Microwave Induced Plasma Optical Emission Research Articles

Evaluation of various nebulizers for use in microwave induced plasma optical emission spectrometry

Three different micronebulizers, the micro3 (M3), the flow focusing pneumatic nebulizer (FFPN) and the microcapillary array nebulizer (NAR-1), were compared with a conventional Meinhard pneumatic concentric nebulizer (PN) working at low liquid flow rates for the elemental analysis of liquid samples by microwave induced plasma optical emission spectrometry (MIP-OES). Three nebulizers (M3, FFPN, PN) were operated in conjunction with the same cyclonic spray chamber. A critical evaluation has been carried out of the nebulization stages, such as the formation of the primary and tertiary aerosol, separation of large droplets (drop size distribution) in the spray chamber (also evaluated for the NAR-1 nebulizer) and aerosol transport to the plasma torch. Atomic emission was measured for Ba, Ca, Cd, Cu, Fe, I, Mg, Mn, Pb, Sr and Zn. Analytical performance of the nebulization systems were characterized by determination of the limits of detection (LODs), the precision (RSDs) and the memory effects (wash-out time) for these elements, and ranged between 0.004–0.099 μg mL−1, 4–8%, and 5–7 minutes, respectively. Analysis of certified reference materials (TORT-1, Human Hair No. 13, Lichen IAEA-336, Soya Bean Flour INCT-SBF-4) were performed to determine the accuracy and precision available with the presented nebulization systems. These materials were microwave/nitric acid digested and analyzed by calibration with synthetic solutions of the analytes. In general, the results indicated that the FFPN nebulizer gave rise to higher emission signals and slightly lower LOD values than the other three nebulizers. The nebulizers exhibited no clogging problems.

Coupling of microwave induced plasma optical emission spectrometry with HPLC separation for speciation analysis of Cr(III)/Cr(VI)

AbstractFeasibility and limitations of direct coupling of high performance liquid chromatographic (HPLC) separation to microwave induced plasma (MIP)-optical emission spectrometry (OES) for elementspecific detection was tested and compared to inductively coupled plasma (ICP)-optical emission spectrometric detection on the basis of the Cr(III)/Cr(VI) speciation analysis of water samples. Coupling was performed by a hydraulic high pressure nebulizer (HHPN) radiative-heating/watercooling interface which provides about 20 % and 80 % aerosol yield in the case of helium and argon carrier gases, respectively. Desolvation efficiency of aqueous solutions was approximately 80 %. Applying the ion-pair HPLC separation, the organic eluents and reagents in the MIP cause a 50–75 % signal suppression for Cr(VI) and 25–50 % for Cr(III). In a pure aqueous solution the MIP Cr(VI) signal was by 20 % lower than that of Cr(III). These effects were lower using the ICP source, but they cannot be neglected. Easily ionizable matrix elements (Na, Ca) can cause 70 % signal suppression in the MIP, and 20 % in the ICP. Therefore, species dependent calibration is required in both cases. In the case of HPLC detection by MIP-OES, the detection limit was 13 ng for Cr(III), and 18 ng for Cr(VI). Using the ICP-OES detection, the detection limit was 0.2 ng for Cr (III) and 0.4 ng for Cr (VI). The linear dynamic ranges in both cases were two orders of magnitude.

Direct spectrometric determination of total fluorine in geological materials by continuous powder introduction into helium microwave induced plasma

A sensitive, direct, spectrometric method for the determination of total fluorine content in a wide variety of geological materials has been developed. Solid samples were ground in a mill and sieved prior to continuous powder introduction microwave induced plasma optical emission spectrometry (CPI-MIP-OES) determination with a helium plasma. The effects of operating conditions and sample particle size on the analytical signal were evaluated. Materials were introduced as a solid–gas aerosol. The amount of fluorine was measured using calibration standards prepared by dropping of a standard fluoride solution on a suitable powdered support (silica or activated carbon) with matrix matching. The experimental detection limit for fluorine at line 685.6 nm, obtained with the CPI-He-MIP-OES method, was of the order of 3–6 μg g−1; the uncertainty was about 5–17%. The developed method was validated by carrying out the analysis of different certified reference materials including soils, fly ash and coals.

Simultaneous determination of hydride forming (As, Bi, Ge, Sb, Se, Sn) and Hg and non-hydride forming (Ca, Fe, Mg, Mn, Zn) elements in sonicate slurries of analytical samples by microwave induced plasma optical emission spectrometry with dual-mode sample introduction system

A slurry sampling method for the simultaneous determination of hydride forming (As, Bi, Ge, Sb, Se, Sn) and Hg and non-hydride forming (Ca, Fe, Mg, Mn, Zn) elements, without total sample digestion has been developed using the commercial dual-mode sample introduction system (MSIS) coupled with microwave induced plasma optical emission spectrometry (MIP-OES) from biological and environmental reference materials and real samples. The main advantage of this system is its simultaneous determination of elements that form volatile vapor species and elements that do not, without any instrumental changes. Optimization of reaction, nebulization and instrumental conditions was performed to characterize the new system. Slurry concentration up to 4% m/v (particles < 100 μm) prepared in 10% HNO 3 containing 100 μL of decanol, by application of ultrasonic agitation, was used with calibration by the standard addition technique. An ultrasonic probe was used to homogenize the slurry in the quartz cup just before its introduction into the reaction/nebulization system; the multimode sample introduction system (MSIS) combines the benefits of nebulization and vapor generation in a single device. Detection limits (LOD, 3 σ blank, peak area) of 0.07, 0.29, 0.25, 0.10, 0.12, 0.14, 0.11, 0.28, 0.42, 0.02, 0.21 and 0.34 μg g − 1 were obtained for As, Bi, Ge, Sb, Se, Sn, Hg, Ca, Fe, Mg, Mn and Zn, respectively. The relative standard deviations were ca. 10%, adequate for slurry analysis. To test the accuracy, six certified reference materials were analyzed with the analyte concentrations mostly in the μg g − 1 level. Measured concentrations are in satisfactory agreement with certified values for the biological reference materials (LUTS-1, DOLT-2) and environmental reference materials (PACS-1, GWB 07302, NIST 2710, NBS 1633b), all adequate for slurry sampling. The method was successfully applied to the determination of the elements in real samples (coal fly ash, lake sediment, sewage). The method requires small amounts of reagents and reduces contamination and losses.

Simultaneous determination of hydride forming elements (As, Sb, Se, Sn) and Hg in sonicate slurries of biological and environmental reference materials by hydride generation microwave induced plasma optical emission spectrometry (SS-HG-MIP-OES)

A slurry sampling hydride generation (SS-HG) method for the simultaneous determination of hydride forming elements (As, Sb, Se, Sn) and Hg, without total sample digestion, has been developed using batch mode generation system coupled with microwave induced plasma optical emission spectrometry (MIP-OES) from certified biological and environmental reference materials. Slurry concentration up to 3.6% m/v (particles < 80 μm) prepared in 10% HCl containing 100 μl of decanol, by the application of ultrasonic agitation, was used with calibration by the standard addition technique. Harsh conditions were used in the slurry preparation in order to reduce the hydride forming elements to their lower oxidation states, As(III), Sb(III), Se(IV) and Sn(II) and Hg, being reduced to mercury vapor, before reacting with sodium tetrahydroborate. An ultrasonic probe was used to homogenize the slurry in the quartz cup just before its introduction into the reaction vessel. For 10 ml of slurry sample, detection limits (LOD, 3 σ blank, peak area) of 0.06, 0.08, 0.15, 0.12 and 0.10 μg g − 1 were obtained for As, Sb, Se, Sn and Hg, respectively. The method offers relatively good precision (RSD ranged from 9 to 12%) for slurry analysis. To test the accuracy, three certified reference materials were analyzed with the analyte concentrations mostly in the μg g − 1 level. Measured concentrations are in satisfactory agreement with certified values for the biological reference materials: NRCC LUTS-1 (lobster hepatopancreas), NRCC DOLT-2 (Dogfish Liver) and environmental reference material: NRCC PACS-1 (Marine Sediment), all adequate for slurry sampling. The method requires small amounts of reagents and reduces contamination and losses.

Simultaneous determination of macro and trace elements in biological reference materials by microwave induced plasma optical emission spectrometry with slurry sample introduction

A slurry sampling technique (SST) has been utilized for simultaneous multi-element analysis by microwave-induced plasma optical emission spectrometry (MIP-OES). Slurry samples from a spray chamber are fed directly into the microwave cavity-torch assembly (power 300 W) with no desolvation apparatus. The performance of SST-MIP-OES was demonstrated by the determination of macro (Na, K, Ca, Mg, P) and trace (Cd, Cu, Mn, Sr, Zn) elements in three biological certified reference materials using a V-groove, clog-free Babington-type nebulizer. Slurry concentrations up to 1% m/v (particles <20 μm), prepared in 10% HNO 3 (pH 1.2) containing 0.01% of Triton X-100, were used with calibration by the standard additions method. The method offers relatively good precision (R.S.D. ranged from 7 to 11%) with measured concentrations being in satisfactory agreement with certified values for NRCC TORT-1 (Lobster hepatopancreas), NRCC LUTS-1 (Lobster hepatopancreas) and IAEA-153 (Milk powder). The concentrations of Na, K, Ca, Mg, P and Cd, Cu, Mn, Sr, Zn were determined in the range 90–22 000 μg/g and 1–420 μg/g, respectively. The method could be useful as a routine procedure.

Emission characteristics of high-powered microwave induced plasma optical emission spectrometry by using nitrogen–oxygen mixture gas

Emission characteristics of high-powered microwave induced plasma optical emission spectrometry by using nitrogen–oxygen mixture gas

Determination of major and trace elements in biological materials by microwave induced plasma optical emission spectrometry (MIP-OES) following tetramethylammonium hydroxide (TMAH) solubilization

A simple, alternative method to acid digestion is presented for the preparation of biological materials for major and trace elements by microwave induced plasma optical emission spectrometry (MIP-OES). Standard reference materials were solubilized using a methanolic solution of tetramethylammonium hydroxide (TMAH) by the application of ultrasonic agitation. Following dilution with water suspensions were pumped to a V-groove Babington-type nebulizer then into argon plasma. Limits of detection and precision are reported for major (Na, K, Ca, Mg) and trace (Cu, Fe, Sr, Zn) elements. Standard addition procedures were used to minimize possible matrix interferences. The method offers relatively good precision (R.S.D. ranged from 6 to 12%). Measured concentrations are in satisfactory agreement with certified values for the biological reference materials: TORT-1 (Lobster hepatopancreas), IAEA-153 (Milk powder) and NIST 1577 (Bovine liver). The simple procedure could be useful as a routine analysis of biological materials.

Emission characteristics of high-powered microwave induced plasma optical emission spectrometry by using nitrogen–oxygen mixture gas

A high-powered, microwave-induced nitrogen–oxygen plasma (N 2–O 2–MIP) generated by using an Okamoto cavity at atmospheric pressure was investigated when the observation height, the flow rate of carrier gas, and the oxygen content were varied as the experimental parameters. The emission characteristics of the plasma were evaluated with regard to the excitation temperature and the intensity ratio of atomic line to ionic line. The excitation temperature of the N 2–O 2–MIP was in the range of 5100–5700 K when the oxygen content was varied from 0 to 30% at the observation height of 7 mm and the carrier gas flow rate of 0.6 l/min. The intensity ratio of atomic line to ionic line was elevated with an increase in the oxygen content.

Simultaneous determination of hydride forming elements (As, Bi, Ge, Sb, Se) and Hg in biological and environmental reference materials by electrothermal vaporization–microwave induced plasma-optical emission spectrometry with their in situ trapping in a graphite furnace

The approach for the simultaneous determination of five hydride forming elements (As, Bi, Ge, Sb, Se) and Hg by microwave induced plasma optical emission spectrometry (MIP-OES) is described. The combination of hydride generation (HG) and in situ preconcentration of the analytes onto the Pd (for As, Bi, Ge, Sb, Se) or Au (for Hg) pretreated interior wall surfaces of a graphite furnace (GF) has been used as a collection technique. The furnace comprised the electrothermal vaporization (ETV) sample introduction unit of a MIP-OES detection system. Compromise conditions are established. The trapping temperature was 300 °C and the vaporization temperature 2100 °C. Calibration was achieved via the method of standard additions. Absolute limits of detection (3σblank criterion, peak height) were 3, 8, 15, 8, 20 and 10 ng for As, Bi, Ge, Hg, Sb and Se, respectively. System efficiency for the generation and sequestration of the hydrides averaged better than 55%. The HG-ETV-MIP-OES method was successfully applied to the determination of As, Bi, Ge, Hg, Sb and Se in several certified biological and environmental reference materials (hair, tissue, leaves, soil, sediment, fly ash) with a precision of 8–15% RSD at a concentration 50-fold above the LOD, following high pressure decomposition and dissolution of the samples by microwave heating in a mixture of acids. The results obtained by this method were in fair agreement with the reference value.

A geração química de vapor em espectrometria atômica

The historical development of atomic spectrometry techniques based on chemical vapor generation by both batch and flow injection sampling formats is presented. Detection via atomic absorption spectrometry (AAS), microwave induced plasma optical emission spectrometry (MIP-OES), inductively coupled plasma optical emission spectrometry (ICP-OES) , inductively coupled plasma mass spectrometry (ICP-MS) and furnace atomic nonthermal excitation spectrometry (FANES) are considered. Hydride generation is separately considered in contrast to other methods of generation of volatile derivatives. Hg ¾ CVAAS (cold vapor atomic absorption spectrometry) is not considered here. The current state-of-the-art, including extension, advantages and limitations of this approach is discussed.

Applicability of microwave induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of mercury in flue gases

The applicability of microwave-induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of the environmentally hazardous element mercury in flue gases has been studied. Microwave induced plasmas have been sustained using both a TM010 cavity (Beenakker resonator) and a so-called Surfatron. The analytical figures of merit for mercury in argon and helium discharges with both types of low-power micro-wave discharges have been examined. To determine mercury in artificial stack gases non-mixed argon/nitrogen discharges have been tested using a tangential flow torch design which allows to introduce a metal-loaded nitrogen gas flow as external gas and argon as internal gas. The addition of main flue gas components such as water vapour (concentration <6 g/m3), oxygen (<4% v/v) and carbon dioxide (<15% v/v) decrease the mercury line intensities to a considerable extent. Trace gases (CO, HCl, SO2, NO) in concentrations typical to waste incineration processes have been found to have no effect on the mercury and the argon line intensities. The detection limit of mercury in nitrogen is 8 μg/m3 using the TM010 MIP and 10 μg/m3 using the Surfatron. As such low detection limits are below the emission limit values of present-day environmental legislation MIP-OES is useful for on-line monitoring of mercury.

The role of total-reflection X-ray fluorescence in atomic spectroscopy

Total-reflection X-ray fluorescence (TXRF) is a universal and economic method for the simultaneous determination of elements with atomic numbers > 11 down to the lower pg-level. It is a microanalytical tool for the analysis of small sample amounts placed on flat carriers and for contaminations on flat sample surfaces. Analyses of stratified near-surface layers are made possible by varying the incident angle of the primary beam in the region of total-reflection. This non-destructive method is especially suitable for thin layers of a few nanometres, deposited on wafer material although not usable as a microprobe method with a high lateral resolution. Furthermore, depth profiles of biological samples can be recorded by means of microtome sectioning of only a few micrometres, as, for example in the gradient analysis of human organs. In addition to micro- and surface-layer analysis, TXRF is effectively applied to element trace analysis. Homogeneous solutions, for example aqueous solutions, high-purity adds or body fluids, are pipetted onto carriers and, after evaporation, the dry residues are analysed directly down to the pg ml region. Particularly advantageous is the absence of matrix effects, so that an easy calibration can be carried out by adding a single internal standard element. A digestion or separation step preceding the actual determination becomes necessary if a more complex matrix is to be analysed or especially low detection limits have to be reached. A critical evaluation of the recent developments in atomic spectroscopy places TXRF in a leading position. Its outstanding features compete with those of e.g. electrothermal atomic absorption spectrometry (ETAAS), microwave induced plasma optical emission spectroscopy (MIP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) in the field of micro- and trace analysis and with Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) in the surface-layer analysis.

An application of electrothermal evaporation using direct solids sampling coupled with microwave induced plasma optical emission spectroscopy to elemental determinations in biological matrices

Electrothermal evaporation of mg-amounts of powders in a graphite furnace and excitation of the analyte vapour in a 50-W argon MIP according to Beenakker is investigated. Detection limits of Cu, Fe and Mn are in the subμg/g concentration range and relative standard deviations of the measured signals are about 0.1. Calibration can be done by using a standard addition with solution aliquots. The analytical accuracy has been shown to improve, when applying time-resolved and simultaneous measurements of line and background intensities. The technique can be applied to microanalysis of real samples as shown for the direct determination of 10 to 170μg/g manganese in some NBS biological standard reference materials.