Microwave-induced Plasma Atomic Emission Detection Research Articles

Determination of bis-carboxyethyl germanium sesquioxide by gas chromatography with microwave-induced plasma-atomic emission detection after derivatization with alkyl chloroformates.

Organic germanium compounds, especially Ge-132, more corrctly denoted as bis-beta-carboxyethyl germanium sesquioxide ([Ge(=O)CH2CH2CO2H]2O), are of continued interest as they are said to promote health and display anticancer activity. Although these beneficial effects have never been substantiated by comprehensive clinical studies, this drug can still be obtained through various sources and is usually marketed as a nutritional supplementation rather than an anticancer medication. As the quality standards under which this drug is produced are unknown, the need for an effective quality control of these products arises. To date, Ge-132 is considered generally as a safe compound for application in contrast to inorganic germanium which demonstrates severe renal toxicity. In this paper, a new approach to the determination of Ge-132, based on derivatization by ethyl chloroformate reagent (ECF), in the presence of ethanol and pyridine in the mixture, and subsequent analysis by gas chromatography coupled with microwave-induced plasma-atomic emission detection (GC-MIP-AED), is reported. Reaction conditions of the derivatization procedure were optimized with particular respect to the reagent (ECF) and catalyst (pyridine) concentrations. The proposed method is capable of distinguishing Ge-132 from inorganic germanium. The derivatization procedure was also tested with the use of methyl chloroformate (MCF) as alternative reagent, providing interesting additional information about the nature of the final product and the proposed reaction scheme. Among the two types of chloroformates, i.e., MCF and ECF, the latter proved to be more suitable for the proposed method, providing a calibration curve of superior sensitivity and linearity compared with the one obtained with MCF. The method was applied successfully in three real samples, two food supplements, and one commercially available fertilizer. The analysis of the Ge-132 derivative showed good linearity in the concentration of 1-250 mg L(-1) (r (2) = 0.9986) and a satisfactory precision (RSD = 6.8%), which qualifies the proposed method for the speciation analysis of Ge in various matrices.

Solid-phase microextraction followed by gas chromatography for the speciation of organotin compounds in honey and wine samples: A comparison of atomic emission and mass spectrometry detectors

An environmentally friendly method for the determination of seven organotin compounds in honey and wine samples, using headspace solid-phase microextraction (HS-SPME) and gas chromatography (GC), was developed. The analytes were derivatized in situ with sodium tetraethylborate, and the derivatization and preconcentration steps were optimized. A 100μm polydimethylsiloxane fiber was the most suitable for preconcentrating the derivatized analytes from the headspace of an aqueous solution containing the sample. When microwave-induced plasma atomic emission (MIP-AED) and mass spectrometry (MS) detection were compared, higher sensitivity was attained for all compounds with MS, although MIP-AED showed more specific chromatograms. Using MS, detection limits ranged roughly from 0.3 to 4.3pg(Sn)/g, depending on the compound for honey samples, and from 0.1 to 2pg(Sn)/mL for wine samples. The optimized method was successfully applied to different samples, and the compounds studied were detected in some wines at 0.05–5ng(Sn)/mL levels.

Determination of dimethylselenide and dimethyldiselenide in milk and milk by-products by solid-phase microextraction and gas chromatography with atomic emission detection

A method based on solid-phase microextraction (SPME) followed by gas chromatography with microwave-induced plasma atomic emission detection for determining dimethylselenide (DMSe) and dimethyldiselenide (DMDSe) in milk and milk by-products is proposed. Parameters affecting the SPME, such as sample volume or mass, ionic strength, adsorption and desorption times and temperatures were optimized in the headspace mode. The matrix effect was evaluated for the different samples studied, concluding that standard additions calibration was required for quantification purposes. The detection limits ranged from 70 to 110 pg mL(-1) for DMSe and from 80 to 400 pg mL(-1) for DMDSe, depending on the sample under analysis. None of the twenty-three samples analyzed contained the studied compounds at concentrations above the corresponding detection limits.

Speciation of organotin compounds in urine by GC–MIP-AED and GC–MS after ethylation and liquid–liquid extraction

A method for the determination of organotin compounds in urine samples based on liquid–liquid extraction (LLE) in hexane and gas chromatographic separation was developed and optimized. Seven organotin species, namely monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), tetrabutyltin (TeBT), monophenyltin (MPhT), diphenyltin (DPhT) and triphenyltin (TPhT), were in situ derivatized by sodium tetraethylborate (NaBEt 4) to form ethylated less polar derivatives directly in the urine matrix. The critical parameters which have a significant effect on the yield of the successive liquid–liquid extraction procedure were examined, by using standard solutions of tetrabutyltin in hexane. The method was optimized for use in direct analysis of undiluted human urine samples and ways to overcome practical problems such as foam formation during extraction, due to various constituents of urine are discussed. After thorough optimization of the extraction procedure, all examined species could be determined after 3 min of simultaneous derivatization and extraction at room temperature and 5 min phase separation by centrifugation. Gas chromatography with a microwave-induced plasma atomic emission detector (MIP-AED) as element specific detector was employed for quantitative measurements, while a quadrupole mass spectrometric detector (MS) was used as molecular specific detector. The detection limits were between 0.42 and 0.67 μg L −1 (as Sn) for the quantitative LLE–GC–MIP-AED method and the precision between 4.2% and 11.7%, respectively.

Determination of butyl- and phenyltin compounds in human urine by HS-SPME after derivatization with tetraethylborate and subsequent determination by capillary GC with microwave-induced plasma atomic emission and mass spectrometric detection

A headspace solid-phase micro-extraction (HS-SPME) method was developed and optimized for gas chromatographic separation and determination of commonly found organotin compounds in human urine after potential exposure. Butyl- and phenyltin compounds were in situ derivatized to ethylated derivatives by sodium tetraethylborate (NaBEt 4) directly in the urine matrix. The relevant parameters affecting the yield of the SPME procedure were examined using tetrabutyltin as internal standard. The method was optimized for direct use in the analysis of undiluted human urine samples and mono-, di- and tri-substituted butyl- and phenyltin compounds could be determined after a 15-min headspace extraction time at room temperature. The selectivity of the microwave-induced plasma atomic emission detector (MIP-AED) as an element specific detector in combination with the relatively selective sample preparation technique of HS-SPME allowed the interference-free detection of the organotin compounds in all cases. A quadrupole mass spectrometer was used in parallel experiments as a detector for the confirmation of the identity molecular structure of the eluted compounds. The performance characteristics of the developed method are given for the determination of mixtures of these compounds. Finally the proposed method was applied to the analysis of several human urine samples.

Solid-phase microextraction combined with gas chromatography and atomic emission detection for the determination of cyclopentadienylmanganese tricarbonyl and (methylcyclopentadienyl)manganese tricarbonyl in soils and seawaters

A method based on solid-phase microextraction with capillary gas chromatography and microwave-induced plasma atomic emission detection (SPME-GC-MIP-AED) for the determination of cyclopentadienylmanganese tricarbonyl (CMT) and its methyl derivative, (methylcyclopentadienyl)manganese tricarbonyl (MMT) in seawaters and soils was optimized and evaluated. The solvent-free preconcentration step was carried out in the headspace (HS) mode. Element-specific detection and quantification was carried out by monitoring the manganese (259 nm) emission line. A matrix effect was found for the soil samples investigated, so that standard additions were required for their quantification. On the other hand seawaters were analyzed by applying direct calibration against aqueous standards. Detection limits of 13 and 15 pg Mn L −1 were obtained for CMT and MMT, respectively, in seawaters, and 0.62 and 0.65 pg Mn g −1, respectively, for the soil samples. The method permitted recoveries of 76–113%, depending on the compound and the sample analyzed, confirming the reliability of the procedure and its suitability for routine monitoring purposes.

Solid-phase microextraction and gas chromatography with atomic emission detection for multiresidue determination of pesticides in honey

A method based on solid-phase microextraction (SPME) followed by gas chromatography with microwave-induced plasma atomic emission detection for determining 16 pesticides of different chemical families (organochlorines, organophosphorus compounds and pyrethrins) in honey is proposed. Parameters affecting the sample enrichment step, such as sample mass, ionic strength, absorption and desorption times and temperatures, were carefully optimized in the direct immersion mode. Element-specific detection and quantification was carried out by monitoring the chlorine (479 nm), bromine (478 nm) and sulphur (181 nm) emission lines, which provided nearly specific chromatograms. The matrix effect was evaluated for samples of different floral origin, it being concluded that standard addition calibration was required for quantification purposes. The detection limits ranged from 0.02 to 10 ng g −1, depending on the compound and the honey sample under analysis. The method is reliable and can be considered useful for routine monitoring. None of the honey samples analyzed contained the studied compounds at concentrations above the corresponding detection limits.

Solid-phase microextraction-capillary gas chromatography combined with microwave-induced plasma atomic-emission spectrometry for selenite determination.

The use of solid-phase microextraction (SPME) with gas chromatography coupled to microwave-induced plasma atomic-emission detection (GC-MIP-AED) is described for selenite [Se(IV)] speciation. Aqueous standards were derivatised with sodium tetraethyl- or tetrapropylborate and extracted by SPME. Headspace extraction of the ethyl and propyl derivatives was studied. Relevant experimental conditions were optimised, including conditions for derivatisation and extraction and those of gas chromatographic analysis. The limits of detection achieved for headspace sampling of derivatised Se(IV) were in the low ng mL(-1) range for both ethylation and propylation. When the method was applied to analysis of selenite in selenised yeast reference material results were in good agreement with the indicated values.

Two-dimensional on-line detection of brominated and iodinated volatile organic compounds by ECD and ICP-MS after GC separation.

Inductively coupled plasma-mass spectrometry (ICP-MS) was coupled to a gas chromatographic (GC) system with electron capture detector (ECD), which enables relatively easy characterization and quantification of brominated and iodinated (halogenated) volatile organic compounds (HVOCs) in aquatic and air samples. The GC-ECD system is connected in series with an ICP-MS by a directly heated transfer line and an outlet port-hole for elimination of the ECD make-up gas during ignition of the plasma. The hyphenated GC-ECD/ICP-MS system provides high selectivity and sensitivity for monitoring individual HVOCs under fast chromatographic conditions. The ECD is most sensitive for the detection of chlorinated and brominated but the ICP-MS for iodinated compounds. The greatest advantage of the use of an ICP-MS is its element-specific detection, which allows clear identification of compounds in most cases. The absolute detection limits for ICP-MS are 0.5 pg for iodinated, 10 pg for brominated, and 50 pg for chlorinated HVOCs with the additional advantage that calibration is almost independent on different compounds of the same halogen. In contrast to that detection limits for ECD vary for the different halogenated compounds and lie in the range of 0.03-11 pg. The two-dimensional GC-ECD/ICP-MS instrumentation is compared with electron impact mass spectrometry (EI-MS) and microwave induced plasma atomic emission detection (MIP-AED). Even if EI-MS has additional power in identifying unknown peaks by its scan mode, the detection limits are much higher compared with GC-ECD/ICP-MS, whereas the selective ion monitoring mode (SIM) reaches similar detection limits. The MIP-AED detection limits are at the same level as EI-MS in the scan mode.

Moderate volatility analyte transport behavior with membrane desolvation reversed-phase liquid chromatography-helium microwave-induced plasma atomic emission spectroscopy

The transport behavior of moderately volatile analyte in a membrane desolvation system is examined. With the goal of atomic emission determination of liquid chromatographic analytes, a tubular polytetrafluoroethylene membrane desolvator interface was used to enhance the performance of a 120 W helium microwave-induced plasma atomic emission detector. To monitor organo-chlorine compounds, Cl emission was observed at 479.5 nm. Membrane desolvator conditions such as temperature, solvent composition and counter current gas flow were optimized. Converse to required conditions for non-volatile inorganic compounds, semi-volatile organic compound transport was maximized at lower membrane desolvator temperatures. Analyte transport was enhanced by modifying the solvent with dilute H 2SO 4. Low vapor pressure H 2SO 4 minimized analyte diffusion across the membrane and helped linearize the calibration plot. The detection limit of 2,6-dichlorobenzamide in pure methanol using ultrasonic nebulization and membrane desolvation with microwave-induced plasma detection was 2 ppm. Chromatographic separation and detection was demonstrated with 2,6-dichlorobenzamide and 4-chlorobenzamide.

On-line packed column supercritical fluid chromatography–microwave-induced plasma atomic emission

Interfacing and evaluation of packed column supercritical fluid chromatography (SFC)–microwave-induced plasma atomic emission detection (AED) is described. Via a flow splitter and an integral restrictor, efficient transfer of solutes from column to detector without band broadening is obtained. Variation of CO 2 flow-rate during pressure gradients has little influence on both AED signal and baseline drift while it provides similar sensitivity as in capillary SFC. Continuous introduction of CO 2 in the plasma reduces the available range of emission domains; nevertheless the region of detection which is free of CO 2 interferences allows selective detection of Cl and Br as reported in this paper.

Easy hyphenation of supercritical-fluid chromatography to atomic-emission detection for analysis of lubricant additives

This manuscript describes the hyphenation of packed-column supercritical-fluid chromatography (SFC) to a microwave-induced plasma atomic-emission detector (MIP-AED), by flow splitting via a restrictor to enable multi-detection including UV or flame-ionization detection. A discussion of requirements for coupling of SFC to plasma detection, and evaluation of conditions critical to detector response for several elements, e.g. chlorine, nitrogen, and phosphorus, is presented. The last part of the paper is devoted to AED analytical performance for detection of P, Cl, N, Si, Fe, and Zn and to a description of the first report of the use of SFC-MIP for the analysis of car lubricant additives containing nitrogen, phosphorus, and zinc.

Speciation of organotin in sediments by multicapillary gas chromatography with atomic emission detection after microwave-assisted leaching and solvent extraction-derivatization

Microwave-assisted leaching of organotin compounds from sediment samples followed by the simultaneous extraction-derivatization of the extracted species was revisited with the goal to compare the existing procedures, improve their recoveries and extend them to phenyltin compounds. The stability of butyl- and phenyltin compounds under microwave field, real recoveries of the whole analytical procedure, effect of the extraction solvent, and the necessity for an internal standard were evaluated using two candidate reference sediments. The combination of the optimized sample preparation procedure with multicapillary chromatography resulted in a rapid (2 min leaching + 5 min extraction-derivatization + 3 min chromatographic separation) and efficient analytical procedure for speciation analysis of organotin compounds in sediment samples. The detection limit achieved with a microwave-induced plasma atomic emission detector was 2 ng g–1.

Enhanced sensitivity and selectivity of a gas chromatography-microwave-induced plasma atomic emission system (GC-MIP) at the 685.6-nm fluorine emission line

As part of the studies for the characterization of a gas chromatography with microwave-induced plasma atomic emission detection (GC-MIP) prototype, its behavior at the 685.6-nm fluorine emission line was studied with isooctane solutions of n-perfluoroheptane and benzene. This test mixture was chromatographed under varied conditions of the plasma support helium flow rate and microwave input power. A relatively high value of (3.9±0.3)×10was found for the fluorine to carbon selectivity, with detection limits for fluorine as low as 1.3±0.2 pg(F)⋅s−1. These levels for the selectivity and for the detection limit compare favorably with previous reports found in the literature for other GC-MIP systems. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 23–27, 1999

Application of chemometric techniques to the optimization of the solid-phase extraction of 27 pesticides before GC-MIP-AES analysis

Determination of heteroelement organic compounds at environmental levels requires highly efficient chromatographic separations and selective and sensitive detection. For this purpose, a capillary gas chromatographic–helium atmospheric pressure microwave-induced plasma atomic emission detection method was developed for the simultaneous determination of 18 organochlorine and nine organophosphorus pesticides in water samples. Monitoring the emission lines for elements such as chlorine, phosphorus and sulfur ensures nearly specific chromatograms for these elements, increasing the selectivity markedly. On the other hand, to allow quantitative recoveries of these pesticides from aqueous samples, the solid-phase extraction (SPE) of the target compounds was optimised using two sequential experimental designs. A 23 factorial design was initially performed to study the relative importance of three SPE main variables: sample volume, volume and percentage of dichloromethane in the elution solvent. Following this factorial design, a central composite design was used to demonstrate that the SPE conditions can be optimised to obtain the best overall recoveries of the 27 compounds studied. The extraction and determination techniques were applied to the determination of pesticides in waste water samples.

Enhanced sensitivity and selectivity of a gas chromatography–microwave‐induced plasma atomic emission system (GC‐MIP) at the 685.6‐nm fluorine emission line

As part of the studies for the characterization of a gas chromatography with microwave-induced plasma atomic emission detection (GC-MIP) prototype, its behavior at the 685.6-nm fluorine emission line was studied with isooctane solutions of n-perfluoroheptane and benzene. This test mixture was chromatographed under varied conditions of the plasma support helium flow rate and microwave input power. A relatively high value of (3.9±0.3)×10was found for the fluorine to carbon selectivity, with detection limits for fluorine as low as 1.3±0.2 pg(F)⋅s−1. These levels for the selectivity and for the detection limit compare favorably with previous reports found in the literature for other GC-MIP systems. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 23–27, 1999

Municipal solid waste incineration bottom ash: Physicochemical characterization of organic matter

The aim of this work was to characterize the initial organic content of a selected municipal solid waste incineration (MSWI) bottom ash. This was realized by elemental carbon analysis using pyroanalysis of untreated samples. In addition, MSWI bottom ash extracts obtained by supercritical fluid extraction (SFE) or hot solvent extraction (Soxtec), were analyzed using gas chromatography (GC) coupled to either a mass spectrometry detector (MSD) or a microwave induced plasma atomic emission detector (MIP-AED). The results showed that the labile organic carbon fraction of the MSWI bottom ash is non-negligible (about 1400 µg/g) and that it includes mainly carboxylic acids, n-alkanes, steroids and phthalates. The latter two families, as well as polyaromatic hydrocarbons that were also determined, would appear to confer a toxic character on MSWI bottom ash. In light of the well-designing and operating of the incineration facility, the results seem to be representative of a widespread quality of bottom ash.

Platinum-selective capillary gas chromatographic determination with microwave-induced plasma atomic emission detection

The volatile platinum(II) complex of N, N-ethylenebis(5,5-dimethyl-4-oxohexane-2-imine) (H 2APM 2en) eluted quantitatively from a GC capillary column and has been used to establish operating parameters and to gain figures of merit for atomic emission detection of platinum with microwave-induced plasma atomic emission. Two recipes have been developed for platinum; at 266 nm for simultaneous monitoring the carbon emission at 248 nm, and at 300 nm for simultaneous determinations with copper and nickel at 325 nm and 301 nm, respectively. Optimum platinum emission was observed using oxygen and hydrogen as reagent gases and high flow-rate of helium as make-up gas. Linear calibration ranges at 266 nm and 300 nm were assessed and, platinum emission being approximately five-times more sensitive at 300 nm than at 266 nm. The detection limit at 300 nm was observed as 65 pg/s. Selectivity of platinum emission over carbon at both wavelengths 266 nm and 300 nm is in the range of 10 5–10 6.

Compound retention dependence of the response in a gas chromatography–atomic emission detection system

The relationship between the response of a laboratory-made GC–microwave-induced helium plasma atomic emission detection (MIP) system prototype and compound nature was studied by monitoring the carbon 247.9 nm atomic emission line. The test samples for this study were solutions of alkanes, arenes and haloarenes prepared at two concentration levels; varied plasma generation conditions (microwave input powers and helium support plasma gas flows) were evaluated. The statistical examination of the data pointed to a dependence between MIP signal and compound retention – less retained compounds tend to show reduced MIP signals.

Interface for time-resolved introduction of gaseous analytes for atomic spectrometry by purge-and-trap multicapillary gas chromatography (PTMGC)

A semi-automated compact interface that enables time-resolved introduction of gaseous analytes from aqueous solutions into an atomic spectrometer without the need for a full-size GC-oven is described. The interface is based on purging the gaseous analytes with an inert gas, drying the gas stream using a 30-cm tubular Nafion membrane and trapping the compounds in a thick film-coated capillary tube followed by their isothermal separation on a 1-m multicapillary GC column. Developments regarding each of the steps of the analytical procedure and effects of operational variables (sample volume, purge flow, trap temperature, speed of injection, GC separation conditions) are discussed using the speciation analysis of a mixture of tetraalkyllead compounds as an example. Recoveries are quantitative up to a sample volume of 50 ml. Figures of merit for the interface coupled to a microwave-induced plasma atomic emission detector are given. The interface allows the full speciation analysis (including sample preparation) to be carried out within less than 5 min with detection limits down to 5 pg l −1.