Suppressed conductivity

Figure 3 Gradient separation of anions using suppressed conductivity detection. Column 0.4 x 15 cm AS5A, 5 p latex-coated resin (Dionex). Eluent 750 pM NaOH, 0-5 min., then to 85 mM NaOH in 30 min. Flow 1 ml/min. 1 fluoride, 2 a-hydrox-ybutyrate, 3 acetate, 4 glycolate, 5 butyrate, 6 gluconate, 7 a-hydroxyvalerate, 8 formate, 9 valerate, 10 pyruvate, 11 monochloroacetate, 12 bromate, 13 chloride, 14 galacturonate, 15 nitrite, 16 glucuronate, 17 dichloroacetate, 18 trifluoroacetate, 19 phosphite, 20 selenite, 21 bromide, 22 nitrate, 23 sulfate, 24 oxalate, 25 selenate, 26 a-ketoglutarate, 27 fumarate, 28 phthalate, 29 oxalacetate, 30 phosphate, 31 arsenate, 32 chromate, 33 citrate, 34 isocitrate, 35 ds-aconitate, 36 trans-aconitate. (Reproduced with permission of Elsevier Science from Rocklin, R. D., Pohl, C. A., and Schibler, J. A., /. Chromatogr., 411, 107, 1987.)...

Figure 10 Separation of monochloroacetate, dichloroacetate, and trichloroacetate on a sulfonated poly(styrene-divinyl benzene) column with suppressed conductivity detection. Column 2% cross-linked sulfonated poly(styrene-divinyl benzene) capacity 0.02 meq/g. Flow rate 64 ml/hr. Eluant 15 mM sodium phenate. Suppressor 0.28 x 25 cm Dowex 50W X8 column (200-400 mesh). Detector Chromatronix conductivity cell connected to a Dow conductivity meter. (Reprinted with permission from Small, H., Stevens, T. S., and Bauman, W. C., Anal. Chem., 47,1801,1975. 1975 Analytical Chemistry.)...

Anions of weak acids can be problematic for detection in suppressed IEC because weak ionization results in low conductivity and poor sensitivity. Converting such acids back to the sodium salt form may overcome this limitation. Caliamanis et al. have described the use of a second micromembrane suppressor to do this, and have applied the approach to the boric acid/sodium borate system, using sodium salt solutions of EDTA.88 Varying the pH and EDTA concentration allowed optimal detection. Another approach for analysis of weak acids is indirect suppressed conductivity IEC, which chemically separates high- and low-conductance analytes. This technique has potential for detection of weak mono- and dianions as well as amino acids.89 As an alternative to conductivity detection, ultraviolet and fluorescence derivatization reagents have been explored 90 this approach offers a means of enhancing sensitivity (typically into the low femtomoles range) as well as selectivity. 

Nowak, M. and Seubert, A., Application of experimental design for the characterization of a novel elution system for high capacity anion chromatography with suppressed conductivity detection, /. Chromatogr. A, 855, 91,1999. 

Many IC techniques are now available using single column or dual-column systems with various detection modes. Detection methods in IC are subdivided as follows [838] (i) electrochemical (conductometry, amper-ometry or potentiometry) (ii) spectroscopic (tJV/VIS, RI, AAS, AES, ICP) (iii) mass spectrometric and (iv) postcolumn reaction detection (AFS, CL). The mainstay of routine IC is still the nonspecific conductometric detector. A significant disadvantage of suppressed conductivity detection is the fact that weak to very weak acid anions (e.g. silicate, cyanide) yield poor sensitivity. IC combined with potentiometric detection techniques using ISEs allows quantification of selected analytes even in complex matrices. The main drawback... 

High-sensitivity detection of non-chromophoric organic ions can be achieved by combining the power of suppressed conductivity detection with these columns. Suppressed conductivity is usually a superior approach to using refractive index or low UV wavelength detection. 

Although AS and AES can be detected at a low UV wavelength, sensitivity is lacking and a more suitable detection was achieved using indirect photometric detection, post-column colour formation reactions, or a pre-column derivatisation, suppressed conductivity detection and refractive index detection [1,42,43]. A comparison of detection limits for the determination of these anionic surfactants shows that photometric and conductivity detectors are better (picomole or nanogram range) than refractive index or fluorometry detectors by about a factor of 1000 [40],... 

Ion chromatography has become an essential tool of the pharmaceutical analytical chemist. The high sensitivity of the technique, coupled with the wide dynamic operating range made possible with modern high-capacity stationary phases makes it ideal for the analysis of ions in pharmaceutical applications. The combination of gradients and suppressed conductivity detection provides a powerful screening... 

FIGURE 6 Effect of p-cyanophenol on the separation of perchlorate. Column 4x250mm lonPac ASII. Flow rate I.OmLmin. Injection volume 25pL. Detection suppressed conductivity utilizing the Anion Self Regenerating Suppressor (4mm), recycle mode. Ion I—perchlorate (20mgL" ). (a) Eluent lOOmM NaOH. (b) Eluent 50 mM NaOH and 5mM p-cyanophenol. 

For ions that are UV transparent, detection is possible through the use of indirect detection. A wide variety of different eluent systems have been described in the literature. Eluents commonly used for indirect UV detection are similar to those used in non-suppressed conductivity detection phthalate and p-hydroxybenzoic acid along with other... 

FIGURE 19 Choline in infant formula. Columns 4x250mm lonPac CSI2A, and 4x50mm CGI2A. Flow rate I mLmin. Eluent l8mM MSA. Injection volume lOpL. Detection suppressed conductivity, CSRS (4 mm), recycle mode. Ions I— sodium 2—ammonium 3—choline 4—potassium 5—magnesium 6—calcium. Sample preparation add 30 mL of I M HCI to 5 g sample, mix well, place in 70°C water bath for 3 h, cool, filter and dilute to 100 mL. 

Determination of Perchlorate in Drinking Water by Ion Chromatography with Suppressed Conductivity and... 

Bromate has also been measured using 1C with conductivity detection. For example, EPA Method 302.0 uses two-dimensional 1C with suppressed conductivity detection to measure bromate at 0.12 pg/L detection limits [166]. Bromate, chlorite, and chlorate can also be measured by an earlier EPA Method (Method 300.1), which uses 1C with conductivity detection [167]. Method detection limits ranging from 0.45 to 1.28 pg/L can be achieved. 

Wagner P, Pepich BV, Pohl C, Srinivasan K, De Borba B, Lin R, Munch DJ (2009) EPA Method 302.0. Determination of bromate in drinking water using two-dimensional ion chromatography with suppressed conductivity detection. U.S. EPA, Cincinnati, OH, Available at http //water.epa.gOv/scitech/drinkingwaterAabcert/upload/met302 0.pdf... 

Ion chromatography is a convenient method for simultaneous determination of alkali, alkaline earth and ammonium ion concentrations in solution. The identity of the analytes is set by the retention times and quantation is carried out by a detector. Conductivity is frequently used, after chemical suppression of the eluate, by which chloride counterions were exchanged by hydroxide. UVV spectrophotometric measurement of hydroxide ions at 200 nm was proposed as an alternative method to suppressed conductivity. Both methods... 

FIGURE 14.2 Separation of ammonium, alkali, and alkaline earth metals on lonPac CSl. Detection suppressed conductivity. Eluent (a) 5mM HCl (b) 2mM HCl, 2mM m-phenylenediamine dihydrochloride. 

FIGURE 14.3 Isocratic separation of morpholine, alkali, and alkaline earth metals on lonPac CS12A column. Eluent lOmM sulfuric acid. Detection suppressed conductivity. Peaks 1, lithium (0.5mg/L) 2, sodium (2mg/L) 3, ammonium (2.5mg/L) 4, potassium (5mg/L) 5, morpholine (25mg/L) 6, magnesium (2.5mg/L) 7, calcium (5mg/L). (From Rey, M.A. and Pohl, C.A., J. Chromatogr. A, 739, 87, 1996. Copyright 1996. With permission from Elsevier.)... 

Non-suppressed conductivity detection furnishes a signal that is the sum of the conductance of the analyte ion, its co-ion, and the decrease in the eluent counterion that remains on the column... 

The direct mode is employed with eluents with significantly lower equivalent conductance than the analyte ion. Increase in sensitivity is obtained as the degree of the ionization of the eluent decreases, that is, with more weakly dissociated eluents, and non suppressed conductivity methods have been extensively developed using benzoate, phthalate [246], oxalate [53] or other partially ionized species as mobile phases. A key factor in the success of this technique is the use of an ion exchanger of low-exchange capacity, which in turn permits the use of a very dilute eluent. 

Suppressed conductivity detection is the most common mode of detection and differs from the previous approach for the use of an additional device, called suppressor, whose function is to reduce the background conductivity of the eluent prior to the conductivity cell and to increase the signal of the analyte. 

Avicel RC and CL are water-dispersible, colloidal, microcrystalline cellulose products made for use in liquid preparations. Avicel RC and CL are coprocessed mixtures of microcrystalline cellulose and sodium carboxymethylcellulose. The amount of NaCMC can be determined using the IC method. About 10 g of Nasonex and about 25 mg of NaCMC NF are separately refluxed with 30 mL of glacial acetic acid for 2 h. The refluxed mixture is transferred to a 100-mL volumetric flask and diluted to volume with purified water, and mixed. The ion chromatograph (IC) was equipped with a suppressed conductivity detector, a 4-mm CSRS suppressor, current at 50 mA, a 250 mm x 4-mm Ion CS 12A column and a 50 mm x 4 mm Ion CG 12A guard column. The mobile phase is 0.13% methanesulfonic acid in water with a flow rate of 1 mL/min. Equal... 

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