English to Spanish Science Chemistry; Chem Sci/Eng biochemistry

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2.4.1. Batch tests
Before the effect of the concentration of carbofuran on its
adsorption characteristics was studied, four soil samples (no. 2, 5,
14 and 15) were used to calculate the time needed to reach the
equilibrium. To this end, an amount of soil of 1 g was shaken at different
times with 10mL of a 2.3Mcarbofuran solution containing
0.005M CaCl2 as background electrolyte for a variable length of
time (0.5, 1, 4, 8, 16, 24 and 48 h). After incubation, the soil suspensions
were centrifuged at 2000rpm and passed through a polyester
filter of 0.45mpore size from Macherey-Nagel (Düren, Germany).
Previous tests revealed that these filters adsorb no carbofuran.
The resulting supernatant was used to determine the pesticide by
HPLC-UV. The amount of soil sorbed carbofuran was calculated by
subtracting that of carbofuran in solution from the amount added.
All tests were carried out in triplicate. Fig. 1 shows the amount of
carbofuran adsorbed as function of time. Equilibrium was always
reached after 8–16 h of incubation. Also, adsorption was negligible
after 24 h of contact in all samples.
Soil adsorption batch tests with carbofuran were performed as
follows: an amount of 1 g of soil was mixed with 10mL of carbofuran
aqueous solutions at concentrations ranging from 2 to 18M,
all containing 0.005MCaCl2 as background electrolyte. After 24 h of
shaking (long enough time as previously), the soil suspensions were
centrifuged at 2000rpm and passed through a filter of 0.45mpore
size, the resulting supernatant being used to determine carbofuran
by HPLC-UV. The amount of pesticide sorbed by the soil was
calculated by subtracting that present in solution after 24 h of equilibrium
from the amount initially added. Dissolved organic matter
was determined from the absorbance at 400nm [27]. Adsorption
tests were carried out in triplicate. The limit of quantitation for carbofuran
was 0.04mol kg−1. The results were modeled by fitting
to the equations of Freundlich (Eq. (1)) and Langmuir (Eq. (2)):