Simultaneous separation and detection of anions and cations in ion chromatography

Preparation of small peptoid-modified zwitterion-exchange/reversed-phase mixed-mode chromatography stationary phases for the separation of arenes and antibiotics

In this study, three small peptoids with different structures, named Sil-peptoids, were developed to improve the separation selectivity of zwitterion-exchange/reversed-phase mixed-mode chromatography stationary phases for multi-component complex drugs. Nonpolar, amphoteric, and alkaline drugs were used as test samples to demonstrate their retention behaviors in reversed-phase, ionic, and mixed-mode interactions. It was observed that different carboxyl anions in the small peptoids of the Sil-peptoids had vast differences in their stereo-selectivity. The stereo-selectivity and the influence of Sil-peptoids on the retention behavior of complex drugs and their interaction mechanism for the drug molecules were effectively evaluated through the combination of chromatographic analysis and molecular modeling. Finally, a mixture of drugs consisting of two polar and six non-polar drugs was used to obtain a separation effect with a resolution >1.5. Two other groups of polar antibiotics were used to verify the separation ability of the Sil-peptoids. The results indicated that the Sil-peptoids could separate multiple substances simultaneously. These novel stationary phases can be applied to the analysis of complex multi-component drugs.

Development of a Method for Multisensory Stripping Voltammetry in the Analysis of Medical Preparations

For the effective dosage of newly developed ophthalmic drugs, an assessment of the dynamics of their concentration in lacrimal fluid over time is required. To express the detection and identification of drugs, new methods are needed that must meet numerous requirements, not the least of which are selectivity, speed, the absence of false-negative results, and cost-effectiveness. The possibility of identifying anesthetics (sevoflurane) in lacrimal fluid has been studied using a new electrochemical method of multisensory inversion voltammetry in the electronic tongue and electronic nose format. The measurements were performed on a planar electrode, which is a three-electrode structure. The solution of the test system consisted of 0.05 M KCl, which contained the metal cations Zn2+, Cd2+, Pb2+, Co2+, and Hg2+ at a concentration of 5 × 10-5 M. It is shown that this method is effective for the determination of anesthetics, and the dynamics of changes in their concentration over time are examined. This study aimed to research the behavioral pharmacokinetics in the lacrimal fluid of the opioid drug sevoflurane in pediatric ophthalmology using multisensory stripping voltammetry in patients during strabismus correction surgery. The dynamics of changes in their concentrations over time were examined. After the instillation of the anesthetics in patients, their concentrations in the tear fluid remained unchanged within 10 min. The list of organic substances that can be determined by multisensory stripping voltammetry has been extended. The class of organic substances determined by the method of multisensory inversion voltammetry has been expanded.

Utilization of Anion-exchange Guard Column as an Ion Chromatographic Column of Anions Including Application to Simultaneous Separation of Anions and Cations

This study demonstrated that a guard column containing anion-exchange resin has the potential for use as a separation column for acid eluent. Specifically, a 1-cm long anion-exchange guard column with a 4.6-mm internal diameter provided good separation of monovalent inorganic anions, by elution of 8 mM tartaric acid or 4 mM malic acid. Using the guard column with acid eluent could be applied to evaluation of nitrite and nitrate ions in mountain and urban river water samples. When the guard column was connected in front of a cation-exchange separation column (15 cm long × 4.6 mm internal diameter) in a series, the system provided simultaneous separation of anions and cations in eluent of 8 mM tartaric acid and 0.5 mM 18-crown-6 ether by a single injection.

Phosphate Removal from Nursery Runoff Water Using an Iron-Based Remediation System

Phosphorous (P) losses from containerized plant production nurseries can be significant due to the low nutrient retention capacities of the media components. As environmental regulators establish, refine, and enforce nutrient criteria, effective methods are needed to reduce amounts of P in runoff and drainage water. This study investigated the use of a small scale flow-through ferrous iron (Fe(II))-based remediation system for chemically precipitating P. This system consisted of four inter-connected tanks, with the first two maintained under anaerobic conditions and the last two maintained under aerobic conditions. FeSO4 was introduced into the first of the aerobic tanks at different rates to achieve Fe:P ratios of 0, 9.0, 16.3, and 21.2. Water samples were collected from the systems, and P removal was monitored by ion chromatography. Phosphorus removal efficiencies of 78, 95, and 99% were observed for each respective treatment, indicating great potential for this conceptual system at Fe:P dosing ratios ≥16.3 and phosphorus concentrations between 3 and 5 mg/L. This type of system may especially be useful for nurseries with space limitations.

Advanced analytical methods and sample preparation for ion chromatography techniques

The recently developed advanced ion chromatography techniques and the various sample preparation methods have been summarized in this mini-review.

Recent progress and applications of ion-exclusion/ion-exchange chromatography for simultaneous determination of inorganic anions and cations

One of the ultimate goals of ion chromatography is to determine both anions and cations found in samples with a single chromatographic run. In the present article, recent progress in ion-exclusion/ion-exchange chromatography for the simultaneous determinations of inorganic anions and cations are reviewed. Firstly, the principle and the control for the simultaneous separation and detection of analyte ions using ion-exclusion/cation-exchange chromatography with a weakly acidic cation-exchange column are outlined. Then, advanced chromatographic techniques in terms of analytical time, selectively and sensitivity are summarized. As a related method, ion-exclusion/anion-exchange chromatography with an anion-exchange column could be used for the simultaneous determination of inorganic nitrogen species, such as ammonium, nitrite and nitrate ions. Their usefulness and applications to water-quality monitoring and related techniques are also described.

Simultaneous determination of inorganic anions, calcium and magnesium by suppressed ion chromatography

Suppressed conductimetric detection ion chromatography (IC) was investigated for the separation and detection of common inorganic anions, calcium and magnesium by anion-exchange chromatography using a sodium carbonate-EDTA mobile phase. The formation of anionic Ca2+ -EDTA and Mg2+ -EDTA complexes allowed its separation from other inorganic anions opening the way for their simultaneous determination in a single chromatographic run. The effect of the pH, carbonate and EDTA concentrations in the eluent and the previous addition of EDTA to the samples has been studied. The optimised experimental conditions were applied to the determination of Ca2+ and Mg2+ in mineral waters with results in agreement with alternative ICP-MS methodologies.

Novel ion chromatographic stationary phases for the analysis of complex matrices

Ion chromatography (IC) has a proven track record in the determination of inorganic and organic anions and cations in complex matrices. Recently, application of IC to the separation and determination of bio-molecules such as amino acids, carbohydrates, nucleotides, proteins and peptides has also received much attention. The key to the determination of all of the above species in the most analytically challenging complex matrices is the ability to manipulate selectivity through control of stationary phase chemistry, mobile phase chemistry and the choice of detection method. This Tutorial Review summarises some of the most significant recent advances made in IC stationary phase technology. In particular, the review details stationary phases specifically designed for ion analysis in complex sample matrices, and considers in which direction future stationary phase development might proceed.

Rapid, low pressure, and simultaneous ion chromatography of common inorganic anions and cations on short permanently coated monolithic columns

Short permanently coated reversed-phase silica based monolithic columns have been investigated for the rapid separation of inorganic anions and cations. One 2.5 x 0.46 cm column was permanently coated with didodecyldimethylammonium (DDAB), for anion analysis; and a second 5.0 x 0.46 cm column was coated with dioctylsulphosuccinnate (DOSS), for cation analysis. The use of a single combined eluent of 2.5 mM phthalate/1.5 mM ethylenediamine, at flow rates of between 4.0 and 8.0 mL/min, resulted in the rapid separation of 8 anions (in under 100 s) and 5 cations (in under 100 s) on the above columns when used individually, with detection limits for common anions ranging from approximately 0.25 to 5 mg/L, and between 2.5 and 50 mg/L for alkaline earth metals, by direct and indirect conductivity detection, respectively. However, with both columns subsequently connected in parallel, with the eluent delivered using a flow splitter from a single isocratic pump, the simultaneous analysis of anions and cations was also possible, based on a single conductivity detector. The potential of this system for the rapid, complete screening of water samples for multiple common anions and cations is shown.

Using ultrapure water in ion chromatography to run analyses at the ng/L level

Thanks to enhanced capabilities, ion chromatography (IC) occupies an increasing position in many types of applications. Achieving ideal performances for an extended life-time can only be reached, however, if the IC system is operated in optimum experimental conditions. Among the various parameters that need to be controlled, water is particularly important, because it is used throughout the analysis, from sample preparation to column rinsing, elution, and mobile phase preparation. More and more, devices are included in IC systems to generate the eluent in situ, and ultrapure water becomes the major reagent. Data of pre-concentration of high purity water show that detection limits at the ng/L level can be expected with water purified using the right combination of technologies.

Simultaneous separation of inorganic anions and cations by using anion-exchange and cation-exchange columns connected in tandem in ion chromatography

Inorganic anions and cations in environmental waters were determined by ion chromatography. Stationary and mobile phases were examined for the simultaneous separation of both anions and cations. Cations detection by UV detection requires a mobile phase with a UV absorbing additive, which indirectly visualizes cations as negative peaks. Simultaneous separation of anions and cations were achieved when using an eluent that consists of inorganic acid with weak basic amino acid as additives. It was convenient to separate both anions and cations by coupling anion-exchange and cation-exchange columns in tandem. The order of the separation columns connected affected the elution profiles. When the eluent comprises of multiple anions and a single cation, the anion-exchange column should be connected in the upper stream, whereas when the eluent comprises multiple cations and a single anion, the cation-exchange column should be connected in the upper stream. Use of switching valves also allowed simultaneous separation of anions and cations in a single chromatographic run. In the present work, operating conditions were optimized for the simultaneous separation of anions and cations.