Ion chromatography (IC) has been widely used with conductivity detection. Conductivity detection is semi-selective to the ionic solutes. The response of conductivity detection depends on limiting equivalent ionic conductances, which are different for various kinds of ions. Most of the analytical instruments, including IC, required a calibration procedure with an analyte standard. The accuracy of the results depends on the quality, stability and purity of the standard. The universal detection, which is the way to quantify without an analyte standard, is an ideal way on the chemical analysis because it can achieve the quantification of unavailable compounds and decrease the labor for preparing the standard especially for multiple quantifications on chromatography. In IC, many kinds of method for universal detection have been reported. Most of these are based on ion exchange. Ions are the chemical form which has a electrical charge. Ions can be exchanged to the other kinds of ions while keeping charge balances. This phenomena is important in universal detection with an indirect photometry, and replacement IC. Furthermore, direct universal detection has been achieved by the detection of charged aerosol, ionic charge, and carbon amounts on organic compounds. In the present review, these universal detection methods are introduced.

Ion chromatography (IC) has been popularized as a testing method of inorganic ions in water samples, especially environmental water, drinking water, industrial water and factory drainage. For the determination of trace ions in a sample containing a high concentration matrix, it will often be difficult to ensure quantitative accuracy because of the interferences based on the large matrices. Therefore, to solve such problems, the elimination or reduction of the matrices by some kind of sample pretreatment methods is indispensable. However, serious contamination might be caused during sample pretreatment operations using a cumbersome manual pretreatment technique because the targeted ions in the measurement would exist in the measurement environment. In this study, inline sample preparation methods for ion analyses were studied. Inline sample pretreatment – IC systems combined with neutralization, dialysis and adsorption/removal devices were constructed. The applicability and quantitative accuracy of the proposed methods were evaluated using several actual samples, such as environmental waters, foods, reagents and organic solvents. Using the proposed methods, the trace inorganic ions in actual samples could be accurately quantified without influences based on large matrices in the samples. The proposed inline sample preparation methods will be not only on an improvement of the quantitative accuracy by the elimination of matrices and the reduction of the sample contaminations, but also valuable techniques for automation and labor saving on the ion analyses.

A quantification method for aminomethylphosphonic acid (AMPA), glufosinate (GLUF) and glyphosate (GLYP) as herbicides by ion chromatography coupled with integrated pulsed amperometric detection (IPAD) has been examined. The detection condition of IPAD and the separation conditions for the three herbicides were optimized. Furthermore, a large-amount injection method was applied for improving the detection limits. Under the optimized conditions, the detection limits (S/N = 3) for AMPA, GLUF and GLYP were 0.18 μg L⁻¹, 0.43 μg L⁻¹ and 1.45 μg L⁻¹, respectively. The relative standard deviations (RSD, n = 5) were 1.16 %, 1.03 % and 3.20 %, respectively. The presented method was applied to the determination of three herbicides in environmental water samples (reservoir water). A 9.91 μg L⁻¹ of AMPA was detected in reservoir water. When injected the environmental water samples without any sample treatment, a baseline change and unknown peaks based on the matrixes in the samples were detected at around AMPA; it was estimated that those matrix interferences were based on inorganic ions in the samples. The matrix interferences could almost be solved by the sample pretreatment using a solid-phase extraction cartridge packed with a cation exchange resin, but the adsorption of AMPA and GLUF to a cation exchange resin was observed. Though further examination for the sample preprocessing was necessary, the application possibility of the presented method as the quantification method of the phosphate type herbicides in environmental samples was suggested.

The simultaneous and selective determination by ion chromatography was examined for inorganic nitrogen species [nitrite (NO₂⁻), nitrate (NO₃⁻), ammonium (NH₄⁺) ions] in seawater. NO₂⁻ and NO₃⁻ in artificial seawater were separated and detected by using an anion-exchange column of the polymer type with a high ion-exchange capacity, an eluent of 1 mM NaOH + 1 M NaCl, and a UV detector (225 nm). On the other hand, NH₄⁺ was detected by using a gas-diffusion system and a fluorometric detection method (410 nm and 470 nm for excitation and emission wavelengths, respectiverly, using o-phthalaldehyde (OPA) solution and potassium phosphate buffer as a reaction solution) as a post-column method. The calibration curves by the peak-area method for each ion in 35‰ artificial seawater showed good linearity (r² = 0.994 or more) in the range of 0.01 to 2 mg L⁻¹. The repeatability (each ion concentration 1 mg L⁻¹, n = 5) was 0.25 % or less (retention time), 0.72 % or less (peak area), and 0.99 % or less (peak height). The detection limit values (S/N = 3, estimated from each ion concentration 1 mg L⁻¹) of NO₂⁻, NO₃⁻, NH₄⁺ were 0.4 μg L⁻¹, 1.6 μg L⁻¹, and 3.7 μg L⁻¹, respectively. This method was applied to the simultaneous determination of inorganic nitrogen species in real seawater samples and the recovery rate by the standard addition method was in the range of 94 to 110 % for all samples.

In this study, we measured trace ions contained in edible salts, and evaluated their types, processes and characteristics using ion chromatography (IC). Under the optimal cationic IC conditions, potassium, magnesium, and calcium were detected within 17 minutes using a Shodex IC YS-50 as a separation column and 4.0 mM methanesulfonic acid as an eluent. On the other hand, fluoride, bromide, and sulfate were detected within 20 minutes under the optimal anionic IC conditions using a Shodex IC SI-35 4E as a separation column and 3.0 mM sodium carbonate/2.0 mM sodium bicarbonate mixture solutions as the eluent. The quantitation limits (S/N = 10) of each cation and anion were 30.2-60.3 μg L⁻¹ and 3.4-22.7 μg L⁻¹, respectively. The quantitation limits of analyte ions obtained by the present IC were expected to be applicable to analyses of trace ions in edible salts. In addition, the calibration curves of each ion at 0-50 mg L⁻¹ showed a very close correlation (R² = 0.999). A recovery test was carried out by adding 1 mg L⁻¹ of each ion to 500 mg L⁻¹ of edible salt dissolved in pure water. The recovery rates of each ion were 96.1-104.8 %. The developed method was applied for the determination of trace inorganic ions contained in edible salts. The content of each ion varied depending on the type and process. In particular, the content differences of magnesium, calcium, and bromide in sea salt and rock salt were distinct. For example, 55.2 mg/100 mg of bromide was detected from Seto Inland Sea salt. It was found that simultaneous determination of the 6 ions in edible salts was possible only using IC without using titration method and atomic absorption spectroscopy.

This study describes inorganic anions using a column packed with a diol-modified silica gel stationary phase (diol-silica; TSKgel OH-120). In an acid eluent, such as tartaric acid or malic acid, the elution order of the analyte anions in ion chromatography using a diol-silica column was comparable to that using conventional anion-exchange columns, except for the fluoride ion. Fluoride ion would be strongly retained onto the silica gel, which is a support to fix diol functional groups. The retentions for anions was found to be enhanced by H⁺ in the eluent. This might electrostatically interact anions by protons retained onto diol functional groups in the column. Furthermore, the retention time of sulfate ion, which is a divalent strong acid anion, was largely reduced with increases of the column temperature up to 80 °C, while nitrite ion was slightly increased. The increase of the retention time of the nitrite ion was considered because of oxidization with elution of acidic eluent at a higher column temperature than 70 °C. The anion separation the by diol-silica stationary phase under acidic elution conditions was expected to be an ion-dipole interaction with the eluent ion and/or an electrostatic interaction with the stationary phase.

The quantification method of hydrophilic food additives in meat products was confirmed using an ion chromatography coupled with mass spectrometry. Nitrate and nitrite (food coloring), sorbate (food preservative) and other hydrophilic food additives in meat products were extracted by water, and separated from the matrix by using a gradient eluent (10-55 mmol L⁻¹ KOH). For confirming food additives extracted from meat products, a single quadrupole mass spectrometer was used after a suppressed conductivity detector. The recovery of formate, nitrate, nitrite, sorbate and malate in sausage were 92-105 %. Lactate and acetate, succinate and malate which could not be discerned and were presented as one peak by conductivity detector, were separated by a mass spectrometry detector in the selected ion monitoring mode.