Preparation And Performance Study Of Capillary Gas Chromatography Column Based On Monohydroxy Seven-membered Cucurbit Ring Derivatives

In the analysis of gas chromatography,the key to the efficient separation of t he samples to be tested is the selectivity of the stationary phase and the preparati on method of the column.Cucurbit[7]urils has a unique hydrophobic cavity and u nique molecular recognition ability,so it has a good application potential as the s tationary phase of gas chromatography.In this paper,in reference to the literature on the basis of the synthesis of 4-vinyl benzyl oxygen radicals cucurbit[7]urils,th is paper reviewed the research progress of gas chromatographic stationary phase,and then combined with gas chromatographic separation principle and the basic p rinciple of sol-gel based on 4-VBOQ[7]-DIL sol-gel method is adopted a new typ e of high efficiency,high heat stability and good repeatability of PDMS/4-VBOQ[7]-DIL chromatographic column.First,the coating of PDMS/4-VBOQ[7]-DIL stati onary phase was characterized by infrared spectroscopy,electron microscopy and thermogravimetric analysis.Then,the Golay curve,column efficiency,polarity,inf luence of different injection volume on the column,thermal stability,repeatability and durability were investigated.Then,the separation performance of the column was investigated by separation of different types of compounds.Finally,the entha lpy and entropy changes of the self-made column during the separation process w ere investigated.According to the experimental results,the main contents are as f ollows:1.Firstly,the single hydroxyl cucurbit[7]urils（（HO）₁Q[7]）was prepared by ammonium persulfate oxidation method,and then eluted with the eluent of V（wa ter:formic acid:acetic acid）=10:10:2.the single hydroxyl cucurbit[7]urils was separated and purified by column chromatography,and the yield was about 10%.Then,4-ethylbenzyloxy cucurbit[7]urils was synthesized according to the literatur e,and 4-VBOQ[7]-DIL was characterized by infrared spectroscopy,¹H-NMR and high resolution mass spectrometry.The results showed that 4-VBOQ[7]-DIL with high purity was obtained in this experiment,and the yield was 60%.2.A polydimethylsiloxane/4-ethylbenzyloxy cucurbit[7]urils（PDMS/4-VBOQ[7]-DIL）column was prepared by sol-gel method.First,the structure of the capilla ry column prepared by sol-gel method was analyzed,then the morphology and thi ckness of the coating were characterized by scanning electron microscopy,and th en the thermal stability of the stationary phase was characterized by thermogravi metric analysis.Scanning electron microscopy（SEM）results showed that the PDM S/4-VBOQ[7]-DIL coating had uniform morphology,compact surface and no crac k,and the coating thickness was about 1um.The results of thermogravimetric anal ysis show that the thermal stability of the coating is good,and 10%of the sampl e is lost when the temperature of PDMS/4-VBOQ[7]-DIL stationary phase reaches320℃,so it can be used as a stationary phase for gas chromatography separation and analysis.3.The basic properties of PDMS/4-VBOQ[7]-DIL column were investigated.Firstly,the influence of carrier gas flow rate on the separation capacity of the col umn was analyzed,and the Golay curve of PDMS/4-VBOQ[7]-DIL column was o btained.The optimal flow rate of naphthalene was about 17.5cm/s,and that of n-dodecane was about 18.3cm/s,both of which were 0.4 m L/min.The column effici ency and polarity of the PDMS/4-VBOQ[7]-DIL column were investigated.Under the condition of carrier gas flow rate of 1 m L/min,the column efficiency could reach the highest theoretical plate number per meter of 1128,the total polarity o f the stationary phase was 607,and the average polarity was 121,which belongs to the stationary phase with moderate polarity.The effect of different injection rate s on the self-made column was also investigated.The results showed that the inje ction rate and peak area of the PDMS/4-VBOQ[7]-DIL column were linear,and h ad no effect on the retention factor.The same column was aged by increasing diff erent aging temperatures,and the changing trend of separation factors and retentio n factors of its components was investigated.The service temperature of PDMS/4-VBOQ[7]-DIL column could be as high as 300℃,and the column had good ther mal stability and met the requirements of chromatographic analysis.The reproduci bility of the columns was good,with intra-day reproducibility RSD less than 0.2%,inter-day reproducibility RSD less than 0.35%,and reproducibility RSD betw een different columns less than 0.7%.Finally,the durability of the PDMS/4-VBO Q[7]-DIL column was investigated.The RSD between the two n-alkane fractions were all within 1%,which was within the normal range.4.The separation selectivity of PDMS/4-VBOQ[7]-DIL column was investiga ted,which mainly included the following parts:（1）to investigate PDMS/4-VBOQ[7]-DIL chromatographic column separation of 10 kinds of compounds,the corresponding normal alkanes was 8 kinds of est er compounds,8 kinds of alcohols,8 kinds of aldehyde compounds,eight kinds o f ketone compounds,such as the ability of five kinds of different polar compound s,the results show that the PDMS/4-VBOQ[7]–DIL of sharp peak shape in chrom atographic column separation material,symmetry,high column efficiency,good fil m-forming ability and the chromatographic column and good adsorption,can sepa rate different polar compounds（from nonpolar compounds to polar compounds）;（2）The ability of PDMS/4-VBOQ[7]-DIL column to separate 10 compounds with high boiling point,5 compounds with low boiling point and 6 compounds w ith similar boiling point was investigated.The results showed that PDMS/4-VBO Q[7]-DIL column had good separation ability for these three compounds,and the peak shape of the chromatographic peaks was sharp and symmetrical.（3）Ten isomers were isolated on a PDMS/4-VBOQ[7]-DIL column.Results s how that because of the 4-vinyl benzyl oxygen radicals cucurbit[7]urils oxygen-co ntaining groups and interactions between analytes and cucurbit[7]urils inside the h ydrophobic cavity have better recognition ability and the ability to pack,the diffe rent molecules can be selectively package,this feature makes PDMS/4-VBOQ[7]-DIL in the chromatographic column to position has more obvious advantages in t he separation of isomers.（4）The separation ability of a self-made PDMS/4-VBOQ[7]-DIL column for complex mixtures（Grob reagents,22 mixtures）was investigat ed.The results show that PDMS/4-VBOQ[7]-DIL column has good separation abili ty and selectivity for complex mixtures such as Grob reagent and 22 mixtures be cause of its hydrophobic cavity structure,molecular recognition ability and oxyge n-containing functional groups in the stationary phase.（5）The separation ability of PDMS/4-VBOQ[7]-DIL chromatographic column for petroleum pollutants BTEX and plasticizer was investigated.The results sho wed that PDMS/4-VBOQ[7]-DIL chromatographic column had good separation sel ectivity for both environmental pollutants,and it could be considered to be applie d in the actual sample detection of water,environmental pollutants and petroleum pollutants in real life.（6）.The retention mechanism and molecular recognition characteristics of fix ed relative solute molecules on a PDMS/4-VBOQ[7]-DIL column were investigate d.Using alcohols and PAHs as probe molecules,the thermodynamic parameters o f the separation process were measured and calculated,including the enthalpy（ΔH）and entropy（ΔS）changes.Results During the separation of probe molecules on PDMS/4-VBOQ[7]-DIL column,the ratio ofΔS/ΔH decreased gradually,indicat ing that the fixation of sol-gel relative to the retention of alcohols and PAHs was controlled by entropy change and enthalpy change.