A procedure based on QuEChERS extraction and a simultaneous liquid-liquid partition
clean-up was developed. The procedure involved extraction of hydrated soil samples
using acetonitrile and clean-up by liquid-liquid partition into n-hexane. The hexane
extracts produced were clean and suitable for determination using gas chromatography-tandem
mass spectrometry (GC-MS/MS). The method was validated by analysis of soil samples,
spiked at five levels between 1 and 200 microg kg(-1). The recovery values were generally
between 70 and 100% and the relative standard deviation values (%RSDs) were at or
below 20%. The procedure was validated for determination of 19 organochlorine (OC)
pesticides. These were hexachlorobenzene (HCB), alpha-HCH, beta-HCH, gamma-HCH, heptachlor,
heptachlor epoxide (trans), aldrin, dieldrin, chlordane (trans), chlordane (cis),
oxychlordane, alpha-endosulfan, beta-endosulfan, endosulfan sulfate, endrin, p,p'-DDT,
o,p'-DDT, p,p'-DDD and p,p'-DDE. The method achieved low limits of detection (LOD;
typically 0.3 microg kg(-1)) and low limits of quantification (LOQ; typically 1.0
microg kg(-1)). The method performance was also assessed using five fortified soil
samples with different physico-chemical properties and the method performance was
consistent for the different types of soil samples. The proposed method was compared
with an established procedure based on Soxtec extraction. This comparison was carried
out using six soil samples collected from regions of Pakistan with a history of intensive
pesticide use. The results of this comparison showed that the two procedures produced
results with good agreement. The proposed method produced cleaner extracts and therefore
led to lower limits of quantification. The proposed method was less time consuming
and safer to use. The six samples tested during this comparison showed that soils
from cotton growing regions contained a number of persistent OC residues at relatively
low levels (<10 microg kg(-1)). These residues were alpha-HCH, gamma-HCH, heptachlor,
chlordane (trans), p,p'-DDT, o,p'-DDT, p,p'-DDD, p,p'-DDE, beta-endosulfan and endosulfan
sulfate.