Mechanized techniques for sample decomposition and element preconcentration

High performance decomposition techniques for organic and inorganic samples are discussed. Wet decomposition in closed vessels with conventional and microwave heating enables the decomposition of a wide variety of sample materials. A complete mineralization of organic samples with nitric acid is just possible by means of the High Pressure Asher®. After microwave digestion 2–20% of the carbon of the introduced sample remains in the digestion solution. Trace elements in aqueous samples or in digestion solutions can be determined with high sensitivity and free of systematic errors by means of a combined analytical method consisting of a computer controlled preconcentration device (TraceCon®) and a simultaneous ICP emission spectrometer.     

Flame AAS/flame AES for trace determination in fresh and used lubricating oils with sample introduction by hydraulic high-pressure nebulization

In hydraulic high-pressure nebulization (HHPN) an aerosol is produced by means of an HPLC-pump and a special nebulization nozzle, applying a pressure of about 200 bar. This spray technique has been employed for sample introduction of mineral oil samples in flame atomic absorption/flame emission spectrometry. The determination of the trace elements Al, Cr, Cu, Fe, K, Na, Ni, Pb, Si and V has been investigated. Viscosity hardly acts upon the sensitivity of the determination, thereby avoiding a time consuming dilution of oil samples. By means of two interconnecting sampling valves a calibration method based on the standard addition technique can be performed which is both simple and easy to carry out. In samples of used oils, results for Cu and Pb equalled those of XRF-analysis. Regarding Fe traces, data obtained from AAS and XRF measurement correlate. In comparison with sample uptake by pneumatic nebulization, which is restricted to diluted oil samples, detection limits decrease by a factor of 2 to 4, indicating the dilution required in pneumatic nebulization.     

Flame AAS/flame AES for trace determination in fresh and used lubricating oils with sample introduction by hydraulic high-pressure nebulization

In hydraulic high-pressure nebulization (HHPN) an aerosol is produced by means of an HPLC-pump and a special nebulization nozzle, applying a pressure of about 200 bar. This spray technique has been employed for sample introduction of mineral oil samples in flame atomic absorption/flame emission spectrometry. The determination of the trace elements Al, Cr, Cu, Fe, K, Na, Ni, Pb, Si and V has been investigated. Viscosity hardly acts upon the sensitivity of the determination, thereby avoiding a time consuming dilution of oil samples. By means of two interconnecting sampling valves a calibration method based on the standard addition technique can be performed which is both simple and easy to carry out. In samples of used oils, results for Cu and Pb equalled those of XRF-analysis. Regarding Fe traces, data obtained from AAS and XRF measurement correlate. In comparison with sample uptake by pneumatic nebulization, which is restricted to diluted oil samples, detection limits decrease by a factor of 2 to 4, indicating the dilution required in pneumatic nebulization.     

Inductively coupled plasma optical emission spectrometric determination of trace elements in sediments after sequential selective extraction: effects of reagents and major elements on the analytical signal

The interfering effects due to the reagents and matrix elements associated with a four step sequential extraction procedure on ICPOES determination of trace elements were investigated in a systematic way. The emission lines were selected in order to include the most interesting elements for environmental studies (Zn, Pb, Ni, Cr, V and Cu) and the concentrations ranged according with the values occurring in the real samples. In order to distinguish between chemical and physical interfering effects, the Mg 280.270–Mg 285.213 line intensity ratio was measured, in each condition. Both pneumatic and ultrasonic nebulization were considered for comparison. It was found that both the elements which constitute the sample and the reagents which are added during the sample preparation steps significantly influence the emission intensity of all the analytes, depending on the analytical concentration and the nebulization system. Generally, the signal variations were higher with ultrasonic nebulization. Concerning the interference mechanism, it was found that the effect of the major elements (Na, K, Mg, Ca, Al and Fe) is essentially related to a change of the aerosol generation and transport processes. Differently, acetic acid, ammonium acetate and hydroxylamine hydrochloride significantly improved the plasma excitation conditions, depending on their concentration. A change of the sample introduction efficiency due to the presence of these reagents was also evident. On the contrary, the effect of hydrochloric and nitric acid emerged to be related only to the processes occurring in the sample introduction system.     

氢化物发生-电感耦合等离子体原子发射光谱法同时测定锑锭中氢化物元素和非氢化物元素

运用改进的同心喇叭口双溶液管雾化器，采用连续氢化物发生法，在酸性介质中，对锑锭样品溶液既发生雾化作用，又对可形成氢化物的元素（Ａｓ、Ｓｅ、Ｐｂ）发生氢化作用，使它们的发射强度得到显著提高，而对非形成氢化物的元素（Ｆｅ、Ｃｕ）的发射强度基本不受影响，利用ＩＣＰ－ＡＥＳ同时测定锑锭中形成氢化物的元素和非形成氢化物的元素。对实际样品进行对比检测，结果令人满意。     

Application of sodium carbonate-zinc oxide decomposition mixture on ICP-AES determination of boron in tourmaline

Boron in tourmaline, a high refractory mineral with a high boron content (approximately 3%), can be determined after aqueous leaching of a sodium carbonate-zinc oxide melt. Boron is separated effectively from the major elements of matrix, such as silicon, calcium and magnesium and especially from iron, the main spectral interfering element. Measurements were performed by inductively coupled plasma atomic emission spectrometry. A determination limit of 4 microg/g could be achieved when 200 mg of sample are analyzed with a precision of 5.2% RSD. This method could be applied to the determination of fluorine in the same solution.     

Application of sodium carbonate-zinc oxide decomposition mixture on ICP-AES determination of boron in tourmaline

Boron in tourmaline, a high refractory mineral with a high boron content (～3%), can be determined after aqueous leaching of a sodium carbonate-zinc oxide melt. Boron is separated effectively from the major elements of matrix, such as silicon, calcium and magnesium and especially from iron, the main spectral interfering element. Measurements were performed by inductively coupled plasma atomic emission spectrometry. A determination limit of 4 μg/g could be achieved when 200 mg of sample are analyzed with a precision of 5.2% RSD. This method could be applied to the determination of fluorine in the same solution.     

Flow injection determination of Pb and Cd traces with graphite furnace atomic absorption spectrometry

The preconcentration and recovery of lead and cadmium traces at ng l(-1) level were evaluated in standard solutions and natural aqueous samples using a FIAS (Flow Injection Atomic Spectrometry) apparatus. The method is based on retention of the complex formed between Pb or Cd and 1,2-dihydroxy-3,5-benzendisulphonic acid (Tiron) on a macroporous anion-exchange resin. The recovery of the analytes was obtained by elution with 0.1 M HCl and their determination was performed by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The detection limits were 9 and 7 ng l(-1) for Pb and Cd respectively. The effects of sample solution pH and composition and of interfering agents as well as reagent purity are discussed. The technique was applied to the analysis of natural waters.     

Flow field-flow fractionation as an analytical technique to rapidly quantitate membrane fouling

The initial fouling behavior of a clean membrane surface was studied using flow field-flow fractionation (flow FFF), an analytical technique typically used to separate and characterize macromolecules and particulates. This work represents the first time flow FFF has been used to quantitatively evaluate membrane performance. Flow FFF is an ideal tool for expeditiously studying sample–membrane interactions for the following reasons: membranes can be quickly installed into the flow FFF channel, each analysis requires only microgram amounts of sample, and sample–membrane interactions can be rapidly quantitated for different flowrates and solution compositions.Suwannee River humic acids were used as a probe to investigate the initial fouling of an XLE reverse osmosis membrane and an NF-200 nanofiltration membrane. Flow FFF was successfully used to quantitate the fouling of each membrane and to demonstrate that the majority of sample loss was due to irreversible adsorption. The fouling on both membranes was enhanced by increasing the flowrate perpendicular to the membrane surface and by adding calcium ions to the solution. The NF-200 membrane was more resistant than the XLE membrane to fouling in the presence of calcium ions, whereas, the fouling resistance of both membranes improved to similar levels with the addition of EDTA to a solution containing calcium ions.     

Isolierung von Magnesium aus biologischem Material für die massenspektrometrische Isotopenanalyse

Magnesium is precipitated as hydroxide after elimination of interfering elements by means of ion-exchange procedures (phosphate, iron, trace elements) and masking with EDTA (calcium). The sample is applied in form of MgCl₂ to the tungsten filament of an 1-filament-ion-source for surface ionization.     

Determination of arsenic by inductively coupled plasma mass spectrometry – comparison of sample introduction techniques

A comparison is made of four sample introduction techniques for the determination of As by inductively coupled plasma mass spectrometry. The techniques studied were 1) flow injection with pneumatic nebulization (FIA-PN), 2) direct electrothermal vaporization (ETV), 3) continuous hydride generation (HG) and 4) hydride generation with in situ trapping followed by electrothermal vaporization (HG-ETV). It was found that FIA-PN and ETV gave similar detection limits in concentration units (about 20 pg mL^–1), although ETV had a much lower absolute detection limit (0.2 pg). Sample introduction by hydride generation gave an inferior detection limit (100–200 pg mL^–1), also in combination with in situ trapping and ETV, owing to the blank signal from traces of As in NaBH₄ which is difficult to eliminate. The results indicate that the more elaborate sample introduction techniques based on ETV and HG may not offer significant advantages compared to normal solution nebulization for the determination of As in simple sample matrices such as natural fresh waters, where matrix removal is not required.     

Determination of ultratrace impurity elements in high purity niobium materials by on-line matrix separation and direct injection/inductively coupled plasma mass spectrometry

The determination of 52 impurity elements in niobium materials (niobium metal, niobium oxide (V), and niobium pentaethoxide) was performed by inductively coupled plasma mass spectrometry (ICP-MS) with on-line anion exchange matrix separation as well as direct nebulization. Niobium material samples were decomposed with a mixture of hydrofluoric acid and nitric acid to prepare 10% niobium solutions. In the on-line anion exchange matrix separation/ICP-MS, the niobium and hydrofluoric acid concentrations in sample solution were adjusted to 5% and ca. 8 M, respectively. The solution was then injected into the carrier stream from the sample loop of injection valve to pass through an anion exchange resin column. In the anion exchange separation, niobium in the fluoro-complex form was adsorbed on the resin, while impurity elements were eluted. The eluted elements were introduced into ICP-MS for the determination of 25 impurity elements. On the other hand, 27 impurity elements could not be separated well from niobium matrix under the above anion exchange conditions, and then the sample solution with the niobium concentration of max. 0.2% containing internal standard elements was injected from the sample loop of injection valve directly to introduce into ICP-MS. As a result, 52 impurity elements in three kinds of niobium materials could be determined at the ng g⁻¹ level.     

Analysis of tocopherols in margarine by on-line HPLC–HRGC coupling

Tocopherol analysis in margarine is usually carried out by HPLC after saponification of the sample and extraction of the vitamin compounds; these steps consume both time and solvents. In this paper we propose an on-line HPLC–HRGC coupling method, which allows us to simplify the preparation of the analytical sample. The sample of margarine is solubilized in hexane in an ultrasonic bath in the dark; the filtered solution is then injected into the liquid chromatograph using a normal phase microbore column eluted with hexane–isopropanol 99.8:0.2. The α-tocopherol, which is eluted with some wax esters, is transferred on-line to the gas chromatograph, using a loop-type interface with the concurrent eluent evaporation and solvent vapor exit, thus it is separated from interfering compounds and determined using an Alltech RSL 300 column (22 m × 0.25 μm i.d., 0.2 μm film thickness). The β, γ, and δ–tocopherols are determined in the same LC run, using fluorimetric detection. The analysis was carried out in 50 min.     

Determination of arsenic by inductively coupled plasma mass spectrometry--comparison of sample introduction techniques

A comparison is made of four sample introduction techniques for the determination of As by inductively coupled plasma mass spectrometry. The techniques studied were 1) flow injection with pneumatic nebulization (FIA-PN), 2) direct electrothermal vaporization (ETV), 3) continuous hydride generation (HG) and 4) hydride generation with in situ trapping followed by electrothermal vaporization (HG-ETV). It was found that FIA-PN and ETV gave similar detection limits in concentration units (about 20 pg mL(-1)), although ETV had a much lower absolute detection limit (0.2 pg). Sample introduction by hydride generation gave an inferior detection limit (100-200 pg mL(-1)), also in combination with in situ trapping and ETV, owing to the blank signal from traces of As in NaBH4 which is difficult to eliminate. The results indicate that the more elaborate sample introduction techniques based on ETV and HG may not offer significant advantages compared to normal solution nebulization for the determination of As in simple sample matrices such as natural fresh waters, where matrix removal is not required.     

Cr(III)/Cr(VI) determination in waste water by ICP/AES with on-line HPLC (HHPN) sample introduction

Using hydraulic high-pressure nebulization (HHPN) for sample introduction, an on-line high-pressure flow system (HPLC system) becomes a functional component of the ICP spectrometer. By placing additionally an HPLC column between the sample valve and the high-pressure injection/nebulization nozzle, an improved species analysis is attained. An example is given by on-line separation and determination of Cr(III)/Cr(VI) in real waste water samples with ICP/AES. The detection limit of each Cr oxidation state is 4 μg L^–1 with an analysis cycle time of 5 min. In comparison to conventional coupling of HPLC and ICP spectrometry a considerably higher sensitivity is achieved. Using spiked samples the recovery of HHPN-ICP/AES was on an average better than 98% in contrast to only 79% for Cr(VI) determination with a UV photometric reference method. Due to chromatographic separation of Cr(VI) from matrix components and Cr (III), the technique no longer shows the typical spectral interferences caused by Ca (267.716 nm Cr line) and Fe (283.563 nm Cr line).     

Studies in hydride generation atomic fluorescence determination of selenium and tellurium. Part 2 — effect of thiourea and thiols

In determination of selenium and tellurium by continuous flow hydride generation atomic fluorescence spectrometry, the effect of thiourea and thiols was investigated in view of their potential to achieve mild reaction conditions and as masking agents of interference from foreign elements. The effect of thiourea and thiols was first tested in the absence of interfering species and using different addition modes to reaction system. In the absence of interfering species, thiols negatively influenced the hydride evolution of both selenium and tellurium and, in general, they did not produce the desired effects. Thiourea was well tolerated in the determination of both elements by appropriate choice of experimental conditions. Possible mechanisms producing the depressive effect of thiourea and thiols were also investigated and are discussed later. Compromise reaction conditions were identified by using on-line addition of a neutral thiourea solution to acidified sample, combined with KI addition to NaBH₄. Mild reaction conditions can be achieved by decreasing the NaBH₄ concentration but at the expense of a reduced linear dynamic range. In the presence of foreign elements, thiourea allowed good control of interferences generated by Cu(II), Co(II), Ni(II), Au(III), Ag(I) and Bi(III). Tolerance limits could be improved by factors in the range of 7–2000, for both selenium and tellurium determination. The method has been successfully applied in the determination of traces of tellurium and selenium in copper, lead and molybdenum ores, stainless steel and pure copper metal without any additional steps other than sample dissolution.     

High-performance flow atomic spectrometry: New nebulization techniques,on-line speciation and on-line sample pretreatment

An interface-free combination of HPLC separation techniques and methods for element determination by atomic spectrometry can be achieved by hydraulic high-pressure nebulization (HHPN). With high-temperature HHPN (300 ( degrees )C) super heated liquids can be nebulized providing aerosol yields of up to 90% in flame AAS. This new nebulization method combines the advantages of HHPN and thermospray techniques (very small aerosol droplets, high aerosol yield, nebulization of saturated salt solutions).     

Investigation of HfO(+) interference in the determination of platinum in a catalytic converter (cordierite) by inductively coupled plasma mass spectrometry

The determination of Pt in cordierite is subject to strong interference by spectral overlap from HfO(+) ions with all Pt isotopes. Two mathematical correction methods based on the HfO(+)Hf(+) ratio and a method for the chemical separation of Hf based on adsorption chromatography and isotope dilution were investigated to correct for this interference. Flow infection was used to prevent clogging of the cone orifice. To enhance the sensitivity and thus lower the detection limit, thermospray nebulization was used for sample introduction and the method was compared with pneumatic nebulization. In addition, the memory effects were evaulated for both systems. Analysis of artificial solutions (1 ng Pt ml(-1)) yielded results within 3% of the true value. Th Pt content (ca. 50 ng g(-1)) of a cordierite sample, previously exposed to exhaust gases, could be determined with precisions of about 10-25% and the results agreed with earlier determinations by other workers.     

Development of multi-elemental method for quality control of parenteral component solutions using ICP-MS

An inductively coupled plasma mass spectrometry (ICP-MS) method for elemental impurities determination in components used for parenteral nutrition solutions is proposed. Solutions of amino acids (10% m/v), glucose (50% m/v) and lipids (20% m/v) were analyzed. Arsenic, Cd, Cu, Pb and Mo were determined by ICP-MS operated at standard mode, whilst pneumatic nebulization was used for introducing the sample solution into the ICP. Mercury was determined using cold vapor generation (CVG) coupled to ICP-MS. Chromium, Mn, Ni and V were determined by means of dynamic reaction cell-inductively coupled plasma mass spectrometry (DRC-ICP-MS), while ammonia was used as reaction gas. The operational conditions of each technique were optimized in order to achieve better sensitivity, precision and accuracy. The influence of the sample matrix, mainly carbon, on all investigated elements was evaluated. The use of DRC was effective to reduce interferences on Cr, Mn, Ni and V determination. The other investigated elements (As, Cd, Cu, Pb, Mo and Hg) were determined directly in the samples, which were properly diluted. Results obtained were in good agreement (between 96 and 103%) with certified values (certified reference materials of water were analyzed), at the same time as the relative standard deviation was lower than 5%. Sample throughput was relatively high (up to 30 samples of components used for parenteral nutrition solution could be analyzed per hour). In this way, the proposed method can be recommended for routine analysis.     

On-line trace preconcentration / matrix separation by high-performance flow atomic spectrometry (HPF-FLAME AAS)

Summary In HPF-atomic spectrometry a high-performance flow / hydraulic high-pressure nebulization (HPF / HHPN) system is used for sample introduction and aerosol generation. By employment of techniques common in HPLC or ion chromatography, on-line trace element preconcentration / matrix separation and atomic spectrometric trace determinations can be carried out. Preconcentration of trace elements in samples of drinking water allows determinations within the lower g/L region by using flame AAS. On-line trace element preconcentration / matrix separation from aluminium leads to detection limits of approx. 0.1 to 1 g/g within less than 3 min of total analysis time. Dependent on concentration and the element involved, the relative standard deviation amounts to approx. 2 to 4% (2.5 to 25 g/g traces/aluminium).Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday