Water Eluent Research Articles

Electrostatic Ion Chromatography of Common Anions and Cations with a Zwitterionic Surfactant-Modified Silica-C18 Column Using Water Eluent

Electrostatic ion chromatography (EIC) of anions and cations with water eluent has been investigated for the development of water-monitoring systems in developing countries, which have the nature of simple, lower running cost, and non-chemical waste. For selecting the separation column, sulfobetaine-type zwitterionic surfactant (CHAPS)-modified silica C18 and silica C30 columns, and a zwitterionic stationary phased column HILIC were compared for anion separations. The retention order of the analyte anions was SO42−<Cl−<NO3−<I−<ClO4− without regard to the types of the columns, depending on the nature of EIC separation. However, the resolutions were different, because the anion separations by EIC were strongly affected by the hydrophobicity of the stationary phase. As a result, the CHAPS-modified silica C18 column was the most suitable as a separation column in EIC in terms of the peak resolution and the retention time. In contrast, cation separations using the CHAPS-modified silica C18 column with a water eluent were in the order of monovalent cations (Li+, Na+, K+ and NH4+) < divalent cations (Mg2+ and Ca2+). This fact means that the sulfobetain-type zwitterionic stationary phase has much higher selectivity for anions than for cations. Moreover, a pre-column (cation-exchange resin in the Li+-form for anion separations, and anion-exchange resin in the Cl−-form for cation separations) was connected in tandem before the separation column, in order to make uniform the counter ion for analyte ions and to apply this method to real water samples. Under the optimized conditions, the linearity of the calibration graph, the detection limit, and the reproducibility for the common anions were tested, and satisfactory results was obtained for all common anions. The potentiality of EIC was demonstrated in practical applications to the determination of common anions (SO42−, Cl−, NO3− and HCO3−) and hardness in river water.

High temperature liquid chromatography with monolithic capillary columns and pure watereluent

Use of an organic polymeric monolithic stationary phase for high temperature liquid chromatography (HTLC) with a pure water eluent is demonstrated for the first time. Separations of n-alcohols at temperatures exceeding 200 degrees C were achieved with no statistically significant reduction in chromatographic performance evident after continuous operation for 1000 column volumes above 200 degrees C.

Advanced characterization of marine dissolved organic matter by combining reversed-phase liquid chromatography and FT-ICR-MS

Marine dissolved organic matter (DOM) was separated by reversed-phase (RP) liquid chromatography method and analyzed with fluorescence/absorption detection and Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). The three key characteristics of the RP method are: (a) The C18-RP column chosen provides enhanced separation when the aqueous phase is 100% buffer-free water, and it does not degrade over time; (b) the water eluent adjusted to pH 7 significantly improves the resolution of water soluble compounds; (c) the initial flow maintained at low levels improves the separation of polar compounds. In samples, containing “fresh” DOM, specific peaks were detected, which were absent in “old” DOM samples. The combination with size exclusion chromatography (SEC) also demonstrated the relation between polarity and molecular size of DOM. FT-ICR-MS was applied to evaluate the quality of separation on a molecular scale demonstrating that physico-chemical characteristics of DOM can be related to molecular formulas. Sample extracts were separated into 4 preparative fractions, and a large suite of the identified molecular formulas only occurred in specific fractions. This is an important basis for the application of further analytical techniques in order to perform a more target-oriented analysis aiming at the determination of source and process biomarkers for DOM.

Ion-exclusion chromatography with the direct UV detection of non-absorbing inorganic cations using an anion-exchange conversion column in the iodide-form

An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na +), ammonium (NH 4 +) and hydrazine (N 2H 5 +) ions was developed by connecting an anion-exchange column in the I −-form after the separation column. For example, NH 4 + is converted to a UV-absorbing molecule, NH 4I, by the anion-exchange column in the I −-form after the ion-exclusion separation on anion-exchange column in the OH −-form with water eluent. As a result, the direct UV detection of Na +, NH 4 + and N 2H 5 + could be successfully obtained as well as the well-resolved separation. The calibration graphs of the analyte cations detected with UV at 230 nm were linear in the range of 0.001–5.0 mM. The detection limits at S/N = 3 of the cations were below 0.1 μM. This method was applied to real water analysis, the determination of NH 4 + in river and rain waters, or that of N 2H 5 + in boiler water, with the satisfactory results. This could be applied also to low- or non-absorbing anions such as fluoride or hydrogencarbonate ions by the combination of a weakly acidic cation-exchange resin in the H +-form as the separation column and the anion-exchange conversion column.

Determination of levoglucosan in atmospheric aerosols using high performance liquid chromatography with aerosol charge detection

A sensitive method for analysis of levoglucosan (1,6-anhydro-β, d-glucopyranose) and other monosaccharide anhydrides, compounds present in biomass combustion smoke, was investigated employing high-performance liquid chromatography (HPLC) with recently developed aerosol charge detection. Aerosol charge detection involves the conversion of the column effluent to an aerosol, which is charged to produce a current. Use of a cation-exchange column and a pure water eluent was found to separate levoglucosan and mannosan from other aerosol components with a detection limit of about 90 ng mL −1 for levoglucosan or 5 ng injected. This method was demonstrated by successful analysis of aerosol filter samples from three locations.

Ion-pair chromatography of bis (sodium-sulfopropyl) disulfide brightener in acidic copper plating baths

Quantitative analysis of the brightener component bis (sodium-sulfopropyl) disulfide (SPS) in acidic copper plating baths poses a real challenge due to the complex chemical matrix containing large amounts of Cu(II) ion and sulfuric acid together with other organic additives and additive decomposition products. We developed a new ion-pair chromatography method to analyze micro-molar amounts of SPS directly in plating bath samples without the need for sample pre-treatment. Addition of tetra- N-methylammonium cation as ion-pairing agent to a methanol–sulfuric acid–water eluent increases the retention time of the anionic SPS 2− on a C 18 column sufficiently to separate this compound from Cu(II) ion and additive by-products.

High temperature liquid chromatography of triazole fungicides on polybutadiene-coated zirconia stationary phase

High temperature liquid chromatography using water-rich and superheated water eluent is evaluated as a new approach for the separation of selected triazole fungicides, hexaconazole, tebuconazole, propiconazole, and difenoconazole. Using a polybutadiene-coated zirconia column at temperatures of 100–150°C, clear separations were achieved when 100% purified water was utilized as organic-free eluent. Excellent limits of detection down to pg level were obtained for the separation of the triazole fungicides under optimum conditions. Van’t Hoff plots for the separations were linear suggesting that no changes occurred in the retention mechanism over the temperature range studied.

HPLC–RIA analysis of steroid hormone profile in a virilizing stromal tumor of the ovary

The pathological steroid biosynthesis of a virilizing ovarian tumor was examined via high performance liquid chromatography–radioimmunoassay (HPLC–RIA) determination of the intratissular steroid concentrations. Sex cord-stromal tumor of the ovary was obtained surgically from an 18-year-old female patient with extremely high androst-4-ene-3,17-dione (4-en-dione) and testosterone (Test) blood serum levels. The tissue specimen was extracted with ethyl acetate and the extract was then purified on a C 18 mini-column with methanol–water eluents. Steroids were isolated by reversed-phase HPLC on a C 18-silica gel column with 51%, 55% and 64% v/v methanol–water eluents. Steroids in the collected eluent fractions were detected by the radioactivity of tritiated internal standards and then quantified by specific RIAs. In the tumor specimen, very high 17α-hydroxyprogesterone (17-OH-Prog; 6300 fmol/g), dehydro-epiandrosterone (2870 fmol/g), androst-4-ene-3,17-dione (3000 fmol/g), testosterone (5700 fmol/g) concentrations, and less progesterone (PROG; 320 fmol/g) and androst-5-ene-3β,17β-diol (5-en-diol; 320 fmol/g), were determined. Tissue levels of 5α-dihydrotestosterone (DHT), 5α-androstane-3α,17β-diol (3α-diol), 5α-androstane-3β,17β-diol (3β-diol), and 17β-estradiol were found to be 71, 20, 28, and 12 fmol/g, respectively. Steroid profile analysis verified a pathological steroid biosynthesis in the ovarian tumor and suggested that the 17α-hydroxylase (17α-H), 17,20-lyase (17,20-L), and 3β-hydroxysteroid dehydrogenase/Δ 5–4-isomerase (Δ 5-3β-HSD) activities were particularly elevated in this tumorous tissue. Present data demonstrate that the analysis of intratissular steroid profile by a HPLC–RIA method may valuably contribute to the steroidal pathophysiology of endocrine tumors.

Demonstration of simultaneous anion-exchange and reversed-phase behavior on a strong anion-exchange column

We demonstrate in this report that a conventional silica-based strong anion-exchange column can exhibit reversed-phase chromatographic behavior simultaneously with ion-exchange in a methanol–aqueous phthalate mobile phase. Reversed-phase behavior is shown for PAHs in relatively high methanol-content mobile phases, while polar organics exhibit reversed-phase behavior in 0–10% (v/v) methanol–water eluents. At low concentrations (0–10% v/v) methanol has little or no effect on anion retention, while the anions exhibit only slight increases in retention in 60–80% (v/v) methanol at near-neutral pH values. Likewise, pH changes used to manipulate anion retention have essentially no effect on PAH retention, and cause only small decreases in retention for most of the polar organics studied. Little or no pH-effect was seen on a phenyl column (no exchange group) or with acetate mobile phase. It is shown that manipulation of pH and methanol content allows the grouping of neutral organic analytes early in a chromatogram, followed by the anions, with no class overlap. Several example chromatograms are given, including that of a red wine sample. Column efficiency was good for anions but only modest for organics.

Sulfonylcalix[4]arenetetrasulfonate as pre-column chelating reagent for selective determination of aluminum(III), iron(III), and titanium(IV) by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection

Sulfonylcalix[4]arenetetrasulfonate (SO 2CAS) has been examined as a pre-column chelating reagent for ultratrace determination of metal ions by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. Metal ions were converted into the SO 2CAS chelates in an acetic buffer solution (pH 4.7). The chelates were injected onto a n-octadecylsilanized silica-type Chromolith™ Performance RP-18e column and were eluted using a methanol (50 wt.%)-water eluent (pH 5.6) containing tetra- n-butylammonium bromide (7.0 mmol kg −1), acetate buffer (5.0 mmol kg −1), and disodium ethylendiamine- N, N, N′, N′-tetraacetate (0.10 mmol kg −1). Under the conditions used, Al(III), Fe(III), and Ti(IV) were selectively detected among 21 kinds of metal ions [Al(III), Ba(II), Be(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ga(III), Hf(IV), In(III), Mg(II), Mn(II), Mo(VI), Ni(II), Pb(II), Ti(IV), V(V), Zn(II), and Zr(IV)]. The detection limits on a 3σ blank basis were 8.8 nmol dm −3 (0.24 ng cm −3) for Al(III), 7.6 nmol dm −3 (0.42 ng cm −3) for Fe(III), and 17 nmol dm −3 (0.80 ng cm −3) for Ti(IV). The practical applicability of the proposed method was checked using river and tap water samples.

Enhanced calculation of optimal gradient programs in reversed-phase liquid chromatography

The resolution of a mixture of 16 β-blockers under gradient elution was optimised using both isocratic and gradient training sets, with a reversed-phase column and acetonitrile–water eluents. Error theory was applied to measure the information extracted from different gradient experimental designs. This allows checking the expected accuracy when gradient predictions exceed the initial solvent concentrations tested in the training set. This work applies the results on modelling found in a previous study [J. Chromatogr. A 1018 (2003) 169] where the performance of several retention models was compared. Enhanced retention predictions were applied to the optimisation of gradient programs involving three factors (gradient slope, initial solvent composition and gradient curvature), using the peak purity criterion as resolution assessment. Peak shape parameters required in peak purity evaluation were modelled by adapting previous developments in isocratic mode. The mixture, which required prohibitive analysis times under isocratic elution, was almost baseline resolved in less than 35 min with linear gradients. Curvilinear gradients did not enhance this result significantly.

QSPR Prediction of Three Partition Properties for Phenylacrylates

The n‐octanol/water partition coefficients (K ow) and water solubilities (S w) of 11 phenylacrylates were determined by the shake‐flask method. Their capacity factors (k′) were determined by reversed‐phase high performance liquid chromatography (RP‐HPLC) with C18 column and methanol water eluent. It was found that both log K ow and log S w had good correlations with log k′, respectively. Linear solvation energy parameters, describing the interaction of molecules accurately, were calculated for these compounds and used to predict their partition properties. Results demonstrated that three partition properties could be predicted precisely with similar models based on linear solvation energy relationships, which indicated the similarity of their partition mechanisms.

Thermodynamic properties of polyethoxylated nonylphenols by reversed-phase high-performance liquid chromatography

Abstract The reversed-phase liquid chromatography (RPLC) was used to investigate the thermodynamic properties of homogeneous ethoxylated nonylphenols (NPE 7–15 ) and their retention mechanism from methanol–water eluents. The enthalpies (ΔH°) and entropies (ΔS°) of transfer from the mobile phase to the octyl- and octadecylsilica stationary phase were determined using the change of the capacity factor (k′) with temperature. The ΔH° and ΔS° values were negative and decreased with the water content of the eluent and with the length of ligand bonded to the stationary phase. The ethylene oxide chain length of the surfactants does not significantly influence the thermodynamic functions of retention. The enthalpy–entropy compensation (EEC) behavior was employed to investigate the mechanism of surfactant retention in the reversed-phase systems. The obtained compensation temperatures were within the 430–590 K range. They were very closed to those of ethoxylated fatty alcohols (455–586 K) and fall within the range of hydrophobic organic compounds. The results reveal the similarity of interactions involved in the RPLC with nonpolar stationary phases and aqueous eluents.

Selective determination of beryllium(II) ion at picomole per decimeter cubed levels by kinetic differentiation mode reversed-phase high-performance liquid chromatography with fluorometric detection using 2-(2'-hydroxyphenyl)-10-hydroxybenzo[H]quinoline as precolumn chelating reagent.

A highly sensitive and selective method for the determination of the Be(II) ion has been developed by the use of reversed-phase high-performance liquid chromatography (HPLC) with fluorometric detection using 2-(2'-hydroxyphenyl)-10-hydroxybenzo[h]quinoline (HPHBQ) as a precolumn (off-line) chelating reagent. The reagent HPHBQ has been designed to form the kinetically inert Be chelate compatible with high fluorescence yield, which is appropriate to the HPLC-fluorometric detection system. The Be-HPHBQ chelate is efficiently separated on a LiChrospher 100 RP-18(e) column with a methanol (58.3 wt %)-water eluent containing 20 mmol kg(-1) of tartaric acid and is fluorometrically detected at 520 nm with the excitation at 420 nm. Under the conditions used, the concentration range of 20-8,000 pmol dm(-3) of Be(II) ion can be determined without interferences from 10 micromol dm(-3) each of common metal ions, typically Al(III), Cu(II), Fe(III), and Zn(II), and still more coexistence of Ca(II) and Mg(II) ions at 0.50 mmol dm(-3) and 5.0 mmol dm(-3), respectively, is tolerated. The detection limit (3a baseline fluctuation) is 4.3 pmol dm(-3) (39 fg cm(-3)). The extraordinarily high sensitivity with toughness toward the matrix influence was demonstrated with the successful application to environmental Be analyses, such as determination of Be in rainwater and tap water.

Bayer’s Aura technology enables processors to colour already-moulded plastics

The aim of the study was to evaluate the biological effects of water eluents from polycarbonate based esthetic orthodontic brackets.The composite polycarbonate brackets tested were Silkon Plus (SL, fiber-glass-reinforced), Elan ME (EL, ceramic particle-reinforced) and Elegance (EG, fiber-glass-reinforced). An unfilled polyoxymethylene bracket (Brilliant, BR) was used as control. The brackets’ composition was analyzed by ATR-FTIR spectrometry. The cytotoxicity and estrogenicity of the eluents obtained after 3 months storage of the brackets in water (37 °C) were investigated in murine fibroblasts (NIH 3T3), breast (MCF-7) and cervical cancer (CCl-2/Hela) cell lines.SL and EG were based on aromatic-polycarbonate matrix, whereas EL consisted of an aromatic polycarbonate-polyethylene terepthalate copolymer. A significant induction of cell death and a concurrent decrease in cell proliferation was noted in the EG eluent-treated cells. Moreover, EG eluent significantly reduced the levels of the estrogen signaling associated gene pS2, specifically in MCF7 cells, suggesting that cell death induced by this material is associated with downregulation of estrogen signaling pathways. Even though oxidative stress mechanisms were equally activated by all eluents, the EG eluents induced expression of apoptosis inducing factor (AIF) and reduced Bcl-xL protein levels.Some polycarbonate-based composite brackets when exposed to water release substances than activate mitochondrial apoptosis.

Retention equations of nonionic organic chemicals in soil column chromatography with methanol-water eluents.

Research efforts dealing with chemical transportation in soils are needed to prevent damage to ground water. Methanol-containing solvents can increase the translocation of nonionic organic chemicals (NOCs). In this study, a general log-linear retention equation, log k' = log k'w - Sphi (Eq. [1]), was developed to describe the mobilities of NOCs in soil column chromatography (SCC). The term phi denotes the volume fraction of methanol in eluent, k' is the capacity factor of a solute at a certain phi value, and log k'w and -S are the intercept and slope of the log k' vs. phi plot. Two reference soils (GSE 17204 and GSE 17205) were used as packing materials, and were eluted by isocratic methanol-water mixtures. A model of linear solvation energy relationships (LSER) was applied to analyze the k' from molecular interactions. The most important factor determining the transportation was found to be the solute hydrophobic partition in soils, and the second-most important factor was the solute hydrogen-bond basicity (hydrogen-bond accepting ability), while the less important factor was the solute dipolarity-polarizability. The solute hydrogen-bond acidity (hydrogen-bond donating ability) was statistically unimportant and deletable. From the LSER model, one could also obtain Eq. [1]. The experimental k' data of 121 NOCs can be accurately explained by Eq. [1]. The equation is promising to estimate the solute mobility in pure water by extrapolating from lower-capacity factors obtained in methanol-water mixed eluents.

Isolation of tetracyclines in milk using a solid-phase extracting column and water eluent

An isolating method using a solid-phase extraction (SPE) ISOLUTE® C8 endcapped syringe-column for routine monitoring of residual tetracyclines (TCs) (oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC), and doxycycline (DC)) in cow's milk is presented. In the simplest and most environmentally harmless method, milk samples could be applied directly to the SPE column, following which all TCs were eluted with water. No organic solvents were used at all. The purified sample was injected into a high-performance liquid chromatography (HPLC) with a photo-diode array detector (PDAD). For the HPLC determination/identification, a LiChrospher® 100 RP-8 endcapped column and a mobile phase of acetonitrile −7% (v v −1) acetic acid solution (in water) (35:65, v v −1) with a PDAD was used. The total time required for the analysis of one sample was <40 min. Average recoveries (spiked 0.1–1.0 μg ml −1 each drug) and their standard deviations were >80 and <5%, respectively.

Reversed-phase liquid chromatographic simultaneous determination of iron(III) and iron(II) as complexes with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol: Determination of iron(III) and iron(II) in water samples and ultrasound field effect on distribution of iron(III) and iron(II) in micellar solution

The formation of Fe(III) and Fe(II) chelates with pyridylazo and thiazolylazo reagents was examined. Optimum conditions for the formation of Fe(III) and Fe(II) chelates with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) were in detail evaluated. The LC method for simultaneous separation of Fe(III) and Fe(II) ions as 5-Br-PADAP chelates was evaluated using the PEEK column with C18 e.c. stationary phase and acetonitrile+water (90:10, v/v) eluent containing the 1×10 −3 mol l −1 C 12H 25SO 3Na, the ion-pairing reagent, pH 3.4–3.6. The simultaneous determination of 20–500 μg l −1 Fe(II) ions (detection at 555 nm) and 20–500 μg l −1 Fe(III) ions (detection at 585 nm) as 5-Br-PADAP chelates (for both ions, detection limit, 18 μg l −1 for 20 μl loop) was established. The chromatographic method was applied to the water analysis. Although the present method is able to determine both Fe(III) and Fe(II) ions, the Fe(III) ion was not detected in all water samples. The Fe(II) was detected only in fresh gathered oligocene water at the level of 135 μg l −1. The present method was used to the investigation of the distribution of Fe(III)/Fe(II) ions in aqueous and micellar solutions after action of external, ultrasonic field.

Automated trace anion determinations in concentrated electronic grade phosphoric acid by ion chromatography

Modifications have been made to the method of ion-exclusion pre-separation followed by ion exchange with conductivity detection for the determination of trace levels of chloride, sulfate and nitrate in concentrated phosphoric acid. Ion-exclusion separation and pre-concentration of impurity anions is performed using Dionex AS6-ICE and AS11-HC (4 mm) columns, respectively, with water eluent. Final separation is performed using Dionex AG11-HC and AS11-HC (2 mm) columns, KOH gradient elution, and suppressed conductivity detection. Improvements to the method include addition of an autosampler and eluent generator, and use of external standard calibration. These instrumental and procedural changes significantly improve the method’s throughput, while the method’s capability relative to phosphoric acid specifications is maintained, as verified through statistical evaluation of control sample analyses. Detection limits of 60, 680, and 40 ppb (w/w) are obtained vs. semiconductor-grade phosphoric acid specifications of 1000, 12 000, and 5000 ppb for chloride, sulfate, and nitrate, respectively.

Superheated water eluent capillary liquid chromatography

A capillary scale reverse phase liquid chromatography (LC) system using a super hot water eluent is described. The system, constructed in-house from readily available components, has been shown to operate at temperatures as high as 370 °C and pressures in excess of 10 000 psi. The capability of the system is demonstrated with the separation of a mixture of polar and non-polar benzene derivatives on polybutadiene and elemental carbon modified zirconia packings with or without temperature gradients. Six benzene derivatives can be separated in ∼2 min.