Quantitative determination of trace metals in high-purity silicon carbide powder by laser ablation inductively coupled plasma mass spectrometry without binders

We have developed a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method to directly determine the concentrations of trace metals in high-purity powdery silicon carbide (SiC) samples. The sample preparation procedure is simple and rapid. The sample was formed into pellets using no binders and heated at 1000 °C for 2 h. The operation parameters for LA and ICP-MS were optimized to achieve a table signal intensity and high sensitivity. National Institute of Standards and Technology Standard Reference Materials glasses were chosen as calibration standards, with ²⁹Si chosen as the internal standard. The relative sensitivity factor obtained from the glass matrix was used to calculate the concentrations of analytes in the SiC ceramic samples. The regression correlation coefficients of the calibration curves for elements with internal standard correction ranged from 0.9981 to 0.9999, which are better than those obtained with an external standard correction method only. The relative standard deviation of the measured trace element concentrations was less than 5%. The limits of detection were 0.02, 0.08, 0.04, 0.005, 0.01, 0.02, 0.004, 0.07, and 0.006 mg kg^− 1 for B, Ti, Cr, Mn, Fe, Ni, Co, Cu, and Sr, respectively. The method was applied to analyze SiC samples with two different particle sizes. The analysis showed good agreement with the results of inductively coupled plasma optical emission spectrometry. The reliability of the proposed method was confirmed by determining the contents of B, Ti, Cr, Mn, Fe, Ni, and Cu in BAM-S003.     

Evaluation of microwave and ultrasound extraction procedures for arsenic speciation in bivalve mollusks by liquid chromatography–inductively coupled plasma-mass spectrometry

Liquid chromatography–inductively coupled plasma-mass spectrometry (LC–ICP-MS) was used for arsenic speciation analysis in tissues of bivalve mollusks (Anomalocardia brasiliana sp. and Macoma constricta sp.). Microwave and ultrasound radiation, combined with different extraction conditions (solvent, sample amount, time, and temperature), were evaluated for As-species extraction from the mollusks' tissues. Accuracy, extraction efficiency, and the stability of As species were evaluated by analyzing certified reference materials (DORM-2, dogfish muscle; BCR-627, tuna fish tissue; and SRM 1566b, oyster tissue) and analyte recovery tests. The best conditions were found to be microwave-assisted extraction using 200 mg of samples and water at 80 °C for 6 min. The agreement of As-species concentration in samples ranged from 97% to 102%. Arsenobetaine (AsB) was the main species present in bivalve mollusk tissues, while monomethylarsonic acid (MMA) and arsenate (As(V)) were below the limit of quantification (0.001 and 0.003 μg g^− 1, respectively). Two unidentified As species also were detected and quantified. The sum of the As-species concentration was in agreement (90 to 104%), with the total As content determined by ICP-MS after sample digestion.     

Controlled dissolution of silicon dioxide layers for depth resolved multielement analysis by inductively coupled plasma-mass spectrometry

Dissolution procedures were developed to control the number of surface layers removed, in an attempt to achieve depth resolved analysis by inductively coupled plasma-mass spectrometry (ICP-MS). NIST 612 glass was chosen because it is a homogeneous material with many elements at interesting concentrations, ~ 50 ppm. Varying dissolution time and HF concentration resulted in the reproducible removal of SiO₂ layers as thin as 70 Å deep. Dissolved trace metals were determined after dilution by inductively coupled plasma-mass spectrometry (ICP-MS) with a magnetic sector instrument. The amount removed was determined from the concentration of a major element, Ca. With the exception of Zn, trace metal concentrations agreed reasonably well with their certified values for removal depths of 500, 300 and 150 Å. Zinc concentration was significantly high in all dissolutions indicating either a contamination problem or that Zn is removed at a faster rate than Ca. For the dissolutions that removed 70 Å of SiO₂, Cr, Mn, Co, Sr, Cd, Ce, Dy, Er, Yb and U recovery results agreed with their certified values (~ 50 ppm); Ti, As, Mo, Ba, and Th could not be determined because net intensities were below 3σ of the blank; and measured concentrations for Cu, Pb and Zn were well above the certified values.     

Study of near infra red femtosecond laser induced particles using transmission electron microscopy and low pressure impaction: Implications for laser ablation–inductively coupled plasma-mass spectrometry analysis of natural monazite

The characteristics of infra red femtosecond laser-induced aerosols are studied for monazite (LREE, Th(PO₄)) ablation and correlations are established with inductively coupled plasma-mass spectrometry (ICP-MS) signals. Critical parameters are tested within wide ranges of values in order to cover the usual laser ablation -ICP-MS analysis conditions: pulse energy (0.15 < E₀ < 1 mJ/pulse), pulse width (60 < τ < 3000 fs), ablation time (t ≤ 10 min) and transport length (l ≤ 6.3 m). Transmission electron microscopy reveals that aerosols are made of agglomerates of ~ 10 nm particles and 20–300 nm phosphorus depleted condensed spherical particles. These structures are not affected by any laser ablation parameter. Particle counting is performed using electronic low pressure impaction. Small changes on particle size distribution are noticed. They may be induced either by a peak of ablation rate in the first 15 s at high fluence (larger particles) or the loss of small particles during transport. We found a positive correlation between I (ICP-MS mean signal intensity in cps) and N (particle density in cm^? 3) when varying E₀ and t, suggesting that N is controlled by the irradiance (P₀ in W·cm^? 2). Elemental ratio measurements show a steady state signal after the initial high ablation rate (mass load effect in the plasma torch) and before a late chemical fractionation, induced by poor extraction of bigger, early condensed spherical particles from the deepening crater. Such chemical fractionation effects remain within uncertainties, however. These effects can be limited by monitoring E₀ to shorten the initial transient state and delay the attainment of an unfavorable crater aspect ratio. Most adopted settings are for the first time deduced from aerosol characteristics, for infra red femtosecond laser ablation. A short transport (l < 4.0 m) limits the agglomeration of particles by collision process along the tube. Short τ is preferred because of higher P₀, yet no benefit is found on ICP-MS signal intensity under 200 fs. Under such pulse widths the increased particle production induces more agglomeration during transport, thereby resulting in higher mass load effects that reduce the ionization efficiency of the plasma torch. Thus, pulse energy must be set to get an optimal balance between the need for a high signal/background ratio and limitation of mass load effects in the plasma torch.     

Linearization of calibration curves by aerosol carrier effect of CCl4 vapor in electrothermal vaporization inductively coupled plasma mass spectrometry

Carbon tetrachloride vapor as gaseous phase modifier in a graphite furnace electrothermal vaporizer (GFETV) converts heavy volatile analyte forms to volatile and medium volatile chlorides and produces aerosol carrier effect, the latter being a less generally recognized benefit. However, the possible increase of polyatomic interferences in inductively coupled plasma mass spectrometry (GFETV–ICP-MS) by chlorine and carbon containing species due to CCl₄ vapor introduction has been discouraging with the use of low resolution, quadrupole type MS equipment. Being aware of this possible handicap, it was aimed at to investigate the feasibility of the use of this halogenating agent in ICP-MS with regard of possible hazards to the instrument, and also to explore the advantages under these specific conditions. With sample gas flow (inner gas flow) rate not higher than 900 ml min⁻¹ Ar in the torch and 3 ml min⁻¹ CCl₄ vapor flow rate in the furnace, the long-term stability of the instrument was ensured and the following benefits by the halocarbon were observed. The non-linearity error (defined in the text) of the calibration curves (signal versus mass functions) with matrix-free solution standards was 30–70% without, and 1–5% with CCl₄ vapor introduction, respectively, at 1 ng mass of Cu, Fe, Mn and Pb analytes. The sensitivity for these elements increased by 2–4-fold with chlorination, while the relative standard deviation (RSD) was essentially the same (2–5%) for the two cases in comparison. A vaporization temperature of 2650 °C was required for Cr in Ar atmosphere, while 2200 °C was sufficient in Ar + CCl₄ atmosphere to attain complete vaporization. Improvements in linear response and sensitivity were the highest for this least volatile element. The pyrolytic graphite layer inside the graphite tube was protected by the halocarbon, and tube life time was further increased by using traces of hydrocarbon vapor in the external sheath gas of the graphite furnace. Details of the modification of the gas supply for HGA-600MS furnace and the design of the volatilization device are described.     

Studies on transport phenomena in electrothermal vaporization sample introduction applied to inductively coupled plasma for optical emission and mass spectrometry

In the present work electrothermal vaporization (ETV) was used in both inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (OES) for sample introduction of solution samples. The effect of (Pd + Mg)-nitrate modifier and CaCl₂ matrix/modifier of variable amounts were studied on ETV-ICP-MS signals of Cr, Cu, Fe, Mn and Pb and on ETV-ICP-OES signals of Ag, Cd, Co, Cu, Fe, Ga, Mn and Zn. With the use of matrix-free standard solutions the analytical curves were bent to the signal axes (as expected from earlier studies), which was observed in the 20–800 pg mass range by ICP-MS and in the 1–50 ng mass range by ICP-OES detection. The degree of curvature was, however, different with the use of single element and multi-element standards. When applying the noted chemical modifiers (aerosol carriers) in microgram amounts, linear analytical curves were found in the nearly two orders of magnitude mass ranges. Changes of the CaCl₂ matrix concentration (loaded amount of 2–10 μg Ca) resulted in less than 5% changes in MS signals of 5 elements (each below 1 ng) and OES signals of 22 analytes (each below 15 ng). Exceptions were Pb (ICP-MS) and Cd (ICP-OES), where the sensitivity increase by Pd + Mg modifier was much larger compared to other elements studied. The general conclusions suggest that quantitative analysis with the use of ETV sample introduction requires matrix matching or matrix replacement by appropriate chemical modifier to the specific concentration ranges of analytes. This is a similar requirement to that claimed also by the most commonly used pneumatic nebulization of solutions, if samples with high matrix concentration are concerned.     

Detection of zinc and lead in water using evaporative preconcentration and single-particle laser-induced breakdown spectroscopy

A novel laser-induced breakdown spectroscopy (LIBS)-based measurement method for metals in water is demonstrated. In the presented technology a small amount of sodium chloride is dissolved in the sample solution before spraying the sample into a tubular oven. After water removal monodisperse dry NaCl aerosol particles are formed where trace metals are present as additives. A single-particle LIBS analysis is then triggered with a scattering based particle detection system. Benefits are the highly increased metal concentration in the LIBS focal volume and the static NaCl-matrix which can be exploited in the signal processing procedure. Emitted light from the emerged plasma plume is collected with wide angle optics and dispersed with a grating spectrometer. In an aqueous solution, the respective limits of detection for zinc and lead were 0.3 ppm and 0.1 ppm using a relatively low 14 mJ laser pulse energy. Zn/Na peak intensity ratio calibration curve for zinc concentration was also determined and LIBS signal dependence on laser pulse energy was investigated.     

Direct determination of trace rare earth elements in ancient porcelain samples with slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

A method for the direct determination of trace rare earth elements in ancient porcelain samples by slurry sampling fluorinating electrothermal vaporization inductively coupled plasma mass spectrometry was developed with the use of polytetrafluoroethylene as fluorinating reagent. It was found that Si, as a main matrix element in ancient porcelain sample, could be mostly removed at the ashing temperature of 1200 °C without considerable losses of the analytes. However, the chemical composition of ancient porcelain sample is very complicated, which makes the influences resulting from other matrix elements not be ignored. Therefore, the matrix effect of ancient porcelain sample was also investigated, and it was found that the matrix effect is obvious when the matrix concentration was larger than 0.8 g l^− 1. The study results of particle size effect indicated that when the sample particle size was less than 0.057 mm, the particle size effect is negligible. Under the optimized operation conditions, the detection limits for rare earth elements by fluorinating electrothermal vaporization inductively coupled plasma mass spectrometry were 0.7 ng g^− 1 (Eu)–33.3 ng g^− 1(Nd) with the precisions of 4.1% (Yb)–10% (La) (c = 1 μg l^− 1, n = 9). The proposed method was used to directly determine the trace rare earth elements in ancient porcelain samples produced in different dynasty (Sui, Ming and Qing), and the analytical results are satisfactory.     

Study of the chemical composition of particulate matter from the Rio de Janeiro metropolitan region,Brazil, by inductively coupled plasma-mass spectrometry and optical emission spectrometry

Air quality in the metropolitan region of Rio de Janeiro was evaluated by analysis of particulate matter (PM) in industrial (Santa Cruz) and rural (Seropédica) areas. Total suspended particles (TSP) and fine particulate matter (PM_2.5) collected in filters over 24 h were quantified and their chemical composition determined. TSP exceeded Brazilian guidelines (80 μg m^− 3) in Santa Cruz, while PM_2.5 levels exceeded the World Health Organization guidelines (10 μg m^− 3) in both locations. Filters were extracted with water and/or HNO₃, and the concentrations of 20 elements, mostly metals, were determined by inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (ICP OES). Water soluble inorganic anions were determined by ion chromatography (IC). To estimate the proportion of these elements extracted, a certified reference material (NIST SRM 1648a, Urban Dust) was subjected to the same extraction process. Concordant results were obtained by ICP-MS and ICP OES for most elements. Some elements could not be quantified by both techniques; the most appropriate technique was chosen in each case. The urban dust was also analyzed by the United States Environmental Protection Agency (US EPA) method, which employs a combination of hydrochloric and nitric acids for the extraction, but higher extraction efficiency was obtained when only nitric acid was employed. The US EPA method gave better results only for Sb. In the PM samples, the elements found in the highest average concentrations by ICP were Zn and Al (3–6 μg m^− 3). The anions found in the highest average concentrations were SO₄^2 − in PM_2.5 (2–4 μg m^− 3) and Cl⁻ in TSP (2–6 μg m^− 3). Principal component analysis (PCA) in combination with enrichment factors (EF) indicated industrial sources in PM_2.5. Analysis of TSP suggested both anthropogenic and natural sources. In conclusion, this work contributes data on air quality, as well as a method for the analysis of PM samples by ICP-MS.     

Characterization of particles made by desolvation of monodisperse microdroplets of analyte solutions and particle suspensions for nanoparticle calibration in inductively coupled plasma spectrometry

Particles produced by low-temperature desolvation of monodisperse microdroplets of analyte standard solution and nanoparticle suspensions in argon were collected on Si-wafers and studied applying scanning electron microscopy and X-ray microprobe techniques. At desolvation temperatures of about 150 °C, the particles from standard solutions are most often spherical and solid with good reproducibility and the analyte elements together with the unavoidable accompanying elements from trace contamination seem to be homogeneously distributed in the particles. However, there are surprising exceptions, particularly at higher temperatures, where analyte elements are separated in the particle by reduction or crystallization, as shown with Au and Ca standard solutions, respectively. Drying droplets of a diluted suspension of 250 nm gold particles at 200 °C revealed another interesting result, the production of relatively stable concave balloons of ∼ 3 µm in diameter including the Au particles. The balloon sheath was formed of compounds made of the contaminant elements in the suspension. The morphology of the particles is discussed in consideration of the Peclet number, the ratio of evaporation rate to analyte diffusion coefficient. The consequences of particle size and morphology for calibration purposes in nanoparticle characterization by ICP spectrometry are discussed.     

Ti in dilute slurries of TiO2 nanoparticles by in-torch vaporization sector field inductively coupled plasma-mass spectrometry☆

A Re coil-filament in-torch vaporization (ITV) sample introduction system was interfaced to a sector field inductively coupled plasma-mass spectrometry (SFICP-MS) system. In this first report on an un-optimized ITV-SF-ICP-MS system, detection limits were established using 5 μL volumes of 100 pg mL^− 1 standard solutions, translating to 0.5 pg absolute. Such absolute amounts of a dried solution are near or below the detection limit of many ICP-based techniques. The absolute detection limits for Cd, Eu, Pb, Ti, U and Zn were in the 0.2–2 fg range (or, in the 10's of millions to millions of atoms for Pb, Cd, Zn and Ti, about one million atoms for U and about 800 thousand for Eu). These absolute detection limits along with the ability of ITV to handle minute amounts of discrete samples (thus eliminating memory effects from nanoparticles adhering to the walls of pneumatic nebulization sample introduction systems and from clogging of the mass spectrometer orifice), use of sonicated water-based slurries (that eliminated contamination from acid digestion reagents or from slurry stabilization reagents), and elimination of oxygen containing molecular ion interferences due to use of dry samples enabled concentration determinations of Ti (and consequently of TiO₂) in pg mL^− 1 concentrations of slurries of manufactured, 20 nm diameter TiO₂ nanoparticles.     

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 1 g 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.     

Computerized simulation of solute–particle vaporization in an inductively coupled plasma

Recent experiments involving aerosol introduction into the inductively coupled plasma have shown that intact droplets and solute particles cause enormous fluctuations in analyte emission and mass-spectral signals. Here, particle-vaporization kinetics are simulated as a detailed function of the operating conditions, fundamental properties and spatial location in the inductively coupled plasma, and as a function of several of the properties of the particles themselves: diameter, chemical composition and size distribution. These simulations portray the particle vaporization as proceeding nominally linearly with respect to the particle radius when the particles are small, but roughly quadratically with radius when the particles are very large. Further, the heat- and mass-transfer-limited rates of vaporization are roughly equal for the typical gas-temperature range in the plasma tail flame, so that at any height either process might limit the rate of vaporization. This similarity gives rise to a dynamic, competitive picture of plasma vaporization kinetics.     

Electrochemical dissolution of gold in acidic medium

Polycrystalline gold dissolves at high potentials in acidic medium even without the presence of complexing agents. In the present work the dissolution of gold is quantitatively studied by an inductively coupled plasma mass spectrometer (ICP-MS) directly connected to an electrochemical scanning flow cell (SFC). It is shown that the onset of gold dissolution coincides with the onset of the formation of 2D surface oxide (ca. + 1.3 V_RHE). An increase in the upper potential limit (UPL) during potential cycling or an increase in the holding potential during potential steps leads to an enhancement in the amount of dissolved gold. Moreover, a change in the dominating mechanism for gold dissolution with increasing potential is found in transient experiments. At lower potentials, gold is dissolved mostly during the gold oxide reduction, while at higher potentials anodic dissolution is the dominating process. Finally, the possible application of gold for stabilization of PtAu-based fuel cell catalysts is discussed.     

Analyte response in laser ablation inductively coupled plasma mass spectrometry

The dependence of analyte sensitivity and vaporization efficiency on the operating parameters of an inductively coupled plasma mass spectrometer (ICPMS) was investigated for a wide range of elements in aerosols, produced by laser ablation of silicate glass. The ion signals were recorded for different carrier gas flow rates at different plasma power for two different laser ablation systems and carrier gases. Differences in atomization efficiency and analyte sensitivity are significant for the two gases and the particle size distribution of the aerosol. Vaporization of the aerosol is enhanced when helium is used, which is attributed to a better energy-transfer from the plasma to the central channel of the ICP and a higher diffusion rate of the vaporized material. This minimizes elemental fractionation caused by sequential evaporation and reduces diffusion losses in the ICP. The sensitivity change with carrier gas flow variation is dependent on m/z of the analyte ion and the chemical properties of the element. Elements with high vaporization temperatures reach a maximum at lower gas flow rates than easily vaporized elements. The sensitivity change is furthermore dependent on m/z of the analyte ion, due to the mass dependence of the ion kinetic energies. The mass response curve of the ICPMS is thus not only a result of space charge effects in the ion optics but is also affected by radial diffusion of analyte ions and the mismatch between their kinetic energy after expansion in the vacuum interface and the ion optic settings.     

Peak broadening from an electrothermal vaporization sample introduction source into an inductively coupled plasma

Signal broadening using electrothermal vaporization with inductively coupled mass spectrometry (ETV-ICPMS) occurs at a rate much faster than would be predicted by simple longitudinal diffusion. A Monte Carlo simulation that focused on particle motion within the transport tubing was created to elucidate the causes of this dispersion within ETV-ICPMS. Several parameters, including the diffusion coefficient, tube diameter, transport tube length, and flow rate were varied to discern their role in signal broadening. Using typical instrumental parameters, the parabolic flow profile generated by laminar flow of the carrier gas was shown to be the primary cause of dispersion. Manipulating the aforementioned variables to lessen the effects of laminar flow led to a decrease in dispersion. Conversely, increasing the role of laminar flow promoted broadening. The broadening processes should be applicable to any transient introduction system where material must be transported to a detection system. Due to the difference in the rate of broadening expected for particles of different sizes, the simulation was used to calculate the average size of particles generated in the ETV using different mass amounts of sample. No change in particle size (∼1 nm) was seen for mass amounts ranging from 10–10 000 pg, which suggests that the particle number is increased with increasing sample mass rather than the average particle size. Using this method of determining particle size, it might be possible to further evaluate the mechanisms of physical ‘carrier’ action.     

A method for direct,semi-quantitative analysis of gas phase samples using gas chromatography–inductively coupled plasma-mass spectrometry

A new and complete GC–ICP-MS method is described for direct analysis of trace metals in a gas phase process stream. The proposed method is derived from standard analytical procedures developed for ICP-MS, which are regularly exercised in standard ICP-MS laboratories. In order to implement the method, a series of empirical factors were generated to calibrate detector response with respect to a known concentration of an internal standard analyte. Calibrated responses are ultimately used to determine the concentration of metal analytes in a gas stream using a semi-quantitative algorithm. The method was verified using a traditional gas injection from a GC sampling valve and a standard gas mixture containing either a 1 ppm Xe + Kr mix with helium balance or 100 ppm Xe with helium balance. Data collected for Xe and Kr gas analytes revealed that agreement of 6–20% with the actual concentration can be expected for various experimental conditions.To demonstrate the method using a relevant “unknown” gas mixture, experiments were performed for continuous 4 and 7 hour periods using a Hg-containing sample gas that was co-introduced into the GC sample loop with the xenon gas standard. System performance and detector response to the dilute concentration of the internal standard were pre-determined, which allowed semi-quantitative evaluation of the analyte. The calculated analyte concentrations varied during the course of the 4 hour experiment, particularly during the first hour of the analysis where the actual Hg concentration was under predicted by up to 72%. Calculated concentration improved to within 30–60% for data collected after the first hour of the experiment. Similar results were seen during the 7 hour test with the deviation from the actual concentration being 11–81% during the first hour and then decreasing for the remaining period. The method detection limit (MDL) was determined for the mercury by injecting the sample gas into the system following a period of equilibration. The MDL for Hg was calculated as 6.8 μg · m^− 3. This work describes the first complete GC–ICP-MS method to directly analyze gas phase samples, and detailed sample calculations and comparisons to conventional ICP-MS methods are provided.     

Determination and assessments of selected heavy metals in eye shadow cosmetics from China,Italy, and USA

This study evaluated the content of heavy metals in samples of eye shadows. Samples were manufactured in different countries (China, Italy, and USA). The content of Pb was measured by flame-atomic absorption spectrometry (F-AAS). The quantification of cadmium, cobalt, chromium, and nickel was performed by inductively coupled plasma-mass spectrometry (ICP-MS). The analyses were preceded by microwave-assisted acid digestion of the eye shadows. In many samples the lead was present within 20 μg g^? 1, the value indicated as safe in good manufacturing practice, but it exceed this limit in four Chinese samples. The levels of cadmium, chromium and cobalt were always low and within acceptable and safe concentrations for the products made in Italy and USA, but the nickel concentrationexceeded the safe limit in many Chinese eye shadows. The overall results indicate that eye shadows are likely harmful when they are made according to current regulations, while products imported from China can be harmful. Therefore, major quality controls are recommended for products designed to enter in direct and long contact with the skin of eyelids when imported from countries with different regulations.     

Sensing of 2,4-dichlorophenoxyacetic acid by surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) spectra of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was obtained by employing a bi-layer gold substrate, assembled by the reduction of Au(III) over gold-seeded nanoparticles immobilized on functionalized glass substrates. The SERS signal was linear with the logarithm of the solution concentrations between 1.0 × 10⁻⁷ mol L⁻¹ and 1.0 × 10⁻³ mol L⁻¹, indicating that the bi-layer gold substrate affords a significant dynamic range for SERS, providing an excellent analytical response within this concentration range, and revealing the high sensitivity of the gold surface towards such analyte. In addition, using the same gold substrate, a similar calibration curve was obtained for crystal-violet (CV), and it was possible to identify the concentration limit corresponding to the transition from the average SERS to the nonlinear SERS response.     

Heavy elements concentrations,physiochemical characteristics and natural radionuclides levels along the Saudi coastline of the Gulf of Aqaba

This paper represents the first work on the concentrations of heavy elements, physiochemical characteristics and activity levels of the naturally occurring radionuclides in the Saudi Arabian coastline of the Gulf of Aqaba. Concentrations of 19 heavy elements were measured, namely: Ag, Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, V and Zn. The radioactivity levels of ²³⁸U, ²³²Th and ⁴⁰K were estimated to be: 17 ± 1.7, 22.5 ± 3.7 and 649.6 ± 64.2 Bq kg^?1, respectively. The measurements were carried out using inductively coupled plasma-mass spectrometry (ICP-MS). In addition, physiochemical characteristics of 19 sediment samples (i.e., saturation percentage, pH, electrical conductivity, organic matter, cation exchange capacity and content of clay, silt and sand) have been determined. Indications for high correlation between most heavy elements are found. The correlation between heavy elements and the radionuclides ²³⁸U, ²³²Th and ⁴⁰K was generally significant.