Ion-exclusion High-performance Liquid Chromatography Research Articles

Some approximations on the effect of the supporting electrolyte towards electrochemical advanced oxidation degradation of Reactive Orange 84 (RO84)

In this paper, some advanced oxidation electrochemical processes such as anodic oxidation (AO), electro-Fenton (EF), and photoelectro-Fenton (PEF) to carry out the degradation of the azo dye Reactive Orange 84 (RO84) are presented. For this, boron-doped diamond (BDD) electrodes were used, and different configurations were taken in a stirred tank cell, like BDD/graphite and BDD/BDD. The effect of different operating parameters on the discoloration process was evaluated, including the concentration of the supporting electrolyte, namely 50 and 75 mM of Na2SO4, along with 50 mM NaCl and mixtures of Na2SO4 + 25 mM NaCl. The effect of the applied current density at 25, 50, and 100 mA cm−2 over the loss of color was also analyzed using initial RO84 concentrations of 100 and 200 mg/L. The production of free radicals was evaluated in the bulk solution. The decrease in chemical oxygen demand (COD) was determined and the evolution of oxalic acid, a nontoxic, short-chain carboxylic acid was quantified as a final product of all treatments by using ion-exclusion high-performance liquid chromatography.

Synthesis and characterization of Sb2O5-doped Ti/SnO2-IrO2 anodes toward efficient degradation tannery dyes by in situ generated oxidizing species

Nowadays, the increasing pollution of natural water effluents with textile dyes is an emerging problem that has not received attention enough. This work presents a study on the preparation of two Ti/IrO2-SnO2-Sb2O5 electrodes so-called E1 and E2 with 0.01 and 0.09 wt% of Sb dopant, respectively, by the Pechini method. The characteristics of these electrodes were analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray diffraction. The E2 anode possessed a higher electroactivity and produced more largely hydroxyl radicals in electrochemical oxidation (EO). The action of this oxidant, along with active chlorine of textile dyes like Violet RL, Green A and Brown DR was assessed in 50 mM Na2SO4 and 10 mM NaCl at pH 3.0 by EO with the E2 anode. It was found that the discoloration of 80 mg L−1 of each individual solution was enhanced with increasing the current density from 25 to 50 mA cm−2, always obeying a pseudo-first-order kinetics. The process was faster in the sequence: Green A < Brown DR < Violet RL, and at 50 mA cm−2, a loss of color > 86% of color was attained in only 6 min. A mixture with 80 mg L−1 of each dye was treated under analogous EO conditions, giving rise to 100% discoloration in 20 min and about 90% chemical oxygen demand removal in 60 min at 50 mA cm−2. Three carboxylic acids, maleic, oxalic and oxamic, were detected as final byproducts by ion-exclusion high-performance liquid chromatography. The results reported in this work demonstrate the large effectiveness of the synthesized Ti/IrO2-SnO2-Sb2O5 electrodes to remove textile azo dyes, with higher rate constants than usual anodes.

Production of free radicals by the Co2+/Oxone system to carry out diclofenac degradation in aqueous medium.

This paper reports the degradation of a solution of 0.314 mM diclofenac (DCF), while using 5-15 mM Oxone as oxidizing agent with the catalytic action of 0.05-0.2 mM Co2+. The best performance was obtained for 10 mM Oxone and 0.2 mM Co2+, achieving the total DCF abatement and 77% removal of chemical oxygen demand after 30 min. Oxidizing of sulfate (SO4 •-) and hydroxyl (•OH) radicals was formed by the Co2+/Oxone system. Oxone was firstly oxidized to persulfate ion that was then quickly converted into the above free radicals. For Oxone contents ≥10 mM, the decay of DCF concentration followed a second-order kinetic reaction, but the apparent rate constant changed with the Co2+ concentration used. High-performance liquid chromatography (HPLC) analysis of treated solutions showed the formation of some intermediates, whereas oxalic acid was identified as the prevalent final short-linear carboxylic acid by ion-exclusion HPLC.

Comparative electrochemical oxidation of methyl orange azo dye using Ti/Ir-Pb, Ti/Ir-Sn, Ti/Ru-Pb, Ti/Pt-Pd and Ti/RuO2 anodes

The relative oxidation power of dimensionally stable anodes, namely Ti/Ir-Pb, Ti/Ir-Sn, Ti/Ru-Pb, Ti/Pt-Pd and Ti/RuO2, has been determined from the anodic oxidation (AO) treatment of 2dm3 of methyl orange azo dye solutions in 0.050moldm−3 Na2SO4 of pH 7.0 at constant current density. The anodes were synthesized by the dip-coating method using the corresponding metallic chlorides in isopropanol/water and their morphology, surface roughness, crystallographic structure and composition were analyzed. A mixture of IrO2, Pb2O3 and Pb3O4 were the components in the outperforming Ti/Ir-Pb anode. The effect of current density, Na2SO4 concentration, and cathode nature on the decolorization of azo dye solutions by AO with Ti/RuO2 was examined. Under favorable conditions, 96%-98% color removal was achieved using Ti/Ir-Pb, Ti/Ir-Sn and Ti/Ru-Pb, with lower decolorization for Ti/Pt-Pd and Ti/RuO2 anodes. In all cases, a pseudo-first-order decolorization process was found. The oxidation ability of anodes rose in the order Ti/RuO2<Ti/Pt-Pd<Ti/Ru-Pb<Ti/Ir-Sn<Ti/Ir-Pb, achieving 76.0% mineralization for the latter electrode. The mixture of active and non-active materials then gave rise to anodes with higher oxidation power than those made solely of active materials, due to the enhancement of the oxidation action of hydroxyl radicals formed in the non-active oxide. The superiority of Ir over Ru in the mixed metal oxides was related to the greater adsorption of organics on its surface, thereby favoring their oxidation. Ammonium and sulfate ions were released as pre-eminent ions. Stable byproducts and final short-linear aliphatic carboxylic acids were identified by gas chromatography-mass spectrometry and ion-exclusion high-performance liquid chromatography. Based on these compounds, a reaction sequence for methyl orange mineralization is proposed.

Solar photoelectro-Fenton flow plant modeling for the degradation of the antibiotic erythromycin in sulfate medium

A solar photoelectro-Fenton (SPEF) plant containing a filter-press FM01-LC flow reactor in series with a compound parabolic collector (CPC) as photoreactor, operating in batch recirculation mode, was simulated using a parametric model. The degradation of 10dm3 of solutions of the heterocyclic antibiotic erythromycin (ERY) in 0.050moldm−3 Na2SO4 at pH 3.0 was used for validation. The filter-press reactor contained a platinized titanium plate anode and a graphite-felt cathode that produced H2O2 from the reduction of dissolved oxygen (0.24mmoldm−3). Trials were performed under potentiostatic and galvanostatic conditions with predominance of H2O2 production, minimizing H2 evolution reaction. The effect of initial catalyst (Fe2+) concentration, current density (j), initial antibiotic concentration as dissolved organic carbon (DOC) and volumetric flow rate on the ERY mineralization was studied. Good agreement between simulations and experimental DOC decays was obtained. Mineralization current efficiencies and specific energy consumptions were also determined. The best performance under galvanostatic conditions was found for 0.225mmoldm−3 ERY (100mgdm−3 DOC), 0.50mmoldm−3 Fe2+, volumetric flow rate of 3.0dm3min−1 and jcath=-0.16mAcm−2, reaching 69% mineralization with current efficiency of 75% and specific energy consumption of 0.059kWh (g DOC)−1. Six organic by-products were identified by gas chromatography-mass spectrometry, whereas final short-chain carboxylic acids like formic and oxalic acid were detected by ion-exclusion high-performance liquid chromatography. The initial N atom of ERY was predominantly converted into NO3− ion, although NH4+ ion was formed as well.

Removal of artificial sweetener aspartame from aqueous media by electrochemical advanced oxidation processes

The degradation and mineralization of aspartame (ASP) in aqueous solution were investigated, for the first time, by electrochemical advanced oxidation processes (EAOPs) in which hydroxyl radicals were formed concomitantly in the bulk from Fenton reaction via in situ electrogenerated Fenton's reagent and at the anode surface from the water oxidation. Experiments were performed in an undivided cylindrical glass cell with a carbon-felt cathode and a Pt or boron-doped diamond (BDD) anode. The effect of Fe2+ concentration and applied current on the degradation and mineralization kinetics of ASP was evaluated. The absolute rate constant for the reaction between ASP and OH was determined as (5.23 ± 0.02) × 109 M−1 s−1 by using the competition kinetic method. Almost complete mineralization of ASP was achieved with BDD anode at 200 mA constant current electrolysis. The formation and generation of the formed carboxylic acids (as ultimate end products before complete mineralization) and released inorganic ion were monitored by ion-exclusion high performance liquid chromatography (HPLC) and ion chromatography techniques, respectively. The global toxicity of the treated ASP solution during treatment was assessed by the Microtox® method using V. fischeri bacteria luminescence inhibition.

Electrochemical destruction of trans-cinnamic acid by advanced oxidation processes: kinetics, mineralization, and degradation route.

Acidic solutions of trans-cinnamic acid at pH3.0 have been comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF). The electrolytic experiments were carried out with a boron-doped diamond (BDD)/air-diffusion cell. The substrate was very slowly abated by AO-H2O2 because of its low reaction rate with oxidizing •OH produced from water discharge at the BDD anode. In contrast, its removal was very rapid and at similar rate by EF and PEF due to the additional oxidation by •OH in the bulk, formed from Fenton's reaction between cathodically generated H2O2 and added Fe2+. The AO-H2O2 treatment yielded the lowest mineralization. The EF process led to persistent final products like Fe(III) complexes, which were quickly photolyzed upon UVA irradiation in PEF to give an almost total mineralization with 98% total organic carbon removal. The effect of current density and substrate concentration on all the mineralization processes was examined. Gas chromatography-mass spectrometry (GC-MS) analysis of electrolyzed solutions allowed identifying five primary aromatics and one heteroaromatic molecule, whereas final carboxylic acids like fumaric, acetic, and oxalic were quantified by ion exclusion high-performance liquid chromatography (HPLC). From all the products detected, a degradation route for trans-cinnamic acid is proposed.

Photoelectrocatalytic/photoelectro-Fenton coupling system using a nanostructured photoanode for the oxidation of a textile dye: Kinetics study and oxidation pathway

In this study, a coupled photoelectrocatalytic/photoelectro-Fenton reactor was designed to enhance the degradation efficiency of organic pollutants and tested using the azo dye Orange G as a model compound. Pt-decorated TiO2 nanotubes were used as a photoanode with an air-diffusion polytetrafluoroethylene cathode for H2O2 generation. The sum of individual effects of coupling the photoelectrocatalytic and photoelectro-Fenton processes was evaluated as a function of the decolorization and mineralization of Orange G solutions. The dye solutions were only completely decolorized in more acidic conditions (pH 3.0). The mineralization of the Orange G solutions increased in the sequence photoelectrocatalytic<electro-Fenton<coupled photoelectrocatalytic/photoelectro-Fenton due to the gradual increase in the production of OH radicals. Total organic carbon reductions of 80% for photoelectrocatalysis, 87% for electro-Fenton and 97% for the coupled processes were obtained when using an applied electric charge per unit volume of electrolyzed solution of 200mAhL−1. The Orange G decays for all treatments followed pseudo-first-order kinetics, suggesting the attack of a constant concentration of OH radicals. Aromatics such as naphthalenic and benzenic compounds were formed as by-products and were identified using LC–MS/MS analysis. In addition, the generated aliphatic acids were identified using ion-exclusion high-performance liquid chromatography. The final by-products of oxalic and formic acid were identified as ultimate by-products and formed Fe(III) complexes that were rapidly mineralized to CO2 by UV–Vis irradiation. Then, according to the identified oxidation by-products, a plausible pathway was proposed for the degradation of Orange G dye by the coupled process.

High‐sensitivity detection of short‐chain fatty acids in porcine ileal, cecal, portal and abdominal blood by gas chromatography‐mass spectrometry

Short-chain fatty acids (SCFA), such as acetate, propionate and n-butyrate, are the main end-products of fermentation in the large intestine. SCFA are rapidly absorbed from the large intestinal mucosa to provide energy to the host. In this study, high-sensitivity detection of SCFA was demonstrated in blood using the gas chromatometry with mass spectrometry (GC-MS). Few studies have measured SCFA in porcine blood. Therefore, SCFA concentrations in the ileal (IV), cecal (CV), portal (PV) and abdominal (AV) vein blood, urine (Ur) and saliva (Sa) were measured by GC-MS. All body fluids were collected from four 5-month-old pigs. Cecal (CD) and ileal (ID) digesta, and cecal (CM) and ileal (IM) mucosa were also collected and their corresponding SCFA concentrations were measured using ion-exclusion high-performance liquid chromatography. GC-MS analyses were successful to determine the SCFA concentrations in the porcine body fluids. n-Butyrate concentration was surprisingly high in CV and its proportion remained higher in CV than that in CD and CM. Acetate showed a constantly high proportion in all porcine body fluids. Propionate was detected at a relatively high proportion in CV, IV and PV, but was low in AV.

Characterization of liquid chromatography-tandem mass spectrometry method for the determination of acrylamide in complex environmental samples

This work describes the characterization of a solid-phase extraction (SPE) and liquid-chromatography-tandem mass spectrometry-based method for the analysis of acrylamide (AA) in complex environmental waters. The method involved the SPE of AA using activated carbon, and the AA was detected with tandem mass spectrometry after separating on an ion exclusion high-performance liquid chromatography column. The method incorporated two labeled AA standards for quantification using isotope dilution and to assess absolute extraction recovery. The method was evaluated for inter- and intra-day precision and accuracy. The method was both accurate (i.e., <30 % error) and precise (i.e., <20 % relative standard deviation), with absolute extraction recoveries averaging 37 %. The mass spectrometry provided excellent sensitivity, with instrumental limits of detection and quantitation values of 23 and 75 pg, respectively. The method detection limit was determined to be 0.021 μg/L. The analysis of AA was successfully performed in real-world samples that contained total dissolved solids concentrations ranging from 23,600 to 297,000 mg/L and AA concentrations ranging from 0.082 to 1.0 μg/L.

High performance column liquid chromatographic analysis of selected carboxylic acids in Biomphalaria glabrata patently infected with Schistosoma mansoni

High-performance liquid chromatography (HPLC) was used to determine the effects of a patent Schistosoma mansoni infection on certain carboxylic acids in the digestive gland gonad complex (DGG) and hemolymph of Biomphalaria glabrata. An analysis of DGG samples was done using extraction with 50% Locke's solution, cleanup of the extract by anion exchange solid phase extraction (SPE), and ion exclusion HPLC with ultraviolet detection. Hemolymph was applied directly to the SPE column. Acetic, fumaric, malic, and pyruvic acids were detected, confirmed, and quantified at concentrations ranging from 12 to 280 ppm in the DGG and less than 124 to 8,000 microg/dl in the hemolymph. Infection with S. mansoni caused a significant reduction (Student's t test, P < 0.05) in the concentrations of acetic, fumaric, malic, and pyruvic acids in the DGG but not the hemolymph of B. glabrata compared to uninfected cohort snails. The significant reduction of certain carboxylic acids in the DGG of B. glabrata patently infected with S. mansoni suggests that these acids are utilized by the sporocysts and cercariae in the snail tissue, or that the infection stimulates reduced production or increased utilization by the snail tissue.

New Analytical Method for the Determination of Levoglucosan, Polyhydroxy Compounds, and 2-Methylerythritol and Its Application to Smoke and Rainwater Samples

Biomass burning is an important source of smoke aerosol particles, which contain water-soluble inorganic and organic species, and thus have a great potential of affecting cloud formation, precipitation, and climate on global and regional scales. In this study, we have developed a new chromatographic method for the determination of levoglucosan (a specific tracer for biomass burning particles), related polyhydroxy compounds, and 2-methylerythritol (recently identified as isoprene oxidation product in fine aerosols in the Amazon) in smoke and in rainwater samples. The new method is based on water extraction and utilizes ion-exclusion high-performance liquid chromatography (IEC-HPLC) separation and spectroscopic detection at 194 nm. The new method allows the analysis of wet samples, such as rainwater samples. In addition, aliquots of the same extracts can be used for further analyses, such as ion chromatography. The overall method uncertainty for sample analysis is 15%. The method was applied to the analysis of high-volume and size-segregated smoke samples and to rainwater samples, all collected during and following the deforestation fires season in Rondonia, Brazil. From the analysis of size-segregated samples, it is evident that levoglucosan is a primary vegetation combustion product, emitted mostly in the 0.175-1 microm size bins. Levoglucosan concentrations decrease below the detection limit atthe end of the deforestation fires period, implying that it is not present in significant amounts in background Amazon forest aerosols. The ratio of daytime levoglucosan concentration to particulate matter (PM) concentration was about half the nighttime ratio. This observation is rationalized by the prevalence of flaming combustion during day as opposed to smoldering combustion during night. This work broadens the speciation possibilities

Comparative study of lactic acid and polylactides using static headspace, gas chromatography and high-performance liquid chromatography

This work investigates the use of analytical methodology to determine lactic acids and/or polylactides. This paper reports three methods that have been successfully developed. Firstly, static headspace gas chromatography (GC) was investigated. The results show precision values of 4–5% RSD and linearity correlation coefficients of between 0.990 and 0.999 in the concentration range 300–700 μg/ml lactic acid. The method is specific for lactic acid. Secondly, an on-column GC method is presented which minimises sample preparation and separation of lactic acid from the polylactides. Finally, an ion-exclusion high-performance liquid chromatography (HPLC) method was developed. The instrumental precision was 0.1%, and linearity correlation coefficients >0.9999 were obtained in the concentration range between 50 and 200 μg/ml lactic acid. A basic hydrolysis is used to convert the polylactides to lactic acid. Collectively, these methods form a successful approach for the determination of lactic acid in consumer healthcare products.

Metabolism and distribution of [2,3-14C]acrolein in Sprague-Dawley rats. II. Identification of urinary and fecal metabolites.

The metabolites of [2,3-14C]acrolein in the urine and feces of Sprague-Dawley rats were identified after either intravenous administration in saline at 2.5 mg/kg or oral administration by gavage as an aqueous solution as either single or multiple doses at 2.5 mg/kg or as a single dose of 15 mg/kg. Selected urine and feces samples were pooled by sex and collection interval and profiled by combinations of reverse-phase, anion-exchange, cation-exchange, and ion-exclusion high-performance liquid chromatography (HPLC). Feces were also profiled by size-exclusion chromatography. Metabolites were identified by comparison with well-characterized standards by HPLC and by mass spectrometry. The urinary metabolites were identified as oxalic acid, malonic acid, N-acetyl-S-2-carboxy-2-hydroxyethylcysteine, N-acetyl-S-3-hydroxypropylcysteine, N-acetyl-S-2-carboxyethylcysteine, and 3-hydroxypropionic acid. The fecal radioactivity from the oral dose groups was partitioned into methanol-soluble, water-soluble, and insoluble radioactivity, some of which could be liberated by dilute acid hydrolysis. HPLC analysis of these extracts revealed no discrete metabolites. Size-exclusion chromatography indicated a molecular weight range of 2,000 to 20,000 Da for the radioactivity, which was unaffected by hydrolysis at reflux with 6 M acid or base. This radio-activity was thought to be a homopolymer of acrolein, which was apparently formed in the gastrointestinal tract. The pathways of acrolein metabolism were epoxidation followed by conjugation with glutathione, Michael addition of water followed by oxidative degradation, and glutathione addition to the double bond either following or preceding oxidation or reduction of the aldehyde. The glutathione adducts were further metabolized to the mercapturic acids.

Metabolism and Distribution of [2,3-14C]Acrolein in Sprague-Dawley Rats

The metabolites of [2,3-14C]acrolein in the urine and feces of Sprague-Dawley rats were identified after either intravenous administration in saline at 2.5 mg/kg or oral administration by gavage as an aqueous solution as either single or multiple doses at 2.5 mg/kg or as a single dose of 15 mg/kg. Selected urine and feces samples were pooled by sex and collection interval and profiled by combinations of reverse-phase, anion-exchange, cation-exchange, and ion-exclusion high-performance liquid chromatography (HPLC). Feces were also profiled by size-exclusion chromatography. Metabolites were identified by comparison with well-characterized standards by HPLC and by mass spectrometry. The urinary metabolites were identified as oxalic acid, malonic acid, N-acetyl-S-2-carboxy-2-hydroxyethylcysteine, N-acetyl-S-3-hydroxypropylcysteine, N-acetyl-S-2-carboxyethylcysteine, and 3-hydroxypropionic acid. The fecal radioactivity from the oral dose groups was partitioned into methanol-soluble, water-soluble, and insoluble radioactivity, some of which could be liberated by dilute acid hydrolysis. HPLC analysis of these extracts revealed no discrete metabolites. Size-exclusion chromatography indicated a molecular weight range of 2,000 to 20,000 Da for the radioactivity, which was unaffected by hydrolysis at reflux with 6 M acid or base. This radio-activity was thought to be a homopolymer of acrolein, which was apparently formed in the gastrointestinal tract. The pathways of acrolein metabolism were epoxidation followed by conjugation with glutathione, Michael addition of water followed by oxidative degradation, and glutathione addition to the double bond either following or preceding oxidation or reduction of the aldehyde. The glutathione adducts were further metabolized to the mercapturic acids.

Effect of irradiation on vitamin C content of strawberries and potatoes in combination with storage and with further cooking in potatoes

The vitamin C content of four varieties of strawberry was determined before and after treatment with ionising radiation at doses of 1, 2 or 3 kGy and after storage for 5 and 10 days at 6°C, and also in potatoes which, having been allowed a period of one month to recover from the effects of post-harvest stress, were irradiated at a sprout inhibition dose of 0·15 kGy, followed by storage and cooking. Total ascorbic acid (TAA), ascorbic acid (AA) and dehydroascorbic acid (DHAA) concentrations were measured using the technique of ion-exclusion high-performance liquid chromatography. Results from analysis of the strawberry samples showed the DHAA content increased immediately following irradiation and must, therefore, be taken into account when reporting vitamin C levels in irradiated produce. In addition it was observed that whilst irradiation did affect the vitamin C concentration in all varieties of strawberry, the change was small in comparison with the large variations observed between varieties. With regard to potatoes results showed that, whilst irradiation, storage and cooking all had the effect of reducing vitamin C concentration, irradiated samples stored for 5 months had similar or marginally higher levels than their non-irradiated counterparts. Cooking did not markedly reduce TAA content of irradiated potatoes compared to non-irradiated potatoes and it was also noted that microwave cooking was more destructive than boiling in lightly salted water. ©1997 SCI

Determination of 2-Oxoglutarate in the Presence of Citrate and/or Isocitrate After Ion-Exclusion High-Performance Liquid Chromatography

A method has been designed for the quantification of 2-oxoglutarate after ion-exclusion high performance liquid chromatography of samples containing high levels of citrate plus isocitrate, which interfere in the quantification of 2-oxoglutarate. The amount of 2-oxoglutarate in a mixed chromatographic peak containing citrate plus isocitrate has been estimated using a diode array detector and calculating the extinction coefficient of these molecules at three wavelengths. The reliability of the method has been ascertained using mixtures of standard organic acids. This procedure has been applied to determine the intracellular content of 2-oxoglutarate in the cyanobacterium Phormidium laminosum.