Review of analytical methods for the quantification of iodine in complex matrices.

Recent advancements in open-tubular liquid chromatography and capillary electrochromatography during 2014-2018.

This review covers advances and applications of open tubular capillary liquid chromatography (OT-LC) over the period 2007-2018. Under the right conditions OT-LC columns have the potential to offer superior column efficiency, higher overall peak capacity, and higher column permeability compared to packed capillary and monolithic columns. However, such advantages are highly dependent upon column format and dimensions, and to date in liquid chromatography the advantages of open tubular format columns have been most widely discussed and applied in the field of proteomics. In this review we have focused on the wider variety of separation mechanisms and applications which can be achieved following the modification of the inner wall of the capillary with a thin-layer stationary phase. In particular the latest advances in stationary phase development and formation, together with new column formats and dimensions are reviewed. Detection options for OT-LC are also discussed and recent advances in this area highlighted. Finally, this review summarises existing applications of OT-LC and illustrates the future potential for this technique.

Recent advances in open tubular capillary liquid chromatography.

A highly selective electrochemical sensor for lead ions was fabricated using mutiwalled carbon nanotube as the backbone. The binding sites for lead ions were sculpted with lead ion as template and NNMBA-crosslinked polyacrylamide as the solid matrix on MWCNTs (MWCNT-IIP) on lead ion sensing and selectivity. System without lead ions was also synthesized (MWCNT-NIP). To check the role of the MWCNT, ion-imprinted polymer (IIP) and non-imprinted polymer (NIP) without MWCNT were also synthesized. In both systems, the ion-imprinted polymer showed high specificity towards lead ion. The developed materials were characterized using various analytical techniques. The sites left by the lead ions in MWCNT-IIP are highly selective to lead ions and resulted in electrochemical response when a platinum electrode was modified with this nanostructure. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to explore the features of the developed electrochemical sensor towards lead ions. The developed material could sense Pb(II) ions in the presence of other metal ions, and the limit of detection was found to be 2 × 10−2 μM. The sensing system could successfully discriminate Pb(II) ions from different real samples which includes environmental sample such as lake water, mining effluent, food sample and cosmetics. Also the same was exploited for the extraction of Pb(II) ions. The recoveries from various samples using MWCNT-IIP were > 99%. But those of MWCNT-NIP were in the range 62–68%.

Ion imprinting approach for the fabrication of an electrochemical sensor and sorbent for lead ions in real samples using modified multiwalled carbon nanotubes

We report an efficient method for the determination of iodide (I–) ions by using gold–iodide hybrid cluster ions on gold nanoparticles (Au NPs) modified mixed cellulose ester membrane (Au NPs-MCEM) by pulsed laser desorption/ionization mass spectrometry (LDI-MS). When I– ions were deposited and concentrated on the surfaces of Au NPs (32 nm) via strong Au+–I– interaction on the MECM, the Au NPs-MCEM was observed to function as an efficient surface-assisted LDI substrate with very low background noise. When pulsed laser radiation (355 nm) was applied, I– binding to Au NPs ions induced the enhancement of the desorption and ionization efficiency of gold–iodide hybrid cluster ions from the Au NPs surfaces. The reproducibility of the probe for both shot-to-shot and sample-to-sample (both less than 10%) ion production was also improved by the homogeneous nature of the substrate surface. Thus, it allows the accurate and precise quantification of I– ions in high-salinity real samples (i.e., edible salt samples and...

Gold-nanoparticles-modified cellulose membrane coupled with laser desorption/ionization mass spectrometry for detection of iodide in urine.

We describe novel cycloolefin polymer (COP)-based open tubular capillary ion exchange columns. COP capillaries (inner diameter of 19–28 μm) were successfully sulfonated at room temperature using a cocktail of ClSO3H (85–95% w/w) and HOAc or H2SO4. The cation exchange capacity is controlled by the sulfonation time and the sulfonation solution composition and can be as high as 300 pequiv/mm2. Following sulfonation, the capillaries were coated with 65-nm-diameter anion exchanger (AEX) latex nanoparticles that attach electrostatically. The typical anion exchange capacities were ∼20 pequiv/mm2. The chromatographic behavior of the AEX latex-coated COP capillaries are greatly dependent on the degree of sulfonation. When the base is heavily sulfonated, neutrals elute after the anions. The position of the water dip varies with the degree of sulfonation; the elution order is normal (water dip appear before anions) only with lightly sulfonated columns. On silica (−SiOH) or poly(methyl methacrylate) (−COOH) surfaces,...

Functionalized Cycloolefin Polymer Capillaries for Open Tubular Ion Chromatography

We describe an electrodialytic capillary suppressor for suppressed conductometric open tubular ion chromatography (SC-OTIC). For practical eluent concentrations, suppressor active lengths less than ∼1 mm are adequate. In its preferred embodiment, the suppressor consists of a solid polymer ion exchanger block. Two 0.45-mm-diameter parallel cylindrical passages are provided: these provide for passage of regenerant water and placement of platinum wire electrodes. The suppression channel is made by making a crack in the soft polymer block, using a needle 0.3 mm in diameter. The suppression channel runs parallel to and is flanked by the two aforementioned electrode channels through which water is pumped. The suppressor ends of the separation and the detection capillaries are tapered. The tapered ends of the capillaries are inserted into the suppression channel with the tips 0.4–1.1 mm apart. Using a suppression length of 1 mm, we were able to suppress 100 mM hydroxide @ 100 nL/min (10 neq/min). With such a sup...

Electrodialytic Capillary Suppressor for Open Tubular Ion Chromatography.

Simultaneous determination of fluorine and iodine in urine by ion chromatography with electrochemical pretreatment

Development of a novel, sensitive amperometric-FIA glucose biosensor by packing up the amperometric cell with glucose oxidase modified anion exchange resin.

Admittance detection, more commonly called capacitively coupled contactless conductivity detection, is widely used. While the true conductance of a solution is linear with concentration up to ∼1 mequiv/L, the admittance signal is nonlinear. In small-bore capillaries and highly resistive solutions, such as in suppressed open tubular ion chromatography (SOTIC), the admittance signal is exponentially related to concentration. Solution contact conductivity detection is common in microfluidics, but no true conductivity measurement efforts have been made with conventional capillaries in the last two decades. We examine five solution contact cell geometries: (A) wire/disk electrodes perpendicular to the flow direction, (B) annular tubular electrodes facing the flow (that exits through the center tube), (C) ring-disk electrodes facing the flow that exits through the annulus, (D) coplanar parallel wire/disk electrodes facing the flow that exits around the electrodes, and (E) planar electrodes separated by a thin i...

Weixiong Huang

Papers

Functionalized Cycloolefin Polymer Capillaries for Open Tubular Ion Chromatography

Electrodialytic Capillary Suppressor for Open Tubular Ion Chromatography.

Simultaneous determination of fluorine and iodine in urine by ion chromatography with electrochemical pretreatment

Development of a novel, sensitive amperometric-FIA glucose biosensor by packing up the amperometric cell with glucose oxidase modified anion exchange resin.

Capillary Scale Admittance and Conductance Detection.