Application Of Molecularly Imprinted Polymer In The Separation And Determination Of Nitramine Explosives

Explosives are dangerous not only because of their explosive properties but also because they are toxic and naturepolluting substances.Forensic analysis or environmental analysis of explosives can be particularly challenging when the residues left are present at trace levels in various and complex matrices.Organic solvents are effective in dissolving explosive traces but many other compounds are also recovered resulting in highly complex samples.Therefore,determining the low concentration of explosives in most samples requires a preconcentration step.Molecularly imprinted polymers?MIPs?as selective SPE sorbents can be used to separate target compounds.2,4,6-trinitrotoluene?TNT?,hexahydro-1,3,5-trinitro-1,3,5-triazine?RDX?,octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine?HMX?and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane?China Lake 20,CL-20?are widely used as explosives or propellant material.In this doctoral thesis,the molecular imprinting technique was used to solve the problems of separation in the synthesis and detection of explosives,and the related mechanism of molecular imprinting and molecular recognition was studied.The main contents and results of this doctoral thesis are summarized as follows:1)The separation of HMX and RDX from their mixtures is difficult because the sizes and physical properties of these homologous compounds are similar.HMX and RDX can be separated indirectly by separating the mixtures of 1,3,5,7-tetraacetyl-1,3,5,7-tetraazacyclooctane?TAT,theprecursorofHMX?and1,3,5-Triacetyl-1,3,5-triazacyclohexane?TRAT,the precursor of RDX?.The MIPs for two structural analogs,TRAT and TAT,have been synthesized respectively under the same conditions.The TAT-MIP showed excellent imprinting effect,whereas the TRAT-MIP did not.To understand the different imprinting effects of the MIPs prepared from these two templates,the geometric structures and energetic properties of complexes formed around TAT and TRAT were studied computationally?molecular dynamics simulation and quantum chemical calculation?.The results indicate that in liquid phase,for the complexes formed with TAT and its nearest neighbor molecules,the magnitude of the binding energy increases with the number of surrounding TAT,methacrylic acid?functional monomer?,and acetonitrile?ACT,porogen?,whereas for the cases of TRAT,the magnitude of the binding energy increases with the number of surrounding TRAT and trimethylolpropane trimethacrylate.The studied systems form stronger and thus more stable networks encapsulating TAT than with TRAT.ACT may also play an important role in the polymerization phase in stabilizing the shapes of the cavities that TATs reside in.2)The method of molecularly imprinted solid-phase extraction is used to separate HMX and RDX from their mixtures.RDX was not detected in the separated HMX by HPLC and vice versa.This newly developed method had the advantages of high recovery?100%?and purity,environmental friendliness and room temperature operability.This study showed that some molecularly imprinted polymers that cannot absorb target analytes well in the solvent in which the polymers were polymerized might have high binding capacity for the analytes and show imprinting effects in other solvents.3)Eight MIPs for CL-20 were synthesized by precipitation polymerization in acetonitrile.MIP 4,which was prepared with acrylamide?AAm?as the functional monomer and ethyleneglycol dimethacrylate?EGDMA?as the crosslinker,was the optimal MIP.When the molar ratio of the template?CL-20?,functional monomer and crosslinker was1/6/24,the MIP possessed optimal absorbability and selectivity.The binding capacity(Q_max)of MIP 4 for CL-20 was 115.7 mg/g and the adsorption reached equilibration within 10 min.MIP 4 as a selective sorbent was used to extract CL-20,using SPE from the mixed solution of its precursor compound,its analogues and soil samples.The recovery of CL-20 was 95%.After 5 SPE cycles,the extraction ability of the cartridge for soil samples did not decrease obviously.4)A molecularly imprinted polymer hollow spheres?MIHSs?were applied to the selective solid-phase extraction?SPE?of several explosives simultaneously by using a newly-developed SPE procedure.For the first time,TNT,RDX,HMX and CL-20 were selectively extracted and determined simultaneously from simulated post-blast samples prepared from motor oil and vacuum pump oil.The matrix effects were successfully eliminated and accurate quantization was achieved.When the loading amounts of HMX,RDX,TNT and CL-20 were respectively below 10,2,5 and 20 nmol for 100 mg of MIHS,these explosives were almost retrieved completely?above 98%?.For the MIHSs and non-imprinted polymer hollow spheres?NIHSs?,in acetonitrile and methanol,the imprinting factors?IFs?of CL-20 and tetraacetyldibenzylhexaazaisowurtzitane?TADB,a structural analogue of CL-20?changed dramatically,from 7.75 to 1.57,0.88 to 2.39,respectively.It highlighted the significant effect of solvent on imprinted sites.