Combination of suppressed and non-suppressed ion chromatography with atmospheric pressure ionization mass spectrometry for the determination of anions

Identification of low molecular weight organic acids by ion chromatography/hybrid quadrupole time-of-flight mass spectrometry during Uniblu-A ozonation

RATIONALE

The balance of organic nitrogen and sulfur during ozonation of organic pollutants often shows a lack of complete mineralization. It follows that polar and ionic by-products are likely to be present that are difficult to identify by liquid chromatography/mass spectrometry (LC/MS).

METHODS

The structural elucidation of low molecular weight organic acids arising from Uniblu-OH ozonation has been investigated by ion chromatography/electrospray tandem mass spectrometry (IC/ESI-MS/MS) employing a quadrupole time-of-flight mass spectrometer. Unequivocal elemental composition of the by-products was determined by a combination of mass accuracy and high spectral accuracy.

RESULTS

The employed identification strategy was demonstrated to be a powerful method of unequivocally assigning a single chemical composition to each identified compound. The exact mass measurements of [M-H](-) ions allowed the elemental formulae and related structures of eighteen by-products to be determined confidently. The main degradation pathways were found to be decarboxylation and oxidation. The experimental procedure allowed the identification of both nitrogen- and sulfur-containing organic acid by-products arising from Uniblu-OH ozonation.

CONCLUSIONS

The obtained results are of environmental relevance for the balance of organic nitrogen and sulfur during the ozonation of organic pollutants due to the lack of complete mineralization of the compounds containing these atoms.

Modification of glassy carbon electrode with a polymer/mediator composite and its application for the electrochemical detection of iodate

A modified glassy carbon electrode was prepared by depositing a composite of polymer and mediator on a glassy carbon electrode (GCE). The mediator, flavin adenine dinucleotide (FAD) and the polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) were electrochemically deposited as a composite on the GCE by applying cyclic voltammetry (CV). This modified electrode is hereafter designated as GCE/PEDOT/FAD. FAD was found to significantly enhance the growth of PEDOT. Electrochemical quartz crystal microbalance (EQCM) analysis was performed to study the mass changes in the electrode during the electrodeposition of PEDOT, with and without the addition of FAD. The optimal cycle number for preparing the modified electrode was determined to be 9, and the corresponding surface coverage of FAD (Γ(FAD)) was ca. 5.11×10(-10)mol cm(-2). The amperometric detection of iodate was performed in a 100 mM buffer solution (pH 1.5). The GCE/PEDOT/FAD showed a sensitivity of 0.78 μA μM(-1) cm(-2), a linear range of 4-140 μM, and a limit of detection of 0.16 μM for iodate. The interference effects of 250-fold Na(+), Mg(2+), Ca(2+), Zn(2+), Fe(2+), Cl(-), NO(3)(-), I(-), SO(4)(2-) and SO(3)(2-), with reference to the concentration of iodate were negligible. The long-term stability of GCE/PEDOT/FAD was also investigated. The GCE/PEDOT/FAD electrode retained 82% of its initial amperometric response to iodate after 7 days. The GCE/PEDOT/FAD was also applied to determine iodate in a commercial salt.

Ion chromatography-atmospheric pressure chemical ionization mass spectrometry for the determination of trace chlorophenols in clam tissues

A novel analytical method has been developed for the determination of 14 trace chlorophenols in clam tissues by ion chromatography (IC) coupled with atmospheric pressure chemical ionization mass spectrometry (APCI-MS) in the negative mode. The method comprised a fast ultrasound-assisted extraction using a mixture of methanol/water (4:1v/v) containing 5% triethylamine (TEA) as extraction solvent, solid-phase extraction with an Oasis HLB cartridge and gradient separation using KOH/acetonitrile at a flow rate of 1.0 mL/min on an IonPac AG11 guard column (50 mm x 4.0 mm I.D.) and an IonPac AS11 analytical column (250 mm x 4.0 mm I.D.). The molecular ions m/z [M-H](-) 127, 129; 161, 163; 195, 197 and 263, 265, 267 were selected for quantification in the selected ion monitoring (SIM) mode for monochlorophenols (MCPs), dichlorophenols (DCPs), trichlorophenols (TCPs) and pentachlorophenol (PCP), respectively. The average recoveries of the objective compounds spiked in clam tissues were between 80.2% and 98.2%. Within-day and day-to-day relative standard deviations were less than 12.6% and 13.2%, respectively. The optimum IC-APCI-MS conditions were successfully applied to the analyses of 14 trace chlorophenols in clam tissues.

Self-Assembly of Molybdophosphate on a Glassy Carbon Electrode Covalently Modified with Choline and Electrocatalytic Reduction of Iodate

Choline can be covalently grafted on glassy carbon electrodes using cyclic voltammetric method, forming a stable cationic monolayer-modified electrode (Ch/GCE). Keggin-type molybdophosphate anions, alpha-PMo(12)O(40)(3-), then were self-assembled on the Ch/GCE through electrostatic interactions for fabrication of an electrochemical sensor, which is denoted as alpha-PMo(12)/Ch/GCE. This two-layer modified electrode was carefully characterized by cyclic voltammetry and X-ray photoelectron spectroscopy. It was found that the sensor exhibits strong electrocatalytic activity and sensitivity toward the reduction of IO(3)(-). The content of IO(3)(-) in a table salt was determined with satisfactory results. The sensor is promising as an electrochemical sensor for the detection of IO(3)(-).

Systematic examination of the signal area precision of a single quadrupole enhanced low mass option (ELMO) MSQ [corrected] mass spectrometer

To examine the precision of the signal area response of an enhanced low mass option (ELMO) MSQmass spectrometer, operated in the negative electrospray ionization (ESI) mode, extended tests were performed, using flow injection analysis mass spectrometry (FIA-MS). Analytes were nitrate, nitrite, malonic acid, and D,L-mandelic acid. Composition and concentration of injected samples, application of an ASRS anion suppressor and of the cone wash unit, methanol addition to the FIA flow medium, and the voltage bias of the hexapole transfer lens were test variables. Individual test cycles comprised up to 90 injections, processed within 20 h. With a few exceptions the signal response tended to decline over time leading to a loss of more than 80% of the initial signal area in extreme cases. A hexapole radio-frequency (RF) voltage bias of -0.3 V led to an overall low detector response and to high losses of sensitivity over time. Other correlations between the insufficient signal reproducibility and FIA-MS operating conditions could not be established. The test scheme gave hints how to localize the cause of the mass spectrometer malfunction. The repetition of the test scheme after remedying the detected electronic default demonstrated that relative standard deviations less than 5% can be achieved for a sequence of 30 injections if methanol is added to the FIA flow medium and if a suppressor is used. Based on these findings a recommendation is formulated to supplement current test schemes for instrument performance verification by a detector response precision criterion.

Chloride interference in the determination of bromate in drinking water by reagent free ion chromatography with mass spectrometry detection

Bromate, a well known by-product of the ozonation of drinking water, has been included among the substances which have to be monitored in the drinking water according to the last EC Directive 251/98 on potable water with a regulated limit of 10 microg l(-1). The need of performing routine analysis at this limit is a driving force for the developing of new simple and sensitive methods of detection, which should be also able to overcome the effect of matrix composition. This work explored the use of mass spectrometry detection with electrospray ionisation hyphenated to a reagent free ion chromatograph with hydroxide gradient elution for the determination of bromate in drinking water. The use of a high capacity hydroxide selective column operated in gradient mode allowed to avoid the interference by carbonate peak, which moved to longer retention times. The effect of increasing chloride concentrations from 0 to 250 mg l(-1), which is the guideline limit for drinking water in Directive 251/98/EC, was to decrease absolute mass spectrometric response and chromatographic efficiency and, on the consequence, to increase the effective detection limits. The effect of the chloride concentration on the detection of bromate is discussed.

Electrochemical reduction and flow detection of iodate on (Bu4N)2Mo6O19 self-assembled monolayer

A stable monolayer of the inorganic-organic hybrid polyoxometalate (Bu4N)2Mo6O19, denoted as Mo6O19, was formed on a sodium-3-mercapto-1-propanesulfonate (MPPS)-covered gold electrode surface, interlaced with an anionic poly(dimethyldiallylammonium chloride) (PDDA) binding layer based on the electrostatic self-assembled (ESA) technique. Electrochemical characterization of the Mo6O19 self-assembled thin films on the solid surface by cyclic voltammetry and AC impedance spectroscopy revealed a stable and sensitive electrocatalytic response to the reduction of iodate. Iodate was determined amperometrically through a flow injection cell at the modified electrode in the concentration range of 1.0 x 10(-6) to 1.0 x 10(-1) M with a detection limit of 8 x 10(-8) M (signal-to-noise ratio = 3). Performance was improved to meet practical needs compared with previously reported analogues.

Ion chromatography–electrospray mass spectrometry for the identification of low-molecular-weight organic acids during the 2,4-dichlorophenol degradation

End-product identification of organic pollutants during oxidation water treatments is of environmental concern due to their potential toxicity. In this work the coupling of ion chromatography (IC), equipped with a membrane ion suppressor, and electrospray ionization mass spectrometry (ESI-MS) has been successfully exploited for the identification of novel low molecular weight organic acids formed as final by-products of 2,4-dichloro-phenol (DCP) degradation by Fenton's reagent, an oxidation method widely employed to degrade recalcitrant organic pollutants in industrial wastewater. The IC-ESI-MS analytical set-up not only allowed the detection of known organic acids but also the identification of 13 new low molecular weight organic acids as a result of extensive oxidation of the parent organic pollutant. Some of the novel organic acids were shown to be chlorine containing by-products and, consequently, of environmental concern. The analytical set-up could be used for characterizing the unknown organic carbon fraction arising from oxidation water treatments.

Preparation of a Novel Iodide-Selective Electrode Based on Iodide-Miconazole Ion-Pair and Its Application to Pharmaceutical Analysis

An iodide-miconazole ion-paired complex was used as a suitable ion-exchanger for the preparation of a plasticized-PVC membrane electrode. Among different solvent mediators tested, dioctylsebacate exhibited the proper response characteristics, including Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of -59.8 +/- 0.5 mV decade(-1) for I- ion over a concentration range of 1.0 x 10(-5) - 1.0 x 10(-2) M with a limit of detection of 7.0 x 10(-6) M. The electrode displays a good selectivity for I- with respect to a number of inorganic and organic species. It canbe used over a pH range of 2.5 - 8.5. The membrane sensor was successfully applied to the determination of iodide in water samples and blood serum, as well as in pharmaceutical products such as iodoquinol and thyroxin.

Bromate analysis in groundwater and wastewater samples

Bromate (BrO(3)(-)) is a disinfection by-product formed during ozonation of potable water supplies containing bromide (Br(-)). Bromate has been classed by the World Health Organisation as a 'possible human carcinogen', leading to implementation of 10-25 microg L(-1)(as BrO(3)(-)) drinking water limits in legislative areas including the United States and European Union. Techniques have been developed for bromate analysis at and below regulatory limits, with Ion Chromatography (IC) coupled with conductivity detection (IC-CD), post-column reaction and ultra-violet (UV) detection (IC-PCR), or inductively coupled plasma-mass spectrometry detection (IC-ICPMS) in widespread use. The recent discovery of bromate groundwater contamination in a UK aquifer has led to a requirement for analysis of bromate in a groundwater matrix, for environmental monitoring and development of remediation strategies. The possibility of bromate-contaminated water discharge into sewage treatment processes, whether accidental or as a pump-and-treat strategy, also required bromate analysis of wastewater sources. This paper summarises techniques currently available for trace bromate analysis in potable water systems and details studies to identify a methodology for routine analysis of groundwater and wastewater samples. Strategies compared were high performance liquid chromatography (HPLC) with direct UV or PCR/UV detection, IC-CD, IC-PCR, and a simple spectrophotometric technique. IC-CD was the most cost-effective solution for simultaneous analysis of bromate and bromide within groundwater samples, having a 5 microg L(-1) detection limit of both anions with limited interference from closely-eluting species. Wastewater samples were successfully analysed for bromate only using HPLC with PCR/UV detection, with detection limits below 20 microg L(-1)(as BrO(3)(-)) and low interference. HPLC with direct UV detection was unsuitable for bromate analysis within the concentration range 50-5000 microg L(-1) which was required for this project, but column choice was shown to be a major factor in determining limits of detection. Spectrophotometry could not reproducibly determine bromate concentration, although the technique showed promise as a quick field method for high-level groundwater bromate analysis.

Simultaneous Kinetic-Spectrophotometric Determination of Hydrazine and Acetylhydrazine in Micellar Media Using the H-Point Standard Addition Method

The H-point standard addition method (HPSAM), based on a spectrophotometric measurement for the simultaneous determination of hydrazine and acetylhydrazine, is described. This method is based on the difference between the rates of their reactions with N,N-dimethylaminobenzaldehyde (DAB) in the presence of sodium dodecyl sulfate (SDS) in acidic media. The results showed that hydrazine and acetylhydrazine could be determined simultaneously in the range of 0.020 - 0.70 and 0.20 - 5.0 mg L(-1), respectively. Under the working conditions, the proposed method was successfully applied to the simultaneous determination of hydrazine and acetylhydrazine in several synthetic mixtures and plasma and water samples.

Applications of ion chromatography with electrospray mass spectrometric detection to the determination of environmental contaminants in water

Ion chromatography (IC) is widely used for the compliance monitoring of common inorganic anions in drinking water. However, there has recently been considerable interest in the development of IC methods to meet regulatory requirements for analytes other than common inorganic anions, including disinfection byproduct anions, perchlorate, and haloacetic acids. Many of these new methods require the use of large injection volumes, high capacity columns and analyte specific detection schemes, such as inductively coupled plasma mass spectrometry or postcolumn reaction with UV-Vis detection, in order to meet current regulatory objectives. Electrospray ionization mass spectrometry (ESI-MS) is a detection technique that is particularly suitable for the analysis of permanently ionized or polar, ionizable compounds. The combination of IC with MS detection is emerging as an important tool for the analysis of ionic compounds in drinking water, as it provides increased specificity and sensitivity compared to conductivity detection. This paper reports on the application of IC-ESI-MS for the confirmation and quantitation of environmentally significant contaminants, i.e. compounds with adverse health effects which are either regulated or being considered for regulation, such as bromate, perchlorate, haloacetic acids, and selenium species, in various water samples.

Recent developments in ion chromatography

This paper summarizes how ion chromatography is now a multimode technique suitable for solving analytical problems in all areas of interest. Current and more recent applications will be overviewed within the new trends.

Spectrophotometric determination of periodate, iodate and bromate mixtures based on their reaction with iodide

A rapid, simple, precise and accurate method is proposed for the determination of ternary mixtures of periodate-iodate-bromate based on their reaction with iodide ion at different pH values. The absorbance was measured at 352 nm. Three sets of reaction conditions were developed. In the first set of conditions, only periodate reacted with iodide, but in the second set the periodate and iodate reacted with iodide and in the third set the three ions reacted with iodide during the first 3 min after initiation of the reaction. The method could be used for individual determinations of periodate, iodate and bromate in the concentration range of 0.05-8.0 microg/ml, 0.05-5.0 microg/ml and 0.2-12 microg/ml, respectively. The data were evaluated by simultaneous equations.

Comparison of on-line coupling of ion-chromatography with atmospheric pressure ionization mass spectrometry and with inductively coupled plasma mass spectrometry as tools for the ultra-trace analysis of bromate in surface water samples

Ion chromatography in combination with atmospheric pressure ionization mass spectrometry (API-MS) as well as with inductively coupled plasma mass spectrometry (ICP-MS) had been compared for trace analysis of bromate. The results indicate that both techniques yield comparable results, which are in excellent agreement with standard methods for bromate determination. Furthermore, both techniques showed almost equal absolute detection limits (approximately 50 pg bromate injected). Contrary to IC-API-MS, IC-ICP-MS can tolerate a higher salt concentration in the mobile phase. This allows the use of high-capacity columns combined with large sample volumes. This lowered the concentration based detection limits by one order of magnitude for IC-ICP-MS compared to IC-API-MS (0.06 microg/l vs. 0.5 microg/l). On the other hand, IC-API-MS is able to allow a positive identification of bromate even in cases when IC does not fully separate bromate from other bromine-containing species. The performance data of both IC-MS techniques have been established by participation in an international round robin test.

Detection techniques in ion analysis: what are our choices?

Trends in detection techniques for ion analysis by ion-exchange chromatography and capillary zone electrophoresis are reviewed. Special attention is paid to conductivity, UV-Vis absorbance, amperometric and potentiometric detection, mass spectrometry (including inductively coupled plasma MS and atmospheric pressure ionization MS) and post-separation reaction detection. Applications reported within the last few years are summarized.