Determination of volatile elements in biological materials by isotopic dilution ETV-ICP-MS after dissolution with tetramethylammonium hydroxide or acid digestion

Isotopic dilution for the determination of Ag, Cd, Hg, Pb and Tl in biological materials by ETV-ICP-MS is proposed. The sample was simply dissolved with tetramethylammonium hydroxide (TMAH) or acid digested in a microwave furnace, with an on line matrix separation. When the dissolution was employed, Ir was used as a chemical modifier for Hg and Pb and Pd was used for Cd and Tl. No modifier was used for Ag. The pyrolysis temperatures were taken from pyrolysis temperature curves. The on line preconcentration was performed in a flow injection system with solenoid valves and was based on the analyte complexation with ammonium diethyldithiophosphate and sorption of the complexes on C(18) bonded to silica gel in a minicolumn. For the digested sample submitted to the analyte preconcentration procedure, a modifier, Ir, was only used for Hg. For the other analytes, since a low pyrolysis temperature, 300 degrees C, was employed, no modifier was added. The isotopic dilution calibration was applied to two certified materials, bovine liver and dog fish muscle, dissolved with TMAH or acid digested, and to another two certified materials, corn bran and rice flour, acid digested and submitted to analyte preconcentration. The obtained concentration values agree with the certified ones, showing that this calibration procedure leads to accurate results in the determination of low concentrations of volatile elements. Due to simplicity, the dissolution with TMAH is very attractive.     

Evaluation of the analytical performance of inductively coupled plasma mass spectrometry for the simultaneous determination of major and minor elements in basic slags

The application of inductively coupled plasma mass spectrometry to the analysis of basic slags has been studied. A conventional dissolution-fusion procedure and a microwave digestion system were used for sample dissolution. Suitable selection of the analyte isotopes and the use of appropriate instrument settings and of internal standardization makes it possible to determine the major and minor elements in the same test sample dilution. Use of the omnirange device and low-abundance isotopes for the determination of the major elements is evaluated. The influence of the attack reagents is tested and the interferences caused by polyatomic ions are studied and corrected by applying elementary mathematical equations. For the major and minor elements considered, precision was found to be better than 1% (RSD). Results are presented for three basic slag reference materials and the agreement between the certified and found values shows the capacity of the method accurately to determine elemental concentrations in basic slags.     

Evaluation of the use of microwave oven systems for the digestion of environmental samples

In most chemical analyses for inorganic determinations in environmental matrices the sample is physically destroyed by dissolution, calcination etc. These digestion procedures have to be validated in order to ensure that no contamination and/or losses have occurred which could affect the accuracy of the final results obtained; this validation can be made by using certified reference materials (CRMs).In the recent past, microwave digestion procedures have been developed and have been shown to offer the benefits of rapid sample preparation and reduced contamination risks; however, an incomplete dissolution was suspected in some cases, e.g. in interlaboratory exercises, for the analysis of organic matrices.The aim of this study was to test microwave digestion procedures for different environmental CRMs and to evaluate the suitability of these methods for the determination of some trace elements. The effects of chemical species (As, Hg and Se-species) on the total element recovery after digestion are discussed.     

A simple,low cost,multielement atomic absorption spectrometer with a tungsten coil atomizer

An inexpensive, multielement atomic absorption spectrometer utilizing a tungsten coil atomizer has been developed. The novel optical arrangement employs three 60° beam combiners to blend the spectral output from four light sources such as electrodeless discharge lamps, or hollow cathode lamps, and then direct that output over an atomizer. This instrument uses an inexpensive tungsten coil atomizer that is extracted from a standard 150 W projector bulb. The temperature of the coil is computer-controlled by changing the voltage across the coil. A low voltage is first used to dry the sample then a higher voltage is used to atomize the sample. Simultaneous detection of the analyte absorption signals is accomplished using a charge-coupled device. The elements of interest in this study were Cd, Pb, and Cu. Near-line background correction was used to correct for nonspecific analyte absorption.     

Aspects of proficiency testing studies of trace elements in environmental samples with a focus on laboratory performance

Four proficiency tests of environmentally significant elements in soil and water are described. The effects of sample matrix, analyte, sample preparation procedure, extraction method efficiency and instrumental technique on laboratory performance were assessed. Participants’ performance was evaluated using z scores and E _n scores. One study included dried sediment and sediment digest as test samples. By testing both dried sediment and sediment digest in the same study, differences in laboratories’ results due to the extraction method or instrumental technique were evaluated. Cadmium and nickel were the elements with the most unsatisfactory z scores for dried sediment compared to sediment digest. The second study had as test samples river water and river water fortified with biosolid. For an evaluation of the efficiency of participants’ extraction method, the results reported for the analysis of river water were compared to the results for analysis of the same river water fortified with biosolid. No consensus could be found between participants’ results for Cr and Ni in this study as the extraction method employed by them produced results that were too variable. The last two studies included saline and fresh water samples. The analysis of fresh and saline water samples with similar analyte concentrations assisted laboratories in developing their methods for trace elements in saline water. For Cr, Pb and Se, the assigned values were reference values traceable to SI, measured using isotope dilution inductively coupled plasma mass spectrometry. Saline water containing low concentrations of analytes presented difficulties to some laboratories. Arsenic and selenium were the analytes most difficult to analyse in all types of environmental samples.     

Determination of cadmium, lead, iron, nickel and chromium in selected food matrices by plasma spectrometric techniques

In the frame of a study aimed at investigating the transfer of metal contaminants through the food chain and the effects of food processing, five elements, namely Cd, Pb, Fe, Ni and Cr, were accurately determined in (i) durum wheat grain and derived products, (ii) wheat-based reference materials, (iii) drinking water, used both as an ingredient and for technological purposes in the investigated industrial process. Microwave closed vessel digestion was selected as the dissolution technique for solid samples, whereas water samples were acidified with ultrapure nitric acid and analysed directly. As several analytes had to be quantified at trace or ultratrace levels, inductively coupled plasma mass spectrometry (ICP-MS) was resorted to for analytical determinations. Overall, this straightforward analytical approach enabled to detect the often small changes in element concentration associated with the different technological steps of processing. Nevertheless, detection of heavily interfered elements, especially Cr, as well as analyte quantification at ultratrace-level level in water, posed analytical challenges that required suited analytical solutions.Changes in the sample introduction system and complementary use of inductively coupled plasma atomic emission spectrometry (ICP-AES) straightforwardly overcame the difficulties in determining the analytes in the selected food matrixes. The benefits of ultrasonic nebulization in reducing the effects of problematic spectral interferences were demonstrated. Overall, a robust and high-throughput analytical method was outlined.     

Flow-through coulometry as a calibrationless method in inorganic trace analysis

The possibility of calibration-less determination of trace concentrations of some electrochemically active elements such as Ag, As, Cd, Hg, Pb, etc. by flow-through coulometry is described. The analyte species are collected quantitative-ly from the flowing sample solution on a porous working electrode made of vi- treous carbon particles set at either a constant potential or constant current. The deposit is stripped by a constant current in the next step and the correspond- ing electrical charge is measured and evaluated. The analyte concentration is calculated by making use of the com- bined Faraday’s laws of electrolysis. The method exerts detection limits about 1 μg/l or lower and a linear concentration range over 3 orders of magnitude.     

IAEA quality control studies on determining trace elements in bioindicators

Twenty laboratories from 17 countries around the world participated in two analytical quality control exercises, coded NAT-5 and NAT-6, on determining trace and minor elements in plant bioindicator samples. 1398 laboratory mean values for 51 elements were submitted for two lichen and two moss materials. The submitted measurement results were evaluated as interlaboratory comparison (IC) exercises and as proficiency tests (PT) following standard procedures developed by the International Atomic Energy Agency (IAEA). The evaluations confirmed good performance of the participating laboratories for many elements. Furthermore, the laboratories performance based on IC criteria improved from the first exercise to the second one. Subsequent NAT-5 evaluation revealed systematic differences between the analytical values obtained non-destructively or after the total sample dissolution and the measurements following nitric acid sample dissolution (without the use of hydrofluoric acid) for some elements. The most critical elements for this kind of discrepancies appeared to be Al, Ca, Cr, Fe, Na, Ni, and Pb. After changing analytical methodologies in the concerned laboratories, more consistent values for those elements were obtained in NAT-6. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analytical Determination and Bio-Monitoring of Platinum Group Elements in Roadside Grass Using Microwave Assisted Digestion and Electrothermal Atomic Absorption Spectrometry

The analytical conditions that enable the determination of traffic related platinum group elements (PGEs) in roadside grass using microwave digestion and electrothermal atomic absorption spectrometry were evaluated as an alternative to the biomonitoring of traffic related PGEs and Pb levels in urban areas. To optimize the analytical conditions and account for matrix effects that could import error in the analysis, method optimization was based on matrix simulation through analyte recovery from spiked unpolluted samples against a matrix blank. A mixture of nitric and hydrofluoric acid under progressively increasing microwave irradiation was optimized to afford the quantitative extraction of platinum group elements from plant matrix. Due to the low levels of platinum group elements in real samples, preconcentration was accomplished using sample evaporation followed by dissolution in dilute nitric acid prior to deliverance to the atomic detector. Quantitation limits below 1 ng g^?1 for Pd and Rh and lower than 2 ng g^?1 for Pt, were accomplished, enabling the monitoring of platinum group elements bioaccumulation in roadside grass with satisfactory recoveries, as determined from the analysis of spiked samples. The results from method application in an annual monitoring survey of PGEs and Pb levels in urban flora and other roadside media are presented and discussed.     

Methodological study of extraction procedures applied to urban particulate matter

The modified BCR three-step sequential extraction procedure has been applied to two different samples of urban particulate matters (PM). The distribution of selected trace elements As, Cd, Cr, Mn, Ni, Pb, Zn was investigated and, in a comparative study, the presence of common organic air filters in extraction procedures was evaluated. Analytes in separate fractions were determined by ICP-OES and GFAAS, respectively, depending on concentration levels. While, due to air filters, a significant increase of some analytes mobility in individual fractions has been observed in case of the jet-milled PM (tunnel Letna), but in case of the PKC sample such effect was not found. The analyte impurities built in some filters has been tested, and the impact on the reliability of analyte results has been discussed. The arsenic species occurrence and their stability in presence of air filters (size 47 mm) were investigated in both urban PM samples as well, using HPLC-ICP-MS technique. Water soluble and by three-step BCR procedure extractable arsenic forms are shown in chromatograms     

Use of multiwalled carbon nanotube disks for the SPE of some heavy metals as 8-hydroxquinoline complexes

A multiwalled carbon nanotube disk was used for the SPE of some toxic heavy metals from environmental samples. Metal ions were adsorbed on the disk as 8-hydroxquinoline complexes, then quantitatively desorbed from the disk by using 10 mL 2 M HNO3. The effects of analytical parameters, including pH, sample volume, and flow rates, on the recoveries of Cd(II), Co(II), Ni(II), Pb(II), Fe(III), Cu(II), and Zn(II) were investigated. The influences of some 1A and 2A group elements and some other ions as concomitant ions on the recoveries of analyte ions were also examined. The LODs of the presented preconcentration-separation system for the analyte ions were found to be in the range of 1.0-5.2 microg/L. In order to validate the procedure, SRM 1577B Bovine Liver, IAEA 336 Lichen, and HR-1 Humber river sediment certified reference materials were analyzed. The proposed method has been applied to the determination of understudy elements in some pharmaceutical samples and natural water samples from different sites in Turkey.     

Determination of refractory elements in used lubricating oil by ICPOES employing emulsified sample introduction and calibration with inorganic standards.

The quantification of trace elements in used lubricating oil is useful for evaluating the wearing of specific components of engines. In the present work, inductively coupled plasma optical emission spectrometry (ICPOES) was used for determining five refractory elements (Ni, Mo, Cr, V and Ti) in lubricating-oil samples. The methodology was developed while aiming at the introduction of such organic samples into the ICP as emulsions. Several nebulization systems were tested with clear advantage for Meinhard K3 coupled with a cyclonic spray chamber. The carbon deposition on the injector tip as well as the plasma background was minimized through careful optimization of the Ar and O2 gas mixture flows into the plasma. The optimization of instrumental and experimental parameters allowed quantification using calibration curves prepared with analyte inorganic standards. An internal standard (Sc) was used to correct the matrix effects and signal fluctuations. The limits of detection (3Sb/m), in the ng g(-1) range were obtained for all five elements. The methodology was validated through an analysis of standard reference materials (SRM 1084a, 1085a and 1085b). Good analyte recoveries (from 92.6 to 104.7%) were achieved. Comparison studies against established ICPOES methodologies (sample acid decomposition or sample direct dilution in an organic solvent) have shown that the proposed methodology present clear advantages in terms of simplicity of sample preparation, overall analysis time, and the use of inorganic standards for calibration instead of expensive metallorganic standards.     

The effect of thermal sample pretreatment on the absorption signal in graphite furnace AAS

The origin of the unusual maxima observed in the decomposition curves for pure solutions of some elements has been investigated theoretically and experimentally. An increase in the atom residence time caused by longitudinal redistribution of the analyte in the tube during the pyrolysis step was found to be responsible. The effect can be observed only if the sample is atomized under gas-flow conditions. To prevent any influence on analytical results, atomization should be done in the gas-stop mode.     

Bulk determination of uranium and thorium in presence of each other by Total Reflection X-ray Fluorescence spectrometry

A study to assess the applicability of Total Reflection X-ray Fluorescence (TXRF) spectrometry as a microanalytical technique for the determination of uranium and thorium as major elements in presence of each other has been made. Effect of dilution of the sample on the analytical results has been investigated. It has been found that dilution of the sample does not affect the analytical results significantly. Also the analytical results of uranium and thorium are similar with different internal standards e.g. cobalt, gallium and yttrium. With a sample size of 10 μL and the concentrations of the analytes in the range of 1–50 μg/mL and total matrix concentration less than 200 μg/mL, the precision and accuracy of the method were found to be better than 3% (1 s) and 4%, respectively. For higher concentration ranges of the analyte (up to about 700 μg/mL), the precision and accuracy values were better than 6% (1 s) and 5%, respectively. The TXRF method has an advantage of using small sample volume of about 10 μL, produces very small radioactive waste and is nondestructive but requires dissolution of the sample.     

Kinetic-chromatographic determination of 4-methylaminoantipyrine in Pentalgin N and Pentalgin FS tablets

4-Methylaminoantipyrine (4-MAAP) is the main product of analgin decomposition in aqueous-organic solutions used in the analysis of Pentalgin N and Pentalgin FS tablets. The determination of 4-MAAP in tablets is complicated by the fast decomposition of analgin in the course of sample dissolution. The use of nonaqueous solvents in subsequent HPLC analysis is unreasonable, because the shapes of analyte peaks are deteriorated and the decomposition of analgin is not prevented. A procedure for the kinetic-chromatographic determination of both 4-MAAP in tablets and its amount at the moment of sample dissolution is proposed.     

A new electrolytic dissolution of aluminum alloys and determination of some constituents by inductively coupled plasma optical emission spectrometry

The new electrolytic dissolution in batch of aluminum alloys samples as grains or turns and the determination of Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb and Ti by ICP OES was investigated. In on-line electrodissolution procedures described in the literature, samples were restricted to be in the form of solid blocks or plates with one polished flat face. Here, the sample was loaded in the barrel of a modified disposable syringe (the anodic semi-cell) and pressed with a modified plunger fitted with a platinum disk to establish electrical contact with the analyte. This arrangement was introduced in a beaker containing the electrolyte (1 mol L⁻¹ HNO₃) and a platinum wire as the cathode. The resulting solution from electrodissolution (0.6 A) was used for the ICP OES determinations. The influence of the aluminum concentration increase on the determination of the elements was evaluated. Electrodissolution of certified reference materials and commercial samples revealed relative errors lower than 10% for the elements Fe, Cu, Mg, Ni, Cr, Zn and Ti (when their content is above 0.1%). Higher inaccuracies (>10%) were observed for Mn and for Fe in B.C.S. 268/1 reference material certified. The proposed method presented a relative standard deviations (R.S.D.) lower or circa 10% to all of the elements (except Pb). In comparison with traditional acid dissolution, the proposed electrodissolution method is relatively fast (about 30 min), it is clean (there is no projection of solution) and simple (heating and fumes exhaust system were not necessaries).     

Study of the factors affecting the performance of microextraction by packed sorbent (MEPS) using liquid scintillation counter and liquid chromatography-tandem mass spectrometry

Microextraction by packed sorbent (MEPS) is a new technique for sample preparation that can be connected on-line with LC or GC. In MEPS, approximately 1-2 mg of the solid packing material is inserted into a syringe (100-250 μL) as a plug. Sample preparation takes place on the packed bed. The bed can be packed or coated to provide selective and suitable sampling conditions. The new method is very promising for extraction of drugs and metabolites from biological samples.In this paper, some factors affecting the performance of MEPS such as recovery, carry-over, leakage, washing volume and elution volume were studied using C18 and hydroxylated polystyrene-divinylbenzene copolymer (ENV+) as sorbents. Radioactively labelled bupivacaine in plasma samples was used as test analyte. For the extraction of this drug, using methanol/water 95:5 (v/v) (0.25% ammonium hydroxide) was used as elution solvent. The analyte response increased with increasing the elution volume and it was linear upp up to 100 μL utilizing liquid scintillation counter. Further, for concentrating the sample, we found that MEPS may be used such that the sample can be drawn through the needle, up and down, several times. The analyte leakage increases as the volume washing increases, though higher washing volumes may also result in cleaner extracts. To eliminate analyte carry-over, the sorbents were washed first with 3 × 250 μL elution solution and then with 3 × 250 μL washing solution. In addition, the reproducibility measurements show relatively good relative standard deviation (RSD) % values concerning analyte recovery and analyte leakage. The present study provides an understanding of basic aspects when optimizing methods for MEPS. In this study, MEPS was used off-line with liquid scintillation counter and on-line with LC-MS/MS.     

Mössbauer study of iron reduction in hematite containing mineral originated from Aswan area in Egypt

Mössbauer spectroscopy was used to study iron reduction in mineral originated from Aswan area in Egypt. The Mössbauer spectra of samples heat treated at 1000 °C in hydrogen atmosphere show a gradually reduction process of hematite. The main phase of sample aged for 1 h is magnetite, while alpha-iron as well as some silicates and wustite type oxide can be detected in sample aged for 3 h. Further aging of sample results in dissolution of alloying elements /Si, Al/, being present in the samples. This process starts already in samples aged at 1000 °C for 4 h, but it is more expressive in minerals heat treated at 1200 °C or 1300 °C, when all paramagnetic phases disappeared.     

Time-resolved measurements of individual ion cloud signals to investigate space-charge effects in plasma mass spectrometry

A new approach to directly monitor space charge induced effects due to high concentrations of efficiently ionized elements in inductively coupled plasma mass spectrometry (ICP-MS) is described. The broadening of ion clouds produced from individual, monodisperse drops of sample is measured by using time-resolved ICP-MS. The extent of broadening due to high concentrations of Pb in the sample is related inversely to the analyte mass. For the lightest analyte investigated, Li⁺, the relative width of the time-resolved analyte peak increases and then shows a dip in the center as the Pb concentration is increased to 500 and then 1500 µg/mL. The initial results of experiments that investigated chemical matrix effects as a function of concomitant species concentration, analyte mass, and sampling location in ICP-MS are consistent with space-charge effects.     

Solid-phase extraction of bismuth, lead and nickel from seawater using silica gel modified with 3-aminopropyltriethoxysilane filled in a syringe prior to their determination by graphite furnace atomic absorption spectrometry

In this study, the use of syringe filled with sorbent for the separation and enrichment of bismuth, lead and nickel prior to their analysis by graphite furnace atomic absorption spectrometry was described to substitute for batch and column techniques. The method proposed in this paper was compared with column technique with respect to easiness, fastness, simplicity, recovery and risk of contamination. The syringe was filled with 0.5 g of sorbent and in order to retain the analyte elements, 5 ml of sample solution (pH≥5) was drawn into the syringe to 15 s and discharged again in 15 s. Then, 2.0 M of HCl, as the eluent, was drawn into the syringe and ejected back to desorb the analyte elements. At optimum conditions, the recoveries of Bi, Pb and Ni were 95-99% with relative standard deviations (RSDs) of around ±2%. Detection limit (δ) was 0.5 μg l⁻¹ for Bi, Pb and Ni, respectively. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only one time. Bi, Pb and Ni added to a seawater sample were quantitatively recovered (>95%) with low RSD values of around ±2-3%. The risk of contamination is less than that with the column technique. In addition, it is much faster, simpler, easier, more practical and handy compared with column technique.