Environmental Engineering Reference
In-Depth Information
Table 1
Power program used for the microwave assisted acid soil digestion
Ramp
Power (W)
Time (min)
Fun
1
1,000
7:00
1
2
800
4:30
1
3
0
15:00
3
All measurements were made using a Perkin Elmer SCIEX 9000 ICP/MS
(Toronto, Canada). Sample solutions were diluted to 1% HNO
3
concentration and
aspirated into the argon plasma (99.995%, Praxair, Madrid, Spain) via a peristaltic
pump. Data were acquired using Perkin Elmer TotalQuant III software for
multi-elemental semi-quantitative analysis. Common isobaric interferences are
pre-programmed and corrections are automatically applied. The software has stored
pre-calibrated intensities per concentration unit covering the required m/z range.
In order to increase the accuracy, these values are updated by running samples
spiked with a few selected elements with known concentration (Ag, Al, As, Cd, Co,
Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Sb, Se, Sn, V and Zn at 20 ng/g) and using rhenium
(Re) as internal standard. Prior to any experiment the mass spectrometer was
optimized for routine multi-elemental analysis by aspirating a solution containing
Mg, Rh and Pb (10 ng/mL of each). The operating conditions for sample introduction
were as follows: plasma Ar flow rate, 15 L/min; auxiliary Ar flow rate, 1 L/min;
nebulizer flow rate, 0.9 L/min, 1 replicate and one sweep per replicate.
Results and Discussion
Fifty elements (Ag, As, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Ga, Gd,
Ge, Hf, Ho, In, K, La, Li, Lu, Mg, Mo, Na, Nb, Nd, Ni, Pb, Pr, Rb, Sb, Se, Sm, Sn,
Sr, Tb, Te, Th, Tl, Tm, U, V, Y, Yb, Zn, Zr) were determined above the detection
limit in soil extracts. These results were statistically treated with “The Unscrambler
9.2” software.
Principal component analysis (PCA) of all available data revealed two main
components accounting for 64% of the total variance (PC1, 48%; PC2, 18%).
The projection of the scores and loadings on the bi-dimensional space defined by
these two principal components is shown in Fig.
3
. Samples can be grouped according
to sampling point in three groups. Samples from the west roadside of the secondary
road (SR L) clearly differentiate from the rest, and are gathered in the left side of
the x axis (PC1). Samples from the highway (H 0.5, H 3 and H 6) form another
group in the upper side of the graphic. Finally, samples from the east roadside of
the secondary road (SR R), further samples from the highway (H 9) and control
soils put together in the left side.
Overlapping the scores and loading plots shows that the concentrations of Cd,
Cr, Cu, Hf, Mo, Nb, Ni, Pb, Sb, Sn, Sr, Zn and Zr, are the variables which explain
most of the variance of the SR L sampling point.
