Comparison of single and double-pulse excitation during the earliest stage of laser induced plasma

This paper deals with comparison of single-pulse (SP) and double-pulse (DP) excited plasmas during their earliest phase of life, from 0 to 500 ns. The samples are Si and Al and the irradiance per pulse is approximately 20 GW cm⁻² under ambient conditions. It was found that at the beginning of a plasma lifespan, Si III and Al III ions were excited even under the SP excitation conditions and became much more abundant under DP excitation. The lifetime of doubly-ionized species was found to be very short, and after a delay of 200–300 ns they were not detected. The DP plasma differs from the SP plasma by the intensity of continuum radiation and by the width of emission lines, which are substantially narrower in the DP plasma. The intensity of light emitted from singly and, especially, doubly-ionized species is higher compared with neutral atoms; whereas the decay time of both neutral and ionized species is longer. An excitation mechanism for the DP plasma is proposed enabling qualitative and a quantitative explanation of the experimental data.     

Net Emission Coefficients of Radiation in Air and SF<Subscript>6</Subscript> Thermal Plasmas

Net emission coefficients of radiation were calculated for isothermal plasmas of air and SF₆ as a function of the plasma temperature 5,000–30,000 K and the arc radius (0.01–10 cm) at various plasma pressures. Calculations take into account continuum and line radiations, special attention has also been taken to influence of molecular species in case of the air plasmas. It has been found that the molecular bands of O₂, N₂, N₂ ⁺, NO and NO⁺ have very strong effect on the net emission coefficients at low temperatures (below 10,000 K). In case of SF₆, effect of PTFE admixture on the net emission coefficients was also studied. It follows from the calculations that the net emission coefficients vary very little with various admixtures of PTFE. Values of net emission coefficients if SF₆ plasma calculated for various spectral regions were compared.     

Emission enhancement using two orthogonal targets in double pulse laser-induced breakdown spectroscopy

The enhancement of emission intensity resulting from the interaction between two laser-induced plasmas on two orthogonal targets was investigated using double pulse laser-induced breakdown spectroscopy (LIBS) at 0.7 Pa, by means of time-resolved spectroscopy and fast photography. The results showed that the interaction between both plasmas improved carbon emission intensity in comparison to a single laser-induced plasma. For all the carbon lines of interest 477.2 nm (CI), 426.7 nm (CII), and 473.4 nm (C₂ Swan band head), the intensity enhancement showed a maximum at a delay between lasers in the range from 2 to 5 μs; moreover it increased with the fluence of the first laser. On the other hand, in the case of C₂ the intensity enhancement reached a maximum at 5 mm from the target; however it decreased with increasing fluence of the second laser. The largest intensity enhancement found was twofold for atomic species and sixfold for molecular species.     

Determination of gallium originated from a gallium-based anticancer drug in human urine using ICP-MS

Urine analysis gives an insight into the excretion of the administered drug which is related to its reactivity and toxicity. In this work, the capability of inductively coupled plasma mass spectrometry (ICP-MS) to measure ultratrace metal levels was utilized for rapid assaying of gallium originating from the novel gallium anticancer drug, tris(8-quinolinolato)gallium(III) (GaQ₃), in human urine. Sample dilution with 1% (v/v) HNO₃ as the only required pre-treatment was shown to prevent contamination of the sample introduction system and to reduce polyatomic interferences from sample components. The origin of the blank signal at masses of gallium isotopes, 71 and 69, was investigated using high-resolution ICP-MS and attributed, respectively, to the formation of ³⁶Ar³⁵Cl⁺ and ⁴⁰Ar³¹P⁺ ions and, tentatively, to a triplet of doubly charged ions of Ba, La, and Ce. The accuracy and precision performance was tested by evaluating a set of parameters for analytical method validation. The developed assay has been applied for the determination of gallium in urine samples spiked with GaQ₃. The achieved recoveries (95–102%) and quantification limit of 0.2 μg L⁻¹ emphasize the practical applicability of the presented analytical approach to monitor renal elimination of GaQ₃ at all dose levels in clinical trials that are currently in progress.     

Experimental evidence for the formation of doubly charged oxide and hydroxide ions in inductively coupled plasma mass spectrometry

The formation of doubly charged polyatomic ions in inductively coupled plasma mass spectrometers was investigated using commercially available instruments. The species observed were ThO²⁺ and ThOH²⁺, which were found in similar amounts with the different instruments used in this study, when operated under routine analytical conditions. The signal ratios for ThO²⁺ were between 1.8 × 10^–4 and 4.2 × 10^–4 relative to the singly charged elemental ion and between 1.4 × 10^–2 and 2.2 × 10^–2 relative to the doubly charged elemental ion. The formation of ThOH²⁺ was between 1.1 × 10^–4 and 2.8 × 10^–4 relative to the singly charged elemental ion and between 0.72 × 10^–2 and 1.3 × 10^–2 relative to the doubly charged elemental ion. A mechanism is proposed for the formation of the doubly charged oxide and hydroxide ions that is based on the condensation of the doubly charged elemental ion with water or oxygen molecules in the interface region of the mass spectrometer. Received: 20 December 2000 / Revised: 19 March 2001 / Accepted: 22 March 2001     

Laser-induced breakdown spectroscopy for branching ratio and atomic lifetime measurements in singly-ionized neodymium and gallium

Precision laboratory astrophysics measurements can be made in laser-induced plasmas created for laser-induced breakdown spectroscopy. Branching ratios from highly-energetic levels in singly-ionized neodymium may be measured by observing spontaneous emission in laser-induced plasmas in an argon environment at decreased pressures (~ 7.7 mbar). Utilizing a broadband Èchelle spectrometer with a spectral range from 200–840 nm, the spontaneous emission intensities from hundreds of transitions originating in 138 energy levels in Nd I, Nd II, and Nd III have been observed simultaneously, allowing the determination of branching ratios for these energy levels for branches greater than 1% in the visible wavelength range. In this study, eight branching ratios from the 23,229.991 cm^− 1 level in Nd II were measured and compared to previously determined values as a method for optimizing experimental conditions such as buffer gas pressure and observation delay time. The branching ratios of the eight branches were found to be in excellent agreement with three previously determined values from both experiment and theory. A plan to utilize this laser-induced plasma apparatus to measure the lifetime of the 4s5p³P₂ level at 118,727.89 cm^− 1 in singly-ionized gallium using a cascade-photon-coincidence method is also presented. Utilizing a solid Ga target ablated in a helium environment, “start photons” at 541.6 nm from a transition into the 4s5p³P₂ level and “stop photons” at 633.4 nm from a transition out of that Ga II energy level were observed. Single-photon detection will be accomplished using avalanche photodiodes with narrowband interference filters and delay times between the detection of coincident photons from these two transitions will be measured.     

Synthesis, structural characterization, and magnetic properties of the metallamacrocycle [Fe6(C11H11N2O3)6(C4H9NO)6]

Abstract  

The 18-metallacrown-6 metallamacrocycle [Fe₆(pmshz)₆(C₄H₉NO)₆] has been synthesized by the self-assembly reaction of iron ions with N-substituted salicylhydrazide ligands. Six Fe(III) ions and six deprotonated N-propanoyl-4-methylsalicylhydrazide (H₃ pmshz) ligands construct a planar 18-membered ring based on Fe–N–N–Fe linkage. Because of the coordination, the ligand enforces the stereochemistry of the Fe(III) ions as a propeller shape with alternating …ΔΛΔΛ… configurations. There is a strong antiferromagnetic exchange interaction between the paramagnetic iron centers.     

Oxidation of Fe(III) to Fe(VI) by ozone in alkaline solutions

The action of ozone on a suspension of Fe(III) hydroxide in alkaline solutions was studied by the spectrophotometric method. A partial conversion of Fe(III) to Fe(VI) is observed at Fe(III) concentrations exceeding 2 mmol l⁻¹. The tenfold increase of the initial Fe(III) concentration raises the Fe(VI) yield by a factor of 2–3. The mechanism of the process includes the decomposition of ozone with the formation of ozonide ions, which oxidize Fe(III) up to Fe(IV), Fe(V), and Fe(VI) in parallel with their conversion to O₂⁻ and HO₂⁻. Fe(VIII) is not formed.     

A study of the aerobic reaction between dopamine and Fe(III) in the presence of S<Subscript>2</Subscript>O<Subscript>3</Subscript><Superscript>2−</Superscript>

The reaction between Fe(III) and dopamine in aqueous solution in the presence of Na₂S₂O₃ was followed through UV–Vis spectroscopy, pH and oxy-reduction potential (Eh) measurements. The formation and quick disappearing of the complex [Fe(III)HL¹⁻]²⁺, HL¹⁻ = monoprotonated dopamine was observed with or without S₂O₃ ²⁻ at pH 3. An unexpected reaction occurs in presence of thiosulfate forming the stable anion complex [Fe(III)(L²⁻)₂]¹⁻, L²⁻ = dopacatecholate (λ = 580 nm) and the auto-increasing of the pH, from 3 to 7. It was proposed that H⁺ and molecular oxygen are consumed by free radical thiosulfate formed during the reaction.     

Temporal evolution study of the plasma induced by CO2 pulsed laser on targets of titanium oxides

This paper reports studies on time-resolved laser induced breakdown spectroscopy (LIBS) of plasmas induced by IR nanosecond laser pulses on the titanium oxides TiO and TiO₂ (anatase). LIBS excitation was performed using a CO₂ laser. The laser-induced plasma was found strongly ionized yielding Ti⁺, O⁺, Ti^2 +, O^2 +, Ti^3 +, and Ti^4 + species and rich in neutral titanium and oxygen atoms. The temporal behavior of specific emission lines of Ti, Ti⁺, Ti^2 + and Ti^3 + was characterized. The results show a faster decay of Ti^3 + and Ti^2 + ionic species than that of Ti⁺ and neutral Ti atoms. Spectroscopic diagnostics were used to determine the time-resolved electron density and excitation temperatures. Laser irradiation of TiO₂-anatase induces on the surface sample the polymorphic transformation to TiO₂-rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy.     

Enhanced extract preparation of native manganese and iron species from brain and liver tissue

To date, no reference method for the extraction of labile Mn species from biological tissues is published which provides sufficient extraction efficiency combined with monitoring speciation. Here, an extraction method is reported using cryogenic conditions (+N) under inert gas atmosphere. Fresh brain and liver tissues were used, then stored either 1 day (+N) or 1 month in N_2liq (+N 1 m) to evaluate degradation effects during long-term storage. Both attempts were compared to a previous extraction method (−N) using neither N_2liq nor storage ability. Mn and Fe concentrations in extracts and pellets were determined with inductively coupled plasma (ICP)-atomic emission spectroscopy (AES) and compared to acid digests of the same sample. Element ratios of extracts/digest indicated the extraction efficiency, which was increased from 17% (−N) to 26% (+N) for Mn in brain or from 28% (−N) to 44% (+N) in liver extracts. For Fe species, the increase was only from 40% (−N) to 44% (+N) in brain but from 64% (−N) to 74% (+N) in liver. Size exclusion chromatography (SEC)-ICP-mass spectrometry (MS) was employed to screen for Mn and Fe species pattern in extracts. In brain, surplus extracted Mn (+N, +N 1 m) was assigned to organic Mn species, mainly from the 0.7–4 kDa fraction, while in the liver, it was seen in the 70–80 kDa fraction. Fe speciation was similar for −N and +N methods in brain extracts. In liver, higher amounts of Fe species were extracted from the 140–160 kDa fraction. Storage at −196 °C for 1 month did neither affect Mn speciation in brain nor in liver extracts. Fe species pattern showed a negligible shift (≤5%) from 140–160 to 70–80 kDa fraction in liver extracts stored 1 month in N_2liq.     

The behavior of molecules in microwave-induced plasmas studied by optical emission spectroscopy. 1. Plasmas at atmospheric pressure

The behavior of molecules in different atmospheric microwave-induced plasmas (MIPs) has been studied by means of optical emission spectroscopy. This is in order to obtain more insight into molecular processes in plasmas and to investigate the feasibility of emission spectroscopy for the analysis of molecular compounds in gases, e.g. flue gases. Various molecular species (i.e. N₂, CO₂, H₂O, SF₆ and SO₂) have been introduced into discharges in argon or in molecular gases such as carbon dioxide or nitrogen. The plasmas were created and sustained by a guide-surfatron or a torch in the power range of 150 W to 2 kW. Only nitrogen sometimes yielded observable emission from the non-dissociated molecule (first and second positive system). Using other molecular gases, only dissociation and association products were observed (i.e. atomic species and diatomic molecules such as CN, C₂, CO, OH, NH and N₂⁺). The intensities of these products have been studied as a function of the concentration of introduced molecules, the position in the plasma and the composition of the plasma environment. Since in most cases the same diatomic association products are seen, observed associated molecules can only to some extend be related to the molecules originally present in the plasma gas. Therefore, it will be difficult to use atmospheric microwave discharges for the analysis of gas mixtures under the experimental conditions studied.     

Rapid and interference free determination of ultra trace level of uranium in potable water originating from different geochemical environments by ICP-OES

Direct determination of uranium in the concentration range of 8 μg L⁻¹ to mg L⁻¹ in water samples originating from different geochemical environments has been done using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). Uranium detection with 2–3% RSD (relative standard deviation) has been achieved in water samples by optimizing the plasma power, argon and sheath gas flow. These parameters were optimized for three different emission lines of uranium at 385.958, 409.014 and 424.167 nm. Interference arising due to the variation in concentration of bicarbonate, sodium chloride, calcium chloride, Fe and dissolved organic carbon (DOC) on the determination of uranium in water samples was also cheeked as these are the elements which vary as per the prevailing geochemical environment in groundwater samples. The concentration of NaHCO₃, CaCl₂ and NaCl in water was varied in the range 0.5–2.0%; whereas Fe ranged between 1 and 10 μg mL⁻¹ and DOC between 0.1–1%. No marked interference in quantitative determination of uranium was observed due to elevated level of NaHCO₃, CaCl₂ and NaCl and Fe and DOC in groundwater samples. Concentration of uranium was also determined by other techniques like adsorptive striping voltametry (AdSv); laser fluorimetry and alpha spectrometry. Results indicate distinct advantage for uranium determination by ICP-OES compare to other techniques.     

Specific Interaction Between Negative Atmospheric Ions and Organic Compounds in Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry

The interaction between negative atmospheric ions and various types of organic compounds were investigated using atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. Atmospheric negative ions such as O₂^–, HCO₃^–, COO^–(COOH), NO₂^–, NO₃^–, and NO₃^–(HNO₃) having different proton affinities served as the reactant ions for analyte ionization in APCDI in negative-ion mode. The individual atmospheric ions specifically ionized aliphatic and aromatic compounds with various functional groups as atmospheric ion adducts and deprotonated analytes. The formation of the atmospheric ion adducts under certain discharge conditions is most likely attributable to the affinity between the analyte and atmospheric ion and the concentration of the atmospheric ion produced under these conditions. The deprotonated analytes, in contrast, were generated from the adducts of the atmospheric ions with higher proton affinity attributable to efficient proton abstraction from the analyte by the atmospheric ion.     

Spectroscopic Characterization of Miniaturized Atmospheric-Pressure dc Glow Discharge Generated in Contact with Flowing Small Size Liquid Cathode

The miniaturized atmospheric pressure glow discharge (APGD) generated between a solid electrode and a flowing small size liquid cathode (dimension 2 mm) was investigated here using optical emission spectroscopy. The discharge was studied in an open air atmosphere, and the spectral characteristics of the plasma source was examined. Analysed APGD was operated at a discharge voltage of 1,100–1,700 V, a discharge current of 20 mA and gaps between a solid anode and a liquid cathode in the range from 0.5 to 3.5 mm. The emission intensities of the main species were measured as a function of various experimental conditions, including the solution flow rate, the gap between the electrodes, and the concentration of hydrochloric acid. The excitation temperature, the vibrational temperatures calculated from N₂, OH, and NO bands, and the rotational temperatures determined from band of OH, N₂ and NO, were found to be dependent on these experimental parameters. The electron number density was determined from the Stark broadening of H_β line. Additionally, the ionization temperature and degree were calculated using the Saha–Boltzmann equation, with the ion to atom ratio for magnesium (MgII/MgI). The results demonstrated that T _exc(H), T _vib(N₂), T _vib(OH), T _vib(NO) and T _rot(OH) were well comparable (~3,800–4,200 K) for selected plasma generation conditions (gap ≥2.5 mm, HCl concentration ≥0.1 mol L⁻¹), while the rotational temperatures determined from band of N₂ (~1,700–2,100 K) and band of NO (~3,000 K) were considerably lower. The electron number density was evaluated to be (3.4–6.8) × 10²⁰ m⁻³ and the ionization temperature varied, throughout in the 4,900–5,200 K range.     

Preparation and certification of arsenate [As(V)] reference material, NMIJ CRM 7912-a

Arsenate [As(V)] solution reference material, National Metrology Institute of Japan (NMIJ) certified reference material (CRM) 7912-a, for speciation of arsenic species was developed and certified by NMIJ, the National Institute of Advanced Industrial Science and Technology. High-purity As₂O₃ reagent powder was dissolved in 0.8 M HNO₃ solution and As(III) was oxidized to As(V) with HNO₃ to prepare 100 mg kg^-1 of As(V) candidate CRM solution. The solution was bottled in 400 bottles (50 mL each). The concentration of As(V) was determined by four independent analytical techniques—inductively coupled plasma mass spectrometry, inductively coupled plasma optical emission spectrometry, graphite furnace atomic absorption spectrometry, and liquid chromatography inductively coupled plasma mass spectrometry—according to As(V) calibration solutions, which were prepared from the arsenic standard of the Japan Calibration Service system and whose species was guaranteed to be As(V) by NMIJ. The uncertainties of all the measurements and preparation procedures were evaluated. The certified value of As(V) in the CRM is (99.53 ± 1.67) mg kg^-1 (k = 2).     

Nanometer SiO2 modified with 5-sulfosalicylic acid as selective solid-phase extractant for Fe(III) determination by ICP-AES from biological and natural water samples

A new modified nanometer SiO₂ using 5-sulfosalicylic acid (SSA) as a solid-phase extractant was used for separation, preconcentration and determination of Fe(III) in aqueous solutions by inductively coupled plasma atomic emission spectrometry (ICP-AES). Its adsorption and preconcentration behaviour for Fe(III) in aqueous solutions was investigated using static procedures in detail. The optimum pH value for the separation of Fe(III) on the newly designed sorbent was 3.5. Complete elution of the adsorbed Fe(III) from the nanometer SiO₂-SSA was carried out using 2.0 mL of 0.01 mol L^− 1 of HCl. The time of 90% sorption was less than 2 min for Fe(III) at pH 3.5. Common coexisting ions did not interfere with the separation and determination of Fe(III) at pH 3.5. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 44.01 mg of Fe(III) per gram of sorbent. The relative standard deviation (RSD) of the method under optimum conditions was 3% (n = 5). The procedure was validated by analyzing three certified reference materials (GBW 08301, GBW 08504, GBW 08511), the results obtained were in good agreement with standard values. The nanometer SiO₂-SSA was successfully employed in the separation and preconcentration of the investigated Fe(III) from the biological and natural water samples yielding 100-folds concentration factor.     

Oxidation of Fe(III) to Fe(VI) by the Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> ion in strong solution of alkalis

Ferricyanide ions oxidize Fe(III) up to Fe(VI) in 7–11 M KOH solutions and 10–16 M NaOH solutions. The completeness of the oxidation increases with increasing alkali and ferricyanide concentrations. The presence of KNO₂, KAc, and K₂C₂O₄ in 7 M KOH solution increases the Fe(VI) yield. Potassium fluoride in the concentration of 0.02 M does not hinder Fe(VI) formation, but in the concentration of 0.1 M completely suppresses Fe(III) oxidation. The attempt to oxidize Fe(VI) up to Fe(VIII) by the disproportionation of Fe(VI) or by the action of Fe(CN)₆³⁻ and ozone was unsuccessful due to a high oxidation potential of the Fe(VIII)/(VI) couple.     

Determination of total Sb,Se, Te,and Bi and evaluation of their inorganic species in garlic by hydride-generation–atomic-fluorescence spectrometry

A sensitive and simple analytical method has been developed for determination of Sb(III), Sb(V), Se(IV), Se(VI), Te(IV), Te(VI), and Bi(III) in garlic samples by using hydride-generation–atomic-fluorescence spectrometry (HG–AFS). The method is based on a single extraction of the inorganic species by sonication at room temperature with 1 mol L⁻¹ H₂SO₄ and washing of the solid phase with 0.1% (w/v) EDTA, followed by measurement of the corresponding hydrides generated under two different experimental conditions directly and after a pre-reduction step. The limit of detection of the method was 0.7 ng g⁻¹ for Sb(III), 1.0 ng g⁻¹ for Sb(V), 1.3 ng g⁻¹ for Se(IV), 1.0 ng g⁻¹ for Se(VI), 1.1 ng g⁻¹ for Te(IV), 0.5 ng g⁻¹ for Te(VI), and 0.9 ng g⁻¹ for Bi(III), in all cases expressed in terms of sample dry weight.