Tungsten Coil Atomic Absorption Spectrometry Research Articles

Flow injection hydride generation for on-atomizer trapping: Highly sensitive determination of cadmium by tungsten coil atomic absorption spectrometry

Here we report the use of the tungsten-coil atomizer of a portable atomic absorption spectrometer as an on-atomizer trapping device and atomizer for the determination of trace cadmium, with flow injection hydride generation for production of volatile cadmium species from sample solutions. By mixing acidic analyte solution with tetrahydroborate solution, volatile cadmium species is produced and separated from the solution, and then transported and impacted onto the surface of the atomizer with a heating current set at 2.3A. Subsequent atomic absorption measurement was accomplished with in situ atomization at 8.5A. Compared to conventional direct injection, the sensitivity and the limit of detection were improved by 58- and 66-fold, respectively, based on 5.0mL sampling volume. In addition, use of flow injection significantly improved sample throughput. The proposed method was used for the analysis of several real water samples with good spiked recoveries.

A new atomization cell for trace metal determinations by tungsten coil atomic spectrometry

A new metallic atomization cell is used for trace metal determinations by tungsten coil atomic absorption spectrometry and tungsten coil atomic emission spectrometry. Different protecting gas mixtures are evaluated to improve atomic emission signals. Ar, N 2, CO 2 and He are used as solvents, and H 2 and C 2H 2 as solutes. A H 2/Ar mixture provided the best results. Parameters such as protecting gas flow rate and atomization current are also optimized. The optimal conditions are used to determine the figures of merit for both methods and the results are compared with values found in the literature. The new cell provides a better control of the radiation reaching the detector and a small, more isothermal environment around the atomizer. A more concentrated atomic cloud and a smaller background signal result in lower limits of detection using both methods. Cu (324.7 nm), Cd (228.8 nm) and Sn (286.3 nm) determined by tungsten coil atomic absorption spectrometry presented limits of detection as low as 0.6, 0.1, and 2.2 μg L −1, respectively. For Cr (425.4 nm), Eu (459.4 nm) and Sr (460.7 nm) determined by tungsten coil atomic emission spectrometry, limits of detection of 4.5, 2.5, and 0.1 μg L −1 were calculated. The method is used to determine Cu, Cd, Cr and Sr in a water standard reference material. Results for Cu, Cd and Cr presented no significant difference from reported values in a 95% confidence level. For Sr, a 113% recovery was obtained.

Determination of Cd in urine by cloud point extraction–tungsten coil atomic absorption spectrometry

Cadmium concentrations in human urine are typically at or below the 1 μg L −1 level, so only a handful of techniques may be appropriate for this application. These include sophisticated methods such as graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry. While tungsten coil atomic absorption spectrometry is a simpler and less expensive technique, its practical detection limits often prohibit the detection of Cd in normal urine samples. In addition, the nature of the urine matrix often necessitates accurate background correction techniques, which would add expense and complexity to the tungsten coil instrument. This manuscript describes a cloud point extraction method that reduces matrix interference while preconcentrating Cd by a factor of 15. Ammonium pyrrolidinedithiocarbamate and Triton X-114 are used as complexing agent and surfactant, respectively, in the extraction procedure. Triton X-114 forms an extractant coacervate surfactant-rich phase that is denser than water, so the aqueous supernatant is easily removed leaving the metal-containing surfactant layer intact. A 25 μL aliquot of this preconcentrated sample is placed directly onto the tungsten coil for analysis. The cloud point extraction procedure allows for simple background correction based either on the measurement of absorption at a nearby wavelength, or measurement of absorption at a time in the atomization step immediately prior to the onset of the Cd signal. Seven human urine samples are analyzed by this technique and the results are compared to those found by the inductively coupled plasma mass spectrometry analysis of the same samples performed at a different institution. The limit of detection for Cd in urine is 5 ng L −1 for cloud point extraction tungsten coil atomic absorption spectrometry. The accuracy of the method is determined with a standard reference material ( toxic metals in freeze-dried urine) and the determined values agree with the reported levels at the 95% confidence level.

Evaluation of a Radio Frequency-Powered Selenium Hollow Cathode Lamp for Tungsten-Coil Atomic Absorption Spectrometry

Evaluation of a Radio Frequency-Powered Selenium Hollow Cathode Lamp for Tungsten-Coil Atomic Absorption Spectrometry

ADVANCES IN ELECTROTHERMAL ATOMIZATION FOR ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE

ABSTRACT Electrothermal atomizers (ETAs) are commonly used atom cells for elemental analysis. In this article, the fundamental principles of ETAs are described, including instrumentation and operating principles. Several recent applications of ETAs are discussed involving atomic absorption spectrometry (AAS) and laser excited atomic fluorescence spectrometry (LEAFS). These include a clean room atomizer cabinet for ETA-AAS, multielement continuum source ETA-AAS, standardless ETA-AAS for medium volatility elements, slurry atomization of food colorants by ETA-AAS, the determination of lead in blood by tungsten coil–AAS, the determination of arsenic and selenium by hydride generation ETA-LEAFS, and the determination of cadmium and zinc by double resonance ETA-LEAFS.

Determination of selenium by tungsten coil atomic absorption spectrometry using iridium as a permanent chemical modifier

Permanent chemical modifiers have been shown to prolong graphite tube lifetime while reducing the furnace cycle time, thus improving cost-effectiveness. In this work, iridium is used as a permanent chemical modifier for the first time in the determination of selenium by tungsten-coil atomic absorption spectrometry (W-Coil AAS). The iridium modifier is thermally coated onto the tungsten coil. After coating, the coil can be used for 300–400 firings without further application of the modifier. Thermal treatment with iridium permits operating with higher pyrolysis temperature and coil lifetime is extended up to 1600 firings. The sensitivity and linearity of the method is improved, and the analytical procedure allows the use of analyte solutions containing up to 8% nitric acid. The short-term stability of the absorbance measurements is demonstrated by the reproducibility in the measurements of a Se amount (6 ng) 30 times higher than the limit of detection (0.2 ng). A 7% relative standard deviation (R.S.D.) was observed for 10 consecutive measurements of 6 ng Se. The long-term stability is almost as good: less than 9% R.S.D. over a 3-week period and 1500 firings. The surface of the tungsten-coil treated with iridium is examined before and after intensive use by scanning electron microscopy. Finally, the thermal treatment of the tungsten-coil with iridium appears to delay the appearance of selenium atoms by approximately 0.2 s although the integrated absorbance measurements are unaffected. The magnitude of delay decreases with coil age.

Field instrumentation in atomic spectroscopy

The techniques of field analytical chemistry (FAC) have the potential to reduce both analysis time and cost by providing analytical data on site while eliminating the need for sample collection and transport. These methods could be of considerable interest in the fields of environmental monitoring and industrial process control. Much of FAC is accomplished through the use of portable analytical instruments. The emphasis of this review was on field-portable atomic spectrometry, with particular focus upon two techniques: laser-induced breakdown spectroscopy (LIBS) and tungsten coil atomic absorption spectrometry (W Coil AAS). LIBS and W Coil AAS have been described in detail, with special attention to instrumentation, analytical performance, applications and examples of portable devices. The two techniques were compared and found to be complimentary. Competing technology, not necessarily based upon atomic spectrometry, was also briefly discussed in order to provide a glimpse of the overall picture of FAC techniques used for the determination of metals. These rival techniques include X-ray fluorescence spectrometry (XRF), immunoassay, capillary electrophoresis (CE), and electrochemical sensors.

Influence of Na, K, Ca and Mg on lead atomization by tungsten coil atomic absorption spectrometry

The atomization of lead in an electrothermal tungsten coil atomizer in the presence and absence of Na+, K+, Ca2+ and Mg2+ was investigated with the objective of understanding the interference processes. The lead atomization was less affected by Ca2+ and Mg2+ than by Na+ and K+. In the absence of concomitants, lead atomization efficiency was improved by the presence of H2 (10% v/v) in the purge gas composition, during pyrolysis and atomization steps. The interference caused by Na+ and Ca2+ was negligible when the pyrolysis step was accomplished without H2 in the purge gas composition. The results showed that Na+, K+, Ca2+ and Mg2+ are directly involved in competition reactions for H2 in condensed phase.

Determination of lead in blood by chelation with ammonium pyrrolidine dithio-carbamate followed by tungsten-coil atomic absorption spectrometry

An inexpensive, bench-top blood Pb analyzer has been developed. The system is based on tungsten-coil atomic absorption spectrometry. Pb atomization occurs on W-coils extracted from commercially available slide projector bulbs. The system has minimal power requirements: 120 ACV and 15 A. A small, computer-controlled CCD spectrometer is used as the detector. A Pb hollow cathode lamp is used as the source. Blood Pb is chelated with ammonium pyrrolidine dithio-carbamate and extracted into methyl iso-butyl ketone (4-methyl 2-pentanone). Twenty-microliter volumes of the organic phase are deposited on the W-coil, dried at 1.4 A, charred at 2.3 A and atomized at 6.0 A. Graphite furnace atomic absorption spectrometry is used as a comparison for W-coil results. Levels 1–4 of a NIST standard reference material 955b ‘lead in bovine blood’ are used to test accuracy and precision. The analytical figures of merit for the system are: 12-pg instrument detection limit, 24-pg blood detection limit and a characteristic mass of 28 pg.

On-line separation and preconcentration of cadmium, lead and nickel in a fullerene (C60) minicolumn coupled to flow injection tungsten coil atomic absorption spectrometry

A flow system was coupled to a tungsten coil electrothermal atomizer (150W) for on-line separation and preconcentration of cadmium, lead and nickel based on the formation of DDC complexes and sorption into a minicolumn packed with fullerene C60. Three way solenoid valves used for sample and reagents management as well as the tungsten coil power supply were controlled by a computer running a programme written in Visual Basic, which was employed in synchronism with the original software of the atomic absorption spectrometer. The fullerene column (5mm length, 2mm i.d.) was inserted into the tip of the autosampler arm, and elution was performed by sampling 35μl of methanol from the autosampler cup. With 3.0ml of sample (loading time of 60s) enrichment factors ranging from 100 to 150 were achieved. The detection limits for cadmium, lead and nickel were 2.2, 23 and 75ngl−1, respectively. No interference effects were observed on cadmium, lead and nickel preconcentration in the presence of up to 106 fold concentrations of sodium, potassium, calcium or magnesium. Application of t-test to the results obtained by the proposed method and the certified values of cadmium, lead and nickel in five water reference materials did not reveal significant differences at the 5% probability level.

Determination of cadmium in fertilizers by flow-injection spectrophotometry

A flow-injection procedure for spectrophotometric determination of cadmium in fertilizers based on formation of the blue ternary complex between cadmium, iodide and Malachite Green (MG) is proposed. Addition order and concentrations of reagents, interaction time between iodide and MG, flow rates, pH and temperature for ternary complex formation, surfactant addition, and presence of potential interferent ions were studied. A 30-s interaction between iodide and MG, a temperature of 20 °C and use of picolinic acid for copper masking were selected. Linearity of the calibration graph was improved with cadmium addition. For selectivity enhancement, masking agents, kinetic discrimination, and ion-exchange separation were investigated and a Chelex-100 resin minicolumn (50–100 mesh) was employed for in-line interferent removal. The proposed system is very stable and handles about 60 samples per hour (10.0–100.0 μg Cd l −1) corresponding to 0.105 mg MG and 166 mg KI consumed per determination. Linearity of the calibration plot is observed up to 200 μg Cd l −1, the detection limit being 2 μg Cd l −1. Results are precise ( R. S. D. = 1.3% and 4.0% for 93.0 and 35.3 μg Cd l −1) and in agreement with tungsten coil atomic absorption spectrometry. Accurate results are also obtained for lobster and soya bean samples.

Determination of barium in waters by tungsten coil electrothermal atomic absorption spectrometry

Investigations were carried out on the use of tungsten coils as electrothermal atomizers for the direct determination of low concentrations of Ba by atomic absorption spectrometry (AAS). The thermal treatment of the analytical sample was carried out in 41 s, a 10 µl sample volume being used for the determination of Ba in waters in the 10–250 pg range, with good precision (relative standard deviation < 5%). The use of hydrogen in combination with argon as purge gas was essential for the atomization of Ba. The lifetime of the coil was up to 400 firings in 0.014 mol l–1 HNO3. No interference from 8000 ng of K, 6000 ng of Na, 1000 ng of Mg, 10 ng of Ca and 10 ng of Sr were found for the atomization of 200 pg of Ba. The interference caused by larger amounts of Ca was minimized by the addition of ethylenediaminetetraacetic acid. It was shown by the paired t-test that there was no significant difference at the 5% probability level between the results obtained by tungsten coil AAS and inductively coupled plasma atomic emission spectrometry in the analysis of water samples. The detection limit was 2 pg and the characteristic mass was 3.6 pg.

Determination of cadmium in biological materials by tungsten coil atomic absorption spectrometry

A simple, low cost tungsten coil furnace was evaluated for electrothermal atomic absorption spectrometry (ETAAS). The open atomizer was resistively heated by using a power supply with a voltage feedback circuit. The analysis time using a manually injected sample volume of 10 µl was 41 s. Acceptable precision (relative standard deviation <3%, n= 12 at 1.0 ng ml–1 of cadmium) was obtained for cadmium values ranging from 0.5 to 6.0 ng ml–1. The characteristic mass for peak height absorbance was 0.5 pg. Results compare well with certified values of different biological materials digested with nitric acid. For certain reference materials better accuracy was obtained from data based on integrated absorbance.