High performance ion chromatography of haloacetic acids on macrocyclic cryptand anion exchanger

Study of Efficiency of Capacity Gradient Ion-Exchange Stationary Phases

Highly efficient columns are necessary for the modern analytical applications of liquid chromatography. In this work, the separation efficiency of ion-exchange capacity gradient stationary phases combined with eluent concentration gradient was studied by a theoretical approach. In the course of our work three different scenarios of capacity gradients were used with different shapes (linear, convex and concave). The resolutions of different gradient columns were calculated for each scenario. As a reference, a uniform column was considered, which had the same analysis time as the non-uniform column. In the case of separation of ions with same charges, the gradient column offered only a marginal advantage compared to the uniform column due to the bandwidth compression caused by the capacity gradient. In the case of ions with different charges, however, the advantage of the gradient column was more significant. This was mainly due to the increased retention time difference of solutes. Ion-exchange capacity gradient columns may be a new way to separate ions more efficiently.

A new approach for trace analysis of guanidine compounds in surface water with resorcinarene-based ion chromatography columns

Trace levels of pharmaceuticals have been detected in surface water and may pose a health risk to humans and other organisms. New chromatographic materials will help identify and quantify these contaminants. We introduce a new ion chromatographic (IC) material designed to separate cationic pharmaceuticals and report its ability to separate a group of guanidine compounds. Guanidine moieties are strongly basic and protonated under acid conditions, and therefore can potentially be separated on the newly designed stationary phase and detected by ion exchange chromatography. The new column packing material is based on glutamic acids bonded to resorcinarene moieties that in turn are bound to divinylbenzene macroporous resin. Detection limits in the range of 5-30 μg L(-1) were achieved using integrated pulsed amperometric detection (IPAD) for guanidine (G), methylguanidine (MG), 1,1-dimethylbiguanide (DMG), agmatine (AGM), guanidinobenzoic acid (GBA) and cimetidine (CIM). Suppressed conductivity (CD) and UV-vis detection resulted in limits of detection similar to IPAD, in the range of 2-66 μg L(-1), but were not able to detect all of the analytes. Three water sources, river, lake, and marsh, were analyzed and despite matrix effects, sensitivity for guanidine compounds was in the 100 μg L(-1) range and apparent recoveries were 80-96%. The peak area precision was 0.01-2.89% for IPAD, CD and UV-vis detection.

Optimized chromatographic conditions for separation of halogenated acetic acids by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry

Emerging halogenated acetic acids (HAAs), especially mixed halogenated acids such as chlorobromo-, chloroiodo- and bromoiodo-acetic acids, are unregulated disinfection by-products in drinking water. Because these compounds are hydrophilic and strongly acidic, they are difficult to detect at trace levels using approved analytical methods. In the present study, 13 HAAs were effectively separated on three ultra-performance liquid chromatography columns. The effects of changing in the aqueous mobile phase, acidic solutions and cationic volatile ion pair reagents were investigated. The samples were pretreated by filtration, and extraction, while derivatization and concentration procedures were not required. The limits of quantitation for regulated HAAs were between 0.5 μg/L and 1.7 μg/L and for unregulated HAAs were 1.2 and 5.8 μg/L, especially for the iodinated acetic acids were 1.5 and 2.1 μg/L. The method was applied to two finished water samples collected in China (Shanghai and Xuzhou) from water treatment plants that use chlorine for disinfection. Multiple unregulated HAAs were found in the two samples, but iodoacids were only detected in the water sample from Shanghai, which could be attributed to the characteristics of the source water. The presence of unregulated HAAs, especially mixed bromo- and iodoacetic acids, in the finished water samples could affect human health, and this warrants further investigation.

Novel insights in Al-MCM-41 precursor as adsorbent for regulated haloacetic acids and nitrate from water

High concentration of NO (3) (-) in groundwater has raised concern over possible contamination of drinking water supplies. In addition, the formation of haloacetic acids (HAAs) as by-products during disinfection with chlorine-based agents is still a relevant issue, since HAAs pose serious health hazard. In this work, we investigated the affinity of a precursor of Al-MCM-41 (a mesostructured hexagonal aluminosilicate containing the template surfactant) towards nitrate and HAAs, for its possible application in the removal of these pollutants from natural and drinking waters. Additionally, adsorption kinetics and isotherms were studied. The adsorbent was synthesized using cetyltrimethylammonium bromide as surfactant and characterized by physico-chemical techniques. Simulated drinking water was spiked with the EPA-regulated HAAs (monochloroacetic (MCAA), monobromoacetic (MBAA), dichloroacetic (DCAA), dibromoacetic (DBAA), and trichloroacetic (TCAA) acids) and placed in contact with the adsorbent. The effect of matrix composition was studied. Adsorption kinetic studies were performed testing three kinetics models. For the adsorption studies, three adsorption isotherm approaches have been tested to experimental data. The pollutant recoveries were evaluated by suppressed ion chromatography. The affinity of the adsorbent was TCAA = DBAA = DCAA > MBAA > MCAA with DCAA, DBAA, and TCAA completely removed. A removal as high as 77 % was achieved for 13 mg/L nitrate. The adsorption isotherms of NO (3) (-) and monochloroacetic acid can be modeled by the Freundlich equation, while their adsorption kinetics follow a pseudo-second-order rate mechanism. The adsorbent exhibited high affinity towards HAAs in simulated drinking water even at relevant matrix concentrations, suggesting its potential application for water remediation technologies.

Efficient reductive dechlorination of monochloroacetic acid by sulfite/UV process

Most halogenated organic compounds (HOCs) are toxic and persistent, and their efficient destruction is currently a challenge. Here, we proposed a sulfite/UV (253.7 nm) process to eliminate HOCs. Monochloroacetic acid (MCAA) was selected as the target compound and was degraded rapidly in the sulfite/UV process. The degradation kinetics were accelerated proportionally to the increased sulfite concentration, while the significant enhancement by increasing pH only occurred in a pH range of 6.0-8.7. The degradation proceeded via a reductive dechlorination mechanism induced by hydrated electron (e(aq)(-)), and complete dechlorination was readily achieved with almost all the chlorine atoms in MCAA released as chloride ions. Mass balance (C and Cl) studies showed that acetate, succinate, sulfoacetate, and chloride ions were the major products, and a degradation pathway was proposed. The dual roles of pH were not only to regulate the S(IV) species distribution but also to control the interconversion between e(aq)(-) and H(•). Effective quantum efficiency (Φ) for the formation of e(aq)(-) in the process was determined to be 0.116 ± 0.002 mol/einstein. The present study may provide a promising alternative for complete dehalogenation of most HOCs and reductive detoxification of numerous toxicants.