Preparation, characterization and application of a new 25,27-bis-[2-(5-methylthiadiazole)thioethoxyl]-26,28-dihydroxy-para-tert-butyl calix[4]arene stationary phase for HPLC

Silica microparticles modified with ionic liquid bonded chitosan as hydrophilic moieties for preparation of high-performance liquid chromatographic stationary phases

Two novel stationary phases, 1-(4-bromobutyl)-3-methylimidazolium bromide bonded chitosan modified silica and 1-(4-bromobutyl)-3-methylimidazolium bromide bonded chitosan derivatized calix[4]arene modified silica stationary phase, were synthesized using 1-(4-bromobutyl)-3-methylimidazolium bromide bonding chitosan as a polarity regulator solving the limitation of the strong hydrophobicity of calixarene in the application of hydrophilic field. The resulting materials were characterized by solid-state nuclear magnetic resonance, Fourier-transform infrared spectra, scanning electron microscopy, elemental analysis, and thermogravimetric analysis. Based on the hydrophilicity endowed by 1-(4-bromobutyl)-3-methylimidazolium bromide bonded chitosan, the retention mode of ILC-Sil and ILCC4-Sil could be effectively switched from the hydrophilic mode to a hydrophilic/hydrophobic mixed mode and could simultaneously provide various interactions with solutes, including hydrophilic, π-π, ion-exchange, inclusion, hydrophobic, and electrostatic interactions. On the basis of these interactions, successful separation and higher shape selectivity were achieved among compounds that vary in polarity under both reverse-phase and hydrophilic interactive liquid chromatography conditions. Moreover, the ILCC4-Sil was successfully applied to the determination of morphine in actual samples using solid-phase extraction and mass spectrometry. The LOD and LOQ were 15 pg/mL and 54 pg/mL, respectively. This work presents an exceptionally flexible adjustment strategy for the retention and selectivity of a silica stationary phase by tuning the modification group.

A supramolecular cavitand for selective chromatographic separation of peptides using LC-MS/MS: a combined in silico and experimental approach

The chromatographic separation of proteomic standards via a silica immobilized pillararene cavitand has been designed in silico using host–guest binding energy studies and realized experimentally to selectively interact with peptides.

Silica bound co-pillar[4+1]arene as a novel supramolecular stationary phase

A novel co-pillar[4+1]arene incorporating two bromo-octyl substituents has been synthesised for the first time, using microwave irradiation in high yield (88%) in under four minutes, and bound to the surface of chromatographic silica particles. The resulting new stationary phase has been successfully utilised to separate xylene isomers via liquid chromatographic techniques.

SPE-UHPLC-FLD Method for the Simultaneous Determination of Five Anthraquinones in Human Urine Using Mixed-Mode Bis(tetraoxacalix[2]arene[2]triazine) Modified Silica as Sorbent

The five anthraquinones compounds (including aloe-emodin, emodin, physcion, chrysophanol, and rhein) are regarded as the main effective ingredients in rhubarb (Dahuang in Chinese, one of the commonly used Chinese herbal medicines). In this work, a simple and effective solid phase extraction (SPE) method based on bis(tetraoxacalix[2]arene[2]triazine) modified silica gel as adsorbent was developed. Coupled with UHPLC-FLD, the developed method was successfully applied for the measuring of main anthraquinones in human urine after oral administration of the extracts of rhubarb. To obtain the highest recoveries of the five anthraquinones in the SPE process, the main parameters which may affect extraction efficiency were optimized. The optimized sorbent amount, sample loading pH, sample loading rate, washing solution, and eluent condition were obtained. The developed method showed good linearity in 0.012-1.800 μg mL-1 for the five anthraquinones with correlation coefficients more than 0.9993. The investigated LOD values ranged from 3.9 to 5.7 ng mL-1, while the LOQs were between 12.0 and 18.2 ng mL-1. The recoveries of the method were also investigated, which were in the range of 94.8-106.6%. The application of the mixed-mode SPE materials in the proposed method was feasible and simple, and suitable for the enrichment of anthraquinones in urine samples.

Simultaneous Analysis of Two Phytohormones in Chili and Wheat Using HPLC Using Novel Calixarene as SPE Sorbent

In this paper, a high-performance liquid chromatography with ultraviolet (HPLC-UV) detection method, using tetraazacalix[2]arene[2]triazine-modified silica gel (NCS) as solid-phase extraction (SPE) sorbent, was developed for extracting and purifying the two phytohormones (indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA)) in chili and wheat samples from different organs of chili and wheat. The limits of detection were about 0.02 and 0.04 μg/mL, and the limits of quantification were 0.04 and 0.20 μg/mL for IAA and IBA, respectively. The intraday and interday RSDs (n = 6) of peak areas and retention times were in the range of 0.76-1.20%. In addition, overall recoveries through the extraction and NCS-SPE purification ranged from 78.4% to 86.8% for IAA and IBA were obtained. Compared with the commercial SPE sorbents, NCS featured excellent selectivity to retain IAA and IBA in the sample matrices. In addition, the results more clearly indicated that high IAA and IBA content existed in roots and leaves of wheat and chili; in other organs of the plants, the concentration of the two phytohormones is lower. The results from theoretical computation were consistent with the retention behaviors of IAA and IBA on NCS. The proposed NCS-SPE-HPLC method is highly effective for trace analysis of the two phytohormones in plant samples.

Determination of trace acrylamide in starchy foodstuffs by HPLC using a novel mixed-mode functionalized calixarene sorbent for solid-phase extraction cleanup

In this paper, a rapid and effective HPLC method, using tetraazacalix[2]arene[2]triazine-modified silica gel (NCSi) as solid-phase extraction (SPE) sorbent, was developed for the purification and determination of trace acrylamide in starchy foodstuffs. The main influence factors of SPE including amount of NCSi sorbent, sample flow rate, and volume and composition of washing solution were investigated and evaluated in the sample pretreatment step. The optimized purification effect was achieved at the sample flow rate of 3 mL/min with 100 mg of NCSi and 2 mL of washing solution (water, 100%). The HPLC separation was carried out on a C18 column (250×4.6 mm i.d., 5 μm) with a mobile phase of methanol/water (10:90, v/v). The linear range of the calibration curve was 4-4000 ng/mL with s correlation coefficient of >0.9999. The intraday and interday RSDs (n=5) of peak areas of acrylamide were 0.22 and 0.90% and the intraday and interday RSDs (n=5) of retention times were 0.50 and 1.63%, respectively. In addition, overall recoveries through the extraction and NCSi-SPE purification ranged from 73.13 to 98%. Compared with the commercial SPE sorbents, NCSi featured excellent selectivity to retain polar and nonpolar interferences in the sample matrices. The improved method was simple, rapid, accurate, and promising for the determination of trace acrylamide in starchy foods with a complex matrix.