Application of a contactless conductometric detector for the simultaneous determination of small anions and cations by capillary electrophoresis with dual-opposite end injection

A contactless conductometric detection (CCD) system for capillary electrophoresis (CE) with a flexible detection cell was applied for the simultaneous determination of small anions and/or cations in rain, surface and drainage water samples. The applied frequency, the amplitude of the input signal, the electrolyte conductivity and electrode distance were found to be the most significant factors affecting the detection sensitivity. 2-(N-Morpholino)ethanesulfonic acid/histidine-based (MES/His) electrolytes were used for direct conductivity detection of anions and cations, while ammonium acetate was selected for indirect conductivity determination of alkylammonium salts. For the simultaneous separation procedure, involving dual-opposite end injection, an electrolyte consisting of 20 mM MES/His, 1.5 mM 18-crown-6 and 20 microM cetyltrimethylammonium bromide provided baseline separation of 13 anions and cations in less than 6 min. The detection limits achieved were 7-30 micrograms/l for direct conductometric detection of various common inorganic cations and anions, excluding F- (62 micrograms/l) and H2PO4- (250 micrograms/l), and 35-178 micrograms/l for indirect conductometric detection of alkyl ammonium cations. The developed electrophoretic method with conductometric detection was compared to ion chromatography.     

Simultaneous capillary electrophoretic separation of small anions and cations after complexation with ethylenediaminetetraacetic acid

A new approach for simultaneous separation of small inorganic and organic anions and metal cations by capillary electrophoresis is demonstrated. Metal cations in the sample are transformed into their chelates with EDTA and are separated together with the anions using an anionic separation mode. Simultaneous separation of 19 common anions and cations was achieved in about 6 min with the electrolyte containing 5 mM K2CrO4, 3 mM boric acid, 35 microM cetyltrimethylammonium bromide and 12 microM EDTA at pH 8. Limits of detection (s/n = 3) were in the range from 4 ppb for Cl- up to 1250 ppb for Cu-EDTA and RSDs of peak areas ranged from 1.4% for Cl- up to 8.5% for Mn-EDTA chelate. The practical applicability of the method was demonstrated on the analysis of anions and cations in various water samples.     

Application of an external contactless conductivity detector for the analysis of beverages by microchip capillary electrophoresis

Quantitative total ionic analysis of alcoholic and nonalcoholic beverages was performed by microchip capillary electrophoresis with external contactless conductivity detection. An electrolyte solution consisting of 10.5 mM histidine, 50 mM acetic acid, and 2 mM 18-crown-6 at pH 4.1 was used for the determination of NH(4) (+), K(+), Ca(2+), Na(+), and Mg(2+). Fast analysis of Cl(-), NO(3) (-), and SO(4) (2-) was achieved in 20 mM 2-(N-morpholino)ethanesulfonic acid /histidine electrolyte solution at pH 6.0 and the simultaneous separation of up to 12 inorganic and organic anions was performed in a solution containing 10 mM His and 7 mM glutamic acid at pH 5.75. Limits of detection ranged from 90 to 250 mug/L for inorganic cations and anions, and from 200 to 2000 mug/L for organic anions and phosphate. Calibration curves showed linear dependencies over one to two orders of magnitude when the stacking effect was minimized by injecting standard solutions prepared in background electrolyte solutions. Total analysis times of 35 and 90 s were achieved for the determination of 5 inorganic cations and for the simultaneous determination of 12 inorganic and organic anions, respectively, which represents a considerable reduction of analysis time compared to conventional separation methods used in food analysis.     

Single-column ion-chromatographic determination of chromium(VI) in aqueous soil and sludge extracts

Single-column ion-chromatography (SCIC) was investigated as a routine, rapid, precise and selective analytical method for the determination of chromium(VI) in aqueous extracts of soil and sewage sludge. Chromatographic parameters were optimized for determination of Cr(VI), NO(-)(3) and SO(2-)(4). A low-capacity resin-based column was used for the separation and the anions were determined by conductometric detection. p-Hydroxybenzoic acid (5mM) at pH 8.5 was used as the eluent. The limit of detection, defined as S/N = 3, was 92 mug/l. The resolution between Cr(VI) and SO(2-)(4) was 2.8, the precision ranged from 0.9% for NO(-)(3) to 2.0% for Cr(VI) with a 500-mul injection. The SCIC results for Cr(VI) agreed closely with those obtained by inductively coupled argon-plasma emission and spectrophotometry.     

Simultaneous determination of inorganic and organic anions,alkali, alkaline earth and transition metal cations by capillary electrophoresis with contactless conductometric detection

Simultaneous separation of up to 22 inorganic and organic anions, alkali, alkaline earth and transition metal cations was achieved in less than 3 min in the capillary electrophoresis system with contactless conductometric detector. The sample was injected from both capillary ends (dual opposite end injection) and anionic and cationic species were detected in the center of the separation capillary. The parameters of the separation electrolyte, such as pH, concentration of the electrolyte, concentration of complexing agents and concentration of 18-crown-6 were studied. Best results were achieved with electrolytes consisting of 8 mM L-histidine, 2.8 mM 2-hydroxyisobutyric acid, 0.32 mM 18-crown-6 at pH 4.25 or 9 mM L-histidine, 4.6 mM lactic acid, 0.38 mM 18-crown-6 at pH 4.25. Other electrolytes containing complexing agents such as malic or tartaric acid at various concentrations could also be used. The detection limits achieved for most cations and anions were 7.5 - 62 micro gL(-1) except for Ba2+ (90 micro gL(-1)), Cd 2+, Cr 3+ and F- (125 micro gL(-1)), and fumarate (250 micro gL(-1)). The repeatability of migration times and peak areas was better than 0.4% and 5.9%, respectively. The developed method was applied for analysis of real samples, such as tap, rain, drainage and surface water samples, plant exudates, plant extracts and ore leachates.     

Ion chromatographic determination of bromate in drinking water by post-column reaction with fuchsin.

Bromate deriving from ozonation treatment of bromide containing waters are analyzed by ion-exchange chromatography with spectrophotometric detection after post-column reaction with fuchsin in low pH medium. An anion-exchange column was used with 2.7 mM carbonate-0.3 mM hydrogencarbonate eluent. The eluent from the column was then allowed to react with a SO2-reduced fuchsin solution and then with a diluted HCl solution at 65 degrees C. The developed colour of the final product was measured spectrophotometrically at 530 nm. Linearity was checked up to 50 micrograms/l with a 200-microliter injection loop (r2 = 0.9997) and up to 100 micrograms/l of bromate with 100 microliters loop (r2 = 0.9939). Nitrate, sulfate, bromide, phosphate, fluoride did not interfere at 100 mg/l concentration level; only nitrite at concentration levels greater than 3 mg/l caused partial overlapping with bromate peak, but this value is not likely to occur in common drinking water. The detection limit (3 sigma) is 0.1 microgram/l (1 microgram/l propagation error approach).     

High-speed simultaneous ion-exclusion/cation-exchange chromatography of anions and cations on a weakly acidic cation-exchange resin column

The simultaneous ion-exclusion/cation-exchange separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin of 3 microm particle size was used to achieve the simultaneous high-speed separation of anions and cations (Cl(-), NO3(-), SO4(2-), Na(+), K(+), NH4(+), Ca(2+) and Mg(2+)) commonly found in environmental samples. The high-speed simultaneous separation is based on a combination of the ion-exclusion mechanism for the anions and the cation-exchange mechanism for cations. The complete separation of the anions and cations was achieved in 5 min by elution with 15 mM tartaric acid-2.5 mM 18-crown-6 at a flow-rate of 1.5 ml/min. Detection limits at S/N=3 ranged from 0.36 to 0.68 microM for anions and 0.63-0.99 microM for cations. This method has been applied to the simultaneous determination of anions and cations in several environmental waters with satisfactory results.     

A novel method for analysis of explosives residue by simultaneous detection of anions and cations via capillary zone electrophoresis

A novel electrolyte has been developed for the simultaneous separation of cations and anions in low explosive residue by capillary electrophoresis. This electrolyte contains 15 mM α-hydroxyisobutyric acid (HIBA) as the buffer, 6 mM imidazole as the cation chromophore, 3 mM 1,3,6-naphthalenetrisulfonic acid (NTS) as the anion chromophore, 4 mM 18-crown-6 ether as a cation selectivity modifier, and 5% (v/v) acetonitrile as an organic modifier. The pH was adjusted to 6.5 using tetramethylammonium hydroxide (TMAOH), an electroosmotic flow modifier. The method was optimized by varying the concentrations of α-HIBA, imidazole, and 1,3,6-NTS at three different pH values. The results provided a simultaneous indirect photometric analysis of both anions and cations with detection limits ranging from 0.5 to 5 ppm for anions and from 10 to 15 ppm for cations with a total run time of under 7 min. The method was then applied to the analysis of Pyrodex^® RS and black powder, as well as several smokeless powders. The results obtained were consistent with previously reported results for separate anion and cation analysis and provide a faster, more complete analysis of each sample in a single chromatographic run.     

Determination of inorganic anions by ion chromatography using a graphitized carbon column dynamically coated with cetyltrimethylammonium ions.

The simultaneous determination of inorganic anions by ion chromatography using a dynamically coated graphitized carbon column with cetyltrimethylammonium (CTA) ions was investigated with suppressed conductivity detection. Column preparations with CTA and sodium carbonate-sodium hydrogencarbonate concentration in the eluent were examined to optimize the separation of seven common anions (F-, Cl-, NO2-, Br-, NO3-, HPO(4)2- and SO(4)2-). Calibration curves were linear from 0.5 to 5 micrograms/ml for F-, from 1.0 to 10 micrograms/ml for Cl-, from 1.5 to 15 micrograms/ml for NO2-, from 2.0 to 20 micrograms/ml for Br- and NO3-, from 5.0 to 50 micrograms/ml for HPO(4)2- and from 3.0 to 30 micrograms/ml for SO(4)2- with correlation coefficients (r) of 0.999 or better. The relative standard deviations of peak areas were between 0.3 and 0.9% for 10 repeated measurements. The application of this newly developed method was demonstrated by the determination of inorganic anions in the water for pharmaceutical purposes. Using CTA-Br as the coating agent, a permanently coated ion-exchange column was obtained, which allowed efficient separations of seven anions without adding any coating agent to the eluent.     

Micellar electrokinetic chromatography as a fast screening method for the determination of 1,4-dihydropyridine calcium antagonists

A micellar electrokinetic chromatographic method (MEKC) was optimized for the separation of six calcium antagonists. The effects of the buffer (concentration and pH), concentration of sodium dodecyl sulphate (SDS), the organic modifier, the injection time, and the voltage applied were studied. A final appropriate electrolyte of 50 mM borate buffer, pH 8.2, containing 20 mM SDS and 15% (v/v) acetonitrile was found to provide the optimum separation with respect to resolution and migration time. The samples were introduced hydrostatically for 4 s at 50 mbar injection pressure and the applied voltage was +25 kV. The screening of the six compounds was achieved in less than 15 min: nifedipine (migration time, tm = 6.9 min), nimodipine (tm = 10.1 min), felodipine (tm = 12.2 min), nicardipine hydrochloride (tm = 12.7 min), lacidipine (tm = 13.5 min) and amlodipine besylate (tm = 14.1 min, tm = 8 min). The method developed showed to be linear at least up to 70 micrograms/ml with a detection limit of about 5 micrograms/ml for each compound. The within-day and inter-day area reproducibility (R.S.D.) were, respectively, lower than 4.8 and 8.6% for six replicate samples.     

Identification of inorganic ions in post‐blast explosive residues using portable CE instrumentation and capacitively coupled contactless conductivity detection

Novel CE methods have been developed on portable instrumentation adapted to accommodate a capacitively coupled contactless conductivity detector for the separation and sensitive detection of inorganic anions and cations in post‐blast explosive residues from homemade inorganic explosive devices. The methods presented combine sensitivity and speed of analysis for the wide range of inorganic ions used in this study. Separate methods were employed for the separation of anions and cations. The anion separation method utilised a low conductivity 70 mM Tris/70 mM CHES aqueous electrolyte (pH 8.6) with a 90 cm capillary coated with hexadimethrine bromide to reverse the EOF. Fifteen anions could be baseline separated in 7 min with detection limits in the range 27–240 μg/L. A selection of ten anions deemed most important in this application could be separated in 45 s on a shorter capillary (30.6 cm) using the same electrolyte. The cation separation method was performed on a 73 cm length of fused‐silica capillary using an electrolyte system composed of 10 mM histidine and 50 mM acetic acid, at pH 4.2. The addition of the complexants, 1 mM hydroxyisobutyric acid and 0.7 mM 18‐crown‐6 ether, enhanced selectivity and allowed the separation of eleven inorganic cations in under 7 min with detection limits in the range 31–240 μg/L. The developed methods were successfully field tested on post‐blast residues obtained from the controlled detonation of homemade explosive devices. Results were verified using ion chromatographic analyses of the same samples.     

Influence of acidic eluent for retention behaviors of common anions and cations by ion-exclusion/cation-exchange chromatography on a weakly acidic cation-exchange resin in the H+ -form

Influence of acidic eluent on retention behaviors of common anions and cations by ion-exclusion/cation-exchange chromatography (ion-exclusion/CEC) were investigated on a weakly acidic cation-exchange resin in the H(+)-form with conductivity. Sensitivities of analyte ions, especially weak acid anions (F(-) and HCOO(-)), were affected with degree of background conductivity level with pK(a1) (first dissociation constant) of acid in eluent. The retention behaviors of anions and cations were related to that of elution dip induced after eluting acid to separation column and injecting analyte sample. These results were largely dependent on the natures of acid as eluent. Through this study, succinic acid as the eluent was suitable for simultaneous separation of strong acid anions (SO(4)(2-), Cl(-), NO(3)(-) and I(-)), weak acid anions (F(-), HCOO(-) and CH(3)COO(-)), and cations (Na(+), K(+), NH(4)(+), Mg(2+) and Ca(2+)). The separation was achieved in 20 min under the optimum eluent condition, 20 mM succinic acid/2 mM 18-crown-6. Detection limits at S/N=3 ranged from 0.10 to 0.51 microM for strong acid anions, 0.20 to 5.04 microM for weak acid anions and 0.75 to 1.72 microM for cations. The relative standard deviations of peak areas in the repeated chromatographic runs (n=10) were in the range of 1.1-2.9% for anions and 1.8-4.5% for cations. This method was successfully applied to hot spring water containing strong acid anions, weak acid anions and cations, with satisfactory results.     

Determination of common inorganic anions and cations by non-suppressed ion chromatography with column switching

An ion chromatography (IC) method has been proposed for the determination of seven common inorganic anions (F(-), H(2)PO(4)(-), NO(2)(-), Cl(-), Br(-), NO(3)(-), and SO(4)(2-)) and/or five common inorganic cations (Na(+), NH(4)(+), K(+), Mg(2+), and Ca(2+)) using a single pump, a single eluent and a single detector. The present system used cation-exchange and anion-exchange columns connected in series via a single 10-port switching valve. The 10-port valve was switched for the separation of either cations or anions in a single chromatographic run. When 1.0mM trimellitic acid (pH 2.94) was used as the eluent, the seven anions and the five cations could be separated on the anion-exchange column and the cation-exchange column, respectively. The elution order was found to be F(-)相似文献   

Modification of a Dionex System 12 ion chromatograph for sequential determination of the main components in atmospheric precipitation

A modification of a Dionex System 12 ion chromatograph is described which enables organic anions (acetate and formate), inorganic cations (ammonium, sodium and potassium) and inorganic anions (chloride, nitrate and sulphate) to be determined sequentially in one measuring procedure. The modified instrument consists of a programmable controller unit, a conductimetric meter, two conductimetric detectors of the Dionex System 12 ion chromatograph, the HPIC-AS4A and HPIC-CS3 modern separation units, AMMS-1 and CMMS-1 micro-membrane suppressor columns, a unique system of valves from Dionex and two dual pumps from Biotronik. The limits of detection are between about 1 and 3 micrograms/l for chloride, nitrate and sulphate and between about 2 and 10 micrograms/l for acetate, formate, ammonium, sodium and potassium. The reliability of the method was demonstrated by analysing two NBS simulated rain water Standard Reference Materials. Some examples are given of the application of the method to the sequential determination of the main precipitation components in typical samples from urban and rural regions of the F.R.G. The ion concentrations varied between about 0.02 and 300 mg/l.     

Speciation of Cr(III) and Cr(VI) and separation of common anions by ion pair chromatography with trans-1,2-diaminecyclohexane-N,N,N',N'-tetraacetic acid

A reversed phase ion pair chromatographic method for the simultaneous determination of Cr species and common anions on a C(18)-bonded stationary phase was developed by using acetonitrile-water (2:98 v/v) containing 1.0 mM tetrabutylammonium hydroxide and 0.5 mM trans-1,2-diaminecyclohexane-N,N,N',N'-tetraacetic acid (DCTA) at pH 6.5 as mobile phase and UV-detection at 210 nm. Chromatographic parameters were optimized for separation of Cr(III)-DCTA complex, chromate and other anions. The detection limits were found as 8 ng/ml for Cr(III) and 35 ng/ml for Cr(VI). Under the optimum conditions, most other ions did not interfere. The method can be applied to separate a number of common anions simultaneously with the separation of Cr(III) and Cr(VI).     

Ion chromatographic determination of cyanate in saline gold processing samples.

An ion chromatographic method was developed for the determination of cyanate (CNO-) in saline gold processing samples. The method is based on the use of a very weak-eluting buffer (5 mM sodium borate) and a Dionex AS4A-SC anion-exchange column. This weak-eluting buffer facilitates the wide chromatographic separation of chloride (Cl-) from CNO-. After CNO- has been eluted, the switch to 1.8 mM Na2CO3-1.7 mM NaHCO3 buffer allows the fast elution of other major inorganic and organic anions. Validation of this method, including identification of interferences, has shown that this method is reliable, accurate, sensitive (detection limit, 0.1 mg/l CNO-) and reproducible.     

Determination of alpha hydroxy acids in fruits by capillary electrophoresis.

Alpha hydroxy acids, malic acid, citric acid, tartaric acid, glycolic acid and lactic acid, were analyzed simultaneously using capillary electrophoresis with direct UV detection at 200 nm. The separation was carried out with uncoated fused-silica (50 cm x 50 microns i.d.), pressure injection at 15 psi s and operated at -15 kV potential. The separation buffers were prepared with 180 mM Na2HPO4, 1 mM cetyltrimethylammonium bromide and 15% (v/v) methanol and adjusted to pH 7.2 by phosphoric acid. Validation was performed for citric acid and malic acid. The obtained parameters were adequate and the limits of detection were 2.5 and 5 micrograms ml-1 for citric acid and malic acid, respectively. AHAs from natural fruit juices (orange and grape) were determined and measured with this method.     

Determination of oxoanions in river water by capillary electrophoresis

A new capillary electrophoresis (CE) procedure was developed for simultaneous determination of ten oxoanions (CrO4(2-), SeO4(2-), MoO4(2-), WO4(2-), VO4(3-), SeO3(2-), As04(3-), TeO3(2-), TeO4(2-), and AsO3(3-)) which were baseline-separated from each other and from the interfering UV absorbing anions (NO3- and NO2-) commonly found in environmental water samples. The new background electrolyte system developed contained 5 mM potassium phosphate and 0.007 mM octadecyltrimethylammonium hydroxide, pH 11.2. The optimized working conditions were electrokinetic sampling at -5 kV for 10 s, running voltage at -15 kV with 5 microA current, and detection wavelength at 205 nm. No interference was observed for non-UV-absorbing anions and UV-absorbing anions up to 20 and 10 times higher concentrations respectively. The speed of analysis was fast, with a complete CE run within 6 min. Wide linear ranges (1-2,000 microg/L), good repeatability in migration time (relative standard deviation RSD 0.55-2.8%), satisfactory precision in peak area (RSD 3.8-5.6%) and peak height (RSD 3.9-5.3%) measurement, and detection limits (1-25 microg/L) sufficiently sensitive to detect oxoanions found in environmental water samples were obtained. The reliability of the CE procedure developed had been established by recovery test and parallel method determination using atomic absoprtion spectrophotometry for real river water sample.     

Determination of thiosulfate, thiocyanate and polythionates in a mixture by ion-pair chromatography with ultraviolet absorbance detection

A sensitive ion chromatographic method has been developed for the determination of mixtures of thiosulfate, thiocyanate and polythionates (tri-, tetra-, penta- and hexathionate). The proposed method is based on the separation of the sulfur anions on an octadecylsilica (ODS) column with an acetonitrile-water mobile phase containing tetrapropylammonium salt (TPA) as an ion-pairing reagent and the ultraviolet absorption detection of the sulfur anions. When an acetonitrile-water (20:80, v/v) solution (pH 5.0) containing 6 mM TPA was used as a mobile phase at flow-rate of 0.6 ml min(-1), the sulfur anions were resolved within 22 min. The detection limits defined at S/N=3 and 230 nm were very low for all anions, except trithionate: 30 nM for thiosulfate, 60 nM for thiocyanate, 20 nM for tetrathionate, 15 nM for pentathionate and 18 nM for hexathionate. The proposed method gave recoveries ranging from 95.0 to 105.0% when applied to the determination of polythionates added to hot spring waters.     

Analysis of naphthalenesulfonate compounds by cyclodextrin-mediated capillary electrophoresis with sample stacking

This study systematically investigates the optimal conditions for analyzing the positional isomers of multi-charged naphthalenesulfonate compounds by cyclodextrin-mediated capillary electrophoresis (CE). Specifically, this work employs large-volume sample injection with the electrode polarity switching technique. The most effective separation and sample stacking conditions were 15 mM borate buffer with a mixture of beta- and gamma-cyclodextrin (concentration ratio 3:7 mM) at pH 9.2, and the sample hydrodynamic injection of up to 60 s at 3 p.s.i. (around 1.8 microl, and 1 p.s.i. = 6.9 kPa). Significantly selective and sensitive improvements were observed and a more than 100-fold enrichment was achieved (based on peak area). The reproducibility of migration time and quantitative results of stacking CE can be improved by using an internal standard. The quantitation limits of these naphthalenesulfonate isomers, based on a signal-to-noise ratio above 10, can be about 4 microg/l with UV detection. This method was successfully applied to determine the trace amount of naphthalenesulfonate isomers in a spiked drinking water sample.