Non-Suppressed-Conductivity Detection

Figure 5.5 Separation of various mono- and dicarboxylic acids on Metrosep organic acids. Eluent 05 mmol/L sulfuric acid/acetone (90 10 v/v) flow rate 05 mL/min detection non-suppressed conductivity injection volume ...

Fig. 9-9. Cation analysis of a rain water sample. - Separator column Metrosep Cation 1-2 eluant 4 mmol/L tartaric acid + 1 mmol/L pyridine-2,6-dicarboxylic acid flow rate 1 mL/min detection non-suppressed conductivity injection volume 10 pL solute concentrations 0.07 mg/L sodium (1), 0.26 mg/L ammonium (2), 0.32 mg/L potassium (3),...

Fig. 9-105. Analysis of organic acids in a zinc bath. - Separator column Metrosep Organic Acids eluant 0.5 mmol/L H2SO4 — aceton (85 15 v/v) flow rate 0.5 mL/min detection non-suppressed conductivity injection 100 pL...

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... 

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... 

Although a very large number of organic anions may be separated by ion chromatography, non-suppressed conductance is not always a viable detection method. Anions of small organic acids can usually be detected but the conductivity of more... 

The data in Table 6.11 indicate that suppressed conductivity methods will give better sensitivity and lower detection limits than non-suppressed. In fact, use of a hydroxide eluent will give even better sensitivity than the carbonate-bicarbonate eluent listed in the table. Figure 6.12 shows a separation of 1 ppm each of seven common anions with non-suppressed conductivity detection. A separation on the same column with a different eluent and suppressed conductivity detection shows significantly higher peaks for the same anion concentration (Fig. 6.13). 

Detection limits depend on several factors in addition to the conductivity system used. These include the sample volume, the goodness of temperature control and the inherent sensitivity of the conductivity detector used. With a direct injection of a 50 iL sample, the detection limits for chloride, nitrate and sulfate in drinking water have been estimated to be around 10 ppb using suppressed conductivity [15], With the same volume of sample the detection limits using non-suppressed conductivity are probably around 100 to 200 ppb. However, considerably lower limits of detection are possible with non-suppressed conductivity of a carboxylic acid eluent is used. Table 6.12 gives detection limits for a 100 pL water sample. 

Riviello et al. made a careful comparison of conductivity changes in cation chromatography between direct- and suppressed conductivity detection [7]. The calculation example is outlined in Fig. 7.5. The change in conductivity, AG, is actually slightly greater with non-suppressed conductivity. Flowever, the noise is much higher in the non-suppressed detection mode. Noise may be defined as the random signal that... 

The equivalent conductances of the aromatic bases listed in Table 7.2 are low enough for non-suppressed conductivity detection. However, the detection limits are generally lower with indirect UV detection and the resolution is often better also. In Fig. 7.8 chromatograms of the alkali metal cations are compared with direct conductivity and indirect UV absorption detection. With the aromatic base eluents Li elutes... 

Suppressed and non-suppressed conductivity methods of detection have a number of things in common. The things in common include the fact that in both cases electric conductivity of the analytes is measured. On the other hand, the most apparent difference is that one method uses a suppressor system while the other does not. 

WMle non-suppressed and suppressed conductivity detection modes are suitable for detection of alkali and alkaline earth metals, for detection of other metal ions only non-suppressed conductivity detection can be used, because these metals would mostly be transferred by the suppressor reaction into insoluble hydroxides. Thus, spec-trometric detection after suitable post- or precolumn deri-vatization is usually carried out. ... 

The major limitation of non-suppressed conductivity detection is that gradient systems cannot be used thus, the background conductivity remains constant. 

Either suppressed- or non-suppressed-conductivity detection is generally satisfactory for these separations. However, under carefully controlled conditions, indirect spectrophotometric detection may sometimes be used to advantage. Haddad... 

A separation of eleven cations with indirect non-suppressed-conductivity detection is illustrated in Figure 7.18. The mobile phase contained both a strong acid (MSA) and oxalic acid as a complexing reagent [16]. The peaks actually denote decreasing conductivity. 

Ca ", Sr, Ba, Mg. In the absence of a complexing mobile phase, magnesium would elute before the alkaUne earth cations. The sample cations are detected with reasonable sensitivity by non-suppressed conductivity. 

Dionex Corporation (2004) Dionex Application Note No. 157 Comparison of Suppressed to Non-Suppressed Conductivity Detection for the Determination of Common Inorganic Cations. Dionex Corporation (now part of Thermo Fisher Scientific), Sunnyvale, CA, USA. 

Only a small modification of the concentration ratio between carbonate and bicarbonate, leading to a change in pH, is necessary to analyze oxy non-metal anions and common mineral acids in a single chromatographic run. However, an exception is arsenic(III) in the form of ortho- or metaarsenite. In analogy to cyanide, it cannot be detected via suppressed conductivity detection, because... 

The latter is a urea derivative in which the three NH2 groups are positioned symmetrically and equidistantly to the central C-atom. Both cations may be detected by either suppressed or non-suppressed conductivity this is shown in Fig. 4-43. 

Transition Metal Analysis with Non-Suppressed Conductivity Detection... 

Finally, note the class of N, N -substituted hydrazinium salts, which may also be investigated by ion-pair chromatography. These compounds do not carry chro-mophores, thus, a sensitive detection is only possible via suppressed or non-suppressed conductivity detection. As an illustration for the great number of compounds that have already been investigated. Fig. 6-53 displays the chromatograms of two compounds that have the following structures ... 

Fig. 7-3. S imulated comparison of the detectability of sodium and potassium with the two application forms of conductometric detection at a solute ion concentration of 0.1 mg/L. - (A) non-suppressed conductivity detection, (B) suppressed conductivity detection. Chromatographic conditions see text (taken from [10]).

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