Membrane-based sample preparation for ion chromatography—Techniques, instrumental configurations and applications

Pretreatment methods in ion chromatography: A review

As an advanced analytical technology, Ion Chromatography (IC) has been widely used in various fields. At present, it is faced with the challenges of sample complexity and instrument precision. It is necessary to select appropriate pretreatment methods to achieve sample preparation and protect the instruments. Therefore, this paper reviews several commonly used sample pretreatment technologies in IC, focusing on sample digestion and purification techniques. Additionally, we introduce some advanced IC technologies and automatic sample processing devices. We provide a comprehensive summary of the basic principles, primary applications and the advantages and disadvantages of each method. Pretreatment methods should be carefully selected and optimized on the specific characteristics of the sample and the ions to be measured, in order to achieve better analysis results.

Green Extraction Processes for Complex Samples from Vegetable Matrices Coupled with On-Line Detection System: A Critical Review

The detection of analytes in complex organic matrices requires a series of analytical steps to obtain a reliable analysis. Sample preparation can be the most time-consuming, prolonged, and error-prone step, reducing the reliability of the investigation. This review aims to discuss the advantages and limitations of extracting bioactive compounds, sample preparation techniques, automation, and coupling with on-line detection. This review also evaluates all publications on this topic through a longitudinal bibliometric analysis, applying statistical and mathematical methods to analyze the trends, perspectives, and hot topics of this research area. Furthermore, state-of-the-art green extraction techniques for complex samples from vegetable matrices coupled with analysis systems are presented. Among the extraction techniques for liquid samples, solid-phase extraction was the most common for combined systems in the scientific literature. In contrast, for on-line extraction systems applied for solid samples, supercritical fluid extraction, ultrasound-assisted extraction, microwave-assisted extraction, and pressurized liquid extraction were the most frequent green extraction techniques.

Open tubular capillary ion chromatography with online dilution for small ions determination in drinks

This work aims to develop a more robust, easy-to-use, low-pressure, and cost-effective nonsuppressed open tubular capillary ion chromatography (NS-OTIC) approach with online dialysis for small ions determination in drinks. The fabricated device was applied for two selected columns, including poly(butadiene-maleic acid) on a 50-μm bore and AS18 Latex on 25-µm bore fused silica capillaries, for the separation of mixed cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and mixed anions (Cl^-, Br^-, NO₂^-, NO₃^-), respectively. High concentrations of ions (up to 100 mM) level can be directly introduced into the NS-OTIC system without an off-line (manual) dilution step. The linear relationship of the peak area and concentration of model ions can be obtained with a resolution > 1.1. The repeatability of the peak area for both OTIC columns was < 6% RSD. Juice and tea samples were successfully analyzed with % recoveries of 77-112 and 90-119 for cation and anion determinations, respectively.

Determination of ammonium and biogenic amines by ion chromatography. A review

The amount and type of chemical compounds found in food products and the environment, which are and should be controlled, is increasing. This is associated with toxicological knowledge, resulting regulations, rapid development of analytical methods and techniques, and sample preparation methods for analysis. These include, among others, ammonia derivatives such as ammonium, and amines, including biogenic amines. Their occurrence in the environment and food is related to their widespread use in many areas of life and their formation as a result of various physical and chemical changes. Analysts use various methods both classical and instrumental to theirs quantify in different matrices such as food, medicinal and environmental samples. Nevertheless, there is still a need for analytical methods with increased matrix-tolerance, selectivity, specificity, and higher sensitivity. While in the determination of ammonium, ion chromatography is a reference method. In the case of biogenic amines, its use for these purposes is not yet so common. However, given ion chromatography its advantages and rapid development, its importance can be expected to increase in the near future, especially at the expense of gas chromatography methods. This paper is a summary of the advantages and limitations of ion chromatography in this important analytical field and a literature review of the past 15 years.

Accurate Analysis of Tricarboxylic Acid Cycle Metabolites and Anion Components in Hemocytes by IC-CD/ESI-MS for Quantifying Insecticide Impairment on Cellular Immunity in Mythimna separata

Insecticides are more broadly known to affect insect cellular immunity, but the components in hemocytes and their response to insecticide stress are still unknown. In this paper, a method based on trifluoroacetic acid extraction, followed by IC-CD/ESI-MS analysis, was developed to simultaneously determine tricarboxylic acid (TCA) cycle metabolites and anion components in hemocytes from Mythimna separata larvae. Validation gave excellent selectivity, recovery (88.7-107.6%), linear correlation (r² > 0.9961), precision (<3.89%), LOD (0.002-0.006 mg/L), LOQ (0.006-0.020 mg/L), and a short chromatographic run. The method was verified by administration of 4-((3-chloro-4-fluorophenyl)amino)-7-methoxyquinazolin-6-yl 3-(1,3-dioxoiso-indolin-2-yl) propanoate (QDP) or emamectin benzoate (EMB) to hemocytes in vitro and larvae in vivo. TCA metabolites including citrate, α-ketoglutarate, fumarate, malate, and oxaloacetate, and anions including acetate, oxalate, chloride, carbonate, and sulfate were identified and clearly separated. QDP and EMB showed a biphasic dose effect on TCA metabolites, and the contrary hormesis paralleled the different actions of QDP and EMB. The inhibition or improvement of cellular immunity depended on the QDP concentration. In conclusion, a highly sensitive, reliable, and robust method was developed, enabling the monitoring of hemocyte immunity by the quantification of TCA metabolites and anion components in minute hemocyte samples.

An electrodialytic device for automated inorganic anion preconcentration with determination by ion chromatography-conductivity detection

A 4-layer sandwiched device (4LSD) well suited for coupling to online ion chromatography (IC) systems was described and simultaneously performed target anion enrichment, matrix removal and sample injection within seconds. The basic assembly consisted of an extraction solution channel, a sample solution channel and two electrolyte channels. Cation-exchange resin (CER) was utilized to support the solution chamber, increase electrical conductivity and improve pressure resistance to achieve compatibility with a peristaltic pump. Filter placement ensured loop circulation of the 4LSD and prevented resin leakage. The 4LSD showed comparable performance to that of conventional solid-phase extraction (SPE) pretreatment in terms of matrix interference removal while enabling automation. The applied current, sample/extraction solution flow rate ratio, and initial concentration were discussed and optimized. Controllable 1-40-fold enrichment can be ensured. The migration phenomenon of different anions was discussed. F^-, Cl^-, NO₂^-, Br^-, NO₃^-, SO₄^2- and ClO₄^- exhibited satisfactory linear detection ranges within 2.5-1000 μg·L^-1, and the calculated limits of detection (LODs) in milk formula were within the 0.097-0.79 mg·kg^-1 range. The 4LSD was successfully applied to the determination of anions in milk formula with good spiked recoveries ranging between 92.54% and 107.2%, except for the NO₂^- recovery. The relative standard deviations (RSDs) ranged from 0.69% to 8.29%.

Ion Chromatography and Related Techniques in Carboxylic Acids Analysis

Ion chromatography (IC) is a variant of high-performance liquid chromatography. Its most important applications include the determination of inorganic and some organic ions in different types of liquid samples. The development of new types of stationary phases with various separation mechanisms, sample preparation methods, and detection modes has extended ion chromatography applications to practically all ionic and ionogenic substances, as well as extending sample types to include gaseous and solid matrices. Carboxylic acids and their derivatives are examples of compounds that are becoming more frequently analyzed using ion chromatography and related techniques. Their occurrence in the environment can be natural or anthropogenic in origin and are broadly used in various industries and daily life. This article discusses the applications of ion chromatography and related techniques for the determination of carboxylic acids in different types of liquid, solid, and gaseous matrices. It also presents detailed methodologies and literature data on this subject from the last 15 years.

Reversed-phase chromatomembrane extraction as a novel approach for automated sample pretreatment: Anions determination in biodiesel by ion chromatography with conductivity detection

In this study, a reversed-phase chromatomembrane extraction (RP-CME) method as a novel approach for automated sample pretreatment was suggested for the first time. The RP-CME was applied to automated separation of anions (formate, chloride, nitrate, phosphate and sulfate) from biodiesel samples as a proof-of-concept example. The novel design of chromatomembrane cell was developed for on-line RP-CME. The RP-CME procedure assumed mass-transfer of water-soluble analytes from organic sample phase (biodiesel sample) to aqueous phase supported in a porous composite mass-transfer block. The composite mass-transfer block based on microporous hydrophobic poly (tetrafluoroethylene) and hydrophilic glass fiber was developed for the RP-CME implementation. The block provided the effective retention of aqueous phase into the cell and simultaneous penetration of organic phase. The hydrophilic membrane-based sheet was used for the on-line separation of hydrophilic emulsion (biodiesel in water) containing target analytes obtained during analytes elution by aqueous phase from the mass-transfer block. The RP-CME was successfully coupled with an ion chromatography with conductivity detection. The limits of detection, calculated from a blank test based on 3σ, were 5 μg kg^-1 for sulfate, 6 μg kg^-1 for nitrate, 3 μg kg^-1 for chloride, 5 μg kg^-1 for phosphate and 1 μg kg^-1 for formate.

Investigation of retention of undesirable organic matter from aqueous samples in stopped-flow dialysis procedures for inorganic anions

Sample preparation is a key issue in the analysis of many real samples using ion chromatography (IC). One of the many means of sample preparation that has received considerable attention in recent years is the stopped-flow in-line dialysis approach hyphenated to IC. Using appropriate dialysis membranes undesirable high-molecular weight compounds, colloids and dispersed particulate matter are retained whereas the analyte ions pass through the membrane and are separated and quantified by IC. However, in the many papers about analytical use of in-line dialysis (not only in connection with IC) the retention of undesirable compounds has never been quantified. This study is a first attempt to fil this gap. The breakthrough (BT) of humic acids (HA) and lignin as model compounds often contained in natural water samples was investigated in the stopped-flow dialysis procedure using different dialysis membranes. BT was measured and quantified by UV-absorption in the receiver solution leaving the dialysis cell. The most important factor for retention of undesired compounds is the pore size or the molecular weight cut-off (MWCO) of the dialysis membrane. In addition, the recovery of analytes in acceptable time needs to be considered. The optimized system addresses these two aspects and permits using the proper membrane almost quantitative recovery of several inorganic ions and at the same time almost complete retention of the model interferents. Artificial natural water samples were prepared and analyzed containing a mixture of HA, lignin and a surfactant and a number of anions. In long-term operation no alterations of the dialysis process occurred and no adverse effects in IC separations were observed.