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846 7000A. Solids and suspended materials were removed using a 0.45-1tm
glass fiber filter. The filtered samples were acidified with HNO3 to pH less than 2.
Calibration standards were prepared by diluting stock standard solutions
purchased from Fisher Scientific, Inc. The calibration standards were acidified
using HNO3 to simulate conditions used for the samples. Calibration of the
SpectraAA began with a blank and proceeded toward the highest concentration.
Concentration of a metal in a liquid sample (C in ag/L) was calculated by:
C = A (D + B)                    (3.1)
D
where A is the concentration (vig/L) of metal in a diluted aliquot, B is the volume
of the acid blank matrix used for dilution (mL), and D is the volume of the aliquot
(mL).
For solid samples, the concentration (Cs in  tg metal/kg soil) was
computed as:
E V
C   EV --(3.2)
W
where E is the concentration (g/L) of metal in the digested sample from the
calibration curve, V is the final volume of the diluted sample, and W is the weight
of the sample (g).
Interference effects were compensated by using standard additions.
Known amounts of standard were added to one or more aliquots of the sample
solution. Standard solutions containing different known quantities of the analyte
were prepared and then added to the sample solution. Additions were prepared