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).     

The use of chemically bonded stationary phases in thin-layer chromatography-a survey

An overview is given of the literature publisned in the field of thin-layer chromatography on chemically bonded phases. Aspects which merit further attention are: quantitative analysis, organic solvent selection, stationary phase characteristics, surface modification of precoated silica plates, ion-pair chromatography and correlation of thin-layer and column chromatographic data.     

Retention of cyanoalkanes and cyanoalkylbenzenes by bonded stationary phases in supercritical fluid chromatography

Summary The retention of cyanoalkanes and cyano-alkylbenzenes during SFC was investigated on alkyl and cyanoalkyl-bonded stationary phases and compared to alkane retention. The particular behaviour of short chain homologues was attributed to a silanophilic interaction with surface-OH groups on the silica and inhibition of specific interactions between solutes and C₁₀CN bonded groups.     

Synthesis of acceptor bonded phases for donor-acceptor liquid chromatography

Summary The synthesis of several electron-acceptor stationary phases has been reviewed the materials evaluated for their capacity to separate polyaromatic hydrocarbons (PAHs). Chemically bonded phases were obtained by the same procedure; the organosilane moiety is monofunctional and the HPLC behaviour is compared under identical conditions. Examples of PAHs separations are given.Presentedat the 13th International Symposium on Polynuclear Aromatic Hydrocarbons, Bordeaux, October 1–4, 1991.     

Comparative evaluation of aromatic bonded phases for reversed-phase chromatography

Summary Retention factors for alkylbenzenes, polyaromatic hydrocarbons, steroids, amino acids, peptides, nucleotides, nucleosides were measured with phenylsilica, benzylsilica, phenethylsilica and octylsilica stationary phases using hydro-organic eluents containing methanol, acetonitrile or tetrahydrofuran. The retention behavior of the three arylsilicas was similar but distinctly different from that of octylsilica. The difference is attributed to the chemical properties of the organic ligates, i.e., of the alkyl- and aryl functions. The slight variations of retention behavior observed with arylsilicas on the other hand are believed to arise from differences in the pertiment phase ratios. The method used for interpretation of data is based on the analysis of the pertinent retention moduli, relative column retentivities and relative phase ratios. In addition, relationships between eluite structure and retention were examined. The results give insight into various phenomena underlying the retention process in reversed-phase chromatography.Part IV in the series on Stationary Phase Effects in Reversed-Phase Chromatography.     

A linear relationship between partition ratio and composition of a binary mobile phase in reversed-phase liquid chromatography using chemically bonded stationary phases

A simple linear relationship which enables the effect of the composition of a binary mobile phase on the retention of a solute to be assessed in reverse phase liquid chromatography using a bonded stationary phase has been derived. The equations have been tested using published experimental data.     

A comparison of temperature and mobile phase composition effects for bonded liquid crystal and polymeric stationary phases in HPLC

Summary Using two polycyclyic aromatic hydrocarbons as solutes, a comparison is made between a bonded liquid crystal stationary phase and a conventional polymeric C-18 phase. The bonded nematic liquid crystal phase was the silanized form of 4-[4-(allyloxy)benzoyl-oxy]biphenyl and the polymeric phase was Vydac 201TP. Both phases display shape and planarity selectivity as indicated by the results of the variable temperature and mobile phase composition studies. The slot theory of retention can be used to explain these results. However, the liquid crystal phase is more sensitive to molecular geometry, probably due to its more ordered structure on the surface. Variable temperature experiments which compare retention during both heating and cooling provides additional support for this conclusion. With the polymeric bonded C-18 phase, each solute had identical retention at the same temperature during both the heating and cooling cycles. On the bonded liquid crystal phase, measurable differences in retention were observed at identical temperatures depending on whether the column was heated or cooled. This effect is attributed to a degree of partially reversible disordering which occurs as the column temperature was increased. However, conditioning with the appropriate mobile phase can restore the original retention characteristics of the bonded liquid crystal phase.     

Optimization of enantiomeric separations with chiral bonded phases

Summary The preparation and properties of chiral bonded phases with amino acid groups are described. These phases were used in non-polar eluents and in aqueous systems in the presence of Cu²⁺ ions in the ligand-exchange mode. The optimization of chiral resolution is demonstrated for both cases. With non-polar eluents similarity between bonded groups and solutes is required. The elution could be accelerated by non-protonic moderators. Ligand-exchange separation is influenced by the copper content of the eluent and the stationary phase, the organic moderator concentration, the pH and ionic strength of the buffer and by the temperature. Structural requirements of both the bonded groups and of the solutes for chiral separation are discussed.     

The study of reversed phases by inverse gas chromatography

Summary The surface properties of three silica-based reversed phases have been studied by inverse gas chromatography. Theoretical deduction indicates that there is a linear relationship between the molar deformation polarisation of the test solute (P_D) and the dispersive interaction energy between the solute and the C18 and non-bonded silica surfaces. The specific interaction energy between the solute molecule and the silica surface (-G^SP) can be measured as the vertical distance between the solute experimental retention data point (RTl_nV_N) and the n-alkane RTl_nV_N vs P_D calibration line. From multiple regression analysis of-G^SP data with proton acceptor solubility parameter {ie290-1} and orientation solubility parameter {ie290-2} as variants, two coefficients can be obtained related to the influence of the residual silanol groups and the trace metal impurities.     

Study on retention behavior of peropyrene-type polycyclic aromatic hydroccrbons with various bonded stationary phases in reversed-phase liquid chromatography

Summary The retention behavior of 15 peropyrene-type polycyclic aromatic hydrocarbons was investigated on various bonded stationary phases in reversed-phase liquid chromatography. On diphenyl and naphthylethyl bonded phases, high correlations were obtained between the molecular polarizability of solutes and their retention. However, very low or no correlations were found on various octadecyl bonded phases. These facts are discussed by using the electrostatic interaction concept between the solutes and the stationary phase. We conclude that these observations are due to two reasons: the difference in the degree of planarity of polycyclic aromatic hydrocarbons and the high ability of planarity recognition of octadecyl bonded phases.     

Preparation and retention characteristics of different phenyl phases for reversed-phase liquid chromatography

Summary Three different phenyl phases were prepared. The amount of organic moiety bound on silica support was determined from thermogravimetric curves of the modified silica gel. The specific surface areas of gels were obtained from nitrogen sorption measurement at –196°C. The effect on separation and selectivity of the different bonded-phenyl functional groups was studied. The selectivity of the phenyl-bonded silica gels was examined and compared with octadecyl (ODS) silica in liquid chromatography. Corresponding to the high surface concentration of functional groups, the capacity factors of solutes, normalized to unit surface area of the adsorbent, k/S_BET were found to decrease in the sequence phenylmethyl>diphenyl>triphenyl. Polar solutes are retained in greater extent on the phenyl phases than on the ODS phase.     

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     

A refined physico-chemical model of solute retention in reversed-phase high-performance liquid chromatography with ternary mobile phases

Summary In our previous publication we have introduced a new model of solute retention in RP-HPLC systems with ternary mobile phases of the B+AB₁+AB₂ type (B: acetonitrile or tetrahydrofuran; AB₁: methanol; AB₂: water). That model proposed no stoichiometric differentiation between acetonitrile and tetrahydrofuran, alternatively present in the solvent system; moreover, it made some very rough assumptions only as to the intermolecular interactions among the mobile phase constituents.This paper introduces a significant refinement to the already established retention model, which is based on the simple quantitative relationships between acetonitrile and tetrahydrofuran, and the remaining components of the ternary liquid system. The refined model is tested with same experimental data.     

A simple test to characterise C8/C18-bonded phases,particularly for toxicological screening

Summary This paper describes a test (DMD-test) to determine chromatographic properties of C8- or C18-bonded phases. The test was developed to select HPLC columns, for clinical and forensic toxicological screening in particular. The three compounds for the DMD-test are: diphenhydramine, 5-(p-methylphenyl)-5-phenylhydantoin (=MPPH) and diazepam. The isocratic mobile phase (acetonitrile/buffer pH2.3) is suitable for analysis of biological samples. 24 commercially available columns were tested.From our work this test enables the selection of commercial HPLC columns with reproducible properties. In this way a reference LC retention list can be developed to identify analytical results on an inter- or intralaboratory basis.     

Superselective aqueous inorganic phases in vapor-phase gas chromatography

Chromatographic characteristcs of aqueous solutions of inorganic electrolytes, a new class of stationary liquid phases (SLP) for vapor-phase chromatography, are considered. The SLP are characterized by an unusually high selectivity to organic compounds of the R-X type (R is a hydrocarbon radical, X is a polar group,e.g., hydroxyl, carboxyl, and amine; for instance, light C₁-C₆ alcohols are eluted from the column with a water-containing phase in the following order: hexanol<pentanol<butanol<propanol<ethanol<methanol). The nature of the electrolyte used and its concentration in the water-containing SLP have a crucial influence on the column selectivity and the degree of separation of the compounds subjected to chromatography. This feature provides the possibility of controlling the column selectivity by changing the content of water vapor in the mobile phase. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1831–1840, October, 1999.     

Prediction of the net retention volumes in gas chromatography using porous polymers coated with different stationary phases

Summary A new expression which permits the prediction of the net retention volumes in gas chromatography with column packings of coated porous polymers is reported. The porous polymers Chromosorb 101 and Chromosorb 102 were used as supports and squalane, Ethofat and Carbowax 20M as stationary phases at three different column temperatures of 80°C, 100°C and 150°C. Several organic compounds of various polarity were used as test compounds and the net retention volumes, V_Ntheor, have been calculated according to this new expression. The V_Ntheor values were compared with the experimental net retention volumes, V_Nexp, and it was found that the difference between these two values is dependent on the type of compound and column packing. Nevertheless, the elution order could be predicted in most cases.     

Factor analysis and experiment design in high-performance liquid chromatography. IX. Silica vs. chemically bonded phases in normal phase-HPLC

Summary The retention of a group of 38 E-s-cis and Z-s-cis chalcones on silica vs. nine polar chemically bonded phases is discussed. It was established that the relatively greatest similarity to silica is observed with the NH₂, DIOL and CN phases, whereas the chargetransfer type phases and the NO₂ one offer a different separation selectivity.