2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
2.2. Posters
P01 uLTRATRACE DETERMINATION OF
SILVER IN PRECONCENTRATED wATER
SAMPLES by ELECTROThERMAL ATOMIC
AbSORPTION SPECTROMETRy
SEYED HAMID AHMADIa , JAVAD DIDEHVAR ASLa ,
MOHAMMAD HASAn AMInIa and ROYA BAHADORIb aChemistry & Chemical Engineering Research Center of Iran
P.O. Box 14335-186, Tehran, Iran,
bResearch Center for Conservation of Cultural Relics,
Tehran, Iran,
ahmadi@ccerci.ac.ir
Introduction
Silver is one of the industrially important elements. It is
used for the preparation of corrosion-resistance alloys and its
compounds are extensively used in the processing of foods,
drugs and beverages and in filters and other equipments to
purify water. It also has an important role in electrical and
electronic application, photographic film production and the
manufacturing of fungicides 1,2 . These widespread applications
have resulted in increased silver content of environmental
water samples. In turns, owing to the toxicity of silver to
many aquatic organisms even at low concentrations, the serious
environmental problems may occur. Therefore, simple
and highly sensitive methods are needed to monitor the Ag
levels in water samples at ever decreasing concentrations.
Several atomic spectrometric techniques such as flame
and electrothermal atomic absorption spectrometry (FAAS
and ETAAS) 3,4 , inductively coupled plasma atomic emission
spectrometry (ICP-AES) 5 and inductively coupled plasma
mass spectrometry (ICP-MS) 6 have been proposed for the
determination of silver in different environmental samples.
In order to improve the detection limit, various preconcentration
procedures have also been used in combination with the
above-mentioned techniques. These include solvent extraction
7 , solid phase extraction 8 , precipitation 9 , adsorption on
tungsten wire 10 and cloud point extraction 11 . However, most
of these procedures are laborious, time-consuming and may
cause sample contamination.
Recently, Assadi and co-workers introduced a novel
microextraction method called dispersive liquid–liquid microextraction
(DLLME) as a highly sensitive, efficient and
powerful method for the pre-concentration and determination
of traces of organic and inorganic compounds in water
samples 12,13 . In the present work, the DLLME was combined
with ETAAS for determination of silver for the first time. In
this method, an appropriate mixture of extraction solvent and
disperser solvent is injected rapidly into an aqueous sample
containing silver ions and sodium diethyldithiocarbamate
(DDTC) by a syringe. Then, the resulting cloudy solution
is centrifuged and the fine droplets sedimented in a fewμl
volume at the bottom of the conical test tube are finally
introduced into the ETAAS for the determination of its silver
s331
content. The applicability of this approach was validated for
the determination of silver in water samples. The proposed
method was also applied to the determination of silver in
several water samples with satisfactory results.
Experimental
R e a g e n t s a n d S o l u t i o n s
Reagent grade carbon disulfide, carbon tetrachloride and
chloroform, as extraction solvents, and acetone, acetonitrile,
methanol and ethanol as disperser solvents from Merck chemical
company. Doubly distilled deionized water was used
throughout. Analytical grade nitrate salts of silver and other
cations (all from Merck) were of the highest purity available
and used without any further purification except for vacuum
drying. The stock solution of silver (1,000 mg dm −3 for atomic
spectroscopy standard) was prepaed by dissolving 0.1575 g
of silver nitrate (Merck) in deionized water containing 1 ml
concentrated nitric acid (Merck) in a 100 mlvolumetric flask
and diluting to mark with deionized water and stored in the
dark. Working standard solutions were prepared by serial
dilutions of the stock solution with ultrapure water prior to
analysis. The chelating agent, 0.001M sodium diethyldithiocarbamate
(DDTC) solution was prepared daily by dissolving
the appropriate amount of DDTC (analytical grade, Merck)
in methanol (suprasolv, Merck).
Tap, underground and river water samples used for
development of the method were collected in PTFE containers
from the Tehran and added appreciated amount of HnO 3
to adjust pH 3 and stored in dark at 4 °C and analyzed within
48 h of collection without previous treatment or filtration.
I n s t r u m e n t a t i o n
The experiments were performed using a Perkin Elmer
atomic absorption spectrometer (AA 1100B), equipped with a
graphite furnace atomizer HGA-700. Deuterium background
correction was employed to correct non-specific absorbances.
All measurements were performed using the peak height.
An Intensitron silver hollow cathode lamp and a pyrolytic
coated graphite tube (Perkin Elmer) were used. The sample
injection volume was 10 μl in all experiments. The instrumental
parameters and temperature program for the graphite
atomizer are listed in Table I. Argon gas with 99.95% purity
was purchased from Roham Gas Co. (Tehran, Iran) was used
as protected and purge gas. A Kendro 1020D centrifuge (Germany)
was used for centrifugation. All 15-ml screw cap falcon
test tubes with conical bottom (extraction vessel) were
maintained into 0.1 mol dm −3 HnO 3 for cleaning of any inorganic
compounds and washed with doubly deionized water
and then with acetone for proper sedimentation of fine droplets
of the extraction solvent in the centrifuging step.
G e n e r a l P r o c e d u r e
A 10.0 ml of aqueous solution contaning 0.2 ppm Ag and
0.01mM DDTC was placed in a 15 ml screw cap falcon test
tube with conic bottom. 0.8 ml methanol, as disperser solvent,
containing 60 μl carbon tetrachloride, as extraction sol-