Pulse Enhanced Electrosorptive Detection of Ions at Silver in Ion Chromatography

Abstract

Differential double-layer capacitance measurements applied to the silver-aqueous interface may serve as the basis of detection for surface-active ions in ion chromatography. There is a caveat to this approach, though, and that is that the electrode is subject to gradual fouling due to the accumulation of adsorbed matter. We report here on the incorporation of potential pulsing sequences to counter this damaging effect. Two approaches have been taken: 1) inclusion of a periodic potential cleaning pulse in the conventional, fixed-potential double-layer capacitance measurement scheme, and 2) utilization of a potential-pulse/coulometric measurement technique. the potential-pulse/coulometric procedure entails measurement of the change in charge required to charge the electrical double layer in response to specific adsorption of analyte. Its response-concentration behavior is similar to that observed for differential capacitance detection. the use of a combined, dual-potential (sequential) capacitive/amperometric detection scheme that provides unique complementation to either amperometric or capacitance detection is also discussed.     

Potentiometric detection in ion chromatography using a metallic copper indicator electrode

Summary A metallic copper electrode housed in a suitable flowcell is shown to be a sensitive and versatile potentiometric detector for ion chromatography. This electrode may be used for direct or indirect detection of many inorganic anions and cations and also for organic acids. In the direct detection mode, electrode response is based on either complexation of copper ions at the electrode surface by eluted species, or on oxidation and reduction reactions for eluted species which are strong oxidants or reductants. Direct detection is therefore applicable to such species as amino acids, organic acids, chloride, bromide, iodide, chlorate, bromate and iodate. Indirect detection is possible for anions which do not complex copper ions, provided a copper complexing ligand (such as phthalate) is used in the eluent; cations which complex this ligand are also detectable. Indirect detection may be used for species such as nitrite, nitrate, acetate, formate, succinate, benzoate, alkaline earth ions and transition metal ions. Electrode calibration relationships are discussed and sample separations are presented, together with some typical detection limits attainable in the direct and indirect detection modes.Presented in part at a National Symposium on Ion Chromatography, held at the University of New South Wales, Kensington, Australia, Nov. 21, 1984.     

Developments in detection methods for ion chromatography

Summary Recent advances in detection methods for ion chromatography are reviewed, with particular emphasis on conductimetric, amperometric, potentiometric and indirect UV absorption methods. It is shown that a wide variety of detection methods now exists and this has decreased the dependence of ion chromatography on conductivity detection.     

Potentiometric detection of monovalent anions separated by ion chromatography using all solid-state contact PVC matrix membrane electrode

Summary An all solid-state contact tubular PVC-matrix membrane electrode has been applied for potentiometric detection of inorganic and organic monovalent anions using phosphate and hydrogen phosphate eluents at low concentrations. This is a “monovalent detection method” as the selectivity of the electrode towards monovalent anions results in some other anions being undetected unless the concentration of those other anions is higher than 10⁻³ mol dm⁻³ in the sample solution injected. It takes only eight minutes to complete the separation with a good resolution. Theoretical and practical considerations are discussed, and in particular, sensitivity, linearity, detection limit and dynamic behaviour are presented. The use of an all solid-state contact bromide-selective electrode as a detector offers so far the best simultaneous sensitivity toward all anions when compared with other detection methods. Determination of Cl⁻ and NO₃ ⁻ ions in river, rain and drinking water samples without any further sample preconcentration has been successfully achieved. The detection limit is sub-ppb for most of anions in a 20 μL injection volume.     

Microcolumn ion chromatography with conductimetric detection

Summary A miniaturized flow cell for an electrical conductivity detector has been made and applied to the ion chromatography of inorganic anions. It consisted of stainless steel tubes (0.13 mm ID×0.31 mm OD) and PTFE tubes (0.25 mm ID×2 mm OD). The detection limit for chloride at S/N=3 was 36 pg or 0.33 ppm for a 0.11 l injection.     

Correlation ion chromatography with indirect UV detection

Summary A binary pseudo-random injection of a sample containing low concentrations of common anions into the anion exchange column was used to enhance the signal-to-noise ratio of indirect UV detection of the ions. The detection limits obtained in our experiment (14 ppb, 14 ppb, and 64 ppb for Cl^–, NO ₃ ^– and SO ₄ ^2– respectively) are in good agreement with theoretical predictions. The large amplitude system peaks inherent to single column IC do not generate remarkable ghost peaks, which is indicative of the suitability of the input devices used in our studies.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

ODS phases for ion chromatography

Several ODS phases have been dynamically modified to act as ion exchangers. Their ability to separate inorganic ions has been evaluated. The different properties of these materials are demonstrated and a method for eliminating the appearance of the system peak is described.     

Simultaneous determination of catecholamines by ion chromatography with direct conductivity detection

A simple method for simultaneous determination of three catecholamines using ion chromatography (IC) with direct conductivity detection (CD) based on the ionization of catecholamines in acidic medium without chemical suppression is developed in the present paper. The method could be used for the determination of these catecholamines in pharmaceutical preparations for the purpose of drug quality control. The recovery of catecholamines was more than 97% (n=3) and the relative standard deviation (R.S.D.) (n=11) was less than 2.1%. In a single chromatographic run, norepinephrine (NE), epinephrine (E) and dopamine (DA) can be determined in less than 10 min. The detection limits were found to be 0.001 μg/ml for NE, 0.01 μg/ml for E and DA respectively. Linear ranges were 0.01–50 μg/ml for NE (r²=0.9998), 0.1–50 μg/ml for E (r²=0.9995) and DA (r²=0.9999), respectively.     

离子排斥色谱-脉冲安培法测定电镀液中的游离CN-

建立了离子排斥色谱-脉冲安培法测定游离CN-的检测方法。方法使用IonPac ICE-AS1离子排斥柱为分析柱,以120 mmol/L HClO4为淋洗液,安培法检测（工作电极为Pt电极）。CN-的检出限为0.42μg/L（50μL进样,三倍基线噪音）;在1-1000μg/L范围内具有良好的线性（r=0.9996）。0.01 mg/L和0.1mg/LCN-分别连续进样9次,峰面积相对标准偏差（RSD）分别为4.0%和3.0%。用该方法检出了电镀液样品中大量的游离CN^-。对实际样品进行加标,其回收率在83%-117%之间。     

Determination of toluene diisocyanate in synthetic-rubber track by ion chromatography with ultraviolet detection after alkaline suppressor

In the present work,a novel analytical method was proposed for the determination of toluene diisocyanate(TDI)in synthetic- rubber track by ion chromatography(IC)coupled with an ultraviolet detector setting at 212 nm.TDI can be hydrolyzed to toluene diamine(TDA)which can be separated by cation-exchange IC easily.The optimum IC separation was performed on an IonPac CS12A column(150 mm×4.0 mm)using 20 mmol L~(-1)sodium sulfate,10 mmol L~(-1)sulfuric acid and 10%acetonitrile as eluent. It was found that a hi...     

Factors affecting selectivity in ion chromatography

Methods for separation of ions by ion-exchange, ion-pair, and zwitterion ion chromatography share at least one common thread--the induced formation of a cation-anion pair in the stationary phase. Selectivity can be defined as the relative ability of sample ions to form such a pair. Examples are given in anion-exchange chromatography to show the effect of variations in the geometry, bulkiness and polarity of the resin cation on selectivity. The type of resin matrix, the hydrophobic nature of the resin surface and the degree of solvation also affect chromatographic behavior. The selectivity series observed in ion chromatography seems to be best explained by the interplay of two components: electrostatic attraction (ES) and the enforced-pairing (EP) that is brought about by hydrophobic attraction and by water-enforced ion pairing. Selectivity in ion-pair chromatography (IPC) and in zwitterion ion chromatography (ZIC) is affected by both the mobile phase cation and anion. This leads to elution orders for anions that are different from conventional ion-exchange chromatography (IC) of anions where cations are excluded from the stationary phase and have little effect on a separation. The elution order of anions in ZIC is similar to that in IC except for small anions of 2-charge, which are retained more weakly in ZIC. A unique advantage of ZIC is that sample ions can be eluted as ion pairs with pure water as the eluent and a conductivity detector. The mechanism for separation of anions on a zwitterionic stationary phase has been a subject for considerable debate. The available facts point strongly to a partitioning mechanism or a mixed mechanism in which partitioning is dominant with a weaker ion-exchange component.     

Reduction of chloride matrix effect using silver oxide as a precipitating reagent for the determination of trace anions in chloride-rich samples via ion 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.     

Microcolumn ion chromatography of inorganic anions using bovine serum albumin stationary phase with indirect photometric detection

Summary Microcolumn ion chromatography of inorganic anions has been studied using bovine serum albumin immobilized on silica gel as a stationary phase. Several mobile phase solutions were examined, involving sodium iodide, potassium hydrogen phthalate, 2,6-anthraquinone disulfonate (2,6-AQDS) and sodium salicylate. 2,6-AQDS achieved better separation of the analytes tested. Chloride, nitrate, iodide, thiocyanate and sulphate could be separated within 8 min. Detection limits were in the range of 0.9–2.9 M, corresponding to mass detection limits of 0.18–0.59 pmol. The system was applied to the determination of inorganic anions in environmental water and biological samples.     

Sensitive quantification of iodide by ion-exchange chromatography with electrochemical detection at a modified platinum electrode

A rapid and very sensitive method for the accurate determination of free iodide in real samples is described. The method is based on anion-exchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification is proposed using an amperometric thin-layer cross-flow detector and a flowing solution 300 mg/L of iodide; the working electrode is polarised to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results indicated that the modified electrode exhibits high analytical response for iodide electrooxidation with good stability and long-life. The signal intensity of daily experimental sessions (8 h), during which standards and real samples were repeatedly injected, exhibits a moderate lowering (i.e. <6%). Using a mixture of 25 mM HNO₃ and 50 mM NaNO₃ as an eluent phase in ion-exchange chromatography, the detection limit of iodide was estimated to be 0.5 g/L (S/N=3) with an injection volume of 50 L. This method was applied successfully to quantify the iodide content of milk samples and in wastewaters as well as trace amounts in common vegetables and solutions containing high chloride levels.     

Direct determination of hydrogen cyanide in cigarette mainstream smoke by ion chromatography with pulsed amperometric detection

The determination of hydrogen cyanide in cigarette mainstream smoke has been achieved by ion chromatography (IC) with pulsed amperometric detection (PAD). The proposed method of totally trapping whole cigarette mainstream smoke by Cambridge filters, which are treated with sodium hydroxide/ethanol solution, possesses the advantage of fast analysis time over the widespread used solution absorption method. The possible co-existing interferents are evaluated under the optimized detection conditions and excellent recoveries of cyanide are obtained. The cyanide content of absorption solution can be directly determined by the optimized IC-PAD method without any pretreatments. The linear range is 0.0147-2.45 μg/mL with R2 value of 0.9997. The limit of the detection is 3 μg/L for a 25 μL injection loop. The overall relative standard deviation of the method is less than 5.20% and the recovery range from 94.3% to 101.0%. The results obtained from the developed method are in good agreement with that of continuous flow analyzer (CFA) method.     

Separation and determination of pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection

A method for rapid and simultaneous determination of multiple pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection was developed.Chromatographic separations were performed on a cation exchange column using ethylenediamine-acetonitrile as the mobile phase.The effects of chromatographic column and the mobile phase,as well as the column temperature on the retention of the cations were investigated.The retention rules of the cations under different chromatographic conditions were formulated.The retention of the cations followed the carbon number rule.The method has been successfully applied to the determination of three ionic liquids synthesized by a chemical laboratory.     

离子色谱法检测印刷电路板中的阴离子

采用Na2CO3 NaHCO3为淋洗液和抑制电导检测,对印刷电路板上浸提出的5种常见阴离子F-、Cl-、Br-、NO3-、SO42-同时进行分离检测。在所采用的色谱条件下各阴离子在15 min内即可完成分析。线性良好,检出限为0.05μg/mL(Cl-为0.01μg/mL),回收率在96.70%~101.25%之间,该方法能够在印刷电路板表面洁净度的评价分析中发挥作用。     

柱切换离子色谱法测定丙酮中痕量阴离子

建立了测定丙酮中痕量阴离子的离子色谱分析方法.采用的是高效液相柱切换进样,其中泵的流速为0.5 mL/min,使低浓度的丙酮水溶液在保护柱上富集,通过离子色谱抑制电导法分离和检测丙酮样品中痕量的阴离子.色谱条件为:以IonPacAG9-HC(50 mm×2 mm)型柱串联在定量环中进行富集,IonPacAG9-HC(50 mm×2 mm)保护柱,IonPac AS9-HC(250 mm×2 mm)阴离子分离柱进行分离,流动相为9 mmol/L Na2CO3-1.667 mol/L NaHCO3,所得回收率在96.21%～101.56%之间,线性良好,且具有较好的重现性和较低的检出限.     

Determination of catecholamines by ion chromatography coupled to acidic potassium permanganate chemiluminescence detection

A simple,fast,sensitive,highly selective and eco-friendly analytical method for the determination of catecholamines in human urine by ion chromatography（IC） with chemiluminescence（CL） detection was described in this paper.Using 12 mmol/L H₂SO₄ without any organic additive as eluent,three catecholamines including epinephrine（EP）,norepinephrine（NE） and dopamine（DA） were well separated on a cation-exchange column.The CL detection was based on the reaction of analytes with acidic potassium permanganate in the presence of formaldehyde as an enhancer.The absence of methanol and acetonitrile in eluent made the proposed method more sensitive and eco-friendly.Under the optimal conditions,the linear range of the proposed method was in the range of 0.02-0.5μg/mL.The limit of detection（LOD） was in the range of 0.6 and 5.1μg/L.The relative standard deviations （RSD） for 0.1μg/mL mixed standard solution were in the range of 0.8-1.9%（n = 11）.The method has been applied to the determination of catecholamines in human urine successfully.Excellent spiked recoveries were achieved for catecholamines ranged from 91.2%to 112.7%.     

Indirect photometric detection of monovalent cations via postsuppressor ion replacement in microcolumn ion chromatography

Summary Monovalent cations were indirectly detected via postcolumn suppressor ion replacement in microcolumn ion chromatography. The ion-repalcement column loaded by chromophoric ions was connected to the suppressor column. The eluent, nitric acid, was converted to water through the suppressor and anion-replacement columns, while the analyte cations were coeluted with the chromophoric anions. The analyte cations were indirectly detected by measuring UV absorptions of the chromophoric anions.