Microwave Induced Plasma Spectrometry Research Articles

Simultaneous determination of As, Bi, Sb, Se and Sn by microwave induced plasma spectrometry using a quadruple-mode microflow ultrasonic nebulizer for in situ hydride generation with internal standardization

A method based on continuous-microflow ultrasonic nebulizer quadruple-mode micro-capillary system (μ-USN/QCS-HG) has been used for the efficient generation of As, Bi, Ge, Sb, Se and Sn hydrides directly formed at vibrating quartz plate before detection by microwave induced plasma-optical emission spectrometry (MIP-OES). The ultrasonic nebulizer incorporates four solution capillaries with independent liquid feeding and a common gas inlet. The μ-USN/QCS-HG allowed the hydride generation directly into the cyclonic spray chamber without using any additional device either for solution and gas control or for gas phase separation. The μ-USN/QCS-HG-MIP OES makes feasible the implementation of an on-line internal standard (IS) calibration strategy and Ge was suggested as internal standard. A univariate approach and the simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the μ-USN/QCS-HG-MIP OES observed at a 50μLmin−1 flow rate. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of the standard deviation of the blank (LOD, 3σblank criterion, peak height) were 1, 5, 2, 3 and 2ngmL−1 for As, Bi, Sb, Se and Sn, respectively. The method offers good precision (RSD ranged from 2% to 3%) for micro-sampling analysis. The potential application of this system was demonstrated by successfully analyzing several certified reference environmental samples (CRM DOLT-2, SRM 2710 and SRM 1643e) with satisfactory results. The measured of contents of elements in certified reference materials were in good agreement with the certified values, according to the t-test, for a confidence level of 95%.

Analytical evaluation of a quadruple-mode micro-flow ultrasonic nebulizer for sample introduction in microwave induced plasma spectrometry

The analytical potential of a coupled continuous-micro-flow ultrasonic nebulizer quadruple-mode micro-capillary system (μ-USN-QCS)-argon-helium microwave induced plasma-optical emission spectrometry (MIP-OES) has been evaluated for the purpose of determination of inorganic elements (Ba, Ca, Cd, Cu, Fe, Mg, Mn, Pb, Sr, Zn). The nebulizer incorporates four solution capillaries with independent liquid feeding and a common gas inlet. Four different spray chambers were evaluated and the geometry of the best performing one was optimized. A univariate approach and the simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by a determination of the limits of detection (LODs) and precision (RSDs) with the μ-USN-QCS-MIP-OES observed at a 40μLmin−1 flow rate. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of the standard deviation of the blank (LOD, 3σblank criterion, peak height) were in the range from 2.8ngmL−1 for Cu to 30ngmL−1 for Ba. The method offers relatively good precision (RSD ranged from 6% to 8%) for micro-sampling analysis. The methodology was validated through determination of elements in certified reference materials (NRCC DOLT-2, NRC GBW 07302, NIST 2710 and NIST 1643e) and by the aqueous standard calibration technique. The measured of contents of elements in the reference materials were in satisfactory agreement with the certified values.

Combination of sonication and heating for metal extraction from inorganic fertilizers prior to microwave-induced plasma spectrometry determinations

This work reports a fast and efficient method for metal extraction in inorganic fertilizers by combining heating and sonication using an ultrasonic bath. Microwave-induced plasma optical emission spectrometry (MIP OES) was applied for the determination of Cd, Cu, Cr, Mn, Pb, and Zn in the extracts. Higher efficiency of metal extraction (∼100% for all metals except to Cd) was obtained for the treatment of 150mg of fertilizer with 4mL of 50% (v/v) HCl sonicated for 10min and heating at 85°C. Extractions applying only heating did not provide satisfactory results. The proposed procedure is simple and contributes to reduced production of waste in comparison to the official method.

Development of interface for online coupling of micro-fluidic chip-based photo-micro-reactor/ultrasonic nebulization with microwave induced plasma spectrometry and its application in simultaneous determination of inorganic trace elements in biological materials

A novel analysis online system based on direct coupling of micro-fluidic μchip-based photo-micro-reactor/ultrasonic nebulization (μchip-UV/MR/USN) to microwave induced plasma-optical emission spectrometry (MIP OES) for simultaneous determination of inorganic trace elements in human body fluids and water samples was developed. A univariate approach and the simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. Minimum dead volume, high photo-decomposition and nebulization efficiency and high sample transport efficiency were obtained by using this interface. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times the standard deviation of the blank (LOD, 3σblank criterion, peak height) were 30, 6, 1, 2, 10, 2, 7, 5, 8, 10, 9 and 30μgL−1 for Ba, Ca, Cd, Cu, Fe, Li, Mg, Mn, Pb, Sr, Zn and C, respectively. Repeatability expressed as the relative standard deviations (RSD, n=6) for the target elements ranged from 4% to 8%. Quantitative data obtained for Seronorm urine and water reference materials were in good agreement with the corresponding reference values, proving the potential of this analysis system for multi-element trace analysis via MIP OES. The proposed method had been successfully applied for the determination of inorganic trace elements in urine, mineral water and implant fluid samples. The developed method is quite suitable for routine analysis of inorganic trace elements in biological and environmental fields and precious biological samples such as implant fluids.

Fast ultrasound-assisted treatment of inorganic fertilizers for mercury determination by atomic absorption spectrometry and microwave-induced plasma spectrometry with the aid of the cold-vapor technique

This work reports a fast and efficient ultrasound-assisted extraction of mercury in inorganic fertilizers for its determination by cold vapor atomic absorption spectrometry (CV AAS) and microwave-induced plasma optical emission spectrometry (MIP OES), using a 10% (w/v) SnCl2 as reductant agent. A multi-mode sample introduction system (MSIS) was coupled to the MIP OES equipment to make possible the generation of mercury vapor in the nebulizer chamber. The optimized protocol involved the treatment of 150mg of fertilizer with 4mL of 30% (v/v) HCl inside glass tubes using a conventional ultrasonic bath for 5min. Comparable analytical results were obtained for mercury determined by both CV AAS and MIP OES, with better detection limits for the latter technique. The proposed extraction procedure is simple and versatile, and contributes to minimal generation of waste (low volume of diluted HCl) in comparison to the official method.

Ultrasonic Nebulization, Multimode Sample Introduction System for Simultaneous Determination of Hydride-Forming, Cold Vapor, and Non-Hydride-Forming Elements by Microwave-Induced Plasma Spectrometry

ABSTRACT A novel synergic effect of ultrasonic nebulization (USN) and a multimode sample introduction system (MSIS) when used in combination has been exploited for efficient generation of conventional hydride-forming (As, Bi, Ge, Sb, Se, Sn), Hg vapor, and non-hydride-forming (Ba, Ca, Li, Mg, Sr) elements. The ultrasonic nebulizer supplied a microliter sample to a quartz oscillator, converting liquid into aerosol at the entrance of the MSIS spray chamber. The argon carrier gas is passed to remove and transport the generated vapor species (from the MSIS) and aerosol (from the USN) to a microwave-induced plasma (MIP) for simultaneous element determination by optical emission spectrometry (OES). The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times the standard deviation of the blank (LOD, 3σblank criterion, peak height) were 0.3, 1.5, 1.9, 0.5, 1.7, 0.6, 0.8, 9, 1.6, 1.9, 2.2, and 2.9 ng mL−1 for As, Bi, Ge, Sb, Se, Sn, Hg, Ba, Ca, Li, Mg, and Sr, respectively. The method offers relatively good precision (RSD ranged from 5% to 9%) for liquid analysis and microsampling capability. The methodology was validated through determination of elements in four certified reference materials (NIST 2710, NRC GBW 07302, NRCC DOLT-2, NIST 1643e) and by the aqueous standard calibration technique. Good agreement with certified values was obtained when this approach was applied to the determination of hydride-forming, cold vapor, and other elements in biological and environmental certified reference materials.

Development of a one-step microwave-assisted subcritical water extraction for simultaneous determination of inorganic elements (Ba, Ca, Cu, Fe, Mg, Mn, Na, Pb, Sr, Zn) in reference materials by microwave induced plasma spectrometry

A “green” procedure has been developed for the simultaneous extraction of total inorganic elements (Ba, Ca, Cu, Fe, Mg, Mn, Na, Pb, Sr, Zn) in certified reference materials by using pressurized subcritical water extraction. Samples (0.1g) were subjected to 10min pressurized microwave-assisted extraction with water modified with 1% (v/v) HNO3 at 280°C and 90bar. A Univariate approach and the Simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. The target elements have been simultaneously determined by microwave induced plasma-optical emission spectrometry (MIP-OES). The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of the standard deviation of the blank (LOD, 3σblank criterion, peak height) were in the range of 2.5 to 11ngmL−1. The method offers relatively good precision (RSD ranged from 5 to 7%) for liquid samples. Method validation was performed analyzing two certified reference materials (IAEA-336 Trace and Minor Elements in Lichen and CRM No. 12-2-02 Essential and Toxic Elements in Green Algae P-ACHK) and by the aqueous standard calibration technique. The measured contents of elements in reference materials were in satisfactory agreement with the certified values.

Ultrasonic Nebulization/UV Photolysis Vapor Generation Sample Introduction System for the Determination of Conventional Hydride (As, Bi, Sb, Se, Sn) and Cold Vapor (Hg, Cd) Generation Elements in Reference Materials in the Presence of Acetic Acid by Microwave-Induced Plasma Spectrometry

ABSTRACT A novel synergic effect of ultrasonic nebulization (USN) and ultraviolet (UV) radiation (photolysis) when used in combination has been exploited for efficient generation of conventional hydride elements (As, Bi, Sb, Se, Sn), Hg vapor, and volatile molecular Cd species. Several UV-based systems were studied, the most advantageous design being an ultrasonic nebulizer fitted with a 6 W mercury pen lamp supplying a microliter sample to a quartz oscillator, converting liquid into aerosol at the entrance of the UV spray chamber. Optimal conditions utilized a 40% v/v solution of acetic acid as the generation medium. The volatile species are detected by microwave-induced plasma optical emission spectrometry (MIP-OES). The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times the standard deviation of the blank (LOD, 3σblank criterion, peak height), were 11, 22, 16, 19, 20, 11, and 15 µg L−1 for As, Bi, Sb, Se, Sn, Cd, and Hg, respectively. The method offers relatively good precision (RSD ranged from 3% to 5%) for liquid analysis and microsampling capability. The methodology was validated through determination of elements in two Certified Reference Materials (NRCC DOLT-2, NIST 1643e) and by the aqueous standard calibration technique.

Development of a new hybrid technique for inorganic arsenic speciation analysis by microchip capillary electrophoresis coupled with hydride generation microwave induced plasma spectrometry

A novel hyphenated technique, a microfluidic chip-based capillary electrophoresis (μchip-CE) hydride generation (HG) system was interfaced with a microwave induced plasma optical emission spectrometry (MIP-OES) to provide two inorganic arsenic species separation capabilities. μchip-CE was coupled with a hydride generation reactor/phase separator using a T interface. A MiraMist CE nebulizer is used as the μchip-CE-HG-MIP interface. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip. A volatile species generation technique was employed to convert the analytes from the μchip-CE effluent into their respective volatile species. Inorganic As(III) and As(V) were chosen as the targets to demonstrate the performance of the present technique. Baseline separation of As(III) and As(V) was achieved within 70s by the μchip-CE in a 26mm long channel at 2.8kV using a mixture of borate buffer and CTAB (pH 9.5) as an electrolyte. The relative standard deviation (RSDs) of peak height, base on six determinations of 50ngmL−1 standard of As(III) and As(V), were 5% and 7%, respectively. The detection limits (3σ) based on peak height measurement were 3.9ngmL−1 and 5.4ngmL−1 for As(III) and As(V), respectively.

Interfacing a microchip-based capillary electrophoresis system with a microwave induced plasma spectrometry for copper speciation

Abstract A microchip-based capillary electrophoresis (µCE) system was interfaced with a microwave induced plasma optical emission spectrometry (MIP-OES) to provide copper species separation capabilities. This system uses an extremely low flow demountable direct injection high efficiency nebulizer (D-DIHEN) sited directly at the liquid exit of the chip. A supplementary flow of buffer solution at the channel exit was used to improve nebulization efficiency. A small evaporation chamber has been incorporated into the interface in order to prevent the losses associated with traditional spray chambers, allowing the entire aerosol sample to enter the plasma. Syringe pumps were used to manipulate the flow rate and flow direction of the sample, buffer, and supplementary buffer solution. Sample volumes of 25 nL can be analyzed. With application of an electric field up to 500 V cm−1, species such as Cu(II) and Cu(EDTA)2− were separated in acidic solution within 90 s using a 26 mm long separation channel etched in a glass base. Resolution of the Cu(II) and Cu(EDTA)2− peaks was 1.1 using the chip-based µCE-MIP-OES system.

Analytical Evaluation of an Integrated Ultrasonic Nebulizer-hydride Generator System for Simultaneous Determination of Hydride and Non-hydride Forming Elements by Microwave Induced Plasma Spectrometry

ABSTRACT The commercial ultrasonic nebulizer NOVA-DUO (ultrasonic nebulizer dual capillary system USN/DCS) has been evaluated for the simultaneous determination of classical hydride forming (As, Bi, Ge, Sb, Se, Sn) and conventional non-hydride forming (Ba, Ca, Fe, Li, Mg, Sr) elements by microwave induced plasma-optical emission spectrometry (MIP-OES). Simultaneous mixing and nebulization of the two solutions (acidified sample and reductant) on the piezoelectric transducer, with the possibility of flow rate adjustment, permits a wide variation of sensitivity. The hydrides and aerosols were rapidly transported via a stream of Ar carrier to a MIP for simultaneous multi-element determination by OES. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the USN/DCS observed at 11 µL min−1 flow rate. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of standard deviation of the blank (LOD, 3σblank criterion, peak height) were 1.3, 5.9, 6.6, 1.8, 3.6, 2.6, 41, 8.1, 11, 7.5, 9.2, and 12 ng mL−1 for As, Bi, Ge, Sb, Se Sn, Ba, Ca, Fe, Li, Mg, and Sr, respectively. The method offers relatively good precision (RSD ranged from 9 to 13%) for liquid analysis and microsampling capability. Interference effects by transition metals have been shown to be corrected by the addition of thiourea, as a pre-reducing agent and masking agent. The accuracy of the method was verified by the use of certified reference materials (NRCC DOLT-2, NRC GBW 07302, NIST SRM 2710, NIST SRM 1643e) and by aqueous standard calibration technique. All results obtained for reference materials were in agreement with certified values at 95% confidence level by Student t-test.

Method development for simultaneous multi-element determination of transition (Au, Ag) and noble (Pd, Pt, Rh) metal volatile species by microwave induced plasma spectrometry using a triple-mode microflow ultrasonic nebulizer and in situ chemical vapor generation

The analytical potential of a coupled continuous-microflow ultrasonic nebulizer triple-mode micro capillary system (μ-USN/TCS)-Ar/He mixed gas microwave induced plasma-optical emission spectrometry (MIP-OES) has been evaluated for the purpose of determination of metal volatile species (Au, Ag, Pd, Pt, Rh). An extremely short reaction time between sample, acid and reductant and a rapid separation of the reaction products is obtained by mixing the sample, acid and the sodium borohydride reductant solution at the quartz oscillator, converting liquids into aerosol at the entrance to the spray chamber. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Results showed that the analytical performance of the new system was superior to that of ultrasonic nebulizer dual-mode capillary system. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the μ-USN/TCS observed at a 15 μL min−1 flow rate. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of the standard deviation of the blank (LOD, 3σblank criterion, peak height) were 1.2, 1.5, 1.1, 2.9 and 1.8 ng mL−1 for Au, Ag, Pd, Pt and Rh, respectively. The method offers relatively good precision (RSD ranged from 7 to 8%) for liquid analysis and microsampling capability. The accuracy of the method was verified using certified reference materials (TORT-1, NIST 2710, NIST 1643e, IAEA-336) and by the aqueous standard calibration technique. The measured contents of elements in reference materials were in satisfactory agreement with the certified value (Ag) and added amounts (Au, Pd, Pt, Rh).

Use of microwave induced plasma spectrometry as detector for the determination of O, N and H traces after carrier gas hot extraction

The determination of O, N and H using a microwave induced plasma coupled to carrier gas hot extraction was exploratory investigated. The signal intensities versus time of blanks and calibration materials were recorded. To check for interferences the signal intensities versus wavelength were recorded at the times just before increase and at the maximum of the time dependent analytical signal. O, N and H were investigated at their prominent wavelengths of 777 nm, 174 nm and 486 nm, respectively. Calibration was performed for O, N and H in the ranges of 0–27 μg, 35–1000 μg and 3–43 μg respectively. For concentration values in the middle of the linear part of the investigated calibration interval, a relative precision of 5% at 13 μg, 2% at 74 μg and 0.6% at 23 μg for O, N and H respectively was found. The maximum matrix load to the plasma used was found to be 150 μg min−1. From the signal to noise ratio and the sensitivity obtained, instrumental limits of detection (3s) of 0.01 μg for O, 1 μg for N and 0.1 μg for H were found. Assuming a typical sample mass of 1 g this corresponds to relative LODs of 0.01 μg g−1, 1 μg g−1 and 0.1 μg g−1 for O, N and H respectively.

Liquid cooling of a torch for microwave induced plasma spectrometry

A simple torch design for use with a microwave induced plasma (MIP) is described that can be internally cooled by synthetic or hydrocarbon based fluids. The MIP is generated within a liquid coolant-cooled concentric quartz discharge torch, energized within a novel microwave plasma cavity. Erosion of the discharge tube by the plasma, assessed by measurement of the emission intensity of ablated silicon, is essentially eliminated. The emission spectra of the liquid-cooled plasmas are compared to those sustained in uncooled discharge tubes.

Use of the Hildebrand grid nebulizer as a sample introduction system for microwave-induced plasma spectrometry

The Hildebrand grid nebulizer (GN) has been successfully interfaced to a novel highly efficient microwave plasma cavity at atmospheric pressure for the introduction of urine. High matrix solutions from a spray chamber are fed directly into the cavity with no desolvation apparatus. The GN performed well when the signal-to-background ratio was optimized for solution by adjusting the nebulizer gas glow, solution uptake rate, gas pressure, impact bead position and forward plasma power. Errors, due to the suppression of the Cu, Fe and Zn signal intensities by matrix elements in urine, were eliminated using calibration by standard additions coupled with background measurements. Results are presented for the analysis of Human Reference Urine, Seronorm. Within the precision of measurement (7–11% for replicate determinations) analytical results for the test elements Cu, Fe and Zn were in agreement with recommended values. The nebulizer exhibited no clogging problems.

An improved Beenakker-type cavity for microwave induced plasma spectrometry

An improved Beenakker-type cavity for microwave induced plasma spectrometry

Low-pressure, microwave-induced plasma spectrometry method for the determination of subnanogram quantities of mercury: Application to mercury-carboxypeptidase analysis

A simple, sensitive, and rapid method for the determination of subnanogram quantities of mercury has been devised using a tantalum-filament vaporization system and low-pressure, microwave-induced emission spectrometry. This method is applied to the analysis of mercury-substituted carboxypeptidase with a sample volume of 5 μl and an analysis time of 3 min. The coefficient of variation for 2 × 10 −10 g of mercury in mercury-carboxypeptidase is 6.0%, and the detection limit is 3 × 10 −12 g.