Nanocomposite-Coated Microfluidic-Based Photocatalyst-Assisted Reduction Device To Couple High-Performance Liquid Chromatography and Inductively Coupled Plasma-Mass Spectrometry for Online Determination of Inorganic Arsenic Species in Natural Water.

To selectively and sensitively determine the trace inorganic As species, As(III) and As(V), we developed a nanocomposite-coated microfluidic-based photocatalyst-assisted reduction device (PCARD) as a vapor generation (VG) device to couple high-performance liquid chromatography (HPLC) separation and inductively coupled plasma-mass spectrometry (ICPMS) detection. Au nanoparticles were deposited on TiO2 nanoparticles to strengthen the conversion efficiency of the nanocomposite photocatalytic reduction. The sensitivity for As was significantly enhanced by employing the nanocomposite photocatalyst and using prereduction and signal-enhancement reagents. Under the optimal operating conditions, the analytical detection limits (based on 3σ) of the proposed online HPLC/nanocomposite-coated microfluidic-based PCARD/ICPMS system for As(III) and As(V) were 0.23 and 0.34 µg·L-1, respectively. The results were validated using a certified reference material (NIST SRM 1643e) and groundwater sample analysis, indicating the good reliability and applicability of our proposed system for the determination of inorganic As species in natural fresh water.

In-vivo evaluation of the permeability of the blood-brain barrier to arsenicals, molybdate, and methylmercury by use of online microdialysis-packed minicolumn-inductively coupled plasma mass spectrometry.

To study the permeability of the blood-brain barrier (BBB) to arsenates, arsenite, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), molybdate, and methylmercury, and the transfer behavior of these species, we constructed an automatic online analytical system comprising a microdialysis sampling device, a minicolumn packed with nonfunctionalized poly(vinyl chloride) beads, and an inductively coupled plasma mass spectrometer for continuous in-vivo measurement of their dynamic variation in the extracellular space of the brains of living rats. By using ion-polymer interactions as a novel working mechanism for sample pretreatment of volume-limited microdialysate, we simplified the operating procedure of conventional solid-phase extraction and reduced the contribution to the blank of the chemicals used. After optimizing this hyphenated system, we measured its performance by analysis of NIST standard reference materials 1640a (trace elements in natural water) and 2672a (trace elements in human urine) and by in-vivo monitoring of the dynamic variation of the compounds tested in the extracellular fluid (ECF) of rat brain. We found that intraperitoneal administration led to observable BBB permeability of arsenates, arsenite, DMA, MMA, and molybdate. Nevertheless, the limited sensitivity of the system and the size of microdialysis samples meant that detection of MeHg in ECF remained problematic, even when we administered a dose of 20 mg MeHg kg(-1) body weight. On the basis of these practical demonstrations, we suggest that our analytical system could be used not only for dynamic monitoring of the transfer kinetics of the four arsenicals and molybdate in the rat brain but also to describe associated neurotoxicity in terms of exposure to toxic metals and their species.

Development of a titanium dioxide-coated microfluidic-based photocatalyst-assisted reduction device to couple high-performance liquid chromatography with inductively coupled plasma-mass spectrometry for determination of inorganic selenium species.

We developed a selective and sensitive hyphenated system employing a microfluidic-based vapor generation (VG) system in conjunction with high-performance liquid chromatography (HPLC) separation and inductively coupled plasma-mass spectrometry (ICPMS) detection for the determination of trace inorganic selenium (Se) species. The VG system exploited poly(methyl methacrylate) (PMMA) substrates of high optical quality to fabricate a microfluidic-based photocatalyst-assisted reduction device (microfluidic-based PCARD). Moreover, to reduce the consumption of photocatalysts during analytical procedures, a microfluidic-based PCARD coated with titanium dioxide nanoparticles (nano-TiO2) was employed to avoid consecutive loading. Notably, to simplify the coating procedure and improve the stability of the coating materials, a dynamic coating method was utilized. Under the optimized conditions for the selenicals of interest, the online HPLC/TiO2-coated microfluidic-based PCARD/ICPMS system enabled us to achieve detection limits (based on 3σ) of 0.043 and 0.042 µg L(-1) for Se(IV) and Se(VI), respectively. Both Se(IV) and Se(VI) could be efficiently vaporized within 15 s, while a series of validation experiments indicated that our proposed method could be satisfactorily applied to the determination of inorganic Se species in the environmental water samples.

Development of a titanium dioxide-assisted preconcentration/on-site vapor-generation chip hyphenated with inductively coupled plasma-mass spectrometry for online determination of mercuric ions in urine samples.

In this study, a novel automatic analytical methodology using a titanium dioxide (TiO2)-assisted preconcentration/on-site vapor-generation (VG) chip hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS) for online determination of mercuric ions (Hg2+) was developed. Interestingly, the TiO2 nanoparticle (nano-TiO2) coating on the channel surface acted not only as a sorbent for preconcentration but also as a catalyst for photocatalyst-assisted VG. Under optimum operation conditions, the developed method was validated by analyzing the certified reference material (CRM) Seronorm™ Trace Elements Urine L-2 (freeze-dried human urine). Based on the obtained results, the dramatic reduction of "hands-on" manipulation and the elimination of hazardous materials (e.g., sodium borohydride (NaBH4) and stannous chloride (SnCl2)) from the process enabled a simple and ultraclean procedure with an extremely low detection limit of 0.75 ng L-1 for Hg2+ in urine samples. To the best of our knowledge, this is the first study to report the direct exploitation of a nano-TiO2-coated microfluidic device for online sample preconcentration and on-site VG prior to ICP-MS measurement.

Sequential photocatalyst-assisted digestion and vapor generation device coupled with anion exchange chromatography and inductively coupled plasma mass spectrometry for speciation analysis of selenium species in biological samples.

We have developed an on-line sequential photocatalyst-assisted digestion and vaporization device (SPADVD), which operates through the nano-TiO2-catalyzed photo-oxidation and reduction of selenium (Se) species, for coupling between anion exchange chromatography (LC) and inductively coupled plasma mass spectrometry (ICP-MS) systems to provide a simple and sensitive hyphenated method for the speciation analysis of Se species without the need for conventional chemical digestion and vaporization techniques. Because our proposed on-line SPADVD allows both organic and inorganic Se species in the column effluent to be converted on-line into volatile Se products, which are then measured directly through ICP-MS, the complexity of the procedure and the probability of contamination arising from the use of additional chemicals are both low. Under the optimized conditions for SPADVD - using 1g of nano-TiO2 per liter, at pH 3, and illuminating for 80 s - we found that Se(IV), Se(VI), and selenomethionine (SeMet) were all converted quantitatively into volatile Se products. In addition, because the digestion and vaporization efficiencies of all the tested selenicals were improved when using our proposed on-line LC/SPADVD/ICP-MS system, the detection limits for Se(IV), Se(VI), and SeMet were all in the nanogram-per-liter range (based on 3σ). A series of validation experiments - analysis of neat and spiked extracted samples - indicated that our proposed methods could be applied satisfactorily to the speciation analysis of organic and inorganic Se species in the extracts of Se-enriched supplements.

Development of chip-based photocatalyst-assisted reduction device to couple high performance liquid chromatography and inductively coupled plasma-mass spectrometry for determination of inorganic selenium species.

In this study, a poly(methyl methacrylate) chip-based photocatalyst-assisted reduction device (PMMA chip-based PCARD) was developed as a reactor based on its excellent optical properties and ease of fabrication. Its transmittance of ultraviolet light at 365nm (UV365) was found to be as high as 92% using a PMMA of 2mm thickness. To optimize the vaporization efficiency, the effect of varying the depth of the geometry trenched on the PMMA-based chip was investigated. After optimization, it required only 29s of UV365 irradiation to vaporize the selenium (Se) species of interest. The PMMA-based chip was successfully used as an interfacing device for the hyphenation of high performance liquid chromatography (HPLC) separation and inductively coupled plasma-mass spectrometry (ICP-MS) detection. Additionally, under the optimized conditions for vaporization, using 1gL(-1) titanium dioxide nanoparticles (nano-TiO2) at pH 5, we found that Se(IV) and Se(VI) were converted quantitatively into volatile Se products. In addition, the optimized vaporization efficiency of the Se species of interest for the online HPLC/PMMA chip-based PCARD/ICP-MS system enabled us to achieve detection limits for Se(IV) and Se(VI) in the nanogram-per-liter range (based on 3σ). A series of validation experiments indicated that our proposed methods could be applied satisfactorily to the determination of inorganic Se species in environmental water samples.