Non-suppressed Conductivity Detection Research Articles

Determination of inorganic anions in biological fluids with direct sample injection by electrostatic ion chromatography using zwitterionic micelles in both stationary and mobile phases.

A new ion chromatographic (IC) system, which uses zwitterionic (e.g., Zwittergent 3-14) micelles as both stationary and mobile phases, highly useful for the analysis of inorganic anions in biological samples, was developed. The zwitterionic micellar stationary phase (which is obtained by immobilizing the zwitterionic surfactant on surfaces of the reversed-phase ODS) showed high ability to confine the elution bands of the large amount of SO4(2-) and Cl- to narrow zones. As a result, a base-line separation of NO2-, Br- and NO3- from SO4(2-) and Cl- is always achieved. The zwitterionic micellar mobile phase, (which is obtained by dissolving the zwitterionic surfactant with a suppressive electrolytic solution, e.g., aqueous NaHCO3 solution), on the other hand, showed high ability for rapid elution of proteins. The separation column is therefore always being cleaned up even after the protein-containing sample is directly injected. The zwitterionic micelles are also insensitive to conductivity detection, therefore either the suppressed or the non-suppressed conductivity detection method is applicable for detection of the analyte ions. Urine and serum were chosen as the model real samples and were analysed with direct sample injection; the results of successful determination of a number of inorganic anions (SO4(2-), Cl-, NO2-, Br- and NO3-) in both samples have demonstrated the usefulness of this new IC system.

Determination of sulfur-containing inorganic anions by dual ion chromatography and capillary electrophoresis - application to the characterization of bacterial sulfur degradation

An analytical characterization of microbiological oxidation and reduction of sulfur anions has been performed with dual ion chromatography. The apparatus consisted of two chromatographic lines combined by a sample injection valve that allows the simultaneous introduction of a sample solution to both systems. With system 1 non-suppressed conductivity detection of sulfite and sulfate after separation in phthalate eluent was performed. For sulfide, thiosulfate and thiocyanate amperometric detection using a carbonate eluent was carried out on system 2. Parallel runs were possible for these species which could not be separated with one system. Optimizing separation and detection, limits of quantification of 0.02–0.3 mg/L could be obtained. The on-line coupling of a reaction vial to the injection valve was used to investigate the bacterial conversions, because the samples could be taken without contamination and air introduction. Thiosulfate was detected as a metabolite in both sulfur reduction and oxidation. Capillary electrophoresis with conductivity detection was applied as a complimentary technique for monitoring the bacterial sulfur oxidation. The results showed good correlation to the concentration values obtained by ion chromatography.

Non-suppressed conductivity and indirect UV detection of carboxylic acids in environmental samples by ion-exclusion chromatography using 2,6-pyridinedicarboxylic acidic eluent

2,6-Pyridinedicarboxylic acid (PDCA) was evaluated as an eluent for indirect UV and non-suppressed conductivity detection of carboxylic acids in ion-exclusion chromatography. The effect of PDCA concentration on the separation and detection sensitivity was investigated. The reasonable resolutions between carboxylic acids were achieved using 1 m M PDCA eluent. Detection limits were 1.0–7.0 μ M for conductivity detection and 8–30 μ M for UV detection. Compared to the eluent containing 1 m M sulfuric acid, the method offers a high resolution and high detection sensitivity for both detectors due to its high molar absorptivity and low background conductance. The proposed method was demonstrated to be useful for the determination of carboxylic acids in environmental samples with direct sample injection.

Non-Suppressed Conductivity Detection of Organic Acids in Plant Tissue Extracts by Ion-Exclusion Chromatography with Aromatic Acid Eluents

Aromatic acids were evaluated as eluents for ion exclusion chromatography of organic acids with non-suppressed conductivity detection. The separation of organic acids, performed on an Aminex HPX-87H ion-exclusion column, using a variety of aromatic carboxylic acid eluents, is described in detail. Phthalic acid was found to be a suitable eluent for the separation of the organic acid tested, giving reasonable resolution and detection sensitivity. When 1 mM phthalic acid was used as eluent, an excellent separation of eight acids was achieved in 20 min. Calibration plots for the test acids were linear in the range 10−2 M to 10−5 M with detection limits of the order of 10−6 M Compared to eluent containing sulfuric acid, the proposed method permits a more sensitive detection for the organic acids tested due to the lower background conductance of the eluent used. The proposed method was used for the determination of organic acids in plant tissue extracts with direct injection of sample extract.

TECHNICAL NOTE

In this paper we describe a simple ion chromatographic method for determination of oxalate in urine. Acidified urine was diluted 1:2 with 0.03 mol/l benzidine hydrochloride in 0.3 mol/l boric acid to precipitate sulphate. The supernatant was passed through a C18-cartridge and 100 microliters of eluant were injected into an ion chromatographic system. Oxalate was measured by nonsuppressed conductivity detection. The detection limit for urinary oxalate was 0.05 mmol/l. The recovery for spiked urine samples was 101.5% with a CV of 4.5%. The within- and between-assay coefficients of variation were less than 4.5% and 2.5%, respectively. We found the results obtained by this method to be statistically equivalent to an enzymatic assay and a different ion-chromatographic method.

Anion chromatography on hydroxyethyl methacrylate-based sorbents

The selectivity of sorbents plays an important role in the design of ion chromatographic separations. The selectivity of the hydroxyethylmethacrylate-based sorbent Tessek Separon HEMA-S 1000 Q-L was compared with those of other commonly used sorbents and the role of the eluent charge was investigated. The selectivity of this sorbent was found to be satisfactory for most commonly used ion chromatographic detection modes, including indirect photometry and both suppressed and non-suppressed conductivity detection.