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

Anion Exchange Chromatography Coupled to Electrospray-Mass Spectrometry: An Efficient Tool for Food, Environment, and Biological Analysis

For over 50 years, ion chromatography has been demonstrated to be a successful technique used to quantify a wide range of ions and ionizable compounds, either organic or inorganic, in various matrices using conductimetric or electrochemical detection. It was only since 1996 that ion chromatography was coupled to electrospray-mass spectrometry, opening the field to new applications in complex matrices and the detection of compounds at trace levels. This review covers the recent developments of ion exchange chromatography and mass spectrometry. It focuses on the choice of mobile phases, column geometry, suppressors, make-up solvents and type of ionization sources reported in the literature. A brief overview of a large range of applications in food analysis, environmental analysis and bioanalysis is presented, and performances are discussed.

Mass spectrometric detection of trace anions: The evolution of paired-ion electrospray ionization (PIESI)

The negative-ion mode of electrospray ionization mass spectrometry (ESI-MS) is intrinsically less sensitive than the positive-ion mode. The detection and quantitation of anions can be performed in positive-ion mode by forming specific ion-pairs during the electrospray process. The paired-ion electrospray ionization (PIESI) method uses specially synthesized multifunctional cations to form positively charged adducts with the anions to be analyzed. The adducts are detected in the positive-ion mode and at higher m/z ratios to produce excellent signal-to-noise ratios and limits of detection that often are orders of magnitude better than those obtained with native anions in the negative-ion mode. This review briefly summarizes the different analytical approaches to detect and separate anions. It focuses on the recently introduced PIESI method to present the most effective dicationic, tricationic, and tetracationic reagents for the detection of singly and multiply charged anions and some zwitterions. The mechanism by which specific structural molecular architectures can have profound effects on signal intensities is also addressed.

Sensitive and robotic determination of bromate in sea water and drinking deep-sea water by headspace solid-phase micro extraction and gas chromatography-mass spectrometry

A robotic method has been established for the determination of bromate in sea water and drinking deep-sea water. Bromate in water was converted into volatile derivative, which was measured with headspace solid-phase micro extraction and gas chromatography-mass spectrometry (HS-SPME GC-MS). Derivatization reagent and the HS-SPME parameters (selection of fibre, extraction/derivatization temperature, heating time and; the morality of HCl) were optimized and selected. Under the established conditions, the detection and the quantification limits were 0.016 μg L(-1) and 0.051 μg L(-1), respectively, and the intra- and inter-day relative standard deviation was less than 7% at concentrations of 1.0 and 10.0 μg L(-1). The calibration curve showed good linearity with r(2)=0.9998. The common ions Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), H(2)PO(4)(-), K(+), Na(+), NH(4)(+), Ca(2+), Mg(2+), Ba(2+), Mn(4+), Mn(2+), Fe(3+) and Fe(2+) did not interfere even when present in 1000-fold excess over the active species. The method was successfully applied to the determination of bromate in sea water and drinking deep-sea water.

Ultra trace determination of bromate in mineral water and table salt by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry method (LC-MS/MS) was developed in order to determine the bromate in mineral water and table salt. The following optimum conditions for the LC-MS/MS detection were established: derivatization reagent (300 mg/L of 2,6-dimethylaniline), acidity (0.2M HCl), reaction temperature (30 °C) and heating time (20 min). The formed derivative was directly injected in the LC system without extraction or purification procedures. In the established conditions, the method was used to detect bromate in mineral water and table salt. The limit of detection and limit of quantification of bromate in mineral water were 0.02 μg/L and 0.07 μg/L, respectively, and those of table salt were 0.07 μg/kg and 0.23 μg/kg, respectively. The 17 common ions did not interfere even when present in 1,000-fold excess over the bromated ion of 10.0 μg/L. The accuracy was in a range of 92-104% and the assay precision was less than 9% in the table salt. The method was successfully applied to determine bromate in mineral water and table salt.

Quantitative surface-enhanced Raman scattering ultradetection of atomic inorganic ions: the case of chloride

Surface-enhanced Raman scattering (SERS) spectroscopy can be used for the determination and quantification of biologically representative atomic ions. In this work, the detection and quantification of chloride is demonstrated by monitoring the vibrational changes occurring at a specific interface (a Cl-sensitive dye) supported on a silver-coated silica microbead. The engineered particles play a key role in the detection, as they offer a stable substrate to support the dye, with a dense collection of SERS hot spots. These results open a new avenue toward the generation of microsensors for fast ultradetection and quantification of relevant ions inside living organisms such as cells. Additionally, the use of discrete particles rather than rough films, or other conventional SERS supports, will also enable a safe remote interrogation of highly toxic sources in environmental problems or biological fluids.

Ratiometric optical sensing of chloride ions with organic fluorophore-gold nanoparticle hybrids: a systematic study of design parameters and surface charge effects

Colloidal nanoparticles are often stabilized by high surface charges. These create an electrical potential that may strongly affect the concentration of dissolved ions, which presents a formidable problem for the use of nanoparticles in ion-sensing applications. This effect is investigated systematically with organic fluorophore-gold nanoparticle hybrids, which have a chloride-sensitive fluorophore attached at varying distances from their surface. The distance-dependent fluorescence response is quantitatively assessed using fluorescence spectroscopy.

Phosphomolybdate-modified multi-walled carbon nanotubes as effective mediating systems for electrocatalytic reduction of bromate

Electrocatalytic properties (towards reduction of bromate in 0.5moldm(-3) H(2)SO(4)) of multi-walled carbon nanotubes (CNTs) modified with phosphododecamolybdate (PMo(12)) monolayers have been diagnosed using cyclic voltammetry and amperometry. The ability of negatively charged PMo(12)-modified CNTs to attract electrostatically ultra-thin, positively charged conducting polymer (PEDOT or polypyrrole) structures is explored to grow in controlled manner hybrid organic-inorganic network electrocatalytic films. Due to the presence of three-dimensionally distributed CNTs, the films' conductivity and porosity are improved. The hybrid systems utilizing polypyrrole, rather than PEDOT, have produced fairly higher bromate electroreduction catalytic currents. Comparison is also made to Nafion-stabilized dispersion of PMo(12)-modified CNTs inks. The latter system is characterized by good stability and relatively the highest sensitivities with respect to bromate concentration.

Liquid-phase microextraction–gas chromatography–mass spectrometry for the determination of bromate, iodate, bromide and iodide in high-chloride matrix

In the determination of bromate and iodate, any free bromide and iodide present was quantitatively removed by anion exchange with silver chloride exploiting the differences in silver salts solubility product, being AgCl, 1.8 x 10(-10), AgBr, 5.0 x 10(-13), AgI, 8.3 x 10(-17), AgBrO(3), 5.5 x 10(-5) and AgIO(3), 3.1 x 10(-8). The oxyhalides were reduced with ascorbic acid to halides and converted to 4-bromo-2,6-dimethylaniline and 4-iodo-2,6-dimethylaniline by their reaction with 2-iodosobenzoate in the presence of 2,6-dimethylaniline at pH 6.4 and 2-3, respectively. Single drop microextraction (SDME) of the haloanilines in 2 microl of toluene and injection of the whole extract into GC-MS, or liquid-phase microextraction (LPME) into 50 microl of toluene and injection of 2 microl of extract, resulted in a sensitive method for bromate and iodate. The latter method of extraction has been found more robust, sensitive and to give better extraction in shorter period than SDME. Total bromine/iodine was determined without any treatment with silver chloride. High concentration of chloride in the matrix did not interfere. A rectilinear calibration graph was obtained for 0.05 microg-25 mg l(-1) of bromate/bromide and iodate/iodide, the limit of detection were 20 ng l(-1) of bromate, 15 ng l(-1) of iodate, 20 ng l(-1) of bromide and 10 ng l(-1) of iodide (by LPME in 50 microl of toluene). The method has been applied to seawater and table salt. From the pooled data, the average recovery of spiked oxyhalide/halide to real samples was in range 96.7-105.7% with RSD in range 1.6-6.5%.

Reduction of chloride matrix effect using silver oxide as a precipitating reagent for the determination of trace anions in chloride-rich samplesviaion chromatography

A new method was developed for the determination of trace anions in chloride-rich samples via ion chromatography by reducing the concentration of chloride ions using silver oxide as a precipitating reagent. In this method the sample pretreatment was started with the addition of silver oxide powder followed by 8 min of stirring and 2 min of centrifugation at a speed of 1500 rpm. The supernatant was diluted with a 1:10 ratio using deionized water and filtered with a 0.22 microm NC filter. All the samples were analyzed in a Dionex ICS-2500 system with an ED50 electrochemical detector in conductivity mode. On the basis of Dionex IonPac AG18 (50 mm x 2 mm) and AS18 (250 mm x 2 mm) columns, 25 AL sample filtrate was eluted isocratically with a mobile phase of 32 mmol/L NaOH at a flow rate of 0.25 mL/ min and each eluted analyte was detected after postcolumn suppression via a Dionex anion suppressor ULTRA II (2 mm). With this method most of the common anions at mg/kg level in chloride-rich samples can be accurately quantified. By controlling the equivalent weight ratio of silver oxide to chloride in sample solutions and the time of pretreatment, the free silver and chloride ions in the sample solution are optimized such that most coexisting common anions can be determined simultaneously.

Determination of trace levels of bromate in flour and related foods by ion chromatography

In this paper, a method of determining trace levels of bromate in flour and related foods by ion chromatography with large volume injection has been proposed. The detection of bromate was performed with a suppressed conductivity detector after separation on an IonPac AS19 column with KOH as the gradient eluent. Parameters affecting the extraction efficiency of bromate, such as the flour-to-water ratio, extraction time, and temperature, were studied in detail. The optimized pretreatment process was then selected. By using the large volume injection technique, the solution detection limit was decreased to 0.5 microg/L. The linear range of this method was from 5 to 1000 microg/L, and the linear correlation coefficient was 0.9998. The method has been applied to the detection of bromate in flour and related foods, and different concentration levels of bromate were detected in various samples. The spiked recoveries ranged from 86 to 110%. The relative standard deviation (RSD) of the bromate peak height for the seven successive injections of the flour sample was 6.4%.

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.