V. Carbonell

On-line microwave oven digestion flame atomic absorption analysis of solid samples

Abstract A manifold has been developed for on-line microwave oven digestion and flame atomic absorption spectrometric (FAAS) determination of metallic elements in solid samples. The use of a closed flow system permits sample treatment before analysis by FAAS, the direct injection of slurries avoids a filtration step and the interconnection of two conventional rotary injection valves allows the rapid introduction of samples and standards. The determination of lead in sewage sludge was employed as a test system for the proposed on-line sample digestion manifold. The procedure has a limit of detection of 0.2 μg Pb g−1.

On-line microwave-assisted digestion of solid samples for their flame atomic spectrometric analysis.

A new procedure has been developed for the on-line digestion of solids in a microwave oven. The direct injection in a water carrier flow of dispersions of solid samples in concentrated nitric acid, the merging of these slurries with 30% (v/v) H(2)O(2) and the microwave-assisted digestion in a Teflon coil of 100 cm permit a fast and quantitative extraction of Cu and Mn from different solid matrices, such as vegetables, powdered dietary products and sewage sludges. The development of an appropriate interphase, in which digested samples are cooled and degassified, previous to their introduction into the nebulizer of a flame atomic absorption spectrometer, makes possible the full automatization of the digestion and measurement steps of the elemental analysis of solids and it provides a sample frequency of 180 injections per hour. The developed procedure has also been applied for Pb and Zn determination in certified sewage sludge samples, with accurate results obtained for Pb but low results found for Zn.

Literature survey of the on-line preconcentration in flow-injection atomic spectrometric analysis

SummaryThe literature on the use of “on-line” preconcentration in flow injection atomic spectrometric analysis is reviewed, taking into account its application both in flame and electrothermal atomic absorption methods as well as in plasma emission spectrometry. The basis of the different preconcentration approaches, such as liquid-liquid extraction, column preconcentration and “on-line” precipitation are discussed. The literature survey reveals the analytical performance of the developed methodologies.

Direct determination of copper and iron in edible oils using flow injection flame atomic absorption spectrometry

A procedure, based on the standard additions method, has been developed for the direct determination of copper and iron in edible oils by flow injection flame atomic absorption spectrometry. An organic standard is added to the sample using a reverse single line manifold. The flow injection standard additions method allows the accurate determination of copper and iron in unrefined oil samples without any pre-treatment or dilution of the samples.

Atomic absorption spectrometric analysis of solids with on-line microwave-assisted digestion

A procedure was developed for the on-line microwave-assisted digestion of solid samples and their analysis by flame atomic absorption spectrometry. The method involves the transport of a slurry of the sample in a 1 + 1 mixture of concentrated HNO3 and H2O2, which provides quantitative extraction of Cu and Mn in a few minutes. Real samples of sewage sludges dispersed in 20 cm3 of HNO3 and H2O2 can be digested in 4 min and other matrices, such as artichoke and diet samples dispersed in 10 cm3 of HNO3 and H2O2 are digested in only 2 min. A closed flow injection system permits the on-line digestion to be carried out; the use of two interconnected injection valves allows the measurement of standards during the digestion of samples. The method permits the analysis of more than 15 samples per hour and provides accurate results, as demonstrated by the analysis of certified samples of sewage sludges ad tomato leaves.

Flow injection flame atomic spectrometric determination of aluminium, iron, calcium, magnesium, sodium and potassium in ceramic material by on-line dilution in a stirred chamber

The on-line dilution of ceramic samples, previously fused with alkaline carbonates, increases the dynamic range of the flame atomic spectrometric determination of aluminium, iron, calcium, magnesium, sodium and potassium. A double-channel manifold with a simultaneous double injector, and a versatile system of dilution, with stirred chambers, allows direct determination of the six elements studied in different ceramic matrices, i.e., clay, kaolin, quartz, felspar, varnish, stoneware and porcelain, rapidly and with low consumption of the reagents. The effect of the flow injection parameters on the analytical characteristics of the flame atomic spectrometric determination has been studied and the results obtained in the analysis of real samples have been compared with those found in batch analyses.

Direct determination of calcium, magnesium, sodium and potassium in water by flow injection flame atomic spectroscopy, using a dilution chamber

SummaryA simple procedure to carry out the direct analysis of calcium, magnesium, sodium and potassium in water by flow injection analysis (FIA) using flame atomic absorption spectroscopy (AAS) or flame photometry (FP) has been developed, using a well stirred dilution chamber to extend the calibration range, and both a double injector and the merging zone technique to add a lanthanum solution to samples and standards. The results obtained in the analysis of real samples agree with those found by a batch flame atomic procedure. The use of the dilution chamber makes it possible to carry out the calibration using the dilution profile of a single concentrate standard for each element, and an empirical dilution equation, which could be employed for all the elements is determined in each work session.

Flow injection flame atomic spectrometric determination of iron, calcium, magnesium, sodium and potassium in ceramic materials by using a variable-volume injector

SummaryA series of different ceramic materials, such as porcelain, feldspar, kaolin, varnish, clay and stoneware have been analyzed. Iron, calcium and magnesium have been determined in these materials by flame atomic absorption and sodium and potassium by flame emission. The use of a variable-volume injector enables one to carry out these analyses in a flow system (after fusion of samples with lithium metaborate) and does not require different dilutions for the determination of each type of sample considered, nor the use of different flow injection manifolds. The developed procedure provides a limit of detection of 100 μg/l for Na, 70 μg/l for Ca, 50 μg/l for both Fe and K and 8 μg/l for Mg. The coefficient of variation obtained for the absorbance measurement is of the order of 0.5–2%. A series of 17 real samples were analyzed by the proposed procedure and the obtained results turned out to be comparable to those found by batch analysis.

Direct FIA-AS determination of potassium and magnesium in cement samples by use of the slurries approach.

A direct procedure has been developed for the flame atomic determination of potassium and magnesium in cement samples. A 50-mg sample is dispersed in 25 ml of 0.13M nitric acid; 100 mul of this slurry is injected in a double channel FIA manifold simultaneously with 100 mul of a 10% (w/v) lanthanum solution. This procedure allows the rapid extraction of potassium and magnesium by leaching of the sample; nitric acid is not necessary if only potassium must be determined and the sample can be diluted with only distilled water. Aqueous standards are used. The manifold employed includes a well-stirred mixing chamber, which provides an adequate on-line dilution of the sample, in order to obtain emission or absorbance measurements in the dynamic range of the elements to be determined. The results obtained in the analysis of real samples agree with those found by flame atomic spectrometry after a previous alkaline fusion with lithium carbonate, and exhibit better precision. The limit of detection of the procedure is 0.007% for K(2)O and 0.01% for MgO and the precision of the entire procedure corresponds to a relative standard deviation of 1%.

Some observations on the sensitivity of flow-injection techniques for atomic absorption spectrophotometry

Abstract Different strategies for coupling flow-injection manifolds to atomic absorption spectrometers in order to obtain better sensitivity are compared. Using a T-connector interface, different carriers and flow compensation solvents have been assayed in an attempt to improve the sensitivity of flow-injection analysis. Manganese and copper determinations in sewage sludge have been used as a test system and the analytical parameters of both batch and flow-injection methods are compared.