Two-dimensional Ion Chromatography Research Articles

Highly sensitive two-dimensional ion chromatography mass spectrometry method for nitrite determination in hydroxypropyl methylcellulose

Due to their potential adverse health effects, some N-nitrosamines in drug products are strictly regulated with very low maximum daily intake limits. Nitrosamines can be formed from the reaction of nitrite and secondary or tertiary amines when both species co-exist in the drug synthesis or formulation process. One key strategy to mitigate nitrosamine risk in drugs is to select low-nitrite containing pharma excipients for formulation. It is necessary to develop a sensitive method for trace nitrite determination in pharma excipients as it enables drug producers to study nitrosamine formation kinetics and select excipient suppliers. This study details the development and validation of a two-dimensional ion chromatography mass spectrometry (2D-IC/MS) method for trace nitrite determination in hydroxypropyl methylcellulose (HPMC), one of the most important pharmaceutical excipients used in many drug formulations. The 2D-IC system was operated in heart-cutting mode with a concentrator column coupling the two dimensions. A standard bore anion-exchange column was used in the first dimension (1D) to enable a large volume injection for increased sensitivity and provide improved resolution between nitrite and the interfering chloride peak. A high efficiency microbore anion-exchange column with different selectivity was used in the second dimension (2D) to resolve nitrite from other interfering species. The use of 2D-IC resulted in significantly improved resolution, solving the sensitivity loss issue due to ion suppression from an otherwise 1D separation. MS detection with selective ion monitoring and isotope labeled nitrite internal standard further improve the method specificity, accuracy, and ruggedness, as compared with conductivity detection. For trace determination, it is also extremely important to have a clean blank. For this purpose, a novel cleaning procedure using a strong anion wash was developed to remove nitrite contamination from labware. The optimized method was validated with linearity of nitrite in the concentration range of 18.5–5005.8 ng/g having a regression coefficient of >0.9999, precision with RSD at 3.5–10.1 % and recovery of 90.5–102.4 %. The limit of detection and limit of quantitation were 8.9 and 29.6 ng/g relative to the HPMC sample, or equivalent to 89 and 296 pg/g in the sample solution, respectively.

Determining haloacetic acids in drinking water by one-pump column-switching ion chromatography: An online and cost-effective tool for matrix removal and sample enrichment

Haloacetic acids (HAAs) are a group of disinfection byproducts ubiquitously found in disinfected drinking water and they are currently regulated by some governments. Conventional HAAs analytic methods employ either gas chromatography (GC), two-dimensional ion chromatography (2D-IC), or ion chromatography with electrospray ionization tandem mass spectrometry (IC-ESI-MS/MS) to reduce the effect of interfering compounds and enhance detection resolution; however, they are either laborious in sample preparation procedures or too expensive to be used by common laboratories. To bypass these problems, this study proposes to analyze HAAs by employing a one-pump column-switching ion chromatography (OPCS-IC) that allows direct sample injection without requiring extraction and derivatization pretreatments. Unlike 2D-IC method, which uses two pumps and two parallel sets of IC columns, this method applies only one pump and one column. The tailored OPCS-IC removes coexisting anions from water and enriches HAAs simultaneously, thereby distinguishing HAAs from interfering anions and magnifying the signals of HAAs. For example, when HAAs were enriched by five times, the coexisting F−, Cl−, Br−, NO3–, and SO42− were removed by 62.4%, 93.9%, 99.7%, 99.9%, and 98.9%, respectively. Meanwhile, the recoveries of HAAs dosed into real samples ranged from 84% to 102%, similar to those obtained from conventional GC method, meaning that the convenience of this method did not compromise its performance. The study hence proves an easy-to-use and relatively cheaper method for measuring HAAs in drinking water.

Portable analyser using two-dimensional ion chromatography with ultra-violet light-emitting diode-based absorbance detection for nitrate monitoring within both saline and freshwaters

A portable and automated IC system with a dual-capability for the analysis of both fresh and saline environmental waters has been developed. Detection of nitrate in complex matrices such as seawater was achieved by the employment of an automated two-dimensional (heart-cut) IC method utilised in tandem with on-column matrix elimination, using a sodium chloride eluent. The system also demonstrated the capability to switch to a second mode of analysis, whereby direct one-dimensional IC analysis was employed to rapidly detect nitrite and nitrate in freshwater, with direct UV LED based absorption detection in under 3 minutes. Calibration curves using a 195 µL sample loop were generated for both freshwater and artificial seawater samples. For marine analysis, an analytical range of 0.1 mg L−1 – 40 mg L−1 NO3− was possible, while an analytical range (0.1 mg L−1 – 15 mg L−1 NO2−, 0.2 – 30 mg L−1 NO3−) appropriate for freshwater analysis was also achieved. Chromatographic repeatability for both marine and freshwater analysis was verified over 40 sequential runs with RSD values of < 1% demonstrated for both peak area and retention times for each mode of analysis. The selectivity of both methods was demonstrated with interference tests with common anions present in environmental waters. Recovery analysis was carried out on marine samples from Tramore Bay, Co. Waterford, Ireland, and the systems analytical performance was compared with that of an accredited IC following environmental sample analysis.

Phosphorus-based metabolic pathway tracers in surface waters.

Trophic status in surface waters has been mostly monitored by measuring soluble reactive phosphorus (SRP) and total phosphorus (TP). Additional to these common parameters, a two-dimensional ion chromatography mass spectrometry (2D-IC-MS) method was used to simultaneously measure soluble phosphate (Pi), pyrophosphate (PPi), and eleven phosphate-containing metabolites (P-metabolites) in Lake Ontario and its tributaries. From the additional P species, PPi, adenosine 5'-monophosphate (AMP), glucose 6-phosphate (G-P), D-fructose 6-phosphate (F-P), D-fructose 1,6-biphosphate (F-2P), D-ribulose 5-phosphate (R-P), D-ribulose 1,5-bisphosphate (R-2P), and D-(-)-3-phosphoglyceric acid (PGA) were detected and quantified in the lake and river samples. The additional multivariate statistical analysis identified similarities between samples collected at different locations. The presence of R-P, R-2P, and F-2P in Lake Ontario tributaries seems to be mainly related to the Calvin cycle, while the lack of all these three P-metabolites and higher PGA levels than G-P in Toronto Harbour samples seems to be the result of depleted Calvin cycle, pentose phosphate, and glycolysis metabolic pathways.

Simultaneous Detection of Anions and Carbohydrates in Cyanobacteria by Two-Dimensional Ion Chromatography

The simultaneous analysis of several anions and carbohydrates by one-dimensional chromatography with a single detector is often complicated by the presence of overlapping peaks. To overcome this problem, analytes are usually analyzed separately making analysis long and tedious. A method combining two-dimensional ion chromatography (2D-IC) and valve switching was developed for the simultaneous determination of anions (F-, Cl-, NO2-, SO42-, NO3-, and PO43-) and carbohydrates (glycerin, glucosyl glycerol, trehalose, mannose, glucose, galactose, fructose, ribose, and sucrose) in cyanobacteria. Interfering color compounds were removed by first passing the sample through graphitized carbon solid phase extraction (SPE) cartridges. Samples were applied to an AS11-HC column, which was used to separate the anions followed by quantification using a conductance detector. Carbohydrates eluted from the AS11-HC column were trapped and separated on a MA1 column and simultaneously quantified using electrochemical detection in the second dimension with valve switching. The following parameters were established: LOD, 0.001-0.030 (mg/L); LOQ, 0.001-0.010 (mg/L); linearity (R2), 0.9940; repeatability, 0.39-3.02%; and spiked recovery, 90.1-107%. The proposed method is adequately linear, accurate, and repeatable. The 2D-IC method provides fast, high-resolution, and completely automated procedure for the simultaneous determination of anions and carbohydrates without co-elution compared to the 1D ion chromatography method. This study provides application perspectives for use in biotechnology and other research fields. An accurate and effective 2D-IC method was developed for determining anions and carbohydrates in cyanobacteria. The method includes pre-treating samples with graphitized carbon SPE cartridges.

Rapid determination of trace level N-nitrosamine precursors in secondary-treated wastewater by using two dimensional-ion chromatography

Nowadays, drinking water treatment involves large usage of chloramines making control of N-nitrosamines formation very challenging. Detecting and removing N-nitrosamine precursors in water is the most effective method to reduce N-nitrosamine formation. Therefore, it is essential to develop methods to detect N-nitrosamine precursors. In this paper, a method based on two-dimensional ion chromatography (2D-IC) is presented for detecting the trace levels of N-nitrosamines precursors, including dimethylamine, trimethylamine, diethylamine, methylethylamine, morpholine and piperidine, in relatively short time with minimized sample preparation. The 2D-IC method exhibits better sensitivity for analytes suffering from matrix interference, by eliminating interfering sample matrix ions, than conventional one-dimensional (1D) IC. Detection limits of the six amines were within the range of 0.035 μg/L to 0.1 μg/L. Excellent linearity was achieved for all the target amines with the method developed. The proposed method in this study was applied in the analysis of real wastewater samples. High recoveries ranging from 91.7 to 109.8% and relative standard deviation of less than 5.3% were obtained. The fully automated and simple method shows high selectivity against interfering metal ions and low detection limits, making routine detection of N-nitrosamines precursors practical.

Unbiased Measurement of Phosphate and Phosphorus Speciation in Surface Waters.

Trace-level phosphate analysis and phosphorus speciation in surface water remained challenging due to adsorption and phosphate uptake by microorganisms. In this study a two-dimensional ion chromatography separation coupled to electrospray ionization high-resolution mass spectrometry (2D-IC-ESI-MS) allowed isotope dilution quantitation of phosphate with simultaneous analysis of 11 phosphate-containing metabolites and two inorganic condensed phosphates. Samples were collected from Lake St. Clair, Lake Ontario, and Georgian Bay (ON, Canada). Comparative experiments showed lower phosphate results for samples not immediately spiked and for external calibration quantitation. Field spiking with 18O-labeled phosphate combined with isotope dilution quantitation allows measurement of the phosphate levels existent at the collection time instead of the phosphate concentrations remaining in the samples at the analysis time. This is a significant advantage against the traditional colorimetric and ion chromatographic (IC) analysis methods, which are unable to compensate for the adsorption loss occurring in standards and samples, especially when phosphate is present at levels below 20 μg L-1 as P (61 μg L-1 as PO43-). Two phosphate-containing metabolites, adenosine 5'-monophosphate (AMP) and d-glucose 6-phosphate (Glucose-P), were detected in a subset of samples collected from Lake St. Clair, with no statistically significant correlation between them and the simultaneously measured phosphate. Directly bioavailable P (phosphate), indirectly bioavailable P (phosphatase-hydrolyzed P) and nonbioavailable P (nonhydrolizable P) fractions were quantified by measuring phosphate, phosphate after phosphatase addition and total phosphorus. The proposed 2D-IC-ESI-MS method developed for a QExactive MS instrument with field spiking of the internal standard provides accurate phosphate results and eliminates quantitation errors caused by phosphate adsorption. This setup allows simultaneous collection of targeted and nontargeted analysis data and thus the detection of trace polar organic phosphorus metabolites as well.

Comprehensive two-dimensional ion chromatography (2D-IC) coupled to a post-column photochemical fluorescence detection system for determination of neonicotinoids (imidacloprid and clothianidin) in food samples

There are increasing concerns about the dietary risks of neonicotinoids (NNIs); therefore their sensitive and accurate determination in dietary products is indispensable. However, the complex composition of agricultural food matrixes makes their extraction and quantitative determination a challenging task. Realizing this need, we herein report a simple, cost-effective, selective and sensitive fluorescence analytical workflow for analyses of two non-fluorescent neonicotinoids imidacloprid (IMI) and clothianidin (CLT) in six complex food samples (honey, ginger, durian, apple, tomato, cucumber) by online clean-up of sample extracts using two-dimensional ion chromatography (2D-IC) and a subsequent online post column UV induced fluorescence detection system. This online clean-up setup has proven advantageous to improve the limit of detection, potentially diminish matrix effects, and reduce analysis time and labor. The developed method showed excellent analytical figures of merit including linearity, selectivity, repeatability, recovery, and resolution for analysis of IMI and CLT in food samples.

Determination of γ-hydroxybutyrate in human urine samples by ion exclusion and ion exchange two-dimensional chromatography system

A two-dimensional ion chromatography system was developed for the determination of γ-hydroxybutyrate (GHB) in human urine samples. Ion exclusion chromatography was used in the first dimensional separation for elimination of urine matrices and detection of GHB above 10mgL−1, ion exchange chromatography was used in the second dimensional separation via column-switching technique for detection of GHB above 0.08mgL−1. Under the optimized chromatographic conditions, the ion exclusion and ion exchange chromatography separation system exhibited satisfactory repeatability (RSD<3.1%, n=6) and good linearity in the range of 50–1000mgL−1 and 0.5–100mgL−1, respectively. By this method, concentrations of GHB in the selected human urine samples were detected in the range of 0–1.57mgL−1. The urine sample containing 0.89mgL−1 GHB was selected to evaluate the accuracy; the spiked recoveries of GHB were 95.9-102.8%. The results showed that the two-dimensional ion chromatography system was convenient and practical for the determination of GHB in human urine samples.

Color and alcohol removal for the simultaneous detection of amino acids and sugars in wine by two-dimensional ion chromatography.

An effective pretreatment method for wine color removal by a PS-DVB SPE cartridge and online alcohol elimination by valve switching was presented. The optimum parameters for color removal were investigated: 40-μm and 100Å poly (styrene)-divinylbenzene (PS-DVB) (0.4g) was selected as the color removal material and 5mL of ethanol (10%) as the elution solvent for sample pretreatment under given condition. Moreover, an accurate and automated two-dimensional ion chromatography method for the simultaneous detection of amino acids and sugars was achieved with two valves after injection without alcohol interference. The method had a mean correlation coefficient of >0.99 and a repeatability of 0.92%-4.30% for eight replicates. The mean recovery of six red wine samples were 97.6%, 96.6%, 96.1%, 95.9%, 97.3% and 96.4% respectively. And this method successfully analyzed the amino acid and sugar contents of six wine samples of different origins.

Two-dimensional ion chromatography for the separation of ionic organophosphates generated in thermally decomposed lithium hexafluorophosphate-based lithium ion battery electrolytes

A two-dimensional ion chromatography (IC/IC) technique with heart-cutting mode for the separation of ionic organophosphates was developed. These analytes are generated during thermal degradation of three different commercially available Selectilyte™ lithium ion battery electrolytes. The composition of the investigated electrolytes is based on 1M lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate/dimethyl carbonate (50:50wt%, LP30), ethylene carbonate/diethyl carbonate (50:50wt%, LP40) and ethylene carbonate/ethyl methyl carbonate (50:50wt%, LP50). The organophosphates were pre-separated from PF6− anion on the low capacity A Supp 4 column, which was eluted with a gradient step containing acetonitrile. The fraction containing analytes was retarded on a pre-concentration column and after that transferred to the high capacity columns, where the separation was performed isocratically. Different stationary phases and eluents were applied on the 2nd dimension for the investigation of retention times, whereas the highly promising results were obtained with a high capacitive A Supp 10 column. The organophosphates generated in LP30 and LP40 electrolytes could be separated by application of an aqueous NaOH eluent providing fast analysis time within 35min. For the separation of the organophosphates of LP50 electrolyte due to its complexity a NaOH eluent containing a mixture of methanol/H2O was necessary. In addition, the developed two dimensional IC method was hyphenated to an inductively coupled plasma mass spectrometer (ICP-MS) using aqueous NaOH without organic modifiers. This proof of principle measurement was carried out for future quantitative investigation regarding the concentration of the ionic organophosphates. Furthermore, the chemical stability of several ionic organophosphates in water and acetonitrile at room temperature over a period of 10h was investigated. In both solvents no decomposition of the investigated analytes was observed and therefore water as solvent for dilution of samples was proved as suitable.

Determination of inorganic anions and gluconate by two-dimensional ion chromatography

A new two-dimensional ion chromatography method was developed to parallelly analyze two different types of samples with the application of valve switching technology-suppressed conductivity and pulsed amperometric analysis system, for concurrent determination of chloride, nitrite, sulfate, nitrate four inorganic anions and gluconate. The first dimensional chromatography was using Ionpac AG18+Ionpac AS18 anion analysis columns with a suppressed conductivity detector for the separation and detection of Cl-, NO2-, SO4(2-) and NO3-. Respectively, the elution was 5 and 20 mmol/L NaOH at an isocratic flow rate of 1.0 mL/min and sample injection volume of 25 μL. The second dimensional chromatography was utilizing two guard columns, CarboPac PA1 and CarboPac PA20, with 90 mmol/L NaOH solution for the isocratic eluent of 0.8 mL/min. Gluconate was enriched by an AG15 column and switched into the pulsed amperometric detector. The results showed that: each inorganic anion in 0. 1-5.0 mg/L and gluconate in 0.085 6-4.282 5 mg/L had a good linear relationship (R2 ≥ 0.994 5). The RSDs of the peak areas were between 1.05%-1.94%. The limits of detection were 0.61-2.17 μg/L for the anions and 24.24 μg/L for the gluconate. The recoveries were between 90.3% - 102.8%. The two detection modes parallelly have good separation efficiency, detection accuracy and the precision of the separation and are suitable for the analysis of complex samples.

Determination of Phosphite, Phosphate, Glyphosate and Aminomethylphosphonic Acid by Two-Dimensional Ion Chromatography System Coupled with Capillary Ion Chromatography

Abstract Phosphite, phosphate, glyphosate and aminomethylphosphonic acid (AMPA) in natural water were determined by two-dimensional ion chromatography system coupled with capillary ion chromatography (2D-CIC). After filtrated by a 0.22-μm filter membrane, 25 μL of samples was injected into the first dimensional analytical column (AS11-HC) for preliminary separation. According to the different retention times in the first dimension, the target ions were divided into two groups (one group was phosphite and phosphate, another group was glyphosate and AMPA), then switched to the second dimensional capillary column (MAX-100) for further separation and detection. The effluent flow rates were 0.38 mL min −1 in the first dimension and 0.01 mL min −1 in the second dimension with KOH gradient elution, respectively. The carbonate removal devices were employed. The external standard method was used in all instances to quantitatively analyze. The results showed that the detection limits ( S/N = 3) were 0.18 nM for phosphite, 0.073 nM for phosphate, 0.15 nM for glyphosate and 2.6 nM for AMPA. The relative standard deviations (RSD, n = 6) of peak area ranged from 2.7% to 4.6%. The recoveries ranged from 80.1% to 118.4%. The results demonstrated that coupled capillary system could afford the simple detection of trace materials in natural water with complex matrix.

Direct determination of trace-level haloacetic acids in drinking water by two-dimensional ion chromatography with suppressed conductivity

During the treatment process of drinking water, disinfectants (chlorine, ozone, chlorine dioxide) react on water containing organic matter and bromide to produce disinfection by-products at trace levels. Among them, five of the nine existing halo-acetic acids (HAAs) are commonly found in drinking water (monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), monobromoacetic acid (MBAA), dibromoacetic acid (DBAA), and Trichloroacetic acid (TCAA)), including four classified in the 2B IARC group of potential carcinogens (BCAA, DBAA, DCAA, TCAA). With respect to drinking water quality, guidelines are proposed by WHO (2006) and water quality standards are imposed in many countries such as less than 100 μg/L for the sum of the five HAAs by US EPA (1998) and Canadian Health Department (2008). For this purpose, two analytical methods are commonly used, GC/MS with derivatization and LC/MS, UV or conductivity. A new method, based on two-dimensional ion chromatography (IC 2D) with suppressed conductivity is proposed. This method presents the main advantage of offering a quick implementation compared to GC or LC methods: direct injection, slight maintenance, lower cost of investment, by leading to good performances (specificity and sensitivity). The use of two different selectivity columns, and the fractionation on the first dimension canceling interferences, improves the specificity. The sensitivity is enabled by interfacing a preconcentration column between the two different internal diameter columns. The analytical conditions are optimized for the analysis of nine HAAs. The performances of the method are evaluated. The optimized method applied to natural water samples demonstrates its ability to quantify HAAs at trace levels in drinking water.

Determination of iodide, thiocyanate and perchlorate ions in environmental water by two-dimensional ion chromatography

A procedure for the determination of iodide, thiocyanate and perchlorate ions in environmental water by two-dimensional ion chromatography has been developed. At first the iodide, thiocyanate and perchlorate ions were separated from interfering ions by a column (IonPac AS16, 250 mm x 4 mm). The iodide ion, thiocyanate and perchlorate ions were then enriched with an enrichment column (MAC-200, 80 mm x 0.75 mm). In the 2nd-dimensional chromatography, iodide thiocyanate and perchlorate ions were separated and quantified by a capillary column (IonPac AS20 Capillary, 250 mm x 0.4 mm). The linear ranges were 0.05 -100 pg/L with correlation coefficients of 0. 999 9, and the detection limits were 0. 02 - 0.05 micro gg/L. The spiked recoveries of iodide, thiocyanate and perchlorate ions were in the range of 85.1% to 100.1%. The relative standard deviations of the recoveries were 1.7% to 4.9%.

Determination of Phosphite, Phosphate, Glyphosate and Aminomethylphosphonic Acid by Two-Dimensional Ion Chromatography System Coupled with Capillary Ion Chromatography

A method was developed for the determination of phosphite,phosphate,glyphosate and aminomethylphosphonic acid( AMPA) in natural water by two-dimensional ion chromatography system coupled with capillary ion chromatography( 2D-CIC).After filtrated by 0.22 μm filter membrane,25 μL of samples was injected into the first dimension,where an AS11-HC analytical column was used,for preliminary separation.According to the retention time in the first dimension,the target ions were switched to MAX-100capillary column of the second dimension for further separation.The flow rates were 0.38 mL/min in the first dimension and 0.01 mL/min in the second with KOH gradient elution,respectively.Suppressed conductivity detectors were employed for detection.The external standard calibration curve was used for the quantitative analysis.The results showed that the detection limits( S/N=3) were 0.18 nmol/L for phosphite,0.073 nmol/L for phosphate,0.15 nmol/L for glyphosate and 2.6 nmol/L for AMPA.The relative standard deviation( RSD,n=6) of peak area ranged from 2.7% to 4.6%.The recoveries ranged from80.1% to 118.4%.

Determination of Phosphite in a Eutrophic Freshwater Lake by Suppressed Conductivity Ion Chromatography

The establishment of a sensitive and specific method for the detection of reduced phosphorus (P) is crucial for understanding P cycle. This paper presents the quantitative evidence of phosphite (P, +3) from the freshwater matrix correspondent to the typically eutrophic Lake Taihu in China. By ion chromatography coupled with gradient elution procedure, efficient separation of micromolar levels of phosphite is possible in the presence of millimolar levels of interfering ions, such as chloride, sulfate, and hydrogen carbonate in freshwater lakes. Optimal suppressed ion chromatography conditions include the use of 500 μL injection volumes and an AS11 HC analytical column heated to 30 °C. The method detection limit of 0.002 μM for phosphite was successfully applied for phosphite determination in natural water samples with recoveries ranging from 90.7 ± 3.2% to 108 ± 1.5%. Phosphite in the freshwater matrix was also verified using a two-dimensional capillary ion chromatography and ion chromatography coupled with mass spectrometry. Results confirmed the presence of phosphite in Lake Taihu ranging from 0.01 ± 0.01 to 0.17 ± 0.01 μM, which correlated to 1-10% of the phosphate. Phosphite is an important component of P and may influence biogeochemical P cycle in lakes.

Direct Injection, Simple and Robust Analysis of Trace-Level Bromate and Bromide in Drinking Water by IC with Suppressed Conductivity Detection

Bromide is ubiquitously found in drinking water. It is introduced into source water primarily by contact with bromide-containing soils or seawater having high bromide content. Bromide is converted into carcinogenic bromate during ozonation processes employed in some drinking water and wastewater treatment plants. Therefore, monitoring of bromate in drinking water and its precursor bromide in source water is required. The purpose of this study was to survey bromide and bromate concentrations in randomly selected bottle waters of various brands and several tap water samples in the coastal Houston area using a direct-injection ion chromatography (IC) and a suppressed conductivity system. The method employs a simple isocratic IC with loop injection with calculated detection limit of 0.009 microg/L for bromate and 0.028 microg/L for bromide (250-microL sample volume). Allowing the detection of both species at the microg/L level in drinking water, this method does not require specialized instrumentation such as two-dimensional IC, expensive sample preparation, or post-column reactions. The results show that, whereas bromate remains undetected in all five tap water samples, there are significant high concentrations of bromide in the coastal Houston area (294.79 +/- 56.97 microg/L). Its link to potential seawater intrusion need to be further investigated. For bottle water samples randomly collected, 18.2% (2 out of 11) showed detectable amount of both bromide and bromate. The detection of bromate coincides with those bottle water samples that underwent ozonation treatment. Further sample campaign with exclusively ozonated bottle water samples (n = 19) showed 100% detection rate for both bromide and bromate. The 99% confidence intervals were 14.45-37.97 microg/L and 0.32-2.58 microg/L for bromide and bromate, respectively. The highest level of bromate among all ozonated bottle water samples was 7.57 microg/L, a concentration close to the U.S. EPA prescribed limit for drinking water standard. Regression analysis indicated that although a positive correlation exists between bromide and bromate concentrations, such a correlation is not statistically significant. This finding is not unexpected since a variety of other parameters in the ozonation process (such as water quality, ozone dose, and time in addition to bromide concentration) affect the formation of bromate. Our results strongly suggest that cautions should be exercised to examine the potential formation of bromate when source water from coastal zone undergoes ozonation treatment. Another strong proof of our findings is that all the tap waters collected were treated in jurisdictions that do not use ozonation for disinfection. The fact that none of these tap water samples contained bromate (despite an abundance in bromide) proves our hypothesis even further.

Two-dimensional ion chromatography using tandem ion-exchange columns with gradient-pulse column switching

A two-dimensional ion chromatography (2D-IC) approach has been developed which provides greater resolution of complex samples than is possible currently using a single column. Two columns containing different stationary phases are connected via a tee-piece, which enables an additional eluent flow and independent control of eluent concentration on each column. The resultant mixed eluent flow at the tee-piece can be varied to produce a different eluent concentration on the second column. This allows analytes strongly retained on the first column to be separated rapidly on the second column, whilst maintaining a highly efficient, well resolved separation of analytes retained weakly on the first column. A group of 18 inorganic anions has been separated to demonstrate the utility of this approach and the proposed 2D-IC method provided separation of this mixture with resolution of all analytes greater than 1.3. Careful optimisation of the eluent profiles on both columns resulted in run times of less than 28 min, including re-equilibration. Separations were performed using isocratic or gradient elution on the first column, with an isocratic separation being used on the second column. Switching of the analytes onto the second column was performed using a gradient pulse of concentrated eluent to quickly elute strongly retained analytes from the first column onto the second column. The separations were highly repeatable (RSD of 0.01–0.12% for retention times and 0.08–2.9% for peak areas) and efficient (typically 8000–260,000 plates). Detection limits were 3–80 ppb.

Selective method for the analysis of perchlorate in drinking waters at nanogram per liter levels, using two-dimensional ion chromatography with suppressed conductivity detection

The United States Environmental Protection Agency (EPA) collected drinking water occurrence data for perchlorate in the Unregulated Contaminant Monitoring Regulation (UCMR 1; 2001–2005) using EPA Method 314.0. To address the interest in increasing sensitivity and selectivity for the analysis of perchlorate, three new methods, EPA Methods 314.1, 331.0 and 332.0, were subsequently published by EPA for the analysis of perchlorate in drinking water. In 2006, an automated two-dimensional ion chromatography (2D-IC) method for measuring perchlorate with suppressed conductivity detection was developed. Two-dimensional IC is essentially an automated “heart-cutting”, column concentration and matrix elimination technique. In the first dimension, a large sample volume is injected onto a first separation column and the separated matrix ions are diverted to waste while the analyte(s) of interest are selectively cut, trapped and concentrated in a concentrator column. In the second dimension, the contents from the concentrator column are eluted onto a second analytical column for separation and quantitation of the analyte(s) of interest. Incorporation of two columns with different affinities for the analyte(s) in a single analysis can provide comparable selectivity and superior sensitivity to a method using second column confirmation in a second separate analysis step. Use of this approach led to the development of a new, highly sensitive and selective 2D-IC, suppressed conductivity method with a Lowest Concentration Minimum Reporting Level (LCMRL) of 55 ng/L for perchlorate in drinking water samples. This new method has comparable sensitivity and selectivity and is simpler and more economical than IC-mass spectrometric (MS) or IC-MS–MS techniques. The method is now being prepared for publication as EPA Method 314.2.