Suppressor electrolyte

To minimize the mobile phase s contribution to conductivity, an ion-suppressor column is placed between the analytical column and the detector. This column selectively removes mobile-phase electrolyte ions without removing solute ions, for example, in cation ion-exchange chromatography using a dilute solution of HCl as... 

In IC this problem of electrolyte background is overcome by means of eluant suppression. Thus in the above example of sodium and potassium analysis, if the effluent from the separating column is passed through a strong base anion exchange resin in the hydroxide form (suppressor column) the following two processes occur ... 

Pipette lOmL of a cadmium sulphate solution (1.0gCd2+ L-1) into a 100 mL graduated flask, add 2,5 mL of 0.2 per cent gelatin solution, 50 mL of 2 M potassium chloride solution and dilute to the mark. The resulting solution (A) will contain 0.100gCd2+ L-1 in a base solution (supporting electrolyte) of 1 M potassium chloride with 0.005 per cent gelatin solution as suppressor. 

Method of standard addition. The polarogram of the unknown solution will have been determined under (1). A new polarogram must now be recorded after the addition of a known volume of a standard solution containing the same ion, care being taken that in the resulting solution the concentrations of the supporting electrolyte and the suppressor are maintained constant. 

The only method that has been described for the assay of technical grades of parathion and its formulations is that of Bowen and Edwards (7). The method makes use of the polarograph. The electrolysis is carried out in an acetone-water solution with potassium chloride as the electrolyte and gelatin as the suppressor. An accuracy of 1% is obtained. 

The use of suppressors in ion chromatography of quaternary ammonium compounds can be of advantage. These are ion exchange membranes that introduce hydroxide ions instead of the counterion present in the analyte. This simplifies the mixture and enhances the electrolytic conductivity of the sample. The effluent of the suppressor may be nebulized and subjected to field-assisted evaporation, yielding a cloud of ions suspended in the gas phase, which can be introduced into an MS analyzer designed for work at atmospheric pressure. Both the molecular weight and the structure of the quaternary cations can be determined by this method419. 

Figure 6.11 Polarogratn of a solution containing three analytes, showing three different waves . The half-wave potential, 1/2, for each is characteristic of the respective analyte couples, while the wave heights reflect the relative concentrations of each ion. The trace has been smoothed to remove the sawtoothed effects seen in Figures 6.7 and 6.8. The solution also contained KCl (0.1 mol dm ) as a swamping ionic electrolyte, and Triton X-lOO (a non-ionic surfactant) as a current maximum suppressor.

This chapter reviews the underlying principles of ion chromatography and its application in pharmaceutical analysis. It provides an overview of eluent systems, applications of gradients, electrolytic eluent generation, suppressors, and stationary phases. Applications of ion chromatography to the confirmation of counter ions, active ingredient analysis, competitive analysis and development work are discussed. 

DS-Plus Alltech Yes Yes Moderate Electrolytic Anion Suppressor module... 

Bhatt et al. have described a method based on the complex formation between chlorpromazine and K3Fe(CN)5 [151]. The latter substance yielded a reduction wave at zero applied potential, and addition of chlorpromazine decreased the wave height in an amount directly proportional to the amount added. Optimum conditions for the determination were reported to be pH 7.4-6.2, use of 0.1 M KCl as the supporting electrolyte, and 0.001% methyl red solution as the maximum suppressor. In this system, chlorpromazine can be determined up to concentrations of 1.4 pg/mL. 

The detection cell placed at the end of the column has a very small volume (ca. 2 pi). In order to increase the sensitivity of this detection method, a device neutralising the ions present in the electrolyte is placed between the column and the detector. This device, called the suppressor, was initially commercialised in 1975. 

Fibre or micromembrane suppressors of high ionic capacity have now taken over from chemical suppressors. With dead volumes in the order of 50 pi, they allow gradient elution with negligible drift in the baseline. Figure 4.8a shows the passage of an anion A- in solution in a typical electrolyte used for anionic columns through a membrane suppressor. 

The suppressors in Figure 26-4 also have been replaced by electrolytic units that generate H or OH- necessary to neutralize the eluate and require only H20 as feedstock.6 With electrolytic eluent generation and electrolytic suppression, ion chromatography has been simplified and highly automated. Readily available software can be used to simulate and optimize ion chromatographic separations.7... 

A variable quantity of ZnO is added to the concentrated KOH solution, depending on the system characteristics required. ZnO can also act as a gassing suppressor. The electrolyte is immobilized generally using carboxy-methylcellulose, and a non-woven fabric separator made of natural or synthetic fibres resistant to the high pH is placed between the electrodes. 

We wish only to remind readers that there are three main methods of electrochemical re-vealment conductivity, direct current (d.c.) amperometry, and integrated amperometry (pulsed amperometry is a form of integrated amperometry). In revealment by conductivity, the analytes, in ionic form, move under the effect of an electric field created inside the cell. The conductivity of the solution is proportional to the mobility of the ions in solution. Since the mobile phase is itself an electrolytical solution, in order to increase the signal/noise ratio and the response of the detector, it is very useful to have access to an ion suppressor before the revealment cell. By means of ionic exchange membranes, the suppressor replaces the counterions respectively with H+ or OH , allowing only an aqueous solution of the analytes under analysis to flow into the detector. 

Fig. 5. An analysis of a coarse atmospheric aerosol extract by CE and IC [49]. CE conditions a 57 cmX75 xm I.D. capillary, distance to detector, 50 cm. Electrolyte 2.25 mM PMA (pyromel-litic acid), 0.75 mM HMOH (hexamethonium hydroxide), 6.50 mM NaOH and 1.60 mM TEA (triethanolamine), pH 7.7 or 2.0 mM NDC (2,6-naphthalenedicarboxylic acid), 0.5 mM TTAB (tetradecyltrimethylammonium bromide) and 5.0 mM NaOH, pH 10.9 30 kV (PMA) or 20 kV (NDC) pressure injection for 10 s indirect UV detection at 254 nm (PMA) or 280 nm (NDC). IC conditions an IonPac-ASlO column with an IonPac-AGlO guard precolumn conductivity detection using an anion self-regenerating suppressor (ASRS-I) in the recycle mode. Analytes 2, chloride 3, sulfate 5, nitrate 6, oxalate 7, formate 10, hydrocarbonate or carbonate 11, acetate 12, propionate 14, benzoate.

In Fig. 2, the columns were IonPac ICE-AS6 (250X9-mm i.d.), AG9-HC (concentrator, 50X4-mm i.d.) and AG9-HC/AS9-HC (analytical, 250X2-mm i.d.). The ion exclusion sample treatment eluent was deionized water and the flow rate was 0.55 ml/min. The sample volume was 750 pi. The ion exchange eluent was 8.0 mM sodium carbonate and 1.5 mAf sodium hydroxide. The flow rate on the 2-mm analytical column was 0.25 ml/ min. Detection was by suppressed conductivity using the ASRS -I electrolytically regenerated suppressor in the external water mode. 

This column describes the composition of the supporting electrolyte. Concentrations are given In moles per liter wherever possible the entry "KOH 0.1" denotes 0.1 F potassium hydroxide. BrItton-RobInson, Mcllvaine, and other buffers, both mixed and simple, are identified by means of abbreviations. The entry "buffer" means that the solution was said to be buffered at the pH quoted in Column 9 but that no Information was given about the composition of the buffer employed. Maximum suppressors are identified In this column and their concentrations are given in weight/volume per cent. 

Two types of ion chromatography are currently in use suppressor-based and single-column. They differ in the method used to prevent the conductivity of the eluting electrolyte from interfering with the measurement of analyte conductivities. 

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