Research On Analysis Method Of Nonionic Surfactant Based On High Orthogonal Comprehensive Two-dimensional Liquid Chromatography

Nonionic surfactants are a class of compounds with hydrophobic groups at one end and hydrophilic groups at the other（generally polyethylene glycol chains）.Phenolic compounds produced by the degradation of some widely used nonionic surfactants（Triton x-100,Tristyrylphenol ethoxylate,etc.）are hazard to the environment.Because of the variable number of chain lengths of hydrophilic groups and the different hydrophobic groups,nonionic surfactants are usually complex mixtures of dozens of congeners,which makes their analysis difficult,and it is important to develop methods that can comprehensively analyze their components.Due to the hydrophobic selectivity of reverse phase chromatography and hydrophilic selectivity of hydrophilic chromatog-raphy,the combined reverse phase/hydrophilic chromatography two-dimensional liquid chromatography system is expected to achieve efficient separation of complex mixtures of nonionic surfactants,which are typically amphiphilic in nature.However,the incompatibility of the reverse phase and hydrophilic elution solvents can strongly interfere with the separation of analytes on this combined two-dimensional liquid chromatography.Therefore,this article intended to combine online splitting,two quantitative loop interface and in-column dilution strategy to comprehensively modulate one-dimensional fractions to solve the problem of incompatibility of two-dimensional elution solvents,Three comprehensive two-dimensional systems,including hydrophilic×reverse phase comprehensive two-dimensional chromatography system（HILIC×C18-RPLC）,reverse phase×hydrophilic comprehensive two-dimensional chromatography system（C18-RPLC×HILIC）and polyethylene two Alcohol-reverse phase×hydrophilic comprehensive two-dimensional chromatography system（PEG-RPLC×HILIC）,were built.Meanwhile,Triton x-100 and Tristyrylphenol ethoxylate were as samples to optimize the two-dimensional separation conditions of different samples.Finally,these separation effects were compared.The research details are as follows:1.Two hydrophilic chromatographic columns and four C18chromatographic columns were screened,and the Click X-Ion hydrophilic column and Ultimate^?XB-C18 reversed-phase column were selected finally as the analytical columns to construct a highly orthogonal comprehensive two-dimensional liquid.HILIC×C18-RPLC system construction:After optimizing the first-dimensional hydrophilic elution conditions of Triton x-100 and Tristyrylphenol ethoxylate,the dilution ratio and elution gradient of the second-dimensional analysis were further optimized.Under the optimal conditions of Triton x-100 separation,a two-dimensional spectrum with dotted bands with peaks according to the law of hydrophilicity and hydrophobicity was obtained.However,in the analysis of Tristyrylphenol ethoxylate,the composition was more complicated,which led to the considerable differences between two fractions in the component,and the retention of this composition on the second dimension C18 column was too strong.During the optimization process,the problems of serious peak detours and peak broadening were observed regardless of multiple optimization strategies.There was thus no good separation in two dimensions.2.Considering that the Click X-Ion column could also provide soft retention for Triton x-100 and Tristyrylphenol ethoxylate,the hydrophilic column was used as the second dimension column,and the C18 column was used as the first dimension column to construct C18-RPLC×HILIC system.Under this system,the first-dimensional reverse elution gradient of Triton x-100 and Tristyrylphenol ethoxylate was optimized first,and then the dilution ratio and two-dimensional gradient were optimized respectively.After optimization,the peak breakthrough of the two has been significantly improved,and the components in Triton x-100 and Tristyrylphenol ethoxylate have been well separated in two dimensions,which was helpful for their further analysis.However,because the first-dimensional separation was carried out at a low flow rate,this means the sample was eluted slowly in the chromatographic column of 4.6 mm inner diameter,resulting in low utilization of the entire two-dimensional space.3.The monolithic column has a high degree of designability and is very suitable for preparing a separation column with a small inner diameter.These characteristics make it very suitable for use as a first-dimensional separation column for comprehensive two-dimensional chromatography.Therefore,in this chapter,we intended to construct PEG-RPLC×HILIC by synthesizing a polyethylene glycol-based 530μm large internal diameter organic polymer monolithic column with high selectivity to nonionic surfactants to replace the first-dimensional C18revers phase chromatography column in order to achieve high-efficiency separation of non-surfactants.First,the ammonium sulfate-PEGDA two-phase aqueous system was used to synthesize the organic polymer monolithic column.After a series of optimizations,the permeability was enhanced,and the column wall was tightly combined at a ratio of 1:4,0.05 M（NH₄）₂SO₄and 75℃.Poly（PEG）column with stable mechanical properties and good repeatability.After elucidating the separation mechanism of Poly（PEG）column and analyzing the feasibility of the two-dimensional construction,it was successfully applied to the RPLC×HILIC system,and showed a superior choice in the subsequent analysis of Triton x-100 and Tristyrylphenol ethoxylate sex.In Triton x-100,by simply optimizing the dilution ratio,a good two-dimensional separation effect can be obtained.On the two-dimensional spectrum,the peaks of all components according to the length of the polyethylene glycol chain can be clearly seen.In the two-dimensional separation of Tristyrylphenol ethoxylate,one major band and three minor bands were obtained.And the two-dimensional effective separation space under the construction of the PEG-RPLC×HILIC system has been significantly improved compared with the C18-RPLC×HILIC system.