Capillary Suppressors

Chromatography by ion exchange on a sulfonated poly(styrene-co-divinyl benzene) phase has been proposed as a replacement for titrimetry.57 Eluted by a dilute solution of a neutral salt such as sodium ethanesulfonate, the conductance of the protons can be measured in the absence of a suppressor from sub-millimolar to molar concentration. The response factors of mono-, di-, and trichloroacetic acid and of o-phthalic acid were large and essentially equivalent to ethanesulfonic acid, while the response factor of acetic acid was far smaller. A syringe pump has generated pressures as high as 72,000 psi (5000 bar) in a capillary column packed with 1 p particles, generating a fraction capacity of 300 peaks in 30 minutes.58... 

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.

Ion chromatography can be used to measure ionic concentrations in solution. It requires a fairly large amount of solvent and usually a suppressor column to neutralize the acidity prior to detection by conductivity. For analytical purposes, most analyses previously performed by ion chromatography are now performed using capillary electrophoresis. However, Katagi et al. used ion chromatography with indirect photometric detection to analyze for nerve agents and hydrolysis products in human serum (8). 

Loss of heterozygosity (LOH) results from a deletion of small or large chromosomal regions and often correlates with the loss of important tumor suppressor genes located in these areas. LOH is typically detected by FISH or by PCR amplification of microsatellite loci followed by capillary gel electrophoresis. 

For suppressed conductivity detection, the end of the separation column is connected to a tubular ion exchange membrane suppressor surrounded by a reservoir of regenerant solution [512,513]. The electrodes for conductivity detection are located in a separate capillary downstream of the suppressor. The high voltage electrode for the separation is located in the regenerant reservoir. In this way, the detector is decoupled from the electric field for the separation, and the electroosmotic flow generated in the separation column is used to drive the electrolyte solution through the suppressor and detector. The function of the suppressor (see section 5.7.4.1) is to neutralize electrolyte solution ions. 

The use of branched uptake capillaries, coimected to the nebulizer using a T-piece, may be advantageous when a buffer or ionization suppressor is required. In addition to avoiding time-consuming solution preparation, it is also possible to calibrate organic extracts using aqueous standards in this way. The approach may also be extended to couple more complex flow injection systems employing novel chemistries in the same way. 

Although capillary suppressors are electrolytically operated, the resulting background noise is not much different from that of a chemically regenerated micromembrane suppressor. 

Two basic modes of suppression can be performed with the CCES 300 capillary suppressor ... 

Dasgupta et al. [22] as well as Avdalovic et al. [23] independently succeeded to miniaturize a conductivity cell and a suppressor device down to the scale required for CE. Since the sensitivity of conductivity detection does not suffer from miniaturization, detection limits achieved for totally dissociated anions and low molecular weight organics compete well with those of ion chromatography techniques. Thus, capillary elechophoresis with suppressed conductivity detection can be regarded as a complementary technique for analyzing small ions in simple and complex matrices. 

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