Statistical evaluation of recovery of 3,4-dichloroaniline in soil as function of particle size and analyte concentration

A great mean value of recovery for extraction of 3,4-dichloroaniline from a soil is calculated from individual recovery values evaluated for four different fractions of the soil. Then the uncertainty associated to this great mean recovery is calculated and used to know whether to apply or not the correction in routine analysis performed for the same kind of soil and the same analyte. The most representative fractions that, as a function of particle size, can be identified in a soil are: sand (2.000-0.063 mm), coarse silt (0.063-0.020 mm), fine silt (0.020-0.002 mm) and clay (≤0.002 mm). These fractions are here considered as sub matrices of the matrix soil. To evaluate the mean recovery and its uncertainty, as a function of the sub matrix and the analyte concentration, the four blank soil fractions were spiked with the analyte at three concentration levels (10.0, 50.0 and 100.0 mg/kg) and three replicates were performed for each experiment. The 36 samples were extracted by accelerated solvent system and the amounts of 3,4-dichloroaniline were determined by RP-HPLC analysis. From the 36 individual recovery values, the great mean and its uncertainty are calculated. Experiments performed on samples of soil of similar composition, spiked with known concentrations of the same analyte showed the goodness of the mean recovery value.