Applications

The name coral comes from the Old Persian sanga (stone), which is the common name for the coral worm community and its skeleton. Coral polyps are corals of the phylum Acanthozoa, with cylindrical bodies, which are also called living rocks because of their porosity and branching growth, which can be inhabited by many microorganisms and fish. Mainly produced in the tropical ocean, such as the South China Sea. The chemical composition of white coral is mainly CaCO₃ and contains organic matter, called carbonate type. Golden, blue, and black coral is composed of keratin, called keratin type. Red coral (including pink, flesh red, rose red, light red to deep red) shell both CaCO₃ and has more keratin. Coral according to the skeletal structure characteristics. Can be divided into plate bed coral, four-shot coral, six-shot coral, and eight-shot coral four categories, modern coral is mostly the latter two categories. Coral is an important carrier to record the marine environment, for the determination of paleoclimatology, ancient sea level change and tectonic movement and other studies have important significance.

Electron paramagnetic resonance (EPR or ESR) is an important tool for studying unpaired electron matter, which works by measuring the energy level jumps of unpaired electrons at specific resonant frequencies in a variable magnetic field. Currently, the main applications of EPR in the coral analysis are marine environmental analysis and dating. For example, the EPR signal of Mn²⁺ in corals is related to paleoclimate. The EPR signal of Mn²⁺ is large during the warm period and decreases sharply when there is a sharp cooling. As a typical marine carbonate rock, corals are affected by natural radiation to produce lattice defects to generate EPR signals, so they can also be used for dating and absolute chronology of marine carbonate rocks. The EPR spectra of corals contain a wealth of information about the concentration of unpaired electrons trapped by lattice and impurity defects in the sample, the mineral and impurity composition of the sample, and therefore information about the age of formation and crystallization conditions of the sample can be obtained simultaneously.

Next, the EPR signal in the coral will be analyzed using a CIQTEK X-Band EPR (ESR) spectroscopy EPR100 to provide information on the composition and defect vacancies in the coral.

CIQTEK X-Band EPR100

Experimental Sample

The sample was taken from white coral in the South China Sea, treated with 0.1 mol/L dilute hydrochloric acid, crushed with a mortar, sieved, dried at 60°C, weighed about 70 mg, and tested on the CIQTEK EPR100.

White Coral Sample

Electron Paramagnetic Resonance Spectroscopy

The CIQTEK EPR100 was used to test the EPR signal in white coral. To achieve accurate measurement of the EPR signal, the specific experimental conditions were as follows.

Experimental Conditions

Experimental Results & Analysis

The structure of corals varies depending on the species, and spectral line overlays are usually present in the EPR spectra of corals. The experimentally measured signals in coral bone samples may be derived from CO₂ - ion free radicals by comparing information from the literature. Mn²⁺ in corals is usually associated with the recrystallization of corals and secondary calcite deposition, while trace amounts of Mn²⁺ also affect the production of paramagnetic centers, so Mn²⁺ is commonly used to discern the recrystallization of samples. The sixfold peak signal of Mn²⁺ was not observed in the experiment.

EPR Spectra of White Corals Detected by CIQTEK EPR100

Conclusions

Coral EPR (ESR) tests are currently used mainly for marine environmental climate analysis and dating. Mn²⁺ in carbonate crystals such as corals is paramagnetic and its six hyperfine structural spectral lines are easily identifiable. EPR tests are mainly for Mn²⁺ on carbonate lattices, and some studies have shown that Mn²⁺ content is related to paleoclimate changes. In addition, because carbonate lattice and impurity defects in corals trap unpaired electrons, and these unpaired electron concentrations can be correlated with natural and annual irradiation dose rates, they are also commonly used for EPR dating in the million-year range.

The CIQTEK EPR100 features high sensitivity, high magnetic field uniformity, and high stability, and can be equipped with a variety of high-performance EPR probes and light, low-temperature, and corner devices to meet customers' needs for a variety of general continuous-wave and pulsed EPR measurements, and the EPR-Pro software provides a fast experimental operation process and scientific data analysis functions to help users quickly establish EPR experimental methods.

References:

1. Strzelczak, Grazyna , et al. "Multifrequency EPR study of carbonate- and sulfate-derived radicals produced by radiation in shells and corallite." Radiation Research 155.4(2001):619- 624.

2. Seletchi, E. D. , and O. G. Duliu . "Comparative study on esr spectra of carbonates." Romanian journal of physics 52.5-7(2007):p.657-666. 

3. Ye Yuguang, Zhou Shiguang, Liu Xinbo. "The ESR Signal of Mn²⁺ in Coral Reefs and Its Paleoclimatic Implications." Ocean and Limnology 000.005(1998):547. 

4. Li Jianping, Diao Shaobo, Liu Chunru, He Xingliang. "Application of ESR dating in marine carbonate dating." Frontiers in Marine Geology 31.010(2015):65-70.