Keng-Chang Hsu

On-line microdialysis–nano-Au/TiO2–high-performance liquid chromatography system for the simultaneous determination of cobalt and nickel in water

An on-line configuration of microdialysis (MD), Au/TiO2 nanoparticle preconcentration, and high-performance liquid chromatography-ultraviolet (HPLC-UV) detection method was developed for the simultaneous measurement of cobalt (Co) and nickel (Ni) concentrations in water. The sample matrix was first cleaned with an MD system using a MD probe. A continuously flowing dialysate stream was introduced into tubing coated with Au/TiO2 nanoparticles to adsorb metals, followed by elution by an acidic eluent. The enriched samples were derivatized on-line using 8-hydroxyquinoline. The separation of Co and Ni were achieved by using a LC-C18 column. The three aforementioned system components were connected on-line using a valve control. The UV detection was performed at 319nm. Validation experiments demonstrate good linearity, precision, accuracy, and recovery. The proposed method offers a simple and reliable procedure to determine the levels of Co and Ni in environmental water samples. Moreover, the methodology described in this study adheres to the concept of green chemistry, including the absence of organic solvents in the MD sampling and extraction processes. To the best of our knowledge, the proposed method is the first reported on-line connection of MD, Au/TiO2 nanoparticle tubing, and HPLC devices for the measurement of Co and Ni concentrations in water.

Selective and eco-friendly method for determination of mercury(II) ions in aqueous samples using an on-line AuNPs–PDMS composite microfluidic device/ICP-MS system

In this study we developed an on-line, eco-friendly, and highly selective method using a gold nanoparticle (AuNP)-coated polydimethylsiloxane (PDMS) composite microfluidic (MF) chip coupled to inductively coupled plasma mass spectrometry (ICP-MS) to separate trace Hg(2+) ions from aqueous samples. Because Hg(2+) ions interact with AuNPs to form Hg-Au complexes, we were able to separate Hg(2+) ions from aqueous samples. We prepared the AuNPs-PDMS composite through in situ synthesis using a PDMS cross-linking agent to both reduce and embed AuNPs onto PDMS microchannels so that no additional reductants were required for either AuNP synthesis or the PDMS surface modification (2% HAuCl4, room temperature, 48 h). To optimize the proposed on-line system, we investigated several factors that influenced the separation of Hg(2+) ions in the AuNPs-PDMS/MF, including adsorption pH, adsorption and elution flow rates, microchannel length, and interferences from coexisting ions. Under optimized conditions (pH 6.0; adsorption/elution flow rates: 0.05/0.5 mL min(-1); channel length: 840 mm), we evaluated the accuracy of the system using a standard addition method; the measured values had agreements of ≥ 93.0% with certified values obtained for Hg(2+) ions. The relative standard deviations of the proposed method ranged from 2.24% to 6.21%. The limit of detection for Hg(2+) for the proposed on-line AuNPs-PDMS/MF/ICP-MS analytical method was as low as 0.07 µg L(-1).

An on-line microfluidic device coupled with inductively coupled plasma mass spectrometry for chromium speciation

In this study, an on-line polyoxometalate cluster (POM)/microfluidic (MF) separation system coupled with inductively coupled plasma mass spectrometry (ICP-MS) detection was developed for the determination of trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium species in aqueous samples. In this system, a POM-immobilized MF device was used to separate the chromium species prior to their determination through ICP-MS. Several parameters were investigated to optimize the performance of the system: the adsorption pH, the adsorption and elution flow rates, the elution solution, the adsorption capacity, and the reaction chamber volume. Under the optimized conditions (carrier solution: deionized H2O; adsorption/elution flow rates: 0.2/1.2 ml L−1; reaction chamber volume: 30 μL), the linearity (>0.9987), precision (<3.69%; n = 7), and accuracy (95.93–108.60%) of this analytical procedure were quite high. To confirm its practical utility, the novel POM-MF separation system was applied to the successful determination of chromium species in real-world samples (including spiked tap water).

Recent trends in nanomaterial-based microanalytical systems for the speciation of trace elements: A critical review

Trace element speciation in biomedical and environmental science has gained increasing attention over the past decade as researchers have begun to realize its importance in toxicological studies. Several nanomaterials, including titanium dioxide nanoparticles (nano-TiO2), carbon nanotubes (CNTs), and magnetic nanoparticles (MNPs), have been used as sorbents to separate and preconcentrate trace element species prior to detection through mass spectrometry or optical spectroscopy. Recently, these nanomaterial-based speciation techniques have been integrated with microfluidics to minimize sample and reagent consumption and simplify analyses. This review provides a critical look into the present state and recent applications of nanomaterial-based microanalytical systems in the speciation of trace elements. The adsorption and preconcentration efficiencies, sample volume requirements, and detection limits of these nanomaterial-based speciation techniques are detailed, and their applications in environmental and biological analyses are discussed. Current perspectives and future trends into the increasing use of nanomaterial-based microfluidic techniques for trace element speciation are highlighted.

Arsenic speciation in biomedical sciences: recent advances and applications.

Speciation analysis of trace elements is an important issue in biomedical and toxicological sciences because different elemental species have different effects on health and the environment. For humans, arsenic (As) is a toxic element; the toxicity of As compounds is highly dependent on its chemical form. Although inorganic As compounds are human carcinogens, organic arsenicals are relatively less toxic. This article deals with recent advances and applications of methods for As speciation in biomedical sciences, with emphasis on the specimens commonly encountered in biomedical laboratories.

Microfluidic desorption-free magnetic solid phase extraction of Hg2+ from biological samples using cysteine-coated gold-magnetite core-shell nanoparticles prior to its quantitation by ICP-MS

The authors describe a microfluidic method for desorption-free magnetic solid phase extraction (MSPE) of Hg2+ ions prior to their determination through ICP-MS. Nanoparticles comprising a gold core and an iron oxide (Fe3O4) shell were functionalized with l-cysteine and then used to extract trace amounts of Hg2+. In contrast to typical solid phase extraction processes, this approach is rapid and does not require a desorption step. The working pH, amount of adsorbent, sample volume, adsorption selectivity, adsorption capacity, and adsorption flow rate were optimized. Under the optimized conditions, the method was validated through determination of a certified reference material (NIST 1641d; mercury in water); the results were in good agreement. The method was applied to the analysis of (spiked) tap water and gave recoveries ranging from 101.5% to 109.3%. It was also applied to the analysis of biosamples available in limited volumes only, including cerebrospinal fluid and microdialysates.

Combining Microdialysis Sampling and Inductively Coupled Plasma Mass Spectrometry for Dynamic Monitoring of Trace Metal Ions during Bacterial Growth Periods

Monitoring the dynamic variations of trace metal ions allows us to understand their roles in basic cellular functions and also in microbial-mediated detoxification of metal pollutants. The objective of this study was to develop an easily operated, simultaneous, and continuous method for dynamic monitoring of trace metal ions during bacterial growth periods. Here, we used a microdialysis (MD) sampling technique combined with detection through inductively coupled plasma mass spectrometry (ICP-MS) to determine and quantify trace metal ions. After optimization, we used a retrodialysis technique and a no-net-flux method to assess the probe recovery and analytical performance of the proposed system. The mean probe recoveries of cobalt, copper, strontium, cadmium, and lead were 64.4, 92.6, 40.8, 84.2, and 54.7%, respectively, with typical precision values of 0.5–6.2, 1.1–7.7, 2.0–6.3, 2.3–7.8, and 1.5–7.8%, respectively. To further evaluate the practical applicability of using our proposed MD/ICP-MS method, we monitored, continuously for 24 h, the dynamic variations of the concentrations of each metal ion in four standardized bacterial species (ATCC 35218, 25922, 25923, 29213). Our analytical results revealed that MD sampling combined with ICP-MS detection had the ability to accurately and continuously monitor the levels of trace metal ions in microbial inoculated culture broths, potentially benefiting research into the bioavailability and detoxification processes of trace metal ions in microbial samples.

Oxidative stress during bacterial growth characterized through microdialysis sampling coupled with HPLC/fluorescence detection of malondialdehyde

Organisms that grow aerobically are routinely exposed to oxidative stress in the form of reactive oxygen species. Monitoring the dynamic variations of oxidative stress allows us to understand its role in basic cellular function and determine mechanisms of antioxidation. In this study, microdialysis (MD) sampling was employed for continuous monitoring of the formation of malondialdehyde (MDA) in a bacterium-inoculated culture broth. To test the practicality of this approach, oxidative stress was induced by cadmium and then a 60-min interval was selected to collect sufficient amounts of dialysate for high-performance liquid chromatography with fluorescence (HPLC-FL) detection. After optimization of this simple-to-operate, simultaneous, and continuous method for dynamic monitoring of MDA during periods of bacterial growth, a retrodialysis technique and a no-net-flux method were used to assess the probe recovery and analytical performance of the proposed system. The mean probe recovery of MDA was 78.6 ± 0.9%, with intra- and interday precisions of 2.7-6.1 and 3.5-7.6%, respectively. To evaluate the practicality of this method, the dynamic variations in the concentrations of MDA in standardized bacterial species (Staphylococcus aureus, ATCC(®) 29213™) were monitored continuously for 24h. The analytical results confirmed that this MD sampling technique combined with HPLC-FL detection can be used to accurately and continuously monitor the levels of MDA in microbially inoculated culture broths.

Ultrasound-assisted hollow fiber/ionic liquid-based liquid phase microextraction using an ionic liquid solvent for preconcentration of cobalt and nickel ions in urine samples prior to FAAS determination

Ultrasound-assisted (UA) hollow fiber (HF) liquid-phase microextraction (LPME) coupled with flame atomic absorption spectrometry (FAAS) has been developed to preconcentrate and determine ultra-trace amounts of cobalt (Co) and nickel (Ni) ions in human urine. To the best of our knowledge, no previous reports have described the coupling of UA-ionic liquid (IL)-HF-LPME with an FAAS system to analyze metal ions in biological samples. In this study, the ILs 1-hexyl-3-methylimidazolium hexafluorophosphate, sodium hexafluorophosphate, and 1-(2-pyridylazo)-2-naphthol were used as extraction, ion-pairing, and chelating agents, respectively. With the assistance of an ultrasonic probe, the analyte exchange between the phases increased, and the extraction efficiency of Co and Ni ions improved significantly. The collected extraction phase was subsequently analyzed directly through FAAS. Under optimized conditions, the detection limits of Co and Ni ions were 0.09 and 0.03 μg L−1, respectively. The precision of the analysis of Co and Ni ions was within a relative standard deviation of 10% under normal operating conditions. The ultrasonic assistance provided enrichment factors of 66 and 82 for Co and Ni ions, respectively. The recoveries of Co and Ni ions spiked in urine samples ranged from 93.8 to 104.3%. The practicality of the proposed method was demonstrated through satisfactory analyses of samples of a standard reference material and real human urine.