Jian-Hua Wang

Selective extraction/isolation of hemoglobin with ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate (BtmsimPF6)

Ionic liquid was for the first time employed for selective isolation of heme-protein species. Direct extraction of hemoglobin into ionic liquid without using any concomitant reagent or extractant was carried out. Hemoglobin at the level of 100 ng microL(-1) could readily be quantitatively extracted into ionic liquid (IL) 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate (BtmsimPF(6)) in the absence of any co-existing extractants/additives at pH 7, at the same time; however, the other protein species do not interfere and remain in the aqueous phase. A back extraction efficiency of ca. 80% for 20 ng microL(-1) hemoglobin in ionic liquid phase was achieved with sodium dodecyl sulfate (SDS) solution as stripping reagent. (57)Fe Mossbauer spectra and circular dichroism (CD) spectra indicated that the penta-coordinated ferrous atom in hemoglobin provide a vacant or free coordinating position, which could be occupied by the cationic Btmsim(+) moiety. The interaction/coordination reaction between the iron atom in the heme group of hemoglobin and the cationic ionic liquid moiety furnishes the driving force for facilitating fast transfer of hemoglobin into BtmsimPF(6). The present system was applied for selective isolation of heme-protein, i.e., hemoglobin from human whole blood without any pretreatment, giving rise to satisfactory results.

Flow injection on-line solid phase extraction for ultra-trace lead screening with hydride generation atomic fluorescence spectrometry

A flow injection (FI) on-line solid phase extraction (SPE) procedure for ultra-trace lead separation and preconcentration was developed, followed by hydride generation and atomic fluorescence spectrometric (AFS) detection. Lead is retained on an iminodiacetate chelating resin packed microcolumn, and is afterward eluted with 2.5% (v/v) hydrochloric acid to facilitate the hydride generation by reaction with alkaline tetrahydroborate solution with 1% (m/v) potassium ferricyanide as an oxidizing (or sensitizing) reagent. The hydride was separated from the reaction medium in the gas-liquid separator and swept into the atomizer for quantification. The chemical variables and the FI flow parameters were carefully optimized. With a sample loading volume of 4.8 ml, quantitative retention of lead was obtained, along with an enrichment factor of 11.3 and a sampling frequency of 50 h(-1). A detection limit of 4 ng l(-1), defined as 3 times the blank standard deviation (3 sigma), was achieved along with a RSD value of 1.6% at the 0.4 microg l(-1) level. The procedure was validated by determining lead contents in two certified reference materials, and its practical applicability was further demonstrated by analysing a variety of biological and environmental samples.

The development of a miniature atomic fluorescence spectrometric system in a lab-on-valve for mercury determination

A miniaturized atomic fluorescence spectrometric system was developed based on a novel lab-on-valve (LOV) configuration. The LOV integrates a micro-scale vapour generation chamber with a PTFE membrane (pore size 0.45 μm, thickness 60 μm) as the gas–liquid separation medium. The mercury cold vapour generated by reaction of sample with tetrahydroborate was separated and immediately excited in the outlet of the membrane gas–liquid separator by 253.7 nm incident light from a mercury hollow cathode lamp, while the fluorescence was monitored using a side-on photomultiplier. Both the incident light and the fluorescence were transmitted by fibre optics (600 or 1000 μm in diameter). A few important parameters governing the performance of the LOV atomic fluorescence spectrometric system were investigated, encompassing the positioning of the fibre optic tips in the excitation chamber, the concentration and volume of NaBH4 solution, as well as the effect of the concomitant hydrogen from the reduction reaction of mercury. The limit of detection of the system for mercury was estimated to be 0.1 and 0.02 μg l−1 by using fibre optics of 600 and 1000 μm diameter, respectively, with volume consumptions of 500 μl and 400 μl for sample and NaBH4 solutions. A sampling frequency of 90 h−1 was achieved along with RSD values of 2.7–4.4% at the concentration level of 1.0 μg l−1 by using 600 μm diameter fibre optics. The present system was applied for the measurement of mercury in certified reference materials, i.e., CRM 176 (Trace Elements in a City Waste Incineration Ash), NASS-5 (Seawater) and SLRS-4 (Riverine Water).

Sequential/bead injection lab-on-valve incorporating a renewable microcolumn for co-precipitate preconcentration of cadmium coupled to hydride generation atomic fluorescence spectrometry

A sequential/bead injection lab-on-valve apparatus incorporating a renewable microcolumn packed with co-polymeric immobilized C18 microbeads was applied to the on-line co-precipitate separation/preconcentration of ultra-trace cadmium by hyphenating with hydride generation atomic fluorescence spectrometry. Cadmium was co-precipitated with lanthanum hydroxide and collected on a microcolumn in the lab-on-valve. The co-precipitate was eluted with hydrochloric acid and directed to meet tetrahydroborate and facilitate hydride generation. The hydride was separated from the reaction mixture and was swept into the atomizer. With a sampling volume of 500 μl, quantitative retention of cadmium was achieved, along with an enrichment factor of 9.8 and a sampling frequency of 11 h−1. A detection limit of 3.5 ng l−1 was derived, along with a RSD of 1.6% (0.1 μg l−1). The procedure was validated analyzing cadmium in certified reference materials.

Iron(III) Modification of Bacillus subtilis Membranes Provides Record Sorption Capacity for Arsenic and Endows Unusual Selectivity for As(V)

Bacillus subtilis is a spore forming bacterium that takes up both inorganic As(III) and As(V). Incubating the bacteria with Fe(III) causes iron uptake (up to ∼0.5% w/w), and some of the iron attaches to the cell membrane as hydrous ferric oxide (HFO) with additional HFO as a separate phase. Remarkably, 30% of the Bacillus subtilis cells remain viable after treatment by 8 mM Fe(III). At pH 3, upon metalation, As(III) binding capacity becomes ∼0, while that for As(V) increases more than three times, offering an unusual high selectivity for As(V) against As(III). At pH 10 both arsenic forms are sorbed, the As(V) sorption capacity of the ferrated Bacillus subtilis is at least of 11 times higher than that of the native bacteria. At pH 8 (close to pH of most natural water), the arsenic binding capacity per mole iron for the ferrated bacteria is greater than those reported for any iron containing sorbent. A sensitive arsenic speciation approach is thus developed based on the binding of inorganic arsenic species by the ferrated bacteria and its unusual high selectivity toward As(V) at low pH.

Biological cell-sorption for separation/preconcentration of ultra-trace cadmium in a sequential injection system with detection by electrothermal atomic absorption spectrometry

The potential of biological cell-sorption for separation/pre-concentration of ultra-trace heavy metals was exploited by immobilizing Chlorella vulgaris and Saccharomyces cerevisiae cells onto silica beads and using them for cadmium sorption. FT-IR investigations showed that when C. vulgaris was used, the functional groups on the cell wall, i.e., hydroxyl and ether, were both involved in the sorption, while for S. cerevisiae, hydroxyl, amide and acetyl served as binding sites, but ether was not active. Because both cells contribute to the sorption, a significant improvement in retention efficiency was observed by immobilizing a mixture of C. vulgaris and S. cerevisiae cells onto silica used for sorption, with respect to those obtained by a single type of cell. A novel procedure for cadmium pre-concentration was developed based on this observation with detection by electrothermal atomic absorption spectrometry (ETAAS), employing cell immobilized silica beads for packing a micro-column in a sequential injection system. The cadmium retained on the column was eluted with a small amount of nitric acid and quantified with ETAAS. Within a range of 0.005–0.2 μg l−1 and a sample volume of 1000 μl, the retention efficiencies achieved by using mixed cells, individual cells of C. vulgaris and individual cells of S. cerevisiae were 97%, 74% and 65%, respectively, with respect to 32% with pure silica. When a cell mixture was employed, an enrichment factor of 38.6, a limit of detection of 1.0 ng l−1, along with a sampling frequency of 20 h−1, was attained, leading to a precision of 2.3% RSD (0.05 μg l−1). The procedure was validated by analyzing cadmium in a certified reference material of riverine water and spike recovery in a lake water sample.

Ionic liquid-polyvinyl chloride ionomer for highly selective isolation of basic proteins.

Hydrophilic ionic liquid-polyvinyl chloride (PVC) hybrids were prepared by immobilizing N-methylimidazole (N-mim) to PVC chains in toluene. The NmimCl-PVC hybrids were characterized by FT-IR, (1)H NMR, surface charge analysis and elemental analysis. The immobilization ratio, i.e., the percentage of chloride on PVC chain reacting with N-mim to form the hybrid, varies from 4.3% to 15.1% by increasing the N-mim/PVC molar ratio. The most distinct feature of the hybrid is its excellent selectivity for adsorbing basic proteins by effective suppression of the non-specific protein adsorption by pure PVC, and a higher immobilization ratio facilitates better selectivity. In Tris-HCl buffer, 100 microg mL(-1) of basic proteins, i.e., lysozyme (Lys), cytochrome c (cyt-c) and hemoglobin (Hb), were favorably adsorbed with efficiencies of 97%, 98% and 94% by the hybrid with an immobilization ratio of 15.1%, while the adsorption of acidic proteins, i.e., bovine albumin serum (BSA), transferring (Trf) and immunoglobulin G (IgG) were negligible. The retained Lys, cyt-c and Hb could be readily recovered by elution with phosphate buffer, carbonate buffer and SDS solution with efficiencies of 89%, 87% and 84%, respectively. Another feature of the hybrid is the significant improvement of the biocompatibility characterized by the maintenance of the activity of hemoglobin after adsorption and elution process. The practical usefulness of the hybrid was demonstrated by selective isolation of hemoglobin from human whole blood.

New Developments in Flow Injection/Sequential Injection On‐line Separation and Preconcentration Coupled with Electrothermal Atomic Absorption Spectrometry for Trace Metal Analysis

Abstract During the last 30 years, flow injection analysis has gone through three generations, that is, the first generation in 1970s, supplemented by sequential injection in the 1990s as the second generation, and the recently emerged lab‐on‐valve system as the third generation, which holds clear advantages for instrumental miniaturization. The three generations have revolutionized the concept of sample pretreatment by facilitating on‐line operation and coupling with various detection techniques, among which its hyphenation with electrothermal atomic absorption spectrometry (ETAAS) has been one of the most attractive research field offering vast potentials and versatilities in the quantification of ultra‐trace metal species in complex matrices. In the present mini‐review, the state‐of‐the‐art developments for flow injection on‐line sample pretreatment coupled to ETAAS for trace metal analysis since 2003 were summarized, with special emphasis on the exploitations of the lab‐on‐valve system.

Live HeLa cells preconcentrate and differentiate inorganic arsenic species

Live HeLa cells immobilized on Sephadex G-50 beads were used as a medium for the preconcentration and speciation of inorganic arsenic. The sorption of arsenic species by live HeLa cells involves both surface uptake and bioaccumulation within the cells. At pH 3.0, the cells accumulate arsenate with high specificity over arsenite: 83.0 +/- 1.3% of the arsenate was sorbed while the retention of arsenite was negligible at 2.1 +/- 0.6%. The speciation of inorganic arsenic could thus be performed by direct determination of arsenate followed by quantifying total inorganic arsenic after conversion of arsenite to arsenate. We formed a disposable live cell preconcentration microcolumn with the live HeLa cells immobilized on Sephadex G-50 beads. After the sample was passed through the column for sorption to occur, the cells and any retained arsenate were stripped with 2 M HNO(3). The arsenic in the 30 microL eluate was directly measured by graphite furnace atomic absorption spectrometry. A new microcolumn was used for each sample. With a sample volume of 450 muL, a S/N = 3 limit of detection (LOD) of 0.05 microg/L and a linear range of 0.15-2.5 microg/L were attained; the relative standard deviation (RSD) was 1.7% at 1.25 microg/L. The procedure was validated by arsenic speciation in certified reference river water.

Speciation of inorganic arsenic in a sequential injection dual mini-column system coupled with hydride generation atomic fluorescence spectrometry.

The separation and speciation of inorganic arsenic(III) and arsenic(V) are facilitated by employing a novel sequential injection system incorporating two mini-columns followed by detection with hydride generation atomic fluorescence spectrometry. An octadecyl immobilized silica mini-column is used for selective retention of the complex between As(III) and APDC, while the sorption of As(V) is readily accomplished by a 717 anion exchange resin mini-column. The retained As(III)-PDC complex and As(V) are effectively eluted with a 3.0 mol L(-1) hydrochloric acid solution as stripping reagent, which well facilitates the ensuing hydride generation process via reaction with tetrahydroborate. With a sampling volume of 1.0 mL and an eluent volume of 100 microL for both species, linear ranges of 0.05-1.5 microg L(-1) for As(III) and 0.1-1.5 microg L(-1) for As(V) are obtained, along with enrichment factors of 7.0 and 8.2, respectively. Precisions of 2.8% for As(III) and 2.9% for As(V) are derived at the concentration level of 1.0 microg L(-1). The practical applicability of the procedure has been demonstrated by analyzing a certified reference material of riverine water (SLRS-4), in addition to spiking recovery in a lake water sample matrix.