Lanlan Jin

Elemental determination of microsamples by liquid film dielectric barrier discharge atomic emission spectrometry.

In this study, a new liquid-film dielectric barrier discharge (LFDBD) atomic emission source was developed for microsample elemental determination. It consists of a copper electrode, a tungsten wire electrode, and a piece of glass slide between them, which serves as the dielectric barrier as well as the sample plate. The sample solution with 1 mol L(-1) nitric acid, when deposited onto the surface of the glass slide, forms a thin liquid film. The plasma is generated between the tip of the tungsten wire electrode and the liquid film surface when alternating-current (ac) high voltage (peak voltage ~3.7 kV, frequency ~30 kHz) is applied on the electrodes. Qualitative and quantitative determinations of metal ions in the sample solution were achieved by atomic emission measurements in the plasma and were demonstrated in this study with elements Na, K, Cu, Zn, and Cd. Detection limits were in the range from 0.6 ng (7 μg L(-1)) for Na to 6 ng (79 μg L(-1)) for Zn. Repeatability, expressed as relative standard deviation from seven repetitive analyses of samples with analyte concentrations at 1 mg L(-1), varied from 2.1% to 4.4%. Compared with other liquid discharge systems that operate at atmospheric pressure, the current system offers several advantages: First, it eliminates the use of a sample flow system (e.g., syringe or peristaltic pump); instead, a small aliquot of sample is directly pipetted onto the glass slide for analysis. Second, it is a microanalysis system and requires sample volume ≤80 μL, a benefit when a limited amount of sample is available. Third, because the sample is applied in aliquot, there is no washout time, and the analysis can be easily extended to sample array for high-throughput analysis. The proposed LFDBD is promising for in-field elemental determination because of its simplicity, cost effectiveness, low power supply, and no inert gas requirement.

Solution cathode glow discharge induced vapor generation of mercury and its application to mercury speciation by high performance liquid chromatography–atomic fluorescence spectrometry

A novel solution cathode glow discharge (SCGD) induced vapor generation was developed as interface to on-line couple high-performance liquid chromatography (HPLC) with atomic fluorescence spectrometry (AFS) for the speciation of inorganic mercury (Hg(2+)), methyl-mercury (MeHg) and ethyl-mercury (EtHg). The decomposition of organic mercury species and the reduction of Hg(2+) could be completed in one step with this proposed SCGD induced vapor generation system. The vapor generation is extremely rapid and therefore is easy to couple with flow injection (FI) and HPLC. Compared with the conventional HPLC-CV-AFS hyphenated systems, the proposed HPLC-SCGD-AFS system is very simple in operation and eliminates auxiliary redox reagents. Parameters influencing mercury determination were optimized, such as concentration of formic acid, discharge current and argon flow rate. The method detection limits for HPLC-SCGD-AFS system were 0.67 μg L(-1) for Hg(2+), 0.55 μg L(-1) for MeHg and 1.19 μg L(-1) for EtHg, respectively. The developed method was validated by determination of certified reference material (GBW 10029, tuna fish) and was further applied for the determination of mercury in biological samples.

Application of ion molecule reaction to eliminate WO interference on mercury determination in soil and sediment samples by ICP-MS

Mercury is subject to severe tungsten oxide (WO) interference in the direct ICP-MS analysis for soil or sediment samples. In this study, a method based on ion molecule reaction (IMR) was used to eliminate the WO spectral interference in a dynamic reaction cell (DRC). Interfered ion (202WO+) was drastically oxidized to higher oxide ions (218WO2+ or 234WO3+) by O2 as the reaction gas in the DRC, while the analyte ion (202Hg+) cannot react with O2. Under the optimized O2 flow rate (1.9 mL min−1) and DRC rejection parameter q (Rpq, 0.80), the background signal was reduced by up to 1000-fold at m/z 202 and the limit of quantitation (LOQ, 10σ) for 202Hg was 1 ng g−1. The proposed method was applied to direct determination of Hg in a series of soil and sediment standard reference materials (SRMs) and the satisfactory results indicate that it has great potential for the determination of trace or ultra-trace level mercury in various environmental or geological samples.

Detection of HIV-1 p24 antigen using streptavidin–biotin and gold nanoparticles based immunoassay by inductively coupled plasma mass spectrometry

A sensitive assay for detection of HIV-1 p24 antigen by inductively coupled plasma mass spectrometry (ICP-MS) was developed using a biotin–streptavidin (BA) system and gold nanoparticles (Au NPs) based immunoassay. In this immunoassay, the p24 antigen was firstly captured by an immobilized anti-HIV-1 p24 monoclonal antibody. After immunoreactions with the biotinylated anti-p24 polyclonal antibody and Au NPs-labeled streptavidin, diluted HNO3 (5%, v/v) was used to dissociate Au NPs, which were then introduced to the ICP-MS for measurements. Under the optimized conditions, the calibration graph for the p24 antigen was linear in the range of 7.5–75 pg mL−1 with a detection limit of 1.49 pg mL−1 (3σ, n = 5). The relative standard deviation (RSD) for three replicate measurements of 37.5 pg mL−1 of the p24 antigen was 3.7%. Other proteins, such as human IgG, human HSA, human CEA and human AFP, did not obviously interfere with the assay for p24 antigen. This method was also applied to measure p24 concentrations in artificially positive human serum samples. Compared with the biotin–streptavidin enzyme-linked immunosorbent assay (BA-ELISA) method for p24 antigen detection, the ICP-MS linked immunoassay process deals with Au NPs – tagged instead of enzyme-conjugated antibodies, making it free of toxic enzyme substrate reagents. In addition, it also simplifies the experimental process and saves the experimental time, since the color rendering steps are omitted. The proposed approach provides a sensitive method for HIV-1 p24 antigen determination.

Quantitative Characterization of Gold Nanoparticles by Coupling Thin Layer Chromatography with Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Metal nanoparticles (NPs) determination has recently attracted considerable attention because of the continuing boom of nanotechnology. In this study, a novel method for separation and quantitative characterization of NPs in aqueous suspension was established by coupling thin layer chromatography (TLC) with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Gold nanoparticles (AuNPs) of various sizes were used as the model system. It was demonstrated that TLC not only allowed separation of gold nanoparticles from ionic gold species by using acetyl acetone/butyl alcohol/triethylamine (6:3:1, v/v) as the mobile phase, but it also achieved the separation of differently sized gold nanoparticles (13, 34, and 47 nm) by using phosphate buffer (0.2 M, pH = 6.8), Triton X-114 (0.4%, w/v), and EDTA (10 mM) as the mobile phase. Various experimental parameters that affecting TLC separation of AuNPs, such as the pH of the phosphate buffer, the coating of AuNPs, the concentrations of EDTA and Triton X-114, were investigated and optimized. It was found that separations of AuNPs by TLC displayed size dependent retention behavior with good reproducibility, and the retardation factors (R(f) value) increased linearly with decreasing nanoparticle size. The analytical performance of the present method was evaluated under optimized conditions. The limits of detection were in the tens of pg range, and repeatability (RSD, n = 7) was 6.3%, 5.9%, and 8.3% for 30 ng of 13 nm AuNPs, 34 nm AuNPs, and 47 nm AuNPs, respectively. The developed TLC-LA-ICP-MS method has also been applied to the analysis of spiked AuNPs in lake water, river water, and tap water samples.

Evaluation of flow injection-solution cathode glow discharge-atomic emission spectrometry for the determination of major elements in brines.

A new method for the determination of major metal elements in high salinity brines was developed by solution cathode glow discharge (SCGD) with flow injection analysis (FIA). The matrix interferences of major cations and anions in brines have been evaluated. It was found that high concentration of Na(+) and K(+) could interfere each other, K(+) at a concentration of 400mgL(-1) enhanced the signal intensity of Na(+) more than 20%. The effect of the anions was observed and it was noted that the signal intensity of both Ca(2+) and Mg(2+) were suppressed significantly when the SO4(2-) reached 100mgL(-1). It was demonstrated that some low molecular weight organic substances such as formic acid, glycerol and ascorbic acid could eliminate interference of SO4(2-) even with volume percentages of 0.5%. Under the optimized condition, the proposed FIA-SCGD can determine K, Na, Ca and Mg with the limits of detection of 0.49 (K), 0.14 (Na), 11 (Ca) and 5.5 (Mg) ngmL(-1). The proposed method has been successfully applied to the analysis of 5 salt lake samples and compared with those obtained with inductively coupled plasma atomic emission spectrometry (ICP-AES). The advantages of small size, low energy consumption, good stability and repeatability indicated that the SCGD is promising for the determination of major ions in brine samples.

Soil monitoring of arsenic by methanol addition DRC ICP-MS after boiling aqua regia extraction

Trace levels of arsenic (As) in soil samples can be determined by conventional ICP-QMS with closed vessel digestion, but always suffer from interference of ions originating from the complicated matrix, mainly including 40Ca35Cl+, 40Ar35Cl+, 39K36Ar+, 150Nd2+, 150Eu2+ and 150Sm2+etc. In this study, 75As+, the mass for general detection, was effectively changed to 75As16O+ which could be detected at m/z 91 by reaction with oxygen in a Dynamic Reaction Cell (DRC). For the new interference of 91Zr+ on 75As16O+, boiling aqua regia extraction was used to remove most of the zirconium in the sample preparation procedure, and the residual 91Zr+ was oxidized to 91Zr16O+ by oxygen in the DRC. In addition, the signal intensity of 75As16O was improved 4-fold by addition of 4% methanol into the sample solution. The signal to background ratio (SBR) of As was obviously improved from 0.18 to 205 (the certified arsenic concentration is 1 μg L−1), and a limit of quantification (LOQ, 10σ) of 0.1 ng g−1 was obtained. The proposed method was successfully applied to analyze 20 soil samples collected from pig farms in livestock farming processes, and shows its great potential for trace As determination in environmental and geological samples.

Significant signal enhancement of dielectric barrier discharge plasma induced vapor generation by using non-ionic surfactants for determination of mercury and cadmium by atomic fluorescence spectrometry

Non-ionic surfactants (NISs) were used to improve the performance of dielectric barrier discharge plasma induced vapor generation (DBD plasma-CVG). The addition of Triton X-114 leads to 5.4 and 5.1 times improvement in the fluorescence signals of DBD plasma-CVG for cadmium and mercury, respectively. The enhancement mechanism was investigated and it was presumed that the presence of NISs increased the reaction kinetics and improved the transport efficiency of volatile species from solutions. Influencing parameters were evaluated in detail, including the concentrations of NISs and flow rates of carrier gas and samples, as well as interferences. The detection limits were 2.4 ng L−1 for Cd and 4.5 ng L−1 for Hg and the relative standard deviations were 3.4% for Cd (1 μg L−1, n = 5) and 2.6% for Hg (1 μg L−1, n = 5), respectively. The accuracy of the proposed method was validated by the analysis of simulated natural water samples, GBW08603, GBW(E)080401 and GBW(E)080402.

Rice cadmium monitoring using heat-extraction electrothermal atomic absorption spectrometry

A simple and high throughput method involving heat-extraction electrothermal atomic absorption spectrometry was developed to monitor the Cd content in rice, and 184 rice samples purchased from supermarkets in Beijing were surveyed. The main advantages of using heat-extraction in comparison to slurry sampling are doubling of the graphite tube lifetime and 80% decrease in the background absorbance signal, most likely because the less sample matrix was introduced into the atomizer, avoiding buildup of carbonaceous residues or silicates on the graphite platform. Heat-extraction provides better detection limits and precision than microwave acid digestion. In the heat-extraction method, slurries in 3% v/v HNO3 were heated on a heating block. After centrifugation, the supernatant was introduced into a graphite tube pretreated with a W–Rh permanent modifier. The optimum conditions for Cd detection were 0.2–5.0% m/v slurry concentration, 3% HNO3 extract, 10 min heating at 120 °C, rice-particle size <150 μm (after 3 min of sample grinding), 600 °C pyrolysis temperature, and 1500 °C atomization temperature. The extraction recovery for Cd in rice standard reference materials was 98.4–101.1%. The characteristic masses and detection limit for Cd based on the integrated absorbance for a 2.5% m/v rice sample were 0.7 ± 0.1 pg and 1 ng g−1, respectively. The mean Cd content was 0.076 μg g−1 (ranging from 0.004 to 0.876 μg g−1), and only 4.3% of investigated rice samples exceeded the maximum allowable Cd concentration of 0.20 μg g−1. This simple and rapid method has great potential for monitoring trace Cd in food samples for market survey.

Determination of cadmium in geological samples by aerosol dilution ICP-MS after inverse aqua regia extraction

The determination of cadmium (Cd) in geological samples by inductively coupled plasma mass spectrometry (ICP-MS) suffers from significant Mo and/or Zr based oxide interference. We have developed a valid method for Cd determination using Ar aerosol dilution ICP-MS after extraction with inverse aqua regia. Over 90% of the Zr was removed in the extraction procedure, and the residual Zr-hydroxides and Mo-oxides or hydroxides were successfully eliminated by adding an amount of Ar to the sample aerosol prior to the plasma. Compared to the conventional mode without adding Ar, the amount of oxide and hydroxide ions formed in the plasma was reduced by up to 90%. The relative yields of the interfering oxides and hydroxides were as low as 0.005% (MoOH/Mo or MoO/Mo) and 0.007% (ZrOH/Zr). Under the optimized dilution gas flow rate (0.85 L min−1) and carrier gas flow rate (0.24 L min−1), the limit of detection (LOD, 3σ) for 111Cd was 1.6 ng g−1. The proposed method was applied to the determination of Cd in 81 soil, sediment, and rock standard reference materials (SRMs). The results for 68 of these geological SRMs were in good agreement with the reference values. The Cd levels in 10 limestone SRMs (GSR-22, GSR-23, GSR-24, GSR-27, GSR-28, GUI-1, GUI-2, DIAN-1, DIAN-2, and DIAN-3) were reported for the first time, and reference Cd values for other 3 geological SRMs (GSD-7, GSD-19, and GSM-1) were updated by this method. The results showed that this method has great potential for Cd determination in geological samples.