Structural characterization of surfactants
Products for various purposes contain more or less surfactants with different functions. For various mixed samples, it is necessary to separate and purify them by physical separation, chemical separation, silica gel column chromatography, chromatographic separation, etc., and then utilize instruments such as spectroscopy, mass spectrometry, chromatography, energy spectroscopy, thermal analysis, etc., to characterize the structure of the contained components and quantify them.
Separation of mixed samples
Step-by-step washing method
Dissolution and precipitation
Chromatographic separation method (column chromatography, thin layer chromatography, HPLC, etc.)
2、The separation principle of chromatography
When the mixture carried in the mobile phase flows through the stationary phase, it interacts with the stationary phase (force action). Since the components of the mixture differ in nature and structure, the magnitude of the interaction with the stationary phase also differs.
Therefore, under the action of a unified driving force, the retention time of different components in the stationary phase is long or short, so that they flow out of the stationary phase in a different order.
3）Drenching
Drenching system: gradient drenching
Volume of eluent: 400-800 parts
Steps: first point plate (TLC) —- plate climbing in 0.3Rf at the drenching system is suitable for washing down the substance.
Precautions: over the column, eluent ready to use, the receiver vessel is changed diligently, so as to avoid crossover
4）It is suitable for analysis:
1）Sample solubility is good
2）Separability is shown on the TLC plate.
3) a certain amount of sample (at least 100mg, too little sample is recommended to use preparative TLC)
⇀ Look at the plate
First look, first observe under daylight, scratch out the spots of colored substances
Two light, in the ultraviolet lamp to observe the presence of dark spots or fluorescent spots
Three iodine, most organic matter in iodine reversible brownish-yellow spots
IV show, substances that are colorless and have no UV absorption can be colored with a color developer
⇀TLC method in the application of surfactants
Instrumental analysis
Surface active analysis focuses on the characterization of the structure with: IR, NMR, GCMS, MS, XRF, IC, acid-base titration, etc.
2、Application of infrared spectrum
Test infrared spectra, through the position of the absorption peak relative intensity and peak shape and other structural information to provide compounds, widely used in small molecules, polymer compounds, qualitative analysis, but also simple quantitative.
It is a simple and fast analytical method.
The surface activities of polyoxyethylene ethers are all in the range of 1000~1250cm-1, and there are stretching vibration peaks of the -O-R group.
Several important parameters for the structure analysis of hydrogen spectrum
Chemical shift Coupling constant Peak shape (s, d, t, q) Integral area
1) Chemical shifts of common functional groups in hydrogen spectra
Factors affecting chemical shifts:
1) Shielding (antimagnetic) versus deshielding (paramagnetic) effects
2) Induced versus conjugated effects
3) Each anisotropy effect 4) Hydrogen bonding effect
5) Proton exchange effects 6) Solvent effects
2) Coupling constants
spin-spin coupling: the interaction of hydrogen nuclei on neighboring carbons coupling constant (Couplingconstant) J: the distance between the two cleavage peaks, unit: Hz coupling constant J is only related to the nature of the chemical bonding, and has nothing to do with the applied magnetic field
3) Split peaks of nuclear magnetism
Due to the spin-spin coupling between protons on neighboring carbon, it is therefore able to cause absorption peak splitting.
1) The coupling of a nucleus with n magnetically equivalent nuclei is such that n+1 spectral lines can be produced;
(2) The spacing of the spectral line splitting is their coupling constant J
(3) The multiple peaks are symmetrically distributed through their focus, with the center position being the chemical shift value
(4) The relative intensities of the multiple peaks are the coefficients of the quadratic expansion (a+b)n, and n is the number of equivalent nuclei.
