Peak parking technique for the simultaneous determination of anions and cations

An ion chromatography method is described for the simultaneous determination of anions (Cl^–, NO₃^–, and SO₄^2–) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) using a single pump, a single eluent and a single detector. An anion-exchange column modified with chondroitin sulfate C facilitated the elution of the above three anions using 5 mM tartaric acid as the eluent in isocratic mode, whereas the same eluent facilitated the separation of the above five cations on a commercially-available cation-exchange column. The separation columns were connected in series via two six-port switching valves, so the required cation-exchange or anion-exchange separation could be carried out by selecting the appropriate positions for the switching valves. The separations were completed in 30 min.     

Applications of Macrocyclic Polyethers in Analytical Sensors and Ion Separation

Artificial macrocyclic polyethers were synthesized and applied as neutral carriers for ion-selective PVC membrane electrodes, ion-chromatographic packing materials, extractants and adsorbents for ion separation, coating materials for piezoeletrical membrane sensors for organic species, and ion-transport carriers through liquid membranes. Ion-selective electrodes such as those for K⁺ Na⁺, UO₂²⁺, Cs⁺, Pb²⁺, Fe³⁺, Hg²⁺ and Ag⁺ ions based on crown ether-phosphotungstic acid (PW) precipitates and dithio crown ethers respectively were prepared and showed good sensitivity and selectivity. Crown ether-PW precipitates were applied as adsorbents of rare-earth ions and some common heavy-metal ions. Some rare-earth ions were easily extracted with crown ethers, especially 15-crown-5. Poly(stytene/divinyl benzene) cryptand-22 resin was synthesized and applied as a bifunctional stationary phase of ion chromatography to separate bom cations and anions, even some organic carboxylate geometric isomers. Crown ethers such as mono-benzo-15-crown-5 was successfully applied as a coating material on piezoelectric quartz membrane sensors for some organic species. The oscillation frequency of the crown-ether quartz-membrane sensor was sensitive to organic vapours such as amines and alcohols. Upon adsorption of organic species on the crown-ether quartz membrane, the oscillation frequency of the sensor decreased obviously. Special crown ether such as dibenzo-16-crown-5-oxyacetic acid, decyl-cryptand-22 and 1, 4-dihydro-pyridine-18-crown-5 were synthesized and successfully applied as ion-transport carriers (ionophores) for transport of Na⁺ K⁺ and Mg²⁺ ions through liquid membranes.     

Tunable separation of anions and cations by column switching in ion chromatography

A convenient ion chromatography method has been proposed for the routine and simple determination of anions (Cl⁻, SO₄²⁻ and NO₃⁻) and/or cations (Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) 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 two 6-port switching valves or a single 10-port valve. The connection order of the ion-exchange columns could be varied by switching the valve(s). The present system therefore allowed the separation of either cations or anions in a single chromatographic run. While one ion-exchange column is being operated, the other ion-exchange column is being conditioned, i.e., the columns are always ready for analysis at any time. When 2.4 mM 5-sulfosalicylic acid was used as the eluent, the three anions and the five cations could be separated on the anion-exchange column and cation-exchange column, respectively. In order to obtain the separations of the target ions, the injection valve was placed between the two columns. Complete separations of the above anions or cations were demonstrated within 10 min each. The detection limits at S/N = 3 were 19-50 ppb (μg/l) for cations and 10-14 ppb for anions. The relative standard deviations of the analyte ions were less than 1.1, 2.9 and 2.8% for retention time, peak area and peak height, respectively. This proposed technique was applied to the determination of common anions and cations in river water samples.     

Ion-exclusion chromatography with the direct UV detection of non-absorbing inorganic cations using an anion-exchange conversion column in the iodide-form

An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na⁺), ammonium (NH₄⁺) and hydrazine (N₂H₅⁺) ions was developed by connecting an anion-exchange column in the I⁻-form after the separation column. For example, NH₄⁺ is converted to a UV-absorbing molecule, NH₄I, by the anion-exchange column in the I⁻-form after the ion-exclusion separation on anion-exchange column in the OH⁻-form with water eluent. As a result, the direct UV detection of Na⁺, NH₄⁺ and N₂H₅⁺ could be successfully obtained as well as the well-resolved separation. The calibration graphs of the analyte cations detected with UV at 230 nm were linear in the range of 0.001-5.0 mM. The detection limits at S/N = 3 of the cations were below 0.1 μM. This method was applied to real water analysis, the determination of NH₄⁺ in river and rain waters, or that of N₂H₅⁺ in boiler water, with the satisfactory results. This could be applied also to low- or non-absorbing anions such as fluoride or hydrogencarbonate ions by the combination of a weakly acidic cation-exchange resin in the H⁺-form as the separation column and the anion-exchange conversion column.     

Preparation of a hybrid monolithic stationary phase with allylsulfonate for the rapid and simultaneous separation of cations in capillary ion chromatography

A hybrid monolithic column with sulfonate functionality was successfully prepared for the simultaneous separation of common inorganic cations in ion‐exchange chromatographic mode through a simple and easy single‐step preparation method. The strong cation‐exchange moieties were provided directly from allylsulfonate, which worked as an organic monomer in the single‐step reaction. Inorganic cations (Li⁺, Na⁺, K⁺, NH₄⁺, Cs⁺, Rb⁺, Mg²⁺, Ca²⁺, and Sr²⁺) were separated satisfactorily by using CuSO₄ as the eluent with indirect UV detection. The allysulfonate hybrid monolith showed a better performance in terms of speed and pressure drop than the capillary packed column. The number of theoretical plates achieved was 19 017 plates/m (in the case of NH₄⁺ as the analyte). The relative standard deviations (n = 6) of both retention time and peak height were less than 1.96% for all the analyte cations. The allysulfonate hybrid monolithic column was successfully applied for the rapid and simultaneous separation of inorganic cations in groundwater and the effluent of onsite domestic wastewater treatment system.     

Application of pure silica gel as cation-exchange stationary phase in lon chromatography with indirect photometric detection for common mono-and divalent cations using aromatic monoamines as eluents

Summary A pure silica gel (Pia Seed 5S-60-SIL), synthesized by the hydrolysis of pure tetraethoxysilane [Si(OCH₂CH₃)₄], was applied as a cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono-and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) using various protonated aromatic monoamines (tyramine [4-(2-aminethyl) phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine) as eluet ions. When using 0.75 mM tyramine-0.25 mM oxalic acid-1.5 mM 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) at pH 5.0 as the eluent, excellent simultaneous separation and highly sensitive detection at 275 nm for these mono-and divalent cations were achieved on the Pia Seed 5S-60-SIL column (150×4.6 mm I.D.) in 20 min.     

Advances in ion chromatography: speciation of μ 1−1 levels of metallo-cyanides using ion-interaction chromatography

Fe(CN)^4?₆, Cu(CN)^3?₄, Co(CN)^3?₆, Fe(CN)^3?₆, Ni(CN)^2?₄ and Cr(CN)^3?₆ are determined by ion-interaction chromatography using a C₁₈ column and methanol-tetrahydrofuran-10 mM phosphate buffer (pH 7.9) (25 + 1 + 74, v/v/v) containing 5 mM tetrabutylammonium hydroxide as mobile phase, with spectrophotometric detection at 214 nm. Detection limits are in the range 0.01–0.5 mg 1^?1. In an alternative approach, an automated on-line sample preconcentration technique is used wherein a 2-ml volume of sample containing metallo-cyanides is loaded onto a C₁₈ precolumn which has been equilibrated with the above mobile phase. The bound solutes are then eluted from the precolumn to a C₁₈ analytical column where they are separated using the same mobile phase as employed to equilibrate the precolumn. Detection limits are in the rate 0.08–1.58 μg 1^?1 and calibration graphs are linear up to 200 μg 1^?1. The preconcentration step is shown to give quantitative recoveries for all species except Fe(CN)^4?₆ and (CN)^3?₄. The iron(II) complex does not bind quantitatively to the precolumn, and extensive studies with the copper complex suggested that low recoveries were due to dissociation and ligand-exchange reactions occurring during the chromatographic separation process. Negative interference effects were observed for Cl^? and SO^2?₄ when present at a level of 250 mg 1^1?, and UV-absorbing anions such as Br^?, SCN^?, NO^?₂ and NO^?₃ caused positive interference when present at concentrations as low as 1 mg 1^?1. The negative interferences could be reduced by diluting the sample and the positive interferences could be eliminated by incorporating an additional step in the preconcentration process, in which UV-absorbing anions bound to the precolumn after sample loading were eluted selectively using an eluent consisting of 10 mM NaCl in phosphate buffer (pH 6.7).     

Liquid-liquid extraction of metal ions with tris (2,6-dimethoxyphenyl) phosphine and its quaternary phosphonium salts

The extraction of various metal ions from hydrochloric acid solutions with tris(2,6-dimethoxyphenyl)phosphine, [2,6-(MeO)₂C₆H₃]₃P, abbreviated to (2,6-MeOPh)₃P, and its tertiary and quaternary phosphonium salts were studied. A series of phosphonium salts, [(2,6-MeOPh)₃PH]⁺ClO^?₄, [(2,6-MeOPh)₃PR]⁺Br^? and {[(2,6-MeOPh)₃P]₂R′}²⁺ (Br^?)₂, where R = C₁₂H₂₅, C₁₈H₃₇ or C₆H₅CH₂ and R′ = p-CH₂C₆H₄CH₂, (CH₂)₃ and (CH₂)₁₀, were synthesized and applied to an anion exchanger for chloro complex anions of various metal ions. (2,6-MeOPh)₃P and [(2,6-MeOPh)₃PR]⁺Br^? were found to be effective for the extraction of metal ions such as iron(III), gold(III) and gallium(III), forming tetrachloro complex anions of the M^IIICl^?₄ type. The extractabilities of the doubly charged cationic quaternary phosphonium salts [{(2,6-MeOPh)₃P}₂R′]²⁺ (Br^?₂, were found to be superior to those of the singly charged cationic phosphonium salts for metal ions such as cadmium(II), platinum(II) and palladium(II), forming a tetrachloro complex doubly charged aion of the M^IICl^2?₄ type. Most of the metal ions are extracted through ion-pair formation between their chloro complex anions and the phosphonium cations.     

Bifunctional Ion‐Selective Electrode Based on C60‐Cryptand 22 for Silver and Iodine Ions

Fullerence C60‐cryptand 22 was prepared and successfully applied as the electric carrier in the PVC electrode membrane of a bifunctional ion‐selective electrode for cations, e.g., Ag⁺ ions as well as anions, e.g., I^? ions. The bifunctional ion‐selective electrode based on C60‐cryptand 22 can be applied as a Silver (Ag⁺) ion selective electrode with an internal electrode solution of 10^?3 M AgNO₃ in water (pH = 6.3), or as an Iodide (I^?) ion selective electrode with an acidic internal electrode solution of 10^?4 M KI_(aq) (pH = 2) in which the cryptand 22 is protonated, and the C60‐cryptand 22 is changed to C60‐Cryptand22–H⁺ and becomes an anionic electro‐carrier to absorb the I^? ion. The Ag⁺ ion selective electrode based on C60‐cryptand 22 gave a linear response with a near‐Nernstian slope (59.5 mV decade^?1) within the concentration range 10^?1‐10^?3 M Ag⁺_(aq). The Ag⁺ ion electrode exhibited comparatively good selectivity for silver ions, over other transition‐metal ions, alkali and alkaline earth metal ions. The Ag⁺ ion selective electrode with good stability and reproducibility was successfully used for the titration of Ag⁺_(aq) with Cl^? ions. The Iodide (I^?) Ion selective electrode based on protonated C60–cryptand22‐H⁺ also showed a linear response with a nearly Nernstian slope (58.5 mV decade^?1) within 10^?1 ‐ 10^?3 M I^? _(aq) and exhibited good selectivity for I^? ions and had small selectivity coefficients (10^?2–10^?3) for most of other anions, e.g., F^? , OH^?, CH₃COO^?, SO₄^2?, CO₃^2?, CrO₄^2?, Cr₂O₇^2? and PO₄^3? ions.     

Serial separation of cations and anions by ion chromatography using the peak parking technique and sulfosalicylic acid as the eluent

An improvement of the peak parking technique is described for the serial determination of cations (Na⁺, , K⁺, Mg²⁺, and Ca²⁺) and anions (Cl⁻, , and ) using a single pump, a single eluent and a single detector. The present system used commercially-available unmodified cation exchange and anion exchange columns, which were attached to each switching valve. When 1.75 mM 5-sulfosalicylic acid was used as the eluent, serial separation of the above cations and anions was achieved in less than 20 min. The proposed ion chromatographic method was successfully applied to the serial determination of cations and anions in tap water and river water samples. The limits of detection at S/N=3 for an injection of 20 μl were 16–68 ppb (μg/l) for cations and 15–28 ppb for anions.     

Determination of nitrite, nitrate, bromide, and iodide in seawater by ion chromatography with UV detection using dilauryldimethylammonium-coated monolithic ODS columns and sodium chloride as an eluent

A method was developed for determination of inorganic anions, including nitrite (NO ₂ ^? ), nitrate (NO ₃ ^? ), bromide (Br^?), and iodide (I^?), in seawater by ion chromatography (IC). The IC system used two dilauryldimethylammonium bromide (DDAB)-coated monolithic ODS columns (50?×?4.6?mm i.d. and 100?×?4.6?mm i.d.) connected in series for separation of the ions. Aqueous NaCl (0.5?mol/L; flow rate, 3?mL/min) containing 5?mmol/L phosphate buffer (pH 5) was used as the eluent, and detection was with a UV detector at 225?nm. The monolithic ODS columns were coated and equilibrated with a 1-mmol/L DDAB solution (in H₂O/methanol, 90:10 v/v). The hydrophilic ions (NO ₂ ^? , NO ₃ ^? , and Br^?) were separated within 3?min and the retention time of I^? was 16?min. No interferences from matrix ions, such as chloride and sulfate ions, were observed in 35?‰ artificial seawater. The detection limits were 0.6?μg/L for NO ₂ ^? , 1.1?μg/L for NO ₃ ^? , 70?μg/L for Br^?, and 1.6?μg/L for I^? with a 200-μL sample injection. The performance of the coated columns was maintained without addition of DDAB in the eluent. The IC system was successfully applied to real seawater samples with recovery rates of 94–108?% for all ions.

On‐site sampling of inorganic contamination on the metal surface and analysis with capillary electrophoresis

Pipes are the primary structural elements used for transporting fluid in various industries. The most common damage mechanism is corrosion, which occurs in pipes surface of turbine. The corrosive compounds for pipes are inorganic ion (Na⁺, Cl^?, NH₄⁺, NO₃^?, etc.) and grinding oil. For rapid and quantitative detection of inorganic ions on site, more reliable and reproducible analytical methods are demanded. A highly efficient solid–liquid sampling collection system is introduced in this work. Papering on the sample surface, inorganic cations and anions were simultaneously collected and analyzed by capillary electrophoresis with indirect ultraviolet detection. As a result, five cations (Na⁺, K⁺, NH₄⁺, Ca²⁺, Mg²⁺) and three anions (Cl^?, NO₃^?, SO₄^2?) were completely separated. The efficiency of the sampling and ability of capillary electrophoresis analysis were presented by the determination of trace‐level (mg/m²) contaminants. The recoveries of cations and anions on the paper from metal surface were between 86.6 and 107.2%, and the relative standard deviations were less than 12.85%.     

Development of Polymeric Resin Ion‐exchanger Based Chloride Ion‐selective Electrode for Monitoring Chloride Ion in Environmental Water

A chloride ion‐selective electrode (ISE) membrane was developed by using a copolymeric ion‐exchanger resin (trimethyl ethenyl quaternary ammonium chloride polystyrene‐divinylbenzene copolymer resin, TMEQAC PSDVB), the ionophore ({μ‐[4,5‐Dimethyl‐3,6‐bis(dodecyloxy)‐1,2‐phenylene]}bis(mercury chloride), ETH9033), the plasticizer (bis(2‐ethylhexyl) sebacate, DOS), and the membrane substrate (polyvinylchloride, PVC). At 25 °C, the electrode exhibited an ideal Nernstian response of 59.2 mV/decade with the linear calibration concentration range from 1.0 × 10^?4‐1.0 × 10^?2 M (r² = 0.9930). The limit of detection was 2.45 ppm (6.9 × 10^?2 mM) and the measurement response time was less than 10 seconds. The working temperature range of electrode was 10‐45 °C. The working pH range for chloride ion measurement was 2.0‐11.0. Among the various anions examined in this work, only I^?, SCN^?, and MnO₄^? ions show significant interference to the electrode measurement. The chloride ISE can be used at least 72 days. The determination of chloride ion content in three kinds of environmental water sample with the electrode method was accurate (92‐95%) and precise (RSD < 4.4%) and did not show significance difference from the high‐performance liquid chromatography method.     

Retention of some glucosinolates in anion exchange chromatography. Part I: Qualitative study on a silica-trialkylammonium exchanger

Summary The retention and separation of glucosinolates, as organic anions, were studied on a silica-based strong anion exchanger under isocratic elution conditions. All glucosinolates carry the same functional ionic group (-OSO ₃ ^– ), however they do not have the same retention in anion exchange chromatography. The plots of capacity factors of organic anions versus the reciprocal of eluent ion concentration show good linearity. From the slope and y-intercept data the major retention mechanisms are interpreted as ion exchange and reversed-phase interactions. The effects of nature and concentration of the eluent ion and the influence of organic modifier addition to the aqueous buffered mobile phase are also investigated. Direct and indirect UV detection were used.Our results open the way for the development of new systems for intact glucosinolate analysis which are easier to use than the present ion-pairing chromatographic method.     

A new chelating resin containing 2-aminothiophenol: Synthesis characterization and determination of mercury in waste water using <Superscript>203</Superscript>Hg radiotracer

A new stable chelating resin was synthesized by incorporating 2-aminothiophenol into Merrifield polymer through C-N covalent bond and characterized by elemental analysis, IR and thermal study. The sorption capacity of the newly formed resin for Hg²⁺ as a function of pH has been studied using ²⁰³Hg radioisotope. The resin exhibits no affinity to alkali or alkaline earth metal ions and common anions. The separation of mercury(II) in presence of different alkali and alkaline earth metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), common anions (ClO₄ ⁻, SO₄ ²⁻) and other diverse ions (Ag⁺, Cu²⁺, Pb²⁺, Fe³⁺, Ni²⁺ and Zn²⁺) has been checked. In column operation it has been observed that Hg²⁺ content of the waste water can be removed at usual pH of natural water. Mercury was determined by isotope dilution method and the concentration of Hg²⁺ in the waste water spiked with ²⁰³Hg was found to be 0.05 to 0.09 μg/ml.     

An improved flow analysis-ion chromatography method for determination of cationic and anionic species at trace levels in Antarctic ice cores

A method was developed for the quantitative determination of cations and anions in Antarctic ice cores at μg L⁻¹ and sub-μg L⁻¹ levels by ion chromatography (IC), after ultra-clean decontamination procedures. Strict manipulation and decontamination procedures were used in sub-sampling, in order to minimise sample contamination. Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ were determined by 12-min isocratic elution (H₂SO₄ eluent). Contemporaneously, in a parallel device, F⁻, MSA (methanesulfonic acid), Cl⁻, NO₃⁻ and SO₄²⁻ were analysed in a single 12-min run with multiple-step elution using Na₂CO₃/NaHCO₃ as eluent. Melted ice samples were pumped from their still-closed containers (polystyrene accuvettes with polyethylene caps), shared between the two ion chromatographic systems, online filtered (0.45 μm Teflon membrane) and pre-concentrated (anions and cations pre-concentration columns) using a flow analysis system, thus avoiding uptake of contaminants from the laboratory atmosphere. Sensitivity, linear range, reproducibility and detection limit were evaluated for each chemical species. Anion or cation detection limits ranged from 0.01 to 0.15 μg L⁻¹ by using a relatively small sample volume (1.5 mL). Such values are significantly lower than those reported in literature for almost all the components. These methods were successfully applied to the analysis of cations and anions at trace levels in the Dome C ice core. The composition of the atmospheric aerosol for the last 850 kyr was reconstructed by high-resolution continuous chemical stratigraphies. Concentration trends in the last nine glacial-interglacial climatic cycles were shown and briefly discussed.     

The Determination of Non-Oxidizable Species Using Electrochemical Detection in Ion Chromatography

Abstract

The use of an electrochemical detector for the ion chromatographic detection of non-oxidizable anions such as F^?, PO₄ ^?3, NO₃ ^?, and SO₄ ^?2 is described. The electrochemical detector is placed in line after a fiber suppressor and responds to eluent pH changes as the dissociated acids pass through the detector. The intensity of the signal is dependent on the applied potential at the cell with 0.3V being an optimum. Minimum detection limits with a 0.10 mL sample injection volume are below 0.5 ppm for F^?, Cl^?, PO₄ ^?3, NO₃ ^?, and SO₄ ^?2. No adverse effects on the silver working electrode have been observed.     

Mixed Beds for Selective Removal of Ammonium Carbonate in Dialysate

We have studied experimentally and theoretically the exchange of NH₄ ⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, and H⁺ ions in zeolite beds, weakly-acidic resin beds, and mixed beds of the zeolite and the resin. The zeolite is highly selective for NH₄ ⁺ and K⁺, whereas the resin with carboxyl functional groups is highly selective for Ca⁺⁺ and Mg⁺⁺. The effluent histories of single exchanger beds can be well predicted by the Multicomponent Chromatography Theory developed by Helfferich and Klein (1970). These histories are mainly the result of ion competition for ion exchanger sites; they can not be adjusted to meet the goal that NH₄ ⁺ ions are removed and simultaneously the pH and concentrations of all the major physiological cations are maintained at normal values. The effluent histories of mixed beds, on the other hand, can be adjusted. We have designed a mixed bed which can meet the goal except that for each equivalent of NH₄ ⁺ removed, 0.3 equivalents of Na⁺ are returned. The effluent histories of K⁺ and NH₄ ⁺ for the mixed beds are similar to those of the zeolite beds, whereas the Ca⁺⁺ and Mg⁺⁺ histories are similar to those of the resin beds.     

Influence of co-ions in the eluent on the separation factor of lithium isotopes

The influence of co-ions in the eluent on the separation factor () of lithium isotope separation has been studied by ion exchange chromatography. A strongly acid cation exchange resin (Dowex 50W-X8) was used for the separation of lithium isotopes. The co-ions used in eluent were H⁺, K⁺, Ba²⁺, Cu²⁺, Al³⁺ and Cr³⁺ as their chlorides. From the experiments, it was found that⁶Li was enriched in the resin phase and⁷Li in solution phase. At the same distribution coefficient (K_d=30), the separation factor increased linearly with the charge of co-ion (=1.0022 to 1.0039).     

Low-voltage thin-layer electrophoresis of inorganic anions on silica gel-G and titanium (IV) tungstate layers: separation of coexisting F−, Cl−, Br− and I−, I−, IO3− and IO4−, Fe(CN)64− and Fe(CN)63−

The electrophoretic behavior of twenty anions has been studied on silica gel-G, titanium (IV) tungstate and silica gel-G- titanium (IV) tungstate admixture layers using 0.1 M solutions of oxalic acid, citric acid, tartaric acid, succinic acid and acetic acid as background electrolyte. The mechanism of migration is explained in terms of adsorption and the solubility of various sodium or potassium salts of the anions in water. Titanium (IV) tungstate behaves only as an adsorbent and not as an ion exchanger. Being a cation exchanger, there is no exchange phenomenon occurring with anions. The migration of halides increase linearly with an increase in the bare ion radii of these ions. Differential migration of the anions on silica gel-G layers led to binary, ternary and quaternary separations of similar anions such as F⁻ – Cl⁻ – Br⁻ – I⁻, I⁻ – IO₃⁻ – IO₄⁻, BrO₃⁻ – IO₃⁻ and Fe(CN)₆³⁻ – Fe(CN)₆⁴⁻. The two cyanoferrate ions are separated from industrial waste water and from fixer and bleach solutions. The migration of anions has also been found to be in accordance with their lyotropic numbers.