2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
of sedimented phase that decreases the enrichment factor and
another is salting-out effect that increases the enrichment
factor. Therefore, the enrichment factor is nearly constant by
increasing the amount of sodium nitrate. Therefore the experiments
were performed in absence of the salt.
E f f e c t o f C o e x i s t i n g I o n s
The effects of common coexisting ions in natural water
samples on the recovery of silver were studied. In these experiments,
10.0 ml of solutions contains 20 ng ml −1 of silver and
various amounts of interfering ions were treated according to
the recommended procedure. A given spices was considered
to interfere if it resulted in a ± 5 % variation of the AAS signal.
The results obtained are given in Table II.
F i g u r e s o f M e r i t
Table. III summarizes the analytical characteristics of
the optimized method, including linear range, limit of detection,
reproducibility, and enhancement factor. The calibration
graph was linear in the range of 6–120 ng ml −1 of
silver. The limit of detection, defined as C L = 3 S B /m (where
C L , S B and m are the limit of detection, standard deviation of
the blank and slope of the calibration graph, respectively),
was 1.2 ng ml −1 . The relative standard deviation (R.S.D.)
for ten replicate measurements of 20 ng dm −3 Ag was 3.6 %.
The enhancement factor was obtained from the slope ratio
of calibration graph after and before extraction, which was
about 66.
Table III
Analytical characteristics of DLLME-ETAAS for determination
of Ag
Element condition DLLME–ETAAS ETAAS
Linear range [ng ml −1 ] 6–120 500–20,000
Correlation coefficient (r) 0.995 0.997
Slope 2.65 0.04
Enhancement factor a 66 –
RSD [%], (n = 8) b 3.6 3.5
LOD [ng ml −1 ] c 1.2 80
a Calculated as the ratio of slope of pre-concentrated samples
to that obtained without pre-concentration.
b At a silver concentration of 20 ng ml −1 .
c Determined as three times of the standard deviation of the
blank signal, and slop of calibration curve after pre-concentration
A n a l y s i s o f n a t u r a l W a t e r s
The proposed DLLME–ETAAS methodology was
applied to the determination of silver in several water samples.
Tap, underground and river water were collected from
the Tehran and were analyzed by DLLME combined with
ETAAS for determination of silver. The concentration of
silver in the tap, underground and river water samples were
determined to be 17.2 ± 0.6 ng ml −1 , 24.7 ± 0.6 ng ml −1 and
30.10 ± 0.4 ng ml −1 respectively (Table IV). The water sam-
s334
ples were spiked with silver standards to assess matrix effects.
The relative recoveries of silver from these waters at
spiking level of 10 and 20 ng ml −1 were 102, 98, and 100 %,
respectively (Table IV). These results demonstrated that the
tap, underground and river water samples matrices, in our
present context, had little effect on DLLME of silver.
Table IV
Determination of Ag in real samples
Sample
Added Found
[ng ml −1 ] [ng ml −1 ] a
Recovery [%]
– 17.2 ± 0.6 –
Tap waterb 10 27.3 ± 0.4 101
20 37.5 ± 0.6 103
Underground
water
– 24.7 ± 0.5 –
c 10 34.6 ± 0. 6 99
River water d
20 44.4 ± 0.5 97
– 30.1 ± 0.4 –
10 40.0 ± 0.5 99
20 50.2 ± 0.8 101
a Mean of three experiments ± standard deviation.
b From drinking water system of Tehran, Iran.
c Obtained from Vardavard, Iran.
d From Karaj river, Iran.
Conclusions
In this paper we introduced a DLLME–ETAAS method
for the analysis of ultra trace amounts of Ag in real samples
such as tap water, river water and underground water. The
important features of DLLME method are low cost, use of
minimized toxic organic solvents, simplicity of operation,
rapidity, high enrichment factor and high sensitivity and selectivity.
High preconcentration factor was obtained easily through
this method and a detection limit at ng ml −1 level was
achieved with only 10.00 ml of sample. In this method sample
preparation time as well as consumption of toxic organic
solvents was minimized without affecting the sensitivity of
the method..This method is characterized with simplicity,
rapidity, reliability, safety and low cost, and is suitable for
the determination of ultra-trace silver in environmental water
samples.
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