Simultaneous Determination of Anions and Cations

Ohta et al. [13] also separated mixtures of Ci and Cy aliphatic carboxylic acids on an unfunctionalized polyacrylate gel column. A 1.0 mM concentration of a Cg carboxylic acid (2methylheptanoic acid) was added to an acidic aqueous eluent to give lower retention times and sharper peaks for the analytes. Although a mixture of twelve carboxylic acids was well separated, a single run required about 40 min. 

Stationary phases containing carboxylic acid functional groups are now frequently used for I EC instead of strong-acid sulfonated resins. The carboxylic acid particles are often a polymethacrylate gel. These materials have found extensive use for the analysis of low concentrations of both cations and anions in acid rain. Acid rain caused by SO2 and NOx in air is a major environmental pollution problem in many parts of the world. The major cationic components of acid rain are Na, NH4, K, Mg and Ca, and the major anionic components are cr, NOg and SO4 . The ionic balance between the total positive charge and negative charge of 

Conductivity detection. Peaks (1) S04 , (From Ref. [14] with permission.) 

Tartaric acid and sulfosalicylic acid eluents, which are acids of low pK, were suitable for rapid separation of strong-acid anions and of cations, but the high background conductivity level gave poor detector response for weak-acid anions. When propionic acid (pK = 4.66) was used as the eluent, resolution of weak-acid anions was improved, but retention times for and Mg were very long. With a succinic acid eluent (pK = 4.00), all analyte ions were well resolved, as shown in 

Several effects, in addition to liquid partition, may attract analytes to the stationary phase  

---

Kwon, S.-M., Lee, K.-P., Tanaka, K., and Ohta, K., Simultaneous determination of anions and cations by ion-exclusion chromatography-cation-exchange chromatography with tartaric acid/18-crown-6 as eluent, /. Chromatogr. A, 850, 79, 1999. 

Classification of methods for simultaneous determination of anions and cations by IC... 

There are still only a few published applications of sorbents with covalently bonded zwitterionic molecules for simultaneous determination of anions and cations. This is related to the difficulties... 

Ikedo, M., Mori, M., Xu, Q., Taoda, H., Sato, S., Hu, W., and Tanaka, K. (2003) Simultaneous Determination of Anions and Cations in Raw Material of Ceramic Glaze by Ion-exclusion/cation-exchange Chromatography with a Weakly Acidic Cation-exchange Resin, Bunseki Kagaku 52, 1173-1180. 

S.-J. Chen, M.-J. Chen and H.-T. Chang, Light-emitting diode-based indirect fluorescence detection for simultaneous determination of anions and cations in capillary electrophoresis, J. Chwmatogr. A, 1017, 215-224, 2003. 

Strohl, G. W., Simultaneous determination of anionic and cationic surfactants in wastewater (in German), Tenside, Surfactants, Deterg., 1969, 6,78-79. 

Frenzel, W., Schepers, D., and Schulze, G., Simultaneous ion chromatographic determination of anions and cations by series conductivity and flame photometric detection, Anal. Chim. Acta, 277, 103, 1993. 

Ion chromatographic methods have been described for the co-determination of anions and cations in rainwater. Thus Jones and Tarter [138], using the conditions given in Table 2.19 reported determinations down to lmg L 1 of anions (chloride, bromide and sulphate) and cations (sodium, potassium, magnesium and calcium) in rainwater without converting the cations to anion complexes prior to detection [139], The technique uses a cation separator column, a conductivity detector, an anion suppressor column, and either a second conductivity detector or an electrochemical detector in sequence. The use of different eluants provides a means for the detection of monovalent cations and anions and divalent cations and anions in each of the samples. Using an eluant with a basic pH, it is possible to separate simultaneously and detect the monovalent cations (with the exception of the ammonium ion) and anions, while an eluant with an acidic pH allows for the separation and detection of divalent cations and anions. 

S. Matsushita, Simultaneous determination of anions and metal cations by single-tx)lumn ion chromatography with ethylenediaminetclraacctate as eluent and conductivity and ultraviolet detection,/. Chromaiogr.. 312,327,1984. 

Capillary electrophoresis Capillary electrophoresis (CE) is used to analyze sodium, potassium, calcium, and magnesium in water samples. The detection is conducted by reverse absorbance measurements. Sufficient separation of the four cations is established with an electrolyte solution of 5 mM imidazole/6.5 mM a-hydroxyisobutyric acid/2 mM 18-crown-6 ether of pEI 4.1 [42]. CE with a contactless conductometric detector is used to determine small anions and cations in water samples from different sources. 2-(N-Morpholino)ethanesulfonic acid/histidine-based (Mes/Elis) electrolytes are used for direct conductivity detection of anions and cations, while ammonium acetate is used for indirect conductivity determination of alkylammonium salts. Eor the simultaneous separation procedure, involving dual-opposite end injection, an electrolyte consisting of 20 mM Mes/EIis, 1.5 mM 18-crown-6 and 20 mM cetyltri-methylammonium bromide provides baseline separation of 13 anions and cations in less than 6 min [43]. Also CE with a capacitively coupled... 

However, ion chromatography has an advantage over spectroscopic techniques for cation analysis in the area of metal speciation. Moreover, ion chromatography is particularly beneficial for the simultaneous determination of cations and ammonia in wastewater containing amines. Examples of anion and cation chromatograms are given in Figs. 1 and 2, respectively. 

Markowska, A. Stepnowski, P. (2008). Simultaneous determination of ionic liquid cations and anions using ion chromatography with tandem ion exchange columns a preliminary assessment. Analytical Sciences, 24 (No.l0) 1359-1361. 

In the case of lithium fluoride the ratio R i /Rj>- is 0.44. In this crystal there is double repulsion the repulsive forces between anion and anion and those between anion and cation are simultaneously operative. The inter-atomic distances are determined neither by the sum of the radii for the anion and cation nor by the radius of the anion alone, but are larger than those calculated by either method. Thus the lithium-fluoride distance is 0.05 A. (2.5%) larger than the sum of the radii, and one-half the fluorine-fluorine distance is 0.06 A. larger than the fluoride radius. 

Simultaneous determination of both cations and anions in acid rain has been achieved using a portable conductimetric ion-exclusion cation-exchange chromatographic analyzer.14 This system utilized the poly(meth-ylmethacrylate)-based weak acid cation exchange resin TSK-Gel OA-PAK-A, (Tosoh , Tokyo, Japan) with an eluent of tartaric acid-methanol-water. All of the desired species, 3 anions and 5 cations, were separated in less than 30 minutes detection limits were on the order of 10 ppb. Simultaneous determination of nitrate, phosphate, and ammonium ions in wastewater has been reported utilizing isocratic IEC followed by sequential flow injection analysis.9 The ammonium cations were detected by colorimetry, while the anions were measured by conductivity. These determinations could be done with a single injection and the run time was under 9 minutes. 

Instruments are offered in the market for clinical determination of electrolytes in blood, plasma or serum. One of them, for example, carries out simultaneous determinations of Na, K, Ca, Mg, hematocrit and pH. The cations are of the free type (see Section m.A) and are measured with specific ion-selective electrodes. In complex matrices such as blood or its derived fractions the concentration of free Ca and Mg is affected by the pH of the solution, for example, a slight change of pH will produce or neutralize anionic sites in the proteins, binding or releasing these cations furthermore, the response of the Mg-selective electrode is also affected by the concentration of free Ca(II). The correction... 

Several papers have reported use of a weak acid/crown ether eluent in ion-exclusion/cation exchange chromatography with conductimetric detection on a weakly acidic cation-exchange column to effect the simultaneous determination of both cations and anions. Resolution was significantly improved when 18-crown-6 was present in the eluent. Detector response was positive for anions and negative for cations. [76-80] A sample chromatogram is shown in Figure 9. 

Jones and Tarter [11] have applied this technique to the simultaneous determination of metals (sodium, potassium, calcium, magnesium) and anions (chloride, sulphate, nitrate, bromide) in potable waters. The technique uses a cation separator column, a conductivity detector, an anion separator column and an anion suppressor column. Two different eluants were used lithium carbonate-lithium acetate dihydrate, and copper phthalate. 

---