Environmental Engineering Reference
In-Depth Information
Analytical Instrumentation
Pulse differential anodic striping analyses, DPASV were carried out by mAutolab
Type II Potentiostat (Eco Chemie B.V. - Utrecht, Netherlands). A GPES 4.5
software was used for electrochemical instrumentation control, acquisition and data
treatment. The flow injection analysis (FIA) system consisted of carrier reservoir,
an Ismatec peristaltic pump model REGLO to propel the electrolyte carrier at
220 mL/min flow rate, a manually operated injector based on three solenoid
valves which was provided with a loop of 200 mL, and microdegasser system to
remove the interference of the dissolved oxygen in flowing solutions on Hg drop
electrode, and the electrochemical detector. A 20-cm long flexible fused silica capillary
(i.d. = 0.53 mm) was used to carry the degassed solution to the flow detector.
The batch electrochemical cell from VA STAND 663 (Metrohm), provided with
multimode mercury electrode, Ag/AgCl reference electrode and glassy carbon
auxiliary electrode, was converted for flow measurements by using a PTFE adaptor
in “L” shape fixed on the glass capillary and with its tip positioned ~0.5 mm apart
from the mercury drop surface
[4]
. A siphon prevents the cell from flooding. It was
connected to the outlet tubing which, together with the inlet channel from the FIA
system, leaves the cell through a hole in the top of cell lid.
Procedure
After assuring a constant level of the electrolyte solution in the flow cell, the sample
solution was injected into the FIA system. The deposition potential for cadmium,
lead and copper on Hg drop electrode was applied (45 s after the sample injection)
for 3 min at −0.8 V. The pre-concentration of zinc amalgam was carried out at −1.1 V
also for 3 min. After this step, a 10 s rest period was observed, and then a 10 mV/s
differential pulse anodic stripping voltammogram scan was started. The heavy
metals quantification was made by standard addition method using three spikes of
each element. The analytical detection limits were 0.50 mg/L for copper, 0.40 mg/L
for lead, 0.010 mg/L for cadmium and 0.95 mg/L for zinc. The analytical precision
was typically about ±5%. All measurements were carried out at 25 ± 1°C room
temperature.
Results and Discussion
Wet Deposition
The amount of rainfall recorded from January to December 2003 was 720 mm.
The dissolved metal concentrations were evaluated for 47 events of rain which
represents a precipitation of 616 mm. The rainy period occurred between October
