Recent developments and emerging directions in ion chromatography

Analysis of Calcium and Phosphate Ion Extraction From Dental Enamel by Bleaching Gels Using Ion Chromatography, Micro-CT, and SEM

OBJECTIVES

To evaluate the volume and depth of enamel loss promoted by 37.5% and 7.5% hydrogen peroxide (HP) gels, and quantify the loss of calcium (Ca) and phosphate (P) ions by using ion chromatography (IC) analysis after bleaching.

METHODS

Sixty bovine enamel specimens were randomly divided into three groups: Control - no bleaching gel; HP37.5%, application of HP 37.5% for 45 minutes for 14 days; and HP7.5%, application of HP 7.5% for 3 applications of 8 minutes. The surface analysis (n=5) was performed using a scanning electron microscope (SEM) and dispersive energy system (EDS) to calcium and phosphorus dosage. The micro-CT was used for the enamel loss analysis (n=5). IC was used to analyze extracted Ca and P (n=10). Data were analyzed by one-way ANOVA and two-way repeated measures ANOVA, followed by Tukey and Dunnett's tests (α=0.05).

RESULTS

Significantly higher volume and depth of enamel loss were found for bleached groups compared with the control group. HP7.5% had significantly higher enamel change than HP37.5%. SEM showed higher enamel porosity for HP37.5% and HP7.5% compared to control. The IC demonstrated a significant increase of Ca incorporated into the gel, however, only HP7.5% had a higher P presence than the control group. The HP7.5% showed higher Ca and P ion exchange than HP37.5% (p<0.001).

CONCLUSION

HP37.5% and HP7.5%, caused enamel mineral changes compared with the control group. The IC method was demonstrated to be an effective methodology for detecting enamel mineral loss by the bleaching gel.

Boron quantification using ion chromatography tandem triple quadrupole mass spectrometry. Application to retention analysis in boron-treated wood

Boron compounds play a crucial role in various industries, and accurate quantification of boron is essential for quality control and environmental monitoring. This study presents a simple, rapid, and reliable method for determining boron in aqueous solutions using suppressed ion chromatography coupled to electrospray ionisation-triple quadrupole mass spectrometry (IC-ESI-QqQ-MS). Boric acid (B(OH)3) was retained as the tetrahydroxyborate ion (B(OH)4-) on a CarboPac PA300-4 μm anion-exchange column using isocratic elution with 40 mM KOH. During the neutralization process at the suppressor, B(OH)4- was converted to B(OH)3, which subsequently generated the metaborate ion [BO2]- (m/z 43) within the electrospray ionisation source. By employing a pseudo-selected reaction monitoring (SRM) transition from m/z 43 to m/z 43, the method achieved a limit of detection (LOD) of 2.45 μg/L of boron, the lowest reported in the literature to-date for an IC-based method. The analytical performance of the method demonstrated no carry-over issues, no matrix interferences, and excellent intra- and inter-run repeatability of 2.03% and 3.41%, respectively. The method was applied to the evaluation of boron uptake and retention by Tasmanian Oak timber blocks, treated by dip-diffusion in a boric acid solution of 2.5% Boric Acid Equivalent (BAE, m/m) under controlled laboratory conditions. Quantitative determination of the retained and unretained boron allowed a mass balance evaluation and confirmed the accuracy and reliability of the method, with recoveries ranging from 99.3% to 100.2%.

One Pot Hydrothermal Synthesis and Application of Bright-yellow-emissive Carbon Quantum Dots in Hg2+ Detection

Carbon quantum dots (CQD) have drawn great interest worldwide for their extensive application as sensors due to their extraordinary physical and chemical characteristics, good biocompatibility, and high fluorescence in nature. Here, we demonstrate a technique for detecting mercury (Hg2+) ion using a fluorescent CQD probe. Ecology is concerned about the accumulation of heavy metal ions in water samples due to their harmful effects on human health. Sensitive identification and removal of metal ions from water samples are required to reduce heavy metals' risk. To find out Mercury in the water sample, carbon quantum dots were used and synthesized by 5-dimethyl amino methyl furfuryl alcohol and o-phenylene diamine through the hydrothermal technique. The synthesized CQD shows yellow emission when exposed to UV irradiation. Mercury ion was used to quench carbon quantum dots, and it was found that the detection limit was 5.2 nM with a linear range of 15-100 µM. The synthesized carbon quantum dots were demonstrated to efficiently detect Mercury ions in real water samples.

Naphthalene-2,3-dicarboxaldehyde as a pulsed-post column derivatization reagent; comparison with two alternative o-phthalaldehyde based chemistries for the determination of histamine

In the present study, naphthalene-2,3-dicarboxaldehyde (NDA) was used in on-line post column derivatization (PCD) coupled to liquid chromatography under the new concept of Pulsed-PCD. In Pulsed-PCD, the reagents are introduced into the flowing stream of the mobile phase under precise timing overlapping the eluted analyte. The consumption of the reagents is minimized to a few microliters, resulting in a significant advantage, that is the use of expensive reagents in PCD. For this reason, NDA-CN chemistry was used for the determination of histamine in food samples, such as eggplant and spinach. Two additional methods were developed based on the reaction of histamine with o-phthalaldehyde (OPA), namely the classic OPA - nucleophilic compound reaction and the specific OPA - histamine reaction in alkaline medium. The chromatographic conditions and the Pulsed-PCD conditions were investigated, while the analytical figures of merit were satisfactory. In all three methods, a pulse of 50 μL was used (OPA/NDA + Buffer), reducing dramatically the consumption of PCD reagents.

Applications of two-dimensional ion chromatography for analytes determination in environmental matrix: A review

Ion chromatography (IC) has grown in usage rapidly since its first introduction in 1975. However, IC is still sometimes unable to separate target analytes from coexisting components well with identical elution time, due to the limited resolution and column capacity, especially in the presence of high-level salt matrix. These limitations hence drive IC to develop two-dimensional IC (2D-IC). In this review, we capture the 2D-IC applications in environmental samples via the perspective of coupling different IC columns, which aim to summarize where these 2D-IC methods fit in. In sequence, we firstly review the principles of 2D-IC and emphasize one-pump column-switching IC (OPCS IC) because it is a simplified 2D-IC that only uses one set of IC system. We then compare typical 2D-IC and OPCS IC performances in terms of application scope, method detection limit, drawbacks, and expectations. Finally, we propose some challenges of current methods and opportunities for future research. For instance, it is challenging to couple anion exchange column and capillary column in OPCS IC due to the incompatibility between flow path dimensions and suppressor; coupling ion exclusion column and mixed-bed column may be promising to simultaneously determine anions and cations in weak acids or salts. The details of this study may help practitioners to better understand and implement 2D-IC methods and meanwhile motivate researchers to fill in the knowledge gap in the future.

A strong anion exchanger of poly(glycidyl methacrylate-divinylbenzene) substrate functionalized with cationic quaternary ammonium monomer

A strong anion exchanger applied for ion chromatography is described by grafting methacrylamido propyl trimethyl ammonium chloride onto hydrolyzed poly(glycidyl methacrylate-divinylbenzene) substrate. The anion exchanger has been in detail characterized and the final capacity of the anion exchanger can be readily manipulated by different monomer amounts. It exhibited obvious temperature-sensitive property and large tolerance to the samples with high ionic strength. The obtained anion exchanger demonstrated effective separation ability towards the common seven inorganic anions within 12 min and high separation efficiency, e.g. 58,000 /m of theoretical plate count for chloride. This article is protected by copyright. All rights reserved.

A novel approach for treating acid mine drainage by forming schwertmannite driven by a combination of biooxidation and electroreduction before lime neutralization

Acid mine drainage (AMD) contains abundant iron, sulfates, and various metal ions, and it causes environmental pollution. The traditional AMD lime neutralization forms a layer of iron hydroxide and gypsum on the surface of the lime particles, preventing continuous reaction and leading to excessive lime addition and neutralized sludge production. In this study, an approach for treating AMD using a cyclic process of biooxidation and electroreduction before lime neutralization was proposed, in which the Fe²⁺ in AMD was oxidized to Fe³⁺ and induced to form schwertmannite through Acidithiobacillus ferrooxidans. The remaining Fe³⁺ was reduced to Fe²⁺ using an electric field. After three biooxidation and two electroreduction cycles, 98.2% of Fe and 62.4% of SO₄^2- in AMD precipitated as schwertmannite (Fe₈O₈(OH)_5.16(SO₄)_1.37). The yield of schwertmannite reached 33.98 g/L_AMD, with a high specific surface area of 112.59 m²/g. The lime dosage and sludge yield of the treated AMD in the subsequent neutralization stage (pH = 7.00) decreased by 85.0% and 74.5%, respectively, than those of raw AMD. The pilot test results showed that the integrated treatment of biooxidation-electroreduction cyclic mineralization and lime neutralization has practical applications.

The Novel Polymethacrylate Based Hydrophilic Stationary Phase for Ion Chromatography

Ion chromatography is widely used as a useful and powerful tool for the analysis of anionic and cationic components found in waters and aqueous media. The performance and selectivity of ion chromatography are based on the stationary phase column packed material. In this study, it is aimed to develop new column material with quaternary ammonium functional group based on monodisperse polymeric particles for ion chromatography and to investigate their chromatographic performance. For the analysis of inorganic anions by ion chromatography, new stationary phases macroporous monodisperse particles based on 3-chloro-2-hydroxy propylmethacrylate-co-ethylene dimethacrylate are obtained as column packing material. 3-chloro-2-hydroxy propylmethacrylate and ethylene glycol dimethacrylate are transformed to porous monodisperse particle form by using glycidyl methacrylate as the seed latex and ethyl benzene as the porogen solvent via micro-suspension polymerization technique. Then macroporous monodisperse particles surface is functionalized by triethylamine so strong anion exchange is obtained for ion chromatography packing material. A series of stationary phases prepared from polymer particles containing different amounts of porogen solvent were tested. The results show that column packing material is successful to separate inorganic anions mixture such as F−, Cl−, NO2−, Br−, NO3− by using the carbonate and bicarbonate solutions as mobile phases.

Simultaneous analysis of 6 inorganic anions in urine by double-suppress ion exchange chromatography

This study is aimed to establish a simple, rapid, and accurate ion chromatography approach for simultaneous detection of 6 inorganic anions in urine. Various performance parameters affecting the determination of anions were optimized, including the selection of sample protein precipitation agent, eluent, and flow rate. The final eluent was 3.6 mmol/L sodium carbonate and 12% isopropanol with a flow rate of 0.6 mL/min. Acetonitrile was used for pretreatment to precipitate proteins, and the volume ratio of urine to acetonitrile was 1:4. The correlation coefficient of the target anion calibration curve ranged from 0.9973 to 0.9999. The limit of detection ranged from 1.50 to 12.0 μg/L, and the method detection limit ranged from 15.0 to 120 μg/L. The standard recovery rate for low, medium, and high concentrations ranged from 90 to 110%. The inter-day and intra-day relative standard deviations were < 5%. The method has high accuracy and good reproducibility, and is suitable for the separation and determination of anions in urine. This article is protected by copyright. All rights reserved.

Advances in the analytical methods for the determination of fluorinated aromatic carboxylic acids in aqueous matrices: A review

Fluorobenzoic acids are critically important chemical tracers in hydrothermal, geothermal, leaching, and oilfield applications. Particularly in oilfield applications, these tracers are used to investigate fluid flow paths between injector wells and producer wells, providing valuable information about the enhanced oil recovery process of the oil reservoirs. The detection limit of tracers is a vital subject in field reservoir work because the amount of chemical tracer that must be injected into the injector well is directly related to the amount detected at the producer well after migration and diffusion. The popularity of fluorinated benzoic acids as the tracers is due to their non-toxicity over radioactive tracers and low detection limit, which is determined using analytical techniques. This review focuses on the improvements/developments in extraction techniques such as solid-phase extraction and determination techniques such as gas chromatography coupled with mass spectrometry, liquid chromatography with mass spectrometry, isotope dilution gas chromatography-mass spectrometry, high-performance liquid chromatography, ion chromatography coupled with electrospray mass spectrometry, and so on for the analysis of fluorinated benzoic acids to achieve the lowest possible limit of concentration.

Hyperbranched anion exchangers prepared from polyethylene polyamine modified polymeric substrates for ion chromatography

High hydrophilic anion stationary phases play a crucial role in the separation behavior of ion chromatography. Herein, we report novel polymeric anion exchangers grafted with polyethylene polyamines, including ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylene pentaamine, via a facile epoxy-amine polymerization method. The anion exchangers were characterized by scanning electron microscopy, thermogravimetry, Fourier transform infrared spectrometry and elemental analysis. The chromatographic performance of the stationary phases was evaluated with the separation of common inorganic anions, organic weak acids and highly polarizable anions. Seven common anions (F^-, Cl^-, NO₂^-, Br^-, NO₃^-, SO₄^2- and HPO₄^2-) can be separated within 18 min by using hydroxide eluent in isocratic mode. By adopting different polyethylene polyamines as hyperbranched units, the four types of new stationary phases displayed high efficiencies and good reproducibility. The columns exhibit large exchange capacities at 76.5-184.8 μmol•column^-1 (4.6 × 150 mm, i.d.) with efficiency up to 20293 plate m^-1 (Cl^-). The RSDs of the retention time were less than 0.27% and the RSDs of the efficiency were less than 1.95% by consecutive injections after working for two months. The self-fabricated column was successfully applied to determine the chloride content in exhaled breath condensate.

Simultaneous quantitation of inorganic ions in oligonucleotides using mixed-mode liquid chromatography coupled with a charged aerosol detector

The amounts of inorganic ions (e.g. sodium, potassium, magnesium, calcium, chloride, and phosphate) in intrathecally administered oligonucleotide drug products need to be controlled in order to meet the final target formulation composition. During process development, these ions are measured to ensure the solution composition does not change during purification or drug product compounding and to ensure the final drug product targets are achieved. A quantitative method for ion analysis in antisense oligonucleotide (ASO) drugs was developed by mixed-mode anion exchange/cation exchange-hydrophilic interaction liquid chromatography (AEX/CEX-HILIC) with a charged aerosol detector (CAD). This thirteen-minute method measures monovalent and multivalent cations and anions simultaneously. LC separation conditions, CAD parameters, and sample preparation were judiciously optimized to ensure that the method is specific, accurate, precise, linear, robust, and rugged. With this LC-CAD approach, ion analysis for oligonucleotide drugs can be performed in most analytical labs to support drug development.

Hydrophobicity of polymer based anion-exchange columns for ion chromatography

The regularities of the retention of alkanoic and alkanesulfonic acids homologues were investigated for the set of 36 anion-exchange columns produced by various manufacturers. The role of hydrophobic and electrostatic interactions in the retention and separation of organic anions was studied. The methylene selectivity increments α(CH2) were measured for the studied columns with 10 mM sodium hydroxide eluent. The influence of matrix, surface area, polar group structure, ion-exchange capacity, the density of charged functional groups on the surface and other characteristics of anion-exchangers on resin hydrophobicity was considered. A unified approach for the measurements of hydrophobic properties of anion-exchange resins is proposed and the ratio of chloride retention factor (k Cl) to α(CH2) was introduced as mixed-mode factor. The synergetic effect of electrostatic and hydrophobic interactions was observed.

Preparation of a polymer-based weak cation exchanger for ion chromatography via atom transfer radical polymerization

A novel polymer-based weak cation exchanger (WCX) for ion chromatography has been described. It was prepared by grafting tert-butyl acrylate and maleic anhydride onto the surface of poly(glycidyl methacrylate-divinylbenzene) microspheres via atom transfer radical polymerization, followed by hydrolytic treatment to produce acrylic and maleic acid groups. The obtained WCX showed better separation and higher selectivity for model cations relative to solely acrylic or maleic acid. Simultaneous separation of alkali and alkaline earth cations (including NH₄⁺) was achieved in a single isocratic run under suppressed mode, and ion exchange was found to dominate the separation process. Its utility was demonstrated for determination of several cations in a beer sample and the recovery was ranging from 98.4 to 109.9%.

Determination of histidine in human serum and urine by cation exchange chromatography coupled to selective on-line post column derivatization

A reliable and highly selective method for the determination of histidine in human serum and urine is described. Histidine was separated from the matrix by cation exchange chromatography and detected selectively using on-line post column derivatization and fluorimetric detection. Unique reaction of histidine with o-phthalaldehyde in the absence of nucleophilic compounds offered specific detection in the complex biological substrate. Linearity was obeyed in the range of 0.5 - 25 μmol L-1 with a limit of detection of 0.160 μmol L-1. The absence of matrix effect (<5%) enabled the processing of real samples after minimal pretreatment. Endogenous histidine has been determined in human serum in the range of 78 - 119 μmol L-1 and random human urine in the range of 266 - 2034 μmol L-1. The percent recoveries were satisfactory in all cases, ranging between 89 and 114%.

Simultaneous separation of 17 anions by capillary electrophoresis with the addition of an organic solvent

Seventeen inorganic and organic anions, that normally are insufficiently separated via ion chromatography, were completely separated by the addition of an organic solvent to a solution of BGE combined with an adjustment of the apparent pH via CE in combination with indirect UV absorbance detection. Methanol, ethanol, and acetonitrile were examined for their utility in manipulating the selective separation of anions. Methanol and acetonitrile were better modifiers than ethanol at enhancing the resolution of anions comigrating in an aqueous solution of BGE. Methanol was selected as the modifier that provided the largest separation window that could achieve a complete separation of the target analytes. Via the use of methanol, manipulation of the selectivity between inorganic anions and that between inorganic and organic anions was enhanced, but the separation between organic anions remained difficult when only methanol was used. By varying the apparent pH of the BGE in the presence of 10% v/v methanol, however, the separation selectivity between organic anions was substantially improved. Eventually, 7 inorganic and 10 organic anions were simultaneously separated using BGE at a pH of 6.3 in the presence of 10% v/v methanol.

Selective post-column derivatization coupled to cation exchange chromatography for the determination of histamine and its precursor histidine in fish and Oriental sauce samples

Histamine is a biogenic amine that is formed from histidine by action of the enzyme histidine decarboxylase and can be toxic at high intakes. Thus, the quantification of these analytes in foods constitutes a significant axis of food safety. In this study we present the development, validation and application of a new method for the determination of histamine and its precursor histidine in fish products and oriental sauces. The analytes were separated rapidly through a cation exchange column using an acidic mobile phase (7 mmol L^-1 nitric acid) and reacted downstream with o-phthalaldehyde in post-column mode in the absence of nucleophilic reagents. The derivatives were detected spectrofluorimetrically at λ_ex/λ_em. = 360/440 nm. Following investigation of the chromatographic and post-column conditions, the method was validated as for its intended applications. The limits of detection were 0.16 and 0.17 μmol L^-1 for histidine and histamine respectively (ca. 0.1 mg kg^-1) and the precision was better than 5%. Various food samples were successfully analyzed without matrix interferences following minimal pretreatment. The percent recoveries ranged between 91.3 and 117.9%.

Nickel Iron Diselenide for Highly Efficient and Selective Electrocatalytic Conversion of Methanol to Formate

The electro-oxidation of methanol to formate is an interesting example of the potential use of renewable energies to add value to a biosourced chemical commodity. Additionally, methanol electro-oxidation can replace the sluggish oxygen evolution reaction when coupled to hydrogen evolution or to the electroreduction of other biomass-derived intermediates. But the cost-effective realization of these reaction schemes requires the development of efficient and low-cost electrocatalysts. Here, a noble metal-free catalyst, Ni_{1- x} Fe_x Se₂ nanorods, with a high potential for an efficient and selective methanol conversion to formate is demonstrated. At its optimum composition, Ni_0.75 Fe_0.25 Se₂ , this diselenide is able to produce 0.47 mmol cm^-2  h^-1 of formate at 50 mA cm^-2 with a Faradaic conversion efficiency of 99%. Additionally, this noble-metal-free catalyst is able to continuously work for over 50 000 s with a minimal loss of efficiency, delivering initial current densities above 50 mA cm^-2 and 2.2 A mg^-1 in a 1.0 m KOH electrolyte with 1.0 m methanol at 1.5 V versus reversible hydrogen electrode. This work demonstrates the highly efficient and selective methanol-to-formate conversion on Ni-based noble-metal-free catalysts, and more importantly it shows a very promising example to exploit the electrocatalytic conversion of biomass-derived chemicals.

The 2021 Winners of the Lifetime Achievement and Emerging Leader in Chromatography Awards

Paul Haddad and Erik L. Regalado are the winners of the 14th annual LCGC Lifetime Achievement and Emerging Leader in Chromatography Awards, respectively. We review their achievements.

Open tubular ion chromatography: A state-of-the-Art review

This review summarizes the progress in open tubular ion chromatography (OTIC) over the period from 1981 to 2020. Although OTIC columns provide superior column efficiency, require very little sample volumes, and consume a minimum level of eluents compared to regular packed columns, not many reports can be found from the literature mainly due to the difficulties in the preparation of OTIC columns and the harsh system requirements, such as pL-nL injections and extremely small detection volumes. However, technical advances, e.g., capacitively coupled contactless conductivity detectors (C⁴Ds), hydroxide eluent compatible polymer-based OTIC columns, electrodialytic capillary suppressors, and nanovolume gas-free hydroxide eluent generators (EGs), have removed the obstacles to OTIC. As such, in this review, the author focused on the development of the key components in an OTIC system from the perspective of instrument development. A brief revisit of open tubular (OT) column theory is first presented, followed by a discussion of the system configuration and component development. Attention is given to the advances in the development of the suppressed open tubular ion chromatography (SOTIC) system.

Analysis of mobile chemicals in the aquatic environment-current capabilities, limitations and future perspectives

Persistent and mobile water contaminants are rapidly developing into a focal point of environmental chemistry and chemical regulation. Their defining parameter that sets them apart from the majority of regularly monitored and regulated contaminants is their mobility in the aquatic environment, which is intrinsically tied to a high polarity. This high polarity, however, may have severe implications in the analytical process and thus the most polar of these mobile contaminants may not be covered by widely utilized trace-analytical methods, and thus, alternatives are required. In this review, we infer the physical and chemical properties of mobile water contaminants from a set of almost 1800 prioritized REACH chemicals and discuss the implications these substance properties may have on four integral steps of the analytical process: sampling and sample storage, sample pre-treatment, separation and detection. We discuss alternatives to widely utilized trace-analytical methods, examine their application range and limitations, highlight potential analytical techniques on the horizon and emphasize research areas we believe still offer the most room for further improvement. While we have a comprehensive set of analytical methods to cover a large portion of the known mobile chemicals, these methods are still only infrequently utilized. Graphical abstract.

Sub-1 mL sample requirement for simultaneous determination of 17 organic and inorganic anions and cations in Antarctic ice core samples by dual capillary ion chromatography

The significant advance of delivering high value multi-species data from sub-1 mL ice core sample volumes allows higher temporal resolution in deposition records of inorganic and low molecular weight organic anions and cations. The determination of these species is a fundamental strategic requirement in modern paleoclimate studies. Herein, for the first time, a dual capillary ion chromatography (Cap-IC) based method for the simultaneous separation of 17 organic and inorganic anions and cations in low volume Antarctic ice core samples is presented. The total amount of sample required for direct injection has been reduced to 190 μL, which is 35 times lower than the amount of sample required by standard ion chromatography methods. A dual Cap-IC system configured for the simultaneous determination of cations and anions was used throughout. A range of chromatographic parameters was optimised for both anion and cation systems to obtain baseline separations of all target analytes in a suitable run time and to minimise the amount of sample required. Baseline separation of matrix and trace 'marker' ions were achieved in less than 35 min, after injecting only 40 μL of sample in each IC system. Limits of detection (LODs) for all analytes determined were within a range similar to that achieved by previously published standard bore IC-based methods. Intra- and inter-day repeatability were evaluated, with both parameters being typically below 3% for peak area. In further validation of the method, a comparative analysis of a set of 420 ice core samples from Aurora Basin North site, Antarctica, previously analysed by standard IC, established that the proposed low sample volume technique was applicable as a routine measurement approach in ice core analysis projects.

Influencing the selectivity of grafted anion exchangers utilizing the solubility of the radical initiator during the graft process

A previously published radical graft-functionalization method for the synthesis of high performance anion exchangers was further investigated to control the capacity and selectivity of the exchangers. Using a hydrophobic radical initiator instead of a hydrophilic one diminished the influence of rivaling homopolymerization of monomer during the functionalization step. Instead of only generating monomer radicals in free solution the radicals are ideally generated on top of the PS/DVB surface. However, in both cases the selectivity factors of polarizable anions bromide and nitrate in relation to chloride increased strongly with increasing capacity of the exchanger. Higher exchanger capacities could lead to coelution of bromide and/or nitrate with other analytes such as sulfate or phosphate when using the eluent as proposed in this work. By variation of the organic solvent used for functionalization it was possible to remove both the rivaling homopolymerization and the strong influence of the capacity on the selectivity. With increasing solubility of the hydrophobic radical initiator in the organic solvent the influence of the homopolymerization and the influence on the selectivity factor of bromide and nitrate decreased. Additionally, a change of bromate selectivity factor could be observed. The bromate signal is shifted closer towards the chloride signal. However, with increasing solubility of the radical initiator in the organic solvent the observed capacity of the exchangers decreases linearly, resulting in higher amounts of monomer needed for functionalization.

Determination of inorganic anions in weak acids by using ion exclusion chromatography - Capillary ion chromatography switching column technique

An improved "heart-cut" column-switching method combining ion-exclusion column, monolithic anion exchange concentrator and capillary anion-exchange column is developed and successfully applied for the determination of inorganic anions (Cl^-, Br^-, NO₃^- and HPO₄^2-) at trace level in weak acids. The quantitative determination of selected inorganic anions in the samples of fifteen weak acids and hydrogen peroxide are accomplished with analysis time of 45 min per sample. The obtained limits of detection (LODs) are in the range of 2.1-32.6 ng/L based on the s/n = 3 and injection volume of 50 μL. RSDs for retention time and peak area were all ≤1.89%. A spike-recovery study was performed under these conditions and satisfactory recoveries between 85.3 and 103.9% for all studied anions were obtained.

COMPARISON OF TWO IODINE QUANTIFICATION METHODS IN AN ARTIFICIAL SEAWATER SYSTEM HOUSING WHITE-SPOTTED BAMBOO SHARKS ( CHILOSCYLLIUM PLAGIOSUM)

Iodine is an essential micronutrient for elasmobranchs in order to prevent goiter. Preventing goiter requires bioavailable iodide: either oral iodide or maintaining adequate aquarium water iodide concentrations. The objective of this study was to determine how oral and water supplementation affected iodine (I₂) and iodide (I^-) concentrations in artificial seawater aquaria housing captive white-spotted bamboo sharks ( Chiloscyllium plagiosum). Daily water samples were collected and free iodine (I₂) was determined using ultraviolet-absorbance spectrophotometry (a relatively simple in-house assay) and total iodide (I^-) via liquid chromatography (a more time- and expertise-intense quantification method) to learn the effects of supplementation. One water system received iodine and iodide supplementation in the form of 5% Lugol's iodine solution added directly to the water, while a second water system received no supplementation. In addition, one tank of sharks in each water system received oral iodide supplementation. Results indicated that oral supplementation provides greater increases in water concentrations of bioavailable iodide (I^-) than direct water supplementation. In addition, the chromatographic results suggested that iodide is present in higher concentrations in the systems not receiving water supplementation. Increased iodide concentrations were detected in water samples after water changes and after oral iodide supplementation was administered, but total iodine (I₂) concentration changes were not detectable within the same time frame.

Resistance-based H2S gas sensors using metal oxide nanostructures: A review of recent advances

Gas sensors play an undeniable role in most fields of technology in the modern world; they are broadly used for public safety, pollution monitoring, quality control, breath analysis, smart homes and automobiles, and so on. Due to their low cost, high sensitivity, compact size, online detection, ease of use, portability, and low power consumption, metal oxide (MO) gas sensors have exceptional potential for detection of more than 150 gases. This paper reviews the current state-of-the-art H₂S conductometric MO gas sensors. In the first part, the H₂S sensing mechanism for MOs is presented in detail. In the next part, the H₂S sensing characteristics of the different MOs are presented, focusing on strategies such as metal doping, heterojunction composites, and different morphologies that are applied to enhance their sensing characteristics. In general, CuO, ZnO, and SnO₂ show the highest sensitivity to H₂S; therefore, most of this review is dedicated to these oxides. In the last part, some unusual and emerging MOs for H₂S sensing are presented.

Identification of Metabolite Biomarkers for Gout Using Capillary Ion Chromatography with Mass Spectrometry

Gout is a common form of inflammatory arthritis, and the detailed pathogenic mechanisms for this metabolic disorder remain largely unknown. In this study, we first profiled the salivary metabolites in 8 patients with gout, 15 patients with hyperuricaemia (HUA), and 15 healthy individuals using capillary ion chromatography (CIC) with tandem mass spectrometry (MS/MS). Forty-nine salivary metabolites were found to be significantly changed between gout patient and healthy control groups, and 26 salivary metabolites were significantly different between gout and HUA patient groups. Three metabolite biomarkers, uric acid, oxalic acid, and l-homocysteic acid (HCA), were selected for validation in the saliva samples of 30 patients with gout, 30 patients with HUA, and 30 healthy control subjects. By using commercial assay kits for the measurements, salivary uric acid and oxalic acid levels were found to be significantly higher in gout patients than healthy controls, whereas salivary HCA level was significantly higher in gout patients than both HUA patients and healthy controls. These assay measurements were in line with those obtained by CIC-MS/MS. In conclusion, we have demonstrated a new application of CIC-MS/MS for the discovery of novel metabolite biomarkers of gout. Validated biomarkers may be used for noninvasive, diagnostic and prognostic applications in gout. Future studies are warranted to investigate the clinical utility of these identified biomarkers for monitoring gout flare and/or treatment efficacy.