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84
RADIOCHEMISTRY, STABLE ISOTOPES,
NUCLEAR ANALYTICAL METHODS, GENERAL CHEMISTRY
DETERMINATION OF CADMIUM, LEAD, COPPER AND BISMUTH
IN HIGHLY MINERALIZED WATERS
BY ATOMIC ABSORPTION SPECTROMETRY
AFTER SEPARATION BY SOLID PHASE EXTRACTION
Jadwiga Chwastowska, Witold Skwara, Elżbieta Sterlińska, Jakub Dudek, Leon Pszonicki
In the last time, the consumption of mineral waters
in Poland grows very quickly and its average value
is equal to 50 L per person and year. It is expected
a farther increase of this value in the nearest years.
In this situation the quality control of the commercially
available mineral waters becomes necessary.
Among many tests applied for this control, the determination
of heavy metals concentration plays a
very important role.
There exist many analytical methods for the determination
of trace amounts of metals in water;
however, most of them are not adequate to be used
for analysis of mineral waters, particularly, for
waters with high concentration of mineral salts.
We prepared a method that enables a relatively
simple separation of the trace amounts of cadmium,
copper, lead and bismuth from the mineral matrix
contained in the water and their preconcentration
by solid phase extraction before determination by
graphite furnace atomic absorption spectrometry.
Looking for the optimal sorbents for separation
of the heavy metals from mineral waters we
tested a dithizone sorbent (H 2
Dz-MM) and a mercaptobenzothiazole
sorbent (MBT-MM), both of
them prepared in our laboratory by fixation of the
chelating agents on a polymethacrylic resin (Diaion
HP-2MG) and applied already for the separation
and preconcentration of platinum and palladium
in the analysis of environmental samples [1] and
for mercury speciation in waters [2]. Thiol cotton
(TC), obtained by chemical reaction of the cotton
gauze with thioglycolic acid, was the third tested
sorbent. It was chosen on the basis of the literature
data [3,4] that point out very good sorption
properties of the cotton with the thiol groups. For
comparison of the sorbents, their sorption curves,
i.e. sorption efficiency as a function of pH, were
estimated in hydrochloric acid medium for all determined
elements. These curves are presented in
Figs.1-3. It results from this comparison that the
mercaptobenzothiazole sorbent is not adequate for
group separation of the investigated metals (Fig.2).
Fig.2. Sorption curves for mercaptobenzothiazole sorbent.
One observes a good sorption in a large range of
pH only for copper. Cadmium is adsorbed at pH
above seven and the sorption for lead and bismuth
is insufficient. Dithizone sorbent and thiol cotton
enable the group separation of all the metals; however,
the first of them is more versatile. It works
correctly in a very large range of pH values from 2
to 6 (Fig.1), whereas this range for thiol cotton is
limited to the pH values between 3 and 5 (Fig.3).
Fig.3. Sorption curves for thiol cotton sorbent.
Fig.1. Sorption curves for dithizone sorbent.
Therefore, the dithizone sorbent was chosen as optimum
for our method. The efficiency of sorption
in the column process does not change in the flow
rate range between 1-5 ml min –1 .