Dual Retention Research Articles

Importance of injection solution composition for LC-MS-MS methods.

For the first time, the influence of the injection solution composition on the quality of LC-MS-MS methods, in terms of column efficiency and peak shape, was systematically investigated. Various types of compounds, including polar ionic acidic, polar ionic basic and non-polar neutral compounds, were prepared in different solutions ranging from 100% water to 100% acetonitrile. Different volumes of these solutions were injected onto either C18 or silica columns connected to tandem mass spectrometry. The mobile phases consisted of acetonitrile, water, and small amounts of volatile acid or buffer. On silica columns, the influence of injection solution on the peak shape and column efficiency was straightforward. The sharpest peaks and the highest column efficiency were obtained with 100% acetonitrile as the injection solvent. On C18 columns, this type of influence was less clear due to the dual retention mechanism of the bonded phase and of the residual silanol groups. On C18 column, retention due to residual silanol groups was significant even with a mobile phase containing less than 50% acetonitrile. Poor peak shape was observed when the injection solution had a stronger eluting strength than mobile phase, particularly for early eluting peaks.

CHROMATOGRAPHIC EVALUATION OF ALKYLPHOSPHONIC ACID-MODIFIED CERIA-ZIRCONIA IN REVERSED-PHASE HPLC

Porous ceria-zirconia sperules were surface modified with alkylphosphonic acid to create reversed phase material. The chromatographic properties of the ceria-zirconia-based stationary phase were evaluated in detail with neutral, basic, and acidic compounds as probes, over a wide range of mobile phase composition and pH. Polycyclic aromatic hydrocarbons (PAHs) were well separated and their elution order were in accordance with those reported on the silica-based reversed-phase column. Typical reversed-phase chromatographic behavior was also observed with basic solutes at pH10.0, whereas dual mode retention mechanism was adopted to elucidate retention characteristics of some of the basic solutes at pH4.0. Acidic compounds exhibited strong interaction with the alkylphosphonic acid modified ceria-zirconia (PA-CeO2-ZrO2) with methanol-water mixture as mobile phases, but these interaction were reduced to different extents in the presence of competing agents, such as acetate, sulfate, and oxalate. o-hydroxybenzoic acid irreversibly adsorbed on the PA-CeO2-ZrO2 stationary phase, even in the presence of oxalate, which may be explained by the formation of chelate ring.

Aminated poly-N-vinylformamide as a modern retention aid of alkaline paper sizing with acid rosin sizes

Partially aminated poly-N-vinylformamides (APNVF) were prepared by the hydrolysis of PNVF and used as the retention aid of rosin size. The dual retention aids system, consisting of this modern polymer and aluminum sulfate (alum) for neutral-alkaline paper sizing using acid rosin sizes, was evaluated by experiment. The results indicated that APNVF was very effective and a small amount of the polymer used together with alum considerably increased the size retention and sizing degree of paper under neutral-alkaline conditions. The cationic charge density of APNVF significantly influenced the sizing efficiency of the rosin sizes. Furthermore, the retention of alkaline filler CaCO3 and paper strength were improved by the polymer addition. It is clear that the polymer can be used as a multifunctional additive for papermaking. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1805–1810, 2000

デュアルシステムによるコート原紙の操業性改善

With the purpose to improve main paper properties, the head-box of papermachine No 2 in the Iwanuma mill was reconstructed and the wire-part was remodeled to an on-top type in October 1996. Base paper for coating is produced on this machine and after the reconstruction paper properties such as two-sidedness, formation and ash profile were improved. However, at the same time one-pass retention (OPR) dropped resulting in some other quality and operational problems. After consideration it was judged that a dual retention aid system may be the most suitable way to over-come these problems to a reasonable chemical cost.In January 1997 machine trials started with this dual retention aid system and in October the same year the machine went into comercial operation with this system. Sometimes paper formation is harmed by too high OPR. Therefore high OPR and good formation at the same time became an important issue. When the dual system was selected it was under the condition that formation would not be harmed and it was found that a microparticle system fulfilled this requirement.After the introduction of the dual system remarkable improvements in operation and paper quality have been recognized. The chemical costs are also low and therefore we can conclude that all our targets have been realized. However some new issues have come up and we are now working to understand and solve these issues in order to further improve our situation.

A study of a permanently coated polymeric column for simultaneous separation of inorganic anions and mono-carboxylic acids

A polymeric PRP-1 reversed-phase column was modified by coating it with hexadecyltrimethylammonium bromide and has been used as an analytical column for the separation of inorganic anions and mono-carboxylic acids. An aqueous solution of sodium salicylate was used as the mobile phase and the detection was performed by indirect UV detection. The exchange capacity of the permanently coated column was controlled by changing the concentration of the organic modifier, acetonitrile, in the coating solution. The coated column with a low ion-exchange capacity has a dual retention mechanism of ion-exchange and surface adsorption for carboxylic acids. The contribution of the two mechanisms in the separation was qualitatively evaluated under three chromatographic conditions, by means of equations for ion-exchange chromatography, an adsorption model of the electrical double layer and the separation factor. The extra-column factors that influence the retention of the surface adsorption of the carboxylic acids were discussed. Among the factors studied, the pH of the mobile phase plays a double role, i.e. adjusting the eluting strength and governing the contribution of each mechanism to the separation. Under the chromatographic conditions selected, simultaneous separation of inorganic anions and mono-carboxylic acids was achieved.

Studies on the retention behaviour of a group of organic anions of biochemical interest on quaternary bonded silica columns equilibrated with a functionally coherent series of counterions: Use of 2-(N-morpholino)ethanesulphonate as a counterion and N-tris(hydroxymethyl)methyl-3-aminopropanesulphonate as an eluent

The anions of a functionally coherent series of Good's buffers have been used to provide the counterions for quaternary bonded silica and the mechanisms of exchange with a test sample of organic anions of biochemical interest studied with the objective of finding strategies which might be suitable for the extraction of organic anions from biological fluids. A dual retention mechanism involving the electrical double layer and the pH related ionisation of the counterion is proposed. The MES [MES = 2-(N-morpholino)ethanesulphonic acid] anion is shown to be a useful counterion and the TAPS − [TAPS = N-tris(hydroxymethyl)methyl-3-aminopropanesulphonic acid] anion a useful eluent in a series of compatible techniques which could be applicable in methods involving either solid-phase extraction or HPLC for separation purposes. An analytical protocol compatible with assay by capillary electrophoresis is described.

Evaluation of Various Phenolformaldehyde Resins in the Phenolformaldehyde Resin—Polyethyleneoxide Dual Retention Aid System

Abstract Retention performance of the polyethylene oxide (PEO)-phenolformaldehyde resin (PFR) retention aid system is affected by the chemical structure and the molecular weight distribution of PFR. 1NMR and high performance liquid chromatography have been used to characterise various resole and novolak-based resins. Of the resins examined, those with the highest molecular weight gave the greatest retention improvement. The type of substitution around the aromatic ring of the resin appears to affect the interaction with PEO and the size and structure of the network formed when PFR and PEO are mixed together.

Reversed-phase thin-layer and gas chromatographic retention behaviour of triphenylmethane derivatives

Reversed-phase thin-layer chromatographic (RP-TLC) R M values and Kováts retention indices ( I) were determined for 26 triphenylmethane derivatives and their analogues (TMDs). The relationship between R M values and organic phase concentration in the eluent was investigated. A non-linear function having a minimum extreme value at about 60% acetone concentration was obtained. This phenomenon is related to the dual retention mechanism observed in reversed-phase high-performance liquid chromatography. The relationship between R M values and gas chromatographic retention indices was also studied. No significant linear relationship was obtained. The poor correlation indicates that gas chromatographic retention indices cannot be used for characterizing the lipophilicity of the TMDs, and RP-TLC is suggested for this purpose.

Silanol group effect of alkylnitrile (cyano) bonded phase in high-performance liquid chromatography

When a cyano bonded phase is used together with a nonaqueous eluent, it is universal that the silanol groups which remain at the surface of the silica gel after bonding affect the retention of solutes. With solutes containing such atoms as N, S and O, hydrogen bond may form between the solute and the residual silanol group, leading to dual retention mechanism. Based on the understanding of retention mechanism, methods were developed to separate metal-diethyldithiocarbamate (DDTC) chelates and crown ethers on cyano bonded phase, the mobile phase being a nonaqueous solvent containing triethylamine (TEA).

High-performance liquid chromatography with concanavalin A immobilized by metal interactions on the stationary phase

Concanavalin A (Con A) was immobilized via metal interactions on macroporous, microparticulate silica support having covalently bound iminodiacetic acid functions (IDA-silica) chelated with Cu(II) at the surface. The amount of copper and of Con A in the column could readily be controlled by the conditions used for chelating the metal by IDA-silica and for immobilization of the lectin. The retention behavior of columns packed with the stationary phase did not change under a wide range of elution conditions, indicating no loss of immobilized lectin. However, the Con A proper could readily be removed from the column at pH 3.0 or together with Cu(II) by perfusion with EDTA at neutral pH. Columns containing Con A immobilized by this technique exhibited dual retention behavior for proteins, glycoproteins, and carbohydrates according to the pertinent glycan-lectin or protein-metal interactions. The glycoproteins, peroxidase and α 1-acid glycoprotein, were retained by the Con A moiety and eluted with eluents containing competing sugars, whereas the proteins, β-lactoglobulin, α-chymotrypsinogen A, and ribonuclease A and B were retained by the chelated copper and were eluted and separated with eluents containing sodium chloride or borate. Binding constants of glycosides on the immobilized Con A were evaluated chromatographically and found to be one-third to two-thirds those reported in the literature on the basis of experiments in free solution.

Dual retention mechanism on commercial acetylcellulose as a stationary phase in planar chromatography

Dual retention mechanism on commercial acetylcellulose as a stationary phase in planar chromatography

Irregular retention properties of 21-aminosteroid antioxidants in octylsilane bonded-phase high-performance liquid chromatography

The retention characteristics of two novel 21-aminosteroid antioxidants, 21-[ 4-(2,6-di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl]-16α-methylpregna-1,4,9(11)-triene-3,20-dione dimethanesulfonate (I) and 21-[4-(2,5-di-N-diethylamine-2-pyridinyl)-1-piperazinyl]-16α-methylpregna-1,4,9(11)-triene-3,20-dione hydrochloride (II), in octylsilane bonded-phase high-performance liquid chromatography were examined in detail. Both I and II exhibited irregular retention behaviour which could be explained by the dual retention mechanism model proposed by A. Nahum and Cs. Horváth [J. Chromatogr., 203 (1981) 53]. Unless an amine modifier was added to competitively inhibit association with exposed silanol binding sites, the retention of both compounds in a 70% acetonitrile mobile phase was primarily due to silanophilic interactions. Addition of amine modifiers, lowering the pH, and increasing the sodium ion concentration of the mobile phase all decreased retention times, and modifiers capable of hydrogen bonding diminished peak tailing.

Lipophilicity measurement of nicotinates by reversed-phase high-performance liquid chromatography : Differences in retention behaviour, but similarities of log kw values, in methanol-water and acetonitrile-water eluents

The lipophilicity of 22 nicotinate esters was examined by reversed-phase high-performance liquid chromatography using methanol-water and acetonitrile-water as eluents. In the former system, a linear relationship exists between the log of the capacity factor (log k) and the fraction of modifier in the eluent. In contrast, the relationship is parabolic in the acetonitrile-water system. This behaviour is interpreted in terms of parabolic in the acetonitrile-water system. This behaviour is interpreted in terms of a dual retention mechanism, namely hydrophobic expulsion and polar (presumably silanophilic) interactions. Linear (methanol-water) and parabolic (acetonitrile-water) extrapolations to 0% modifier yielded practically identical log k w values ( r 2 = 0.980), indicating that for a given stationary phase, log k w is an index of hydrophobic effects independent of specific solute-modifier interactions. The log k w values correlate well with calculated log P oct values ( r 2 = 0.962 and 0.948).

Effect of the mobile phase composition on the retention behaviour of diphenylsilica pre-coated plates

The retention of some rifamycins and steroids on diphenyl bonded pre-coated silica gel plates, in relation to the mobile phase used, was examined by thin-layer chromatography. Neat organic solvents, non-aqueous and aqueous binary mixtures were tested as eluents. By comparison of retention data for rifamycins and steroids, respectively, under non-aqueous and aqueous conditions, a dual retention mechanism on this diphenyl phase was found. Interactions with the residual silanol groups seemed to prevail when employing as mobile phase the more lipophilic solvents tested, such as chloroform or dichloromethane, whereas interactions with the aryl groups of the bonded phase prevailed when using high polarity alcohols or aqueous mixtures. As a consequence, by changing the mobile phase, a large variation in selectivity with a concomitant change in retention order fo the test compounds was observed.

Lipophilicity measurements of protonated basic compounds by reversed-phase high-performance liquid chromatography : I. Relationship between capacity factors and the methanol concentration in methanol-water eluents

The retention behaviour of protonated basic compounds in reversed-phase high-performance liquid chromatography, using methanol-water mixtures as the eluent, is reported. A minimum is found in the relationship between the logarithm of the capacity factor (log k) and the percentage of methanol ( x) in the eluent. The deviation from linearity is postulated to be caused by a dual retention mechanism, namely polar interactions between the solute and eluent molecules in water-poor eluents, and hydrophobic expulsion in water-rich ones. The influence of the pH, p K a and lipophilicity on retention behaviour is also investigated.

Retention behaviour and molecular structure of the solute in thin-layer chromatography

Dual retention behaviour on cellulose, silica and alumina in thin-layer chromatography, that is, the separation of solutes either in normal phase or in reversed phase mode is discussed as a function of the mobile phase polarity utilizing the solubility parameter theory and then correlated with the molecular structure of the solute.

Surface silanols in silica-bonded hydrocarbonaceous stationary phases : I. Dual retention mechanism in reversed-phase chromatography

“Irregular” retention behavior of crown ethers in reversed-phase chromatography with silica-bonded hydrocarbonaceous stationary phases is interpreted by using a dual binding model. It is assumed that retention is caused not only by the usual solvophobic interactions but also by “silanophilic” interactions between the eluite and the accessible silanol groups at the surface of various alkyl-silica bonded phases. Minima observed in the dependence of the retention factor of dibenzo-18-crown-6 on the composition of methanol-water mixtures used as the eluent are in agreement with the theory. The model also correctly predicts the temperature dependence of retention under various conditions as far as the nature of the stationary phase and the eluent composition are concerned. Thus curved Van 't Hoff plots of the experimental data are attributed to the sufficiently dissimilar enthalpies involved in the solvophobic and silanophilic binding. It is likely that minima exhibited by plots of retention factor against eluent composition in reversed-phase chromatography are in most cases manifestations of the countervailing effect of the solvophobic and silanophilic forces on retention.

Surface silanols in silica-bonded hydrocarbonaceous stationary phases : II. Irregular retention behavior and effect of silanol masking

Dibenzo-crown ethers and certain peptides with unprotected amino groups do not exhibit the regular linear dependence of the logarithmic retention on the composition of binary hydro-organic eluents on silica-bonded C 8 and C 18 hydrocarbonaceous stationary phases but the plots have minima. Similar results are found when the stationary phase is “naked” silica having no ligates. The results are interpreted in terms of a dual retention mechanism that postulates solute retention as a result of both solvophobic (hydrophobic) and silanophilic interactions between the eluite and stationary phase even in the case of “naked” silica. Masking of the surface silanols by increasing the water concentration of the eluent or by the addition of a suitable amine, which can also be a buffer component, is shown to attenuate silanophilic interactions so that regular retention behavior is observed with both crown ethers and peptides. Beyond its traditional use, this approach may make possible the measurement of chromatographic data without interference by silanophilic effect and, thus, facilitate the development of a retention index system. On the other hand, silanol groups at the surface of bonded phases may be essential to obtain adequate selectivity as illustrated by reversed-phase chromatography of a peptide mixture. The similarity between the retention data obtained with aqueous eluents on “naked” silica gel and on C 8 and C 18 alkyl-silicas implies that the relative polarity of the mobile and stationary phase is the chief distinguishing mark for classification of various chromatographic systems. Furthermore, it also suggests that the dual retention mechanism may be a rather common phenomenon which needs to be taken into account for interpretation of retention data and designing chromatographic separations.