Ageing processes of alkyl bonded phases in HPLC; a chromatographic and spectroscopic approach

Summary Laboratory use of HPLC columns packed with C₈ and C₁₈ bonded phases leads to changes in selectivities and retention volumes. FTIR,¹H NMR of hydrolysed bonded phases and solid state¹³C- and²⁹Si NMR were applied to characterize the materials. The results of the various techniques are in fair agreement except solid state NMR. Loss of silane and hydrolysis of surface siloxane groups have been observed for the C₈ bondes phase, while for the C₁₈ material the latter process seems to dominate. The solid state NMR results have been tentatively explained in terms of changing chain arrangements and mobilities.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday.     

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

Three different cholesterol-based stationary phases were investigated with respect to their time-dependent separation behavior. The examined stationary phases differ in the used spacer molecule and the synthesis route and were used under routine laboratory conditions over a period of two years. The chromatographic behavior of the three phases was determined by using a standard reference material in addition to a separation of a steroid mixture. The surface chemistry and the modification of these with the chemically bonded moiety were investigated with nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. Through applying different techniques we determined changes in retention and selectivity; solid-state NMR spectra showed changes in the surface chemistry dependent on the synthesis route. Superior long-term stability was observed for the undecanoate-cholesterol (UDC-Chol) column in terms of hydrophobic retentiveness and selectivity.     

Variable-temperature,solid-state NMR studies of bonded liquid crystal stationary phases for HPLC

Summary The spin-spin relaxation time measured from the line width (T ₂*) is used to study bonded phase dynamics of two liquid crystal materials in the solid state as a function of temperature. The motion of these two bonded phases is much more restricted than either C-18 or butyl phenyl bonded to the same substrate. Plots ofT ₂* vs. 1/T indicate a structural transition of the bonded phase moiety for the two liquid crystal materials but no such change is seen for either C-18 or butyl phenyl over the same temperature range (243–353 K), suggesting a higher degree of association between adjacent bonded moieties for the two liquid crystal materials in comparison to the other two phases. The conclusions from solid-state NMR data coincide with results obtained in earlier chromatographic studies.     

Comparative study of some commercial chemically bonded phases in classical reversed-phase chromatography and in ion-pair reversed-phase liquid chromatography

Summary The behaviour of various octadecyl commercial bonded phases are compared in classical reversed-phase chromatography and in ion-pair reversed-phase chromatography. Great differences are exhibited by the packings studied according to the polarity of the solutes. Whereas hydrocarbonaceous bonded phases show very similar selectivity versus apolar or weakly polar solutes, great differences are observed when analyzing more polar solutes even when ion-pair reversed-phase chromatography is performed.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Comparison of octadecyl bonded titania phases

Summary The structure of a C₁₈ phase based on titania (C₁₈-A), synthesized by the method of solution polymerization, is investigated by diffuse reflectance infrared Fourier transform (DRIFT) and solid-state nuclear magnetic resonance (NMR) spectroscopy. The findings are compared with the results of a second C₁₈ phase based on titania (C₁₈-B) which was synthesized by the method of surface hydrosilation. The dynamic behavior of both phases is examined by¹H MAS NMR detection of spinlattice relaxation times in the rotating frame (T_1pH) and conventional spin-lattice relaxation times (T₁). Due to a smaller ligand density, phase C₁₈-A appears to be a somewhat more mobile than phase C₁₈-B. The chromatographic capability of the phase C₁₈-A is demonstrated by the separation of samples containing benzene derivates or anilines. The elution order is analogous to the phase C₁₈-B, but for both test mixtures the polarity of the mobile phase has to be increased. Phase C₁₈-A is classified as being polymeric by the Sander and Wise test, whereas phase C₁₈-B shows intermediate retention behavior.     

Some observations regarding different retention properties of HPLC stationary phases

Summary The retention of 32 monocyclic aromatic compounds and 14 polynuclear aromatic hydrocarbons (PAHs) has been studied on four different bonded phases in each of two mobile phases. An additional data set of 21 monocyclic aromatics judiciously chosen for their well-established solvatochromic parameters, 12 PAHs and 12 polychlorinated biphenyls (containing up to 10 chlorines), were studied on a single column. The results indicate that despite the accuracy of the solvatochromic linear solvation energy method for predicting and correlating the octanol/water partition coefficients and water solubilities of these environmentally important materials, the methodology is limited to only certain types of bonded phases. As a corollary to this observation, we caution others that the common practice of estimating log K_ow (K_ow=octanol-water partition coefficient) based on measurement of the reversed-phase capacity factors should be limited to specific types of columns. Part 5 of Solute-Solvent Interactions in Chemistry and Biology.     

Solution and solid state NMR studies of some selenium analogues of auranofin (an anti-arthritic gold drug)

Three mixed ligand complexes of gold(I) with phosphines and selenones, [Et₃PAuSe=C<]Br as analogues of auranofin (Et₃PAuSR) have been prepared and characterized by elemental analysis, IR and NMR methods. A decrease in the IR frequency of the C=Se mode of selenones upon complexation is indicative of selenone binding to gold(I) via a selenone group. An upfield shift in ¹³C NMR for the C=Se resonance of the selenones and downfield shifts in ³¹P NMR for the R₃P moiety are consistent with the selenium coordination to gold(I). ¹³C solid state NMR shows the chemical shift difference between free and bound selenone to gold(I) for ImSe and DiazSe to be ca 10 and 17?ppm respectively. Large ⁷⁷Se NMR chemical shifts (55?ppm) upon complexation in the solid state for [Et₃PAuDiazSe]Br compared to [Et₃PAuImSe]Br (10?ppm) indicates the former to be more stable and the Au–Se bond to be stronger than in the latter complex.     

The relationship between crystal structure and NMR relaxation in molecular solids with tert-butyl groups

We correlate an X-ray determination of the molecular and crystal structures of 2-tert-butylanthracene and 2-tert-butylanthraquinone reported here with the previously reported dynamical nuclear magnetic resonance determination of the motions of the tert-butyl groups and their resident methyl groups in the solid state [P.A. Beckmann, K.S. Burbank, M.M.W. Lau, J.N. Ree, T.L. Weber, Chem. Phys. 290 (2003) 241].     

Effect of the alkyl chain length of the bonded stationary phase on solute retention in reversed-phase high-performance liquid chromatography

Summary A comparison of the chromatographic retention characteristics of nonpolar bonded stationary phases was investigated. The results show that the interactions between the solutes and the stationary phases having C₂, C₈ and C₁₈ alkyl groups are almost similar in the range of the mobile phase investigated. This interaction is considered as the solvophobic effect.     

Correlations between magnetic resonance parameters of ESR and NMR spectra

Empirically established correlations between magnetic resonance parameters of free radicals (g-factors, isotropic hyperfine coupling constans) and isostructural molecules (chemical shifts, isotropic spin-spin coupling constants) or structurally similar ligands in paramagnetic transition metal complexes (isotropic chemical shifts) are systematized and critically discussed. Quantum-chemical analysis of the suggested spin distribution damping coefficients in model systems and structurally similar chemical compounds is performed. Based on the results obtained, physicochemical interpretation of the observed correlations between the parameters of ESR and NMR spectra is given. Dedicated to the memory of Academician V. V. Voevodskii (to the 80th anniversary). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1575–1583, September, 1997     

NMR and HPLC study of chiral selectors with naphthyl unit

Doubling of resonances in NMR spectra of chiral selectors with naphthyl group attached to the tertiary amide nitrogen atom has been noticed what revealed the presence of two isomers. To test the enantiorecognition ability of these chiral selectors they are covalently bonded to the HPLC silica gel. Those kind of chiral stationary phases were compared with analogous commercial leucine chiral stationary phase. They exhibit the better enantioseparation results which indicate that the existence of cis/trans isomers does not have the negative influence on their enantioselective ability.

杂氮硅三环类化合物结构的固体NMR实验研究

采用固体NMR实验方法研究了取代的三个杂氮硅三环羧酸化合物的结构,针对实验结果讨论了环上取代对化合物构型和配键的影响,以及硅和氮化学位移对环上取代的反映。     

Chromatographic properties of mixed cyano/ODS chemically bonded phases for HPLC

Summary A number of different cyano/ODS polymeric modified silica gel phases were prepared by simultaneous bonding of cyanoalkylsilanes and octadecylsilane. Cyano contents between 10–80% were obtained. High surface coverage (above 4 μmole/m²), as well as low hydroxyl content, characterised all phases. The modified silica was suitable for separations in both straight and reversed phase mode. Significantly reduced retention times were obtained in the reversed phase mode for high mole-cular weight polyaromatic compounds (Mw above 300).     

Spectroscopic characterization of crystalline AlF3 phases

A comprehensive spectroscopic characterization of all known crystalline AlF₃ phases (α-, β-, η-, κ-, θ-AlF₃) is presented for the first time in this study. Beside their X-ray diffraction powder patterns, which were already published in the literature, ²⁷Al and ¹⁹F MAS NMR, FT IR and XPS spectroscopic techniques were applied for all phases in a consistent manner. For all phases prepared the utilization of ²⁷Al satellite transition (SATRAS) NMR allowed to determine the quadrupolar parameters of the aluminium sites including their distributions.In addition, η-AlF₃ was isolated with high phase purity and characterized following a new preparation path different from those known so far in the literature.     

Hydrolysis of some imidazole, benzimidazole, and 1,2,3-benzotriazole derivatives according to HPLC and NMR diffusimetry data

Hydrolysis of 1-mesylimidazole, 1-mesylbenzotriazole, and 1-tosylbenzimidazole was studied by reversed-phase HPLC and pulsed field gradient NMR diffusimetry. The hydrolysis rate constants and half reaction times were determined. The self-diffusion coefficients of the substances in aqueous solutions were measured. The reversed-phase HPLC data agree well with those of NMR diffusimetry.     

TS-1分子筛酸性的固体核磁表征

钛硅分子筛是一种具有广泛用途的环境友好催化剂 .它的开发和应用 ,使分子筛由酸催化作用扩展到了催化氧化过程 .TS- 1作为氧化催化剂 ,在以双氧水为氧化剂的烯烃环氧化、芳烃环的羟基化、环己酮的肟化、醇以及饱和烃的氧化等反应中显示出优良的催化性能 ,因而倍受关注 [1～ 4 ] .然而 ,尽管钛以四配位的形式进入分子筛的骨架 ,但仍然存在弱酸中心 ,这种弱酸中心在一些催化氧化反应中起着一定的作用[5] .人们对分子筛的酸性进行了长期研究 ,从最初的化学滴定法到量热法以及 NH3- TPD,尽管可得到分子筛酸性位的一些信息 ,但无法区分酸的种…     

High-resolution solid-state MAS 73Ge NMR spectra of some organogermanes

High-resolution solid-state magic angle spinning (73)Ge NMR spectra of some organogermanium compounds were measured. Most tetrasubstituted germanes with identical substituents exhibited signals except for one case. Tetrasubstituted germanes with two kinds of different but somewhat similar substituents exhibited broad peaks. Trisubstituted germanes failed to show signals, indicating the importance of symmetry around germanium.     

高效液相色谱-核磁共振光谱法测定纺织品及纺织助剂中烷基酚聚氧乙烯醚

建立了高效液相色谱-核磁共振光谱法测定纺织品及纺织助剂中烷基酚聚氧乙烯醚(APEO)的方法。用色谱保留时间及核磁共振光谱定性,色谱外标法定量,流动相为甲醇-乙酸铵溶液,紫外检测器检测波长为277 nm,APEO的质量浓度在5~250 mg.L-1范围内,浓度与峰面积呈线性关系,相关系数为0.992 8;保留时间的相对标准偏差小于0.21%,峰面积的相对标准偏差小于3.69%,回收率在91%~98%之间。纺织品中检测下限可达到1.0 mg.kg-1。该法已用于纺织品及纺织助剂的进出口检验。