Examination of proficiency and control recovery data from analyses for pesticide residues in food: Sources of variability

We examined a number of large proficiency and control databases supporting the values reported for pesticide residues in agricultural commodities at f ractions of a part per million (mg/kg), The average recovery from > 100 000 recovery records in 13 databases was 94%. The overall average single-value relative standard deviation (RSD) of the reported recoveries was 17% at a mean concentration (C) of about 10(-7) (0.1 mg/kg), The average apparent HO RRAT value (RSD found/RSDR predicted from the Horwitz formula [2*C-0.1505]) was 0.8. Analysis of variance indicated that about 60-70% of the variance could not be associated with any particular factor or combination of factor s-analyte, commodity, method, laboratory, concentration, database, or their interactions. The most predominant factor, analyte, and its third-order in teraction with laboratory and concentration contributed most of the assigna ble variance. These findings suggested that most of the variability of trac e analysis for pesticide residues is "random" in the sense of being inheren t and not assignable to specific factor fluctuations.