Self-Assembly of Poly(ethyleneimine)-Modified g-C3N4 Nanosheets with Lysozyme Fibrils for Chromium Detoxification.

We disclose a straightforward approach to fabricate nanocomposites for efficient capture of Cr(VI) from an aqueous solution through the self-assembly of poly(ethyleneimine)-modified graphitic carbon nitride nanosheets (PEI-g-C3N4 NSs) and lysozyme fibrils (LFs). The as-made PEI-g-C3N4 NSs@LFs exhibited mesoporous structures with a high specific surface area of 39.6 m2 g-1, a large pore volume of 0.25 cm3 g-1, several functional groups (e.g., -N, -NH, -NH2, and -COOH), and a zero-point charge at pH 9.1. These merits allow the PEI-g-C3N4 NSs@LFs to further enhance their physical adsorption and electrostatic attraction with the negatively charged Cr(VI) species of HCrO4- and CrO42-, which is beneficial for the uptake of Cr(VI), >80%, from an aqueous solution in a wide pH range. Interestingly, X-ray photoelectron spectra indicate that the PEI-g-C3N4 NSs@LFs converted Cr(VI) to Cr(III) through visible-light-induced photoreduction. The adsorption of Cr(VI) on the surface of PEI-g-C3N4 NSs@LFs was found to obey the Freundlich isotherm model, signifying that they have a heterogeneous surface for the multilayer uptake of Cr(VI). In contrast, the PEI-g-C3N4 NSs and LFs as Cr(VI) adsorbents followed the Langmuir isotherm model. Adsorption kinetic studies showed that the uptake of Cr(VI) through the PEI-g-C3N4 NSs@LFs was highly correlated with a pseudo-first-order model, suggesting that physisorption dominates the interaction of Cr(VI) and the PEI-g-C3N4 NSs@LFs. In real-life applications, the PEI-g-C3N4 NSs@LFs were used for the detoxification of the total chromium in the industrial effluent and sludge samples.

Determination of Cr(VI) in rice using ion chromatography inductively coupled plasma mass spectrometry.

Determination of Cr(VI) in rice is reported using ion chromatography (IC) and dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS). Cr(VI) is separated from other Cr species within 4.5 min using NH4NO3 solution at pH 8.8 as mobile phase. Spectral interferences on 52Cr+ are minimized with NH3 in DRC. The detection limit of (LOD) Cr(VI) is 0.06 ng mL-1. This methodology is utilized for the determination of Cr(VI) in different rice samples and can also be applied for screening of rice for toxicity with respect to Cr. The Cr species are leached from rice powder into 5% (v/v) tetramethyl ammonium hydroxide (TMAH) solution in an ultrasonic bath. The extracts are analyzed by IC-DRC-ICP-MS for Cr(VI). Spike recoveries of Cr(VI) are 98-102% and precision between sample replicates is better than 6.3%. No Cr(III) is converted to Cr(VI) during extraction. Cr(VI) is present in all the rice samples analyzed.

Determination of antimony compounds in waters and juices using ion chromatography-inductively coupled plasma mass spectrometry.

A method was developed by coupling ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) for the speciation of antimony. In this study, antimony species such as antimonite [Sb(III)], antimonate [Sb(V)] and trimethyl antimony(V) (TMeSb) were separated in less than 8min using anion exchange chromatography with a Hamilton PRP-X100 column as the stationary phase. Mobile phase A was 20mmolL-1 ethylenediaminetetraacetic acid (EDTA), 2mmolL-1 potassium hydrogen phthalate (KHP) in 1% v/v methanol (pH 5.5) and 20mmolL-1 EDTA, 2mmolL-1 KHP, 40mmolL-1 (NH4)2CO3 in 1% v/v methanol (pH 9.0) formed mobile phase B. Detection limits and relative standard deviations (RSD) were 0.012-0.032ngmL-1 and 2.2-2.8% respectively. This method was applied to bottled waters and fruit juices purchased in Kaohsiung, Taiwan. In water samples, Sb(V) was the major species where as in juices organometallic Sb species were also present.

Determining lead, cadmium and mercury in cosmetics using sweeping via dynamic chelation by capillary electrophoresis.

International limits have been established for metal impurities in cosmetics to prevent overexposure to heavy metal ions. Sweeping via dynamic chelation was developed using capillary electrophoresis to analyze lead (Pb), cadmium (Cd) and mercury (Hg) impurities in cosmetics. The sweeping via dynamic chelation mechanism involves a large volume of metal ions being swept by a small quantity of chelating agents that were electrokinetically injected into the capillary to chelate metal ions and increase the detection sensitivity. The optimized conditions were as follows: Firstly, the capillary was rinsed by a 0.6 mM TTAB solution to reverse the EOF. The sample solution, which was diluted using 25 mM ammonium acetate (pH 6.0), was injected into the capillary using a pressure of 3.5 psi for 99.9 s. Then, EDTA was injected at -25 kV for 1 min from the EDTA buffer (25 mM ammonium acetate containing 0.6 mM TTAB and 5 mM EDTA), and the metal ions were swept and stacked simultaneously. Finally, the separation was performed at -20 kV using a separation buffer (100 mM ammonium acetate (pH 6.0)). A small quantity of chelating agents introduced into the capillary could yield 33-, 50- and 100-fold detection improvements for Pb, Cd and Hg, respectively, more sensitive than conventional capillary zone electrophoresis. Correlation coefficients greater than 0.998 indicated that this method exhibited good linearity. The relative standard deviation and relative error were less than 8.7%, indicating high precision and accuracy. The recovery value of the homemade lotion, which was employed to simulate the real sample matrix, was 93-104%, which indicated that the sample matrix does not affect the quantitative results. Finally, commercial cosmetics were employed to demonstrate the feasibility of the method to determine Pb, Cd and Hg without complicated sample pretreatment. Graphical Abstract The procedure of analyzing metal ions in cosmetics by sweeping via dynamic chelation.

Synthesis and Characterization of Two-Dimensional Transition Metal Dichalcogenide Magnetic MoS2@Fe3O4 Nanoparticles for Adsorption of Cr(VI)/Cr(III).

Recently, two-dimensional transition metal dichalcogenides (TMDs) have received tremendous attention in many fields including environmental remediation. Magnetic nanoparticles (Fe3O4NPs) decorated with MoS2 (MoS2@Fe3O4NPs) have been synthesized via a new one-step synthesis route and utilized as an efficient adsorbent for removal of Cr(VI)/Cr(III) from aqueous solutions. The obtained MoS2@Fe3O4NPs with numerous surface hydroxyl groups show uniform size and shape, excellent water-dispersibility, and superior magnetic property to enhance the adsorption. The physicochemical properties of the adsorbent prior to and after adsorption of Cr(VI)/Cr(III) were extensively characterized using several advanced instrumental techniques.The adsorption of Cr(VI)/Cr(III) on MoS2@Fe3O4NPs was performed under batch conditions aiming at identification of optimal contact time, pH value of chromium solution, and influence of the presence of competitive ions. This study was supported by modeling of adsorption equilibrium and kinetics by using empirical equations.

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.

Determination of As, Hg and Pb in herbs using slurry sampling flow injection chemical vapor generation inductively coupled plasma mass spectrometry.

Analysis of herbs for As, Hg and Pb has been carried out using slurry sampling inductively coupled plasma mass spectrometry (ICP-MS) with flow injection vapor generation. Slurry containing 0.5% m/v herbal powder, 0.1% m/v citric acid and 2% v/v HCl was injected into the VG-ICP-MS system for the determination of As, Hg and Pb that obviate dissolution and mineralization. Standard addition and isotope dilution methods were used for quantifications in selected herbal powders. This method has been validated by the determination of As, Hg and Pb in NIST standard reference materials SRM 1547 Peach Leaves and SRM 1573a Tomato Leaves. The As, Hg and Pb analysis results of the reference materials agreed with the certified values. The precision obtained by the reported procedure was better than 7% for all determinations. The detection limit estimated from standard addition curve was 0.008, 0.003, and 0.007 ng mL(-1) for As, Hg and Pb, respectively.

Application of a multivariate approach for analyte focusing by micelle collapse-micellar electrokinetic chromatography for analyzing sunscreen agents in cosmetics.

The operating parameters that affect the performance of the online preconcentration technique "analyte focusing by micelle collapse-MEKC (AFMC-MEKC)" were examined using a multivariate approach involving experimental design to determine the sunscreen agents in cosmetics. Compared to the single-variable approach, the advantage of the multivariate approach was that many factors could be investigated simultaneously to obtain the best separation condition. A fractional factorial design was used to identify the fewest significant factors in the central composite design (cCD). The cCD was adopted for evaluating the location of the minimum or maximum response in this study. The influences of the experimental variables on the response were investigated by applying a chromatographic exponential function. The optimized condition and the relationship between the experimental variables were acquired using the JMP software. The ANOVA analysis indicated that the Tris pH value, SDS concentration, and ethanol percentage influenced the separation quality and significantly contributed to the model. The optimized condition of the running buffer was 10 mM Tris buffer (pH 9.5) containing 60 mM SDS, 7 mM γ-CD, and 20% v/v ethanol. The sample was prepared in 100 mM Tris buffer (pH 9.0) containing 7.5 mM SDS and 20% v/v ethanol. The SDS concentration in the sample matrix was slightly greater than the CMC value that makes the micelle be easily collapsed and the analytes be accumulated in the capillary. In addition, sunscreen agents in cosmetics after 1000-fold dilution were successfully determined by AFMC-MEKC.

Slurry sampling flow injection chemical vapor generation inductively coupled plasma mass spectrometry for the determination of trace Ge, As, Cd, Sb, Hg and Bi in cosmetic lotions.

A slurry sampling inductively coupled plasma mass spectrometry (ICP-MS) method has been developed for the determination of Ge, As, Cd, Sb, Hg and Bi in cosmetic lotions using flow injection (FI) vapor generation (VG) as the sample introduction system. A slurry containing 2% m/v lotion, 2% m/v thiourea, 0.05% m/v L-cysteine, 0.5 µg mL(-1) Co(II), 0.1% m/v Triton X-100 and 1.2% v/v HCl was injected into a VG-ICP-MS system for the determination of Ge, As, Cd, Sb, Hg and Bi without dissolution and mineralization. Because the sensitivities of the analytes in the slurry and that of aqueous solution were quite different, an isotope dilution method and a standard addition method were used for the determination. This method has been validated by the determination of Ge, As, Cd, Sb, Hg and Bi in GBW09305 Cosmetic (Cream) reference material. The method was also applied for the determination of Ge, As, Cd, Sb, Hg and Bi in three cosmetic lotion samples obtained locally. The analysis results of the reference material agreed with the certified value and/or ETV-ICP-MS results. The detection limit estimated from the standard addition curve was 0.025, 0.1, 0.2, 0.1, 0.15, and 0.03 ng g(-1) for Ge, As, Cd, Sb, Hg and Bi, respectively, in original cosmetic lotion sample.

Determining ultraviolet absorbents in sunscreen products by combining direct injection with micelle collapse on-line preconcentration capillary electrophoresis.

The on-line preconcentration technique of analyte focusing by micelle collapse-micellar electrokinetic chromatography (AFMC-MEKC) was combined with direct injection without extraction to determine ultraviolet absorbents in sunscreen products. The stacking mechanism is based on the transport, release, and accumulation of analytes bound to micelle carriers that are collapsed into the micelle dilution zone. The following optimized conditions were determined: the running buffer was 10mM Tris buffer (pH 9.5) containing 60mM SDS, 7mM γ-CD and 20% ethanol; the SDS concentration was required to be slightly above the critical micelle concentration (cmc) value (7.4mM) in the sample matrix, which allowed the micelle dilution zone to form when voltage was applied; and finally, the sample was prepared in 100mM Tris buffer (pH 9.0) containing 7.5mM SDS and 20% (v/v) ethanol to provide sufficient resolution and to improve the sensitivity. Samples were injected at 0.5psi for 40s, and the separation voltage was set at 15kV for first 15min and then increased to 23kV to decrease the analysis time. The detection sensitivity for ultraviolet absorbents was enhanced by approximately 41-fold using AFMC-MEKC compared to conventional MEKC. The limit of detection (S/N=3) was 98nM for benzophenone-2 and benzophenone-4. The correlation of the regression curve was greater than 0.995. The relative error and relative standard deviation were lower than 9.94% with high precision and accuracy. The recoveries of nine ultraviolet absorbents in a homemade emulsion were between 95.08% and 104.57%. After optimization and validation, this AFMC-MEKC method combined with direct injection is considered to be established and successfully applicable to commercial sunscreen products.

Determination of trace elements in medicinal activated charcoal using slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry with low vaporization temperature.

The determination of Cd, Sb, Te, Hg, Tl and Pb in medicinal activated charcoal by ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) was described. EDTA was used as the modifier to enhance the volatility of elements studied. The influences of instrument operating conditions and slurry preparation on the ion signals were studied. A relatively low vaporization temperature of 1000°C was used, which separated the analyte from the major matrix components that improved ion signals. The method has been applied to determine Cd, Sb, Te, Hg, Tl and Pb in an NIST SRM 1633b Coal Fly Ash reference material and three brands of medicinal activated charcoal capsules using isotope dilution and standard addition calibration methods. The concentrations that are in ng g(-1) levels were in good agreement between different calibration methods. The precision between sample replicates was better than 7% with USS-ETV-ICP-MS technique. The method detection limit estimated from standard addition curves was 0.4, 0.3, 0.3, 0.3, 0.04 and 0.9 ng g(-1) for Cd, Sb, Te, Hg, Tl and Pb, respectively, in original medicinal activated charcoal.

Combined use of HPLC-ICP-MS and microwave-assisted extraction for the determination of cobalt compounds in nutritive supplements.

Speciation analysis of cobalt in nutritive supplements has been carried out using HPLC and ICP-MS equipped with a membrane desolvation sample introduction system as detector. In this study, cobalt containing compounds, namely Co(II), cyanocobalamin (CN-Cbl) and hydroxylcobalamin (OH-Cbl), were well separated by reversed phase HPLC with a C8-HPLC column as the stationary phase and 8 mmol L(-1) ammonium acetate in 22%v/v methanol solution (pH 4) as the mobile phase using isocratic elution. Detection limit was in the range of 0.008-0.014 µg CoL(-1) for various Co species. Over 98% of the total cobalt species was extracted in nutritive supplements using a 0.5%v/v HNO3 solution in a microwave field; and the spike recovery was in the range of 92-108% for various species. The HPLC-ICP-MS results showed a satisfactory agreement with the total cobalt concentrations obtained by ICP-MS analysis of completely dissolved samples.

Determination of Cu, As, Hg and Pb in vegetable oils by electrothermal vaporization inductively coupled plasma mass spectrometry with palladium nanoparticles as modifier.

The determination of Cu, As, Hg and Pb in vegetable oils by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) was investigated. The oils were injected in the form of emulsions containing 5% m/v vegetable oil, 1.5% v/v Triton X-100 and 50 µg mL(-1) ascorbic acid. Palladium nanoparticles (Pd-NPs) were used as modifier. The interference of (40)Ar(35)Cl(+) at arsenic mass m/z 75 was reduced significantly using dynamic reaction cell (DRC). Standard addition and isotope dilution methods were used for the quantifications. The method reported has been applied to the determination of Cu, As, Hg and Pb in selected vegetable oil samples purchased from a local market. The analytical results obtained were in good agreement with those of digested samples analyzed by pneumatic nebulization ICP-MS with 95% confidence according to Student t-test (except for Cu). Precision between sample replicates was better than 10% with the ETV-ICP-MS method. The detection limits obtained from standard addition curves were 0.4, 0.5, 1.1 and 0.4 ng g(-1) for Cu, As, Hg and Pb, respectively, in the original oil samples.

Determination of Pd, Rh, Pt, Au in road dust by electrothermal vaporization inductively coupled plasma mass spectrometry with slurry sampling.

Inductively coupled plasma mass spectrometry coupled with ultrasonic slurry sampling electrothermal vaporization (USS-ETV-ICP-MS) has been applied to determine Pd, Rh, Pt and Au in 0.5% m/v slurries of several road dust samples. 2% m/v ammonium pyrrolidine dithiocarbamate (APDC) was used as the modifier to enhance the ion count. The influence of instrument operating conditions, slurry preparation and interferences on the ion count was reported. This method has been applied to the determination of Pd, Rh, Pt and Au in BCR 723 Road Dust and NIST SRM 2709 San Joaquin Soil reference materials and two road dust samples collected locally. The analysis results of the standard reference materials agreed with the certified values. Precision between sample replicates was better than 10% for all the determinations. The method detection limits estimated from standard addition curves were 0.9, 0.4, 0.6 and 0.4ngg(-1) for Pd, Rh, Pt and Au, respectively, in original dust samples.

Determination of As, Cd, Hg and Pb in herbs using slurry sampling electrothermal vaporisation inductively coupled plasma mass spectrometry.

Inductively coupled plasma mass spectrometry coupled with ultrasonic slurry sampling electrothermal vaporisation (USS-ETV-ICP-MS) has been applied to determine As, Cd, Hg and Pb in 0.5% m/v slurries of several herb samples. 1% m/v 8-Hydroxyquinoline was used as the modifier to enhance the ion signals. The influences of instrument operating conditions, slurry preparation and interferences on the ion signals were reported. This method has been applied to the determination of As, Cd, Hg and Pb in NIST SRM 1547 peach leaves and SRM 1573a tomato leaves reference materials and three herb samples purchased from the local market and ground to 150 µm. The analysis results of the standard reference materials agreed with the certified values which are at sub µg g(-1) levels. Precision between sample replicates was better than 4% for all the determinations. The method detection limits estimated from standard addition curves were about 0.3, 0.1, 0.1 and 0.2 ng g(-1) for As, Cd, Hg and Pb, respectively, in original herb samples.

Application of HPLC-ICP-MS and HPLC-ESI-MS procedures for arsenic speciation in seaweeds.

Speciation of arsenic in seaweeds was carried out using ion chromatography (IC) for separation and inductively coupled mass spectrometry (ICP-MS) for detection. The arsenic species studied were arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), and arsenocholine (AsC). Chromatographic separation of all the species was achieved in <9 min in gradient elution mode using (NH(4))(2)CO(3) and methanol at pH 8.5. The outlet of the IC column was directly connected to the nebulizer of ICP-MS for the determination of arsenic. The speciation of arsenic has been carried out in several seaweed samples. A microwave-assisted extraction method was used for the extraction of arsenic species from seaweed samples. With a mixture of mobile phase A and methanol as extractant, the extraction efficiency was >84%, and the recoveries from spiked samples were in the range of 90-106%. The unknown compounds detected in different seaweeds were identified by coupling IC directly with electrospray ionization-mass spectrometry (ESI-MS). Two arsenosugars and tetramethylarsonium ion (TETRA) were identified in different seaweeds. A fat-soluble arsenolipid compound was identified in the extract of certified reference material BCR-279 Ulva lactuca when 1% HNO(3) was used as the extractant. The precision between sample replicates was >9% for all determinations. The limits of detection were in the range of 0.006-0.015 µg L(-1) for various arsenic species based on peak height.

Speciation analysis of arsenic compounds in edible oil by ion chromatography-inductively coupled plasma mass spectrometry.

An inductively coupled plasma mass spectrometer (ICP-MS) was used as an ion chromatographic (IC) detector for the speciation analysis of arsenic in edible oil. The arsenic species studied include arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine and arsenocholine. Gradient elution using (NH(4))(2)CO(3) and methanol at pH 8.5 allowed the chromatographic separation of all species in less than 8 min. Effluents from the IC column were delivered to the nebulizer of ICP-MS for the determination of arsenic. The concentrations of arsenic species have been determined in several used and fresh vegetable oil samples. In this study, a microwave-assisted extraction method was used for the extraction of arsenic species from oil samples. The extraction efficiency was better than 92% and the recoveries from spiked samples were in the range of 90-105%. The precision between sample replicates was better than 8% for all determinations. The limits of detection were in the range of 0.008-0.024 ng mL(-1) for various arsenic species based on peak height, which corresponded to 0.08-0.24 ng g(-1) in the original oil sample. The major arsenic species in the used oil samples varied based on the food items cooked.

Microwave-assisted extraction and ion chromatography dynamic reaction cell inductively coupled plasma mass spectrometry for the speciation analysis of arsenic and selenium in cereals.

An ion chromatography dynamic reaction cell inductively coupled plasma mass spectrometric (IC-DRC-ICP-MS) method for the speciation of arsenic and selenium compounds is described. Chromatographic separation was performed in a gradient elution mode using 0.5 mmol L(-1) ammonium citrate in 1% methanol (pH 4.5) and 15 mmol L(-1) ammonium citrate in 1% methanol (pH 8.0). The potentially interfering (38)Ar(40)Ar(+) and (40)Ar(40)Ar(+) at selenium masses of m/z 78 and 80 were reduced in intensity by approximately 3 orders of magnitude by using 1.0 mL min(-1) CH(4) as a reactive cell gas in the DRC. Arsenic was determined as the adduct ion (75)As(12)CH(2)(+) at m/z 89. The detection limits of the procedure were in the ranges of 0.006-0.009 ng As mL(-1) and 0.009-0.03 ng Se mL(-1), respectively. This method has been applied to determine various arsenic and selenium compounds in cereal samples. The accuracy of the method has been verified by comparing the sum of the concentrations of individual species obtained by the present procedure with the total concentration of elements. The arsenic and selenium compounds were quantitatively extracted with a Protease XIV and α-amylase solution in a microwave field at 70°C during a period of 30 min. The spike recoveries were in the range of 94-105% for all determinations.

Speciation analysis of arsenic and selenium compounds by CE-dynamic reaction cell-ICP-MS.

A dynamic reaction cell ICP-MS was used as a CE detector for the speciation analysis of arsenic and selenium. Samples containing arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, selenite, selenate, selenocysteine, selenomethione, and Se-methylselenocysteine were subjected to electrophoretic separation before being introduced into the microconcentric nebulizer (CEI-100) for their determination by ICP-MS. The separation has been achieved in a 60 cm length x 75 microm id fused-silica capillary. The electrophoretic buffer used was 25 mmol/L CAPS, and 0.5 mmol/L SDS at pH 9.5, whereas the applied voltage was set at 25 kV. The potentially interfering (38)Ar(40)Ar(+) and (40)Ar(40)Ar(+) at the selenium masses m/z 78 and 80 were reduced in intensity by approximately three orders of magnitude by using 1.4 mL/min CH(4) as reactive cell gas in the dynamic reaction cell. Arsenic was determined as the adduct ion (75)As(12)CH(2) (+) at m/z 89. The LOD for arsenic and selenium was in the range of 0.6-1.8 ng/mL, and 0.5-1.4 ng/mL, respectively, based on peak height. This method has been applied to determine various arsenic and selenium compounds in NIST SRM 1633a Coal Fly Ash and NRCC DOLT-3 Dogfish Liver reference materials and a selenium dietary supplement. The arsenic and selenium compounds were extracted from fish liver and dietary supplement by using Protease XIV and Lipase, and from coal fly ash with HF solution. The spike recoveries were in the range 91-103% for all the species studied.

Determination of Hg and Pb in fuels by inductively coupled plasma mass spectrometry using flow injection chemical vapor generation.

An isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) method has been developed for the determination of Hg and Pb in fuels using flow injection vapor generation (VG) as the sample introduction system. A simple and inexpensive in-situ nebulizer/vapor generator was employed in this study. An emulsion containing 10% v/v fuel, 2% m/v Triton X-100 and 1.0% m/v tartaric acid was injected into VG-ICP-MS system for the determination of Hg and Pb. Sodium borohydride was used for vapor generation. Since the sensitivities of Hg and Pb in emulsion and those in aqueous solution are quite different, isotope dilution and standard addition methods were used for the determination of Hg and Pb in selected fuel samples. The influences of vapor generation conditions and emulsion preparation on the ion signals are reported. This method has been applied for the determination of Hg and Pb in various fuel samples such as diesel, gasoline and engine oil obtained locally. The analytical results obtained by isotope dilution and standard addition methods were in good agreement with each other and also with those of digested samples analyzed by pneumatic nebulization ICP-MS. Under the optimum operating conditions, the detection limits obtained were 0.02 and 0.03 ng mL(-1) for Hg and Pb, respectively, in prepared emulsified solutions, corresponding to 0.2 and 0.3 ng mL(-1) of Hg and Pb, respectively, in the original fuel samples.