Development And Applications Of Chemical Ionization Time-of-flight Mass Spectrometry For Real-time Detection Of Ammonia And Organic Amines

Ammonia and organic amines have played an increasingly important role in environmental pollution in recent years.As very important alkaline pollutants in the atmosphere and water environment,they can pass through oxidation reactions,salt-forming reactions,water-phase reactions,etc.This pathway changes the chemical composition,reactivity,hygroscopicity,and optical properties of aerosol particles,affecting the formation of secondary organic aerosols and the nucleation rate in the atmosphere.Due to its adsorption properties,large concentration differences,etc.,the development of high-sensitivity,on-line rapid detection of ammonia and organic amines is one of the important directions of air pollution research.In this thesis,the limitations of using radioactive ion sources and the interference of humidity on sensitivity and stability faced by chemical ionization mass spectrometer(CIMS)online analysis of ammonia in the atmosphere are as follows:(1)The traditional 210Po radioactive source was replaced by a vacuum ultraviolet krypton lamp(VUV-Kr),and the protonated acetone reagent ion chemically ionized ammonia gas was obtained under normal pressure.The ionization zone of the instrument was designed as a three-zone structure separated by the acetone protonation zone,the chemical ionization zone and the dilution zone,and dry nitrogen was added to the dilution gas zone to dilute the high-humidity sample to achieve direct analysis of 90%of the high-humidity sample,with a sensitivity of sub-ppbv.Using the ratio of the sample signal intensity to the reagent ion after deducting the background,a signal normalization method based on ratio processing was designed,which reduced the interference of the unstable reagent ion signal and made the quantitative relative standard deviation(RSD)of the instrument from 17.5%.Reduced to 9.1%,the correlation coefficient of the standard curve increased from 0.8340 to 0.9856.The laboratory simulates ammonia gas under different humidity for testing,and calculated the humidity calibration parameters of the instrument.Using these calibration parameters,the ammonia concentration obtained under different humidity was converted into the concentration under zero humidity condition,which was the ammonia gas online under different humidity in the field.Accurate quantitative analysis and instrument comparison test lay the foundation.The analysis time for a single sample was only 60 seconds with a limit of detection(LOD)of 9 pptv(signal-to-noise ratio S/N=3),the linear range was 1-150 ppbv.The technique was applied to the on-line analysis of ammonia in the local atmosphere and detected local ammonia concentrations ranging from 1-130 ppbv.(2)The real-time detection of ammonia using atmospheric pressure chemical ionization mass spectrometry can be used for high-sensitivity analysis of high-humidity samples.The second work of the thesis was to apply it to the detection of organic amines in seawater.Using nitrogen purging bubbling,the trimethylamine in seawater was transformed into the gas phase when the bubbling was broken,and was introduced into the mass spectrometer for analysis by carrying nitrogen gas.The humidity of trimethylamine gas bubbling and purging in seawater was 90%.This experiment referred to the method of detecting high-humidity ammonia gas.The method of adding dry nitrogen to dilute effectively reduced the influence of high humidity on the sensitivity of the instrument.The analysis time for a single sample was 80 seconds with a limit of detection(LOD)of 0.04 μg/L,the linear range was 0.1-10 μg/L.(3)The solubility of dimethylamine is higher than that of trimethylamine,and it is difficult to purge it from water to the gas phase by the purging bubbling method,so it cannot be detected together by the purging bubbling method.In this thesis,the derivatization reaction of sodium hypochlorite and dimethylamine was used to obtain chlorinated dimethylamine.The reaction rate is fast and chlorinated dimethylamine is highly volatile.Then,chlorinated dimethylamine was introduced into O2+chemical ionization online mass spectrometry by nitrogen purge and bubbling for analysis.According to the physical and chemical properties of dimethylamine and chlorodimethylamine,the RF voltage,ionization zone air pressure,water bath temperature,and solution salinity were optimized.The analysis time for a single sample was 120 seconds with a limit of detection(LOD)of 0.07 ng/L,the linear range was 0.025-10 μg/L.