Autosampler Cups Research Articles

On-line microwave-assisted sample decomposition for lead determination in fish slurry samples by electrothermal atomic absorption spectrometry

An on-line microwave-assisted decomposition procedure for the determination of lead in fish is proposed. 300 µL slurry and 400 µL of a 6 mol L-1 HNO3 solution were simultaneously injected, and the mixture was positioned inside a microwave oven. The decomposed sample inside the flushing solution was collected in the autosampler cup of a graphite furnace. The proposed procedure covered the 2.5 to 25 µg L-1 Pb range and presented a detection limit of 0.72 µg L-1 Pb. Precision expressed as RSD, was 10.5% (n = 20) for repeatability and 14.3% (n = 10) for reproducibility. Accuracy was assessed using standard reference material, and also by comparing the results to a nitric-perchloric decomposition procedure.

Comparison of chemical modifiers for the determination of gold in biological fluids by electrothermal atomic absorption spectrometry

The use of various isomorphous metals as chemical modifiers on the determination of gold has been investigated. The temperature programmes and the masses of modifiers were carefully optimized. Noble metals, copper, nickel, and rhenium increased the atomic absorption signal of gold and raised the maximum pyrolysis temperature from 700 to 1000 °C. In the presence of 20 µg of ascorbic acid this temperature was 1000 °C, whereas in combination with 1 µg of Pd it increased to 1150 °C. On the basis of platform atomization and integrated absorbance measurements, the best sensitivity for aqueous solutions was obtained with the mixed modifiers rhodium–rhenium (m0= 7.3 pg), ascorbic acid–palladium (m0= 7.1 pg) or ascorbic acid–rhodium (m0= 6.8 pg), whereas the characteristic mass in the absence of modifiers was 12.2 pg. The limit of detection was 0.23 µg l–1 in the absence of modifier, whereas it was 0.12 µg l–1 in the presence of the mixed modifier rhodium–rhenium. In the absence of chemical modifiers, a fractional order of release was observed for gold, whereas in the presence of modifiers an approximately first-order release was observed. The determination of gold in biological fluids was interference-free and complete recovery was obtained when stabilized temperature platform furnace conditions were fulfilled. Constant signals, without double peaks and shoulders, were obtained only in the presence of modifiers. It was found that gold solutions stored in the autosampler cups during measurements of the samples were stable only in the presence of 0.5 g l–1 NH4SCN or 1.0 g l–1 ascorbic acid.

Flow-through microwave digestion system for the determination of aluminium in shellfish by electrothermal atomic absorption spectrometry

A flow-injection system incorporating a microwave oven was constructed for the digestion of food samples for the subsequent determination of aluminium by electrothermal atomic absorption spectrometry. A volume of 100 µl of sample slurry was simultaneously injected with 200 µl of 3 mol l–1 HNO3 and transferred into a PTFE reactor (coiled around an Erlenmeyer flask filled with water) located inside a microwave oven. The digested sample and flushing solution were collected in an autosampler cup. The sample was diluted 20-fold within the manifold. The performance of the procedure was evaluated by determining aluminium in an oyster tissue reference material. The recovery of aluminium was about 90%; however, the results for replicate analyses showed no significant differences. The proposed method was applied to the determination of aluminium in shellfish.

Determination of arsenic in plant tissue using a slurry sampling graphite furnace

Abstract Commonly used methods of arsenic (As) determination in plant material require dissolution of tissue in strong acids prior to analysis. Progress in the graphite furnace atomic absorption spectrometry (GFAAS) technique has made the determination of metals in solid samples possible. This study was undertaken to evaluate the possibility of As determination directly in ground plant tissue using GFAAS. The Perkin‐Elmer Model 4100 ZL atomic absorption spectrometer with Zeeman background correction and AS‐70 autosampler has been used for analysis. Spinach (Spinacia oleracea) and com (Zea mays L.) tissues samples containing various As levels were used as test materials. Before injection of the plant slurry into the furnace, the ultrasonic agitator was used to mix the slurry in the autosampler cup to assure uniform distribution of plant powder in the whole volume of liquid. The furnace program contained a pyrolysis step using palladium as the modifier. The GFAAS method was compared with the hydride generat...

Determination of selenium in fruit juices by flow injection electrothermal atomization atomic absorption spectrometry

An automatic flow injection method for the determination of Se in fruit juices by electrothermal atomization atomic absorption spectrometry is proposed. The flow manifold used, which is coupled to the autosampler cup, enables dilution of the slurry, addition of a chemical modifier and the determination of Se in the filtered liquid phase. The effects of various chemical modifiers, furnace temperatures and major foreign ions present in fruits were investigated. Selenium was successfully determined in fruit and tomato juice by using the standard additions method (juice samples were diluted 10-fold) with a relative standard deviation of 4.5–12.0%. The limit of detection (3sb) of the proposed method is 5 µg l–1.

Determination of Sb, Ni and V in slurry from airborne particulate material collected on filter by graphite furnace atomic absorption spectrometry

A microdigestion procedure performed directly in the autosampler cup is proposed. Small quartz filter pieces loaded with the particulate material are transferred to the cup. The sample is digested by a mixture of nitric, sulfuric and hydrofluoric acid (1:1:1) under sonication. After the addition of a boric acid solution the elements are determined by graphite furnace atomic absorption spectrometry using the autosampler to deliver the slurry into the furnace. A mixture of palladium and magnesium nitrates was used as a modifier for Sb. Spiking studies showed recoveries close to 100% using aqueous analytical curves for Ni and Sb. For V, an analytical curve in the blank slurry, obtained by submitting an unloaded filter to the same procedure, was used. The method was applied to two standard reference materials, Coal Fly Ash (NIST 1633a) and Urban Particulate (NIST 1648) and the concentrations showed good agreement with the certified or recommended values using aqueous analytical solutions.

Determination of lead and copper in kerosene by electrothermal atomic absorption spectrometry: stabilization of metals in organic media by a three-component solution

The instability of copper and lead in kerosene and in analytical organic solutions is the main problem with their direct determination. When propan-1-ol is added to a mixture of kerosene and water a homogenous three-component solution is obtained. It was verified that the metals in this solution placed in an autosampler cup are stable for at least 3 h in a closed calibrated flask and remain stable for at least 24 h. The three-component solutions containing purified kerosene and enriched with metallic ions in aqueous solution or with copper or lead cyclohexanebutyrate or tetraethyllead are also stable. In spite of some differences in the absorption pulses, the maximum pyrolysis temperatures, characteristic masses and precision are similar for the three-component solutions in comparison to aqueous solutions.

Metal extraction by hydrofluoric acid from slurries of glass materials in graphite furnace atomic absorption spectrometry

A method for extraction of slurries has been developed for the analysis of siliceous materials by graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction. The different materials are powdered and suspended in water containing 3% HF. The preparation of the sample is carried out in autosampler cups and the slurries are stirred by passing a flow of argon through them. The argon flow achieves effective mixing of the slurry and removes part of the silicon as silicon fluoride. The analyte is extracted into the aqueous component of the slurry and consequently the precision is improved. Homogeneous slurries are obtained without the use of stabilizing or dispersing agents. Stabilized temperature platform furnace (STPF) conditions and calibration against aqueous standards have been used for the determination of Cu, Co, Cr, Mn, Fe and Ni in the NIST standard reference materials SRM 1003a, SRM 610, SRM 612, SRM 614 and in quartz. The results of the slurry extraction procedure have been compared with the conventional approach of acid digestion of the sample materials.

Rapid slurry analysis of solid coal and fly ash samples

Coal and coal fly ash samples were analyzed as solid slurries. These preliminary experiments used fast sampling STPF procedures which omitted the pyrolysis step and the matrix modifier. The experiments also used an ultrasonic mixing device that automatically stirred the suspension just before the autosampler probe withdrew the aliquot which it would dispense onto the platform. The combination of these techniques made it possible to reduce the analytical time to less than 1 min per sample. Simple aqueous standards were used for calibration. The NIST SRM 1633a Coal Fly Ash was successfully analyzed for As, Pb and Tl, with results for Se in this material that suggested that more work was required to gain confidence in the determination. The SRM 1632a Coal was successfully analyzed for As and Pb. The methods were the same for both materials. A few mg of the dry solid powder was weighed directly into the autosampler cup followed by a weighed amount (about 1.5 ml) of suspending diluent The characteristic mass was calculated from several aliquots of simple aqueous standards and this value was used to calculate the amount of analyte delivered to the furnace. In the work reported here the detection limits for the elements determined were about 0.5–1 μg g in the solid sample. With further experience these limits may be improved. The precision for replicates of slurries from the same cup varied from 2 to 10% depending upon the amount of solid sample delivered to the furnace.

Palladium as a chemical modifier for the determination of lead in food slurries by electrothermal atomisation atomic absorption spectrometry

Palladium is shown to be superior to ammonium dihydrogen phosphate as a modifier for lead in the analysis of food slurries by electrothermal atomisation atomic absorption spectrometry. A conventional autosampler was modified to permit magnetic stirring of the slurry samples in the autosampler cups. Stirred slurries can be accurately and precisely pipetted into a graphite furnace up to concentrations of 5%m/V. Above this, systematic errors occur. A method is described for the determination of lead in slurries up to a concentration of 4%m/V. The procedure involves calibration with aqueous standards, palladium matrix modification and platform atomisation.

Evaluation of microwave heating digestion and graphite furnace atomic absorption spectrometry with continuum source background correction for the determination of iron, copper and cadmium in brine shrimp

Iron, copper and cadmium are determined in brine shrimp specimens using graphite furnace atomic absorption spectrometry. Four different digestion procedures, (i.e., dry ashing, hot-block, high pressure and microwave heating digestion) are compared. It was concluded that microwave heating digestion in polyethylene autosampler cups is excellent for the rapid dissolution of sub-milligram amounts of biological material. Applying platform atomisation and peak-area integration, a calibration against acid standards can be used for the determination of the three metals. The use of the ammonium phosphate-magnesium nitrate sample modification for the determination of cadmium allows a maximum pre-treatment temperature of 1000 °C. Continuum source background correction does not cause correction errors and background-corrected analyte absorbance signals appear undistorted. There is good agreement between the results obtained from furnaces and flames, confirming that the chemical and spectral interferences have been overcome.