rare earth ions; biradicals and triplets.

Advantages

 INCDTIM offers CDI services based on ESR spectroscopy, used on its own or in combination with other complementary analytical techniques, covering almost the whole range of practical applications

 Before entering into a contractual relationship, we offer consultancy to define the customer/partner’s needs as accurately as possible and, if necessary, we carry out preliminary tests free of charge

 Our existing facilities allow us to address most of the ESR methods used in current practice, many of which are already implemented in our laboratory

 We have specialized staff, able to cover with the highest professionalism all stages of a contractual collaboration: definition of the problem to be solved, experimental design, data collection, interpretation of results and correlation with other complementary information if necessary

Estimated costs

The total cost of R&D services based on RES spectroscopy consists of two components:

spectrometer usage time, which includes consumables and wear. For one measurement at room temperature: 145 lei

 labor, which includes personnel and indirect costs associated with sample preparation operations, analysis and interpretation of results, preparation of the analysis/research report: negotiable, depending on the complexity of the study