NaOH Eluent Research Articles

Liquid Chromatographic Arsenic Speciation with Gas-Phase Chemiluminescence Detection

We present a newly developed gas-phase chemiluminescence (CL) detection method for the separation and quantification of inorganic and organic arsenic species. Arsenite, arsenate, dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) were separated by anion exchange using carbonate-bicarbonate and NaOH eluents with step-gradient elution. The separated species were passed through a UV photooxidation reactor which decomposed the organic species and converted them to inorganic As(V). Subsequent on-line hydride generation with acid and sodium borohydride produces AsH3 and H2, which are separated from the liquid in a gas-liquid separator. The produced AsH3, driven by H2, reacts with ozone in a small reflective cell located atop a photomultiplier tube, resulting in intense CL. In the present form, the limits of detection (LODs, signal-to-noise = 3), based on peak height, for arsenite, arsenate, MMA, and DMA are 0.4, 0.2, 0.5, and 0.3 microg/L, respectively, for a 100 microL injected sample. This analyzer demonstrates the robustness of the CL detection system for arsenic and provides an affordable alternative to atomic spectrometry for use as a detector after chromatographic speciation. We found no significant practical interferences.

Development and validation of an assay for citric acid/citrate and phosphate in pharmaceutical dosage forms using ion chromatography with suppressed conductivity detection

The paper describes the development and validation of a simple, rapid, accurate, and sensitive ion chromatographic procedure to assay total citrate (citric acid/citrate) and phosphate in nine dosage forms. The dosage forms chosen represent all dosage forms in USP27-NF22 for which the respective monographs require an assay for either citric acid/citrate or citric acid/citrate and phosphate. Citrate and phosphate were separated in <10 min by a hydroxide-selective column using anion-exchange chromatography with a 20 mM potassium hydroxide eluent and detected by suppressed conductivity. The method showed linear responses over the concentration ranges 0.2–100 μg ml −1 ( r 2 > 0.9990) for citrate and 0.2–60 μg ml −1 ( r 2 = 0.9999) for phosphate, with limits of quantitation (signal-to-noise (S/N) = 10) of 0.2 μg ml −1 for both analytes. The accuracy of the procedure, determined by spiked recovery measurements, was within 95–105%. The intraday and the interday precision were demonstrated by the relative standard deviations (R.S.D.) of <1 and <2%, respectively, for both analytes. The ruggedness was determined by a full factorial design using analyst, equipment, column lot, and eluent preparation procedure as variables. The results show an overall R.S.D. of <3% and that an electrolytically generated 20 mM KOH eluent produces assay results equivalent to a manually prepared 20 mM NaOH eluent.

Determination of amino acids in cell culture and fermentation broth media using anion-exchange chromatography with integrated pulsed amperometric detection

Cell culture and fermentation broth media are used in the manufacture of biotherapeutics and many other biological materials. Characterizing the amino acid composition in cell culture and fermentation broth media is important because deficiencies in these nutrients can reduce desired yields or alter final product quality. Anion-exchange (AE) chromatography using sodium hydroxide (NaOH) and sodium acetate gradients, coupled with integrated pulsed amperometric detection (IPAD), determines amino acids without sample derivatization. AE-IPAD also detects carbohydrates, glycols, and sugar alcohols. The presence of these compounds, often at high concentrations in cell culture and fermentation broth media, can complicate amino acid determinations. To determine whether these samples can be analyzed without sample preparation, we studied the effects of altering and extending the initial NaOH eluent concentration on the retention of 42 different carbohydrates and related compounds, 30 amino acids and related compounds, and 3 additional compounds. We found that carbohydrate retention is impacted in a manner different from that of amino acid retention by a change in [NaOH]. We used this selectivity difference to design amino acid determinations of diluted cell culture and fermentation broth media, including Bacto yeast extract–peptone–dextrose (yeast culture medium) broth, Luria–Bertani (bacterial culture medium) broth, and minimal essential medium and serum-free protein-free hybridoma medium (mammalian cell culture media). These media were selected as representatives for both prokaryotic and eukaryotic culture systems capable of challenging the analytical technique presented in this paper. Glucose up to 10 mM (0.2%, w/w) did not interfere with the chromatography, or decrease recovery greater than 20%, for the common amino acids arginine, lysine, alanine, threonine, glycine, valine, serine, proline, isoleucine, leucine, methionine, histidine, phenylalanine, glutamate, aspartate, cystine, and tyrosine.

Quantitative determination of sugars and myo-inositol in citrus fruits grown in Japan using high-performance anion-exchange chromatography.

Fifteen commercial samples of citrus fruits grown in Japan were analyzed for their sugar contents by high-performance anion-exchange chromatography (HPAEC) and electrochemical detection (ED) coupled with a stationary phase D10 column prepared using chloromethylated styrene-divinylbenzene copolymer and N,N,N',N'-tetramethyldiaminodecane. Myo-inositol, glucose, fructose, and sucrose in all of these various citrus fruits could be successfully separated within 25 min using 0.5 M NaOH eluent at a flow-rate of 0.4 mL/min. Myo-inositol, as a better nutritional source, was found in all the citrus fruits grown in Japan (0.7 +/- 0.04-2.1 +/- 0.2 g/L). The sugar contents of twelve citrus fruits grown in other countries were also determined.

Effect of ion-exchange site and eluent modifiers on the anion-exchange of carboxylic acids

The chromatographic behavior of carboxylic acids has been investigated, on three different latex-based anion-exchange columns, in order to define the effect of the ion-exchange site structure on selectivity. The analytical columns produced are characterized by alkyl amines containing zero, one or two hydroxyl groups on the anion-exchange functional site. Divalent carboxylic acids, namely fumaric, maleic, trans-β-hydromuconic, trans, trans-muconic, oxalic, malonic, succinic, glutaric, adipic, malic, tartaric and mucic acids, have been chosen as test solutes. The performance of the three stationary phases has been studied employing NaOH eluents and has been discussed with respect to the different hydrophilicity of the ion-exchange sites and analytes. Considering on previous results obtained using organic solvents (methanol and acetonitrile) with carbonate eluents on a highly hydrophilic column, the performance of the three exchangers has also been studied using acetonitrile, methanol and n-propanol. The chromatographic behavior was similar for the three columns studied, but the different organic solvents gave variations in selectivity. In order to characterize these differences, particle size measurements of the latices were performed both in pure water and in the presence of each organic solvent studied.

Developments of a rugged method for selenium speciation

The need for selenium speciation in an unknown bacterial sample brought by a customer initiated the setup of a hyphenated method of IEC-ICP-MS. First a published method from Gilon et al. (J. Chromatogr. A, 1996, 750, 327) was modified to analyze selenurea, seleno ethionine, seleno methionine (SeM), Se(IV), seleno cystine (SeC) and Se(VI) by a hyphenated ICP-MS technique. LODs of 4–15 µg L−1 were achieved and a 1/10 diluted protease digestion (Pronase E) of the Se-containing bacterial sample was measured. However, the ruggedness of the method was insufficient. Separation was compromised even at a 1/10 dilution of the sample and identification of the species was poor. Another method was set up and developed to analyze anionic Se species. This method used a Dionex AS 11 column with NaOH and tetramethylammonium hydroxide as eluents. Now, LODs of ca. 0.1 µg Se L−1 were achieved and the method proved to be very rugged. No alteration of the separation was observed. During 30 consecutive runs, retention times and peak areas varied only slightly in spite of the high material load on the column (e.g., for the major compound the retention time was 6.26 min ± 6 s, and the peak area variation was ±0.7%). The protease digestion of the bacterial sample could be analyzed without dilution. The separation was not compromised, although the bacterial material load of the sample was 30 mg mL−1. Therefore low concentration Se species were not below the detection limit. Several species were identified, such as Se(IV), SeC and in small amounts SeM. However, some species remained unidentified due to unavailable standards for comparison. Mass balances were also performed. The protease digestion provided 25% Se of the total Se determined after pressure digestion (148 mg kg−1), and 98.7% recovery was obtained when the protease digestion was speciated.

Determination of epichlorohydrin by ion chromatography

In this work we developed a new method for epichlorohydrin determination with suppressed ion chromatography. The technique is based on a reaction between the analyte and sulfur(IV) to form a product with a terminal sulfonate group that can be analyzed by anion-exchange chromatography. The reaction conditions were optimized as a function of temperature, type and concentrations of reagents and pH. Due to the characteristics of the product formed, the columns used were an IonPac AS11 and AS11-HC with a NaOH eluent. The eluent concentration was optimized in order to achieve a complete separation of epichlorohydrin, chloride and nitrate ions, commonly occurring in drinking waters. In order to improve the detection limits, a preconcentration step, using reversed-phase materials, has been optimized. The method developed was suitable for epichlorohydrin determination in drinking water.

Capillary Ion Chromatography with On-Line High-Pressure Electrodialytic NaOH Eluent Production and Gradient Generation

A small inexpensive system is described that allows high-performance suppressed anion chromatography on a capillary scale. A fully computer-controlled stepper motor-driven syringe-type dispenser, equipped with a 500 μL-capacity glass syringe is capable of pumping at pressures up to 1000 psi when equipped with an appropriate inlet check valve. Fused-silica capillary columns ∼50 cm in length and 180 μm i.d., packed in-house with a commercial packing, provide excellent performance, significantly exceeding the efficiencies observed for the same packing in commercially available 2 mm bore format. The system operates with a pressure drop of <800 psi at a flow rate of 2 μL/min. The system utilizes a novel electrodialytic NaOH eluent generator that is deployed on the high-pressure side of the pump and thus requires no special measures for electrolytic gas removal. This device permits both isocratic and gradient operation with excellent eluent purity; the NaOH concentration is generated linearly with applied current with near-Faradaic efficiency, up to a concentration of at least 100 mM.

Mixed-mode liquid chromatography of carboxylic acids and inorganic anions on a latex-based pellicular stationary phase

The retention behaviour of mono-, dicarboxylate and inorganic anions on latex-based pellicular anion-exchanger was investigated. This paper is focused on the possible retention mechanism providing a retention database on a variety of mobile phase compositions. It has been demonstrated that anions can interact with the cation-exchange layer on the highly crosslinked latex-based pellicular phase as well as with the anion-exchange sites. A hypothesis is proposed to explain a mixed-mode retention of the series of analytes. A combination of two mechanisms has been found responsible for the enhanced selectivity: ion-exchange and ion-exclusion. Applications include the separation of formate, acetate, propionate, lactate, pyruvate, oxalate, malonate, succinate, tartrate, fumarate, maleate , chloride, nitrate and sulphate with NaOH eluent using suppressed conductivity detection. The study effectively characterizes the behaviour of different analytes under elution conditions of practical importance.

Application of ion chromatography to the analysis of high-purity CdTe

Ion chromatography is widely used in different fields of analytical chemistry and there is an extensive literature dealing with it, but not many papers describe the application of ion chromatography to the analysis of high-purity materials. A matter of topical interest in this field is the determination of impurity or dopant elements in the high-purity semiconductor compounds of A II B VI type (CdTe) with detection limits from 10 −4% to 10 −6%. In order to eliminate the matrix effects and to reduce the detection limits, methods of concentration are commonly used; ion chromatography has been proved successful to separate impurities in the presence of large amounts of micro- and macro-components without any preconcentration and/or pre-separation steps. The proposed procedure deals with the ion chromatographic determination of chlorine, sulphur, selenium and phosphorus using a NaOH eluent, iron and copper using a PDCA eluent, lead, cobalt, zinc and nickel using an oxalate eluent. Detection limits range between 1 and 3 10 −5% and calibration curves were found to be linear up to three orders of magnitude higher. The clear sample solutions were injected directly on to an iron chromatograph equipped both with a conductivity detector, for the determination of chloride, sulphate, selenate and phosphate ions, and a post-column membrane reactor and variable-wavelength UV-Vis detector, for the determination of iron, copper, lead, cobalt, zinc, nickel (and cadmium, if required). Ion chromatographic responses were compared to graphite furnace atomic absorption spectrometry and results were found to be in good agreement (±5%).

Two-Dimensional Conductometric Detection in Ion Chromatography. Analyte Identification, Quantitation of Very Weak Acid Anions, and Universal Calibration

A universal and sensitive detection method for anion chromatography is described. Following suppressed conductometric detection carried out with an NaOH eluent and an electrical suppressor, the eluite is transported through a microscale electrodialytic NaOH generator and a second conductivity detector. While the first detector responds primarily to strong acid anions, the second detector records a decrease in the NaOH background signal, regardless of the pK a of the analyte. Routine detection of very weak acids at the low micromolar level is possible. The dual detection method not only constitutes the most generally applicable approach to IC by combining the detection merits of both suppressed and single-column IC, it provides possibilities of peak identification beyond retention characteristics. Area ratio values from the two detector signals provide unique signatures for each analyte ion. It is possible to estimate the limiting equivalent conductance of an unknown eluite and the analyte concentration without specific calibration. The method is also effective in diagnosing the occurrence of coelution.

Two-dimensional conductometric detection in ion chromatography: sequential suppressed and single column detection

A novel approach to simultaneously practicing both suppressed and nonsuppressed ion chromatography (IC) is proposed. Following the detector of a conventional NaOH eluent suppressed IC system, a constant concentration of NaOH is introduced by an in-line microelectrodialytic NaOH generator, and this is followed by a second conductivity detector. The second detector background is typically maintained at a level of 20-30 [mu]m/cm (corresponding approximately to 0.1 mM NaOH), and the detector output is the same as what would be observed in a single column mode with a low concentration NaOH eluent. Together, the two detector outputs provide detectabilities at the microgram per liter level across the pK[sub a] range-from fully dissociated to very weak acids (up to pK[sub a] 9.5). Excellent linearity of response is observed, and the system provides qualitative information about peak purity and eluite pK[sub a]. In addition to the usual ratio plots, it is suggested that multidimensional detection in any separation system is best served by plotting the raw detector outputs against each other. 16 refs., 11 figs.

Determination of Ultra Low Content of Carbon in Iron by Ion-Chromatography

A study on the determination of ultra low content of carbon was made by using ion-chromatography, coupled with the combustion method in oxygen gas stream. The considerable increase in the variation of conductivity with the content of carbonate ion was observed because of the high ionic conductivity of OH− in the NaOH eluent. The Na+ (OH−) ion could be removed by a cation exchange column according to the reaction: R–H++NaOH→R–Na++H2O. Therefore, carbonate ions in NaOH absorbent, which absorbed CO2 gas produced by the reaction of carbon in metal with oxygen gas, could be concentrated on the concentration column. It was found that 1.67 mass ppm of carbon in pure iron sample was determined within the accuracy of 0.24 mass ppm of standard deviation.

イオンクロマトグラフィーによる鉄中極微量炭素の定量

A study on the determination or ultra low content of carbon was made by using ion-chromatography, coupled with the combustion method in oxygen gas stream. The considerable increase in the variation or conductivity with the content or carbonate ion was observed because or the high ionic conductivity or OH - in the NaOH eluent. The Na + (OH - ) ion could be removed by a cation exchange column according to the reaction: R-H + +NaOH→R-Na + +H 2 O. Thererore, carbonate ions in NaOH absorbent, which absorbed CO 2 gas produced by the reaction or carbon in metal with oxygen gas, could be concentrated on the concentration column

PREDICTION OF RETENTION TIME FOR GRADIENT ELUTION USING STEPWISE ELUTION EQUATION

Prediction of retention tines for gradient elution of inorganic ions was tried out using the stepwise elution equation. Retention the for some inorganic anions was isocratically measured with NaOH eluent on the anion exchange resin column. The slope frog a plot of log k' against log [OH-] was obtained by a linear regression. The calculated k' was applied to predict retention time of each inorganic anion for a gradient elution. Retention tine of lanthanides was measured using α-HiBA and mandelic acid as a complexing agent on the cation exchange resin column. Capacity factor for each metal-ligand complex was obtained frog the measured k' by non-linear regression. The same calculation was performed on the retention time of metal ions for gradient elution.