Performance of a microwave induced plasma (MIP) operated in a liquid-cooled discharge tube for atomic emission spectrometry

Different types of microwave induced plasma (MIP) discharge operated in liquid-cooled tubes, namely a glass tube of Duran^®, a quartz tube of Herasil^®, and a very simple demountable discharge tube made of glass and quartz have been investigated. The last tube leads to the best analytical properties and the longest lifetime. The intensities of silicon lines and of the continuum spectral background, together with the signal-to-background ratios for B, Ca, Cd, Co and Zn in the case of the pneumatic nebulization of solutions have been measured and used as an indicator for the cooling efficiency. The MIP torch was cooled with a thermostated silicon oil. The decrease of the temperature of the cooling medium causes a measurable decrease of the spectral background intensity. Diagnostic measurements of the plasma include radial profiles of spectral line intensities and excitation temperatures with the lines of Fe I; values of 5000–6000 K are found. The influence of different plasma parameters, e.g. microwave power and helium flow rate, is investigated. The preliminary analytical characterization of a helium MIP maintained with the liquid-cooled demountable discharge tube is presented. Limits of detection for Al, B, Ca, Co, Fe, P, Sb and Zn (between 0.002 and 1.2 μg ml⁻¹) are comparable with or better than those reported for low power helium MIPs with sample introduction in the form of a wet aerosol.     

Investigations on laser ablation–microwave induced plasma–atomic emission spectrometry using polymer samples

The potential of laser ablation–microwave induced plasma–atomic emission spectrometry (LA–MIP–AES) for the analysis of plastic materials has been investigated. A Nd/YAG laser, operated in its fundamental mode at 1064 nm, was used to ablate small amounts of various plastics. The sample atoms were transported and excited in a closely neighbored continuously running microwave induced plasma (MIP) operated in argon or helium at reduced pressure. A 0.5-m échelle spectrometer, equipped with an intensified charge coupled device (ICCD) as a detector was used for recording the spectra. The amount of ablated material was found to be strongly dependent on the matrix (10–190 ng/shot). Signals for some metals often used as additives in polymers (Al, Ca, Cu, Sb, Ti) and for the elements F, Cl, Br, J, and P in various polymers were recorded in the spectral range 250–840 nm. The estimated detection limits were found to be in the range 0.001–0.08% for metals and 0.05–0.7% for non-metals. Spectral lines of fluorine and iodine could only be measured in the helium MIP. For high concentrations of chlorine and carbon in the samples (polyvinylchloride), a memory effect was observed.     

Real-time analysis of CuO by inductively coupled plasma emission without external calibration

The study of a method, devoted to real-time detection of metallic pollutants present in stack gas, is investigated. This method is based on spectroanalysis using an inductively coupled plasma (ICP) emission system without external calibration. The fluidized bed technology is employed to inject metallic species into the ICP emission. The mass fluxes of copper oxide (CuO) are then determined by using the intensity ratios of the metallic element spectral lines with those of the plasma gas element (argon or dry air). These ratios and the plasma characteristics (atomic excitation temperature, degree of thermal disequilibrium θ=T_e/T_h) are inserted into a calculation code of plasma composition to determine the mass flux. The results are in good agreement using either argon plasma or dry air plasma. A study of the fluidized bed properties is made to compare our values with those resulting from the elutriation calculation of the copper oxide.     

Thermodynamic considerations and optical emission diagnostics of a N2/O2 mixture in an inductively coupled air plasma

Composition, monatomic spectral line intensities (Cu, O, N) and enthalpy are calculated for thermal and non-thermal equilibrium conditions in a plasma composed of three plasma gas mixtures of N₂, O₂ and an aerosol of copper sulfate in water. With these mixtures, the excitation and rotational temperatures are measured in an inductively coupled plasma (ICP) torch using monatomic Cu spectral lines and CuO molecular spectra, respectively. It is shown that with the enthalpy it is possible to deduce the electronic translation temperature for other mixtures and that this ICP torch allows us to check the diatomic simulated spectra.     

Evaluation of the detection capability of a U-shaped d.c. arc for spectrometric analysis of solutions

A gas-stabilized arc with aerosol supply, originally designed for atomic absorption studies, has been used for emission spectrometric analysis of solutions. A characteristic of the arc is a fairly long horizontal part of the arc column which makes possible “end-on” observation of the spectral emission and selection of a well-defined region of the arc column for analysis. The most intense emission of continuum is at the arc column axis while the emission maxima of the nebulized elements are located at different distances from the axis, which mainly depend on the ionization potential of the corresponding element.The presence of alkali elements in the arc plasma enhance considerably the spectral emission of the elements with medium and low ionization potentials. The effect depends mainly on the first ionization potential of the element and its extent is approximately the same for atom and ion lines. In the case of potassium chloride the intensity increase approaches a plateau at a concentration of 2.5 mg ml^?1. The magnitude of the effect justifies the use of potassium chloride as a spectroscopic buffer.Detection limits obtained with this source on 60 spectral lines are compared with those found in inductively coupled plasmas and in an inverted V-arc echelle spectrometer system. Comparison reveals that inductively coupled plasmas yield consistently lower detection limits with the ion lines used, while with the atom lines it retains the advantage only for elements having a high ionization potential.     

Some analytical characteristics of an argon—nitrogen d.c. plasma arc for emission spectrometry

A low-power d.c. plasma arc device was used to estimate the analytical characteristics of an Ar—N₂ plasma arc compared to those of an argon plasma arc. When the flow rate of added nitrogen was varied from 0 to 1 l min^-1, the Cd I 228.802-nm line showed a maximum signal-to-background ratio at a nitrogen flow rate of approximately 0.3 1 min^-1 which corresponds to 0.23% of the total argon flow rate. Ratios of the signal intensities with the Ar—0.23%N₂ and argon plasma arcs are given for the spectral lines of seventeen elements. Relatively higher ratios were found for the atom lines of the group VIII through IIIA elements in the periodic table. Better precision and lower detection limits were attained for aluminium and cadmium with the Ar—0.23%N₂ plasma arc than with the argon plasma arc.     

Preliminary investigation for the development of surrogate debris from nuclear detonations in marine-urban environments

The effect of ambient gas on measurements with microwave-assisted laser-induced plasma in microwave-assisted laser-induced breakdown spectroscopy (MA-LIBS) was studied with relevance for the analysis of nuclear fuel. A pelletized gadolinium oxide (Gd₂O₃) sample, which was used as a simulated nuclear fuel, was irradiated by a pulsed Nd:YAG laser (532 nm, 5 mJ) coupled with microwaves (2.45 GHz, 400 W) under various gases of air, Ar, and He. Microwaves can be effectively used to enhance laser-induced plasma emissions. The emission spectrums of Gd obtained by MA-LIBS in Ar and He gases are much better than those of the air case. Namely, the spectral lines can be clearly identified and are far from molecular bands. Furthermore, the emission intensity is highest with low background emissions. Linear calibration curves of Ca in the concentration range between 0 and 500 mg/kg as an impurity in Gd₂O₃ have been successfully obtained in all gases. The detection limits of Ca impurity in air, Ar and He gases were 2, 0.8 and 0.6 mg/kg, respectively, which are much lower than the required limits of Ca impurity in nuclear fuels.     

A Study on Determination of Some Trace Nonmetals by Microwave Induced Plasma Atomic Emission Spectrometry

In general, atomic emission spectrometry (AES) is an excellent technique for determination of metal elements. However, its capability of determining nonmetals has not been developed well. The major reasons are the resonance lines of most nonmetals lie in the vacuum ultraviolet spectral region and the ionic lines of these elements are difficult to be used because the ionization potentials of the elements are very high. And furthermore only He plasma can efficiently excit those ionic resonance lines. The practical application of HeICP-AES to determining the nonmetals is also difficult because its operating and perchace costs are very high. In contrast to HeICPAES, the costs of He microwave induced plasma (MIP)-AES are relatively low, HeMIP has a high excitation capability which can excite ionic lines of various nonmetals and the nonmetals can be determined by HeMIP-AES with a high sensitivity.     

A three-electrode direct current plasma as compared to an inductively coupled argon plasma

Summary A direct comparison of some analytical properties of a three-electrode direct current plasma and an inductively coupled argon plasma in the case of pneumatic nebulization of aqueous solutions was performed. The measurements were carried out under similar conditions using a 3.4-m spectrograph. The spectra to be compared were recorded on photographic plates in the spectral range from 250 nm to 430 nm. Strong molecular band systems of OH, NH, and N ₂ ⁺ were observed in the case of the direct current plasma. Detection limits for 27 spectral lines of 20 elements were determined for both sources yielding a slight advantage in favour of the inductively coupled plasma. The effect of sodium upon line and background intensities was investigated and found to be generally higher in the direct current plasma.

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Ein Drei-Elektroden-Gleichstromplasma im Vergleich zu einem induktiv gekoppelten Argonplasma

     

In-situ vaporization and matrix removal for the determination of rare earth impurities in zirconium dioxide by electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A novel method for the determination of trace rare earth impurities in ZrO₂ powder has been developed based on electrothermal vaporization inductively coupled plasma atomic emission spectrometry. A polytetrafluoroethylene slurry was used as a fluorinating reagent to convert both the matrix (Zr) and the analytes (rare earth elements) into fluorides with different volatilities at a high temperature in a graphite furnace. The more volatile ZrF₄ was removed in-situ by selective vaporization prior to the determination of the analytes, removing matrix spectral interferences. Under optimum operating conditions, the absolute detection limits of the analytes varied from 0.04 ng (Yb) to 0.50 ng (Pr) with relative standard deviations less than 5%. The recommended approach has been successfully applied to the determination of trace rare earth impurities (La, Pr, Eu, Gd, Ho and Yb) in ZrO₂ powder and the results were in good agreement with those obtained by pneumatic nebulization inductively coupled plasma atomic emission spectrometry after the separation of the matrix using a solvent extraction procedure.     

Study of a Low-Powered He Microwave-Induced Plasma for Determination of P, Cl, Br, and I by Atomic Emission Spectrometry

Aqueous sample solutions were nebulized by an ultrasonic nebulizer and the solvent was removed by a desolvation apparatus before introduction of the aerosol into the microwave-induced plasma (MIP). The desolvation system consists of a heating tube and a condenser associated with a concentrated H₂SO₄ desiccator. The water vapor was removed almost completely with the desolvation system. The detectability of microwave-induced plasma atomic emission spectrometry was therefore improved. The detection limits for P, Cl, Br, and I were 0.0045, 0.12, 0.23. and 0.06 μg/ml, respectively. Based on a study of the emission spectra of P, Cl, Br, and I in the range of 200 to 600 nm in He MIP, the optimum analytical lines for determination of corresponding elements were chosen.     

Some analytical characteristics of a three electrode d.c. argon plasma source for optical emission spectrometry

An investigation of a commercially available three electrode d.c. plasma source burning in an inverted Y configuration was carried out. It is shown that (i) for atoms the position of maximum line intensity in the plasma is determined by the norm temperature of the spectral line, (ii) the source is stable over long periods of time, (iii) high concentrations of alkali metals in the sample can disturb the plasma resulting in an enhancement of both atomic and ionic spectral lines, (iv) detection limits are generally less than one order of magnitude higher than those obtained with an inductively coupled plasma (ICP), and (v) precision of analysis is better than 2% expressed as relative standard deviation.     

Comparative study of microwave-induced plasma atomic emission spectrometry and atomic fluorescence spectrometry as gas-chromatographic detectors for the determination of methylmercury in biological samples

In order to attain a lower detection limit with the HS GC MIP analytical method (Head-Space Gas Chromatography with Microwave-Induced Plasma detection) recently developed for the analysis of methylmercury in biological samples, the quarter-wave Evenson-type cavity used until now was replaced by a TM₀₁₀ Beenakker-type cavity, which was used with both argon and helium as carrier gas. With an argon plasma, an eightfold increase in detection limit was gained compared with the argon plasma sustained by the Evenson cavity, while only a four-fold increase was gained with the helium plasma. In a second step of the study, the MIP detector was replaced by an AFS (atomic fluorescence) detector (CVAFS Model-2, Brooks Rand Ltd, Seattle, USA). With this AFS detector a detection limit of 1 ng methyl mercury per g biological tissue could be reached; i.e. measurements were 40 times more sensitive than those using the Evenson cavity. This detector has some other advantages compared with MIP detection: it is less expensive and easier to manipulate, while the same precision and accuracy are obtained. The use of AFS as detector in the headspace gas chromatographic system is therefore an important improvement for the analysis of methyl-mercury in biological samples.     

Advantages and effects of nitrogen doping into the central channel of plasma in axially viewed-inductively coupled plasma optical emission spectrometry

The effects and benefits of N₂ addition to the central channel of the ICP through the nebulizer gas used in ICP OES with axial view configuration were investigated in the present study. The N₂ flow rate, nebulizer gas flow rate, RF power and sample uptake rate were evaluated and compared for two sample introduction systems (pneumatic nebulization/aerosol desolvation and conventional pneumatic nebulization). It was observed that N₂ did not affect solution nebulization and aerosol transport but affects the ICP characteristics. The higher thermal conductivity of N₂ (in comparison with Ar) changes energy distribution in the ICP, observed by monitoring the signals of Ar emission lines and sodium emission. The ratio Mg(II)-280.270 nm/Mg(I)-285.213 nm was utilized as a diagnostic tool for plasma robustness. The addition of N₂ (20 mL min⁻¹) increased plasma robustness significantly and mitigated effects caused by Na, K and Ca. For 40 spectral lines evaluated, it was observed that the emission signals of ionic spectral lines were in general more affected by N₂ than those of atomic spectral lines. Detection limits, precision, sensitivity and linearity of calibration curves obtained using N₂-Ar-ICP were almost similar to those obtained using Ar-ICP. The analysis of 5 different reference materials revealed that accuracy was not degraded by adding N₂ to the Ar-ICP.     

Spectral interference in the determination of Ho,Tm and Ga as dopants in single crystals of potassium titanylphosphate by inductively coupled plasma atomic emission spectrometry

The present article discusses the spectral interferences affecting the determination of Ga, Ho and Tm as dopants in single crystals of potassium titanylphosphate (KTiOPO₄) by inductively coupled plasma atomic emission spectrometry (ICP-AES). The Q concept, as proposed by Boumans and Vrakking [Spectrochim. Acta Part B 43 (1988) 69] was used for this study, which covers: (a) spectral data for potassium, titanium and phosphorous as interferents (at a concentration of 4 mg/ml) in 400 pm wide spectral windows around the prominent lines of the analytes; (b) a database of Q values for line interferences (Q_I) and for wing interferences (Q_W); and (c) the interelement interferences in doubly doped crystals of KTP.     

Analysis of superconductor oxides YBa2Cu3O8−x by inductively coupled plasma atomic emission spectrometry and complexometric titration

The elemental composition of superconductor oxides YBa₂Cu₃O_8−x were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and complexometric titration. Samples were dissolved in dilute HCl. A sequential PU 7000 Philips inductively coupled plasma atomic emission spectrometer was used for the measurements. A comparison of the different atom and ion emission lines of yttrium, barium and copper was carried out. The effect of changes of forward radio frequency (RF) power coupled into the plasma on emission intensity of various spectral lines was studied. The RF power was changed from 0.8 to 1.2 kW. The changes in the net intensities (%) of the emission lines of Cu(I) at 324.754 nm, Cu(II) at 224.700 nm, Ba(II) at 455.403, Ba(II) at 493.409 nm, Y(II) at 371.030 nm and Y(II) at 360.073 nm were calculated. The indicator 1-(2-Pyridylazo)-2-Naphthol (PAN) and different buffers were used for the complexometric titration of Cu, Y and Ba. No statistically significant differences were found between the results of ICP-AES and chemical methods of analysis.     

Use of tandem calibration for analyzing steels and alloys by inductively coupled plasma atomic emission spectrometry

A method is proposed for plotting calibration graphs by reference analyte solutions (tandem calibration) for the analysis of steels and alloys by inductively coupled plasma atomic emission spectrometry (ICP-AES) with spark ablation. The use of spectral lines of analytes and an internal standard with similar values of sums of ionization and excitation energy ensures an excellent repeatability and accuracy of the results of analysis using tandem calibration. A nebulizer chamber for the simultaneous introduction of solutions and solid sample aerosols into inductively coupled plasma (ICP) is designed. The optimal parameters of the introduction of sample aerosols and a method of plasma observation are chosen; the requirements for the choice of the analytical lines of analytes are proposed.     

Computational approaches to design a molecular imprinted polymer for high selective extraction of 3,4-methylenedioxymethamphetamine from plasma

In this work, a molecular imprinted polymer (MIP) as a novel selective sorbent for extraction of 3,4-methylenedioxymethamphetamine (MDMA) from plasma samples was prepared. For selecting a more suitable monomer and polymerization solvent a methodology based on density functional theory calculations was developed. This computational design is based on the comparison of stabilization energies of the prepolymerization adducts between the template and different functional monomers. The effect of polymerization solvent was studied using of polarizable continuum model (PCM). The computational results revealed that the best suitable monomer and polymerization solvent for preparation of MIP is methacrylic acid (MAA) and chloroform, respectively. Also, another MIP with methacrylic acid (MAA) as monomer in acetonitrile was prepared to evaluate the validity of polarizable continuum model for selection of polymerization solvent. The performance of each polymer was evaluated by using Langmuir-Freundlich (LF) isotherm. As it is expected, the best results were obtained for the MIP which was prepared in chloroform. This MIP was used as a selective sorbent in solid-phase extraction coupled with high performance liquid chromatography-ultraviolet detector (MISPE-HPLC-UV) for rapid screening of MDMA in human plasma. For the proposed MISPE-HPLC-UV method, the linearity between responses (peak areas) and concentrations was found over the range of 3.6-11500 ng mL(-1) with a linear regression coefficient of 0.998. The limit of detection (LOD) and quantification (LOQ) in plasma were 1.0 and 3.3 ng mL(-1), respectively. The %RSD (n=5) data for five plasma samples containing 15, 25, 50, and 100 ng mL(-1) of MDMA were 1.02, 1.12, 2.05, 2.54, respectively.     

Synthesis and study of a molecularly imprinted polymer for specific solid‐phase extraction of vinflunine and its metabolite from biological fluids

A molecularly imprinted polymer (MIP) was synthesized in order to specifically extract vinflunine, an anticancer agent, and its metabolite (4‐O‐deacetylvinflunine) from bovine plasma and artificial urine by solid‐phase extraction (SPE). Vinorelbine, a non‐fluorinated analogue of vinflunine, was selected as a template for MIP synthesis. The selectivity of MIP versus the template (vinorelbine) and other alkaloids (catharanthine, vinblastine, vincristine, vinflunine and 4‐O‐deacetylvinflunine) was shown by a SPE protocol carried out with non‐aqueous samples. A second protocol was developed for aqueous samples with two consecutive washing steps (AcOH–NH₂OH buffer (pH 7, I=10 mM)–MeOH mixture 95:5 v/v and ACN–AcOH mixture 99:1 v/v) and an elution step (MeOH–AcOH mixture 90:10 v/v). Thus, MIP‐SPE of bovine plasma brought high recoveries, 81 and 89% for vinflunine and its metabolite, respectively. This protocol was slightly modified for artificial urine samples in order to obtain a good MIP/NIP selectivity; furthermore, elution recoveries were 73 and 81% for vinflunine and its metabolite, respectively. Repeatability was assessed in both biological matrices and RSD (%) were inferior to 4%. The MIP also showed a suitable linearity (r² superior to 0.99), between 0.25 and 10 μg/mL for plasma, and between 1 and 5 μg/mL for artificial urine.     

The effect of two gases forming supercritical fluids (Xe and CO2) on the spectral characteristics and analytical capabilities of microwave induced plasmas

A comparative study of the effect of CO₂ and Xe added along with the plasma gas to He and Ar microwave induced plasmas (MIPs), simulating possible conditions to be used when a MIP is employed as specific detector for supercritical fluid chromatography (SFC), has been carried out. The proportions of CO₂ and Xe to the plasma gas investigated are comparable to the typical percentages used for SFC-MIP couplings. The study has been performed with two different MIP systems: an atmospheric pressure discharge held in a Beenakker cavity TM₀₁₀ and a reduced pressure surfatron-MIP.The influence of CO₂ and Xe addition on the spectrochemical properties of the discharge has been studied by using the atomic emission of mercury and some typical non-metals (chlorine, carbon and sulfur) at different wavelengths (atomic and ionic lines). Results showed that ion line emission intensities are always reduced more significantly than atom line emissions by both dopant gases on study, whatever the pressure. In general terms, however, the effect of adding Xe is less severe, both for atom and ion lines, than that of CO₂; in most cases the detection limits (DLs) observed are better for Xe than for CO₂ as dopant gas. In fact, the DLs obtained for the selected lines of mercury measured were practically unaltered by the addition of 0.2% Xe to atmospheric pressure Ar or He MIPs. CO₂ addition (0.2%) produced about 1.5 times worsening of the observed DLs for mercury. For non-metal analyses better DLs were also obtained, in general terms, with Xe than with CO₂ as dopant gas.