Study On Accurate Measurement Method Of Total Reflection X-ray Fluorescence Spectrometry

Total reflection X-ray fluorescence?TXRF?spectrometry is a mature and reliable multi-element micro-trace analysis technology developed from X-ray fluorescence?XRF?spectrometry,which has a wide range of applications in the geological,chemical,environmental,pharmaceutical,medical objects,food and other aspects.Compared with the modern analytical techniques of Graphite Furnace Atomic Absorption Spectrometry?GF-AAS?,Inductively Coupled Plasma Optical Emission Spectrometry?ICP-OES?and Inductively Coupled Plasma Optical Mass Spectrometry?ICP-MS?,TXRF can detect the different presentations of the samples,including solutions,suspensions,particles and thin films,which has a great significance for the rapid analysis of the sample.In order to establish an accurate and rapid TXRF analysis method,this paper starts from the sample pretreatment methods?sample being prepared as solution or suspension?.Stream sediments are prepared as the suspension and then being directly analyzed by TXRF.And gasoline sample are also analyzed by TXRF after microwave acid digestion.A TXRF analysis method of trace elements in stream sediments and method of microwave digestion combined with TXRF analysis for gasoline samples are established.The main contents of this paper are as follows:?1?The angle of incidence,the time of measurement and the detecting atmosphere of the sample are analyzed through the single variable method.The optimum parameters of the instrument are as follows:the incident angle of X-ray for Mo target is 0.05°and the incident angle of X-ray for Cu target is 0.1°,the best measurement time is greater than 100 s,the detecting atmosphere of sample is helium.Under this optimum parameter,the maximum measured intensity of the element in the standard sample Multi-STD which is being calibrated the instrument can be obtained,and the light element S can also achieve maximum sensitivity.?2?Compared with the method of microwave digestion,stream sediments being prepared as the suspension and then being directly analyzed by TXRF,has a lot of advantages:it avoids the tedious?laborious and time consuming?sample dissolution procedure and the use of HF;it lowers the risks of contamination,and avoids loss of elements by volatilization.In order to obtain a kind of uniform and stable suspension and better elemental measurement result,the factors are optimized,such as the dispersant type,the mass concentration of the suspension and the particle size of the sample.Using ultrapure water as dispersants,the stream sediments with the particle size ranging from 50?m to 74?m are firstly prepared as aqueous suspensions with the sample mass concentration ranging from 10mg/mL to 20mg/mL,then the aqueous suspensions are dropped and dried on the glass substrate to form thin films followed by TXRF measurements.The recoveries of K,Ti,Mn,Fe,Cu and Zn in the stream sediments are 90%¹10%.This method has the element recovery and measurement accuracy consistent with the microwave digestion combined with the TXRF analysis.?3?Gasoline samples are digested by microwave digestion instrument.In order to make the gasoline sample being digested completely,the acid system,the amount of acid,microwave digestion power,microwave digestion time and pre-digestion are optimized.It is found that pre-digestion is the key factor affecting whether sample is digested completely,and the temperature of pre-digestion and the added amount of acid are the key factors affecting recovery of the volatile element.The best digestion conditions were as follows:pre-digestion is at 130?for 2 h?the amount of HNO₃ and H₂O₂ added are 2.5mL and 0.5mL respectively in pre-digestion processing for each 1 h?and then 5mL HNO₃ and 1mL H₂O₂ being added before it is microwave acid digested for 900W?4 Teflon cans?and 30min.Under the optimum digestion conditions,the measured values of the elements S?Mn?Fe?Cu and Pb in the simulated gasoline are very close to configuration value in the weight method.The spiked recoveries of the elements S?Mn?Fe?Cu and Pb are 90%¹01%.The reproducibility obtained by ICP-OES is good using optimized microwave digestion conditions to treat the gasoline standard material.Based on the detection of stream sediment and gasoline samples,it establishes the method of stream sediment being direct analyzed by TXRF and the method of gasoline samples being analyzed by microwave digestion and TXRF.It shows that these two methods are suitable for TXRF analysis of different present's samples,and it is an accurate and reliable method for analysis of element.