Development of the Thermo Scientific Dionex IonPac AS26 Column for Haloacetic Acid Analysis

Transcription

1 Development of the Thermo Scientific Dionex IonPac AS Column for aloacetic ong Lin, Kannan Srinivasan, and Chris Pohl, Thermo Fisher Scientific, Sunnyvale, CA, USA Introduction aloacetic acids are a group of disinfection byproducts resulting from the reaction between the naturally occurring organic matters and the disinfectants used during water treatment. These disinfection byproducts pose potential health hazard due to longterm exposure and are currently regulated by EPA. The Stage Disinfection/Disinfection Byproduct rule sets a maximum contamination level of 0 ppb for AA, which includes monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, dibromoacetic acid and trichloroacetic acid (Table ). The predominant method for AA analysis is U.S. EPA Method., a GC/electron capture detection (ECD) method. It is a timeconsuming and laborintensive process, often resulting in operational errors. U.S. EPA Method describes a suppressed ion chromatography (IC) MS or MS/MS detection method using direct injection and matrix elimination. The MS detection is required to selectively detect coeluting species. The work presented here describes the development of a new IC separation column (Thermo Scientific Dionex IonPac AS) for haloacetic acid analysis by utilizing amineepoxide hyperbranch chemistry. Various synthesis strategies for improving the haloacetic acid resolution and quantitation are shown, and a twodimensional (D) method allowing sensitive conductivity detection is described. Table. What Are AAs? Acid Abbreviation Chemical Formula pka Boiling Point C Monochloroacetic Acid MCAA* ClC CO.. Dichloroacetic Acid DCAA* Cl CCO. Trichloroacetic Acid TCAA* Cl CCO 0.. Monobromoacetic Acid MBAA* BrC CO. 0 Dibromoacetic Acid DBAA* Br CCO A Tribromoacetic Acid TBAA Br CCO 0. Bromochloroacetic Acid BCAA BrClCCO A 0. Dibromochloroacetic Acid DBCAA Br ClCCO A A Dichlorobromoacetic Acid DCBAA Cl BrCCO A A *MCAA, DCAA, TCAA, MBAA, DBAA are collectively referred to as AA

2 aloacetic Acid Methods U.S. EPA Method. requires liquidliquid microextraction and derivatization before GC/ECD analysis. A 0 ml sample is adjusted to p 0., then extracted either with methyl tertbutyl ether (MTBE) or tertamyl methyl ether. AAs are converted to their methyl esters by adding acidic methanol and heating for two hours. The sample is separated from the acidic methanol by adding a concentrated aqueous solution of sodium sulfate, and is then neutralized with saturated solution of sodium bicarbonate. Analysis using GC/ECD requires 0 min. This method provides good selectivity, low Minimum Detection Limits (MDLs) from μg/l for AA, and a wide applicable concentration range from 0. 0 μg/l. owever, it requires sample pretreatment that is time consuming, labor intensive, and subject to multiple procedural errors, with recoveries ranging from 0% for AA. U.S. EPA Method using suppressed ion chromatography with MS or MSMS detection is a direct injection method, with no need for liquidliquid extraction, sample pretreatment, or derivatization. It uses a fully automated matrix diversion setup to eliminate column overloading due to highionicstrength matrices, and coelution is not an issue since MS is a selective detector. ecoveries are more than 0%. Figure shows the typical separation of nine haloacetic acid anions using a Dionex IonPac AS column. MBAA, CDBAA, and TBAA degrade readily at high p, so to minimize degradation, the separation is performed at C. Chlorite and MCAA coelute under these conditions. FIGUE. Analysis of AA using the Dionex IonPac AS column at C. esults and Discussion Polmer Formation Figure illustrates the schematics of the stepgrowth electrostaticgraft porous polymeric substrate. The ionexchange site is highlighted. FIGUE. Stepgrowth electrostaticgraft porous polymeric substrate. Figure illustrates the basic chemistry behind amineepoxide condensation polymer chemistry. By using a : molar ratio of primary amine and a diepoxide, it is possible to synthesize a predominantly linear polymer with residual tertiary amine functionality. If the condensation polymer is formed in the presence of an anionic surface, the resulting polymer will form a coating over the entire surface. The residual tertiary amine sites can be used for growth of hyperbranched polymer chains with anionexchange groups located at regular distances along the growing chain. FIGUE. ypothetical product of : ratio (diepoxide:amine)..0 MCAA O DBAA.00 Peaks:. MCAA. MBAA. DCAA. BCAA. DBAA. TCAA. BDCAA. CDBAA. TBAA O O O O + ( O O ) n 00 Concentration:.00 mm K Development of the Thermo Scientific Dionex IonPac AS Column for aloacetic

3 Figure illustrates a representative section of the stationary phase substrate surface after the initial reaction in the presence of the substrate, forming the basement layer followed by two subsequent reaction cycles of a diepoxide followed by a primary amine. This alternates in the following sequence: diepoxide, water rinse, primary amine, water rinse, diepoxide, water rinse, primary amine, and a final water rinse. With each reaction cycle (each cycle consisting of diepoxide followed by primary amine), the number of quaternary sites in the growing polymer doubles. Substantial capacity can be created with three and four reaction cycles. At the end of each reaction cycle, residual secondary amine groups remain available for further reactions. Figure illustrates the effect of high concentration of epoxide on the column capacity and selectivity. This phase shows very high capacity and excellent separation for the early eluting peaks. owever, the overall run time is too long. FIGUE. Example of high capacity phase and its impact on AA separation.. O % Diepoxide 0 mm Concentration: 0.00 mm K Peaks:. MCAA 00 µg/l. MBAA 00. DCAA 00. BCAA 00. DBAA 00. TCAA 00. BDCAA 00 FIGUE. Layer after diepoxide and amine treatment. Crosslink 0% Diepoxide ClO 0 mm O.00 Concentration:.00 mm K Sulfonated esin Surface Figure illustrates the effect of temperature during the basement layer synthesis on the separation of the early eluting peaks. The separation between bromate and MBAA improves when higher temperature is used. The separation between the chlorite and MCAA peak also improves at higher temperature. A new invial synthesis strategy was used for the Dionex IonPac AS columns. A basement layer was applied to the sulfonated resin by mixing the diepoxide/amine solution mixture (: mole ratio of epoxide to amine) with the resin (sulfonated) at 0 C for 0 min. This was functionalized by reacting the diepoxide with the resulting resin at C for h then treating the resin with the same amine mixture solution at C for h. Selectivity Figure illustrates the effect of epoxide concentration on the column selectivity. As the epoxide concentration increases, the resolution between bromate and MBAA, nitrite and DBAA improves. FIGUE. Selectivity optimization using different basement layer reaction conditions..0 C Column: Prototypes Eluent: K Gradient Flow ate: 0. ml/min Inj. Volume: 0 µl BrO Column Temp.: C Suppressor: Thermo Scientific Dionex ASS 00, mm 0. Current: ma (recycle mode) Peaks:. MCAA 00 µg/l.0 0 C. MBAA 00 BrO 0. 0 FIGUE. Effect of the diepoxide concentration on selectivity BrO Concentration:.00 mm K O.00 % Diepoxide Peaks:. MCAA 00 µg/l. MBAA 00. DCAA 00. BCAA 00. DBAA 00. TCAA 00. BDCAA 00. CDBAA 00. TBAA 00 0% Diepoxide BrO O Concentration:.00 mm K

4 Figure illustrates the separation using the new Dionex IonPac AS column. All nine haloacetic acid anions are separated from the matrix anions. FIGUE. Separation of AAs using the new Dionex IonPac AS column...00 Column: Dionex IonPac AS 0 mm Eluent: K Gradient Flow ate: 0. ml/min Inj. Volume: 0 µl Column Temp.: C Suppressor: Dionex ASS 00, mm Current: ma (recycle mode) Peaks:. MCAA. MBAA. DCAA. BCAA. DBAA. TCAA. BDCAA. CDBAA. TBAA Ions of interest are diverted to a concentrator column after suppression in the first dimension and focused. The hydroxide eluent is converted to DI water by the suppressor, providing an ideal environment for focusing or concentrating the ions of interest. Analysis is performed in the second dimension using a column with a smaller crosssectional area, yielding enhanced sensitivity. For example, the crosssectional area of a mm column is one sixteenth the area of a mm column, providing a sensitivity enhancement factor of ~. Analysis in the second dimension using a different chemistry provides complementary retention, leading to enhanced selectivity. This method can be automated easily using the Dionex ICS000/ICS000 systems (Figure ). Concentration:.00 mm FIGUE. Instrumental setup for the matrix elimination ion chromatography (MEIC). Matrix Elimination Ion Chromatography (MEIC) A variety of methods for determining trace levels of contaminants in water are commonly employed. Samples with low levels of matrix ions (e.g., ultrapure water [UPW]) are typically analyzed using preconcentration or largevolume direct injections. For samples with high levels of matrix ions (e.g., drinking water, wastewater), preconcentration or largevolume direct injection may not be possible because the matrix ions may coelute with species of interest or may elute species of interest, leading to recovery and integration issues due to band broadening. Sample pretreatment steps using solidphase extraction (SPE) cartridges may be used to remove matrix interferences (e.g., a silver form cationexchange resin used to remove high levels of chloride). Such offline SPE methods are labor intensive, and multiple cartridges may be needed, adding cost. Matrix elimination is an automated method in which the highconcentration matrix ions are separated from the analytes using a mm firstdimension column and diverted to waste. A larger loop volume than the standard approach can be used because the capacity and selectivity of the analytical column in the first dimension dictates the recovery, and the analyte of interest is analyzed in the second dimension. st Dimension nd Dimension Large Loop Load Inject Injection Valve Pump st Dimension Column ( mm) External Water Suppressor EG Autosampler CD CD To EG Degas in Transfer to D Load Concentrator Diverter Valve External Water Injection Valve Pump Concentrator Column (UTACULP) nd Dimension Column ( mm) EG CD CD Suppressor To EG Degas in Development of the Thermo Scientific Dionex IonPac AS Column for aloacetic

5 Figure 0 shows the analysis of nine haloacetic acid anions using the twodimensional matrixelimination ion chromatography, both in the reagent water (black trace, A) and the high ionic water (IW, blue trace, B), containing 00 mg/l each of Cl, CO, and SO and 0 mg/l each of as O and P as PO. The top chromatograms show the firstdimension analysis using a Dionex IonPac ASA mm column and the bottom chromatograms show the seconddimension analysis using a Dionex IonPac AS mm column. etention time shifts and peak broadening observed in the firstdimensional IW sample are absent in the second dimension. Excellent recovery is observed for all AAs. Conclusion The Dionex IonPac AS column was developed by optimizing amine epoxide reaction conditions Excellent resolution of AAs was achieved in the presence of inorganic matrix ions Preliminary studies with the MEIC methodology allowed analysis of AA in the presence of matrix ions with suppressed conductivity detection Matrix diversion and selective concentration of AA species in the first dimension Separation and enhanced detection by suppressed conductivity detection in the second dimension FIGUE 0. MEIC analysis of AA in reagent water and high ionic water (IW). B A First Dimension Second Dimension B A ecovery >0% for AAs First Dimension Column: Dionex IonPac ASA, mm Flow ate:.0 ml/min Column Temp.: C Inj. Volume: 000 µl Suppressor: Dionex ASS 00, mm Current: ma (ecycle) Second Dimension Column: Dionex IonPac AS, mm Flow ate: 0. ml/min Suppressor: Dionex ASS 00, mm Current: ma (ecycle) Column Temp.: C Concentrator: Dionex IonPac UTACLP Samples: A) AA in DI water B) AA in IW Peaks:. MCAA 00 µg/l. MBAA 00. DCAA 00. BCAA 00. DBAA 00. TCAA 00. BDCAA 00. CDBAA 00. TBAA 00 0 Thermo Fisher Scientific, Inc. All trademarks are the property of Thermo Fisher Scientific Inc. and its subsidiaries. This information is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others. Dionex Products: Titan Way, PO Box 0, Sunnyvale, CA 00, (0) 000 orth America: U.S./Canada () 00 South America: Brazil () 0 Europe: Austria (), Benelux () 0 () Denmark () 0 0, France () 0 0 0, Germany () 0 Ireland () 00, Italy () 0, Sweden () 0, Switzerland () 0, United Kingdom () Asia Pacific: Australia () 0, China (), India (), Japan (), Korea () 0, Singapore () 0, Taiwan () LP 0 /