On-line dialysis as a sample preparation technique for ion chromatography

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.

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.

Online microchannel preconcentrator for carbofuran detection

A simple and rapid online microchannel preconcentrator coupled with an amperometric detection for the analysis of carbofuran using polyethylene glycol coated onto magnetic particle (PEG-magnetic particles) sorbents was developed. This simple-to-prepare microchannel preconcentrator used an external magnet to retain the PEG-magnetic particle sorbents inside the microchannel. Under optimum conditions, the system provided two linear ranges, from 0.01 to 10.0 mg L(-1) and from 10.0 to 130.0 mg L(-1) with a limit of detection of 8.7 ± 0.1 μg L(-1). The microchannel preconcentrator provided very good stability; it can be used for up to 326 consecutive injections of 5.0 mg L(-1) carbofuran with a relative standard deviation of less than 3%. The developed system provided a good microchannel-to-microchannel and a good electrode-to-electrode reproducibility (n = 6, %RSD < 1). It also provided an excellent selectivity when it was tested with two other carbamate pesticides, carbaryl and methomyl, with a 43 and 256 times higher detection sensitivity for carbofuran, respectively. The developed system was successfully applied to detect carbofuran in surface water samples obtained near vegetable plantation areas. The concentrations of carbofuran in these samples were found to be in the range of non-detectable to 0.047 ± 0.001 mg L(-1). The developed system is easy to operate and easy to couple with other analytical instruments and it could be easily adapted for the analysis of other polar organic contaminants.

Recent applications of sample preparation techniques in food analysis

Even with the emergence of advanced techniques of separation and identification, it is rarely possible to analyse food without manipulation. The traditional techniques for sample preparation are time consuming and require large amount of reagents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. The more analytical techniques have become highly developed, the more has sample clean-up become important in order to fully take advantage of them. Due to the multiplicity of food matrices, it is not possible to use one sample preparation technique, so many methods have been proposed for meeting all the requirements. The newest variations of wet digestion, solvent and sorbent extraction and membrane separation are summarised and their most recent applications to food analysis are provided.