MINI-ROUND-ROBIN STUDY OF A SUPERCRITICAL-FLUID EXTRACTION METHOD FORPOLYNUCLEAR AROMATIC-HYDROCARBONS IN SOILS WITH DICHLOROMETHANE AS A STATIC MODIFIER

A mini-round-robin study of a supercritical fluid extraction (SFE) met hod for polynuclear aromatic hydrocarbons (PAHs) from soil samples was conducted. Three laboratories participated in the study, and each lab oratory extracted three real-world samples in triplicate. The cryogeni cally milled samples were extracted at 350 atm (1 atm = 101 325 Pa) an d 90 degrees C for 20 min in the dynamic mode using supercritical carb on dioxide at a flow-rate of 1 to 1.5 ml/min and the extracted materia l was collected in 10 ml dichloromethane, which was then subjected to silica chromatography. The SFE method accuracy (percent recovery) was determined relative to the sonication extraction since the true levels of PAHs in these samples are not known. The PAHs were recovered quant itatively (recovery > 80%) by SFE when present at concentrations of 1 mg/kg or higher. The interlaboratory method precisions (overall R.S.D. s) appear to be concentration-dependent; at concentrations above 1 mg/ kg, they were 27% or lower; at concentrations below 1 mg/kg, they rang ed from 19 to 80%. From these results, we concluded that the method ap pears quite rugged, and the interlaboratory data compare well with oth er SFE interlaboratory studies.