¹H HR/MAS NMR in the suspended state: Molecular recognition processes in liquid chromatography between steroids and a silica hydride‐based cholesterol phase

Abstract

A mixture of eight steroids was separated by HPLC on a silica hydride-based stationary phase modified with a moiety of cholesteryl 10-undecanoate. Within the steroid mixture progesterone showed the longest retention time suggesting the strongest interaction with the stationary phase material. To obtain more detailed information upon the effective separation process, interaction studies were performed by high resolution/magic angle spinning (HR/MAS) NMR spectroscopy recorded in the suspended state. (1)H saturation transfer difference (STD) NMR experiments with T(1rho) suppression showed significant hydrophobic binding affinities of progesterone toward the cholesterol column material. These NMR results can be correlated directly to the chromatographic data obtained by HPLC.

Time‐dependent column performance of cholesterol‐based stationary phases for HPLC by LC characterization and solid‐state NMR spectroscopy

“…AP‐Chol SP with the shorter linker shows better separation capability for the pairs of analytes 3 and 4 which is comparable to that of the polar embedded C 18 EPS. Under these conditions the UDC‐Chol SP shows little separation capacity although good results for steroid separations, using a different method, have been achieved previously []. This is probably due to the different surface chemistry and thereby different separation properties, furthermore the lower carbon percentage results in fewer recognition sites and retentiveness.…”

Synthesis and evaluation of silica hydride‐based fluorinated stationary phases

“…A recent advance in the study of solid materials like stationary phases involves suspension in an appropriate solvent and obtaining the NMR spectrum of the heterogeneous mixture 26. Both of the phases synthesized in this study and the silica hydride starting material were suspended in deuterated methanol and the proton spectra acquired.…”

Selectivity enhancement for the separation of tocopherols and steroids by integration of highly ordered weak interaction sites along the polymer main chain

“…Several tailor-made stationary phases, such as, cholesteryl-based, carbazole-based, molecularly imprinted polymers, temperature responsive phases were used for the separation of steroids and their isomers [43][44][45][46][47][48][49][50][51][52][53]. Figure 4 shows the separation of a mixture of eight steroids having a wide range of polarities on the newly developed alternating copolymer-based Sil-poly(ODA-alt-DGMI) column.…”