Phenylaminopropyl silica--a new specific stationary phase for high-performance liquid chromatography of phenols

The chromatographic properties of a new stationary phase, phenylaminopropyl silica (PhA-silica), containing phenylaminopropyl residues covalently bonded to the silica surface were studied. The presence of secondary amino groups, phenyl rings and alkyl linkers in the attached molecule makes it especially suitable for the separation of phenols by mixed mode retention mechanism including a combination of hydrogen-bonding, hydrophobic, electrostatic and pi-pi interactions with the stationary phase. The effects of mobile phase pH, ionic strength, nature and concentration of organic modifier on the retention of phenols on PhA-silica were investigated under conditions of reversed-phase HPLC. To elucidate the role of the amino group in the attached molecule in retention of phenols the selectivity of PhA-silica was compared with that obtained for phenylpropyl silica in the framework of a linear solvation energy relationship (LSER) model. The isocratic separation of phenol, and its nine methyl-, chloro- and nitro-substituted derivatives was achieved on a 150x4.6 mm I.D. chromatographic column packed with 7 microm particles of PhA-silica.     

Phenylaminopropyl silica monolithic column for pressure assisted capillary electrochromatography

A novel stationary phase phenylaminopropyl silica (PhA-silica) monolith was successfully prepared for pressure assisted capillary electrochromatography (pCEC). The monolithic silica matrix from a sol-gel process was chemically modified by using [3-(phenylamino)propyl]trimethoxysilane as surface modification reagent to produce the phenylaminoporpyl function. The secondary amino groups on the surface of the monolithic stationary phase contributed to the generation of anodic electroosmotic flow (EOF) under acidic conditions. The phenyl group together with the spacer (-(CH(2))(3)-) in PhA-silica provides sufficient hydrophobic properties. To evaluate the column performance, effects of buffer pH and mobile phase composition on the mobile phase linear velocity and the retention factors of alkylbenzenes, phenols and anilines were investigated in pCEC mode. The monolithic stationary phases exhibit typical reversed-phase (RP) electrochromatographic behavior toward neutral solutes. Hydrophobic as well as electrophoretic migration process within the monoliths was observed for the separation of basic solutes such as anilines without peak tailing.     

An ion-exchange separation of Cu(2+), Cd(2+), Pb(2+) and Tl(+) on silica gel with polarographic detection

The HPLC separation of heavy metal cations was studied with a column packed with Separon SGX silica gel. The retention of the cations is controlled by an ion-exchange mechanism. The ion-exchange capacity is primarily dependent on the mobile phase pH. The analyte retention is further affected by the type and concentration of the completing agent present and of the counterion. The effect of acetate, tartrate and -hydroxyisobutyrate as complexing agents and that of methanol as the organic modifier were studied in detail and the results were compared with the theoretical model of ion-exchange separation. Simple mixtures of metals can be rapidly separated on a short column (30 × 3.3 mm i.d.), e.g., with a mobile phase containing 10⁻²M tartrate at pH 6.0. The metals separated can be detected by dc amperometry at a hanging mercury drop electrode. The limits of detection at an electrode potential of −0.95 V (Ag/AgCl) are in the units—tens of ng range with 20-μl samples with satisfactory precision (RSD values of 2–6%). The main advantages of the method are rapidly and simplicity because derivatization of the analytes is not required.     

Histidine-functionalized silica and its copper complex as stationary phases for capillary electrochromatography

A histidine-functionalized silica was prepared by covalent bonding of the functional groups to silane-treated silica gel. Conversion of functional groups was confirmed by infrared (IR) spectra, elemental analysis, and potentiometry. The functionality of the silica gel is 0.293 mmol g(-1). The coordination behavior of the histidine-functionalized silica was investigated by metal capacity and electron paramagnetic resonance (EPR). EPR measurements at different copper loadings were made. The results showed that the copper histidine complex might be distorted tetragonal. Both histidine-functionalized silica and its copper complex were employed as stationary phases for packed capillary electrochromatography (CEC). Electrical current was found helpful for evaluating the properties of frit construction and the stationary phase packing. Test samples include neutral compounds, inorganic anions and organic anions. Factors influencing the separation behavior have been studied. With copper-histidine functionalized silica under the condition of citrate buffer (10 mM, pH 4.0) and applied voltage of -20 kV, the separation of benzoic acid, D- and L-mandelic acid, phthalic acid and salicylic acid could be achieved within 12 min. The column efficiency for these acids was more than 1.2 x 10(5) plates m(-1), except salicylic acid.     

Capillary electrochromatographic separation of metal ion species with on-line detection by inductively coupled plasma mass spectrometry

A bonded phase capillary column containing macrocyclic polyamine, [28]ane-N₆O₂ functional groups was used for the electrophoretic separation of arsenic, chromium and selenium species. A simple device interfacing this capillary electrochromatography (CEC) systems to an inductively coupled plasma mass spectrometer (ICPMS) is described. The dimension of the capillary column was 160 cm×100 μm i.d. To accommodate this electrophoretic separation, an auxiliary capillary was used with nitric acid (0.05 M) as makeup liquid. With the electrokinetic method at –20 kV, 20 s and a nebulizer gas flow rate of 1 l min⁻¹, the sample injected was analyzed with an applied potential of −20 kV. The background electrolyte buffer for the separation of CrO₄²⁻–Cr³⁺ was phosphate (20 mM, pH 6.5). That for HAsO₄²⁻–Ph₄As⁺ was pyromellitate (20 mM, pH 6.0) and for SeO₄²⁻–SeO₃²⁻ was acetate (20 mM, pH 6.0). The role of the buffer’s anion was also discussed. The separation efficiency of the bonded phase was compared with the bare fused silica. Concentration detection limits for these metal ions were in the low ppb range. In addition, the matrix effect of the established system with the bonded phase was found smaller than that with the bare fused silica.     

Double gradient ion chromatography using short monolithic columns modified with a long chained zwitterionic carboxybetaine surfactant

The rapid separation of inorganic anions on short monolithic columns permanently coated with a long chained zwitterionic carboxybetaine-type surfactant is shown. The surfactant, N-dodecyl-N,N-(dimethylammonio)undecanoate (DDMAU), was used to coat 2.5, 5.0 and 10 cm long reversed-phase silica monoliths, resulting in a permanent zwitterionic exchange surface when used with aqueous based eluents. The unique structure of the surfactant results in a charge double layer structure on the surface of the stationary phase, with strong internal anionic and weak external cationic exchange groups. The dissociation of the weak external carboxylic acid group acts to shield the inner anionic exchange site, resulting in substantial effective capacity changes with eluent pH. Utilising this effect with the application of an eluent pH gradient, simultaneously combined with eluent flow-rate gradients, very rapid simultaneous separations of both weakly retained anions and strongly retained polarisable anions was possible, with up to 10-fold decreases in overall run times. Coating stability and retention times under isocratic and isofluentic eluent conditions were shown to be reproducible over >450 repeat injections, with peak efficiency values averaging 29,000 N/m for the 2.5 cm column and 42,000 N/m for the 10 cm monolithic column, again under isocratic elution conditions.     

Preparation and evaluation of a silica-based 1-alkyl-3-(propyl-3-sulfonate) imidazolium zwitterionic stationary phase for high-performance liquid chromatography

A new zwitterionic stationary phase based on silica bonded with 1-alkyl-3-(propyl-3-sulfonate) imidazolium was synthesized and characterized in this paper. The materials have been confirmed and evaluated by elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. Potassium and calcium were separated simultaneously with several common inorganic anions including an iodate, chloride, bromide, nitrate and iodide on the phase. The effects of the concentration, organic solvent and pH of the eluent on the separation of anions were studied. Operated in the anion-exchange mode, this new stationary phase shows considerable promise for the separation of anions. Bases, vitamins and three imidazolium ionic liquids with different alkyl chains are also separated successfully on this column. The stationary phase has multiple retention mechanisms, such as anion-exchange, electrostatic attraction and repulsion interactions, and hydrophobic interaction between the zwitterionic stationary phase and specimens.     

Novel imidazolium stationary phase for high-performance liquid chromatography

A new imidazolium anion-exchange phase immobilized on silica is synthesized. HPLC separations of common inorganic anions (IO3-, Cl-, NO2-, Br-, NO3-, I-, SCN-) have been performed using a HPLC column (200 mm x 4.6 mm I.D.) packed with this stationary phase, with a phosphate buffer solution as the mobile phase and UV detection at 200 nm. The effects of pH and concentration of eluent on the separation of anions have been studied. Chromatographic parameters are calculated and the results show that the new stationary phase is of significant potential for the analysis of these anions. Successful separations of some ordinary organic anions have also been achieved with the said stationary phase. Meaningfully, organic and inorganic anions can be determined simultaneously and satisfactorily with several neutral compounds using the column. The separation of some organic compounds including hydroxybenzenes, bases and amines by this stationary phase with only water as the eluent has been investigated.     

Fast ion chromatography of inorganic anions and cations on a lysine bonded porous silica monolith

A 0.46 cm x 10.0 cm silica monolith column was modified through the in situ covalent attachment of lysine (2,6-diaminohexanoic acid) groups. Due to the zwitterionic nature of the resultant stationary phase, the modified monolithic column contained both cation and anion exchange capacity. In the case of cation exchange, the capacity was found to be relatively low at between 5 and 6.5 micromoles Me2+ per column. However, as expected, the lysine monolith exhibited a higher anion exchange capacity at 12-13 micromoles A- per column (at pH 3.0), which was found to be dependent upon column pH, due to the dissociation of the weak acid carboxylic acid groups. High-performance separations of transition metal cations and inorganic anions were achieved using the modified monolith, with the effects of eluent concentration, pH and flow rate evaluated. Using elevated flow rates of up to 5 mL/min the separation of nitrite, bromate, bromide, nitrate, iodide and thiocyanate was possible in approximately 100 s with peak efficiencies of between 50 and 100,000 N/m and retention time %RSD of under 0.3%.     

Retention of some monoamine oxidase inhibitory drugs on a β-cyclodextrin polymer-coated silica column

The retention of seventeen monoamine oxidase inhibitory drugs (mono- and disubstituted derivatives of propargylamine) was determined on a β- cyclodextrin polymer (β-CDP)-coated silica column using methanol-0.05 M K₂HPO₄ (6:4, v/v) as the eluent. The inclusion complex formation between the drugs and a water-soluble β-cyclodextrin polymer was studied by charge-transfer chromatography carried out on reversed- phase TLC layers. The capacity factors were correlated with the various physico-chemical parameters and with the inclusion complex-forming capacity of the monoamine oxidase inhibitory drugs. Calculations indicated that the inclusion complex-forming capacity of the drugs does not influence their retention on a β-CDP column, that is, the water-soluble and water-insoluble β-CDPs show different retention characteristics. The specific hydrophilic adsorption surface of the solutes significantly influences the retention in HPLC. The results suggest that the selectivity of the β-CDP-coated silica support may be different from that of the traditional alkyl-bonded reversed-phase columns.     

Sinopak-s-DEAE高效弱阴离子交换色谱填料的研究

以多孔硅胶为基质,用改进的合成方法制备了Sinopak-s-DEAE高效弱阴离子交换色谱填。考察了反应条件对填料合成的影响,并以标准蛋白为样品进行了色谱行为的研究,结果表明：所制备的填料对蛋白质的分离性能良好,且对蛋白质的非特异性吸附小。     

Retention Behavior of Proteins on Glutamic Acid-Boned Silica Stationary Phase

A glutamic acid-bonded silica (Glu-silica) stationary phase with cation-exchange properties was synthesized using l-glutamic acid as ligand and silica gel as matrix. The effects of solution pH value, salt concentration and metal ion on the retention of proteins were examined. The standard protein mixture was separated with a prepared chromatographic column and an iminodiacetic acid column, and compared. The influence of the binding capacity of an immobilized metal ion on the complexation of metal chelate column was studied. The results indicate that the obtained column displays cation-exchange characteristic and better separation ability for proteins. As fixing metal ion on the Glu-silica column, retention of proteins on the column is a cooperative interaction of metal chelate and cation-exchange. The stationary phase shows the typical metal chelate properties with the increase of the sorption capacity of immobilized metal ion.     

On-line concentration of s-triazine herbicides in micellar electrokinetic chromatography using a cationic surfactant

A new method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was investigated using high-performance ion-exclusion/cation-exchange chromatography with conductimetric detection on a separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin in the hydrogen-form and an eluent comprising 1.5 mM sulfosalicylic acid–6 mM 18-crown-6 at pH 2.6, operated at 1.5 ml/min. Effective separation and highly sensitive conductimetric detection for the anions and the cations was achieved in about 14 min. Since the ionic balance (equivalents of anions/equivalents of cations) of acid rain waters of different pH (4.40–4.67) ranged from 0.97 to 0.94, evaluation of the water quality of acid rain was possible. This method was successfully applied to the simultaneous determination of the anions and the cations in acid rain transported from mainland China and North Korea to central Japan monitored by a meteorological satellite data analyzer.     

溶胶-凝胶开管电色谱柱的制备及评价

以溶胶-凝胶（sol－gel）技术制备开管毛细管电色谱（OTCEC）柱,考察了制柱过程中盐酸pH值和凝胶溶液在毛细管内反应时间对柱性能的影响。对制得的电色谱柱进行了评价,在最佳制柱条件下,硫际、苯乙酸、萘、联苯、2,6－二甲基萘的平均柱效分别为46．6×104,52．4×104,50．2×104,47．7×104,35．8×104塔板数／m。     

A polar-copolymerized method to prepare silica-based anion exchanger for ion chromatography

A novel silica-based strong anion exchanger was developed for ion chromatography by copolymerizing methyltrichlorosilane and 3-chloropropyltrichlorosilane. The method allows the column capacity to be easy control simply by adjusting the ratio of silanes. The unwanted residual silanol groups onto the surface of silica gel could also be greatly reduced by this strategy. The effective column capacity of the column used was measured to be 50.8 μequiv/column (2.03 μequiv/cm). The exchanger was characterized by solid state CP/MAS ¹³C NMR and elemental analysis and its separation performance was evaluated for the separation of common inorganic anions. The results showed that the column had good separation efficiency (e.g. the plate number of nitrite is 80,000/m) and the separation mechanism was observed to be dominantly governed by ion exchange mechanism. The utility of the column was demonstrated for the determination of nitrite and nitrate in saliva sample.     

Pressurized-flow anion-exchange capillary electrochromatography using a polymeric ion-exchange stationary phase

The feasibility of using capillary columns equipped with silica frits and packed with a polymer-based anion exchanger (Dionex AS9-HC) for CEC separations of inorganic anions has been investigated. Experiments using a conventional 25 cm packed bed, and mobile phase flow that is a combination of hydrodynamic and electroosmotic flow were used to demonstrate that by varying the applied voltage (electrophoresis component) or the concentration of the competing ion in the mobile phase (ion-exchange component), considerable changes in the separation selectivity could be obtained. Using an artificial neural network, this separation system was modelled and the results obtained used to determine the optimum conditions (9 mM perchlorate and −10 kV) for the separation of eight inorganic anions. When a short (8 cm) packed bed was used, with detection immediately following the packed section, the separation of eight test analytes in under 2.2 min was possible using pressure-driven flow and a simple step voltage gradient. A more rapid separation of these analytes was obtained by only applying high voltage (−30 kV), where many of the same analytes were separated in less than 20 s and with a different separation selectivity to that obtained in conventional ion-exchange or capillary electrophoresis separations.     

Ion-chromatographic behavior of alkali metal cations and ammonium ion on zirconium-adsorbing silica gel

The preparation and evaluation of zirconium-adsorbing silica gel (Zr-Silica) as an ion-exchange stationary phase in ion chromatography for inorganic anions and cations was carried out. The Zr-Silica was prepared by the reaction of silanol groups on the surface of the silica gel with zirconium butoxide (Zr(OCH2CH2CH2CH3)4) in ethanol. The ion-exchange characteristics of the Zr-Silica were evaluated using 10 mM tartaric acid at pH 2.5 as eluent. The Zr-Silica was found to act as a cation-exchanger under the eluent conditions. The retention behavior of alkali and alkaline earth metal cations was then investigated. The Zr-Silica column was proved to be suitable for the simultaneous separation of alkali metal cations and ammonium ion. Excellent separation of the cations on a 15 cm Zr-Silica column was achieved in 25 min using 10 mM tartaric acid as eluent.     

On-line preconcentration of organic anions in capillary electrophoresis by solid-phase extraction using latex-coated monolithic stationary phases

Quaternary ammonium functionalised polymeric latex particles were coated onto the wall of a fused-silica capillary or onto a methacrylate monolithic bed synthesised inside the capillary in order to create ion-exchange stationary phases of varying ion-exchange capacity. These capillaries were coupled in-line to a separation capillary and used for the solid-phase extraction (SPE), preconcentration and subsequent separation of organic anions by capillary electrophoresis. A transient isotachophoretic gradient was used for the elution of bound analytes from the SPE phase using two modes of separation. The first comprised a low capacity SPE column combined with a fluoride/octanesulfonate discontinuous electrolyte system in which peak compression occurred at the isotachophoretic gradient front. The compressed anions were separated electrophoretically after elution from the SPE preconcentration phase and resolution was achieved by altering the pH of the electrolyte in which the separation was performed. In the second approach, a latex-coated monolithic SPE preconcentration stationary phase was used in combination with a fluoride/perchlorate electrolyte system, which allowed capillary electrochromatographic separation to occur behind the isotachophoretic gradient front. This method permitted the removal of weakly bound anions from the SPE phase, thereby establishing the possibility of sample clean-up. The effect of the nature of the strong electrolyte forming the isotachophoretic gradient on the separation and also on the preconcentration step was investigated. Capillary electrochromatography of inorganic and organic species performed on the latex-coated monolithic methacrylate column highlighted the presence of mixed-mode interactions resulting from the incomplete coverage of latex particles onto the monolithic surface. Analyte preconcentration prior to separation resulted in compression of the analyte zone by a factor of 300. Improvement in the limit of detection of up to 10400 times could be achieved when performing the preconcentration step and the presented methods had limits of detection (S/N=3) ranging between 1.5 and 12 nM for the organic anions studied.     

氯甲基苯乙烯包夹硅基单柱强阴离子色谱柱的研究

采用氯甲基苯乙烯包夹硅胶基质制备出一种新型强阴离子色谱柱填料，该填料具有良好的色谱柱性能，可以较地的分离常见的６种无机阴离子，６种低碳链有机酸以及甲酸，乙酸和一些无机阴离子的混合物。     

Retention and selectivity properties of carbamate pesticides on novel polar-embedded stationary phases

This study describes the use of stationary phases with polar functionality suitable for the chemical analysis of carbamates pesticides and comparing with conventional alkyl C8 and C18 phases. The emphasis of this study was to compare the selectivity and retention of the pesticides on different stationary phases, bonded onto 1.7 μm partially porous silica particles under isocratic separation condition. Four stationary phases including: phenylaminopropyl (PAP) phase, bidentate propylurea-C18 (BPUC₁₈), C8 and C18, were successfully bonded on the partially porous silica spheres as evidenced by ²⁹Si and ¹³C solid-state NMR analysis. The phenylaminopropyl phase exhibited smaller retentivity and enhanced selectivity compared to the alkyl C8 phase; the analysis time to run separation of the six carbamate pesticides (i.e., methomyl, propoxur, carbofuran, carbaryl, isoprocarb, and promecarb) on the PAP phase was threefold faster than alkyl C8 phase. In a similar manner, the BPUC₁₈ phase shows similar selectivity to that of the PAP phase, but with longer retentivity; although the BPUC₁₈ phase is characterized with a lesser degree of retentivity for the carbamate pesticides than the conventional alkyl C18 phase. We propose that π–π and weak polar interactions between the carbamate pesticides and the PAP phase dominates the separation mechanism and providing a superior selectivity; faster separation time was also achieved as a result of smaller retentivity. Whereas the C8 and C18 bonded phases exhibits only hydrophobic interactions with the pesticides, leading to larger retentivity. The BPUC₁₈ phase is shown to interact via polar–polar interactions in addition to hydrophobic interactions with the pesticides, providing similar selectivity with the PAP phase but with larger retentivity.