Portable analyser using two-dimensional ion chromatography with ultra-violet light-emitting diode-based absorbance detection for nitrate monitoring within both saline and freshwaters

Mitigating the effects of organic solvents in sample diluents for ion chromatography: A comprehensive study and guidelines for optimization

Ion Chromatography (IC), the gold standard for the separation and analysis of ionic species, has been extensively used for detection of ions in industrial applications. Pharmaceutical samples with limited water solubility often require the use of organic solvents as diluents, which can pose significant challenges on IC analysis. Herein, the effects of various organic solvents as sample diluents in IC for anion analysis are systematically investigated. Electrochemically stable solvents such as 2-propanol (IPA), acetone, and dimethyl sulfoxide (DMSO) were found to have the least impact on the IC baseline. For solvents with a greater impact, a solvent dilution device (SDD) has been designed to minimize their effects. The device effectively diluted the organic solvents before they reached the suppressor electrode, reducing the generation of oxidized products. The results showed that the baseline stability and separation efficiency of IC can be maintained when using a wide range of organic solvents as diluents. Notably, the use of a solvent dilution device enabled good recovery of ions in various active pharmaceutical ingredients and significantly enhanced the signal to noise ratio of early-eluting ions compared to analyses conducted without the device. Guidelines are proposed to minimize the impact of organic solvents in IC sample preparation and anion analysis. The study also investigates the origin of impurity peaks introduced by the organic solvents and demonstrated the effectiveness of an ion-exchange resin treatment for their removal. Overall, this study provides insights for the use of organic solvents as IC diluents and offers practical solutions to overcome their challenges in pharmaceutical applications.

Adaptable 3D printed detector for absorbance monitoring of column chromatography separations using deep-UV LED at 280 nm

Column chromatography has been extensively used in the field of chemistry for a variety of applications, from the purification of synthesized compounds for pharmaceutical products to the isolation of natural products. Typically, the separated compounds are collected at the end of the column based on elution time, mobile phase volume, or colored markers. However, many target substances exhibit absorption in the ultraviolet range, making it challenging to monitor the elution process without an expensive instrumental detection system. In this study, we describe a flow-through absorbance-based detector for column chromatography using a deep-UV light-emitting diode with peak emission centered at 280 nm as light source for the first time. A 3D-printed holder was designed to house the LED and a UV-sensitive photodiode, positioned at 180° to measure radiation through a quartz tube with a diameter of 5 mm. The current generated by the photodiode was converted to absorbance using a log-ratio amplifier circuit and monitored via a USB data recorder. A noise level of 2.1 mAU was achieved, suitable for qualitative analysis. As a proof of concept, this detector was coupled with column chromatography to monitor the elution of (i) caffeine, (ii) a caffeine-hesperetin mixture, and a (iii) coffee extract sample. Absorbance spectra and thin-layer chromatography (TLC) experiments were performed to confirm the detector's capability to evaluate the efficiency of identifying UV-absorbing compounds. With this approach and the potential use of various deep-UV LEDs, we anticipate a cost-effective and efficient solution for monitoring the elution of non-colored compounds in column chromatography.

Measuring Nitrite and Nitrate in Rain and River Water Samples Using a Portable Ion Chromatograph in Step-gradient Mode and High Sensitivity Detection Flow Cell

With the increasing environmental pollution issues, there is a growing need for sensitive and real-time monitoring of pollutants. Nitrite and nitrate are common nutrients that are related to water quality. This study aims to enhance nitrate and nitrite detection capabilities using a portable ion chromatography-based nutrient analyzer, Aquamonitrix. By optimizing it for ultra-low detection limits (LODs), we address challenges in environmental water quality assessment in Tasmania, Australia. Using step-gradient mode with a stereolithography three-dimensional printed flow cell with a 5 cm optical path length, a 300 µL injection loop, and 60 mM KOH as eluent, LODs of 0.004 µg/mL for nitrite and 0.023 µg/mL for nitrate were achieved. Further improving to 0.008 µg/mL for nitrate with a 10 cm optical path length flow cell and 120 mM NaCl as eluent. A repeatability assessment over 84 automatic runs showed a relative standard deviation under 1.42% for peak area and 0.49% for retention time. The system demonstrated tolerance to salinity, handling up to 5 parts per thousand in artificial seawater. Comparative analysis of environmental samples revealed that nitrate levels in Tasmanian rainwater were five times lower than in Ireland. An average concentration of 2.08 µg/mL nitrate was found in Tamar River samples, aligning with local commercial lab data. Real-time, on-site analysis along the Derwent River detected an average nitrate concentration of 0.17 µg/mL. Validation against conventional standard ion chromatography showed no significant differences (p > 0.05), underscoring Aquamonitrix's robustness for field-based water quality monitoring. A 5-day deployment of Aquamonitrix further demonstrated the system's reliability under significant temperature fluctuations between day and night.

Applications of two-dimensional ion chromatography for analytes determination in environmental matrix: A review

Ion chromatography (IC) has grown in usage rapidly since its first introduction in 1975. However, IC is still sometimes unable to separate target analytes from coexisting components well with identical elution time, due to the limited resolution and column capacity, especially in the presence of high-level salt matrix. These limitations hence drive IC to develop two-dimensional IC (2D-IC). In this review, we capture the 2D-IC applications in environmental samples via the perspective of coupling different IC columns, which aim to summarize where these 2D-IC methods fit in. In sequence, we firstly review the principles of 2D-IC and emphasize one-pump column-switching IC (OPCS IC) because it is a simplified 2D-IC that only uses one set of IC system. We then compare typical 2D-IC and OPCS IC performances in terms of application scope, method detection limit, drawbacks, and expectations. Finally, we propose some challenges of current methods and opportunities for future research. For instance, it is challenging to couple anion exchange column and capillary column in OPCS IC due to the incompatibility between flow path dimensions and suppressor; coupling ion exclusion column and mixed-bed column may be promising to simultaneously determine anions and cations in weak acids or salts. The details of this study may help practitioners to better understand and implement 2D-IC methods and meanwhile motivate researchers to fill in the knowledge gap in the future.

A Portable Measurement Device Based on Phenanthroline Complex for Iron Determination in Water

In this work, a newly developed self-contained, portable, and compact iron measurement system (IMS) based on spectroscopy absorption for determination of Fe²⁺ in water is presented. One of the main goals of the IMS is to operate the device in the field as opposed to instruments commonly used exclusively in the laboratory. In addition, the system has been tuned to quantify iron concentrations in accordance with the values proposed by the regulations for human consumption. The instrument uses the phenanthroline standard method for iron determination in water samples. This device is equipped with an optical sensing system consisting of a light-emitting diode paired with a photodiode to measure absorption radiation through ferroin complex medium. To assess the sensor response, four series of Fe²⁺ standard samples were prepared with different iron concentrations in various water matrices. Furthermore, a new solid reagent prepared in-house was investigated, which is intended as a "ready-to-use" sample pre-treatment that optimizes work in the field. The IMS showed better analytical performance compared with the state-of-the-art instrument. The sensitivity of the instrument was found to be 2.5 µg Fe²⁺/L for the measurement range established by the regulations. The linear response of the photodiode was determined for concentrations between 25 and 1000 µg Fe²⁺/L, making this device suitable for assessing iron in water bodies.

Ion chromatograph with three-dimensional printed absorbance detector for indirect ultraviolet absorbance detection of phosphate in effluent and natural waters

An ion chromatography system employing a low-cost three-dimensional printed absorbance detector for indirect ultraviolet detection towards portable phosphate analysis of environmental and industrial waters has been developed. The optical detection cell was fabricated using stereolithography three-dimensional printing of nanocomposite material. Chromatographic analysis and detection of phosphate were carried out using a CS5A 4 × 250 mm analytical column with indirect ultraviolet detection using a 255 nm light-emitting diode. Isocratic elution using a 0.6 mM potassium phthalate eluent combined with 1.44 mM sodium bicarbonate was employed at a flow rate of 0.75 ml/min. A linear calibration range of 0.5 to 30 mg/L PO₄ ^3- applicable to environmental and wastewater analysis was achieved. For retention time and peak area repeatability, relative standard deviation values were 0.68% and 4.09%, respectively. Environmental and wastewater samples were analyzed with the optimized ion chromatography platform and the results were compared to values obtained by an accredited ion chromatograph. For the analysis of environmental samples, relative errors of <14 % were achieved. Recovery analysis was also carried out on both freshwater and wastewater samples and recovery results were within the acceptable range for water analysis using standard ion chromatography methods.