Combination of flow injection analysis with flame atomic-absorption spectrophotometry: determination of trace amounts of heavy metals in polluted seawater

Abstract

A simple flow injection system, the FIAstar unit, was used to inject samples of seawater into a flame atomic-absorption instrument allowing the determination of cadmium, lead, copper and zinc at the parts per million level at a rate of 180-250 samples per hour. Further, on-line flow injection analysis pre-concentration methods were developed using a microcolumn of Chelex-100 resin, allowing the determination of lead at concentrations as low as 10 parts per los (p.p.b.) and 1 p.p.b. for cadmium and zinc. The sampling rate was between 30 and 60 samples per hour and the readout was available within 60-100 s after sample injection; the sampling frequency depended on the pre-concentration required.Atomic-absorption spectrophotometry (AAS) is a well established, extremely valuable technique for the determination of trace amounts of metals. Since its introduction by Walsh,l the method has gone through a number of development stages aiming at obtaining an increase in reliability, ease of operation and, above all, improvement in the limit of detection. Hence, atomisation by a flame has been supplemented or replaced by the graphite furnace technique, background correction has been introduced to compensate for non-specific absorption phenomena and most recently background correction has, by exploiting the Zeeman effect, become more sophisticated by incorporating a polariser and a magnetic field into the commercial instruments.However, despite all these improvements, the assay of trace amounts of metals in samples with high salt content, such as seawater, still remains a time-consuming and difficult task. Because the high salt content in evaporated samples might result in clogging of the burner, or poisoning of the inner surface of a graphite tube, heavy metals generally have to be preseparated from the salt matrix either by solvent extraction or by ion exchange. While diethyldithiocarbamate extraction into isobutyl methyl ketone is widely used, this method is far from ideal because besides being laborious, it also requires very careful work if blank values are to be kept low. Further, analysis of a large number of samples yields, along with the analytical results, considerable volumes of used organic solvents that have to be disposed of in environmentally acceptable ways. Therefore, there is a marked tendency to use another preconcentration technique, that is, ion exchange on Chelex-100 resin,2 which is efficient and yields low blanks3 A recent paper by Danielssen et and an older, yet much more detailed, paper by Kingston et aZ.,5 have summarised the present state of seawater assays based on ion exchange. Thus, a typical procedure requires 100-500 ml of seawater, which is to be passed through a column containing 5 g of Chelex-100, at a rate of 2 ml min-l, followed by elution into 10 ml of 5 M nitric acid. Hence, pre-concentration of a single sample by a factor of ten will require over 1 h, while one 1-1 sample volumes have to be pre-concen-* Present address: ReagentsAll chemicals were of analytical-reagent grade and re-dist...

Determination by AAS of Some Trace Heavy Metal Ions in Some Natural and Biological Samples after Their Preconcentration Using Newly Chemically Modified Chloromethylated Polystyrene-PAN Ion-Exchanger

“…4,5 Various methods of preconcentration and separation procedures, such as electrodeposition, coprecipitation, solvent extraction, evaporation and freeze drying can be used prior to the atomic absorption spectroscopic measurements. [6][7][8][9][10][11][12] Cellulose-hyphan (1-(2′-hydroxyphenylazo)-2-naphthol) as an ion-exchanger was used for the preconcentration of various trace heavy metal ions in different water samples. [13][14][15][16][17][18] Other types of ion and modified exchangers were reported.…”

Advancement of Flow-based Analysis with Alternative Chemical Reactions and New Devices for Environmental and Biological Samples

“…In 1983, Olsen proposed a preconcentration method using a microcolumn of Chelex-100 resin and a flame atomic absorption spectrometry (FAAS), 55 allowing the determination of Pb(II), Cd(II) and Zn(II) at ppb levels. The preconcentration and matrix removal with solid-phase extraction (SPE) are useful for the analysis of trace amounts of organic compounds and metals.…”

Atomic spectrometry and flow injection analysis: a synergic combination

“…Plasma spectrometry does not suffer from chemical interferences (such as stable com pound formation or ionisation) to nearly the same extent as flame-based tech niques but is more prone to spectral interferences and suffers from inadequate sensitivity for a number of anion-forming elements such as P, S and B and some commonly determined heavy elements such as lead. The design features of one of the earliest reported manifolds [ 19], used for the determination of heavy metals in sea-water, by flame a.a.s. would seem to be the most sensible.…”