Mateo Sánchez-Merlos

Slurry sampling for the determination of lead, cadmium and thallium in soils and sediments by electrothermal atomic absorption spectrometry with fast-heating programs

Abstract To determine the lead and cadmium content of soils and sediments, the samples are suspended in water containing 5% ( v v ) concentrated hydrofluoric acid before injected into the electrothermal atomizer. For thallium determination a 30% hydrofluoric acid solution is used as the suspension medium. In accordance with fast-heating methodology, the conventional ashing step is replaced by a modified drying stage performed by programming the instrument to 400°C. No modifier other than hydrofluoric acid is required. Calibration is performed directly using aqueous standards for cadmium and lead determination. For thallium the standard additions method is recommended. The results obtained for five certified reference materials show the reliability of the procedures.

Rapid determination of selenium in soils and sediments using slurry sampling–electrothermal atomic absorption spectrometry

An electrothermal atomic absorption spectrometric procedure for the rapid determination of selenium in soil and sediment samples is presented. The samples were suspended in concentrated (40% m/v) hydrofluoric acid containing 1% m/v nickel nitrate and then injected into the electrothermal atomizer. A fast heating programme, with no conventional ashing step, was used. Platform atomization at 2300 °C and Zeeman-effect background correction were used. Calibration was performed directly by using aqueous standards prepared in a 10% v/v hydrofluoric acid solution. The determination limit was 0.1 µg g–1 of selenium when using the maximum recommended slurry concentration of 10% m/v. The results obtained for five certified reference materials show the reliability of the procedures.

Determination of mercury in soils and sediments by graphite furnace atomic absorption spectrometry with slurry sampling

Abstract A graphite furnace atomic absorption spectrometric procedure for the determination of mercury is presented, in which the samples are suspended in a solution containing hydrofluoric and nitric acids. Silver nitrate (4% m/v) and potassium permanganate (3%) are incorporated, in the order specified, and aliquots are directly introduced into the graphite furnace. A fast heating programme with no conventional pyrolysis step is used. The detection limit for mercury in a 125 mg ml −1 suspension is 0.1 μg g −1 . Calibration is performed by using aqueous standards. The reliability of the procedure is proved by analysing certified reference materials.

Arsenic and antimony determination in soils and sediments by graphite furnace atomic absorption spectrometry with slurry sampling

Abstract Slurry-based procedures for the rapid determination of arsenic and antimony in soil and sediment samples by graphite furnace atomic absorption spectrometry are discussed. For the determination of arsenic, the samples are suspended in a solution containing dilute hydrofluoric acid. Sodium hydrogen carbonate is added and aliquots are introduced into the graphite furnace. A fast heating programme with no pyrolysis step is used. For the determination of antimony, direct suspension in concentrated hydrofluoric acid is recommended. In this way, the interference of silicon is avoided and the background level is reduced, allowing a fast heating programme to be used. The limit of detection of antimony for a 100 mg ml −1 suspension is 0.03 μg g −1 . The results obtained for five certified reference materials using both direct calibration against aqueous standards and the standard additions method demonstrate the reliability of the procedures.

Slurry sampling for the rapid determination of cobalt, nickel and copper in soils and sediments by electrothermal atomic absorption spectrometry

Electrothermal atomic absorption procedures for the rapid determination of cobalt, nickel and copper in soil and sediment samples are presented. The samples are suspended in a hydrofluoric acid solution before being injected into the electrothermal atomizer. Prior mild heating in a microwave oven is recommended for nickel and copper determination. No modifier other than hydrofluoric acid is required. The conventional ashing step is unnecessary since the fast-heating programmes lead to well defined atomization profiles with low background levels that can be corrected using a common deuterium device. Calibration is performed directly using aqueous standards. The results obtained for six certified reference materials confirm the reliability of the procedures.

Slurry Sampling Device for Use in Electrothermal Atomic AbsorptionSpectrometry

A device which uses argon bubbles to homogenize slurries in the cups of an autosampler is described. The system can be adapted to any commercial autosampler because no changes in the software controlling the instrument are required.

Peristaltic pumps-Fourier transforms: a coupling of interest in continuous flow flame atomic absorption spectrometry

The use of a simple continuous manifold, together with data treatment by means of Fourier transforms, permits the dynamic range of flame atomic absorption spectrometry to be extended. A peristaltic pump is used to move the analyte solution, the difference between the pumping flow rate and the nebulizer uptake rate being compensated by aspirating solvent through a T-piece. The time-variable absorbance profile which results from the action of the rollers is transformed into a frequency spectrum, the large signal caused by the periodical roller movement being used as the analytical signal. The effect of different experimental conditions on the signal is studied and the improvement in the signal/noise ratio lowers the determination limit. The dynamic range can be further extended, since the system also permits the measurement of solutions which are too concentrated to be measured by direct aspiration. Calibration is performed by means of a single standard solution.

Use of hydrofluoric acid to decrease the background signal caused by sodium chloride in electrothermal atomic absorption spectrometry

Electrothermal atomic absorption spectrometric measurements are frequently hindered by the presence of sodium chloride, a high background absorption signal being obtained. This drawback is reduced by the addition of hydrofluoric acid. Thus, sodium fluoride, instead of sodium chloride, is present inside the atomizer at the atomization stage and advantage can be taken of the different absorbance profiles originating during the atomization of these two chemicals. The background signals are considerably reduced at wavelengths above 240 nm and below 205 nm. No damage is caused to the pyrolytic material or quartz windows of the atomizer when solutions containing high proportions of hydrofluoric acid are used.

Automatic dilution system for use in flame atomic absorption spectrometry

A fully computer-controlled manifold allowing the automatic dilution and measurement of solutions which are too concentrated to be measured by direct aspiration in FAAS is described. The sample solution is pumped by using a peristaltic pump equipped with two pump tubes of different diameters, the difference between the nebulizer uptake rate and the flow rate delivered by the pump being compensated for with solvent through a T-piece. Absorbance data are acquired by the computer during a time interval which is an exact multiple of the period of the rollers’ pulse. The absorbance is averaged and the pump turning speed automatically increased or decreased until an absorbance value centered within the linear response of the spectrometer is obtained. Calibration is carried out using a single standard solution.

Improvement of selectivity of flame atomic absorption spectrometry using Fourier transforms

Two solutions of the same analyte are propelled towards the nebulizer of the flame spectrometer by two peristaltic pumps running at different turning speeds. This produces periodical fluctuations in spectrometer readings, which can be translated to a frequency spectrum by means of Fourier transform. This transformation makes it possible to discriminate between the signals from each of the solutions being pumped. Two different strategies are studied, with the absorbance fluctuations being caused by the periodic movement of the rollers or by running the pumps at periodic turning speeds. The latter approach proved to be the most versatile. The system could be extended to the case of several solutions of the same analyte being simultaneously supplied to the nebulizer by means of several propelling devices.