Capacitively Coupled Microwave Plasma Research Articles

Development of a Transformable Plasma Device for Materials Processing

In this paper, we have developed transformable-sheet electrodes for a capacitively coupled microwave plasma (CCMP) and diagnosed parameters of the CCMP in air, such as the rotational temperature of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (400-600 K at 80-230 torr) and the electron density (approximately 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> at 300 torr). We applied the CCMP to surface modification of polycarbonate to improve the hydrophilic property of the surface. We also performed generation of a homogeneous plasma, which could be of various shapes, developing different transformable-sheet electrodes in air by ac (1.6 kV) at 10 kHz at 3 torr. These results suggested that on-demand plasma processing without an operating gas could be achieved by utilizing transformable-sheet electrode technology.

Investigations on the on-line determination of metals in air flows by capacitively coupled microwave plasma atomic emission spectrometry

Plasma optical emission spectrometry with a capacitively coupled microwave plasma (CMP) operated with air has been investigated with respect to its possibilities for real-time environmental monitoring of combustion processes. The unique feature is the possibility to operate the CMP with air as working gas, as is usually the case in exhaust gases of combustion processes. The CMP also is shown to be stable in the presence of large amounts of water and CO 2, which makes this source ideally suitable for this purpose. The detection limits obtained for the environmentally relevant elements Cd, Co, Cr, Fe, Mg, Ni and Pb show the possibility to monitor directly heavy metals in air in an on-line mode and down to the 2–160-μg m −3 level. These detection limits are generally lower than the threshold limit values of the ‘Federal Law for Immission Protection’ in Germany in the gaseous effluents of industrial plants. In order to investigate the influence of the water loading (32–222 g m −3) on the detection limits a comparison of results obtained with three different nebulizers (Légère nebulizer, hydraulic high-pressure nebulizer and ultrasonic nebulizer) was made, with which aerosols with different water loading are entered into the plasma. For the hydraulic high-pressure nebulizer and the ultrasonic nebulizer no desolvation unit was found to be necessary. It was shown that especially for elements with lines having high excitation energy (Cd) or for which ion lines are used (Mg II) the increase in water loading deteriorates the detection limits. The rotational temperatures ( T rot) and excitation temperatures ( T exe) in the case of different amounts of water are of the order of 3700–4900 K and 4700–7100 K, respectively. The temperatures show that changes in the geometry and temperature distribution in the case of T rot but also the values of T exe themselves are responsible for this increase in detection limits. Furthermore, different amounts of CO 2 mixed to the working gas (3–22%) while the total gas flow rate was kept constant at 1.2 l min −1 were also shown to increase the detection limits.

Use of a capacitively coupled microwave plasma (CMP) with Ar, N 2 and air as working gases for atomic spectrometric elemental determinations in aqueous solutions and oils

A comparative study was performed of 600 W capacitively coupled microwave plasmas (CMP) with different plasma gases (Ar, N2 and air) and aerosol generation with the aid of a Legere pneumatic nebulizer. Detection limits with the different working gases are in the order of 15–4000 ng/mL for Fe, Cr, Zn, Mg and Ca in aqueous solutions. The influence of organic solutions on the stability of the plasma is discussed. The determination of Co, Cr, Fe, Mg and Ni in different oil samples by OES is described, using an air-CMP and pneumatic nebulization after dilution of the oils by 20% with cyclohexane. The detection limits for these elements are in the 100–400 ng/g range. Results obtained for a waste motor oil for the elements mentioned in the concentration range of 4–50 μg/g were found to be in good agreement with those obtained by ICP-OES after digestion of the oils at high pressure in PTFE vessels.

Direct determination of cadmium in solids using a capacitively coupled microwave plasma atomic emission spectrometer

A capacitively coupled microwave plasma (CMP) operating at 800 W was examined for the direct determination of cadmium in solids. The laboratory-constructed system contained a tungsten cup electrode capable of holding microsample quantities. A low-powered plasma was used to heat the sample, while at higher powers the plasma was used for sample vaporization and excitation. This plasma enabled thermal vaporization (TV) sample introduction to be accomplished in situ as the plasma formed directly around the sample. Thus, the need for sample preparation, procedural steps and sample transport was eliminated. This technique was capable of the direct determination of trace elements in solid samples in less than 5 min. The effects of experimental parameters such as gas flow rate, atomization power and electrode position were investigated. Detection limits obtained for Cd by TV-CMP-AES were in the picogram range with a relative standard deviation of <20%. The accuracy and precision of the method were also evaluated by measuring Cd in several NIST Standard Reference Materials.

The use of different plasma gases (Ar, N(2) and air) for CMP-OES: figures of merit and temperature measurements.

A comparative study of a 600 W capacitively coupled microwave plasma (CMP) operated with different plasma gases (Ar, N(2) and air) with respect to the achieved detection limits for Fe, Cr, Zn, Ca and Mg have been carried out. Radially and axially resolved rotational temperatures (T(rot)), excitation temperatures (T(exc)) and electron number densities (n(e)) of these plasmas have been determined using OH (T(rot)), Fe (T(exc)) and Mg (n(e)) as thermometric species. The influence of different gas flow rates on T(rot), T(exc) and n(e), and of Li as an easily ionized element on T(exc) has been investigated.

Determination of lead in whole blood by capacitively coupled microwave plasma atomic emission spectrometry

A capacitively coupled microwave plasma (CCMP) has been developed as a screening method for lead in whole blood. Whole blood was deposited on a tungsten filament electrode and subsequently dried, ashed and atomized. The emission of the lead at the 405.8 nm line was measured using a photodiode array spectrometer. The analytical curve produced by this method showed excellent linearity with a detection limit of 30 ng ml–1. The precision is better than 10% for concentrations of 100 ng ml–1 and above. The accuracy was evaluated by determining lead in blood Standard Reference Materials (SRM's). Good agreement was obtained with concentrations of 135.3, 306.3 and 544.3 ng ml–1. The CCMP method is advantageous over other screening methods for lead in blood because no sample treatment or dilution is necessary.

Investigation of Halogen Determination in a Helium Capacitively Coupled Microwave Plasma Atomic Emission Spectrometer

The measurement of halogens by optical emission spectroscopy is difficult because the resonance lines occur in the vacuum–UV (VUV) region of the spectrum where oxygen and nitrogen absorb light and optical components are less efficient. However, plasmas still show promise as sources for the determination of halogens. Helium plasmas offer an advantage over argon plasmas since helium has a higher ionization potential (24.6 eV for He and 15.8 eV for Ar). Chlorine and fluorine have been measured by a helium hollow cathode discharge (He-HCD), helium capacitively coupled microwave plasma (He-CMP), helium microwave-induced plasma (He-MIP), argon and helium inductively coupled plasmas (ICP), and ICP-mass spectrometry. The majority of sample introduction techniques have involved using the effluent from a gas chromatograph, electrothermal vaporization, or volatile compound formation. Several researchers have used pneumatic nebulization. In this research, organic samples containing organic chlorine or fluorine compounds and aqueous samples of chloride or fluoride ions were introduced into the He-CMP with the use of pneumatic nebulization.

Diagnostics in a High-Flow-Rate (&gt;6 L min−1) Helium Capacitively Coupled Microwave Plasma: Aqueous versus Organic Solution

A helium capacitively coupled microwave plasma (CMP) with a high plasma gas flow rate (&gt;6 L min−1) is described. Plasma gas flow rates above 6–8 L min−1 produce a cylindrical-shaped plasma. Diagnostic studies were performed. Electronic excitation ( Texc), rotational ( Trot), and ionization-recombination ( Tion) temperatures were determined, along with the electron number density ( ne). Texc was calculated from the slope of the Boltzmann plot with the use of Fe as the thermometric species. Values for Texc in aqueous and organic solution were 3430 and 3450 K, respectively. Trot determined with the use of both OH and N2+. With OH, Trot values were 1620 and 1660 K for aqueous and organic solutions, respectively. If no solution was introduced, a Trot value of 2350 K was determined with N2+. N2+ also gave Trot values of 1900 and 1930 K with aqueous and organic solutions, respectively. The Tion values were 6220 and 5610 K with the use Cd and Mg, respectively. The ne value was on the order of 4 × 1014 cm−3. Background spectra and limits of detection are also presented.

Direct Introduction of Steel Samples into a Capacitively Coupled Microwave Plasma for Atomic Emission Spectrometry

The feasibility of analyzing steel samples by direct introduction into a helium/hydrogen mixed-gas capacitively coupled microwave plasma was assessed with steel standard reference materials (NIST 442-450). Linear calibration curves were obtained for various concentration ranges. Limits of detection for Sn and Pb were 5 μg/g and 0.08 μg/g, respectively.

Microsample introduction by tungsten filament electrode into capacitively coupled microwave plasma for atomic emission spectroscopy: analytical figures of merit

A tungsten filament electrode for sample introduction into a capacitively coupled microwave plasma (CCMP) is described for its use in atomic emission spectroscopy (AES). Samples vaporize rapidly off the filament and are excited in the microwave plasma upon the initiation of the microwave discharge. The maximum emission signals of He and Cu were found at similar spatial coordinates, gas flow-rates and microwave powers. The addition of 100 ml min −1 hydrogen dopant into the plasma gas suppressed both the background and emission from the tungsten. The filament temperature increased with the power. The absolute detection limits of 12 elements were within the range of 1 to 100 pg. The linear dynamic range was 3–4 orders of magnitude, and precision was better than 10%.

Temperature and electron density measurements in a helium/hydrogen capacitively coupled microwave plasma

Various temperature and electron density measurements have been carried out in a capacitively coupled microwave plasma (CMP) with a mixture of hydrogen and helium as the plasma gas using a photodiode array spectrometer for detection. FeI lines were used for excitation temperature, OH lines for rotational temperature and the H gb line for electron number density measurements. Rotational temperatures were found to be between 1800 K and 3000 K, excitation temperatures varied between 2000 K and 5000 K and electron number densities varied between 4 × 10 14 cm −3 and 9 × 10 14 cm −3, depending on operating conditions. The influence of power, observation position, solution uptake rate and carrier gas flow have been investigated.

A thermal vaporizer-capacitively coupled microwave plasma system for trace Hg determination.

A system has been constructed, which couples a new type of thermal vaporizer to a capacitively coupled microwave plasma (CMP). It is used to determine trace levels of Hg in water. A sample solution of 2-7ml is jetted onto a fused silica wool heated to 630-945°C and thermally vaporized. A large volume of the resulting steam is removed by a highly efficient double coaxial wall condenser. The desolvated mercury solute enters the CMP; 253.65 nm emission is monitored. Basic system characteristics studied include vaporizer temperature, gas flow rates, detection limits, dynamic range and matrix effects. Linear calibration curves are obtained for concentrations ranging from 1 to 1000 μg/l.

Das kapazitiv gekoppelte mikrowellenplasma (CMP) als atomisierungsquelle in der atomabsorptions-spektralanalyse

The capacitively coupled microwave plasma (CMP) with N 2 as working gas is shown to be suitable as an atomizer for atomic absorption spectroscopy. The sensitivities for Ba, Ca, Co, Cr, Fe, Mg, Mo, Ni, Sr, W and Zn are given. Their relative position in this sequence reflects the differences in the dissociation energies of the monoxides. The type of CMP used has an excitation temperature of 5600 to 4750 K and a kinetic temperature of 4450 K. Referring to equal optical path lengths the sensitivity in the CMP (and also in the ICP) is not better than in the 1500 K “cooler” reducing acetylene flames. A high kinetic temperature alone is not sufficient; better degrees of atomization will only be achieved if plasmas with much higher analyte residence time or with reducing chemical properties can be developed.

Determination of trace amounts of arsenic using a capacitively coupled microwave plasma combined with hydride generation: applications to sewage sludge, iron and steels

A capacitively coupled microwave plasma (CMP) combined with an arsine generation system for the determination of trace amounts of arsenic is described. Factors affecting the spectral intensity of As 228.8 nm in the CMP were examined, and optimal working conditions for the determination of arsenic were established. A sensitive, precise and practical method for the determination of arsenic in sewage sludge, iron and steels was elaborated.

Inductively coupled plasma-atomic emission spectroscopy: Its present and future position in analytical chemistry

Inductively coupled plasma-atomic emission spectroscopy: Its present and future position in analytical chemistry

An assessment of a microwave-induced plasma generated in argon with a cylindrical TM 010 cavity as an excitation source for emission spectrometric analysis of solutions

A cross-flow pneumatic nebulizer with spray chamber was directly coupled to a microwave-induced plasma (MIP) generated with a cylindrical TMO 010 cavity in argon flowing through an alumina capillary. The detection limits of 15 elements were determined with 23 spectral lines and the interference effect of KCl on these spectral lines was measured. The results were compared with those reported in the literature for MIP systems based on conventional or newly designed cavities, and incorporating desolvation facilities. A comparison was also made with an inductively coupled plasma (ICP) and a capacitively coupled microwave plasma (CMP) for which the reported results were obtained under spectrometric conditions that closely matched those used in the present work and for which the rate of sample injection into the plasma was approximately the same as that used here.

A comparative investigation of some analytical performance characteristics of an inductively-coupled radio frequency plasma and a capacitively-coupled microwave plasma for solution analysis by emission spectrometry

This paper reports results of an inter-laboratory investigation involving standardized experiments performed with standard measuring equipment to establish unambiguously the differences in analytical performance of an inductively-coupled radio frequency plasma (ICP) and a capacitively-coupled microwave plasma (CMP) for simultaneous multi-element analysis (SMEA) of solutions. The authors compared a laboratory-built, prototype ICP and a standard commercial CMP. The analytical characteristics covered were the following: (i) detection limits, (ii) matrix effects produced by cesium sulfate, cadmium sulfate, and di-amnioniumhydrogenphosphate, (iii) sensitivities, and (iv) precision. These characteristics were evaluated for 14 spectral lines of 12 representative elements. The results were corrected for differences in the performance (aerosol injection rate into the plasma) of the nebulizers used with the two excitation sources and for differences in transmission factor, optical conductance and photomultiplier responsivity between the two “identical” measuring equipments. It was definitively established that in all respects the ICP (investigated here) is superior to the CMP (considered here) as an excitation source for SMEA of solutions.