Simultaneous Detection Of Multiple Ions Research Articles

A compact and high-performance setup of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D).

Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) has the advantages of high throughput (simultaneous detection of multiple ions), high separation efficiency (higher than 105 theoretical plates) and rapid analysis capability (less than 5 min for common inorganic ions). A compact CE-C4D system is ideal for water quality control and on-site analysis. It is suitable not only for common cations (e.g. Na+, K+, Li+, NH4+, Ca2+, etc.) and anions (e.g. Cl-, SO42-, BrO3-, etc.) but also for some ions (e.g. lanthanide ions, Pb2+, Cd2+, etc.) that require complex derivatization procedures to be detected by ion chromatography (IC). However, an obvious limitation of the CE-C4D method is that its sensitivity (e.g. 0.3-1 μM for common inorganic ions) is often insufficient for trace analysis (e.g. 1 ppb or 20 nM level for common inorganic ions) without preconcentration. For this technology to become a powerful and routine analytical technique, the system should be made compact while maintaining trace analysis sensitivity. In this study, we developed an all-in-one version of the CE-C4D instrument with custom-made modular components to make it a convenient, compact and high-performance system. The system was designed using direct digital synthesis (DDS) technology to generate programmable sinusoidal waveforms with any frequency for excitation, a kilovolt high-voltage power supply for capillary electrophoresis separation, and an "effective" differential C4D cell with a low-noise circuitry for high-sensitivity detection. We characterized the system with different concentrations of Cs+, and even a low concentration of 20 nM was detectable without preconcentration. Moreover, the optimized CE-C4D setup was applied to analyse mixed ions at a trace concentration of 200 nM with excellent signal-to-noise ratios. In typical applications, the limits of detection based on the 3σ criterion (without baseline filtering) were 9, 10, 24, 5, and 12 nM for K+, Cs+, Li+, Ca2+, and Mg2+, respectively, and about 7, 6, 6 and 6 nM for Br-, ClO4-, BrO3- and SO42-, respectively. Finally, the setup was also applied for the analysis of all 14 lanthanide ions and rare-earth minerals, and it showed an improvement in sensitivity by more than 25 times.

Current analytical methods for the determination of persulfate in aqueous solutions: A historical review

• The methods for the determination of persulfate are systematically reviewed. • The advantages and limitations of each method in practice are analyzed. • Fluorescence method is suitable for measuring PMS in colored samples. • UV–vis spectrophotometry can be chosen for colorless samples. • Titration is the most recommended method if no lab equipments are available. Persulfate (peroxymonosulfate or peroxydisulfate) ions, as strong oxidants, have a broad application in the field of advanced oxidation processes (AOPs) for oxidative degradation of organic pollutants in soil and contaminated water. Persulfate concentration is an important operational parameter in persulfate degradation of organic pollutants based on SO 4 •− -AOPs. At present, the analytical methods used for quantification of persulfate mainly include traditional titration, polarography, electrochemiluminescence, electrochemical methods, spectrometry and chromatography. These methods vary in their limit of detection (LOD), execution time, operational difficulty, accuracy and sensitivity. The traditional methods are cheap and easy to operate, but the poor sensitivity and the high LOD limit its application. Electrochemiluminescence methods are highly sensitive with low detection limit, but requires rather specialized instruments. Electrochemical methods are repaid and have high sensitivity, low LOD and wide detection range, but relatively large reagent volume is needed in the determination process. Spectrophotometry has high accuracy with low consumption rate of sample and reagents, but it is susceptible to colored substances. Ion chromatography has the advantages of high sensitivity, less reagent consumption and simultaneous detection of multiple ions, but no advantage in detection time and LOD. This review presents the principles, merits and demerits of various existing analytical methods for persulfate determination, and discusses the limitations and applicability of various methods. This review is expected to provide some references for the establishment of novel detection methods for persulfate in the future.

Chip-based ion chromatography (chip-IC) with a sensitive five-electrode conductivity detector for the simultaneous detection of multiple ions in drinking water

The emerging need for accurate, efficient, inexpensive, and multiparameter monitoring of water quality has led to interest in the miniaturization of benchtop chromatography systems. This paper reports a chip-based ion chromatography (chip-IC) system in which the microvalves, sample channel, packed column, and conductivity detector are all integrated on a polymethylmethacrylate (PMMA) chip. A laser-based bonding technique was developed to guarantee simultaneous robust sealing between the homogeneous and heterogeneous interfaces. A five-electrode-based conductivity detector was presented to improve the sensitivity for nonsuppressed anion detection. Common anions (F−, Cl−, NO3−, and SO42−) were separated in less than 8 min, and a detection limit (LOD) of 0.6 mg L−1 was achieved for SO42−. Tap water was also analyzed using the proposed chip-IC system, and the relative deviations of the quantified concentration were less than 10% when compared with that a commercial IC system.