High-performance liquid chromatography of di- and trisubstituted aromatic positional isomers on 1,3-alternate 25,27-dipropoxy-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel stationary phase

Mesoporous nanomaterial-assisted hydrogel double network composite for mixed-mode liquid chromatography

By introducing functional groups such as quaternary amine groups, sulfonic acid groups, triazine groups, and other mespore nanomaterials into the hydrogel, better separation effect of some organic framework materials has been obtained. Due to a reasonable design and preparation strategy, the hydrogel composite-modified silica can be used in the selective separation of various analytes such as pesticides, alkylbenzenes, polycyclic aromatic hydrocarbons, nucleosides/bases, benzoic acids, antibiotics, and carbohydrates. Through the exploration of chromatographic retention behavior, it is proved that the column can be used in mixed-mode liquid chromatography. The intra-day relative standard deviation for retention time of this new stationary phase is 0.12-0.16% (n = 10), and the inter-day relative standard deviation is less than 0.39% (n = 5). This new stationary phase can also be used for separation in complex samples. The limit of detection (LOD) for chlorotoluron in farm irrigation water is 0.21 µg/L and the linear range is 2-250 µg/L. After optimizing the chromatographic conditions, the highest efficiency of the hydrogel column in RPLC and HILIC modes has reached 32,400 plates/m (chlorobenzuron) and 41,300 plates/m (galactose). This new type of hydrogel composite is a porous network material with flexible functional design and simple preparation method and its application has been expanded in liquid chromatography separation successfully. The hydrogel composed of triallyl cyanate cross-linking agent and 3-(2-(methacryloyloxy) ethyl) dimethylamine) propane-1-sulfonate (SBMA) monomer which were co-modified on the surface of mesoporous silica with MOF-919 for separation in mixed-mode liquid chromatography.

Preparation and chromatographic performance of calix[4]crown-5 macrocycle-bonded silica stationary phase

A new calix[4]crown-5 macrocycle-bonded silica stationary phase (CL-CIMS) was prepared and applied at the same time to develop a chromatographic procedure to separate aromatic amines, phenols and drugs in this study. The chromatographic behaviors of the prepared stationary phase for these analytes were studied and compared with those of ODS (octadecylsilane). The effect of organic modifier content and pH of the mobile phase on retention and selectivity of these compounds were investigated. Some aromatic amines, phenols or drugs on CL-CIMS were successfully separated. The results show that CL-CIMS exhibits high selectivities for the above analytes in high aqueous mobile phases and a bright prospect in routine, fast separation of aromatic amines, phenols and drug compounds. From chromatographic data, it can be concluded that hydrophobic interaction is mainly responsible for the retention behavior as well as hydrogen-bonding interaction, π-π and dipole-dipole interaction.

Determination of 2,6-dichlorobenzamide and its degradation products in water samples using solid-phase extraction followed by liquid chromatography-tandem mass spectrometry

An analytical method was developed for the determination of 2,6-dichlorobenzamide (BAM) and five degradation products thereof including 2-chlorobenzamide (OBAM), 2,6-dichlorobenzoic acid (DCBA), 2-chlorobenzoic acid (OBA), benzoic acid (BA) and benzamide (BAD) in water samples. Solid-phase extraction was combined with liquid chromatography coupled to tandem mass spectrometry using electrospray ionisation. Groundwater spiked at a concentration of 1.0 microg/L gave recoveries on day 1 between 91 and 102% (relative standard deviation: 2.2-26.5%) for OBAM, BAM, DCBA, BA and OBA, while BAD showed a somewhat lower recovery of 60% (relative standard deviation: 25%). Corresponding figures on day 3 gave recoveries of 97-110% (relative standard deviation: 3-22%) for OBAM, BAM, DCBA, BA and OBA, while BAD had a recovery of 51% (relative standard deviation: 4%). The final SPE-LC-MS/MS method had a LOD(Method) of 0.009, 0.007, 0.010, 0.021, 0.253 and 0.170 microg/L groundwater for BAD, OBAM, BAM, DCBA, BA and OBA and a LOQ(Method) of 0.030, 0.023, 0.035, 0.071, 0.842 and 0.565 microg/L groundwater in the same order of appearance. Analysis of three different Danish groundwaters confirmed the occurrence of BAM at levels exceeding the threshold value of 0.1 microg/L, while no degradation products were found above LOD(Method).

Preparation and characterization of six calixarene bonded stationary phases for high performance liquid chromatography

Six calixarene bonded silica gel stationary phases were prepared and characterized by elemental analysis, infrared spectroscopy and thermal analysis. Their chromatographic performance was investigated by using PAHs, aromatic positional isomers and E- and Z-ethyl 3-(4-acetylphenyl) acrylate isomers as probes. Separation mechanism based on the different interactions between calixarenes and analytes were discussed. The chromatographic behaviors of those analytes on the calixarene columns were influenced by the supramolecular interaction including pi-pi interaction, space steric hindrance and hydrogen bonding interaction between calixarenes and analytes. Notably, the presence of polar groups (-OH, -NO(2) and -NH(2)) in the aromatic isomers could improve their separation selectivity on calixarene phase columns. The results from quantum chemistry calculation using DFT-B3LYP/STO-3G* base group were consistent with the retention behaviors of PHAs on calix[4]arene column.