Research On Optofluidic Laser For The Detection Of Dissolved Oxygen

The concentration of dissolved oxygen in water is an important technical index to measure the self-purification ability of water body and evaluate the condition of water body.It is of great significance for water source protection,production and manufacturing,fishery and aquaculture,scientific experiments and other aspects.Existing methods for the detection of dissolved oxygen all have some problems.The reading of sodium thiosulfate in iodometric method is easy to produce error in the titration process,and the end point is easy to judge wrong.The electrode of dissolved oxygen meter needs to often replace the electrolyte and breathable film.Spectrophotometry requires dilution to make measurements.Optofluidic laser combines optofluidics and laser technology,which has the characteristics of less reagents,high sensitivity and low detection limit.Based on the optofluidic laser technology to detect the concentration of dissolved oxygen,this thesis mainly carried out the following work:(1)The existing methods for the detection of dissolved oxygen and the development status of optofluidic laser technology were investigated.A method for detecting dissolved oxygen by optofluidic laser was designed,and a laser spectrum detecting device with Fabry-Perot cavity(F-P cavity)as the laser resonator was built.The detection principle was analyzed,which laid a foundation for the subsequent experiments.(2)Under the action of sodium tripolyphosphate,ferrous ion and dissolved oxygen will react to generate an oxygen-activated molecule hydroxyl radical(OH),then the reaction of hydroxyl radical with rhodamine B will result in the decrease of laser intensity.Based on this,a method was designed to detect the concentration of dissolved oxygen using the laser spectrum generated by the system of ferric divalent ion(Fe²⁺)-sodium tripolyphosphate(STPP)-rhodamine B(RhB).The linear range of dissolved oxygen detection is 0-14mg/L.The effects of reaction reagents including rhodamine B,sodium tripolyphosphate and ammonium ferrous sulfate on the detection performance were studied.Reaction time and p H value were also stydied.Under the optimized experimental conditions,the dynamic range could reach 0-28mg/L.The repeatability and stability of the experimental device were further optimized and verified.The effects of environmental factors including salinity and temperature were analyzed,and the methods to reduce these effects were discussed.(3)Iodine reacts with dissolved oxygen to generate iodine trianion,and iodine trianion combines with rhodamine B to generate(RhB-I₃)_n,resulting in the decrease of laser light intensity.Based on this,a method was designed to detect the concentration of dissolved oxygen using the laser spectrum generated by the system of iodine(I₂)-potassium iodate(KIO₃)-rhodamine B(RhB).The effects of reaction time and reagents including manganese sulfate,potassium iodide,sulfuric acid and rhodamine B were studied.Under the optimized experimental conditions,the detection limit of dissolved oxygen can reach 0.0002mg/L.The influence of interference ions in water was analyzed and it was found that the influence of common ions in water could be ignored.The experimental principle was further verified,and the influence of the formation of(RhB-I₃)_n on the experiment was analyzed.