Detect Ultra-trace Molecules In Liquid By Means Of Optical Fiber And Spectra

Spectral analysis method like other instrumental methods of estimation has a wide range of content.Not only the analysis of ultrapure material, but also the analysis in environmental science and space science or the analysis of super-trace and remote control, all use the spectral analysis method. There are many spectral analysis methods. Each method has different feature. Because the enlarging of analysis task and analysis object and the complicating of contact samples, there are new demands to spectral analysis method. With the rapid development of Molecule Biology, bioscience, medicine and pharmacology, the study of detecting, identifying and controlling ultra-trace and single biological molecule in water is one of the profound and significant projects. The ultraviolet and visible absorption spectra belong to electron spectra. It is the transition spectra of molecule's outside electron or valence electron (bonding electron, nonbonding electron, anti-bonding electron). Raman spectrum is a effective method, it uses the phenomenon that scatter light's frequency deflect from incident light's frequency to investigate material structure. Resonance Raman spectra technical could enhance the intension of Raman spectrum to 106 times. So resonance Raman spectrum has become one of the most active domain of linear laser Raman spectrum in late years and an important method especially in detecting biological molecule in water. One of this paper introduced is that we researched the forming and equilibrium constant of molecular complex with ultraviolet and visible absorption spectra, the other is we designed the technique of the resonance Raman spectrum in liquid-core optical fiber. We used it to detect the trace biological molecules in liquid. In the first part of this paper what we introduced is to research the forming and equilibrium constant of molecular complex with ultraviolet and visible absorption spectra. The application and pertinent range of molecular complex chemistry is very wide, so chemist had a regard for it at large. Here we investigated pyridine and iodine to form a 1:1 complex Py.I2 in the non-polar solvent heptane. In the experiment we observed as pyridine in increasing but small amounts is added to a dilute solution of iodine in heptane. The color of samples measured go through violet→reddish→yellow→golden brown. Wave form change obviously at 235nm and 422nm. At 235nm the charge transfer band appear; the peak value of uncomplexed iodine at 520nm begins to shift toward shorter wave length 422nm and gradually increase with the pyridine concentration increased. At last we use the values of absorbance of measured samples to work out the equilibrium constant K=230.3250 and the molar absorptivity ε=1015.9 of the molecular complex. In the second part of the paper what we introduced is the technique of the resonance Raman spectrum in liquid-core optical fiber, which is used to detect the trace biological molecules in liquid. Measuring the molecule's vibration spectrum is one of the most important means to explorer molecule structures, interaction and reaction. For many years laser Raman spectroscopy has been an important tool for the investigation of microscopic molecular structure. There is close relation between molecule's inner structure and other information.In this paper we use liquid-core optical fiber (LCOF). When the excited laser light launched into the LCOF, the Raman scattering (forwards and backwards, only the forwards is useful for us) is produced and gradually cumulated with the light transmitting in the fiber. On the other hand, the intensity of excited laser light and Raman scattering light were attenuated by the all sorts of loss factor in LCOF. So the intensity of Raman spectroscopy is the strongest only when the length of LCOF meets a need. The value of this length called the optimum length. It depends on the concentration of sample and the molar absorptivity for the exciting light and for the Raman band. It is noted that when the sample concentration is low enough the absorption loss due to sample is very small. Furthermore, the absorption loss of sample for the exciting light is equal to that of sample for a Raman light. Thus, the total loss coefficient of the optical fiber for exciting light is equal to that for Raman light. It can be computed by a formula, which can give off a conclusion L =1α, it is evident that the optimum length of a liquid core optical fiber is the reciprocal of the total loss coefficient. When the concentration of sample is very low, the total loss coefficient of the optical fiber is mainly due to the structural defects of the optical fiber. It is reported that the Raman spectrum intensity can be enhanced 102~104 times in a liquid core optical fiber. Moreover, the Raman spectrum intensity can be enhanced 106 times using resonance Raman technique. Hence, if the resonance Raman effect is produced in a liquid core optical fiber, the Raman spectrum intensity can be enhanced 108~1010 times. It is very significance for us to study on the molecules'inner structures.We designed the technique of the resonance Raman spectrum in liquid-core optical fiber and use it to detect the trace biological molecules in water, and obtained high intensity, high sensitivity Raman spectrum. In our experiment, we used the hollow-core optical fiber was made of high quality quartz which was produced in Germany and its inner diameter is 200μm, β-carotene was bought from Biosciences Inc, DILOR-OMARS89 Raman spectrometer was produced in France and its sensitivity is 1~2 cm ?1, CCD(LN/CCD-1100-PB/UVAR)produced by PI company was used to incept the signal. We used Ar+ laser for exciting light which wavelengths is 514.5 nm. Because of the high refractive index, lowe fluorescence background and other excellence, we used the pyridine to enhance the refractive index of the solution which we would pour into hollow-core optical fiber. The solution in LCOF is airtight in order to keep its stabilization. We get the Raman spectrum of β-carotene in water phase with the concentration of 10-7~10-8mol/L, and observed the C=C bond π—π* transition (1520cm-1) and C-C bond transition (1155 cm-1) variation with the concentration. And we got several parameters elementarily in optimum conditions. In this paper, we illuminated the classical and quantum theory of Raman scattering spectrum, analyzed experiment results and any other influence factors such as the optimum, bending and loss of the liquid-core optical fiber, the concentrations of the solution etc. In the end we summarized the whole experiment, which would be helpful for us in future experiments. Resonance Raman and absorption spectra should be regard as...