Study On The Methodology Of The Speciation Of Vanadium Based On HPLC

Vanadium has excellent physical and chemical properties,which is widely used in chemical industry,metallurgy and materials.Vanadium also exists in plants and animals,which is a necessary trace element for life.The speciation of vanadium can accurately obtain the content and distribution of vanadium in industry and biology,which is of great significance to the research of industrial development,environmental protection,geochemistry and so on.At present,the quantitative analysis of vanadium is mainly on the total vanadium content,however,there is little research on the simultaneous separation and determination of different vanadium speciation.Therefore,it is really necessary to establish an accurate,sensitive and widely applicable vanadium speciation analysis method.HPLC is a commonly used specitiation analysis method,which has the advantages of easy operation and wild application,and its detection limit can meet the requirements of general samples.Since the HPLC method requires the sample to have ultraviolet absorption,the V(III)-EDTA,V(IV)-EDTA,and V(V)-EDTA complexes were used as research objects to study the stability constants and stereo structure.The results proved the feasibility of speciation analysis of vanadium by determination their chelates with HPLC.Then the HPLC analysis methods of V(III),V(IV)and V(V)were optimized,and an analytical method was established to determine these three forms of vanadium.This method has been applied to analyze metallurgical industry samples and natural environment samples,and good results have been obtained.The main results in this paper are as follows:(1)Calculated by the equimolar continuous change method:the complex ratio of V(IV)-EDTA is 1:1,the stability constant of V(IV)-EDTA is log K_V(IV)-EDTA=7.03±0.14,the complex ratio of V(V)-EDTA is 1:1,the stability constant of V(V)-EDTA is log KV(V)-EDTA=5.47±0.25.(2)Single-component samples were detected by ESI-MS mass spectrometry,and the results proved that V(III)-EDTA,V(IV)-EDTA,and V(V)-EDTA complexes can exist stably in aqueous solutions,and the existing forms are[V(EDTA)]^-,[VO(EDTA)]^2-and[VO₂(EDTA)]^3-.Two-component sample was detected by ESI-MS mass spectrometry,and the results showed that in the aqueous solution:V(III)-EDTA and V(IV)-EDTA can coexist stably;V(IV)-EDTA and V(V)-EDTA can coexist stably;V(III)-EDTA and V(V)-EDTA do not coexist,and will react to form V(IV)-EDTA.(3)Through XPS spectrum,Raman spectrum,CD spectrum,⁵¹V NMR spectrum,it was proved that the most stable molecular structure of the V(IV)-EDTA complex is composed of three 5-membered rings,in which the central atom V form a bond with two O atoms and two N atoms from the ligand EDTA;the most stable molecular structure of the V(V)-EDTA complex consists of an 8-membered ring,with the central atom V bonding to 2 oxygen atoms from the ligand EDTA,however,the central atom vanadium not boding to nitrogen atoms from EDTA.(4)A new HPLC method was developed for the speciation of V(III),V(IV)and V(V)in solution.Key conditions of LC were optimized:reverse-ion-pair chromatography mode;Inert Sustain AQ-C18 column;isocratic elution mode;injection volume was 10?L;flow rate was 1.2 m L/min;The detection wavelength is 261 nm.The optimal mobile phase composition was determined:phosphate buffer(20 m M,p H 6)containing 4 m M EDTA and 5 m M TBAOH,the organic phase was acetonitrile,and the ratio of the water phase to the organic phase was 88:12.Under the above experimental conditions,the detection limit of V(III)is 0.042 mg/L;the detection limit of V(IV)is0.070 mg/L;the detection limit of V(V)is 0.059 mg/L.The correlation coefficients were all greater than 0.9999,and the RSDs met the requirements.Through the stability test,it was proved that the V(III)-EDTA,V(IV)-EDTA,and V(V)-EDTA complexes can be kept stable in the aqueous solution,and the vanadium valence state in the actual sample can be kept original and stable.(5)The metallurgical industry and natural environment samples were adopted to evaluate the practical application of this method.A set of vanadium slag leaching solution was used as the HPLC analysis sample.The contents of soluble V(V)and V(V)in the vanadium slag leaching solution were obtained at different roasting times.The evolution of soluble vanadium valence during roasting was revealed,and the feasibility and accuracy of the method for determining samples in the metallurgical industry were demonstrated;a set of natural soil sample and a set of natural surface water were used as HPLC samples with this method,it is revealed that the selected soil and water environment meets the safety standards and there is no vanadium pollution.At the same time,the feasibility and accuracy of the HPLC method for the determination of natural environment samples are proved.