2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
at pH 4 for Al 3+ , c L = 1.5 × 10 –5 M at pH 3 for Ga 3+ and
c L = 3.5 × 10 –5 M at pH 8 for In 3+ (Figs. 1. and 2.).
no fluorescence was observed for the sole reagent in this
pH interval.
Fig. 2. Fluorescence intensity dependence on ph for each complex
(0.3 μg cm –3 of each element) at optimal conditions
The first derivations of the fluorescence and excitation
spectra under the same conditions as the normal spectra with
λ max(em) = 460 nm (AlQSA), λ max(em) = 472 nm (GaQSA)
and λ max(em) = 478 nm (InQSA)are given in Fig. 3. Higher
derivations could not be used because of a big noise of the
instrument.
The calibration plots are stricly linear in solution with
c L = 7.4 × 10 –5 M for Al 3+ at pH 4 or c L = 5.8 × 10 –5 M QSA
for Ga 3+ at pH 3 and c L = 1.78 × 10 –5 M and pH 8 for In 3+ .
Although the calibration plots are strictly linear till
2 μg cm –3 , the meaningful metal concentration range was
0.04–1 μg cm –3 . The decrease of QSA concentration in solution
negatively influence the extent of the linear part of the
calibration plot, the increase of QSA concentration causes
quenching.
There is no considerable difference in the values of detection
limits for normal spectra, derivative spectra and values
in the presence of 0.0012 M cationic surfactant Zephyramine
Fig. 3. The first derivative excitation(a) and emission(b) spectra
of Aluminium(III) in the presence of 7.4 × 10 –5 mol dm –3 QSA
at 620 V in dependence on concentration of Al(III).
1 – 1.6 μg cm –3 , 2 – 0.8 μg cm –3 , 3 – 0.4 μg cm –3 , 4 – 0.2 μg cm –3 ,
5 – 0.05 μg cm –3 , 6 – 0 μg cm –3
s514
when values according to Graham and IUPAC recommendation
are compared.
Cationic surfactants increase considerably the intensity
of fluorescence with no λ max shift, but some little bathochromic
shift (lesser than 20 nm) of excitation maximum is observed.
The fluorescence increase is time dependent and takes
1 hour either during radiation or when the sample is left in
darkness. Since the largest effect of the cationic surfactant is
often observed for the CMC the formation of a fluorescent
ion associate is assumed with the anionic metal complexes.
The fluorescence, however, slowly decreases after reaching
the micellar concentration of the surfactant.
The largest positive effect was found for 0.0012 M
Zephyramine but for the subsequent increase of concentration
a considerable decrease of fluorescence is observed for
all cationic surfactants.
The anionic surfactants such as dodecylsulphate have
a negative influence with the increasing concentration. no
effect is observed for selected non ionic surfactants such as
Triton X 100 and Brij 35, and β-cyclodextrine.
The effect of various surfactants follows from the Fig. 4.
which shows relative fluorescence intensity dependence
on surfactant concentration for GaQSA. The influence of
surfactants for the AlQSA and InQSA is similar to that of
GaQSA complex.
Fig. 4. Surfactants influence on the GaQSA complex at pH 3.
Septonex, Zephyramine, Ajatine, SDS – mol dm –3 , CTAC (hexadecyl
trimethyl ammonium chloride – c/4 [mol dm –3 ], DDAb
(Didodecyldimethyl ammonium bromide), β-Cyklodextrine –
c/5 [mol dm –3 ], Triton x 100 – c/4 × 10 –5 [ppm], brij –
c/15 [mol dm –3 ].
Critical micellar concentrations are highlighted by the fulfilled
marks
The fluorimetric method of continuous variations for at
least two concentrations c o gives unambiguously the simple
mole ratio M : L = 1 : 1 in the Al 3+ , Ga 3+ and In 3+ complexes
at pH 3–4. For the increasing pH 8 and In 3+ a higher complex
is also indicated (Fig. 5.).
In the presence of constant concentration 0.0012 M of
cationic surfactant Zephyramine a ratio M : L = 1 : 3 appears
which may indicate the formation of a ternary species, ML 3 3–
.3 T + .