Preconcentration and atomic spectrometric determination of rare earth elements (REEs) in natural water samples by inductively coupled plasma atomic emission spectrometry

The usage of a variety of sorbents has been shown as promising matrix removal/preconcentration strategies for the determination of rare earth elements (REEs) in various natural water samples by inductively coupled plasma atomic emission spectrometry (ICP-AES). The sorption efficiency of various zeolites (clinoptilolite, mordenite, zeolite Y, zeolite Beta), ion-exchangers (Amberlite CG-120, Amberlite IR-120, Rexyn 101, Dowex 50W X18) and chelating resins (Muromac, Chelex 100, Amberlite IRC-718) towards REEs was investigated in terms of solution pH, shaking time and sorbent amount. The results have shown that most of the materials can take up REEs at a wide pH range. The experiments were continued with clinoptilolite, zeolite Y and Chelex 100 and it was demonstrated that all three materials displayed very fast kinetics for REE sorption (higher than 96% in 1 min). Desorption from the sorbents was realized with 2.0 M HNO₃ for clinoptilolite and 0.1 M HNO₃ for zeolite Y and Chelex 100. Only the lower concentration range (0.01-2.0 mg l⁻¹) of matrix-matched standards were used in quantitation although the calibration graphs were linear at least up to 10.0 mg l⁻¹ for all REEs studied. The limit of detection (3 s) without preconcentration was 0.1, 1.0, and 0.2 μg l⁻¹ for Eu, La, and Yb, respectively. The validity of the method with the selected sorbents was checked through spike recovery experiments.     

Determination of total dissolved phosphorus in water samples by axial inductively coupled plasma atomic emission spectrometry

A procedure was developed to determine total dissolved phosphorus in groundwater-like samples using axial ICP-AES. Severe and peculiar matrix effects (strongly positive at lower and leveling off at higher matrix concentrations) in the presence of Na and Ca were observed. To reduce these matrix effects, a double approach was utilized consisting of a so-called minimum matrix in combination with an internal standard (Ga in this case). The ‘minimum matrix’ (small amounts of K, Mg and Na) was only added to the standard solution(s) used for the calibration. The detection limit for the whole procedure was 12 μg/L using the P213 nm line. Residual matrix effects were less than 3% (P213 nm line). Received: 21 February 1997 / Revised: 5 June 1997 / Accepted: 6 June 1997     

Determination of total dissolved phosphorus in water samples by axial inductively coupled plasma atomic emission spectrometry

A procedure was developed to determine total dissolved phosphorus in groundwater-like samples using axial ICP-AES. Severe and peculiar matrix effects (strongly positive at lower and leveling off at higher matrix concentrations) in the presence of Na and Ca were observed. To reduce these matrix effects, a double approach was utilized consisting of a so-called minimum matrix in combination with an internal standard (Ga in this case). The ‘minimum matrix’ (small amounts of K, Mg and Na) was only added to the standard solution(s) used for the calibration. The detection limit for the whole procedure was 12 μg/L using the P213 nm line. Residual matrix effects were less than 3% (P213 nm line). Received: 21 February 1997 / Revised: 5 June 1997 / Accepted: 6 June 1997     

Sulfur analysis of conifer needles by inductively coupled plasma atomic emission spectrometry

Zusammenfassung Nadelproben werden in einem Druckaufschlu\gefÄ\ mit SalpetersÄure aufgeschlossen und die erhaltenen Lösungen mittels ICP-AES auf Schwefel analysiert. Die Messung erfolgt bei 182,04 nm in einem mit Stickstoff gespülten Spektrometer. Die Ergebnisse korrelieren gut mit unabhÄngigen Bestimmungen durch Wickbold-Aufschlu\ und Ionen-Chromatographie. Das Verfahren hat den Vorteil, da\ keine Verluste des Analysenelements auftreten und da\ die Aufschlu\lösung auch für die simultane Bestimmung von Spurenmetallen mit der ICP-AES geeignet ist.     

Bulk analysis by IR laser ablation inductively coupled plasma atomic emission spectrometry

Two laser ablation systems dedicated to bulk analysis were evaluated for steel and PVC samples, using inductively coupled plasma atomic emission spectrometry detection. These systems were characterized by the use of a Nd:YAG laser operating at 1064 nm, the absence of observation device and a large laser spot size. The 1064 nm wavelength was selected to avoid the use of frequency-multiplying optics, and to be less critical to the sampling position. Calibration graphs and limits of detection are given for both types of materials. LODs were in the range 3-120 microg/g for steel, and in the range 0.07-15 microg/g for PVC. In the case of steel samples, similar calibration graph slopes were obtained between polished and unpolished samples.     

Bulk analysis by IR laser ablation inductively coupled plasma atomic emission spectrometry

Two laser ablation systems dedicated to bulk analysis were evaluated for steel and PVC samples, using inductively coupled plasma atomic emission spectrometry detection. These systems were characterized by the use of a Nd:YAG laser operating at 1064 nm, the absence of observation device and a large laser spot size. The 1064 nm wavelength was selected to avoid the use of frequency-multiplying optics, and to be less critical to the sampling position. Calibration graphs and limits of detection are given for both types of materials. LODs were in the range 3–120 μg/g for steel, and in the range 0.07–15 μg/g for PVC. In the case of steel samples, similar calibration graph slopes were obtained between polished and unpolished samples.     

On-line preconcentration and determination of mercury in biological samples by flow injection vapour generation inductively coupled plasma atomic emission spectrometry

An FI-ICP-AES method for the determination of trace levels of mercury in biological samples has been described, which is based on the extraction of the mercury complex with 1,5-bis (di-2-pyridyl)methylene thiocarbonohydrazide (DPTH) on-line into isobuthyl-methyl ketone (IBMK). The organic phase (containing the complex) has been mixed on-line with SnCl₂ in N,N-dimethylformamide. Thus, mercury vapour can be generated directly from the organic phase and separated in a gas-liquid separation device. The detection limit for mercury is 4 ng/ml and the calibration curve is linear at least from 10 to 2500 ng/ml. The relative standard deviation for 10 replicate measurements is ±1% for 100 ng/ml of Hg(II). Results from the analysis of some certified biological reference materials are given.     

Comparison between X-ray fluorescence and inductively coupled plasma atomic emission spectrometry in the analysis of sediment samples

Two multielemental analytical techniques, X-ray fluorescence analysis (XRF) and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used for the analysis of the elemental composition of sediment samples from a marsh and standard reference materials. The sediment samples were pretreated with different methods which are widely used in practice. A comparison was made not only between the concentrations obtained by the different methods, but also between the statistical conclusions derived from the processing of the experimental results. Good agreement was found for some elements, e.g. Mn, Zn and Sr, while the concentrations and the statistical conclusions were shown to depend on the analytical method used in the case of other elements, e.g. Fe and Zr.     

Preconcentration of platinum group metals on modified silicagel and their determination by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry in airborne particulates

Modified silicagel (C18) was studied for separation and preconcentration of platinum group metals (Ru, Rh, Pd, Os, Ir and Pt) as ion associates of their chlorocomplexes with cation of onium salt N(1-carbaethoxypentadecyl)-trimethyl ammonium bromide. Sample containing HCl and the onium salt was pumped through the column. After elution with ethanol the eluate was evaporated in the presence of HCl. Resulting aqueous solutions were analysed with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Recovery values of 1-20 mug Pt and Pd from 50 ml of synthetic pure solution were 100+/-3 and 100+/-1%, respectively, however, they diminished with increasing sample volume and in the presence of the real sample matrix or nitrate ions. Samples of engine soot (NIES No. 8), decomposed by low pressure oxygen high-frequency plasma, and airborne particulates from dust filters of meteorological stations, leached with HNO(3) and H(2)O(2), were analysed. A reasonable agreement was found between ICP-MS and ICP-AES results for airborne dust samples and the values comparable with those in literature were determined in NIES No. 8.     

Determination of trace amounts of molybdenum in water samples by inductively coupled plasma atomic emission spectrometry after cobalt-dithiocarbamate coprecipitation

Summary A method for the determination of trace amounts of molybdenum in fresh water and seawater samples by sequential ICP-AES with microsampling technique after cobalt-dithiocarbamate coprecipitation was developed. The precipitate was dissolved in 100 l of diluted nitric acid (1:2), and the solution obtained was then introduced into an ICP via a concentric nebulizer. By use of 1.7 ml sample, a preconcentration factor of 17 was achieved. Different factors including integration time, sample volume, pumping rate as well as coprecipitation conditions such as pH of the solution, amounts of reagents, standing time for the precipitate and matrix effects were examined and optimized in detail. Under selected conditions the detection limit of the method for Mo is 0.52 g/l using 1.7 ml sample. The procedure was applied to the analysis of water samples (artificial water and open ocean seawater reference material) with quantitative recovery. The analytical results were in good agreement with the certified value. The method is sensitive, simple, accurate and effective, also in the presence of interfering salts and can be applied to small sample volumes.On leave from the Department of Chemistry, Wuhan University, Wuhan, 430072 China     

Direct analysis of fly ash materials by inductively coupled plasma atomic emission spectrometry using slurry nebulization

Fly ash samples of cement works were analysed using slurry nebulization inductively coupled plasma atomic emission spectrometric (ICP-AES). Because of the influence of the experimental factors on the signal intensity, the optimal conditions of the analysis circumstances were determined. Control analyses (wet digestion followed by ICP-AES, and XRF of dry powders (pressed pellets)) were also carried out to compare the results. Based on the result, it was concluded that the slurry nebulization method using slurry standard of same type reference material for calibration can be applied for rapid but less precise (RSD 5–10%) determination of the elements in fly ash.     

Speciation of mercury by continuous flow liquid-liquid extraction and inductively coupled plasma atomic emission spectrometry detection

An accurate, precise, sensitive and automated non-chromatographic method for methylmercury speciation based on a selective continuous liquid-liquid extraction of methylmercury, into xylene, as bromide and cold mercury vapour generation directly from the organic phase and final ICP-AES mercury detection is proposed. Both separation steps, liquid-liquid and gas-liquid are accomplished in a continuous mode and on line with ICP-AES as detector. The detection limit attained for methylmercury was 4ng·ml^–1 (as mercury). The precision of the determination at a concentration level around 20 times the detection limit was +-5%. The proposed methodology has been applied successfully to the speciation of methylmercury and inorganic mercury in spiked sea water and spiked urine samples.     

A helium inductively coupled plasma for atomic emission spectrometry

An annular helium inductively coupled plasma (He ICP) was generated at atmospheric pressure. No external cooling was used to stabilize the plasma. Aqueous solution was injected into the plasma without any difficulty. Preliminary results revealed that the annular He ICP was capable of exciting elements such as Cl and Br which possess high excitation energies. Atomic emission detection limits for Cl and Br were improved by factors of 63 and 34, respectively, as compared to the results obtained from the argon inductively coupled plasma. The excitation temperature of the annular He ICP (4180 K) was less than that of an Ar ICP (5570 K).     

Quality of calibration in inductively coupled plasma atomic emission spectrometry

Calibration is a crucial step during the whole analytical process. A procedure is suggested to assess the quality of linear regression used for the calibration graph, based on the use of confidence limits for the concentration, as the regression coefficient is not appropriate for this purpose. This procedure has been applied to inductively coupled plasma atomic emission spectrometry. It indicates that the use of only three standards should be discouraged because of unacceptably high confidence limits for the concentration. Moreover, use of weighted regression is more adequate in performing the least squares method and provides more constant confidence limits over the concentration range used to construct the calibration graph. This procedure could be easily added to any commercially available ICP system software.     

Modified Babington nebulizer for inductively coupled plasma atomic emission spectrometry.

A PTFE Babingtonnebulizer equipped with a hood was investigated for inductively coupled plasma atomicemission spectrometry in conjunction with a PTFE cyclone chamber, in order to nebulize various sample solutions containing high salts, hydrofluoric acid and/or suspended solid. A hood of 3 mmphi (nozzle side) - 5 mmphi (outlet side) and 6 mm in length gave a comparable or higher sensitivity compared to a system with a commercially available concentric nebulizer and a glass cyclone chamber. Moreover, the present nebulizer was fully interchangeable with a concentric one at normal argon pressure, attaining sufficient stability, a short wash-out time and good nebulizing of high matrices solutions. The present system was successfully applied to the determination of trace impurities in highly pure silica powders.     

Determination of phosphorus in fertilizers by inductively coupled plasma atomic emission spectrometry

An inductively coupled plasma atomic emission spectrometry (ICP-AES) method was developed for the determination of phosphorus in fertilizers. Total phosphorus, direct extraction available phosphorus (EDTA), and water-soluble phosphorus, reported as phosphorus pentoxide (P205), in 15 Magruder check fertilizers were measured by ICP-AES, and the results were compared with those obtained by the AOAC official method. Five analytical wavelengths of phosphorus, 177.499, 178.287, 213.618, 214.914, and 253.565 nm, were tested for the determination of phosphorus in fertilizers, and their detection limits were obtained. Acid effects of perchloric acid and possible matrix effects of aluminum, calcium, magnesium, potassium, and sodium were negligible for phosphorus determination. Wavelength 213.618 nm was the best analytical wavelength for phosphorus determination by all 3 sample preparation methods for the selected Magruder fertilizers. The results demonstrated that the accuracy and precision of the ICP-AES method were comparable with those of the official methods.