A single pump cycling-column-switching technique coupled with homemade high exchange capacity columns for the determination of iodate in iodized edible salt by ion chromatography with UV detection

Analyte-triggered cascade signal amplification strategy for highly sensitive detection of iodate in table salt with dual-readout signals

A novel and highly sensitive upconversion fluorescence and colorimetric dual readout iodate (IO₃^-) nanosensor system was constructed by using both the outstanding optical performance of NaYF₄:Yb, Tm upconversion nanoparticles (UCNPs) and the analyte-triggered cascade signal amplification (CSA) technique. The construction of the sensing system consisted of three processes. First, IO₃^- oxidized o-phenylenediamine (OPD) to diaminophenazine (OPDox), while IO₃^- was reduced to I₂. Second, the generated I₂ can further oxidize OPD to OPDox. This mechanism has been verified by ¹H NMR spectra titration analysis and HRMS measurement, which effectively improves the selectivity and sensitivity of the measurement of IO₃^-. Third, the generated OPDox can effectively quench the fluorescence of UCNPs via the inner filter effect (IFE), realize analyte-triggered CSA, and allow quantitative determination of IO₃^-. Under the optimized conditions, the fluorescence quenching efficiency showed a good linear relationship to IO₃^- concentration in the range of 0.06-100 μM, and the detection limit reached 0.026 μM (3RSD/slope). Moreover, this method was applied to detect IO₃^- in table salt samples, yielding satisfactory determination results with excellent recoveries (95.5-105%) and high precision (RSD <5.5%). These results suggest that the dual-readout sensing strategy with well-defined response mechanisms has promising application prospects in physiological and pathological studies.

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.

Smartphone-based optical transduction for the rapid microscale assessment of iodate in table salt

The measurement of iodine in table salt is vital for the successful implementation of the universal salt iodization (USI) program to fight iodine deficiency disorders (IDDs). This paper presents a smartphone-based optical transduction system for iodine measurement in table salt. The method was based on the response in the blue color space generated by the complex formed between the starch/iodide reagent and iodate in the salt sample. The parameters for the color reaction and for the image capture affected the response and were optimized. A matrix effect caused by NaCl was observed and was eliminated through matrix matching by incorporating NaCl in the standard solutions. The optimized method yielded a highly linear response to iodate concentrations ranging from 10 to 160 mg kg^-1 (r = 0.9993) with a limit of detection of 2.8 mg kg^-1. The method exhibited good accuracy and precision, based on AOAC standards. It produced results that were in agreement with those obtained using the reference method at the 95% confidence level. The smartphone performs optical transduction, as well as signal processing, to yield a display of the iodate concentration in the salt sample. The use of smartphones presents a simple, inexpensive, portable, and widely available device for on-site analysis of iodate in table salt.

Foldable paper-based analytical device for membraneless gas-separation and determination of iodate based on fluorescence quenching of gold nanoclusters

A new design of a paper-based analytical device (PAD) for membraneless gas-separation with subsequent determination of iodate is presented. The rectangular PAD was invented as the folded pattern, where two circular reservoirs: the donor reservoir and the acceptor reservoir were situated in "a single paper" for convenient use. The hydrophobic barrier of each reservoir was easily fabricated by painting with a permanent marker. The PAD was demonstrated for the quantitative analysis of iodate, based on the fluorescence quenching of the bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs). The BSA-AuNCs were fast prepared by a microwave-assisted approach. The nanoclusters solution was applied into the acceptor reservoir, while the sample, iodide and sulfuric acid were sequentially aliquoted into the donor reservoir. After folding the PAD, the donor and the acceptor were mounted together via a two-sided mounting tape. The headspace between the two reservoirs allows membraneless gas-separation of free iodine from the donor to diffuse into the acceptor. Etching of gold core of the nanoclusters in the acceptor resulted in quenching of the red emission, was monitored by two methods, i.e. "fluorometric detection" (λ_ex: 490 nm, λ_em: 630 nm) and "image capture" of the acceptor under the UV irradiation by a smart phone's camera. Two calibrations were plotted accordingly to their detections and good linearities (r² ˃ 0.98) were observed from 0.005 to 0.1 mmol L^-1 iodate. High accuracy (mean recovery: 95.1 (±4.6) %) and high precision (RSD < 3%) were obtained. The lower limits of detection were 0.005 mmol L^-1 (with fluorometric detection) and 0.01 mmol L^-1 (with image capture). The method was effectively applied for the measurement of iodate in iodized salts and fish sauces without prior sample pre-treatment.

Smartphone digital image colorimetry combined with solidification of floating organic drop-dispersive liquid-liquid microextraction for the determination of iodate in table salt

Smartphone digital image colorimetry (SDIC), combined with solidification of floating organic drop-dispersive liquid-liquid microextraction (SFOD-DLLME), was proposed for the determination of iodate ions. A colorimetric box was designed to capture images of sample solutions. Factors affecting the efficiency of SDIC included type of phone, region of interest, position of camera, and distance between camera and sample solution. Optimum SFOD-DLLME conditions were achieved with 1-undecanol (500 µL) as the extraction solvent, ethanol (1.5 mL) as the disperser solvent within 20 s extraction time. Limit of detection (LOD) was found as 0.1 µM (0.2 µg g^-1) and enrichment factors ranged between 17.4 and 25.0. Calibration graphs showed good linearity with coefficients of determination higher than 0.9954 and relative standard deviations lower than 5.6%. The proposed method was efficiently applied to determine iodate in table salt samples with percentage relative recoveries ranging between 89.3 and 109.3%.

Iodine-mediated etching of gold nanorods for plasmonic sensing of dissolved oxygen and salt iodine

A plasmonic sensing method for detection of dissolved oxygen and salt iodine based on iodine-mediated etching of gold nanorods is developed.