The Ion Chromatographic System

A detailed description of this separation method is given in Chapter 5. 

In addition to the three classical separation methods mentioned above, reversed-phAse liquid chromatography (RPLC) can also be used for the separation of highly polar and ionic species. Long-chain fatty acids, for example, are separated on a chemically bonded octadecyl phase after protonation in the mobile phase with a suitable aqueous buffer solution. This separation mode is known as ion suppression [30]. 

Chemically bonded aminopropyl phases have also been successfully employed for the separation of inorganic ions. Leuenberger et al. [31] described the separation of nitrate and bromide in foods on such a phase using a phosphate buffer solution as the eluent. Separations of this kind are limited in terms of their applicability, because they can be applied only to UV-absorbing species. 

Moreover, applications of multidimensional ion chromatography utilizing mixedmode phases are very interesting. In those separations, ion-exchange and reversed-phase interactions equally contribute to the retention mechanism of ionic and polar species [32,33]. These alternative techniques are also described in Chapter 6. 

A pump delivers the mobile phase through the chromatographic system. In general, dual-piston pumps are employed. A pulse-free flow of the eluent is necessary for employing sensitive conductivity, UV/Vis, and amperometric detectors. Therefore, a sophisticated electronic circuitry (sometimes in combination with pulse dampeners) is used to reduce residual pulsation as much as possible. 

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Agilent G3154A/101 was used for the separation of iodate and iodide. In order to minimize salt deposition on the sampler and skimmer cones of the mass spectrometer, NH4NO3 solution was used as the mobile phase, and a low volume of 10 pi with diluted sample was directly injected into the ion chromatographic system. The linear range was 5.0—500 pg Ch The detection limits were 1.5 pg for iodate and 2.0 pg for iodide. The proposed method was used to determinate iodate and iodide in seawaters without sample pretreatment, except dilution. The chromatogram of iodate and iodide in seawater by nonsuppressed IC with inductively coupled plasma mass spectrometric detection is shown in Figure 1.7. 

Crown ethers can be introduced into the ion chromatographic system via the mobile and/or the stationary phase. Sousa et al [67] used them for the first time as mobile-phase additives describing a separation of amino acid isomers separated with dinaphthal-18-crown-6. But even simple inorganic anions can be separated with this method [68]. However, the number of applicable crown ethers is limited because of their solubilities. Moreover, crown ethers are relatively expensive, so their application at higher concentrations is not justified. 

An ion chromatographic system that included column switching and gradient analysis was used for the deterrnination of cations such as Na", Ca ", Mg ", K", and NH" 4 and anions such as Cf, NO, NO , and in fog water samples (72). Ion-exchange chromatography compares very well with... 

Ion chromatography (see Section 7.4). Conductivity cells can be coupled to ion chromatographic systems to provide a sensitive method for measuring ionic concentrations in the eluate. To achieve this end, special micro-conductivity cells have been developed of a flow-through pattern and placed in a thermostatted enclosure a typical cell may contain a volume of about 1.5 /iL and have a cell constant of approximately 15 cm-1. It is claimed15 that sensitivity is improved by use of a bipolar square-wave pulsed current which reduces polarisation and capacitance effects, and the changes in conductivity caused by the heating effect of the current (see Refs 16, 17). 

The term system peak refers to signals that may not be attributed to solutes. System peaks are characteristic for ion chromatographic systems that have have no suppressor system when weak organic acids are used as the eluent. Despite numerous publications concerning this subject [72-76], system peaks were often the reason of misinterpretations. However, some facts about the thermodynamic and kinetic processes that occur within the separator column may be inferred [77,78] from their occurrence and help in understanding the chromatographic processes. 

Fig. 8-108. Schematic setup of an ion chromatographic system for the analysis of heavy and transition metals in a 50% sodium hydroxide solution.

With the anion detection system on the ion chromatograph and sodium carbonate solutions in various pH ranges as an eluent, an effort was made to distinguish the 0x0 phosphorus acids that existed in a hydrofluoric acid solution of PSG films. The phosphate and phosphite ions were readily detected and quantitated when compared with known standards of these ions, as shown in Figure 6 (a) - (i). 

R. Saari-Nordhaus, I. K. Henderson and J. M. Anderson, Jr., Universal stationary phase for the separation of anions on suppressor-based and single-column ion chromatographic systems,. /. Chromatogr... 546, 89, 1991. 

The sample solutions injected into an ion chromatographic system must be free of particulate matter to avoid plugging of the capillary connecting tubing and the frits at the head of the analytical column. Even samples that appear to be clear may contain unsuspected fine particles. It is more or less standard procedure to filter sample solutions prior to their injection. Disposable membrane filters with a pore diameter of... 

In aqueous chemistry, tellurium is mainly found as telluride (Te- ), tellurite (Te03 ), and tellurate (Te04 ). Zolotov et al. [19] developed an IC procedure for the separation of TeOi, and Te04 by a suppressed ion-chromatographic system. In the method, F interfered with the determination of TeO., while S04 " interfered with the determination of Te04. In a report by Chen et al. [20], a similar method was used to speciate tellurium. The detection limits for Te04 were very poor in both methods. The studies were confined only to standard solutions. 

Overall, AEC is a well-developed separation technique which is widely applied for organic acid analysis. Some of the current trends include the implementation of eluent generators " development of and increased accessibility to ion chromatograph/MS systems which are now commercially available " miniamrization of complete ion chromatographic systems and the development of monolithic columns which have been used for fast analysis of inorganic... 

To analyse qualitatively and quantitatively the inorganic anion contaminants in aqueous samples using an ion chromatograph system fitted with a suppressor column and conductivity cell. 

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